United States
Department
of Agriculture
Pacific Southwest
Research Station
General
Technical
Report
PSW-130
Proceedings of the IUFRO
Technical Session on
Geomorphic Hazards in
Managed Forests
August 5-11, 1990
Montreal, Canada
-
Rice. Ravmond M.. technical coordinator. 1991. Proeeedlncs of the IUFRO technical session
on geomorphic hazards in managed forests: 5-1 I August 1990: Montreal, Canada. Gcn.
Tech. Rep. PSW-GTR-130, Berkeley, CA: Pacilic Saulhwest Research Slslion, F o r m
Service, U.S. Department of Agriculture; 82 p.
The proceedings contains I I of the 17 papers presented at the technical session on
forests at the XIX World Conmss.
International Union ol
"
Foreslry Research Organizations, August 5-11, 1990, Montreal, Cmuda, plus o m paper no1
presented orally. Two papers report research on lorrents, two are about snow, three concern
landslides, and five discuss watershed management problems.
-reamorehic hazards in manaeed
-
Relrieval Temrs: natural disasters, torrent control, watershed management, landslides, snow,
avalanches, floods, erosion
Technical Coordinator:
RAYMOND M. RICE was, before his retirement, chief hydralogisl in the Effects of Forest
Management on Hillslope Processes, Fishery Resources, and Stream Environmenls Research
Work Unit, at the Slation's Redwood Scicnces Labomtary, 1700 Bnyview Drive, Arcata, CA
95521-6098.
Authors assumed full responsibility for the submission ol camera-ready manuscripts. Views
expressed in each paper are those of the authors and not necessarily those of the sponsoring
organizations. Trade names and commercial enterprises are mentmed solely for inlamation
and do not imply endorsement of the sponsoring organizations.
Publisher:
Pacific Southwest Research Station
P.O. Box 245
Berkeley, California 94701
December 1991
Proceedings of the IUFRO Technical Session
on Geomorphic Hazards in Managed Forests
August 5-1 1, 1990, Montreal, Canada
Raymond M. Rice, Technical Coordinator
Contents
Foreword ......................................................................................................................................................................................
Invited Papers
...
111
..............................................................................................................................................................................
1
.
.
Severe Snow Loads on Mountain Afforestation In Japan ..............................................................................................................
Ryazo Nifln, Yoslzio Ozeki, mid Slioichi Nibvnno
1
Priority Setting for Government Investment in Fosestly Conservation Schemes- An Example f1-0111New Zealand .................... 6
Colin L. O'Louglilin
Voluntary Papers
.......................................................................................................................................................................
11
Effect of Tree Roots on Shallow-Seated Landslides ....................................................................................................................
Ka7rttokiAbe m ~ Robert
d
R. Zie~ner
1L
Watershed Concerns and Recent Policy Formulat~onsin Sri Lanka and Australia ......................................................................
Rohan Ekannyake
2I
Sul~oundingthe Consequences of Watershed Disasters in the Periphety of the Indian TI-iangle................................................. 28
Roha~iEknnnyake
High-speed High-Stress Ring Shex Tests on Granular Sods and Clayey Soils ..........................................................................
Hiroshi Fukuokn mid Kyoji Snssa
Morphological Study on the Prediction of the Site of Surface Slides .............................
Hiromasa Hiurct
33
.................................................... 42
.
.
.
Experimental Study ou Impact Load on a Dam Due to Debris Flow ........................................................................................
hvno Miyoslii
48
Sediment Dynamics of a High Gradient Stream in the Oi River Basin of Japan ......................
..............................................
.
Hideji Maita
56
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991.
Contents
Snow-Cover Condition in Japan and Damage of the Sugi (C~yptomeriaJnponica D. Don) ...................... .
.
.
.......................... 65
Taira Hidenki
Study on Shearing Force and Impact Force of a Volcanic Mud Flow on Mt . Sakurajimn ...................
Yoshinobu Taniguclzi
.
.
.
...............................
Research of Wind Erosion lnlensity in the Region of Subotica-Horgos Sands .........................................................................
Velizm Velasevic and Lj~honzirLefic
72
79
USDA Forest Service Gm . Tech. Rep . PSW.GTR.130 . 1991.
Foreword
The Technical Session of the Subject Group on Natusal
Disasters was held on the afternoon of August 7, 1990 as part of
the XIX World Congress of the lnlernational Union of Forestry
Research Organizations in Montreal, Canada. About 35 scie~ilists representing 10 nations were in attendance. Seventeen papers were presented, addressing the topics of all four Working
Pxties in the Group. Two papers reported research on torrents,
three were about snow, five concerned landslides, and seven
discussed watershed management problems. Four of the invited
papers can be found in Volume 1 of the Proceedings of Division
I , and two are in this volume. The remainder of this volume
includes nine of the contributed papers presented at the technical
session plus one that was not orally presented. 11 is hoped that
this volume, together with others supported by the Subject Group
in recent years, will foster increased understanding of natural
disasters in forested environments.
Raymond M. R~ce,Leader
I W R O Subject Group S1.04
Proceedings Technical Coord~nator
USDA Forest Service Gcn. Tech. Rep.
PSW-GTR-130. 1991.
Severe Snow Loads on Mountain Afforestation in Japan1
Ryuzo Nitta, Yoshio Ozeki, and Shoichi Niwano2
Abstract: A s i m p l e d e v i c e f o r e s t i m a t i n g
snow s e t t l i n g f o r c e on t r e e b r a n c h e s was
u s e d t o d e t e r m i n e t h e d i s t r i b u t i o n o f snow
s e t t l i n g force a t various heights i n a
snowy m o u n t a i n o u s r e g i o n i n J a p a n . A
t r a p e z o i d a l d i s t r i b u t i o n o f snow s e t t l i n g
f o r c e was f o u n d t o e x i s t a t a l l s i t e s
I t i s t h o u g h t t h a t a z o n i n g scheme
tested.
b a s e d on t h e damaging p o t e n t i a l o f snow on
young man-made f o r e s t s would become
p o s s i b l e , with t h e a c q u i s i t i o n of
One o f t h e l a r g e s t p r o b l e m s i n J a p a n e s e
f o r e s t r y l i e s i n t h e low s u r v i v a l r a t e o f
young man-made f o r e s t s i n t h e heavy snow
areas. It i s r a r e t o see a beautiful
c o n i f e r p l a n t a t i o n where snow r e a c h e s o v e r
4 m i n d e p t h b e c a u s e o f m e c h a n i c a l damage
c a u s e d b y l a r g e snow p r e s s u r e .
Both on
f l a t l o c a t i o n s a n d g e n t l e s l o p e s , snow
s e t t l e m e n t c a u s e s branch and stem
d e f o r m a t i o n which o f t e n b r i n g s f a t a l
breakage.
To d e c r e a s e s u c h u n s u c c e s s f u l
p l a n t i n g s much b a s i c d a t a f o r f o r e s t z o n i n g
a r e indispensable.
Out of s u c h n e c e s s i t y
t h e a u t h o r s h a v e d e v i s e d a n d s e t new snow
p o l e s i n mountains t o o b t a i n tree-deforming
f a c t o r s s u c h as maximal snow d e p t h a n d snow
s e t t l i n g f o r c e w i t h o u t b a t t e r i e s o r power
S u p p l y . The d a t a from t h e new snow p o l e s
e x p l a i n t o u s how s e v e r e l y snow l o a d s work
on young t r e e s .
CrvDtomeria D .
Don. ( J a p a n e s e
c e d a r ) F i g . 1 . The t y p e s o f snow damage
t o C r y p t o m e r i a [ I w a t s u b o a n d N i t t a 19871
S t r a i g h t stems h a v e
a r e shown i n F i g . 2 .
much h i g h e r m a r k e t v a l u e t h a n c r o o k e d
stems. Therefore i n f i e l d survey, t h e
aurhors c l a s s i f y every cryptomeria t r e e t o
The Japan Sea
7DOm
A
F i g . l--The s i t e s s u r v e y e d .
C i r c l e : Snow s e t t l e m e n t r e c o r d e r
T r i a n g l e : P l o t of Cryptomeria
DAMAGES TO CRYPTOMERIA I N SNOW REGIONS
The F o r e s t r y a n d F o r e s t P r o d u c t s
Research I n s t i t u t e h a s a long e s t a b l i s h e d
snow e x p e r i m e n t s t a t i o n a t Tokamachi C i t y
i n N i i g a t a P r e f e c t u r e , C e n t r a l Honshu. The
Tokamachi S t a t i o n i s e n c i r c l e d b y t h e snowy
Naeba M o u n t a i n s i n which t h e a u t h o r s h a v e
s u r v e y e d many c o n i f e r p l a n t a t i o n s o f
l p r e s e n t e d a t t h e S u b j e c t Group 5 1 . 0 4
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s i n
Managed F o r e s t s , X I X World F o r e s t r y
C o n g r e s s , I n t e r n a t i o n a l Union o f F o r e s t r y
R e s e a r c h O r g a n i z a t i o n s , August 5-11, 1990,
M o n t r e a l , Canada.
2 ~ o r e s t r ya n d F o r e s t P r o d u c t s R e s e a r c h
I n s t i t u t e , Tsqkuba N o h r i n , I b a r a k i , J a p a n .
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
F i g . 2--Damage t o C r y p t o m e r i a c a u s e d by
snow l o a d s .
Table 1 C l a s s d i s t r i b u t i o n of Cryptomeria
a t p l o t s of v a r i o u s a l t i t u d e s .
Altitude
m a.s.1.
Height
Age Share
y r A+B(pct) of B m
Max. snow Altitude
depth m
m a.s.1.
*Mean of unsusceptible
t r e e height (meter)
t h e following four types:
A : Middle a n d u p p e r s t e m s i s s t r a i g h t .
Normal v a l u e .
B : Middle a n d u p p e r s t e m s a r e c r o o k e d ,
o r t h e y h a v e t r a c e s o f r e c o v e r y from
stem t o p breakage.
Lower v a l u e .
C : T i l t e d and crooked stem w i t h lower
t r e e height.
NO v a l u e .
D : Stem w i t h b r e a k a g e o r l a r g e b e n d i n g ,
t o t a l l y s u p p r e s s e d o r dead i n n e a r
future.
NO v a l u e .
Unless t h e proportion of t r e e s i n
c l a s s e s A a n d B r e a c h e s 50 p e r c e n t i n a
s u r v e y e d p l o t ( 2 0 m b y 20 m) when t h e t r e e
h e i g h t r e a c h e s t w i c e t h e mean o f maximal
snow d e p t h , t h e p l a n t i n g would e n d i n
f a i l u r e [ S h i d e i 19541.
F i g . 3--Snow
damage t o a C r y p t o m e r i a s t a n d .
b u t a l s o o f t h e lower b r a n c h e s .
If the
b e n t a n g l e s o f t h e b r a n c h e s from t h e
h o r i z o n t a l d i r e c t i o n show g r e a t v a r i e t y
a c c o r d i n g t o above-ground h e i g h t , t h e
a n g l e s would i n d i c a t e t h e d i f f e r e n c e o f
snow s e t t l i n g power o f t h e l a y e r s which
c a t c h and deform t h e b r a n c h e s .
To o b t a i n more i n f o r m a t i o n on snow
l a y e r s e t t l i n g , 20-cm l o n g g a l v a n i z e d i r o n
w i r e s o f r e g u l a t i o n q u a l i t y were f i x e d
h o r i z o n t a l l y t o a 5-m t a l l p o l e a t e v e r y
20-cm h e i g h t i n c r e m e n t . L a t e e a c h f a l l ,
t h e s e p o l e s w i t h h o r i z o n t a l w i r e s were s e t
a n d , a f t e r t h e snow m e l t e d , t h e a n g l e s t h a t
t h e w i r e s h a d b e e n b e n t down by snow
s e t t l i n g were measured ( F i g . 4 ) .
T a b l e 1 shows t h e r e s u l t o f p l o t
s u r v e y s o f C r y p t o m e r i a s t a n d s on f l a t s i t e s
a t s e v e r a l a l t i t u d e s . The t r e e s a t t h e
1250 m l e v e l would r e c e i v e much more snow
damage i n t h e f u t u r e b e c a u s e t h e i r crowns
c o u l d n o t p r o j e c t o v e r t h e snow s u r f a c e f o r
t h e n e x t f i v e - y e a r p e r i o d , t h o u g h t h e y show
a l a r g e r s h a r e of A + B a t t h e age of 15.
I n s h o r t , a l l o f t h e man-made f o r e s t s
s u r v e y e d would b r i n g no wood m a r k e t v a l u e
in the future.
INDICATIONS OF SNOW SETTLEMENT
Lower b r a n c h e s a r e o f t e n b e n t down due
t o p a r t i a l d e s t r u c t i o n o f t h e i r b a s e s by
heavy snow p a c k i n g a n d s e t t l i n g ( F i g . 3 ) .
The h e i g h t a b o v e g r o u n d o f t h e h i g h e s t b e n t
b r a n c h e s i n d i c a t e s t h e maximal snow d e p t h .
T h i s d e f o r m a t i o n i s b e i n g r e p r o d u c e d by a n
i n e x p e n s i v e r e c o r d e r f o r maximal snow d e p t h
i n Japan.
The r e c o r d e r c o n s i s t s o f a p o l e
w i t h h o r i z o n t a l " b r a n c h e s " made o f s o f t
m e t a l f i x e d a t e v e r y 1 0 cm h e i g h t i n c r e m e n t
[ T a k a h a s h i K . 19681 .
Long t e r m snow s e t t l i n g c a u s e s t h e
bending n o t o n l y of t h e h i g h e s t branches,
F i g . 4--Snow
s e t t l i n g recorder.
USDA Forest ServiceGcn. Tech. Rep. PSW-GTR-130. 1991
Table 2
~eason
Average t e m p e r a t u r e d u r i n g snow
s e a s o n a t Tokamachi E x p t . S t n .
Dec
Jan
Feb
Mar
AD r
Mean
The w i r e was c a l i b r a t e d b y l o a d i n g i n
t h e basement o f Tokamachi S t a t i o n where
room t e m p e r a t u r e s t a y s a t a r o u n d O°C d u r i n g
t h e whole w i n t e r (Tab. 2 ) . P o i n t l o a d s
w e r e a p p l i e d a t t h e f r e e e n d s o f 20-cm l o n g
c a n t i l e v e r s f o r 150 d a y s c o n t i n u o u s l y
d u r i n g w i n t e r , and a f t e r t h a t t h e
b e n t down a n g l e s were measured ( F i g . 5 ) .
The c a l i b r a t i o n c u r v e i n r e l a t i o n t o wire
d i a m e t e r , a n g l e a n d p o i n t l o a d , shown i n
F i g . 6 , p r o v i d e s u s a good i n d i c a t i o n o f
d i s t r i b u t i o n o f snow s e t t l i n g f o r c e a l o n g
t h e v e r t i c a l p r o f i l e o f t h e snowpack.
The d a t a o f t h o s e a n g l e s i n w i n t e r
1982/83 i n d i c a t e a f e a t u r e common t o t h e
f i v e p r o f i l e s , t h a t is, a trapezoidal
d i s t r i b u t i o n o f t h e a n g l e s ( F i g . 7) . The
w i r e s p l a n t e d a t between +60 c m above
g r o u n d a n d -40 cm from t h e h i g h e s t snow
s u r f a c e o f t h e s e a s o n were b e n t a t a l a r g e
b u t almost c o n s t a n t a n g l e i n each c a s e .
F i g u r e 8 i n d i c a t e s t h a t maximum snow
d e p t h a t t h e 1360 m a l t i t u d e s i t e i s a b o u t
1 m d e e p e r t h a n t h a t a t 500 m a l t i t u d e a n d
0
5
4
POINT L O A D (kg)
I
2
3
6
F i g . 6--The c a l i b r a t i o n c u r v e i n r e l a t i o n
t o w i r e d i a m e t e r , bent-down a n g l e
and p o i n t l o a d ( a p p l i e d a t t h e f r e e
e n d o f 20-cm l o n g c a n t i l e v e r s ) .
t h a t t h e a n g l e i n t h e middle l a y e r s of t h e
former i s about 5 degrees g r e a t e r t h a n t h a t
of t h e l a t t e r .
By p i c k i n g s i t e s where t h e a v e r a g e b e n t
a n g l e i n t h e m i d d l e l a y e r s e x c e e d e d 60
d e g r e e s , a n d s i t e s where t h e maximum snow
h e i g h t e x c e e d s 4 m, T a b l e 3 i s o b t a i n e d .
I t i s c l e a r from t h i s t a b l e t h a t e x t r e m e l y
severe conditions p r e v a i l a t a l t i t u d e s over
700 m .
C o n s i d e r i n g T a b l e s 1 a n d 3, it i s
p o s s i b l e t o a p p l y a zoning i n t h i s region,
a c c o r d i n g t o which a l t i t u d e s o f 700 m a n d
o v e r a r e u n s u i t e d t o economical f o r e s t
planning.
Although l i t t l e d a t a i s a v a i l a b l e a t
t h e p r e s e n t , a z o n i n g scheme b a s e d on
damaging p o t e n t i a l s h o u l d become p o s s i b l e
i n t h e f u t u r e b y c o l l e c t i n g l a r g e amounts
of d a t a on damaging p o t e n t i a l i n d e x w i t h
Table 3
Fig. 5--Calibration of
t h e wires b y
loading.
S e v e r i t y of f o r e s t r y environment
b a s e d on max. snow d e p t h a n d b e n t
angle.
Winter
1982/83
83/84
84/85
A
200
500
700
900
1100
136Q
A
A+B
A+B
A+B
A+B
A
ava
A+B
A+B
A+B
A+B
A
A
: Angle more than 60 d e g r e e s
Diameter o f w i r e : 3 . 2 mm
B : Max. snow depth more than 4 m
ava: Snow p o l e l o s t by a v a l a n c h e s .
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
3m
TOKAMACHI
KOSHlCHlGAWA
YAHABUSHIYAMA
MYOHO
KOMATSUBARA
1
Fig. 7--Distribution of the wire angle along the vertical profile. Data for
winter 1982/83 at five altitudes.
Wire diameter: 3.2 mm
x : S-side of snow pole
- - : N-side of snow pole
500m a d . (Koshichigawa)
1360m a.s.1. (Komatsubara)
351 86
X
X
x
*
L
li
X
X
*
X
Y
I
X
X
x
X
*
X
I
*
X
f
60 90deg.
30
U-w.J-4
10
60 90 deg.
Fig. 8--Distribution of the wire angle along the vertical snow profile. Four
season data at the sites on 1360 m and 500 m a.s.1.
Wire diameters:
x x : 4.0 mm
0-0: 3 . 2 mm
USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130.1991
t h e s i m p l i f i e d method s t a t e d a b o v e . I n
such b e l i e f , d a t a i s p r e s e n t l y being
a c q u i r e d i n s e v e r a l r e g i o n s i n Japan
[ T a k a s h i n o a n d Wakabayashi 1975; N i t t a e t
a l . 1982 a n d 1 9 8 4 1 .
REFERENCES
I w a t s u b o , G . a n d N i t t a , R . 1987. Snow. I n
[ S h i d e i , T. e d i t e d : F o r e s t P r o t e c t i o n .
48,Asakura S h o t e n , T o k y o . ]
N i t t a , R . , O z e k i , Y . a n d Niwano, S . 1982.
Development o f s i m p l e snow s e t t l i n g
r e c o r d e r . T r a n s , J p n . S o c . Snow a n d I c e .
147.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
N i t t a , R . , O z e k i , Y . a n d Niwano, S . 1984.
Height i n d i c a t o r of branches
s u s c e p t i b l e t o s e t t l i n g snow. P r o c . 9 5 t h
J p n . F o r . S o c . 313-314.
S h i d e i , T . 1 9 5 4 . On t h e snow damages o f
f o r e s t t r e e s b y snow p r e s s u r e . R e s .
B u l l e t i n Government F o r e s t Exp. S t n . 73.
1-89.
T a k a h a s h i . K . 1 9 6 8 . On t h e snow s c a l e f o r
m e a s u r i n g maximum snow d e p t h . Seppyo
30. 1 1 1 - 1 1 4 .
T a k a s h i n o , K . a n d Wakabayashi, R . 1 9 7 5 .
Wire ( b r a n c h model) d e f o r m a t i o n by snow
s e t t l i n g . T r a n s , J p n . S o c . Snow a n d I c e .
105.
( A l l papers w r i t t e n i n Japanese)
Priority Setting for Government Investment in Forestry
Conservation Schemes-An Example from New Zealand1
Colin L. 0'Loughlin2
Abstract: In New Zealand responsibility for funding
flood protection and erosion prevention and control
projects rests largely with local regional authorities.
However, in 1988 Central Government decided to
provide direct funding for a major forestry conservation
scheme in the erosion-susceptible East Coast region.
Government's investment decision was influenced by a
number of factors, the most important being the extent
and severity of erosion in the East Coast region and its
negative impact on the region's social and economic
development.
A large part of New Zealand's wealth depends on
pastoral farming. Pastoral land occupies 7.5 million
hectares or 28 percent of the country's land surface, much
of it steep hill country, and supports about 67 million
sheep, 8 million dairy and beef cattle and 1 million deer
and goats (New Zealand Department of Statistics 1989).
Most of the pastoral land was carved out of indigenous
forest between 1840 and 1970. It has been publically
acknowledged since the beginning of the present century
that high soil erosion rates cause pastoralism to be an
unsuitable land use over large tracts of New Zealand's
steeplands. Over the last 15 years several studies
(Trustrum
1983, New Zealand Ministry of Works
and Development 1980) have shown that pastoralism on
erosion-susceptible hill country is not a sustainable land
use. Pastoral farming continues to be a major land use on
some of New Zealand's most unstable hill country which,
to some, may seem to be an enigma considering New
Zealand's international reputation for its technically
advanced approaches to conservation and protection of
soil and water values. Over the last 5 decades a number
of soil conservation schemes have been initiated to
stabilise soil on eroding pastoral land.
It is not the intention of this paper to unravel the
reasons why unsuitable pastoral land use practices are
widespread in New Zealand but rather the paper will
endeavour to examine the way in which conservation
schemes on eroding land are initiated and funded and how
priorities are set. The role of Central Government will be
examined. To this end the paper will concentrate on a
forestry conservation scheme known as the East Coast
Forestry Project located in the North Eastem part of New
Zealand.
In New Zealand, forestry conservation schemes
generally involve the blanket planting of eroding land
with fast growing exotics, usually Pinus radiata but other
species of conifers,
or Populus are also often used.
Open plantings of poplars are a commonly used soil
stabilisation technique in poorly-drained gullies and other
localised areas of instability.
POLICIES TO ENCOURAGE EROSION AND FLOOD
CONTROL
There exist a number of Government policies that aim
to provide protection against or control of erosion and
flooding in New Zealand.
(i)
Land use Controls
There exists legislation known as "the Soil
Conservation and Rivers Control Amendment
Act 1959" which was again amended in 1988,
which provides catchment authorities with the
power to control land use to prevent erosion. For
instance catchment authorities can require land
owners to plant trees on eroding land. However,
this legislation is rarely used to enforce tree
planting.
119th IUFRO World Congress August 5-11 1990,
Montreal, Canada.
2~ssistantSecretary (Research), Ministry of Forestry,
Wellington, New Zealand.
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130.1991
Catchment Grants
The Government contributes to flood
protection and erosion control schemes through
grants for specific works administered by
regional catchment authorities. Nationwide
catchment grants have averaged about
$90 million per year over the last 20 years. It is
planned to replace grants for specific works with
a block subsidy system in the near future.
District Planning Schemes
These schemes can be used under the Town
and Country Planning Acts (1954 and 1977) to
designate areas of land for particular ultimate
land uses (for example forestry). District
planning schemes have not been effective in
changing land use.
bodies. New legislation is presently being introduced
under the general title "Resource Management Law
Reform". Essentially the new legislation will consolidate
a large number of existing pieces of legislation covered
by a variety of Acts and replace them with a single
Resource Management Act. Some of the policies
outlined above will probably disappear with the
introduction of the new Act which aims to provide
Regional Governments (Councils) with greatly increased
responsibility for managing natural resources and funding
conservation schemes. Central Government is already
playing a much reduced role in funding land use proiects
and conservation/erosion control/floodcontrol schemes
compared to the recent past.
EAST COAST FORESTRY PROJECT
Disaster Relief
The Government has in the past contributed
substantial amounts of money to disaster relief
from flooding and siltation. For instance
between 1968 and 1981 there were 7 major
floods which cost the Government $2.9 billion or
$223 million per year. Some of this money has
been used for tree planting to stabilise soils and
for retiring land from grazing.
established
,'
f'
1
Priority area for
new East Coast
forestry scheme
'L-.
Other Subsidies and Grants
In the past the Government provided for
encouragement of farm scale forestry and
agriculture conservation schemes through a
variety of grants and subsidies. However, the
present Government has introduced a market-led
development strategy for New Zealand which has
involved the removal of agricultural and forestry
grants and subsidies. This has discouraged
private afforestation and other conservation
measures by private land holders.
Since 1984 the New Zealand Government has reshaped
and reformed local (Regional) Government. The end
result has been the amalgamation of more than 600
separate public agencies into 94 new district and regional
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130. 1991
Wairoa
HAWKE BAY
Figure 1: Map showing East Coast region and
general area of the East Coast forestry scheme
A major economic appraisal of land use and
development options for about 6,500 kilometres2 of
severely eroding pastoral steeplands of the Raukumara
Peninsula led to the initiation of a large scale forestry
conservation scheme in 1969. The ori inal aim was to
plant approximately 1,000 kilometres of fast growing
exotics, mainly radiata pine, at a rate of about
3
2,500 hectares per year. By 1987 when the scheme was
halted, 36,100 hectares of dual purpose
protection/production forest had been established at a
total cost of $229 million. In addition to afforestation a
large number of on-farm conservation schemes covering
28,200 hectares of sensitive terrain, had been
implemented by 1987. Government contributed
64 percent of the total cost of $14.3 million for these
schemes.
The on site benefits of afforestation include
substantially reduced earthflow movement rates,
cessation of gullying processes and a marked reduction in
shallow landsliding (Pearce et1987). To date the
downstream benefits have not been quantified although in
several upper catchment tributaries there are strong
indications that a reduction in sediment supply from
afforested slopes to stream channels is resulting in stream
channel degradation.
Other benefits resulting from the East Coast forestry
project are the commercial retums from the production of
logs after the forest is 25 years old. Recent projections by
the Ministry of ~ o r e s b ysuggest
~
both existing plantings
and future plantings are commercially viable in most
areas except the areas to the far north and west of the East
Coast region. The project also provided social benefits as
it helped to prevent mral depopulation and unemployment
in this rather isolated and economically depressed region.
EFFECTS OF CYCLONE BOLA AND SUBSEQUENT
GOVERNMENT DECISIONS
When a subtropical cyclone, Cyclone Bola, moved
across northern New Zealand between 6 and
9 March 1988 the torrential rainfall that fell on the East
Coast region caused severe landsliding, erosion, flooding
and siltation. Pastoral land was particularly damaged.
Some pasture slopes lost 70 percent or more of their grass
cover to shallow landslides. However, on hillslopes
protected by mature native forest and older pine forests,
landslides were less frequent. Damage to farms, forests,
horticulture, roads, bridges and houses exceeded
$120 million. The Central Government contributed
approximately $80 million to the East Coast region as
disaster relief to help defray the cost of damages resulting
from Cyclone Bola.
%npublished data, Ministry of Forestry, Wellington,
New Zealand.
8
The impacts of Cyclone Bola extended into the
socio-economic area. The East Coast is presently one of
the most depressed regions in New Zealand. The region
is charactensed by a declining total population, falling
property prices, a high economic and social dependency
on agriculture and forestry which account for 23 percent
of the total employment, and a high Maori population
which comprises 37 percent of total East Coast
population (New Zealand Officials Committee Report
1988). The severe impacts of the cyclone on the
agriculture/forestry industries and the inability of the
region to cope with the damage from a financial point of
view were important factors in subsequent Government
decision making. The results of the storm reinforced the
fact that the East Coast was New Zealand's most
susceptible region to widespread erosion and flooding
damage and that erosion and flooding negatively
influences the regional economy more than in other parts
of New Zealand. The cyclone also highlighted the need
for better land use on much of the unstable hill country in
the region.
The severe damages caused by the cyclone (the largest
of five severe storms to influence the East Coast in
20 years) was a major factor in the setting up of a
Government Officials Committee to examine the original
East Coast Project and an earlier review of this project.
Among other things, the Committee was required to make
recommendations to the Government on the future of the
project and the Government's involvement in it. In its
recommendations the Committee was split between those
who recommended no Central Government funding
should be provided for restarting the East Coast forestry
project and those who strongly recommended that Central
Government should intervene and provide additional
funding for conservation plantings.
GOVERNMENT DECISIONS
In 1988 Government agreed to provide $8 million to
directly subsidise a new East Coast Forestry Conservation
Scheme on the East Coast pastoral forelands. The
funding was to be spread over a 5 year period; 1989 to
1994; and was aimed at establishing about 3,000 hectares
of protection forests per year. The scheme was to be
targetted at erosion control on unstable pastoral hill
country upstream of Gisborne City, Poverty Bay flats and
Tologa Bay where the greatest assets at risk are located.
The Government also agreed that the funding would be
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
provided as a subsidy covering two thuds of the cost of
establishment and that the remaining one thud of the
costs should be met by the region through the East Cape
Catchment Board.
The Government also insisted that all protection forests
would come under covenants which precluded logging for
at least 25 years after planting and then only with the
permission of the local catchment authority.
The main factors influencing Central Government to
invest in such a scheme included:
Survey (1977) concluded that forest planting of poorer
grade land within a farm unit generally has little or no
impact on stock numbers. However, in the case of a
few farm units more than 50 percent of the farm area
needed afforestation. Naturally, farmers were reluctant
to yield up large parts of their farms for forestry and
substantially reduce stock numbers.
A perception that tree plantations would not yield any
return to the land holder in the foreseeable future but
rather, would result in additional silvicultural and
fencing costs.
.
The real extent of severe erosion which is much greater
than elsewhere in the country and has substantial
negative impacts on the region's social and economic
development.
The low profitability of many pastoral farms and low
farm incomes which prevents landholders from being
attracted by the long term benefits resulting from
conservation forestry.
.
The need to cany out erosion control quickly and
comprehensively to reduce future costs of erosion and
flood damage, both to the region and to the Central
Government.
.
The lack of money and resources within the region for
carrying out a comprehensive erosion control scheme.
If unstable farmland is not relinquished for
conservation forestry at the rate required by the East
Coast Forestry Project, then the local regional authorities
(the East Cape Catchment Board) may have to enforce
afforestation in the priority areas requiring protection.
The five year scheme aims at afforesting 15,000 hectares.
However, this represents only 20 percent of the total area
of severely eroding pastoral hill country in the East Coast
region. There is clearly a need for a long term land use
rationalisation scheme which will lead to the close
integration of exotic and native forests, pastoral farming,
horticulture and viticulture. Carefully located forests on
the steeper unstable slopes and along riparian areas would
provide improved protection to fertile valley bottoms and
river plans where horticulture and other types of intensive
farming are concentrated. Government Officials and East
Cape Catchment Board staff agree that such a scheme
would substantially increase farm productivity and reduce
the costs of sustaining farming and horticulture on the
better classes of land by reducing recurrent storm
damage. In addition, recent Ministry of Forestry analyses
of the economic viability of exotic forestry on the East
Coast indicate that radiata pine forestry on the pastoral
forelands has potential internal rates of return exceeding
7 percent4 .
Under the existing economic environment in New
Zealand and the Government's intentions to devolve all
responsibility for resource management to regional
authorities, it is most unlikely that other regions in New
Zealand will qualify for Central Government funding for
major forestry conservation schemes in the future.
PROGRESS TO DATE
Despite the generous subsidies available for
establishing conservation forests on unstable East Coast
hill country, the East Cape Catchment Board who
administer the Scheme, have found it difficult to obtain
agreement from landowners to provide land for planting.
After two planting seasons only about 4,500 hectares
have been afforested. Farmers' reluctance to provide
erosion prone pastoral land for afforestation stems from
several factors:
.
Concern that afforestation of sizeable portions of
farmland will result in a decline in the stock carrying
capacity of farms. The Department of Lands and
USDA Forest Service Gen. Tech.Rep. PSW-GTR-130. 1991
4~npublisheddata, Ministry of Forestry, Wellington,
New Zealand.
REFERENCES
Department of Land and Survey (New Zealand) 1977.
King Country land use study. Wellington, New Zealand.
Department of Statistics (New Zeaiand) 1989. New
Zealand Official Yearbook 1988-89. 93rd Annual
Edition. 884p.
Ministry of Works and Development (New Zealand)
1980. Proceedings of a workshop on the influence of soil
slip erosion on hill country pastoral productivity.
Aokautere Science Centre Internal Report 21.
Officials Committee Report on East Coast Project
Review (1988). A report to the Cabinet Development and
Marketing Committee (unpublished), July 1988. 38p.
Pearce, A.J., O'Loughlin, C.L., Jackson, R.J.,
Zhang, X.B. 1987. Reforestation: on site effects on
hydrology and erosion, eastern Raukumara Range, New
Zealand. International Association of Hydrological
Sciences Publication 167. 489-497.
USDA Forest Service Gen. Tech.Rep. PSW-GTR-130.1991
Effect of Tree oots on Shallow-Seate
Kazutoki Abe and Robert R. Ziemer2
Abstract:
Forest vegetation, especially
t r e e r o o t s , h e l p s s t a b i l i z e h i l l s l o p e s by
reinforcing s o i l shear strength.
To
e v a l u a t e t h e e f f e c t o f t r e e r o o t s on s l o p e
s t a b i l i t y , i n f o r m a t i o n a b o u t t h e amount o f
r o o t s a n d t h e i r s t r e n g t h s h o u l d b e known.
A
simulation
model
for
the
root
d i s t r i b u t i o n o f G r v w t o m e r i a i a w o n i c a was
p r o p o s e d where t h e number o f r o o t s i n e a c h
0.5-cm d i a m e t e r c l a s s c a n b e c a l c u l a t e d a t
a r b i t r a r y d e p t h s . The p u l l - o u t s t r e n g t h o f
r o o t s was u s e d t o a n a l y z e t h e s t a b i l i t y o f
f o u r d i f f e r e n t t y p e s of f o r e s t e d s l o p e s .
Root r e i n f o r c e m e n t i s i m p o r t a n t on s l o p e s
where r o o t s c a n e x t e n d i n t o j o i n t s and
f r a c t u r e s i n bedrock o r i n t o a weathered
t r a n s i t i o n a l l a y e r between t h e s o i l a n d
bedrock.
Root r e i n f o r c e m e n t of s o i l
increases quickly a f t e r afforestation f o r
a b o u t t h e f i r s t 20 y e a r s , t h e n r e m a i n s
&out c o n s t a n t t h e r e a f t e r .
S e d i m e n t d i s a s t e r s by d e b r i s f l o w s , mud
flows, and l a n d s l i d e s o c c u r almost e v e r y
year during t h e r a i n y J u l y t o October
Typhoon s e a s o n i n J a p a n .
I n J u l y 1982, a
h e a v y r a i n f a l l o f 488 nun i n a d a y , w i t h a
maximum i n t e n s i t y o f 1 2 7 . 5 mm p e r h o u r ,
c a u s e d 4300 d e b r i s f l o w s i n N a g a s a k i
p r e f e c t u r e , Kyushu I s l a n d .
This storm
d e s t r o y e d 2200 h o u s e s a n d k i l l e d 299
people.
D u r i n g J u l y 1983, i n t e n s i v e
r a i n f a l l i n i t i a t e d many d e b r i s f l o w s a n d
199 people
were
killed
in
Shimane
p r e f e c t u r e , a l o n g J a p a n S e a on w e s t e r n
Honshu I s l a n d .
l p r e s e n t e d a t t h e S u b j e c t Group S1.04
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s i n
Manaqed F o r e s t s ,
X I X World C o n q r e s s ,
I n c e r n a r l o n a l Union o f F o r e s c r y R e s e a r c h
O r s a n l z a c l o n s , Aususc 5-11, 1990, Clonereal,
2 ~ e s e a r c hS c i e n t i s t , F o r e s t r y a n d F o r e s t
Products Research I n s t i t u t e ,
Tsukuba,
I b a r a k i , 305 J a p a n ;
and P r i n c i p a l Research
Hydrologist, P a c i f i c Southwest Research
Station, Forest Service, United S t a t e s
~ e ~ a r t m e notf A g r i c u l t u r e , A r c a t a , C A .
U.S.A. 95521
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
The c a u s e o f s o much d e s t r u c t i o n a n d
d e a t h might be unprecedented i n t e n s i v e
rainfall.
In addition,
expansion of
c i t i e s , r e s o r t s , and roads o n t o h i l l s l o p e s
a n d m o u n t a i n areas h a s b e e n a l s o t h o u g h t t o
be a primary c a u s e .
In response, n a t i o n a l
and l o c a l governments have adopted a
p r o g r a m o f a g g r e s s i v e l y c o n s t r u c t i n g many
e r o s i o n c o n t r o l works a t g r e a t e x p e n s e .
B u t , e v e n s o , it i s i m p o s s i b l e f o r s u c h
c o n s t r u c t i o n t o p r o t e c t a l l mountain
h i l l s l o p e s from d e b r i s f l o w s .
An
important
cause
of
increased
f r e q u e n c y o f d e b r i s f l o w s i s t h e removal o f
f o r e s t s t o accommodate u r b a n i z a t i o n a n d
r o a d c o n s t r u c t i o n i n mountainous a r e a s . I n
monsoon a r e a s , l i k e J a p a n , w h e r e s t e e p
m o u n t a i n s a r e c o v e r e d w i t h f o r e s t s , mass
wasting i s t h e p r e v a i l i n g type of erosion.
T h e r e i s a f r a g i l e b a l a n c e o f s t a b i l i t y on
s u c h s t e e p h i l l s l o p e s where t h e f o r e s t
cover i n t e r a c t s with s o i l moisture, s o i l
strength, geological condition, h i s t o r i c a l
r a i n f a l l , and o t h e r f a c t o r s t o s t a b i l i z e
t h e r e g o l i t h on a s l o p e .
From a v i e w p o i n t
o f s o i l m e c h a n i c s , on many h i l l s l o p e s t h e
f a c t o r of s a f e t y o f a s l o p e (FS) a p p r o a c h e s
1 . 0 during a r a i n f a l l event t h a t occurs
o n c e e v e r y s e v e r a l y e a r s . Under c o n d i t i o n s
of s u c h d e l i c a t e b a l a n c e , removal of t h e
t r e e s b y l o g g i n g may r e s u l t i n a r e d u c t i o n
i n s o i l strength s u f f i c i e n t t o cause
landslides.
The i n f l u e n c e o f f o r e s t s o n s l o p e
s t a b i l i t y h a s been one of
t h e most
i m p o r t a n t s u b j e c t s of s t u d y - - e s p e c i a l l y ,
t h e r o l e o f t r e e r o o t s on r e i n f o r c i n g s o i l
s h e a r s t r e n g t h . To e v a l u a t e t h e m e c h a n i c a l
e f f e c t of r o o t s i n s t r e n g t h e n i n g s o i l ,
however, t h e q u a n t i t y and d i s t r i b u t i o n o f
r o o t s i n s u b s u r f a c e s o i l l a y e r s must b e
quantified.
I n t h i s p a p e r , a s i m u l a t i o n model f o r
t h e d i s t r i b u t i o n and s t a b i l i z i n g e f f e c t of
r o o t s i s i n v e s t i g a t e d using an i n f i n i t e
s l o p e s t a b i l i t y a n a l y s i s model.
ROOT
A
can
DISTRIBUTION
s t a b i l i t y a n a l y s i s of f o r e s t slopes
b e made b y a d d i n g t h e s o i l s h e a r
s t r e n g t h a n d a r e i n f o r c i n g component
p r o v i d e d by t h e s t r e n g t h of r o o t s (Endo a n d
T s u r u t a 1969; Gray a n d Ohashi 1 9 8 3 ) . T h i s
r e i n f o r c i n g s t r e n g t h i s g e n e r a l l y shown by
e q u a t i o n [ I ] (Waldron 1977; Wu 1 9 7 6 ) .
C r = xtri ( s i n
8 + cos 8 * tan a
),
[I]
where C r : R e i n f o r c i n g s t r e n g t h p r o v i d e d
by r o o t s
t r i : Root t e n s i l e s t r e s s g e n e r a t e d
i n root i a t the landslide
shear plane
8 : Slope g r a d i e n t
a : Angle o f i n t e r n a l f r i c t i o n o f
the soil.
The t e n s i l e s t r e s s f o r v a r i o u s s p e c i e s h a s
been r e p o r t e d t o be a f u n c t i o n o f r o o t
diameter
(Ziemer and Swanston
1977;
B u r r o u g h s a n d Thomas 1977; O ' L o u g h l i n a n d
Ziemer 1982; Abe a n d Iwamoto 1 9 8 6 ) . Thus,
t o model t h e i n f l u e n c e o f t r e e s on s l o p e
s t a b i l i t y , t h e number a n d d i a m e t e r o f r o o t s
a t s p e c i f i c d e p t h s must b e o b t a i n e d .
3 . The d i a m e t e r a t b o t h e n d s a n d t h e
l e n g t h o f c u t r o o t s l a r g e r t h a n 0 . 5 mm
i n d i a m e t e r were m e a s u r e d i n e a c h 10cm-thick l a y e r .
4 . The number, volume, a n d t o t a l l e n g t h of
r o o t s were t h e n c a l c u l a t e d f o r e a c h
layer.
o f t h e Root Dlstrlhutlon
Root volume i n 10-cm-thick
l a y e r s (V(z))
About 8 5 t o 90 p e r c e n t o f t h e t o t a l
r o o t volume o f a t r e e w a s f o u n d i n t h e
upper h a l f of t h e r o o t i n g d e p t h .
Root
volume d e c r e a s e s e x p o n e n t i a l l y w i t h d e p t h .
To i n v e s t i g a t e t h e p a t t e r n o f r o o t
V(z),
the
distribution
by
depth,
a c c u m u l a t e d r o o t volume r a t i o , F ( z ) , was
c a l c u l a t e d ( e q . [21) .
Zmax
To d e v e l o p t h e r o o t m o d e l a n d t o
understand t h e influence of d i f f e r e n t
environmental
conditions
on
root
d i s t r i b u t i o n , r o o t s of about 16 t r e e s of
iaoonica, t h e most p o p u l a r
s p e c i e s p l a n t e d i n J a p a n , were sampled i n
five different fields.
The s a m p l i n g was
done a s f o l l o w s :
The s t u d y t r e e was c u t down a n d i t s
entire
root
s y s t e m was
carefully
excavated.
A l l r o o t s were c u t a l o n g p l a n e s a t 10cm d e p t h i n t e r v a l s below t h e g r o u n d a n d
p a r a l l e l t o t h e surface ( f i g . 1).
5
%
Vr =
C
V(Z)
z=o
where, V r : e n t i r e r o o t volume o f one t r e e
C V ( z ) : a c c u m u l a t e d r o o t volume from t h e
ground s u r f a c e t o t h e depth "z"
Zmax:
maximum d e p t h o f r o o t g r o w t h .
The r e l a t i o n s h i p between F ( z ) a n d d e p t h " 2 "
c o u l d b e a -u -u r o x i m a t e d b v t h e u r o b a b i l i t v
function of
t h e weidull-d<stribution
(ficr. 21.
The s o l i d l i n e i n f i s u r e 2 i s
t h e - Weibull p r o b a b i l i t y function, f ( z ) ,
c a l c u l a t e d from e q u a t i o n I31 (Makabe 1 9 6 6 ) .
T h e r e a r e t h r e e p a r a m e t e r s t h a t must b e
e s t i m a t e d : a, y, a n d m.
"y" i s a l o c a t i o n
parameter t h a t determines a beginning p o i n t
of t h e c u r v e .
In t h e root d i s t r i b u t i o n
c a s e , "y" i s 0 , b e c a u s e t h e g r o u n d s u r f a c e
(z=0) i s t h e i n i t i a l p o i n t .
"m" i s a s h a p e
It c a n b e r e a d o f f t h e Weibullparameter.
g r a p h a s a g r a d i e n t of t h e l i n e , a n d a l s o
c a l c u l a t e d by e q u a t i o n [ 4 1 w i t h "ZmaXu a n d
"Xo"
Fig. 1.Method
of
sampling
for
root
A l l r o o t s were c u t
distribution.
a l o n g p l a n e s a t 10-cm i n t e r v a l s
below t h e
ground s u r f a c e and
diameters of b o t h ends and t h e
l e n g t h s o f c u t r o o t s were m e a s u r e d
Zmax i s
i n e a c h 10-cm t h i c k l a y e r .
a maximum r o o t p e n e t r a t i n g d e p t h .
p o i n t where d i a m e t e r i s m e a s u r e d .
XO i s an i n t e r s e c t i n g p o i n t o f F n ( z ) = O a n d
the solid line (fig. 2).
From o u r d a t a , it a p p e a r e d t h a t i f Zmax i s
d e e p e r , t h e g r a d i e n t o f "m" may b e s t e e p e r .
( f i g . 2 ) . A r e g r e s s i o n between Zmax a n d XO
r e s u l t e d i n e q u a t i o n [51.
XO = 0.3522*Zmax
-
10.799
[51
USDAForest ServiceGen. Tech. Rep. PSW-GTR-130.1991
S u b s t i t u t i n g e q u a t i o n [51 i n t o e q u a t i o n
[ 4 ] , "m" c a n be e s t i m a t e d b y e q u a t i o n [ 6 ] .
Site
Minakami
"a" is
a s c a l e parameter and can
d e f i n e d as a d e p e n d e n t v a r i a b l e o f Zmax
e q u a t i o n (71 .
Tap
zone
7.91 i-1.47
Middle zone
Bottom
4.91 i-*'ll
5.95 i-l'
Z<
be
by
A c c o r d i n g l y , t h e r o o t volume i n e a c h
10-cm-thick
l a y e r V(z) i s o b t a i n e d by
e q u a t i o n [81 .
0 . 5 cm i n d i a m e t e r
z+10
V(z) = {
f ( z ) dzl
*
Vr
Z
[el
Root Number
I n g e n e r a l , t h e most r o o t s a r e f o u n d 20
The number o f r o o t s t h e n
gradually decreases with depth.
Sixty t o
85 p e r c e n t o f t h e r o o t s a r e s m a l l e r t h a n
t o 50 c m d e e p .
To c o m p a r e r o o t d i s t r i b u t i o n b e t w e e n
each f i e l d site, t h e t o t a l rooting depth
was d i v i d e d i n t o t h r e e z o n e s : t o p , m i d d l e ,
and bottom.
I n t h e t o p zone, t h e r e a r e
many l a t e r a l r o o t s t h a t v a r y w i d e l y i n
diameter.
I n t h e b o t t o m z o n e , most r o o t s
grow v e r t i c a l l y a n d t h e r e a r e few r o o t s
g r e a t e r t h a n 1 . 0 cm i n d i a m e t e r .
In the
m i d d l e zone, many r o o t s d e v e l o p v e r t i c a l l y
a n d d i a g o n a l l y , b u t t h e r e a r e few l a t e r a l
roots.
Even t h o u g h t h e d e p t h z o n e s d o n o t
c o i n c i d e with s o i l horizons and t h e
t h i c k n e s s o f t h e zones v a r i e s between
s i t e s , e a c h r e s p e c t i v e d e p t h zone h a s
similar
root
distributions.
Root
d i s t r i b u t i o n was e s t i m a t e d a s t h e r o o t
number r a t i o ,
o b t a i n e d by r e g r e s s i o n
b e t w e e n t h e p r o p o r t i o n o f t h e number o f
r o o t s i n e a c h 0.5-cm d i a m e t e r c l a s s , Y ( i ) ,
and t h e diameter c l a s s , i ( t a b l e 1 ) .
Mean volume of
c l a s s (Vm ( i ) )
a
root
in
each
diameter
T h e r e was n o d i f f e r e n c e i n t h e mean
volume o f a r o o t i n e a c h d i a m e t e r c l a s s ,
Vrn(i),
among t h e t h r e e d e p t h z o n e s .
Consequently, r e g r e s s i o n s were c a l c u l a t e d
f o r each f i e l d site ( t a b l e 2 ) .
Maximum r o o t d e p t h (Zmax)
F i g . 2 . R e l a t i o n s h i p between d e p t h ( z ) and
accumulated
r o o t volume
ratio
(F(z)) in
t h e Weibull graph.
W e i b u l l c o e f f i c i e n t "mu i s t h e
g r a d i e n t of a r e g r e s s i o n l i n e ,
o b t a i n e d b y " b / a , "a" , a n d "b".
: T r e e 1 i n Minakami,
0 : T r e e 3 i n Minakami,
: T r e e 5 i n Komatubara,
9 i n Misugi,
+:Tree
10 i n Ksukuba.
+:Tree
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
It i s important t o note t h e depth of
r o o t p e n e t r a t i o n when e s t i m a t i n g t h e e f f e c t
of r o o t s i n s t a b i l i z i n g slopes.
The more
roots t h a t penetrate a potential shear
plane, t h e g r e a t e r i s t h e chance t h a t
vegetation w i l l increase slope s t a b i l i t y .
Some o f t h e f a c t o r s r e s t r i c t i n g Zmax a r e
e x i s t e n c e of bedrock, s o i l p o r o s i t y , s o i l
moisture, s o i l structure, s o i l consistency,
and s o i l f e r t i l i t y .
Morimoto ( 1 9 8 2 ) a n d
Ikemoto and T a k e s h i t a (1987) r e p o r t e d t h a t
Zmax c o u l d b e e s t i m a t e d a s t h e d e p t h where
the
soil
hardness,
using
a
cone
p e n e t r o m e t e r , i s 27 mm, o r t h e N v a l u e
(number Of f a l l s p e r 10-cm p e n e t r a t i o n ) i n
t h e s o u n d i n g t e s t i s 5 . However, much more
d a t a on t h i s s u b j e c t i s n e e d e d .
T a b l e 2--Mean
root
four f i e l d sites
volume,
Vm(i),
of
the
having d i f f e r e n t environmental c o n d i t i o n s .
The model was composed a s f o l l o w s :
Site
Coefficient of Sample
determination number
Mean root
volume
Minakami
7 . 6 2 i2'"
0.96
51
Komatsubara
7.84
0.94
24
j,2.32
(1)
(2)
I n p u t DBH, H,
C a l c u l a t e whole r o o t w e i g h t , W r , i n
g.
W r c a n b e c a l c u l a t e d by a n a l l o m e t r i c
f o r m u l a , e q u a t i o n 191 (Karizumi 1 9 7 7 ) .
log W r
Tsukuba
7.81
i2.l4
0.97
and Z m a x .
=
0.8216*10~(~~~~*~)-0.3
[91
085
53
YODEL
(3)
Figure 3 i s a flow c h a r t of t h e r o o t
d i s t r i b u t i o n s i m u l a t i o n model.
The i n p u t
f a c t o r s a r e f i e l d measurements of h e i g h t
( H ) , d i a m e t e r ( D B H ) , a n d Zmax of t h e o b j e c t
tree.
The model o u t p u t i s t h e number o f
r o o t s i n e a c h 10-cm l a y e r a n d e a c h r o o t
diameter c l a s s .
Y t ( i ) , Y m ( i ) , Y b ( i ) , and
V m ( i ) a r e u s e d i n t h e model a s v a r i a b l e s ,
s o t h e y must b e m e a s u r e d f o r e a c h r e g i o n
C a l c u l a t e whole r o o t volume,
cm3 .
in
1101
V r = Wr/Gs
(4)
Vr,
C a l c u l a t e r o o t volume i n e a c h 10-cm
layer, V(z).
V ( z ) c a n b e c a l c u l a t e d by e q u a t i o n 181,
where f ( z ) i s o b t a i n e d from e q u a t i o n
131 by s u b s t i t u t i n g Zma,
i n t o equations
APPLIED PRINCIPLES
M)OB
Aiiometric formula
Whole root
volume (Vr)
Weibull distribution
probability function
k
10-cm-thick layer
in each diameter class and
each to-cm-thick layer
root diameter class
in each diameter class
Temporary volume of roots in
each 10-cm.thick layer
diameter class and each
to-cm-thick layer (N(i.2))
F i g . 3 . Flow c h a r t o f t h e r o o t d i s t r i b u t i o n s i m u l a t i o n model.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
[61 a n d 171.
(5)
S e t u p t h e t e m p o r a r y r o o t number i n
e a c h d i a m e t e r c l a s s a n d e a c h 10-cmthick s o i l layer, f?(i,z).
The maximum r o o t d i a m e t e r ( i m a x ) s h o u l d
be determined, and f i ( i , z ) i n each
d i a m e t e r c l a s s (0.5-cm i n t e r v a l s i n
t h i s p a p e r ) u p t o imaxi n e a c h zone i s
s e t u p i n p r o p o r t i o n t o t h e r o o t number
A l l
r a t i o s Y t ( i ) , Y m ( i ) , and Y b ( i ) .
10-cm l a y e r s t h a t b e l o n g t o o n e z o n e
h a v e t h e same i n i t i a l v a l u e o f fi ( i ,z )
.
(6)
C a l c u l a t e temporary
10-cm l a y e r , v ( z ) .
r o o t volume
in
(7)
C a l c u l a t e t h e r a t i o between V ( z ) a n d
V(z), k .
(8)
D e t e r m i n e t h e number o f r o o t s i n
each r o o t d i a m e t e r c l a s s and each
10-cm l a y e r , N ( i , z ) .
Even f i n e r o o t s h a v e a s t r o n g i n f l u e n c e
i n p r e v e n t i n g l a n d s l i d e s (Burroughs and
Thomas 1977; Abe a n d Iwamoto 1 9 8 6 ) . Thus,
t h e model must b e a b l e t o e s t i m a t e t h e
number o f s u c h f i n e r o o t s .
Also, t h e
l a n d s l i d e shear plane has a tendency t o
o c c u r n e a r t h e l i m i t o f r o o t i n g d e p t h where
t h e r e a r e few r o o t s on t h e s h e a r p l a n e (Abe
a n d o t h e r s 1 9 8 5 ) . T h i s model can e s t i m a t e
t h e number o f r o o t s i n e a c h d i a m e t e r class
i n t h e deeper l a y e r s .
Furthermore, it i s
important t h a t r o o t d i s t r i b u t i o n under
d i f f e r e n t c o n d i t i o n s can b e expressed by
one model.
ROOT
BTRENGTE
The c o n t r i b u t i o n o f r o o t s t o i n c r e a s i n g
s o i l s h e a r s t r e n g t h h a s been mainly
e s t i m a t e d by f o u r kinds of experiments:
t e n s i l e t e s t , pull-out t e s t ,
'
shear
t e s t , and l a b o r a t o r y s h e a r t e s t .
-
r e s i s t a n c e when a r o o t i s p u l l e d o u t o f t h e
Tsukamoto ( 1 9 8 7 ) a n d Abe
soil (fig. 4 ) .
a n d Iwamoto
(1986) r e p o r t e d p u l l - o u t
s t r e n g t h c o u l d b e p r e d i c t e d by r o o t
d i a m e t e r a n d was i n d e p e n d e n t o f s l o p e
c o n d i t i o n s and r o o t t y p e , such a s l a t e r a l ,
t a p , o r s i n k e r r o o t . P u l l - o u t s t r e n g t h was
composed of t a n g e n t i a l f r i c t i o n between
s o i l a n d r o o t s , a n d was i n f l u e n c e d b y r o o t
bending, branching, r o o t h a i r s , and t h e
t e n s i l e s t r e n g t h a t breakages.
D a t a from in-situ s h e a r t e s t s (Endo a n d
T s u r u t a 1969; Ziemer 1981; O ' L o u g h l i n a n d
o t h e r s 1 9 8 2 ; Abe a n d Iwamoto 1 9 8 7 ) a r e
important
for
evaluating
the
a p p r o p r i a t e n e s s of t h e o r e t i c a l concepts.
B u t , it i s d i f f i c u l t t o p e r f o r m s u c h t e s t s
on s t e e p r o c k y h i l l s l o p e s .
Laboratory
shear t e s t s
have been
p e r f o r m e d t o r e v e a l t h e mechanism o f t h e
r o o t r e i n f o r c i n g e f f e c t (Waldron 1977; Wu
1976; Waldron a n d D a k e s s i a n 1981; Gray a n d
We
Ohashi
1983;
Shewbridge
1985).
conducted direct s h e a r tests u s i n g sand
t h a t contained r o o t s and modified t h e
r e i n f o r c e m e n t model p r o p o s e d b y Waldron
( 1 9 7 7 ) a n d Wu (1976) :
AS= [ { ( l c ~ ~ b ~ e '/*-I)
- ' ~ ~ )*E*arl ( c o s 8
t a n @ t s i n 8) + E * I * ~ ~ * B
[I41
where, E :
ar:
8:
Young modulus
c r o s s s e c t i o n a l a r e a of t h e
roots
one h a l f o f a s h e a r d i s p l a c e m e n t
modulus o f s e c t i o n
root angle a t t h e origin
:
i n t e r n a l f r i c t i o n a n g l e of sand.
B:
I:
From o b s e r v a t i o n s o f s h a l l o w l a n d s l i d e
s i t e s , t h e r e were o n l y a few f i n e r o o t s on
t h e b o t t o m s h e a r p l a n e s (Abe a n d o t h e r s
1 9 8 5 ) . And, f o r f a l l e n trees, most o f t h e
r o o t s were b r o k e n n e a r t h e i r t i p s where t h e
Recorder
Many t e n s i l e s t r e n g t h t e s t s o f r o o t s
A segment o f a r o o t
have been performed.
specimen i s u s u a l l y loaded i n t e n s i o n and
t h e maximum v a l u e a t f a i l u r e i s m e a s u r e d
( O ' L o u g h l i n 1 9 7 4 ; B u r r o u g h s a n d Thomas
1977; Ziemer a n d Swanston 1977; Nakane a n d
From
o t h e r s 1 9 8 3 ; Abe a n d o t h e r s 1 9 8 6 ) .
t h e s e t e s t s , t h e t e n s i l e s t r e n g t h of l i v e
r o o t s and i t s d e c l i n e a f t e r t h e r o o t s d i e
h a v e b e e n m e a s u r e d f o r many o f
the
important t r e e species.
The p u l l - o u t
t e s t m e a s u r e s t h e maximum
USDA Forest Sewice Gen. Tech. Rep. PSW-GTR-130. 1991
F i g . 4 . Diagram o f t h e r o o t p u l l - o u t t e s t
d i a m e t e r was l e s s t h a n 1 t o 2 cm.
This
s u g g e s t s t h a t most r o o t s were p u l l e d o u t .
B u r r o u g h s a n d Thomas ( 1 9 7 7 ) r e p o r t e d t h a t
t h e w i d t h o f t h e s h e a r zone r a n g e d from 7
t o 25 cm a n d t h e m a j o r i t y o f t r e e r o o t s h a d
failed i n tension.
Studies of slope
f a i l u r e i n s o i l over g l a c i a l till i n Alaska
i n d i c a t e d t h a t t h e expected width of t h e
s o i l s h e a r z o n e r a n g e d f r o m 7 . 5 t o 30 c m ,
a n d t h a t t h e e x p e c t e d mode o f r o o t f a i l u r e
i s i n t e n s i o n (Wu, 1 9 7 6 ) . We assume t h a t
t h e r o o t s c r o s s i n g a s h e a r zone g e n e r a t e
t e n s i l e strength, a r e elongated i n tension,
and break a t t h e t i p s , n o t i n t h e s h e a r
zone.
Thus, t h e mode o f r o o t f a i l u r e i s
s i m i l a r t o t h a t during a pull-out t e s t .
Abe a n d Iwamoto ( 1 9 8 6 ) c o n d u c t e d t e s t s on
CrvDtomeria iaDonica a n d measured b o t h t h e
pull-out
resistance
and t h e t e n s i l e
s t r e n g t h a t t h e p o i n t of breakage ( f i g . 4 ) .
The r e s u l t s w e r e q u i t e d i f f e r e n t .
The
pull-out resistance includes t h e t e n s i l e
s t r e n g t h a t breakage, p l u s t h e t a n g e n t i a l
f r i c t i o n between r o o t s and s o i l a n d t h e
m e c h a n i c a l s t r e n g t h c a u s e d by p u l l i n g b e n t
p a r t s of t h e r o o t through t h e s o i l .
C o n s e q u e n t l y , it i s n o t a p p r o p r i a t e t o u s e
t h e maximum t e n s i l e s t r e n g t h t o r e p r e s e n t
root reinforcing strength.
Although t h e
r e l a t i o n s h i p between p u l l - o u t r e s i s t a n c e
and t h e t h e o r e t i c a l
reinforced
soil
we
strength is not f u l l y understood,
p o s t u l a t e t h a t both a r e about e q u a l .
S t a b i l i t y of a f o r e s t e d s l o p e w a s
simulated using t h e pull-out resistance
(PO), o b t a i n e d by a r e g r e s s i o n a n a l y s i s
( e q . [151) of t h e r o o t d i a m e t e r ( D ) a t p u l l
points (fig. 4 ) .
SLOPE
STABILITY
ANALYSIS
Geology,
s o i l mechanics,
and s o i l
m o i s t u r e a f f e c t s l o p e s t a b i l i t y and a l s o
affect t h e d i s t r i b u t i o n of t r e e r o o t s ,
especially t a p roots.
Tsukamoto ( 1 9 8 7 )
c l a s s i f i e d slopes i n t o four types.
i s t h i n a n d u n d e r l a i n by
b e d r o c k w i t h few c r a c k s a n d j o i n t s .
The
r o o t s cannot p e n e t r a t e t h e bedrock and a r e
densely d i s t r i b u t e d i n t h e regolith.
Tap
r o o t s a r e n o t important. S o i l water cannot
permeate t h e bedrock,
and p o r e water
p r e s s u r e i s e a s i l y g e n e r a t e d on t h e b e d r o c k
surface.
Thus, t h i s t y p e o f s l o p e i s
r a t h e r u n s t a b l e a n d m o s t l y f o u n d on d i p p i n g
slopes i n t e r t i a r y parent materials.
p r e s s u r e i s seldom g e n e r a t e d because of
high permeability.
Accordingly, t h i s t y p e
of s l o p e i s q u i t e s t a b l e and i s found i n
a r e a s with mesozoic and p a l e o z o i c p a r e n t
material.
C type--Regolith
i s t h i n and t h e r e is a
t r a n s i t i o n a l (weathered) l a y e r between t h e
r e g o l i t h and bedrock.
Root g r o w t h may b e
a f f e c t e d by s o i l d e n s i t y and h a r d n e s s o f
this transitional layer.
S o i l moisture
does not e a s i l y permeate t h e t r a n s i t i o n a l
l a y e r , because o f i t s h i g h d e n s i t y , and
pore water p r e s s u r e i s e a s i l y generated.
R o o t s a r e most e f f e c t i v e on t h i s t y p e o f
As root strength declines a f t e r
slope.
logging,
many d e b r i s f l o w s w o u l d b e
e x p e c t e d . T h i s t y p e i s f r e q u e n t l y found i n
g r a n i t e mountains.
type--Regolith
i s t h i c k and r o o t s can
grow w i t h o u t r e s t r i c t i o n b y s o i l l a y e r s .
T h i s t y p e of s l o p e i s u s u a l l y found a t t h e
base of h i l l s l o p e s and have a g e n t l e a n g l e .
D e b r i s f l o w s n e v e r o c c u r on t h i s t y p e o f
slope.
D
The s t a b i l i t y o f t h e s e f o u r t y p e s o f
slope
was
investigated
by
assuming
r e a s o n a b l e v a l u e s o f i m p o r t a n t s o i l and
slope characteristics (table 3 ) .
The A-type s l o p e h a s 8 0 cm o f r e g o l i t h
t h i c k n e s s u n d e r l a i n by bedrock without
c r a c k s a n d t h e r o o t s c a n n o t p e n e t r a t e more
t h a n 80 c m d e e p . The B-type s l o p e a l s o h a s
80 c m o f r e g o l i t h , b u t b e d r o c k i s f r a c t u r e d
a n d r o o t s c a n i n v a d e t h e c r a c k s up t o
1 0 0 cm d e e p .
The C - t y p e s l o p e a l s o h a s
80 c m o f r e g o l i t h , p l u s a 40-cm-thick
t r a n s i t i o n a l l a y e r underlain by bedrock.
The D-type s l o p e h a s 150 c m o f r e g o l i t h a n d
a 40-cm-thick t r a n s i t i o n a l l a y e r u n d e r l a i n
by b e d r o c k .
The s t a b i l i t y c a l c u l a t i o n s
assumed t h a t t h e g r o u n d w a t e r r e a c h e d t h e
ground s u r f a c e .
Forests of w t o m e r h
i a ~ o n i c aa g e d 1 0 , 20, 30, a n d 40 y e a r s were
assumed t o b e g r o w i n g on e a c h s l o p e .
The
Table 3--Characteristics
--- -- --S l o p e
A type--Regolith
B type--Regolith i s t h i n and u n d e r l a i n by
b e d r o c k h a v i n g many j o i n t s a n d c r a c k s .
Roots a r e a b l e t o p e n e t r a t e i n t o bedrock
and c o n t r i b u t e t o s t a b i l i t y .
Pore water
of t h e four slopes
Slope angle (O)
T h i c k n e s s of r e g o l i t h (cm)
T r a n s i t i o n a l zone (cm)
Cohesion of s o i l ( t o n / m 2 )
I n t e r n a l a n g l e of s o i l ( o )
Cohesicnofbedrock(ton/m2)
I n t e r n a l a n g l e of b e d r o c k ( O )
Ground w a t e r t a b l e d e p t h (cm)
D e n s i t y of s o i l ( g / c c )
D e n s i t y of b e d r o c k ( g / c c )
zmax (cm)
A
B
32
80
0
0.2
30
20
40
0
1.3
2.5
80
32
80
0
0.2
30
20
40
0
1.3
2.5
100
type------C
32
80
40
0.2
30
20
40
0
1.3
2.5
100
D
15
150
40
0.2
30
20
40
0
1.3
2.5
170
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
s i z e of t r e e s i n each f o r e s t was o b t a i n e d
from y i e l d t a b l e s .
Root d i s t r i b u t i o n s
(number of r o o t s i n each 10-cm-thick s o i l
l a y e r f o r each 0.5-cm d i a m e t e r c l a s s ) were
The
s i m u l a t e d u s i n g t h e model ( f i g . 3 ) .
r e i n f o r c i n g s t r e n g t h (AS) i n e a c h 10-cmt h i c k l a y e r was c a l c u l a t e d u s i n g e q u a t i o n
[161.
where, AS
reinforcing strength a t
depth z cm
N ( 2 , i ): number of r o o t s of d i a m e t e r
i cm a t d e p t h z cm
P O ( i ) : p u l l - o u t s t r e n g t h of a r o o t
with d i a m e t e r i cm.
(2)
:
The s i m u l a t i o n r e s u l t s o f t h e f o u r
s l o p e t y p e s a r e shown i n f i g u r e 5 .
Soil
shear strength,
Ss,
shows an a b r u p t
i n c r e a s e a t t h e boundary between s o i l and
bedrock of t h e A-type and B-type s l o p e s ,
b u t on t h e C-type
slope t h a t has a
transitional
soil
layer,
soil
shear
SO IL-STRENGTH lk f / m a I
strength gradually increases.
Shear
s t r e s s , P s , exceeds t h e s o i l s h e a r s t r e n g t h
a t a d e p t h of 40 t o 80 cm on t y p e A, B, and
C slopes.
This i n d i c a t e s a p o t e n t i a l shear
zone a t t h e s e d e p t h s l e a d i n g t o t h e
possibility
of
a
landslide.
The
r e i n f o r c i n g s t r e n g t h by r o o t s (AS) was
c a l c u l a t e d by e q u a t i o n [I61 and added t o Ss
(fig. 5).
On t h e A-type s l o p e , t h e growth of t a p
r o o t s i s r e s t r i c t e d by t h e bedrock s o t h e r e
i s no r e i n f o r c i n g e f f e c t a t t h e boundary
(potential shear zone).
AS i s i n c r e a s e d
by t h e growing f o r e s t o n l y t o a d e p t h of
70 cm. I n o t h e r words, a l t h o u g h t h e number
of r o o t s i s i n c r e a s e d a s t h e f o r e s t becomes
o l d e r , r o o t reinforcement of t h e s o i l never
develops a t t h e boundary and P s w i l l exceed
S s a t t h i s d e p t h when t h e ground w a t e r
surface r i s e s .
This c o n d i t i o n can l e a d t o
a d e b r i s flow.
On t h e B-type s l o p e , however, r o o t s
p e n e t r a t e t h e c r a c k s i n t h e bedrock, and
r o o t reinforcement develops a t t h e s o i l bedrock boundary. When t h e f o r e s t i s o l d e r
SO I L-STRENGTH (k f/n' 1
134
103
134
105
:Soil shear strength
-- -- -- - :Promoting sliding ~ t r e nth
a:Rooted
o:Rooted
-:Rooted
+:Rooted
oil of a fore~taged
soi 1 of a forest aged
soil of a forest aged
soi l of a forest aged
i'
0
20
30
40
F i g . 5 . S i m u l a t e d r o o t e d s o i l s h e a r s t r e n g t h of f o r e s t s having f o u r
d i f f e r e n t ages on A, B, C, and D t y p e of s l o p e s
USDA Forest Service Gem Tech. Rep. PSW-GTR-130.1991
t h a n 20 y e a r s , AS becomes s t r o n g e r t h a n
Ss, and P s never exceeds s h e a r s t r e n g t h of
t h e r o o t e d s o i l , S r ( f i g . 5 ) . But, f o r t h e
10-year-old
f o r e s t , AS i s n o t s t r o n g
enough t o p r e v e n t a d e b r i s flow on t h e
slope.
The C-type s l o p e i s s i m i l a r t o t h e Btype.
Roots i n v a d e and r e i n f o r c e t h e
t r a n s i t i o n a l zone, and t h e p r o b a b i l i t y of
l a n d s l i d e s d e c r e a s e s a s t h e f o r e s t becomes
older.
The D-type s l o p e i s always s t a b l e w i t h
o r without a f o r e s t .
The f a c t o r of
safety
(FS) a t t h e
p o t e n t i a l s h e a r zone i n c r e a s e s f o r t y p e B
and C s l o p e s a s t h e a g e of a f o r e s t
i n c r e a s e s , up t o an age of 20 t o 2 5 y e a r s ,
a f t e r which it remains about c o n s t a n t a t
about 2.0 ( f i g . 6 ) . For t h e s e s l o p e t y p e s ,
t h e FS of 10-year-old f o r e s t s i s under 1 . 0 ,
indicating
a
high
probability
of
landslides.
The FS v a l u e s were c a l c u l a t e d
f o r a c o n d i t i o n where t h e ground w a t e r
r e a c h e s t h e ground s u r f a c e .
For A-type
s l o p e s , FS does n o t change with i n c r e a s i n g
f o r e s t age because r o o t s cannot r e i n f o r c e
t h e s o i l and bedrock i n t e r f a c e .
Type-D
s l o p e s remain s t a b l e a t a l l ages of f o r e s t .
DISCUSSION
A s f o r e s t s grow, r o o t systems d e v e l o p
t o provide s t r u c t u r a l support t o t h e t r e e s
and t o a b s o r b water and n u t r i e n t s .
Roots
a r e important i n s t a b i l i z i n g h i l l s l o p e s .
To
quantify
the
amount
of
root
reinforcement
A S , it i s necessary t o
u n d e r s t a n d t h e r e l a t i o n s h i p between r o o t
g r o w t h , s l o p e s t r u c t u r e , a n d d e p t h of
sliding surface.
In t h i s paper, root
r e i n f o r c e m e n t was modelled f o r f o u r t y p e s
of s l o p e s .
P r e v i o u s r e s e a r c h h a s shown
t h a t t h e r e a r e h i g h s l o p e f a i l u r e r a t e s on
g r a n i t e , s h a t t e r e d p a l e o z o i c and mesozoic,
and t e r t i a r y s l o p e s a s s o c i a t e d w i t h young
I t i s expected
f o r e s t s (Tsukamoto 1 9 8 7 ) .
t h a t t h e r e a r e d i f f e r e n c e s i n AS r e l a t e d
t o differences i n geologically related
s l o p e s t r u c t u r e . Thus, it i s important t o
identify those factors t h a t r e s t r i c t the
growth of r o o t s and t o q u a n t i f y t h e number
and s i z e of r o o t s t h a t can p e n e t r a t e i n t o
j o i n t s of bedrock o r t r a n s i t i o n a l s o i l
l a y e r s and r e i n f o r c e t h e p o t e n t i a l s h e a r
zone.
Logging can c a u s e a l a r g e d e c r e a s e i n
A s t h e r o o t s decay, a f t e r a 40-yearAS.
o l d f o r e s t h a s been c u t ,
the shear
r e s i s t a n c e of r o o t e d s o i l i n t h e p o t e n t i a l
s h e a r zone w i l l d e c r e a s e t o one t h i r d of
t h a t i n t h e uncut f o r e s t ( f i g . 5 ) , and t h e
p r o b a b i l i t y of s l o p e f a i l u r e w i l l i n c r e a s e .
Kitamura and Namba (1981) n o t e d t h a t t h e
r e s i s t a n c e of t r e e stumps t o u p r o o t i n g
d e c r e a s e s r a p i d l y a s t h e r o o t systems decay
following timber h a r v e s t .
They concluded,
when c o n s i d e r i n g t h e combined e f f e c t of
r o o t decay of t h e c u t t r e e s and r o o t growth
of t h e p l a n t e d t r e e s , t h a t t h e f o r e s t s o i l
would r e a c h a minimum s t r e n g t h between 5
and 10 y e a r s a f t e r c u t t i n g and r e p l a n t i n g .
Ziemer and Swanston (1977) measured t h e
changes i n s t r e n g t h of r o o t s remaining i n
t h e s o i l a f t e r l o g g i n g and noted t h a t even
the
largest
roots
lost
appreciable
strenath .
I n g e n e r a l , t h e i n f l u e n c e of f o r e s t
l o g g i n g on d e b r i s f l o w s a r e g r e a t e s t i n
g r a n i t i c and t e r t i a r y s l o p e s ( C - t y p e )
P a l e o z o i c and mesozoic s l o p e s ( 8 - t y p e )
g e n e r a l l y do n o t
h a v e an
increased
i n c i d e n c e of d e b r i s flow a f t e r f o r e s t
removal.
Tsukamoto (1987) e x p l a i n e d t h a t
t h e reason f o r t h i s i s t h a t t h e high
p e r m e a b i l i t y of t h e f r a c t u r e d bedrock
prevents
the
build-up
of
lateral
groundwater flow a l o n g t h e bedrock.
Ohta
( 1 9 8 6 ) s u g g e s t e d t h a t r o u g h n e s s of t h e
b e d r o c k a l s o makes t h i s t y p e of s l o p e
stable.
.
Forest age
o:A type of slope
o:B type of slope
A:C type of slope
+:D type of slope
F i g . 6. Change i n t h e f a c t o r of s a f e t y a s
the forest ages.
AS t e n d s t o i n c r e a s e a s t h e f o r e s t
becomes o l d e r , up t o an a g e of about 20
years,
a f t e r which AS r e m a i n s a b o u t
constant.
The c o n t r i b u t i o n of a s i n g l e
t r e e t o AS c o n t i n u e s t o i n c r e a s e a s t h e
t r e e becomes o l d e r . However, t h e number of
t r e e s i n t h e f o r e s t decreases with f o r e s t
a g e ( t a b l e 4 ) and t h e n e t e f f e c t i s a
c o n s t a n t AS a f t e r about 20 y e a r s .
Fortyy e a r - o l d s t a n d s of Uygwtomerla laxmica
. .
USDA Forest Service Gem Tech. Rep. PSW-GTR-130. 1991
CrvDtomeria iaDonjca
---------- Tree aqe (yr)----------
T a b l e 4--Sizes
(cm)
Height (m)
DBH
Number
(ha-l)
2
Area (m
)
of
5.0
5.4
3430
2.9
13.8
12.1
2265
4.4
20.0
15.8
1345
7.4
24.3
18.1
1030
9.7
have a h i g h density--one
tree per 3.1 x
3.1 m.
F o r t h i s s t a n d d e n s i t y , it i s
a c c e p t a b l e t o e s t i m a t e AS on a u n i t a r e a
basis.
However,
f o r old-growth
and
s c a t t e r e d t r e e s , it may n o t b e p r o p e r t o
e s t i m a t e t h e r e i n f o r c e d s t r e n g t h by u n i t
a r e a , because t a p r o o t s t e n d t o concentrate
below t h e w i d e l y - s p a c e d t r e e t r u n k s .
Most r o o t s i n t h e p o t e n t i a l s h e a r z o n e
In t h i s
a r e l e s s than 1 . 0 cm i n diameter.
paper, only t h e e f f e c t of roots within t h e
s h e a r z o n e were c o n s i d e r e d . However, s o i l
r e i n f o r c e m e n t by l a t e r a l r o o t s s h o u l d a l s o
b e c o n s i d e r e d . B u r r o u g h s a n d Thomas ( 1 9 7 7 )
r e p o r t e d t h a t z o n e s o f weakness d e v e l o p e d
between stumps t h a t c o u l d l e a d t o t h e
i n i t i a t i o n of slope f a i l u r e .
CONCLUSIONS
U s i n g a model o f t r e e r o o t d i s t r i b u t i o n
and t h e pull-out
strength of roots t o
e s t i m a t e t h e e f f e c t o f r o o t s upon s l o p e
s t a b i l i t y , we c o n c l u d e t h a t :
(1) Root r e i n f o r c e m e n t c o u l d b e e x p e c t e d on
s l o p e s where r o o t s grow i n t o j o i n t s o f
bedrock o r weathered t r a n s i t i o n a l
layers.
DS i n a p o t e n t i a l s h e a r zone
on such s l o p e s had t w i c e t h e s h e a r
s t r e n g t h of s o i l without r o o t s .
( 2 ) Most r o o t s d i r e c t l y a f f e c t i n g s l o p e
s t a b i l i t y a r e a b o u t 1 . 0 cm o r l e s s i n
diameter.
( 3 ) A f t e r a f f o r e s t a t i o n , DS would i n c r e a s e
q u i c k l y f o r a b o u t 20 y e a r s , t h e n r e m a i n
nearly constant.
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USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130. 1991
Watershed Concerns and Recent Policy Formulations
in Sri Lanka and Australia1
Rohan Ekanayake2
Abstract:
Addressing
the
problems
associated with watersheds
in both
c o u n t r i e s i s t h e aim o f t h i s p a p e r a s
well
as
assessing
the
respective
watershed p o l i c i e s . A t t e n t i o n h a s been
drawn t o s p e c i f i c economic, e n v i r o n m e n t a l
and s o c i o c u l t u r a l c o n s i d e r a t i o n s i n t h e
r e c e n t p a s t . An i n t e r e s t i n g f e a t u r e o f
t h e most r e c e n t p o l i c y developments i s
t h e tendency t o follow a balanced
approach t o w a t e r r e s o u r c e development i n
e i t h e r s i t u a t i o n . I n A u s t r a l i a , it i s
e n v i s a g e d t o f o l l o w a co-ordinated and
s u s t a i n a b l e u s e a n d management o f l a n d
w a t e r , a n d v e g e t a t i o n r e s o u r c e s on a
water catchment b a s i s .
I n S r i Lanka
however, a f t e r a p r o l o n g e d l u l l i n p o l i c y
approaches it i s o n l y beginning t o
p r e p a r e t h e framework t o w a r d s a b e a r a b l e
e.
While
accommodating
a
similar
p o p u l a t i o n t o A u s t r a l i a , S r i Lanka i n i t s
t i n y 270 m i l e s s t r e t c h , h a s i t s p e o p l e
c l u s t e r e d on t h e m o i s t s o u t h w e s t e r n t h i r d
o f t h e i s l a n d known a s t h e 'wet z o n e ' . I n
A u s t r a l i a , where t h e m a i n c o n c e n t r a t i o n
i s i n t h e e a s t e r n p a r t of t h e continent,
t h e r e i s h e a v y r e l i a n c e on c a t c h m e n t s o f
Great
Dividing
Range
and
the
the
a s s o c i a t e d run-off
f o r a g r i c u l t u r e and
h y d r o e l e c t r i c i t y . I n S r i Lanka, t h e
catchments f o r n e a r l y a l l i t s major
r i v e r s r e s t i n the central highlands
where most o f i t s h y d r o e l e c t r i c i t y i s
P r e s e n t e d a t t h e S u b j e c t Group S 1 . 0 4
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s
o n Managed F o r e s t s , X I X World C o n g r e s s
I n t e r n a t i o n a l Union o f F o r e s t r y R e s e a r c h
Organisations,
August
5-11,
1990,
M o n t r e a l , Canada.
R e s e a r c h Economist, Water
R e s o u r c e s D i v i s i o n , Department
I n d u s t r i e s and Energy,
and
Research School of
Social
Australian National University,
a n d Land
of Primary
formerly
Sciences,
Canberra.
USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130.1991
generated
and
water
diverted
for
downstream
purposes.
Compared
t o
Australia,
Sri
Lanka
receives
a
r e l a t i v e l y h i g h e r r a i n f a l l mainly from
t h e monsoonal r a i n s .
WATERSHED MANAGEMENT
S r i Lanka
Irrigation structures i n the dry
z o n e o f S r i Lanka h a s a h i s t o r y o f 2000
its
first
water
years,
and
thus,
management p r a c t i c e s c a n b e r e l a t e d t o
t h a t t i m e . However, i n modern S r i Lanka,
s o i l e r o s i o n a n d w a t e r s h e d p r o b l e m s were
f i r s t r e c o g n i s e d and a d d r e s s e d i n t h e
l e g i s l a t u r e i n t h e e a r l y 1 9 4 0 ' s . But
policy formulation did not take place
t i l l r e c e n t t i m e s b e f o r e a major r i v e r
b a s i n d e v e l o p m e n t programme was i n i t i a t e d
s u r r o u n d i n g t h e Mahaweli r i v e r . L a r g e l y ,
t o w a r d s t h e s u s t e n a n c e o f t h i s programme,
it
was
inevitable
some p o l i c y
be
introduced
t o
manage
the
natural
resources surrounding i t s catchments.
T h i s m a t e r i a l i z e d o n l y i n t h e l a t e 1989
when a n i n t e r i m r e p o r t o n w a t e r s h e d
m a n a g e m e n t was c o n s i d e r e d b y p o l i c y
makers i n S r i Lanka.
The r e l e v a n t l e g i s l a t i o n were f i r s t
i n t r o d u c e d i n A u s t r a l i a i n 1915, a n d i t s
maiden
water
resource
assessment
programme b e g a n i n 1 9 6 3 . A u s t r a l i a ' s main
w a t e r management programme i n v o l v e s t h e
Murray-Darling r i v e r b a s i n t h a t s p r e a d s
o v e r f o u r of i t s m a j o r s t a t e s .
More r e c e n t l y , a B i l l was t a b l e d i n
t h e New S o u t h W a l e s L e g i s l a t u r e t o
i m p l e m e n t t o t a l c a t c h m e n t management o f
t h e S t a t e ' s n a t u r a l r e s o u r c e s , namely,
t h e c o - o r d i n a t e d and s u s t a i n a b l e u s e and
management o f l a n d , w a t e r , a n d v e g e t a t i o n
r e s o u r c e s on a c a t c h m e n t b a s i s . Such
p o l i c y developments followed t h e r e c e n t
F e d e r a l concerns o v e r a balanced approach
t o natural
resources
management
in
Australia.
CONCERNS
FOCUS
While d e f o r e s t a t i o n i n t h e c a t c h m e n t
v e g e t a t i o n i s common i n b o t h c o u n t r i e s
and
excessive
pressure
on
water
resources, is t h e r e genuine concern i n
S r i Lanka a n d i n A u s t r a l i a t o a m e l i o r a t e
t h e s i t u a t i o n a n d a c h i e v e a b a l a n c e ? The
e x t e n t of t r e e c l e a r i n g i n A u s t r a l i a i n
t h e main c a t c h m e n t ( G r e a t D i v i d i n g Range)
of t h e Murray-Darling Basin a l o n g t h e
e a s t e r n c o a s t i s shown i n t h e map. S r i
its l a s t
Lanka,
having c a r r i e d out
p a r t i a l f o r e s t i n v e n t o r y i n 1956, f a c e s
similar excessive deforestation i n the
main c a t c h m e n t o f t h e Mahaweli a n d i t i s
estimated t h a t i t s f o r e s t cover has
d w i n d l e d f r o m 56 p e r c e n t i n 1 9 5 6 t o a
mere 1 5 p e r c e n t i n t h e p r e s e n t t i m e s .
In t h i s paper, an assessment of
watershed p o l i c i e s of both c o u n t r i e s
been c a r r i e d o u t drawing a t t e n t i o n
s p e c i f i c economic,
environmental
sociocultural considerations
in
recent past.
ienl ot Tree Clearing in Australia Since European Setllernent
the
has
to
and
the
INSTITUTIONS a n d p o l i c y
Government p o l i c y i n t e r v e n t i o n i s
two-pronged i n w a t e r s h e d c o n c e r n s . D i r e c t
and i n d i r e c t . D i r e c t p o l i c i e s a r e o f t e n
regulating
measures
that
affect
a
watershed.
I n d i r e c t p o l i c i e s c o n v e r g e on t h e
integrated
land-uses
in
an o v e r a l l
w a t e r s h e d r e g i o n . U s u a l l y t h e s e measures
do n o t f a l l w i t h i n t h e scope of a
p a r t i c u l a r p o l i c y c o n s i d e r a t i o n . I t would
be f a i r t o say t h a t i n e f f e c t , i n d i r e c t
p o l i c y once a p p l i e d h a s i n d i r e c t e f f e c t s
on t h e w a t e r s h e d . T h e s e i n d i r e c t e f f e c t s
a r e t h e n moulded i n t o e x p l i c i t p o l i c y i n
t h e next application.
Indirect
Policy
I
( a t y p i c a l t h e o r e t i c a l e x p l a n a t i o n of an
e f f e c t on a w a t e r s h e d )
I
i n t r o d u c t i o n ......p r i c e s u b s i d y f o r
a g r i c u l t u r a l production
/
i n t e n s i v e a n d ...... e f f e c t s from t h e
e x t e n s i v e land v e s e t a t i o n cover reduction
use
/
i n c r e a s e d s o i l ......i n c r e a s e d s e d i m e n t a t i o n
erosion
-
I n b o t h s i t u a t i o n s , environmental
f l o w management a n d f l o o d m i t i g a t i o n
remain u n r e s o l v e d p o l i c y i s s u e s mainly
because o f l a c k of i n f o r m a t i o n and t h e
a s s o c i a t e d s o c i a l and economic f a c t o r s .
I t i s i n t h e same i n t e r e s t t h a t it h a s
become a p p a r e n t t h o s e i s s u e s b e a d d r e s s e d
i n a c o h e r e n t p o l i c y frame f o r b r o a d
i n t e r - t e m p o r a l r e a s o n s . The s u s t a i n a b l e
f r a m e s t i l l r e m a i n s t h e same- t h e T r i n i t y
o f S o i l , T r e e s a n d Water ( d i a g r a m 1).
Trees and Soil Conservolion
A .led,.,,b
/
r e s e r v o i r ......
power c u t s , o i l i m p o r t s
water l e v e l s
t o fuel extra turbines
I
diminishing
o v e r a l l...economic, r e s o u r c e
and environmental
e f f e c t s on s o c i e t y
The p o l i t i c a l economy w i t h i n which
p o l i c i e s a r e formed, r e s h a p e d a n d a p p l i e d
is a r t i c u l a t e d uniquely according t o t h e
s p e c i f i c s p a t i a l c o n d i t i o n i n S r i Lanka
and A u s t r a l i a .
I n S r i Lanka, i t i s more c e n t r a l l y
c o n t r o l l e d and r e g i o n a l l y a p p l i e d . I n
A u s t r a l i a however, i t i s more r e g i o n a l l y
c o n t r o l l e d and r e g i o n a l l y a p p l i e d . For
instance,
the
role
of
the Central
Government i n i n s t i t u t i o n a l m a t t e r s i n S r i
Lanka i s a u t h o r i t a t i v e i n n a t u r e , w h e r e a s
i n Australia t h e r o l e of t h e Federal
Government i n w a t e r a f f a i r s i s more
oriented
towards
a
pro-active
participation.
USDA Forest SelviceGen. Tech. Rep. PSW-GTR-130. 1991
I n managed a n d unmanaged w a t e r a n d
watershed a f f a i r s , S r i Lanka's c e n t r a l l y
is
dominated
and
directed
policy
e s s e n t i a l l y a l i n e f u n c t i o n a l system ( n o t
n e c e s s a r i l y though t h e y a r e e f f i c i e n t ) . In
Australia,
several regional
(States)
governments
have
different
policy
approaches, i n s t i t u t i o n a l s t r u c t u r e s i n
p l a c e , and l e g a l frameworks i n w a t e r s h e d
s e t t i n g s ( n o t n e c e s s a r i l y though t h e y a r e
inefficient) .
Consider
the
two-nation's
main
w a t e r s h e d r e g i o n s . The f o c u s i s on t h e
more n a t u r a l l y i m p o r t a n t a s w e l l a s
s o c i a l l y desired productive regions ( i . e .
Basins) .
These
Basins
serve
as
their
r e s p e c t i v e economic a n d e c o l o g i c a l n e r v e s
where most s o c i a l t r a n s f o r m a t i o n s o c c u r ,
v a l u a b l e c u r r e n c y e x c h a n g e e a r n e d , more
importantly food produced, t h e people
p r o d u c t i v e l y employed and s c a r c e and
b e a r a b l e w a t e r managed.
The r e c e n t phenomenon i s n o t s o much
an o p t i m i s t i c and problem s o l v i n g water
f r o n t t o both countries, but c o n s i s t of
overwhelming problem s o l v i n g h o r i z o n s . It
is i n f a c t inheritance in both s i t u a t i o n s .
The g r e a t e s t t a s k s t h a t b o t h c o u n t r i e s
have a s p i r e d a r e t h e c h a l l e n g e s faced with
the a c c e n t u a t e d e n v i r o n m e n t a l c o n s e q u e n c e s
from t h e c o n t i n u e d r e s o u r c e d e g r a d a t i o n .
c r o s s roads a r e t h e f a v o u r i t e
concepts f o r p o l i c y manipulation i n flood
mitigation,
energy sustenance,
water
q u a l i t y maintenance, t o t a l approach t o
b a l a n c e d r e s o u r c e u s e and of c o u r s e
sustainability.
At
D e s p i t e t h e optimism, t h i s b r i n g s u s
t o a t h i r d s e t of p o l i c y a p p l i c a t i o n .
N a t u r a l R e s o u r c e s Management S t r a t e g y
(NRMS) f o r o v e r a l l r e s o u r c e p l a n n i n g a n d
management f o r a B a s i n w i d e s y s t e m . The
i n i t i a t i v e s a r e (following t h e maps);
S r i Lanka- Mahaweli A c c e l e r a t e d Program
A u s t r a l i a - Murray-Darling B a s i n
N a t u r a l R e s o u r c e s Management
S t r a t e g y a n d Program.
S o i l conservation A c t follows a f t e r
p r i v a t e member B i l l i n t h e L e g i s l a t u r e
i n 1940.
u
A considerable
through t o 1960's.
lull
in
Absence of i n t e g r a t e d
watershed a n a l y s i s .
Lack o f i n d e p t h
catchment hydrology.
the
Basin
s t u d y on
D e f f i c i e n c y i n r e s o u r c e s and h i g h
l e v e l of
resource
degradation
with
p l a n t a t i o n a g r i c u l t u r e and p r i v a t e f e l l i n g
i n t h e main c a t c h m e n t .
A l l Basins:
R i v e r s 103, t o t a l catchment a r e a
5 9 , 2 1 7 s q km a n d number o f s t r e a m g a u g i n g
s t a t i o n s ( R i v e r Gauging S t a t i o n s ) ; 6 8 .
The Mahaweli B a s i n c a t c h m e n t 1 0 , 4 4 3
s q km a n d 1 8 RGS, number o f r u n - o f f
s t a t i o n s : on a d a i l y b a s i s - n i l , monthly7.
R e c e n t on w a t e r s h e d d e v e l o p m e n t s :
of
catchments
Land Development O r d i n a n c e 1 9 3 5 .
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
wide
detailed
S r i Lanka:
Optimum c o n s e r v a t i o n
i s i n pursuance.
1950's
F i r s t I n t e r i m R e p o r t on Land 1 9 8 5 .
Second I n t e r i m R e p o r t on Land 1989
1
Basin developments:
The Murray-Darling Basin
\
In the Mahaweli Accelerated Program
total run-off in the project at lowest
points of diversion is 10,000 cu m or 25
percent of the total run-off.
A Forestry Master Plan (1986) to
circumvent the acute deforestation has
been introduced
1/7th
of
Australia's
surface
catchment falls within the purview of
Murray-Darling Basin.
20 major
Dividing Range.
rivers
off
the
Great
40,000 years history of the Basin
associated Aboriginal Culture.
The length of the River is 3780 km
30 to 40 percent of Australia's
total natural resource based production
occurs in the Basin.
Australia:
7000 wetlands within the Murray waters.
First Legislation in 1915 on MurrayDarling Basin Agreement between New South
Wales, Victoria and South Australia.and
River Murray Waters Amendment Act 1987.
Murray yields 12,000 gigalitres and
the Darling carries 12 percent of the runoff over 50 percent of the Basin area.
Catchment management
management follows.
CONSTRAINTS
and
water
Federal level New directions of
Water Management 1987 and Instream Uses of
Water.
Recently, NSW State Legislation on
Total Catchment Management, 1989 (see
community participation as per media
publicity) .
Basin wide:
135 RGS and 10 within the MurrayDarling Basin.
River Murray Waters Act 1987.
Conflicts in the institutional
arrangements create external diseconomies
and in turn have created duplication and
overlapping of institutions in both
situations.
These
impediments have
caused
disincentives to achieve efficiency and
there is a large resource value depletion
in both watersheds. This is largely
reflected in undercharging for water and
lack of appreciation of the resource has
been aggravated by the absence of a rent
which is the key to secure the resource
for intergenerational purposes.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
The way t h e p o l i t i c s
interpret
p r i o r i t i e s , i g n o r a n c e , postponement o f
a c t i o n s and u n d i s c l o s e d d e f i n e d regimes
particularly in the sustainability issues
have caused t h e g r e a t e s t i n e q u i t y i n
watershed concerns i n t h e s e s i t u a t i o n s .
In Australia,
inter-governmental
quangos s u c h a s t h e R i v e r Murray Agreement
p r e s e n t bona f i d e commitment by t h e S t a t e s
t o co-ordinated,
comprehensive r e g i o n a l
approach t o i n t e r s t a t e water and r e s o u r c e
issues.
is l e g a l opinion t h a t a
There
r a t i o n a l scheme f o r b a l a n c i n g c o n f l i c t i n g
i n t e r e s t s w i t h i n t h e Murray-Darling Basin
and f o r a d m i n i s t e r i n g t h e system i s
u n l i k e l y t o s p r i n g up, a l o n e a n d u n a i d e d ,
a s a v o l u n t a r y p r o d u c t of S t a t e c o n s e n t .
I n S r i Lanka, t h e i n f a n t s t a g e o f
i t s handling of n a t u r a l resources and
i n i t i a t i v e s , and t h e slow p r o g r e s s and
c a u t i o u s a p p r o a c h v i n d i c a t e t h e whole
o b j e c t i v e o f w a t e r s h e d p r o t e c t i o n f o r good
e c o n o m i c a n d e n v i r o n m e n t a l r e a s o n s . The
e x p e c t a t i o n t h a t f o r e i g n h e l p would a l w a y s
b e f o r t h c o m i n g t o s a l v a g e t h i n g s t h a t have
g o n e wrong f o r d e c a d e s d u e t o p o l i t i c a l
mishandling of important i s s u e s i s i n
i t s e l f a summation o f t h e i d e o l o g y b e h i n d
t h e scene.
I n A u s t r a l i a , a major problem t h a t
the
Murray-Darling
Basin
watershed
p l a n n i n g c o n f r o n t s i s t h e v o l u n t a r y nonp a r t i c i p a t i o n of t h e Queensland s t a t e i n
t h e S t r a t e g y t o manage t o t a l w a t e r ,
vegetation and environmental flows. In
t e r m s o f key t r i b u t a r i e s , t h e S t a t e ' s p a r t
of t h e catchment i s c r i t i c a l t o a c h i e v e a
b e a r a b l e l e v e l of water flows i n t h e
d o w n s t r e a m . They a r e a l s o t h e u n d e r l y i n g
c a u s e s f o r most o f t h e f l o o d i n g i n t h e
a d j o i n i n g S t a t e o f NSW
(during the
preparation of t h i s manuscript t h e i r has
been
a
positive
development
t o conglomerate Queensland t o t h e River
Murray W a t e r s A g r e e m e n t ) .
and s u s t a i n e d p r o d u c t i v e r e s o u r c e f o r t h e
respective regions.
Intergenerational issue is another
i m p o r t a n t p o l i c y d e b a t e t h a t looms g i v i n g
p e r t i n e n t a t t e n t i o n t o i n t e r temporal
e q u i t y v a l u e of t o t a l r e s o u r c e s i n a
watershed. A t t h i s point i n t i m e t h e best
c o u l d b e a c h i e v e d i s t o l e a r n from t h e
past
mistakes
and
accommodate
comprehensive s e t s of o b j e c t i v e s n o t o n l y
t o circumvent p r e v i o u s impediments b u t t o
guard against reoccurrence of degradations
a n d d e n u d a t i o n s . Because s i n g l e i s s u e
o r i e n t e d s o l u t i o n s i n a watershed region
d o e s n o t c a r r y t h a t much o f w e i g h t i n
p o l i c y j u s t i f i c a t i o n anymore.
However, t h e d e t e r m i n i n g f o r c e i s
n o t t h e way t h a t p o l i c y i s f o r w a r d e d i n a
package,
but the trade-offs
desired
p o l i t i c a l l y and implemented c o n c e r n i n g
whether e q u i t y o r e f f i c i e n c y i s t h e
c r i t e r i o n o f t h e d a y . I t i s paramount
because n e i t h e r w i l l be achieved i f both
c r i t e r i a a r e pursued.
A
conceptual model
of watershed
policy
I
Level of p o l i c y s u b s t i t u t i o n
=
l e v e l of
program/NRMS p o l i c y
I
Take NRMS f o r i n s t a n c e a s a f u n c t i o n o f
T o t a l Catchment
I
Management
[NRMS f (TCM) I
I
TCM f
( s o i l , vegetation, watershed)
I
Therefore, t h e s i g n i f i c a n c e f o r water
policy
CONCLUSION
I
N a t u r a l r e s o u r c e management i s t a k e n
up by a b r o a d l y modelled t o t a l catchment
c o n c e p t which h a s i m p o r t a n t p a r a m e t e r s a n d
i m p l i c a t i o n s . However, it i s a b r a n d new
p h e n o m e n a . Only t i m e c a n d e t e r m i n e t h e
significance of t h e strategy a s well a s
the accelerated initiatives.
T o t a l c a t c h m e n t management h a s s c o p e
f o r flood mitigation, s o i l conservation
and sedimentation problems i n e i t h e r
s i t u a t i o n . The c o n c e p t i s i n harmony w i t h
an o v e r a l l supply of vegetation resources
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
a s t h e i n s t i t u t i o n f o r watershed concerns
note:
NRMS= N a t u r a l R e s o u r c e s Management S t r a t e g y
TCM= T o t a l Catchment Management
REFERENCES
COMMUNITY REPRESENTATIVES
CATCHMENT MANAGEMENT
COMMITTEE
for the Lower Murray-Darling Region
Australia Murray-Darling Basin by MurrayDarling Basin Ministerial Council.
1990. Natural Resources Management
Strategy Towards a Sustainable
Future; ii.
CATCHMENT MANAGEMENT ACT, 1989
Clark, S.D.; 1983. Intergovernmental
Quangos: The River Murray
Commission. Australian Journal of
Public Administration XLII (1): 155171.
The N S W Government is erlablirhing Calchment Managcmenl
Cammillecr, under the Catchment Management A c l 1989. to
implement Tola1 Catchmen! Manrgcmenl ( T C M ) objcctiver.
T C M k a community-based approach 10 natural resource management.
I1 is the co-ordinated and ~ustainableurc and management of land.
water, veaclalion. fauna and other natural resources. Its aim is in
balvncc r&ouicc use and canrcivation
To allow various and d i k i n g Wcslern N S W land use management
lssucs to be adequately and effectively addressed i t is proposed to divide
the Wcstcrn R c ~ i o ninto two reeionr:
Commonwealth of Australia; 19897. River
Murrav Waters Amendment Act. No. 154
of 1987. Australia; Commonwealth
Government Printer.
The boundary between these regions follows the Sydney-Broken Hill
Railway line until Menindee Lakes. The Menindee Lake System.
Broken Hill and the enlirc Lake Viclaria catchment lies within the
Lower M u r r a y - D a r l i n ~Region.
Thc eartcrn boundary of ihc Lowcr Murray-Darling region iollows ihc
catchmen1 boundary wilh the Lachlan and Murrumbidgce, being the
boundary t o the Lachlan and Muriumbidgee T C M regions. The
southern and western boundaries follow the Murray RivcrjVictorian
border and South Australian border rerncclivelv.
Pcrsun, who ace landhuldcir, laodu&% or who ham an intercst i n
environmenval m a l i e n in the Lawer Murray-Darling are invited to
apply l o be represenlalives o i i h c region on the T C M Cornmillee.
Members o i lhe exisling W W e r n Calchment Management Cammiltcc
will becamo members o i (he Cammiltee within which they reside and do
not nced to reapply.
Applicanu rhould Dossesr the followine oualities:
coirm t m w : io su.!din~b e dc.cl~pmcn1.
k n s ~ l c a g c .lntererl ~r ckpcrien:e n nalur2l rcrodrce m m l g e m m l .
3 b d 1) 10 rcprejcn! commun t y ,cur.
moucdgc o i mt.ri
rcromcc I r r x r .n the catcnmcm and hou
thcsc tisuer 3ifc:t 1 k pc.ap.c. r n d
r x r 8 ::lpml.r, 75 P I I ~ ~ ~ C W L U 1b.ni n~ ~ n thc
d %bll.t, l o uork wc..
Day, Diana G.; 1988. River Mismanagement:
Policy, Practice or Nature?; Centre
for Resource and Environmental
Studies Working Paper 1988/1;
Australian National University; 142.
Democratic Socialist Republic of Sri
Lanka; 1985. First Interim Report of
the Land Commission; Sessional Paper
No.1- 1986. Department of Government
Printing Sri Lanka.
-.
....
Democratic Socialist Republic of Sri
Lanka; 1989. Second Interim Report
of the Land Commission- 1985.
Department of Government Printing
Sri Lanka.
F--r.-.
Further iniormation is available from M r . Brenda" Diacono, T C M
Comdinatoi: (Ohill
RR 0 2 5 5 ~
..,..
Wrillcn applications providing details in terms o f the above ualitics
should bc with M r . Diacono (c/- N S W Soil Conservation %,,vice.
32 Sulphidc Slrccl, Brakcn H i l l 2880) by 11 August. 1990.
~
Department of Primary Industries and
Energy; 1988. Instream Use of
Australia's Water Resources;
Australian Water Resources Council
Water Management Series No.11.
Australian Government Printing
Press; 1-13.
1. Western
2. Lower Murray-Darling
THE NEW SOUTH WALES GOVERNMENT
q
Putting people first by managing better Bo
de Silva, Chandrananda R.K. 1982. Sri
Lanka Country Paper. In: Water and
Soil Miscellaneous Publication No.
45; Catchment management for optimum
use of land and water resources:
Documents from an ESCAP seminar;
1982 Wellington; 191-202.
Extent of Tree Clearing in Australia Since
European Settlement by Ive and Cock.
1989. Rural Land Degradation in
Australia: The Australian
Conservation Farmer; 1 (3)
.
ACKNOWLEDGEMENTS
I thank my friend S. Gunatunqa, Sri Lanka;
for sending research material. This paper
was supported by the Scientist Assistance
Program of Canada.
26
Murray-Darling Basin Ministerial Council;
1990. Natural Resources Management
Strategy Murray-Darling Basin:
Towards a Sustainable Future;
August, 1990.
USDA Forest ServiceGen.Tech. Rep.PSW-GTR-130.1991
Murray-Darling Basin Ministerial Council;
1987. Murray-Darling Basin
Environmental Resources Study; july
1987; State Pollution Control
Commission, Sydney. 27-113; 251-281.
NEDECO; 1979. Mahaweli Ganga Development
Program Implementation Strategy;
Netherlands Engineering Consultants;
The Hague September 1979; Volume 1
Main Report; 17-21.
New South Wales Government. Community
Representatives Catchment Management
Committee. The LAND. 1990 July 26.
2 (col.1) . New South Wales.
New South Wales (NSW) State Parliament;
1989. Catchment Management Bill.
First Print.
Soil Conservation Service of New South
wales; 1990. Total Catchment
Management: A State Policy Including
State Soils Policy, State Trees
Policy.
USDA Forest SewiceGen. Tech.Rep. PSW-GTR-130.1991
Sri Lanka Mahaweli Basin and Accelerated
Program b.y IIM1.1986.; 19.
Sri Lanka Mahaweli Basin and Mahaweli
River Catchment appeared in a paper
presented by Rohan Ekanayake;
Economics of Multiple Use of
Production Forests in Sri Lanka.
1986. 30th Annual Conference of the
Australian Agricultural Economics
Society; February 3-5, 1986; 20.
The Global Water Runoff Data Project.
1989. World Climatic Programme
Research, Workshop on the Global
Runoff Data Set and Grid Estimation,
WCRP - 22 and WMO/TD - No. 302, 1988
November 10-15; Klobenz, FRG; 6-12.
Trinity of Soil, Trees and Water based on
a diagram in a publication of the
NSW Soil Conservation Service.
Surrounding the Consequences of Watershed Disasters
in the Periphery of the Indian Triangle1
Rohan Ekanayake2
A b s t r a c t : The w a t e r s h e d o f t h e ' I n d i a n
T r i a n g l e ' i s f o r m e d b y t h e f l o w o f two
mighty r i v e r s which emanate from t h e
H i m a l a y a . The G a n g e s a n d B r a h m a p u t r a
embrace t h e l a n d s and t h e p e o p l e s o f
Nepal*,
I n d i a * and Bangladesh* b e f o r e
e m p t y i n g i n t o t h e Bay o f B e n g a l . A r e c e n t
monsoon submerged two t h i r d s o f t h e lowl y i n g B a n g l a d e s h r e n d e r i n g 25 m i l l i o n
p e o p l e h o m e l e s s . Can t h e f u t u r e o f t h e s e
p e o p l e b e s e c u r e d by l o w e r i n g t h e w a t e r
l e v e l s downstream? A r e t h e r e a l t e r n a t i v e
s t r u c t u r a l p r o p o s i t i o n s and a r e t h e y
economically and p o l i t i c a l l y f e a s i b l e ?
What e f f e c t w i l l t h e e x c e s s i v e r e m o v a l o f
n a t u r a l b a r r i e r s t o r a i n i n t h e upper
c a t c h m e n t s h a v e on p o l i c y ?
A major
i s s u e addressed i n t h i s paper is
t h e s u s t a i n a b l e development and e c o l o g i c a l
s t a b i l i t y i n t h e s e watershed r e g i o n s . A
m a j o r i t y o f t h e e n v i r o n m e n t a l problems i n
t h e r e g i o n ' s watersheds i n t h e p a s t have
o c c u r r e d m a i n l y d u e t o u n d e s i r a b l e human
i n t e r f e r e n c e i n regional environmental
flows and v e g e t a t i o n r e s o u r c e s . P l a u s i b l e
solutions
t o
on-going
and
future
e n v i r o n m e n t a l c r i s i s w i l l l a r g e l y depend
o n how b r o a d t h e r e g i o n a l c o n s e n s u s i s
surrounding t h e c o n f l i c t i n g water .resource
i s s u e s . D e p e n d i n g o n how t h e d o m i n a n t
r u r a l s o c i a l base a d j u s t t o important
dynamics
of
t h e problem,
t h e paper
concludes t h a t s u s t a i n a b i l i t y w i l l be an
issue
vulnerable
t o
political
interDretation.
P r e s e n t e d a t t h e S u b j e c t Group 5 1 . 0 4
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s on
XIX
World C o n g r e s s
Managed F o r e s t s ,
I n t e r n a t i o n a l Union o f F o r e s t r y R e s e a r c h
Organisations,
August
5-11,
1990,
M o n t r e a l , Canada.
R e s e a r c h E c o n o m i s t w o r k i n g i n t h e Water
B r a n c h o f t h e Land R e s o u r c e s D i v i s i o n i n
t h e Department of Primary I n d u s t r i e s and
Energy a n d f o r m e r l y Research School o f
Social Sciences,
Australian National
University, Canberra.
L i k e most w a t e r s h e d r e g i o n s i n t h e
world, t h e watershed r e g i o n o f t h e ' I n d i a n
t r i a n g l e ' i s on i t s h i s t o r y ' s r a p i d g r o w t h
t r a c k . A s u d d e n p r o g r e s s o f e v e n t s on
s e v e r a l i n t e r r e l a t e d f r o n t s - t h e economic,
t h e e c o l o g i c a l and t h e p o l i t i c a l has
combined t o s p u r s i g n i f i c a n t c h a n g e s b o t h
i n t h e r e l a t i o n s h i p s between p e o p l e s ,
policy-makers and governments and i n t h e
way
these
forces
interact
in
the
management-use
and conservation-of
the
w a t e r and v e g e t a t i o n r e s o u r c e s a s a whole.
THE PEOPLE
The s i g n i f i c a n c e ( p e r c e n t ) o f r u r a l
population t o t h e r e l e v a n t South Asian
n a t i o n s i s shown from t h e U n i t e d N a t i o n s
Population Studies (1989).
Year
Nation
1955 1965 1975 1985
India
82.4 81.2 78.5 74.5
B'desh
95.3 93.8 90.9 88.1
Nepal
97.3 96.5 95.2 92.3
The c o m p o s i t i o n o f t h e p o p u l a t i o n i n
t h e t r i a n g l e i s n o t d i f f e r e n t from t h e
r e s p e c t i v e n a t i o n a l a g g r e g a t e s a n d t h u s it
is based s i g n i f i c a n t l y i n t h e r u r a l a r e a s .
A g r i c u l t u r e i s predominant and a l a r g e
d e p e n d e n c e on n a t u r a l r e s o u r c e s i s common
i n t h e r e g i o n . The i m p o r t a n c e o f w a t e r
r e s o u r c e t o t h e people i n t h e watershed i s
immense f o r t h e i r l i v e l i h o o d a n d s o d o e s
t h e f o r e s t r y r e s o u r c e (Ekanayake 1 9 9 0 ) .
THE PROBLEM
It i s a r e g u l a r f e a t u r e i n Bangladesh
l i f e t o experience floods every year
and
it i s not s u r p r i s i n g t o expect flooding
w i t h a l m o s t e v e r y monsoon f o l l o w e d u p by a
d r o u g h t . A r e c e n t monsoon s u b m e r g e d two
thirds
of
the
low-lying
areas
of
B a n g l a d e s h r e n d e r i n g 25 m i l l i o n p e o p l e
homeless.
D e s t r u c t i o n s t o crops and
e c o n o m i c l o s s e s a r e i n s u r m o u n t a b l e . The
S e p t e m b e r 1988 f l o o d s i n u n d a t e d 2 m i l l i c n
h a o f f a r m l a n d (FEER 1 9 8 9 ) .
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
Like t h e r i v e r dispute involving t h e
E u p h r a t e s - T i g r i s a n d S h a t t a 1 Arab i n t h e
Mediterranean, t h e long-running d i s p u t e
between I n d i a , B a n g l a d e s h and Nepal on t h e
c o n t r o l of
waterways of
Ganges a n d
Brahmaputra h a s l e d t o a sequence o f
u n c o n t r o l l e d f l o o d s and droughts i n t h e
region of t h e t r i a n g l e .
O c c u r r e n c e of heavy f l o o d s 3 i n t h e
t r i a n g l e i n t h e p a s t have been;
Decade
1950 1960 1970 1980
AS s am
-
2
2
4
3
3
3
4
(India)
Bangladesh
It
is
claimed
that
increasing
p o p u l a t i o n h a v e a d d e d i m p e t u s on t h e
w a t e r s h e d d i s a s t e r s b y way o f e x t r a
d i m e n s i o n s of human a n d economlc c o s t s .
p o p u l a t i o n . But l a r g e p a r t s of c u l t i v a t e d
l a n d u s u a l l y e x p e r i e n c e t h e problem of
i n s u f f i c i e n t r a i n f a l l f o r crop growth
e i t h e r i n terms of p r e c i p i t a t i o n o r i t s
d i s t r i b u t i o n t o match w i t h c r o p w a t e r
requirements.
N a t i o n a l Commission on
Agriculture estimates India's u t i l i s a t i o n
o f a n n u a l p r e c i p i t a t i o n would improve i n
t h e e a r l y p a r t of t h e n e x t c e n t u r y from
i t s c u r r e n t l e v e l of 2 5 p e r c e n t .
14.4
Bangladesh has an a r e a of
m i l l i o n ha l y i n g i n t h e d e l t a of t h e
r e g i o n ' s t h r e e g r e a t r i v e r s ; t h e Ganges,
t h e B r a h m a p u t r a a n d t h e Meghna o f which
9.1
million
ha
(64
percent)
are
c u l t i v a t e d . A b o u t 80 p e r c e n t o f t h e
p o p u l a t i o n a r e engaged i n a g r i c u l t u r e (Map
i n d i c a t i n g Bangladesh and surrounding
c o u n t r i e s with p r i n c i p a l r i v e r s ) .
population4 ( t o t h e c l o s e s t million)
1955 1967 1977 1987 I n c r e a s e
'77-'87 (pet)
India
386
504
B'desh
Nepal
9
11
626
781
25
83
103
24
13
18
38
Consumer P r i c e s Index ( C P I ) 1980=100
Averaga
1964
1972
1980
1987
India
31.5
51.8
100.0
184.4
Bangladesh
12.6
24.9
100.0
212.7
Nepal
33.0
51.3
100.0
204.3
The e x t r a b u r d e n o f CPI i n c r e a s e on t h e
economy a s a r e s u l t o f p o p u l a t i o n i n c r e a s e
f o r t h e n a t i o n s i s e v i d e n t from t h e a b o v e
d a t a a s w e l l a s t h e r u r a l dimension of t h e
problem.
Agriculture accounts f o r nearly half
o f t h e n a t i o n a l income o f I n d i a a n d i t
s u p p o r t s a b o u t 70 p e r c e n t of t h e c o u n t r y ' s
I n f o r m a t i o n on f l o o d o c c u r r e n c e i n t h e
r e g i o n i s from C e n t r e f o r S c i e n c e and
Environment of I n d i a .
P o p u l a t i o n a n d economic i n d i c a t o r s a r e
from I n t e r n a t i o n a l F i n a n c i a l S t a t i s t i c s
(1988).
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
The
mean
annual
rainfall
in
B a n g l a d e s h v a r i e s from a b o u t 1 , 3 0 0 mm i n
t h e w e s t e r n p a r t t o a l m o s t 5,000 mm i n t h e
northeast
of
the
country
and
is
characterised
by
wide
seasonal
f l u c t u a t i o n s w i t h a b o u t 90 p e r c e n t of t h e
r a i n f a l l o c c u r r i n g i n t h e f i v e month
p e r i o d of t h e monsoon (May t o S e p t e m b e r ) .
I n s p i t e o f a n o v e r a l l abundance of
r a i n f a l l , s e r i o u s d r o u g h t s do o c c u r .
N e p a l h a s a n a r e a o f 1 4 1 , 0 0 0 s q km
l i e s p a r a l l e l t o t h e main Himalaya r a n g e
o f m o u n t a i n s . About two t h i r d s o f l a n d
a r e a i s t a k e n up by h i g h m o u n t a i n s and t h e
l o w e r s l o p e s , t h e r e m a i n i n g one t h i r d , a
narrow s t r i p t o t h e s o u t h c a l l e d t h e
T e r a i , i s t h e b o r d e r - l i n e of t h e IndoG a n g e t i c p l a i n s . About 10 p e r c e n t o f t h e
p o p u l a t i o n l i v e s i n t h e Himalaya r e g i o n ,
50 p e r c e n t i n t h e h i l l s o f t h e l o w e r
s l o p e s and t h e remainder i n t h e T e r a i .
THEORY AND EMPIRICS
The t r i a n g l e r e g i o n l i k e many r e g i o n s
i n d e v e l o p i n g e c o n o m i e s r e l y h e a v i l y on
w a t e r r e s o u r c e development t o f o s t e r
economic g r o w t h . The n a t i o n s i n t h e r e g i o n
a l s o have t h e p o t e n t i a l t o develop hydro
power t o e a s e b u r d e n o f h i g h i m p o r t b i l l s
on f u e l . I n a d d i t i o n , f l o o d m i t i g a t i o n i s
c r u c i a l f o r enhancing t h e p r o d u c t i v i t y of
low-lying l a n d s .
Even w i t h modern mechanisms o f w a t e r
r e s o u r c e management, it h a s n o t been a b l e
t o c o n t r o l f l o o d s i n t h e low l y i n g a r e a s
o f t h e t r i a n g l e . None o f t h e c o u n t r i e s i n
t h e r e g i o n have r e a l i s e d even h a l f of
t h e i r h y d r o power p o t e n t i a l .
So f a r , t h e e f f o r t s t o s e c u r e w i d e r
e c o n o m i c b e n e f i t s f o r t h e r e g i o n by
p r o v i d i n g f o r d r o u g h t s i n Ganges d e l t a
have f a i l e d . S i m i l a r l y , f i n d i n g a s o l u t i o n
t o a n n u a l f l o o d i n g h a s been an e q u a l l y
i n t r a c t a b l e impasse.
While r e s e r v o i r s i n Nepal would
r e l i e v e f l o o d i n g i n t h e Ganges, most o f
i n u n d a t i o n i s c a u s e d by t h e BrahmaputraMeghna w a t e r w a y , which c a r r i e s t w i c e t h e
G a n g e s ' s volume o f w a t e r (Asiaweek M a p ) .
I n d i a n s t r o n g view i s t h a t t h e p r o p o s e d
Ganges-Brahmaputra
link
c a n a l would
greatly contain flooding i n the delta.
T h i s i s c o n t r a s t e d b y B a n g l a d e s h on t h e
l a c k of a p p r e c i a b l e e f f e c t of lowering
w a t e r l e v e l s downstream.
To s u s t a i n p r o d u c t i o n , w a t e r a n d l a n d
u s e p o l i c i e s must b e i n t e g r a t e d . T h i s i s
theory. In p r a c t i c e , t h e countries i n t h e
r e g i o n l a c k o v e r a l l water r e s o u r c e and
vegetation
management
strategies.
Deforestation
i n t h e catchments and
e x c e s s i v e removal o f n a t u r a l b a r r i e r s t o
r a i n i n t h e r e g i o n ' s h i g h l a n d s have
f u r t h e r disturbed t h e ecological balance.
it
is
shown
by
In
summary,
environmental science t h a t d e f o r e s t a t i o n
i n highlands
reduces t h e absorptive
c a p a c i t y o f i t s w a t e r s h e d s . When t h i s i s
r e l a t e d t o t h e c u r r e n t t o p i c , monsoonal
r a i n s run i n h i b i t e d o f f t h e denuded
slopes, causing erosion i n t h e f e r t i l e
s o i l . The s e d i m e n t a t i o n i n d o w n s t r e a m s
c a u s e s f l o o d s . The t a r n i s h e d g r o u n d w a t e r
retention
levels
calibrate
droughts
f u r t h e r i n g t h e imbalance i n a g r i c u l t u r a l
p r o d u c t i o n ( s e e I v e s and M e s s e r l i 1989.
'The
Himalayan
dilemma:
reconciling
development
and c o n s e r v a t i o n '
for a
H i m a 1a y a n
contrasting
but
subtle
E n v i r o n m e n t a l D e g r a d a t i o n Theory) .
POLICY
Water h a s become a d i p l o m a t i c i s s u e
i n t h e r e g i o n . B a n g l a d e s h b e i n g a lowlying s t a t e is a t a disadvantage i n
n e g o t i a t i o n s r e c e i v i n g n e a r l y 90 p e r c e n t
o f w a t e r from a c r o s s t h e b o r d e r . Nepal h a s
a n enormous c a p a c i t y t o d e v e l o p i t s h y d r o
energy having harnessed only 0.5 percent
of i t s p o t e n t i a l s o f a r . Being a upstream
s t a t e is t o i t s advantage i n water
negotiations. India, according t o Far
E a s t e r n Economic Review, b y w i t h h o l d i n g
hydrological
and
climatological
information can e f f e c t i v e l y i n f l u e n c e
s t r u c t u r a l undertakings i n t h e t r i a n g l e
r e g i o n . Some o f t h e most e l e m e n t a r y d a t a
on h y d r o l o g y a n d power g e n e r a t i n g c a p a c i t y
o f North I n d i a remain c l a s s i f i e d a s
military secrets (ibid) .
C o n s t r u c t i n s s t o r a s e dams i n t h e
Indian t e r r i t o r y - w i t h exclusive benefits
t o B a n g l a d e s h ' s downstream i s n o t f a v o u r e d
by t h e
cost bearing side.
However,
considering t h e northern Indian s i t u a t i o n ,
where t h e w o r l d ' s h i g h e s t m o u n t a i n s meet
some o f t h e w o r l d ' s f l a t t e s t p l a i n s a n d
t h e r a i n f a l l i s c o n c e n t r a t e d i n 90 s h o r t d a y s , it a p p e a r s t h a t t h e u n r i v a l l e d t r u s t
f o r w a t e r r e s o u r c e management i s c o n t a i n e d
i n upland s t o r a g e .
~
~
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Some a r g u e s u c h p o l i c y a s p u r e l y
issue
centred
and
brand
them
as
' m a k e s h i f t s ' . The c o n f l i c t b e t w e e n e n e r g y
a n d i r r i g a t i o n p r i o r i t i e s becomes m o s t
a c u t e d u r i n g t h e d r y s e a s o n when t h e r e i s
more demand f o r w a t e r a t f a r m - l e v e l w h i l e
t u r b i n e s need t o maintain s p i l l l e v e l s f o r
e n e r g y g e n e r a t i o n . . T h e q u e s t i o n i s , who
c a n s u g g e s t e q u i t y by d i s p l a c i n g h i g h l a n d
p e o p l e i n c a t e r i n g t o e n e r g y needs of t h e
city-dwellers?
w i l l
in
Lack
of
political
implementing
far-reaching
forestry
o r i e n t e d f l o o d c o n t r o l measures i n t h e
t r i a n g l e r e g i o n have been t h e c a s u a l t y of
opting
t o
more
locally
beneficial
a c t i v i t y . Ignoring t h e best possible patht h e l e s s p a i n f u l n a t u r a l ways, a n d w i t h o u t
any glimpse a t s e i s m i c b r e a c h i n g and
e x c e s s i v e m e l t i n g o f snow, t h e more
l o c a l i s e d s u g g e s t i o n s are c a r v e d i n s m a l l
t o medium s c a l e i n t e r v e n t i o n t o p r e v e n t
s a t u r a t i o n of water-flows.
v
A c c o r d i n g t o Myres ( 1 9 8 9 ) , i n t h e
cause
of
sustainable
development
e n v i r o n m e n t a l r e s o u r c e b a s e makes a
c r i t i c a l contribution a s the ultimate
support
of
much
economic a c t i v i t y .
E x p a n d i n g on t h a t , o t h e r s h a v e a d d e d t h a t
sustainability
concept
has
major
implications
for
intergenerational
r e s p o n s i b i l i t y . T h i s means, i n s t i t u t i o n a l
arrangements should t a k e i n t o account of
socially
unjustified
environmental
degradation
associated
with
intragenerational activity.
Economic j u s t i f i c a t i o n o f s u s t a i n e d
w a t e r p r o v i s i o n t o a n y s i t u a t i o n must t a k e
i n t o account of c l i m a t i c v a r i a b i l i t y . T h i s
has important implications f o r both dry
land water preservation a s well a s
m o n s o o n a l - f l u s h s i t u a t i o n s . The e v i d e n c e
from t e m p e r a t e r e g i o n a l w a t e r management
i n i t i a t i v e s a s w e l l a s sub-temperate and
monsoon r e g i o n s a r e i m p o r t a n t i n t h i s
respect.
A s mentioned i n F r e d e r i c k and Gleick
1988,
it
is
crucial
to
identify
shortcomings i n t h e c a p a c i t y of t h e w a t e r
r e s o u r c e r e g i o n t o a d a p t t o l a r g e changes
i n water-flows
i n t h e a b s e n c e o f new
i n f r a s t r u c t u r e o r i n s t i t u t i o n a l changes o r
t e c h n o l o g i c a l developments.
USDAForest Service Gen.Tech. Rep. PSW-GTR-130.1991
This i n v e s t i g a t i v e approach with
l i t t l e economic o r s o c i a l s t r a i n w i l l b e
proven u s e f u l t o t h e r e g i o n given f u t u r e
changes i n water-flow p a t t e r n s .
THE OUTCOME
Given t h e
e q u i t y q u e s t i o n s and
s e n s i t i v e d e c i s i o n making h o r i z o n s i n t h e
r e g i o n ' s p o l i t y , t h e r e i s no g u a r a n t e e t o
suggest t h a t s u s t a i n a b l e guide-lines w i l l
be e a s i l y c o n s t i t u t e d here. In t h e v a s t
majority of t h e s e s o c i e t i e s , subsistence
i s t h e main f o r c e t h a t d r i v e s l i v i n g
beings f u r t h e r . Likewise,
the policy
makers
are
overwhelmed by
domestic
p r i o r i t i e s and a r e u n a b l e t o s u g g e s t any
b e t t e r s u s t e n a n c e . F o r example, even u n d e r
a r e a s o n a b l e e d u c a t i o n system, a m a j o r i t y
o f t h e p o p u l a t i o n would b e u n i n t e r e s t e d i n
e n v i r o n m e n t a l problems a s economics b i t e
h a r d . S r i Lanka,
with i t s very high
educational attainment l e v e l s , i s unable
t o respond t o any environmental c r i s i s and
t h i s is widely e v i d e n t i n i t s handling of
h i g h occurrence i n p e s t i c i d e contaminated
deaths.
T h e r e f o r e , even a t t h e p e r i l of a
r e g i o n ' s long-term economic v i a b i l i t y ,
p o l i c y may n o t i n t e r v e n e f o r r e m e d i a l
action not
merely because
of t h e i r
educational
background
and s p e c i f i c
e x p e r i e n c e . Most e n v i r o n m e n t a l c r i s i s , a r e
r e g i o n a l l y based and need t o be handled a t
regional levels.
The a p p r o a c h i s t o f i n d t r a d e o f f s t o
o f f s e t g a i n s and l o s s e s u n t i l no one i s
worse o f f ( o r b e t t e r o f f ) . U n t i l such t i m e
t h a t t h e p o l i c y makers a r e non-ignorant,
then a p o s s i b i l i t y e x i s t s f o r cooperation.
However, e v e n a t r e g i o n a l l e v e l s , s u b
regional b i a s engulfs t h e issue t a b l e s . A t
t h o s e l e v e l s , d e c i s i o n s b a s e d on h o u s e h o l d
s e n s i t i v i t i e s have p r i o r i t y over t h e
i n t e r g e n e r a t i o n a l i s s u e s . The p a i n o f
t h o s e d e c i s i o n s t h o u g h i s p a s s e d on t o t h e
s o c i e t y o r possibly t o t h e next generation
f o r a b s o r p t i o n . T h i s i s a resemblance of
t h e c u r r e n t i s s u e surrounding i t s ecology
a n d f u t u r e economic w e l l - b e i n g .
CONCLUSION
The
future
of
a
harmonious
relationship t h a t t h e peoples of t h i s
r e g i o n a s p i r e , w i l l l a r g e l y h i n g e on t h e
decision-makers'
a b i l i t y t o grapple with
r e a l i s s u e s a f f e c t i n g t h e waters and
forests
of
the
region
and
their
productivity.
However,
there
i s no
guarantee t h a t they w i l l be s e n s i t i v e t o
g e n e r a t i o n a l i s s u e s o r wider b e n e f i t s
o u t s i d e t h e i r h o r i z o n s . N e i t h e r , t h e y can
be e n t r u s t e d with t h e f u l l e s t confidence
t o h a n d l e d y n a m i c i s s u e s t h a t we a r e
d i s c u s s i n g i n a way c o m p a t i b l e w i t h
n a t u r a l l i m i t a t i o n s . A t t h e end of t h e
day,
t h e most r e s p e c t e d n o t i o n s w e d e b a t e
f o r p o l i c y may show v u l n e r a b i l i t y t o t h e
expediency and i n t e r p r e t a t i o n of t h e
politician.
ACKNOWLEDGEMENT
T h i s p a p e r was s u p p o r t e d by t h e S c i e n t i s t
A s s i s t a n c e Program o f Canada.
REFERENCES
Asiaweek map on R e g i o n a l - f l o w s T e r r a i n s
and Locat i o n s
Asiaweek; Number 4 1988 Defence p l a n s
a f t e r t h e d e l u g e ; 34-35.
Bangladesh and Surrounding C o u n t r i e s , with
P r i n c i p a l Rivers; Australian National
University
E a s t e r , Wil1iam.K.; Dixon, John A . ; a n d
H u f s c h m i d t , Maynard M . 1989 e d .
W a t e r s h e d R e s o u r c e Management: An
I n t e g r a t e d Framework w i t h S t u d i e s
from A s i a a n d t h e P a c i f i c . S t u d i e s i n
Water P o l i c y a n d Management, No. 1 0 .
B o u l d e r : Westview P r e s s ; 3-15
Ekanayake, Rohan. 1 9 9 0 . Women a n d a c c e s s
t o s o u r c e s of household energy: v a l u e
o f l a b o u r and r e s o u r c e s c a r c i t i e s i n
p e a s a n t economies of S o u t h A s i a .
C o n t r i b u t e d P a p e r t o t h e 3 4 t h Annual
Conference of A u s t r a l i a n A g r i c u l t u r a l
Economics S o c i e t y , 1990 F e b r u a r y 1216; B r i s b a n e A u s t r a l i a
F a r E a s t e r n Economic Review 2 F e b r u a r y
1 9 8 9 . The Wasted W a t e r s , Himalayan
B l u n d e r a n d R e s o u r c e a n d R i g h t s ; 1622.
F r e d e r i c k , Kenneth D . ; G l e i c k , P e t e r H .
1 9 8 8 . Water R e s o u r c e a n d C l i m a t e
Change. I n : R o s e n b e r g , Norman J . ;
E a s t e r l i n g , William E.; Crosson,
P i e r r e R . ; Darmstadter, J o e l . e d
P r o c e e d i n g s o f a Workshop on
Greenhouse Warming: Abatement a n d
A d a p t a t i o n h e l d i n Washington, D . C .
1988 J u n e 14-15; 133-143
M a c N e i l l , J i m . 1 9 8 9 . The G r e e n i n g of
International Relations.
I n t e r n a t i o n a l J o u r n a l l ( 1 ) W i n t e r : 135
Myers, Norman ; 1 9 8 9 . The E n v i r o n m e n t a l
B a s i s o f S u s t a i n a b l e Development. I n :
Schramm, G u n t e r a n d Jeremy W.Warford
e d . P u b l i s h e d f o r t h e World Bank,
The John Hopkins U n i v e r s i t y P r e s s ,
B a l t i m o r e : 57-68.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
High-speed High-Stress Ring Shear Tests on Granular
Soils and Clayey Soils1
Hiroshi Fukuoka and Kyoji Sassa2
Abstract: The purposes of this study is to obtain exact
knowledge of the influences on friction angle during shear
by shearing speeds. Ring shear tests on sandy and clayey
materials have been carried out with a newly developed
High-speed High-Stress Ring Shear Apparatus t o examine
if there are some changes in the frictional behaviors of these
materials at high shearing speeds of O.OIcm/sec-100cm/sec
and high normal stress of 0-3.8k$/cm2. Samples used for
tests were glass beads, tennis court sands in the university campus, the Toyoura standard sands (uniform beach
sands) and bentonite clays. All tested samples were dry.
Although result on the glass beads showed that the friction angle during shear was independent of shear speed under the normal stress up to 3.8kgf/cm2, 2 5 degrees of
change in friction angle were observed on the tennis court
sands, the Toyoura standard sands and the bentonite clays.
In the tests on the Toyoura standard sands and the bentonite clays, friction angle increased as the shear speed increased. On the contrary, friction angle during shear of
the tennis court sands decreased a t a shearing speed of
lOOcm/sec.
Change in grain size distribution implies that heavy
crushing or grinding of particles occurred during shear.
The grain size distribution become wider during shear by
grain crushing in samples except glass beads. It could
result in the increase of density and accordingly increase
of the friction angle. Crushing or grinding of grains during shear can change the shape of grains. The Toyoura
standard sands have round shape, because they are beach
sands, it may become angular by crushing during shear. On
the contrary, the tennis court sands have angular shape because they are taken from mountain slopes, it may become
round by grinding during shear. Round grains have a small
friction angle. It may be interpreted that the tennis court
sands had a smaller friction angle during shear because of
the change of angular grains to round grains by grindings.
Hence, it can be said that the friction angle is affected by
crushing or grinding of grains during shear, which appears
in a higher normal stress and a greater shear speed (shear
distance).
N
To measure the friction angle during shear, it is most
appropriate to use ring shear apparatus because landslide
motion usually causes long distance shearing of about several meters t o some hundred meters. Bishop, 1961, developed a ring shear apparatus and carried out ring shear
tests on samples of several kinds of clays in order t o examine residual strength of clays which is a steady strength appearing after the peak strength. In reactivation of old landslides, the mobilized shear strength is not the peak strength
in the virginal shear of the soil, but the residual strength
which is a small steady state strength appearing after the
peak strength. Bishop's ring shear apparatus had a sample box of which diameter was about 15cm (outside) and
lOcm (inside). The maximum normal stress is 2.5k$/cm2.
The shear speed in his experiment was 1.3~lO-~crn/sec
and the maximum shear displacement was 132cm. But it
is not enough for research of the motion of landslide, it
needs a faster shear speed up t o some meters per a second,
and longer shear displacement up t o some meters.
Sassa, 1984, developed a Low-Stress High-speed Ring
Shear Apparatus in 1984 for the research of motion of debris flow. The diameter of the sample box is 30cm (inside)48cm (outside). The maximum normal stress is 0.4kgf/cm2.
The shear speed is 0.001 to 150cm/sec.
In order t o know whether the shear friction during shear
depends on shear speed or not, Sassa carried out ring shear
tests on glass beads, the Toyoura standard sands. The results of ring shear test on glass beads of 2.0mm diameter are
shown in Figure 1. Measured data on normal stress versus
shear resistance which has a stress dimension are plotted.
The tests were carried out under the normal stress up to
0.3kgf/cm2. The normal stress was continuously increased
under the constant shear speed. Such tests were repeated
of same sample on different shear speeds of 0.001, 0.1, 1,
90cm/sec. Almost all data are on a straight line inclined
19" and there are little scatters among the data. So, this
To know the frictional characteristics of soils during
high speed shearing is very important for the research on
motion of landslides.
lPaper presented at the XIX World Congress of the International Union 01Forestry Research Organizations, 5-11 August, 1990,
MontrCal, Canada.
2Post Graduate Student and Associate Profesor, respectively,
Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto, Japan
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Normal Stress
2
(kqflcrn )
Figure 1-Result of low-stress high-speed ring shear tests
on dry glass beads of 2.0mm diameter. Void ratio
e=0.65- 0.67 (Kaibori, 1986).
F
3
i? 1
E
-
;;
$
0
2
(kgflcm )
Figure 2-Result of low-stress high-speed ring shear tests
on Toyoura standard sands. Void ratio e=0.88-0.91
(Kaibori, 1986).
Normal Stress
result means that the shear friction of the glass beads is
independent of shear speed in the range of shear speed and
the normal stress as mentioned above.
Results of ring shear tests on Toyoura standard sands
are shown in Figure 2. Procedure of the tests are almost
same with the tests on the glass beads. Shear tests are carried out under the normal stress up to 0.15kgf/cm2. Shear
speeds of these tests are 0.01, 0.1, 1 and 90 cm/sec. The
friction angle of all shear speed is 33.5".
Hungr and Morgenstern, 1984, developed a high velocity ring shear apparatus in 1984. The diameter of the
sample box was 15cm (outside) and l l c m (inside). The
maximum normal stress is about 2kgf/cm2 and the maximum shear speed is 2m/sec. In use of the apparatus, they
carried out ring shear tests on polystyrene beads and the
Ottawa quartz sands of various grain sizes under two shear
speeds of 0.025cm/sec and 98cm/sec. Results of the tests
showed that the friction angle was almost independent of
shear speed.
Sassa, 1988, developed a High-Stress High-speed Ring
Shear Apparatus in 1988 for the research of landslide. It
attained high normal stress up to 3.8kgf/cm2 and it corresponds t o the depth of about 19w23m of landslide mass,
hence research on the motion of real landslides has become possible. The diameter of the sample box is 33cm
(outside) and 2lcm (inside). The maximum shear speed is
i50cm/Sec.
With the apparatus, Vibert, Sassa and Fukuoka, 1989,
carried out the ring shear tests on torrent deposit of the
Denjo river and soils of the Jizukiyama landslide in order
to examine whether the shear friction depends on shear
speed or not. Result of the tests on dry torrent deposits
of the Denjo river showed that the friction angle during
shear under the shear speed u p t o lOcm/sec is 35.0" but
the friction angle at 100cm/sec under the normal stress up
t o 1.2kgf/cm2 is 36.5" (Figure 3).
Result of the tests on unsaturated (degree of saturation
was 20%) Jizukiyama landslide soil showed that the friction angle during shear was 32.8" a t O.Olcm/sec, 35.0" at
O.lcm/sec, and 38.5" at lcm/sec and lOcm/sec (Figure 4).
The magnitude of the variation is about 6",larger than the
result on the sample of the Denjo river. The friction angle
during shear of both sample tended to increase as the shear
80
1
2
N o r m a l Stress 0
kgf l3cm2
Figure 3-Result of high-stress high-speed ring shear tests
on dry torrent deposit of the Denjo river. Void ratio
e=0.50-0.57 (Vibert et al., 1989).
,
I
1
2
N o r m a l Stress 0
3
kgf/cm2
I
4
Figure 4-Result of high-stress high-speed ring shear tests
on unsaturated Jizukiyama soil. De ree of saturation
S, = 20%. Void ratio e=0.50~0.57f ~ i b e r et
t al., 1989).
speed increased.
Examination of both sheared samples after the tests
showed that so much fine ground grains were found on the
shear plane. It seemed that this grinding of soil particles
relates t o the variation of friction angle during shear, and
the magnitude of the variation relates t o the grain size.
So using the High-speed High-stress Ring Shear Apparatus, we have done ring shear tests of various samples at
various shear speed to examine what causes the variation
of friction angle.
SAMPLES AND APPARATUS
Samples for tests
Samples of different material and different grain size
were chosen. Tested samples are glass beads of 0.2mm diameter, tennis court sands, Toyoura standard sands (uni-
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
beach sands) and the bentonite clay. Because pore pressure
of the sample is not measured during shear test, effective
stress can not be measured. So when dry or not-saturated
sample were used, no excess pore water pressure would be
generated and total stress would be equal to effective stress.
So all of the samples tested by the apparatus were dry.
Counter Weight
Glass Beads
Glass beads are of 0.2mm uniform diameter. The specific gravity of the glass beads is 2.50.
Tennis Court Sands
Tennis court sands are taken iron1 the tennis court in
the university campus. They are taken from mountain
slope and consist of angular grains. The specific gravity
is 2.60. They are dried before the tests.
Toyoura Standard Sands
Toyoura standard sands is Japanese uniform beach sands
sold by a Japanese company and used as a standard sands
for calibration of test apparatus for soils by Japanese soil
mechanics researchers. It is a uniform, clean fine quartz
sands with round grains. The grain size is 0.05 0.5mm.
The specific gravity is 2.49.
-
Bentonite Clays
Bentonite clays used in the tests is a dry clay powder
sold in Japan and usually used for civil engineering works.
It is well ground and with grain size smaller thau 0.3mm.
The specific gravity is 2.58. Permeability of the clays is
always very small and it takes so much time lor dissipation
of excess pore water pressure, so the sample used for shear
test was completely dry to prevent generation of pore water
pressure.
Structure of the Apparatus
Figure 5 is the schematic diagram of High-speed HighStress Ring Shear Apparatus. The sample box is shaped
circular channel. The diameter of the sample box is 33cm
(outside) and 21cm (inside). It is made of transparent
acrylic resin, retained by metal fran~eand the outside of
the sample can be observed during test. Section of the
sample boxis 6cm wide and about 6-8cm high. The width
of the section is constant. The loading plate can move vertically, so only the height of the sample can change. The
sample box is separated horizontally a t about midheight
(Figure 6). The lower one is rotated by servo-control motor for shear. Several non-skid needle assemblies are fixed
on the base and the ceiling (loading plate) of the sample
box and they prevent the sample from slipping on either
side. So, rotation of the lower sample box causes shear
of sample. After the shear test, horizontal shear plane is
usually formed between the upper and the lower part of
the sample box. There is a rubber edges at the inside and
outside gaps between the upper and the lower part of the
sample box and they are bound on the upper part of the
sample box t o seal the gap, and preventing leak of sample
from the sample box.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
Figure 5-Schematic diagram oi the High-speed
High-Stress Ring S h e a Apparatus. A: servo-control
motor lor shear, B: servo-control motor for gap control,
C: servo-control air regulator, D: load cell for normal
stress, E: load cell for shear stress, F: dial gauge for
volume change, G: shear displacement detector, H: dial
gauge for gap.
The electric servo-control motor (marked as A in the
Figure 5) can rotate the lower part of the sample box at
constant speed, so it enables constant shear s eed shear
test. Available shear speed is from 0.001cm$ec t o 150
cm/sec with use of four different gears in the gear box (also
in A in the Figure 5).
The normal stress to the sample is given by an air compressor. The compressed air is put into six air pistons
through an servo-control air regulator. The air pistons
push down the loading plate (ceiling of the sample box)
and the normal stress is loaded on the sample uniformly.
The maximum normal stress is 3.8kgf/cm2.
The gap distance between the upper and the lower part
of the sample box should be constant throughout the test
procedures, because too much narrowing of gap distance
or contact of the upper and the lower part of the sample
box may increase the measured value of the normal stress.
While, too much widening of gap distance may lead to leak
of sample from the sample box during shear test.
So, the apparatus has a servo-control motor for gap
control (marked as B in Figure 5) and a electric distance
meter for gap distance measurement on the order of 1/1000
mm. With them, gap distance is kept constant during a
test as the same value at which shearing of the sample
starts.
LOAD
stainless
steel
L
frarne
A
Figure 7-The
Apparatus.
High-speed High-Stress Ring Shear
sample box
load cell
Figure 6-Section of sample box of the High-speed
High-Stress Ring Shear Apparatus.
Monitoring System
Normal load on the sample is measured with a load cell
set beneath the axis (marked as D in Figure 5). The compressed air which produces the normal load on the sample
push up the air pistons and axis, then normal load is measured as tension force.
Shear resistance of the sample is measured with a load
cell (marked as E on Figure 5). The upper part of the
sample box and the upper unit (including air pistons) are
fixed and restricted not to rotate with the lower part of
the sample box, (marked E in Figure 5) with load cell for
shear resistance. So, shear resistance is measured as tension force. As the shear resistance is supposed to originate
uniformly on the shear plane, the shear resistance is easily
calculated from the equation of shear torque. Above mentioned two load cells are electrically connected to dynamic
strain meters with cables, and tension forces are measured
with them.
Vertical displacement of the sample is measured with
the dial gauge (marked as F on Figure 5). As the sample box cannot deform sideways, the measured vertical displacement multiplied by the area of loading plate is variation of volume of the sample.
Shear displacement is measured with rotary encoder
which contact with the lower part of the sample box which
rotates during test. The shear speed is calculated from the
rate of rotation and it is displayed at each result of the
tests shown below as the shear speed at the center of the
sample.
All these measured parameters (normal load, shear resistance, sample height and shear displacement) are output
as electric voltage through the amplifier unit. All values
are recorded on the sheet of a pen-recorder and also put
Figure 8-Calculation of shear resistance and shear torque
of the High-Stress High-speed Ring Shear Apparatus.
Figure 9-Screen copy of real-time monitoring system of
the apparatus, assisted by personal computer. Displaying
normal stress and shear resistance relation.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
into personal computer through A/D converter board in it,
then the data are saved on magnetic floppy disk and the
normal stress (u)-shear resistance (r,) relation are plotted on the computer display at real time. Figure 9 is the
screen copy of the computer display of the real-time monitorinn system plotting stress conditions (normal stress and
shea;reiistance).
Pore Dressure is not measured because it is difficult to
measure pore pressure at the shear plane. Only total stress
on the sample can be measured. Thereiore, tests were carried out under dry conditions.
Calculation
Normal stress a (kgf/cm2) is calculated from:
Here, W: Normal load acting on the sample through
loading plate measured by the load cell, TI: diameter of
the sam le box (inside), r2: diameter of the sample box
(outside! yt: total unit weight of the sample, h,,: sample
height above shear plane (about 3-4cm). yt. hWpis at most
0.008kgf/cm2. The normal stress loaded on the sample
during the ring shear tests are between 0.5-3.8kgf/cm2,
so this term is almost negligible. So, this term was not
calculated during
Shear resistance r
from the equation of rotational
ple, which was dry powder, also completed consolidation
quickly.
Ring shear test
After the sample is consolidated, normal stress is decreased t o 0.5kgf/cm2. Then slowest gear is connected to
the servecontrol motor, corresponding signal voltage for
O.Olcm/sec is set on servo-control unit, and then servocontrol motor starts. Confirming that the sample reaches
residual condition, increase normal stress gradually up t o
3.8kgf/cm2 at constant rate and decrease to 0.5kgf/cm2
again, then stop the servo-control motor. During shear
test, stress path (relation between normal stress and shear
resistance) is drawn continuously on computer display at
real time.
Ring shear tests a t shear speed of 0.1, 1, 10, 100 cm/sec
follow after the test at O.Olcm/sec step by step. At each
test, appropriate gear is selected and test is executed in
same way except test at 100cm/sec. As it takes about
some minutes t o complete one cycle of a test, during which
servo-control air regulator increases and decrease the normal stress, at the test of 100cm/sec sample sometimes leaks
outside through the gap between the upper and the lower
part of the sample box. I t is difficult t o keep running for
long time at 100cm/sec. Then the test a t 100cm/sec is done
in different way, that for about only three or ten seconds
the sample box is rotated for the discrete normal stresses
of 0.5, 1.5, 2.5 and 3.5kgf/cm2.
After shear test on each sample is completed, the upper
unit, the upper part of the sample box and also the sample
above the shear plane is removed and shearing plane of the
sample is closely examined.
RESULT OF TESTS
Glass beads
Here, R: distance from the axis t o the load cell for shear
resistance, F: shear load measured a t load cell which retains
the upper part of the sample box from rotation.
PROCEDURE OF TESTS
Dry glass beads were tested under the normal stress up
t o 3.8kgf/cm2. Figure 10 is the result of uniform dry glass
beads of 0.2mm diameter. Ring shear test was executed
at constant shear speed of O.Olcm/sec as the normal stress
was increased gradually. Then, another test a t faster shear
speed (0.1, 1, 10, 100cm/sec, step by step) followed it in
Sample Preparation
The soils for the sample was compacted inside the sample box up t o about 6cm high with steel bar. Compaction
is carefully executed t o make homogeneous sample.
Then set the upper unit including loading plate and
air pistons, connect electric cables of measuring device to
amplifiers and strain meters and connect air tubes of air
pistons t o the air regulator. The air compressor start,s t o
run and supply pressure to air regulator.
Consolidation
Before shear test begins, sample is consolidated with
normal stress of 3.8kgf/cm2. Progress of consolidation is
monitored by the dial gauge for measurement of sample
height on pen-recorder. All soils for sample except bentonite were sandy soil and dry, consolidation completed
quickly within about several seconds. Bentonite clay sam-
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
2m
.c
(0
,
0
1
2
Normal stress
3
( k g f / c m2
Figure 10-Result of high-stress high-speed ring shear
tests on the 0.2mm glass beads. Void ratio during shear
test: e=0.87-0.88.
4
the same procedure. So continuous normal stressshear
resistance relation was gained at each test. Plotted points
in the figures of normal stress v.s. shear resistance in this
paper are picked up from the recorded data at the normal
stresses of every 0.5kgf/cma between 0.5 and 3.5kgf/cm2.
The friction angle scattered little, mean friction angle
is 23.0°, being independent of shear speed of O.Olcm/sec
to lOcm/sec. Test at 100cm/sec was carried out, but some
sample leaked out of the sample box and the test was terminated. From the examination of sample after shear test,
no grinding or crushing of the glass beads occurred.
Tennis court sands
Results of high stress ring shear test on dry tennis court
sands are shown on Figure 11. It displays the relation
between normal stress and shear resistance. The friction
angle at the shear speed slower than lOcm/sec is 35.1°,
hut it decreases to 31.9' at 100cm/sec. After the test,
removing the upper unit and the upper part of the sample
box and cross section of the sample was closely examined.
So much fine ground grains were observed on and near the
shearing plane (Figure 13 (a) and (b) ). Variation of grain
size distribution between before and after the shear test
are shown in Figure 12. Curve of after the test is that of
1
3
2
Normal Stress
4
2
(kgffcm
)
Figure 11-Result of high-stress high-speed ring shear
tests on the dry tennis court sands in the university
campus. Void ratio during shear test: e=0.51~0.68.
Figure 13 (a) The campus soils after test. (b) Well
ground soil particles of the shear zone on the fingers.
the sample taken from fine ground grains around the shear
plane. It shows dearly that shearing causes grinding of
grains.
Toyoura Standard Sands
-
,L
0
e,
Grain Size
lmml
Figure 12-Grain size distribution of the tennis court
sands. - 0 : before the test, 0 - 0 : after the test
Figure 14 is the test results of the dry Toyoura standard sands at shear speed of 0.01-100 cm/sec. The test
was done from the slowest speed of O.Olcm/sec to the highest speed of 100cm/sec step by step. The friction angle during shear increased from 31.7" to 33.8" under the
respective shear speed. Thereafter, tests were continued
at slower speeds; lcm/sec, O.lcm/sec, O.Olcm/sec step by
step. These tests at reducing shear speeds were carried in
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
1,
I
order t o examine whether shear friction depends only on
the shear speed or not. Results of the tests were shown
on Figure 15. Change of the sample height which means
change of the sample volume and friction coeficient which
is tan$, (tangent of friction angle) versus shear speed is
plotted. Plots with number of 1-5 are the same data of
Figure 14. Plots with number of 6-8 are the results of successive tests following Figure 14. Sample height increased
until1 the test of No. 3 and then continued t o decrease
during tests of No. 4-7. Increasing process was maybe dilatancy of the sample. The decreasing process seemed t o
be owing t o crushing of the sample. I t is proved by the
comparison of grain size distribution between before and
aiter the test, shown in Figure 16. Smaller grains finer
than 0.05mnm which was not included in the sample before
a,
14
Grain S i z e
lmm)
Figure 16. Grain size distribution of the Toyoura standard
sands. 0 - 0 : before the test, 0 - 0 : after the test
the ring shear test appear in the distribution curve of the
sample after the test. Although Figure 16 is not comparison of the sample of shear plane, but of total sample, it is
obvious that grain crushing occurred in the sample. Friction coefficient tends to increase during the tests of No. 1-5
and almost keep constant (or slightly decreased) during the
tests of No. 6-8.
Bentonite Clay
Figure 14-Result of high-stress high-speed ring shear
tests on the dry Toyoura standard sands. Void ratio
during shear test: e=0.65~0.83.
Shear Speed
(cmlsec)
Figure 15-Shear speed v.s. sample height and frictiond
coefficient relationship for the dry Toyoura standard
sands.
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130. 1991
Test result of ring shear tests on the bentonite clays is
shown in Figure 17. It showed the greatest difference of
friction angle with the change of shear speed. The friction an le was 28.6" a t the first test with shear speed of
O.Olcm/sec. And then it varied as 34.1" at O.lcm/sec, and
34.8" at 1 and lOcm/sec. In this test, test a t the speed of
O.Olcm/sec was executed again after the test at lOcm/sec.
But the friction angle remained almost same with that at
lOcm/sec speed.
Figure 18 shows the entire process of shear test at shear
speed of O.lcm/sec. The normal stress increased up to
3.5kgf/cm2 and decreased again. Shear resistance also changed in proportion with the normal stress. The most important is the behavior of the friction coefficient, namely tangent of friction angle (tan$,). It increased with increase of
normal stress (during the shear displacement of 0-20cm)
Normal S t r e s s
(kgf/cm2)
Figure 17-Result of high-stress high-speed ring shear
tests on the dry bentonite. Void ratio during shear test:
e=1.74-2.04.
2 zE
I
!..........
f ~ r i
.ri
T
i
-.A?-
c t ~ o n ' a ..l
Coefflceient
0
!
Sample Heigl
UJ
1
0
10
20
Shear
30
40
50
Displacement (cn)
Figure 18-Variation of frictional coefficient, sample
height, shear resistance during a cycle of test. (shear
velocity:0.lcm/sec)
Figure 19-Grain size distribution of the dry bentonite.
0 - : before the test, 0- 0 : after the test
and also while the normal stress kept constant peak (shear
displacement of 2 0 ~ 3 0 c m While the normal stress is de. remained constant (shear
creasing, the friction coe cient
diplacement of 3 0 ~ 4 5 c m ) . The sample height decreased
during shear and didn't recover the initial height at the end
of the test.
Figure 19 is the comparison of grain size distribution of
bentonite sample between before and after the test. This
is from the sample of shear zone. It still clearly exhibited
the effects of grain crushing through shearing.
k
Influence of Grain-crushing on the Friction Angle
during Shear
The results shown above by the High-speed High-Stress
Ring Shear Apparatus suggest that friction coefficient may
be affected by crushing (grinding) of grains a t increasing
Figure 20-Bentonite sample after ring shear tests,
showing polished and striated slip surface (upper portion
of the sample is removed).
process of normal stress. And high speed shearing may
have worked for a rapid crushing. We observed heavily
crushed grains in shear zones after the tests of each sample
except the glass beads. Glass beads are enough strong not
t o be crushed under the normal stress of the apparatus and
the friction angle does not change with shear speed.
Here, we suppose two factors influencing the variation
of friction angle during shear caused by grain crushing.
One is the variation of grain size distribution and another
is the variation of grain shape, i.e. round or angular.
As for the variation of grain size distribution, crushing
of grains during shear, especially in the material of uniform
grains makes a lot of finer grains and the sample becomes
wider in grain size distribution. It should increase the density of the sample and the interlocking between grain particles. Increase of density of soils usually causes increase
of internal friction angle. This seems t o be the reason why
the friction angle increased in the test of Toyoura standard
sands and bentonite clays.
However, in the test on the tennis court sands, the friction angle at a high speed shearing decreased in spite of
occurring of grain crushing. What can be the cause of this
is not clear at present, but one possibility is the shape of
grains. The initial shape of Toyourasands which were from
beach was round, so crushing can make them angular. So
the variation of grain shape in the Toyoura standard sands
didn't act for decreasing of the friction angle and so the factor of variation of density had t o be dominant. We could
not observe the initial and sheared grain shape of bentonite
clays by eyes, then the influence of the variation of grain
shape on the friction angle of bentonite clays was unknown.
On the contrary, the tennis court sands were mountain
sands, the initial shape was rather angular, so crushing
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
could increase the roundness of grains. Because sample of
round grains usually have smaller friction angle than that of
angular grains, crushing of grains during shear can reduce
the friction angle. It can be one interpretation.
ACKNOWLEDGMENTS
We thank Professor Michiyasu Shima, Disaster Prevention Research Institute, Kyoto University, for his supervision and cooperation to our research. We acknowledge
Dr. Christophe Vibert from &ole des Mines, Paris for his
cooperation t o the high-speed ring shear tests.
REFERENCES
Bishop, A. W.; Green, G. E.; Garga, V. K.; Andresen,
A,; Browns, J. D. 1961. A new ring shear apparatus
and its application t o the measurement of residual
strength. G6otechnique 21(4): 273-328.
Hungr, 0.; Morgenstern, N. R. 1984. High velocity ring
shear tests on sand. G6otechnique 34(3): 415-421.
Kaibori, M. 1986. Study on the movement of the slope
failure materials. Doctor thesis for the Faculty of
Agriculture, Kyoto University.; 99 p.
Sassa, K. Computer simulation of landslide motion. 1990.
In: Proceedings, XIX World Congress of the International Union of Forestry Research Organizations,
volume 1; 351-362.
Sassa, K. and others. 1984. Development of ring shear
type debris flow apparatus: Report of Grant-in-Aid
for Scientific Research by Japanese Ministry of Education, Science and Culture (No.57860028). 30p.
Sassa, K. 1988. (Special Lecture) Geotechnical Model for
the Motion of Landslides. In: Proceedings, 5th international symposium on landslides, volume 1; 1988
July 10-15; 37-55.
also In: Bonnard C., editor. Landslides. Rotterdam:
A.A. Balkema Co., Inc.; 37-55.
Vibert C.; Sassa, K.; Fukuoka, H. 1989. Friction characteristics of granular soils subjected to high speed
shearing. In: Proceedings of the Japan-China symposium on landslides and debris flows, volume 1; 1989
October 3 and 5; Niigata and Tokyo: The Japan
Landslide Soc. and The Japan Sac. of Erosion Control Engineering.; 295-299.
USDA Forest Service Gen. Tech. Rep. PSWIGTR-130. 1991
Morphological Study on the Prediction of the Site
of Surface Sli
Hiromasa Hiura2
Abstract: The annual continual occurrence of
surface slides in the basin was estimated by
modifying the estimation formula of Yoshimatsu.
The Weibull Distribution Function revealed to be
usefull for presenting the state and the
transition of surface slides in the basin. Three
parameters of the Weibull Function are recognized
to be the linear function of the area ratio a/A.
The mapping of the hazardous zones could be
successfully done using the stream line
distribution map and the relief map.
Sediment yield produced by frequent surface
slides on the mountain slopes of granitic rocks
become as dangerous as those produced by gigantic
landslides or large scale slope failures, because
of the high frequency of occerrence in a basin in
spite of the dimension.
It is recognized that surface slides will
occur on the mountain slopes of every geology. As
for the investigations on surface slides, almost
all papers in Japan deal with surface slides
which occur on the mountain of granitic rocks
which are often severely weathered and distribute
widely in the soutb-western district of Japan and
disasters due to this geology occur frequently on
the occasion of heavy rain which will he brought
about by the typhoon or the frontal storm.
where, "R" is the amount of precipitation of one
continual rain which has led to the disaster occurrence of surface slides, "r" is the invalid limited precipitation being of no effect on the occurrence of surface slides, Rr is the relief ratio
and K is the coefficient.
In Table 1, values concerning the above formula by Yoshimatsu are indicated;area of the basin,
total area of surface slides in the basin, area
ratio and relief ratio and Figure 1 shows the
relation between the area ratio and the amounts of
continual precipitation both for measured and calculated are shown, and both values show good conformity.
Table l--States of the occurrence of surface
slides due to heavy rain(by Yoshimatsu(2))
(i)R.Kamanashi basin
.................................................
Precipi- Area of Total area
tation(mm)basin
of slides
Area
ratio
Relief
ratio
................................................
(ii)R.Tenryuu basin
.................................................
ESTIMATION FORMULA OF SURFACE SLIDES
In order to express the condition of the occurrence of surface slides in a basin, usually the
parameter a/A; the ratio of the total area of
surface slides to the area of a basin (the terminology "area ratio" is used hereafter)is used. In
most of the studies concerning the occurrence of
surface slides, efforts were made to express the
area ratio as the function of the precipitation
and formulas by Uchiogi(1) and Yoshimatsu(2) are
the presentative ones. Here, the formula below by
Yoshimatsu is taken to be discussed.
a/A = K x Rr x (~-r)l.5
------ (1 )
~ X I Xl!orld Congress of IUFRO, August 5-1 1 ,
1990 Montral, Canada
Precipi- Area of Total area
tation(mm) basin
of slides
Area
ratio
Relief
ratio
Area
ratio
Relief
rxtio
.................................................
(iii)R.Kizu basin
-------------
~
Precipi- Area of Total area
of sli.des
tation(mrn) basin
2~ssociateProfessor of Forestry, Kohchi Univ.
Nangoku City, Kohchi Prefecture (before October
1990; Research Associate of ICyoto Prefectural
Univ. )
USDA ForestSelviceGen.Tech.Rep.PSW-GTR-130.1991
(iv)R.Arita basin
Precipi- Area of Total area
of slides
tation(mm) basin
Area
ratio
Relief
ratio
The values of the relief ratio could be considered to have constant value when we think of it
for a fixed basin. The value of the coefficient K
can be the presentative constant of a basin and
when the value of K is bigger, sediment yield due
to surface slides or other mass movements seem
rather vivid in the basin than others.
lo
0-0
Measured
represents that the more the the amount of precipitation augments, the bigger the value of the
area ratio becomes. In other words, the temporal
increase of the number of surface slides in a
fixed basin can not be estimated.
As for the value of the invalid precipitation;
r of these formula are determined by the data in
order to reduce the formula and subsequently the
precipitation of one continual rain which would
lead to the occurrence of surface slides is not
necessarily bigger than the derived "r" value. So,
in the following part, in order to predict the
amount of surface slides which will occur repeatedly in the same basin, derived value of "r" are
not used, and treating "ru as a variable, determined it to suit the real state of the temporal
increase of surface slides.
TRANSITION OF THE AREA RATIO IN A BASIN
Before discussing about the transitionsin of
the value of area ratio, it is necessary to know
the upper limited value of the area ratio. Figure
2 shows the relation between the total area of
surface s1ides;a and the area of the basin;A. The
oblique line in the Figure is the line when a/A =
1.0 and in this case, all part of the mountain of
a basin is bare due to surface slides, consequently, the total area of surface slides should be
plotted beneath the oblique line.
When the area of two basin are decided arbitrary and if there are no surface slides, the initial states are plotted on the abscissa as shown
and these two points
in Figure 2 by 0 and
move directly upwards as the total area of the
surface slides increases. Even when the values of
"a" are same for two different basins, the values
of a/A differ to each other because of the value
of the area of the basin are not the same. In this
condition, the larger the area of the basin
becomes, the less the value of a/A becomes.
Subsequently, in the case of discussing exactly
about the area ratio, the value of the area of
basins should be made uniform. But, to discuss
about it here is not the aim of this paper,
the author only point out the importance of this
subdect.
e,
One continual rain (mm)
1
V
Figure I--Relation between the area ratio and
precipitation of one continual rain
As a result, this formula represents only the
state of the occurrence of surface slide and only
USDA Forest Service Gen. Tech.Rep. PSW-GTR-130. 1991
+
1
A: Area of The basin
-
Figure 2--Relation between the total area of
surface slides and the area of the
basin
Figure 3 and 4 show the relation between the
total area of surface slides and the area of the
basin by the author and Yoshimatsu respectively.
As shown in both figures, common envelope curves
are drawn and in this case, the value of the area
ratio is 1.5 and this value can be the upper
limited value of the area ratio. This value coincides with that of the R.Kamanashi basin which is
given by Yoshimatsu, though the conditions of the
occurrence of surface slides seems extremely
ruined condition.
Year
and the maximum precipitation of a year during
1971 and 1976 are as follows;
..................................................
Year
1971
Precp.(mm)l66.3
0
Figure 3--Relation between the total area of
surface slides and the area of the
basin by Riura
A
Area ratio
1972 1973 1974 1975 1976
203.0 133.1 144.0 157.5 240.0
L
1966.
1971
1976
Year
Figure 5--The yearly fluctuation of the
area ratio of R.Kiau basin
These values do not exceed the invalid precipitation 325mm which is presented by Yoshimatsu.
Thus, it is clear that the formula can not be used
for the estimation of the yearly increment of the
area ratio. So, as mentioned above, taking the
invalid precipitation as a variable, and dividing
precipitation into two groups;R>200mm and R<200mm
and assuming the value of the area ratio to be a/A
=0.0012 and 0.0006 correspondingly to the precipitation respectively. The results of the estimation
of the invalid precipitation are indicated in
Table 2 as well as the maximum precipitation, the
difference of both precipitations;the valid
precpitation;(R-r) and the area ratio. As the mean
value of the area of the basin is approximately
ten km from Table 1 , then annually fifty slides
when R>200mm and twenty-five slides when R<2OOmm
will occur accoding to the estimation of this
paragraph and these values seem reasonable.
t!"')
Figure &--Relation between the total area of
surface slides and the area of the
basin by Yoshimatsu
Table 2--Maximum continual precipitation;R, area
ratio;a/A, invalid precipitation;r and
valid precipitation;(R-r) for Tuchiyabara
district(R.Kizu basin)
Year
Maximum conti- Invalid
nual precip.
precip.
Valid
precip
Area
ratio
Transition of the number of surface slides
Figure 5 shows the yearly fluctuation of surface slides of the Tsuchiyabara district(R.Kizu).
As seen in Figure 5, the values of the area ratio
tends to increase and converge to a final value.
The values of the area ratio in 1971 and 1976 are
indicated below;
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
PRESENTATION OF THE STATE OF SURFACE SLIDES IN USE
OF THE WEIBULL DISTRIBUTION FUNCTION
It was recognized above that the state of the
occurrence of surface slides in a basin at an
arbitrary state can be expressed by the area ratio
which is the function of the precipitation. On the
other hand, the Weibull Distribution Function
which the author has employed has successfully
presented the state of the yearly fluctuation of
surface slides(3). Here, by combining both method,
the hazard mapping of surface slides is presented.
Sumiyoshi district
0
0
\
R.Inubuse basin
Firstly, the foregoing results are summarized
and then the method for mapping is presented. It
is natural that the value of area ratio of a basin
differs to each other according to the difference
of the state and history of the occurrence of
surface slides in a basin. The Weibull Distribution Function is one of the statistic density
functions and originally adopted for the treatment
of the experimental data and because of its easiness and conformity, it has come to be used
frequently. The formula of this function is
expressed below;
district
(R.Kizu basin)
Figure 6--The location map of the survey areas
Three parameters included are the location parameter: y , the scale parameter:a and the shape
parameter:m respectively. Thus, the state of the
distribution of surface slides of a basin at an
arbitrary time can be expressed by these three
parameters. The author has already recognized that
when the number of surface slides increase yearly
in a basin, a and m increase, but y decreases,
and confirmed that the values of three parameters
fluctuate in accordance with the transition of the
slide numbers.
Table ?--Yearly fluctuation of Weibull parameters
(i)Tsuchiyabara district
................................................
Year Total number Area
of slides ratio
1966
1971
1976
1109
1768
1936
0.0282
0.0450
0.0492
a
Parameter
Y
m
0.994 -0.353
1.011
1.573
1.802
1.155-0.441
1.240 -0.528
................................................
(ii)Minamiyamashiro district
Area ratio and Weibull parameters
Table 3 indicates the number of slides, the
area ratio a/A and values of three parameters of
five survey basins(Figure 6). These basisns have
different situations concerning the occurrences of
surface s1ides;for exemp1e:numerous slides have
just occurred, the number of slides is increasing
or decreasing and so on. Figure 7 shows the
relation between Weibull parameters and area ratio
The scale parameter a and the shape parameter m
increase with the increase of a/A, and location
parameter Y decreases inversely. So, the
conditions of the occurrences of surface slides
could be presented by a set of Weibull parameter
values at an arbitrary value of a/A and in that
case, the scale parameter is the most effective
one. Following formulas to calculate Weibull
parameters using the value of the area ratio were
derived using data in Table 3.
a = 37.5091 (a/~)-0.1272
---------(3)
m = 18.2635(a/~)+0.4645
---------(4)
y = -10.5580(a/A)-0.0614
--------- (5)
.
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130.1991
................................................
Year Total number Area
of slides ratio
a
Parameter
Y
m
................................................
................................................
(iii)Sumiyoshi district
................................................
Year Total number Area
of slides ratio
I966
1967
937
0.0196
1296
0.0403
1971
623
0.0130
a
Parameter
Y
m
0.685
1.587
0.801 -0.316
1.215-0.544
0.448 0.771 -0.216
................................................
(iv)Misumi district
(v)R.Inubuse basin
Year Total number Area
of slides ratio
a
Parameter
m
Y
................................................
1964
1972
1321
4054
0.0049
0.0151
0.067 0.000 0.116
0.934 -0.291
0.626
SIMULATION OF THE FUTURE SLIDE DISTRIBUTION AND
MAPPING
Of five districts investigated hitherto, in
the case of Tsuchiyabara district(R.Kizu basin),
the number of surface slides continues to increase
So, the author tried to simulate the plane
distribution of slides and to draw them on the map
The simulation was done according to the flow
chart shown in Figure 8 and following procedures;
.
.
1) As a basis, the distribution map of surface
slides existing in 1971 was used and the area
ratio was a/A = 0.0450(Table 3). 2) Establish
maximum precipitation of each year and calculate
annual value of area ratio. 3) In five years
from 1971 to 1976, the increment of surface slides
is a/A = 0.0042. 4) Substituting a/A = 0.0450 into
formulas;(3), (4)and (5), the values of parameters
were calculated as follows: a = 1.718, m = 1.363
and Y = -0.581. 5) Calculate by the equation (2),
the ratio of each mesh(75mx75m) containing zero to
nine slides, and multiplying them by the total
number of meshes of the basin(1678 for Tsuchiyabara district), the real number of each mesh is
estimated. Table 4 indicates the values of real
and estimated number of meshes. 5) Draw the
distribution map indicating hazardous mesh
suffering from the occurrence of surface slides by
the number of slides in 1976.
Table 4--The estimated and real number of each
mesh containing slides in 1976
(Tsuchiyabara district:R.Kizu basin)
Number of slides
Real
in each mesh
Number Ratio
Area ratio
Figure 7--Relation between the Weibull parameter
and the area ratio
Fix the value of
area ratio
1
Estimation of
Weibull parameters
I Calculate the ratio of
I
each mesh in use of
Weibull Distribution Function
1
I
Decide the number of
each mesh containing
Estimated
Number Ratio
................................................
0
1
2
3
4
5
6
7
8
9
719
416
286
156
55
28
10
5
2
1
42.8
24.8
17.0
9.3
3.3
1.7
0.6
0.3
0.1
0.1
682
530
280
120
45
15
5
1
0
0
40.6
31.6
16.7
7.2
2.6
0.9
0.3
................................................
Total number of slides:1936
Total number of meshe: 1678
Morphlogical analysis
46
0.1
0.0
0.0
1742
1678
I
Draw the distribution map indicating
hazardous mesh suffering from surface
slides bs the number of slides
Figure 8--Flow chart to map the hazardous zone of
surface slides
Before drawing the map, subsequent morphlogical analysis was done.
In general, a knick point in the longitudinal
profile of a stream is recognized as the place
USDA Forest SewiceGen.Tech.Rep. PSW-GTR-130.1991
where mass movement occurs vividly and many slides
also occur at this point. The knick point is located at the uppermost point of a river where a
stream line disappear on the topographical map.
A point of abrupt change of the inclination seen
in the longitudinal profile of a slope can be the
point of the occurrence of surface slides and this
point can be distinguishes as where the relief of
a mesh suddenly diminishes, in other words, the
inclnation of the slope turns from steep to gentle
when going upstream or going upwards on the slope
on the relief map.
In the first meaning, the
stream line distribution map and in the second
meaning, the relief map were used.
Distribution map of the future slides
The mesh on which the knick point is found and
the mesh whose relief indicates the steep inclination are not always the same. So, both when two
conditions are overlapped and when either condition is satisfied, the increase of number of
slides in the mesh is decided, the former preferentially. As the total number of the meshes is
limited, the meshes which are to be increased were
selected carefully considering the topographical
conditions surrounding them.
Figure 9 shows the numerical map of simulated
plane distribution of slides. The circled numerals
in Figure 9 are those who make good guesses. There
are 600 meshes among 1687 meshes, of which the
place of the occurrences of slides were guessed
and the ratio of the guess is about 35.8pct.
Of meshes containg zero slide, there are 350
meshes among 682 meshes could be guessed and in
this case, the ratio is 51.3pct. Consequently,
the simulation could be considered to be done
successfully, considering the complexity of the
process of the mass movement on the mountain
slopes.
As for the total number of the surface slides,
the real number exceeds the estimated value by 194
This is due to the difference of the number of
meshes containing more than three slides in them.
The estimated number of meshes containing one
slide in them is fairly large. The ratio of the
estimated value to the real value is 1.3, so this
value could be considered as the safty factor and
to prepare for the dangerousness of the disaster
using hazard map, this value never seem to
indicate the excess value.
.
ACKNOWLEDGEMENTS
The author greatfully acknowledge the
contribution given by M. Ken Ashida, Master of
Agriculture of Kyoto Prefectural University,
for his contribution to discussion and drawing
figures.
REFERENCES
(1) UCHIOGI Tamao 1971. Landslide due to One
Continual Rainfall. Journal of Japan Soc. of
Erosion Control Eng.: No.79, 21-34
(2) YOSHIMATSU Hiroyuki 1977. The Estimation of
Expression on Landslides. Journal of Japan
Soc. of Erosion Control Eng.: No.102, 1-9
(..3 ). HIURA Hiromasa 1988. Hazard M a ~ ~ i nin
e Use
of Surface ~1ide'Transition~ohk1.-1988
International Symposion "INTERPRAEVENT 1988
- GRAZ"; 297-313
Figure 9-Simulated
slides
distribution map of surface
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Experimental Study on Impact Load on a Dam Due
to Debris Flow1
lwao Miyoshi2
ABSTRACT
When a dam is struck by mud or debris
flow, it is put under a great impact load
and sometimes is destroyed. To prevent
such destruction, it is important to
perform basic research about the impact
load on a dam due to debris flow.
Thus, we have made an experimental
study and tried to establish a method to
estimate such a impact load on the dam.
The experiment was performed with glass
beads of 5mm in diameter as bulk solid,
in an open channel which is 7m in length,
and 15cm in both width and depth.
In
these experiments, the load on the dam
was measured by a dam-type load measuring
device, and simultaneously the behavior
of the debris flow was observed by a high
In
speed video (200 frames per second).
the high velocity area, the load consisted of the dynamic pressure on the flow,
and most agree at each point in time with
the one assessed from the flow's momentum
variation. However there is no method to
estimate debris flow's momentum variation
on an obstructed object. Consequently, a
model is proposed to estimate quantitatively the deformation of the flow and
the load on the dam. The results from the
computer simulation of this model agree
well with the experimental results.
INTRODUCTION
Debris flow is one of the most disastrous phenomena in mountain.area.
This
is a flow of the mixture of soil, cobble,
boulder, and water, that run down with
great energy. The debris flow has given
1.
2.
Paper presented at the XIX World
Congress of the International Union
of Forestry Research Organizations,
Montreal, Canada, August 5-11, 1990.
Department
of Forestry,
Kyoto
University, Japan.
huge damage to our life. To prevent this
kind of disaster, we have made great
efforts, and have built a great number of
dams, as one of these efforts. Dams have
a certain effect on the control of sediment transportation, and usually
the
energy of the debris flow is attenuated
or completely dissipated by the time it
reaches a dam or by a dam itself.
Recently in Japan, where steep mountains
are close to cities, the debris flow is
stopped by a dam directly. However, when
such a flow strikes a dam, it generates a
great impact load, sometimes destroying
the dam. In such a case, the debris flow
increases its energy by taking up the
sediment and water on the dam and the
situation becomes more dangerous.
To
prevent such accident, it is important to
establish a method to estimate the impact
load on a dam, when the debris flow
strike it.
The impact load of debris flow can be
roughly categorized in two groups by
means of the generating mechanism (Mizuyama,1979). One is the load generated
when boulders or floodwood in the flow
hit the dams (solid impact load), and the
other one is the load when the hydraulic
bore of the debris as a fluid hits the
dam (fluid impact load).
The former
tends to cause partial break of the
concrete dam and the latter tends to
cause large scale destruction of the dam.
Therefore, from the stand point of disaster prevention, it is rather important to
be able to estimate the fluid impact
load.
In Japan, the dynamic fluid load of
the debris flow that decides the design
strength of the concrete dam is accounted
for from the dynamic pressure of debris
flow as the steady jet flow as seen in
follow equation.
2
F = Dqv = DAv
(1)
where F is the load, D is the bulk densi-
USDA Forest ServiceGen.Tech.Rep.PSW-GTR-130.
1991
ty of the fluid, q is the discharge, v is
the velocity, and A is the cross sectional area of the fluid. The dynamic pressure of the steady jet flow is the pressure on the wall during the steady jet
flow changes its direction on the wall.
Several previous works on the impact
load on fluid theory can be seen.
But
if the behavior of the debris flows
different from that of regular jet flow,
then reconsideration is required.
Hirao et a1.(1970) made an experimental study on impulsive force on the bank
due to hydraulic bore. In their experiment, the pressure on the wall, which was
fixed in the channel in right angle, was
measured, when it was hit by hydraulic
bore of a few kind o f fluid running down
the channel.
They reported that the
measured load on the wall was 1.0-4.5
times lager than the load that calculated
from the dynamic pressure of the flow as
the steady jet flow. But the mechanism
of load generation was not referred in
this report. Miyamoto and Daido(1983)
also studied on the impact load of muddebris bore on the bank. In this work,
the load was discussed theoretically and
some experiments had be made. But some
simplifications in their theory make it
hard to apply to actual phenomena directly. Some more previous works on similar
themes can be seen, but those are not
enough to estimate the impact load of the
debris flow yet.
In this paper, both the load and the
behavior of the head part of debris flow
is made clear on the basis of results of
experiments ..and the load is discussed
with the deformation of the flow head.
EXPERIMENT
A diagram of experimental apparatus
is shown in Fig.1. The flow channel was
made of steel and transparent acrylic
board so that the side view of the flow
can be observed. The size of the channel
is 7m in length, 150mm in both width and
depth. The channel bed was roughened by
gluing glass beads (5mm in diameter) onto
it.
The channel's angle of inclination
was 16 degree. Bulk solid were spherical
glass beads with a diameter of 5mm and a
specific gravity of 2.53. A t the upper
end of the channel, main and sub water
supply device were attached, and at the
bottom, dam-type load measuring instrument was set. The front face of the dam
was at a right angle to the channel
direction and the size of loading board
is 120mm height and 150mm width.
The
load on the dam-type measuring instrument
was measured by a dynamic skrain meter
and recorded by a oscillograph. As the
same time, the side view of the flow on
the dam was recorded by a high speed
video recorder (200 frames per second).
The glass beads were put on the
channel bed on the upper side of the dam
making a movable bed 4m in length with
50mm depth. The glassbeads were saturated entirely by water from the sub water
supply device, and then, the pre-determinded volume of water from the main
water supply device was released all at
once, and this forced the glassbeads from
Main water supply device
Sub water supply device
High speed video
Movable bed
Dam type load measuring instrument
Fig. 1
Diagram of experimental apparatus
1991
USDA Forest ServiceGen.Tech.Rep.PSW-GTR-130.
the movable bed to move downstream as a
debris flow. The velocity of the debris
flow could be controlled by the volume of
water in the main water supply device.
The debris flow was checked by the dam at
the bottom of the channel; the load on
the dam was measured and the behavior of
the flow was recorded from the channel
side by the high speed video recorder.
The record of both the load and the
behavior of the flow were to be analyzed
on the same axis of time. For this purpose, a pilotlamp was turn on in the site
of the video recorder, and simultaneously
in common circuit, a signal was sent to
the oscilograph.
The flow's velocities were in the
range of 0.4m/s to 2 4 s . In all cases,
distinct hydraulic bores could be observed and the flow could be considered
as a steady flow at the dam point.
The
load on the dam measured in the experiment was recorded by the oscirograph.
The measured loads can be classified in
three types by the variation in time as
shown in Fig.2. The load in type A has a
clear peak in a very short time (from
0.01 to 0.07second) after impact; t,he
load in type B also become maximum in
very short time, but doesn't have a clear
peak; the load in type C increases rather
slowly.
The relations hi^ between the
Time
Time
Fig.2
velocities and the measured maximum loads
are shown in Fig.3. The measured maximum
loads increased with the velocities and
each type of the load has its velocity
range. The morphology of the flow on the
dam, when maximum load generated, varied
with the velocity or/and type of the
load. Fig.4 shows the side views of the
each type's typical flow, when the maximum load was recorded. In the case of
type C , when the maximum load generated,
the dam was filled with debris. In this
case, the load is relatively small and
can be explained as the static load of
debris.
On the other hand, in the case
of type A and B , in spite of rather
larger maximum load, the static load is
much smaller than that of type C. This
means that, in the case of type A and B ,
the maximum load mainly consists
of
dynamic load. Consequently, it is important to estimate this dynamic load so as
to estimate the impact load on the dam.
In general, the dynamic load
of
debris flow has been discussed in comparison with the dynamic load of the
steady jet flow in the same profile.
Fig.5 shows the relationships between the
velocities and the maximum measured load
per cross section of the bore.
The
broken line "P" in Fig.5 is the dynamic
pressure of the steady jet flow, calcu-
Time
Type of load
Type A
B
I:
O : Type
I
0
50
1DO
150
velocity
Fig.3
200
250
(cm/s)
Relation between velocity and
measured load
Fig.4 Flow morphology when maximum load
generated
1991
USDA ForestSelviceGen.Tech.Rep. PSW-GTR-130.
lated in the relationship of eq.(2).
2
P = DV
(2)
The
bulk density was determined to be
3
1.4gf/cm
from results of preliminary
experiments. This figure shows that the
maximum load is larger than the one due
to the dynamic pressure of steady jet
flow at each velocity.
Fig.6 and Table 1 shows the variation
of the form of flow's head part and the
measured load. After impact, the debris
flow change its direction along the damfront surface just like the behavior of
the jet flow. From 0.05 to 0.06 second
after impact, the head part jumps up
above the dam, and makes overflow.
The
maximum load measured at this point.
Then the debris begins to stop and makes
sedimentation from the corner between the
channel bed and the dam face, and static
part grows to the final sedimentation.
The sedimentation makes the impact angle
larger between the flow and the dam face
and the load on the dam becomes smaller.
Fig.7 shows the relationship between
the velocity and timelag (the difference
of time between the moment at which
flow's head touch the dam face and at
which the load become maximum).
The
timelag seems to be in inverse proportion
to the velocity. In other words, the
length of the head part of the flow, that
reach the dam until maximum load arises,
is constant (about lOcm in this experiment), in spite of the difference in
velocity.
This means that the shape o f
the flow's head has an important role in
the mechanism of load generation and that
this part's properties should be adopted
in estimating the impact load.
I I
Movable bed
/
f
/
/
I
,,
Channel bed
Fig.6
1'0 c m
/
/
Morphological variation of debris
flow's head at intervals of 0.01
second
Table 1
time
Tine
Load
bet)
(Kpf)
Variation of impact load with
-u
-
1agXVelocity
= lOcm
a,
"I
e
A A %A@
/
x
d
ffl
Z
0
50
100
150
Velocity
Fig.5
a: Type A
e: Type B
A: Type C
-
0
200
250
( cm/s)
Relation between velocity and
maximum load per cross secsion area
of flow
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
50
100
150
Velocity
Fig.?
200
(cm/s )
Relation between velocity and
time lag
250
A DISCUSSION OF THE LOAD ON THE BASIS
MOMENTUM VARIATION OF THE FLOW HEAD
OF
In this chapter, the mechanism of
load generation will be discussed in the
relation with the variation of the load
and the deforming process of the flow
head.
If the flow is in a fully steady
state before the impact point, the debris
flow' head, that include enough part
concerning the generation of the impact
load, can be treated as a series of
momentum points. On the assumption that
the flow depth of this part is equal in
each section, the discussion can be made
in two dimension. Then, this part is
expressed as a plane with some mass on
X-Y two dimensional axis, as shown in
Fig.8, and the surEace line is described
as a function h(x,t). At the time t ,
this fluid part exists in O<x<xe, and the
center of gravity on X axis xg is in the
relation of
where, B is the width of channel. As a
consequence, the load on the dam is
regulated by the function h(x,t) that
express the surface line of the flow
head.
These way of analysis was applied in
results of the experiment.
In
this
analysis, the head part of the flow, that
include enough part concerning the generation of the impact load, is considered
to be cut off and be independent from the
following flow, as shown by the broken
Fig.S(a) shows the
line in Fig.S(a).
morphology of the flow head at each 0.01
second interval after impact on the dam,
that was observed in the experiment by
the high speed video. The variation of
the flow' gravity center is calculated
from this morphological variation and the
average loads that should be generated on
the dam during each 0.01 second are
The center of gravity given by this
equation varies with the deformation of
the flow head, and is defined as a function of time xg(t). Then, the acceleration of the gravity center is also defined as a function of time ag(t) as
dt'
It is the dam that gives the force which
makes this acceleration, thus the load on
the dam is described as follow.
Fig.g(a)
Behavior of the system of X
material points in flow's head at
interval of 0.01 second
w
-3
0 : Observed
0 : Calculated
a
a
0
A
Time
Fig.8
Model of flow head as a
of material points
system
(sec
Fig.S(b) Relation between measured and
calculated load
USDA Forest SelviceGen. Tech.Rep. PSW-GTR-130.1991
calculated from this and the bulk density.
It is determined that the bulk
density used in the calculation is to be
3
1.4g/cm
The comparison between the
measured and the calculated load is shown
in Fig.S(b). The two loads are in good
agreement until the maximum point, and
this means that the impact load of the
debris flow is regulated by the deformation of the debris flow head. After the
maximum point, the measured load becomes
lager than the calculated one.
This
difference may be caused by the static
load due to sediment of the debris.
a series of this behavior, the fluid goes
up to y direction along y axis. when the
fluid shifts its position, each part of
the flow changes its flow depth from H to
Hd.
Hd at each time is decided by R
which is the ratio of Hd and H (R=Hd/H).
R is also a function of the distance from
the flow front. These functions of the
distance from the flow front can be
transformed to the functions of the time
by means of velocity. Therefore the load
on the dam and the morphology of the flow
head at each time can be obtained by
completing these functions of time as
Ht(t),
Dt(t), Rt(t).
The load can be
described as a function of time as
FLOW MODELING AND COMPUTER SIMULATION
2
Ft(t)=Dt(t)llt(t)Bv t
.
The impact load of the debris flow is
regulated by the deformation of
the
debris flow head, as described in previous chapter. Therefore, the best method
to roughly calculate the impact load is
by estimating the deformation process of
the flow head quantitatively using the
initial conditions (flow velocity, flow
depth, bulk density).
Although h(x,t)
may have complex form affected by many
factors, here a simple model is proposed
that is analogous to the behavior of a
jet flow checked by a perpendicular wall.
In this model, some functions are
prepared. The original flow depth is to
be described as a function of the distance from the flow front H(x). The bulk
density in each part of the flow is also
to be described as a function of the
distance from the flow front too, to take
up the effect of the density distribution
in x direction. As shown in Fig.10, the
debris flow flows from x direction to y
axis which represent the dam face with
keeping initial velocity. The flow come
to y axis and shift its position on the
surface of original flow at each time in
order from the front and, as a result of
(cml
k,
Bv
d
7 -(Dt(t)Ht(t)
.
dt
2
Rt(t))
- Calculated
Fig.ll(a) Comparison between observed
and calculated morphology of debris
flow head. (Each line indicates
0,0.1,0.3,0.5,0.7 second after
impact )
- Calculated
----.Observed
0.05
Time
Hd
Fig. 1 0
0.1
( sec)
x
Flow deformation model
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
(6)
Fig.ll(b) Simulated result of impact
load on high velocity(l.70m/s).
-Calculated
After some transformations are made on
this equation, the maximum load can be
expressed by giving each value of composing functions D t , Ht, Rt and their time
differential functions (Dm, Hm, Rm, D'm,
H'm and R'm respectively) at that time.
K=lt
HmR'm
2~
t -
RmH'm
v
.---_.
Observed
D'm
t -
aomv
Where K is a coefficient that mean
ratio between the maximum load and
load by dynamic pressure of a steady
flow in same profile.
the
the
jet
Now this modeling is applied to the
experiment. The composing functions are
decided as follow.
H(x), the function that represents
the flow depth, is to be described in a
simple form that suits the morphology of
the flow head in each experimental run,
as follow
where, H10 is the flow depth at lOcm from
the front; a and b are the parameters
that are decided in each run for better
suitabilities, which have the range of
0.5-0.7 and 0.6-0.7 respectably.
This
function is applied to about 20cm length
in the flow front. D(x), the function
that represents the bulk density in each
part of the flow, is decided on the basis
of the preliminary experiment, as
a
empirical equation.
Fig.l2(a) C o m ~ a r i s o nbetween observed
andcalcuiated morphology of debris
flow head. (Each line indicates
0,0.1,0.3,0.5,0.7 second after
impact. )
Calculated
Observed
Time
(sec)
Fig.lZ(b) Simulated result of impact
load on low velocity.
R(x) is the function that represents the
deforming property of the flow, and also
considered to express the ratio between
the velocity components rise along the
dam face and these which turn back to
upstream after impact. This function is
also decided so as to suit the experimental result.
Fig.11 is the comparison between the
observed and the calculated morphology of
the flow's head and the load on the dam.
The velocity of this flow is 170cm/s a 1
the flow depth at lOcm from the front is
4.8cm and parameter a and b in equation
( 9 ) are 0.5 and 0.6 respectively.
The
function R(x) used in this calculation is
In this function, the x is given in
unit.
This function of the distance
cm
is
0
1
2
3
Load by dynamic pressure
of steady jet flow
4
5
(Kgf)
Fig.13 Relation between load by dynamic
pressure of steady jet flow and
measured load.
1991
USDA Forest ServiceGen.Tech.Rep.PSW-GTR-130.
transformed to function of the time
the velocity (170cm/s) as
with
Both the deforming process of the flow
and the load on the dam are well simulated.
Fig.12 is the simulated result of
another experimental run, by same R(x).
The velocity of this flow is 108cm/s, and
the flow depth at lOcm from the front is
6.3cm, and the parameters of the flow
depth function a , b are 0.7 and 0.7. The
calculated results can be said to agree
well with the observed one in spite that
function R(x) is decided to suit for
other experimental run. The difference
of the load between the calculated and
the observed after the maximum point is
most likely caused by the effect of
overflow above the dam, which is ignored
in this model.
The estimation of the maximum load is
one of the most important problem in the
practical aspect. The maximum load can
be estimated with the model and the functions above. With these functions and
the condition that the maximum
load
arises when vt=lOcm in this experiment
(see Fig.7), eq.(9) is transformed to
(13
Since Hm is in the range of 4.1-6.3 and
parameter a is 0.5-0.7, b is 0.6-0.7 as
the results of the experiments, K should
be in the range of 1.47-2.70. Fig.13 is
the relationship between the load by the
dynamic pressure of steady jet flow and
the maximum measured load. The calculated value of K expresses the entire tendency of the experimental results.
CONCLUSION
The impact load on the dam when
debris flow strikes it was measured and
the behavior of the flow was observed in
1991
USDA ForestServiceGen.Tech.Rep.PSW-GTR-130.
the experiment.
In the low velocity
area, the measured load could be explained as the static load by the sediment of debris. On the other hand, in
the high velocity area, the measured load
was rather great and corresponded to the
momentum variation ~f the debris flow
head.
Then a model was proposed that
estimate
the characteristic
momentum
variation of the debris flow. Both the
load on the dam and the deformation
process of the flow could be well simulated by means of this model. The measured maximum load was 1.47-2.70 times
larger than the load by the dynamic
pressure of the steady jet flow in same
profile of each debris flow.
In this way, the impact load on the
dam due to debris flow has been made
clear and, although more investigation
will be required to apply this model to
practical situations, the impact load can
be estimated at least on an experimental
level.
REFERENCES
Hirao,K. et a1 1970. An Experimental
Study on Impulsive Force due to
Hydraulic Bore. Journal of Japan
Society of Erosion Control Engineering No.76 : pp.11-16.
Miyamoto,K. and Daido,A. 1983. Study on
the Impact load of Mud-Debris Bore
on the Bank. Memoirs of the Research
Institute of Science and
Encineerinc.
- . Ritumeikan Univ. No.42.
: pp.61-79.
Miyoshi,I. and Suzuki,M. 1990. Experimental Study on Impact Load on a Dam
Journal of the
Due to ~ e b r i sFlow:
Japan Society of Erosion Control
Engineering No.169. : pp.11-19.
Mizuyama,T. 1979. Estimation of impact
force on dam due to debris flow and
its problems. Journal of the Japan
Society of Erosion Control Engineering No.112 : pp.40-43.
Sediment Dynamics of a High Gradient Stream in
the Oi River Basin of Japan1
Hideji Maita2
Abstract: This paper discusses the effects of
the valley width for discontinuities of sediment
transport in natural stream channels.
The results may be summarized as follows:
1)ln torrential rivers. deposition or erosion
depend mostly on the sediment supply. not on the
magnitude of the flow discharge. 2lWide valley
floors of streams are depositional spaces where
the excess sediment from the upper stream area
is temporarily deposited. In the erosional
process that follows, the sediment runs off down
stream in a way that can be explained by an
exponenti a1 process.
STUDY AREA
Topoqraphy and Geoloqy
The Higashigochi river basin, with a drainage
area of about 28 km2, is a small tributary of the
Oi river system emptying into the Pacific side of
Honshu Island. A 2406 meter peak, located at the
north corner of the basin is the highest point,
Numerous researches in the area of sediment
control work in mountainous areas have been
carried out. However, our Understanding of the
effect of discontinuities in the history of
sediment transport is still insufficient. In
order to gain a fuller Understanding, it is first
necessary to examine the morphology of streams in
their natural state without sediment control
structures. With this in mind we selected the
Higashigochi basin of a small tributary of the Oi
river as our study area. During 1982 the basin
was subjected to a period of intense rainfall of
more than 900mm This released abundant sediment,
about 150,000m3 in the observed reach. As a
result the morphology of the stream changed.
Taking this opportunity, we were able to study
and come to a greater understanding of the
dynamics of sediment transport.
This paper
analyzes a series of changes in the mor~holos~
of
a high gradient gravel-bed stream that resulted
from nine floods.
'presented at the Subject Group 51.04
Technical Session on Geomorphic Hazards in
Managed
Forests,
XIX
World
Congress,
International Union of Forestry
Research
Organizations, August 5-1 1,1990,
Montreal, Canada.
'~ssistant Professor of the Institute of
Agricultural and Forest Engineering. University
of Tsukuba, Ibaraki, Japan
Figure I--The study area.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
while the elevation of the confluence with the
main river, about 770 meters, is the lowest point
in the study area. This gives a relief of about
1640 meters over a linear distance of 7.5 km.
Reflecting this high relief, slopes are in
general very steep with an average of about 38'
(Fig. I).
The bedrock is mainly composed of shale and
sandstone from the Cretaceous period. The rock
is generally fractured because the basin is
situated in the high, uplifting zone of the
Japanese Southern Alps.
As a result of these topographical and
geological conditions, the ratio of landslide
scars to the area of the basin is 2.9 percent and
this figure reaches 7.6 percent in the upper
basin.
Stream C h m U i ! ! 2 2
Observed reach
The observed reach extended about 1 km, where
the stream, coming through the V-shaped narrow
valley first meets a wide floor of about 40 to
130 meters. Then the stream again enters a narrow
valley section at the end of the observed reach
(Fig. 4). The gradient of the stream bed in the
observed reach ranges from 1/8 to 1/15.
Because no modification of the channel of the
reach by sediment control structures had been
undertaken, we were able to examine the
morphology of the channel in its natural state.
METHOD
In this research we regarded the actual stream
channel itself as the place for the field
experiments. As a result, various measurements
The longitudinal profile of the Higashigochi
river is shown in Figure 2. This figure shows
that the stream is steep and the profile can be
divided into three parts in terms of it5
gradient. The lower part, with a gradient of
about 1/30, the middle part with a sradient of
about 1/20 and the upper section the sradient of
which is more than 1/10. The observed reach was
located in the upper section. As to the planar
shape of the stream, the meander and the
variation of channel width is remarkable.
-
According to the climatic records at the
Sannosawa station (Fig. I ) , the average rainfall
between the months of April and November from
1970 to 1981 was about 2,500 mm. Consequently,
the mean annual precipitation may reach about
3,000 mm, but it is very variable.
5
0
Climate
Figure 2--The longitudinal profile of the
Higashigochi river.
The mean annual temperature is 9.E°C, with the
highest temperature occurring in August and the
lowest in January. Temperature records of daily
maxima and minima suggest that freeze/thaw
processes are normally active from the latter
half of November to the first half of April
(Fig. 3).
Veqetation
Vegetation is predominantly deciduous below
the 1,500-1.800 meter zone and conifers dominate
at higher elevations. Below the 1.500-1,800
meter zone, Japanese cedar (Chryptomeria japonica
D. Don), Japanese cypress (Chamaecyparis obutusa
S. et Z.) and Japanese larch (Larix leptolepis
Gordon) have been planted.
F
MONTH
Figure 3--The climate of the study area.
USDA ForestServiceGen.Tech.Rep.PSW-GTR-130.1991
10
DISTANCE FRON THE CONFLUENCE(km)
were carried out in the study area. In order to
record a sequence of changes in the channel
morphology of the observed reach, whenever a
river bed fluctuation occurred over the period
1979 to 1985, the leveling of 22 cross sections
of the observed reach at intervals of about 50
meters was carried out(Fig. 4). Plane surveying
was mostly carried out at the same time. The
vertical and horizontal distribution of the grain
size of the stream bed was investigated after the
river bed fluctuations in September 1980 and
September 1982. In order to measure the volume
of the deposits on the bedrock of the observed
reach, seismic prospecting was carried out after
the river bed fluctuation in August 1981.
Rainfall was measured by several rain gauges
placed around the basin (Fig. I ) and the flood
discharge was calculated by a storage function
run-off model below (Maita et al. 19841.
0.I4,,-O. 4
Pz0.6, K = 8 . 6 ~ ~ ' ~ * .TI=2.5A
Sl=KQP
.
Here. SI is the hypothetical storage depth of
rainwater over a basin considering the time lag
TI between rainfall excess re and flood discharge
Q, and A is the area of a basin.
SHAPE CHANGES OF THE STREAM CHANNEL
Threshold Rainfall
Nine river bed fluctuations were confirmed in
the observed reach from 1979 to 1985. Table I
shows the largest values recorded for the
continuous rainfall and hourly rainfall measured
at several precipitation stations. It also shows
the maximum calculated peak discharge at the end
of the observed reach for each of the rainfall
events and when a river bed fluctuation occurred.
Table I--The magnitude of rainfall and discharge
for each flood .
flood
name
continuous
rai nfal 1
(mm)
max. hourly
rainfal l
(mm/h)
peak
discharge
(m3/s)
Figure 4--The observed reach after the 8209 flood
and the location of the cross sections
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
8506
Q
SCALE
From the f i g u r e s in Table 1, i t seems t h a t a
continuous r a i n f a l l level of about 200 mm o r a
maximum hourly r a i n f a l l of about 30 mm is t h e
threshold r a i n f a l l f o r a r i v e r bed f l u c t u a t i o n in
the Higashigochi r i v e r basin.
Such f i9ureS
occurred about once every 1.3 t o 1.5 years.
Chanses of Channel Shape
Figure 5 shows t h e lowest longitudinal Stream
bed p r o f i l e in t h e observed reach.
The p r o f i l e ,
formed by t h e 8208 flood ( t h e flood in August
19821, is divided into two s t a g e s . One. shown a s
82081 in Figure 5, i s t h e bed p r o f i l e of the
depositional peak. The o t h e r , shown a s 8208I1 , i s
t h e p r o f i l e a f t e r t h e recession flow of t h e 8208
flood p a r t i a l l y eroded t h e buried bed.
Because
of t h e c l a r i t y of t h e p r o f i l e changes, each
p r o f i l e is compared t o t h e p r o f i l e a f t e r t h e 8009
flood ( t h e flood in September 19801.
Other
floods were named in t h i s manner.
Figure 5--The changes in t h e lowest lon9i tudinal
stream bed p r o f i l e i n t h e observed reach.
n
E BED PROFILE OF THE
D E P O S l T l O N A L P E O K IN
E
w
=
0
C
4
=rim
-1
W
DISTANCE FROM THE CONFLUENCE(km)
Figure &-The changes i n t h e longitudinal bed
p r o f i l e of t h e 3.3 km of stream between a check
dam and t h e observed reach before and a f t e r t h e
8208 flood.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Figure 6 shows the longitudinal stream bed
P r o f i l e of t h e approximately 3 . 3 km of stream
between a check dam and the observed reach before
and a f t e r t h e 8208 flood.
As shown in Figure 4
and 5, t h e l a r g e deposition of t h e 8208 flood was
caused by a continuous r a i n f a l l of 933 mm and an
hourly r a i n f a l l of 69.5 mm ( a recurrence i n t e r v a l
of more than 30 y e a r s ) , which Typhoon no. 10
produced between August 1 and 3, 1982 (Fig. 7 ) .
This event r a i s e d t h e stream bed from 3 meters t o
8 meters.
Subsequently, rapid erosion ensured
t h a t the bed p r o f i l e regained its former shape
very rapidly. As shown i n Figure 6, t h e check dam
had no influence on t h e deposition in the
observed reach caused by t h e 8208 flood. Besides
i t was noted t h a t t h e r e was almost no d r i f t wood
debris in the observed reach in s p i t e of such a
l a r s e flood.
Figure 8 shows the changes in the cross
s e c t i o n a l channel p r o f i l e s i n t h e observed reach.
The black shaded p a r t s of t h e diagram represent
deposition.
Erosion i s shown by the unshaded
area between t h e l i n e s describing t h e cross
section.
The l a r g e deposition almost f l a t t e n e d
t h e bed in t h e observed reach. After the flood,
incision of t h e stream hed meant t h a t these
p r o f i l e s nearly recovered t h e i r former shape.
The recovery was more rapid in t h e narrow p a r t of
t h e valley than in t h e wide p a r t .
Figure 9 shows t h e changes in t h e planar shape
of t h e stream bed in t h e observed reach. The
l a r g e deposition not only caused l a r g e changes in
t h e planar shape but a l s o t h e location of t h e
thalwegs.
The erosional process of t h e stream
bed meant t h a t t h e shape of t h e bed returned t o
its former shape and t h e thalwegs returned t o
t h e i r former positions.
Thus, l a r g e depositions have a marked e f f e c t
on the stream bed but t h e s e changes a r e not
permanent and t h e erosional process causes t h e
channel shape t o r e v e r t to i t s former one.
toy
Figure 8--Some examples of the changes in the
cross sectional profiles in the observed reach.
Figure 9--The changes in the planar shape of the
stream bed in the observed reach. The black
shaded parts of the diagrams represent the low
water flows.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
other hand, erosion caused the grain size to
become larger as the smaller sediment was removed
from the stream bed.
WANT ITAT IVE CHANGES OF RIVER BED FLUCTUATION
Changes
-
Figure 7--The observed hyetograph in the study
area and the calculated hydrograph at the end of
the observed reach in the 8208 flood.
7+ LINE(LEFT BANK)
O
,,"ean
range
of the Volume of Deposit
Figure I 1 shows the changes of the volume of
the deposits on the bedrock in the observed
reach. This was found by using the volume of the
river bed fluctuation and cross sectional bedrock
Profiles measured by seismic prospectins in
October 1981. The volume of the river bed
fluctuation can be obtained by the following
steps. First, as shown in Fisure 12, the volume
of the river bed fluctuation of the segment is
calculated by the equation below.
unit: cm
,:grain diameter
locm
Fisure 10--The structure of the deposit formed by
the 8208 flood at 7t line.
Here, V is the volume of the river bed
fluctuation of the segment, L is the distance
between
two
adjacent
cross
sections,
El 1 ,E12,..etc, and Dl 1 ,D12,..etc, are the areas
surrounded by the two cross sectional profiles
before and after a flood at the Al cross section.
EIl,E12,..etc, represents the area eroded and is
negative, DIl,D12,..etc, represents the deposited
area and is positive.
E21,E22,..etc, and
021,D22,..etc, represent the same variables
measured at the A2 cross section. The volume of
the river bed fluctuation of the observed reach
can be obtained by taking the sum of the volumes
of each segment. Thus, the overall volume may be
positive or negative in sign.
As can be seen from Figure 1 1 , the volume of
the depo3its was decreased gradually to about
120,000 m by the process of erosion between 1980
and 1981. But the 8208 flood jn 1982 deposited
sediment of more than 150,000 m and the total
volume 05 sediment on the bedrock increased to
270,000 m . Af5er that, it decreased rapidly to
about 130,000 m . As the changes between 1982
and 1985 show, the erosional process continued in
the observed reach after the 8208 flood despite
the fact that there were some large rainfalls in
this period. This means that there was little
sediment in the upper basin of the observed reach
because unstable debris had been mostly swept
from the stream beds and the slopes of the upper
basin by the heavy rainfall associated with the
8208 flood.
Structure of Deposits Formed by the 8208 Flood
ANALYSIS AND DISCUSSION
Fisure 10 shows the structure of the deposit
formed by the 8208 flood at 7+ line shown in
Fisure 4. Although the deposition was formed by
one flood there are several parts with laminar
structures. As Iseya et a1.(1990) described, it
is thought that this structure was formed when a
shallow and high velocity flow transported
heterogeneous sediment, raising the bed at a high
rate. Because of the large deposition, the grain
size of the stream bed became smaller. On the
Figure 13 shows the relation between the
absolute value of the river bed fluctuation in
the observed reach and the peak flow discharge.
This peak flow discharge was adopted as an index
of the magnitude of discharge. As the graph
shows, the volume of the river bed fluctuation
is not always large in comparison with the
increase of flow discharge and it seems probable
that the ordering of the floods is an important
factor. To attempt to unravel this complicated
USDA ForestServiceGen.Tech.Rep.PSW-GTR-130.1991
I\*'
W
u
(
-
51
er
4
e
betore a flood
A
n
3
f: 101
k(
ma/:
r
u
w
n.
( X
u,
IOS mS
201
- Uu
C E
V1
0 Y
n. PC
w
n n
w
w >
e PC
Figure 12--The schematic diagram to obtain the
volume of the river bed fluctuation.
IOC
relationship, the idea of the specific volume of
the river bed fluctuation was introduced. The
specific volume was obtained by dividing the
volume of the river bed fluctuation by the peak
discharse adopted as an index of the flood
discharse.
k m
0 0
w w
==
*
> 2
-1
0 1
0
ORDER OF F L O O D O C C U R R E N C E
Figure 11--The changes of the volume of the
deposits on the bedrock in the observed reach.
Figure 14 shows the specific volume of the
river bed fluctuation in the observed reach
arranged in the order in which the floods
occurred. As this graph shows, a regularity is
The specific volume decreases
apparent.
exponentially in the erosional process following
the large deposition of the 8208 flood. As shown
in Figure 15, this regularity of the erosional
process in the observed reach can be expressed by
the following exponential equation.
Here S is the specific volume of the river bed
fluctuation per unit distance, t is the occurrent
order expressed as 1
2 etc, during the
erosional process. In the case of the series of
events in the observed reach a is 3.3 and 8,
Figure 13--The relation between the absolute
value of the river bed fluctuation in the observed
reach and the peak flow discharge.
Figure 16 shows the different ways in which
the specific volume decreases during the
erosional process, depending on the width of the
valley . This difference can be expressed in
terms of the parameters of the exponential
equation above. In the wider parts of the valley
in the observed reach (average width 72 meters),
n is 3.3 and 3, is 0.8. In the narrower parts
in the observed reach (average width 50 meters),
n is5.0and p is 1.4. Thus, as thevalley
becomes wider p decreases. It is believed that
,3
can be used as an index to shown how the
valley floor width influences the volume of the
river bed fluctuation.
USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130.1991
(8209X6305X8308X830SX8506)
t : ORDER OF FLOOD OCCURRENCE
ORDER OF F L O O D OCCURRENCE
Fiqure i6--The different ways in which the
specific volume decreases during the erosional
process, depending on the width of the valley.
Figure 14--The specific volume of the river bed
fluctuation in the observed reach arranged in the
order in which the floods occurred.
CONCLUSION
The magnitudes of the flow discharge and the
river bed fluctuation did not exhibit a one to
one correspondence. We were able to find a
regularity in the quantitative changes by
arranging the river bed fluctuations in the order
of the occurrence of the floods. This implies
that the history of sediment transport plays an
important role. That is to say, when little
unstable debris remains in the upper reaches and
slopes of the basin, a trend towards the erosion
of the river bed continues even if a larger flood
occurs. Thus, in torrential streams in headwater
regions, deposition or erosion depend mostly on
the sediment supply, not on the magnitude of the
flow discharge.
t
: ORDER OF FLOOD OCCURRENCE
Figure 15--The exponential relation between the
specific volume in the observed reach and the
order of the flood occurrence during the
erosional process.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
The valley floor width is closely related to
the dynamics of sediment transport.
In the
erosional process, the specific volume of the
river bed fluctuation decreases rapidly in narrow
valley floors, but only decreases slowly in wide
floors. On the other hand, in the depositional
Process, the wider the valley floors are, the
more sediment from the upper reach they can
retain. Therefore, the wide valley floors of a
stream are depositional spaces where the excess
sediment from the upper stream area is
temporari IY deposited. In the erosional process
that follows, sediment runs off down stream in a
way that can be explained by an exponential
process. In other words, wide valley floors
represent spaces that retard sediment transport.
I thank Michio Kaijo, Motoyuki Sunasaka, Teruo
Otsubo, Toru Endo, Akira Takinami, Masanori Wade
and Kunihiro Segawa, Agricultural and Forestry
Research Center, University of Tsukuba, for their
assistance to the field work.
REFERENCES
Iseya, Fujiko; lkeda Hiroshi; Maita Hideji. 1990.
Fluvial deposits in a torrential gravel-bed
stream by extreme sediment supply: sediment
structure and depositional mechanism. The 3rd
International Workshop on Gravel-Bed Rivers,
Florence,ltaly, September 25-29.1990.
Maita, Hideji; Otsuho,Teruo; Kaijo, Michio. 1984.
Hydraulic geometry in a natural torrent.
Transactions, the 95th Meeting of the
Japanese
Forestry Society: 641-643 (in
Japanese).
USDAForest ServiceGen. Tech. Rep. PSW-GTR-130.1991
Snow-Cover Condition in Japan and Damage of the Sugi
(Cryptomeria Japonica D. Don)'
Hideaki Taira2
Abstract: Japan is one of the most snowiest
regions in the world. Particularly the mountainous
area of Honshu (the main island), along the Japan
Sea has heavy snow in winter. In some places, snow
piles up more than four meters and the ground is
coverd with snow about one hundred and forty days
a year. The sugi tree is widely planted in snowy
regions, and snow-pressure damages, such as basal
bending, occure in juvenile stands, and after
that crown snow-damage, such as stem breakage,
happen in younger stands about 10-30 years-old.
Basal bending is formed by the difference in
recovery rate between the upper part and the lower
part of the stem during growing season. Root
damage occurs when the stem is prostrated, and the
compression wood is formed in the process of the
reelection of the fallen stem. Crown snow-damage
happens during the condition of comparative warm
air temparatures ranged from three degrees below
zero to three degrees above zero. The strength of
the stem against crown snow-damage depends on
the diameter of the tree, tree taper,constunt
rr for the root, and the modulus of elasticity.
Pulling up the fallen stem, and controlling the
tree density are important in preventing these
snow damage.
Introduction: It is said that Japan is the
snowiest region in the world. The Japan sea area
of Honshu has a lot of snow every year. Though the
snow protects plants from severe coldness in
winter and is an important source of water, it
also is the cause of damages such as basal bending
and stem breakage. The sugi is an important
spicese for reforestation in Japan and the total
area of sugi reforestation exceeds 4.15 million
ha., making it about 48 percent of the total
artifical forest in Japan. The sugi is widely
planted. in snowy regions, but suffer many kinds
of snow damages every year. Basal bending, stem
breakage,stem bending and uprooting are recognized
problems in the sugi reforestation, and these snow
damages are classified in to two types; one is
snow-pressure damage which occurs in younger aged
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
trees until1 they are about ten-years-old and the
other is crown snow-damages which occur in trees
over ten years old. But the types of snow damage
depends on the snow-cover condition. The author
will talk about the relationship between the
snow-cover condition in Japan and the type of snow
damage, the mechanism of main snow damage and its
control.
THE SNOW COVER CONDITION IN JAPAN AND
SNOW DAMAGE
The mean annual maximun snow depth of Japan is
shown in Fig-1. A high percentage of snowy areas
are distributed along the Japan Sea, and in some
areas, snow depth exceedes four meters.ln contrast
there is only about 10-50 centimeters in the area
along the Pacific Ocean, and the mountainous area
of Shikoku and Kyushu island, and most areas of
Shikoku, Kyushu and the southern part of the main
island have less than 10 centimeters.
The Pacific Ocean
Fig.-1.
Distribution map of annual maxmun
snow depth
crn
C
0..
0
LO
80
120
160
Basal bending
200
c rn
Fig.- 2. The relation between annual maxmun
snow depth and basal bending
Quality of snow also varies. There is dry
snow in Hokkaido, and the northern and mountainous
areas of Honshu, but in the area along the Japan
Sea there is wet snow which sticks easily on
trees. Snow pails up on the tree crown, and causes
stem breakage, which is called crown snow-damage.
Also in the Pacific Ocean area of Honshu, crown
snow-damage occurs when tropical low pressure
passes by the Pacific Ocean and brings wet snow
in early spring.
The relationship between basal bending and the
mean annual snow depth are shown in Fig-2. Basal
bending is about 20 centimeters in the areas where
snow depth is below 1 meter. As the snow depth
reaches 2 meters, basal bending increase over 60
centimeters, and at depths over 2.5 meters, basal
bending increase to 178 centimeters. Basal bending
increases as the snow depth increases.
Fig:
3
Basal bending of cryptomeria
Fig.- 4. Crown snow-damage of cryptomeria
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
Less snowy region
(less than 1.0 m )
---._
___
--..-
-
- - - _ _- - - - - - _ _ _
.
Tree height less than 1.5 n
Stem is Pressed on the ground
Less damage
------_____
---__
....
Tree height 4-5 m
Tree is unburied by snow
m
Tree height 2-3
Leaning stem
Damage of roots begin
- - - - _ _- _- - - _ _ _
Tree height more than 10.
height 6-7
Crown snov-damage occur
Turn over, stem breakage,
crack of stem occur under
much snow
rree
- - - .-_
- -_
_ _ -_- - _ _ _
Heavy snowy region
(more than 2.5 m )
.
-*1-
- - - - - - _ _- - - _ _
*
Stem is Pressed on the ground
Damage of roots begin. Roots
come out under the stem
Fig.- 5.
Tree is buried by snow
Turn over,stem breakag,
crack of stem occur. Under
Part of stem is transformed
into root
Stem is stabilized by developed
roots, s o the tree is unburied
Variation of snow damage of cryptomeria by
relation between snow depth and tree height
The extent of tree damage varies according
to the snow depth and tree height(Fig-5).
In areas
with snow depths of less than 1.0 meters, only
trees less than 2.0-2.5 meters in height are
prostrated in winter. Root damage is not serious
and stem breakage which becomes fatal seldom
occurs. As the tree reaches more than 2.0-2.5
meters in height, the stem does not prostrate
with average snow fall depth. However, in heavy
snow the p o & ~ b ~ l ~ t yof stem breakage and cracklng
at the bottom of the stem Increases and many trees
fall and pull out their roots. Snow damage on
trees varies from the pulling out of roots to stem
breakage (als ocalled crown snow-damage). Crown
snow-damage occurs in trees more than 10 meters in
height because the stem becomes stiff (and hence,
resistant to bending ) and the roots are large
enough to resist stem prostration. In regions of
heavy snow, the young stem repeatedly prostrates
and the uprooting of the trees is common. The new
roots develop under the part of stem still
touching the ground, and the tree then develops
resistance against futher prostration. The effects
of snow damage during the growing stages rangs
USDA Forest Service Gen.Tech.Rep.PSW-GTR-130.1991
from
pulling
out stem
of roots
to the
cracking
of thethe
basal
stem and
brakage.
In areas
with
depths of over 2.5 meters of snow, the ratio of
dieing trees due to snow damage increases
drastically, and it is difficult to forest the
sugi in this area.
THE MECHANISUM OF MAIN SNOW DAMAGE
Snow Pressure Damage
The stem of the sugi leans with the initial
snow fall and is buried by subsequent snow falls.
The snow-covered stem is pressed down by the
weight of the accumulated snow and subsequent
sedimentation of snow, and is subjected to elastic
strain, elastic after-strain and permanent
deformation.
In younger trees ( one to two years ) where
stems are soft and thin, the stress is mainly put
on the stem and the stem does not lean from the
base when the snow press it down on the ground.
But,for trees more than three-years-old (height :
67
1.5-2.0 nmeters), the stem leans from the base
because of the increase in its bending stiffness.
In early spring after the release of snow
pressure,the stem begins its straightening process
with rapid, simple elastic recovery, then elastic
after-strain follows. The -stem completes its
recovery through elastic after-strain until the
end of April or early May at which time the stem
resumes its recovery with growth and the formation
of compression wood. For one-and two-year old
trees, stem straigthening is completed by the
middle of June or early July ; after that, some
of the trees increase in weight with tree growth,
and this also contributes to the basal bend
formation (Fig-6).
Since straightening of the stem with growth
is great in one-, two-and three-year-old trees,
there is less basal bending on these trees. On the
other hand, since straightening of the leaning
stem decreases with age, there is greater basal
bending in older trees.
The recovery rate observed at each stem
positions varies in relationship to the stem's
distance from the base. The nearer the stem is to
the base, the slower the recovery rate. This
difference in recovery rate at various stem
positions causes basal bending (Fig-7).
The basal bending of the sugi increases
every year. During the early stages of growth,
snow depth has no effect on the basal bending
of the sugi, but, when the tree attains a height
of more than 1.5 meters, increase in snow depth
greatly affects stem prostration resulting in
greater basal bending. In addition to the two
factors mentioned, the slope of the site also
affects basal bending. if the snow depth and the
height of tree are the same, the
stem prostration is affected by the
slope. As the slope steepens, the
stem prostration increases resulting
basal bending.
amount of
degree of
amount of
in greater
When the stem is prostrated by snow, the roots
suffer damage at the upper part by stretch, at
the lower part by pressure, and at the left and
right sides by twist. The left and right twisting
of the roots, however, does not badly injure them
so that they can develop well on both side of the
slope. Roots on the down slope side are only
slightly damaged due to an increase on the
compression force. But roots on the upper slope
side are the ones that are severely damaged. They
are pulled out,resulting in poor root development.
Therefore, mature bent trees have deformed
roots and large side roots (Fig-8). In areas with
snow depths of less than 1.0 meters, most of the
trees more than 2.5 meters in height are not
easily prostrated and the amount of stem
prostration is small. Hcnce, the damage on roots
is not so severe and the roots develop normally.
In areas of heavy snow, beside root damage and
deformation, the lower part of the stem is
transformed into roots. When this stem touches
the ground due to the weight of snow, roots start
to develop from it and the part touching the
ground is transformed into a main root.
Roots on both the side and the lower part
of the slope are not easily damaged and hence, can
develop well. The transformation of the lower part
of the stem into a main root increases the
resistance of tree against prostration by snow.
Morever, the tree is not readily buried in
the snow because the transformed main roots
effectively prevent stem prostration.
Horizmlal deuiafion(cm)
Fig.- 6.
Process of straightening of t h e prostrated
s t e m o f a typical 2-year-old t r e e
Fig.- 7.
Relationship between t h e d e v i a t i o n from
former
position ( f ) and r a t e s of
straightening o f prostrate s t e m s ((rlf)
x 100) a t each position during a growing
season
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130.1991
Fig:
8
Deformation of roots
After basal bending is stabilized, surface
roots on the down slope develop and the diameter
of the lower stem increases towards the down
slope. Therefore, the curve of the lower part
of the stem is apparently corrected.
Crown Snow-Damage
Snow damage after basal bending has
stabilized is called crown snow- damage. It is
the phenomena in which the stems are broken
by an accelerating snow load on the tree crown.
This is roughly classfied into breakage of the
stem, breakage of the tip of the stem, and
uprooting. Uprooting is the predominant damage
among trees less than twenty-years-old, and is
sometimes difficult to distinguish from snow
pressure damage. Breakage of stem is common in
twenty-to thirty-years old stands, and this
stand is most sensitive to snow crown damage. In
stands More than thirty-years-old, the breakage of
the tip of the stem is common, but it is not
serious. Also trees with larger stems are more
resistant to crown snow-damage than those with
smaller stems. But it is difficult to evaluate
tree strength against snow crown damage by the
shape factor of stem. It is only a comparative
standard and it dose not become an absolute one.
As mentioned before, crown snow-damages is the
phenomena in which the stem is broken by an
unendurable snow load, so crown snow-damages can
look as if the broken stem is a failure of the
tapered column receiving an eccentric compressive
load of snow, i .e. the buckeling load (PC,) of
stem can be estimated by the following equation.
USDAForestServiceGen.Tech.Rep. PSW-GTR-130.1991
PC, = u 2 * r S 2 -E*I./L2
r ,' : satisties following the equation
tan r/r=-I /81a-u r 2 *L2-IoIL
6 : ratio of taper the stem
8:I - S
E :Mudulus in elasticity
L : Height of gravity of a snow-laded crown
I,: Second moment of cross cection base at the
stem
It is understood from the equation that
the strengthen against snow crown damage is
determined by the diameter of the stem, the taper
of the stem, the height of gravity of a snowload, modulus in elasticity in bending, the
u-index whose value was obtained from the
regression coefficient between the turning angle
of the tree stem and the turning moment at the
stem base. The estimated breaking load is 200-500
kilogram of trees about 20 centimeters at diameter
breast height and is agreed with the experimental
load which is gotten from broken trees receiving
vertical loads as shown Fig-11 .
CONTROL METHODS OF MAIN SNOW DAMAGE
Many methods of controlling snow damage have
been adapted in the past.0f these control methods,
the author will mentioned the most useful ones in
this paper.
Snow Pressure Damage
As the cause of basal bending of young trees
is stem prostration by snow, pulling up the
fallen stem is the most effective method of
. ..
~ i11. ~ ~ . i of~ snow-loaded
~
~
~trcc . and vertical loading test procedure for resistance
of tree stem (Hakntani and othcrs.l981).
Legend: G : lhc ccntcr of grrvily of r m o w l a d m
crown. a : h o r i z m l r l dirptjlccment of the cenlcr oigrav.
ily o i the snow.iadcn crown lrom the rlem axis. P:
snow lord. 8: lurning rndc ~t the stem bate. L: hcighl
of the cenlcr o i gravity 01 the mowladen crown lrom
lhc ground. 6 : delicction at the height L. D.: dismeler
11 the r i m bare, A : dirmclcr nl the hcighl L.
control. In regions of heavy snow, slant planting
which deforms the roots is adaptable because
the deformed roots is unsusceptible to stem
prostration. Fertizetion increases tree growth,
but basal bending also increases at the same time.
The degree of basal bending is different largely
among the cultivares, so planting of small bend
cullivares is an effective way to reduce basal
bending. But, it is hard to lean with initial
snow, so cultivares with a small degree of basal
bending were less frequent in stems leaning under
snow, but many stem breakage were observed in
heavy snow regions (with snow depths over 1.5
meters).
Crown Snow-Damage
One of the most effective methods for
controlling crown snow-damage is to decreas the
height/diameter
ratio by control 1 ing stand
density. The most desirable stand density is 800
-1200/per
hectare at planting, and repeated
thinnings are requied when the competition occurs
in the stand as the tree grow. Also, as modulus
in elasticity in bending is different in the
cultivarer, it is important to choose cultivar
with large modulus in elasticity in bending
for forest owners in the area of much crown
snow-damage.
LITERATURE CITED
Fujimori, T. ; Matsuda, and Kiyono, Y. 1987. Stand
structure and snow damage in relation to stand
age -Sugi plantations in Fukui prefecture in
the 1981 heavy-snowfall-. Journal of Japan
forest society
~.fiR(3):
...., 96-106
.Kato, A.;
Taira, H. and Nakatani, H. 1986.
Differences of snow damage and resistive
performance of tree stem in three Sugi
- - - - -
70
cul tivars. B G letin
~
of the Toyama prefectual
forest experiment station 11: 7-17.
Kato, A. ; Nakatani, H. ; Taira, H. and Aiura, H.
1988. Estimation snow-load required to cause
stem failure in Boka-sugi stand. Journal of
the Toyama forestry and forest products
research center 1: 1-6.
Katsuta, M. and Matsuda, K. 1984. Differences in
the damage from snow crowning
among
Cryptomeria japonica cultivars (1).
Rinboku
no ikusyu ( Forest tree breeding ) 131: 12-17.
Kitamura, M. 1981. Uber die Schneeshaden des SugiBestandes in Schneereichen Gebiet Japans.
Beitrage zur Wildbacherosions Lawinenforschung
(4). FBVA. Wine: 257-262.
Maeda, T.; Miyakawa, K. and Tanimoto, T. 1985.
Vegitation and regeneration of beech forest
in Gomisawa (Niigata Prefecture).- Performance
of Sugi planted in beech forest zone and a
proposaI for natural regeneration in the
zone -. Bulletin of the government forest
experiment station 333: 123-171.
Nakatani, H. ; Kato, A. ; Taira, H. ; Iijima, Y.
and Sawada, M. 1984. Deflection and resistance
performance of tree stems subjected to
snowload in sugi stands, Journal of the Japan
wood research society 30(11): 886-893.
Nitta, R. 1983. The variety of heavy-snowfall
conditions causing disastrous forest damage
during the winter of 1980181, Trans. 94th
meeting of Japan forest society: 727-728.
Shidei, T. 1954. Studies on the damages on forest
tree by snow pressures. Bulletin of the
government
forest experiment stastion 73 :
.
--
1-68.
Taira, H. 1982. The influence of differences in
the degreeof initial snow throw effected
by early winter snow on basal bending in
young sugi( Cryptomeria japonica D. Don ). J.
Jap. For. soc. 64: 453-460.
-.
1984. The process of bend forming and
USDA ForestService Gen.Tech.Rep.PSW-GTR-130.1991
reerecting of the lower part in the stem
due to the snow pressure and the tree weight
increase in Tateyama sugi ( Cryptomeria
japoni ca D.Don). Bei trage zur Wi ldbacherosions
-und Lawinen-forschung(5) .FBVA. WI EN: 139-147.
----. 1985. Basal-bend formation in young sugi
( Cryptomeria japonica D.Don ). J. Jap. For.
soc. 67:. 11-19.
-.
1986. Eeffects of inclined planting,
fertilization and tying up the stem with
rope on characters in young sugi ( Cryptomeria
japonica D,Don ).J. Jpn. For. soc. 68:333-337.
-----. 1987. The study of mechanism of Sugi
. basal bending and its control methods,
Bulletin of the Toyama prefectual forest
USDA Forest Service Gen. Tech. Rep.PSW-GTR-130. 1991
experiment station. 12: 80.
1988. The role of snow in coniferous stem
bend formation Beilrage zur Wildbacherosions
-und Lawenenforschung(7).
FBVA. WIEN. 275-283.
Takahashi, K. and Nitta. R. 1984. Wind' s role
in snow damage distribution at two man-made
forests, Trans. 95th meeting of Japan
forestsciety: 309-310.
Tsukahara, H. ; Ohtani, H. and Suto. S. 1975. The
bending of root sides of the forest trees
planted by Cryptomeria seed1 ings on the
steep stands in the heavy snowrr region.
Jurnal of Yamagata agriculture and forestry
sociaty. 32: 21-30.
----.
Study on Shearing
- Force and Impact Force of a Volcanic
Mud Flow on Mt. Sakurajimai
Yoshinobu Taniguchi2
Abstract: Two k i n d s o f s h e a r i n g stress
m e t e r s ( t y p e A a n d t y p e B ) were s e t on t h e
c h a n n e l b o t t o m i n t h e Arimura R i v e r a n d t h e
Mochiki R i v e r on M t . S a k u r a j i m a . V o l c a n i c
mud f l o w s t a k e p l a c e t h e r e a b o u t 100 t i m e s
a year.
The r e s u l t s o f t h e s u r v e y s
demonstrated t h a t t h e a c t u a l s h e a r i n g f o r c e
o f a v o l c a n i c mud f l o w on M t . S a k u r a j i m a
was from 0 . 4 6 t o 2 . 5 0 k g f / c m 2 . The a c t u a l
impact f o r c e c a u s e d by c o l l i s i o n s of b i g
s t o n e s , which were c o n t a i n e d i n a mud f l o w ,
w i t h t h e c h a n n e l b o t t o m was c a l c u l a t e d
t h e o r e t i c a l l y a t a b o u t 1 5 times g r e a t e r
t h a n t h e d e a d l o a d s o f t h e s t o n e s . The
c o l l i s i o n o f s t o n e s i n a mud f l o w c a u s e d
g r e a t a b r a s i o n of c o n c r e t e ,
A g r e a t number o f v o l c a n i c mud f l o w s
t a k e p l a c e e v e r y y e a r on M t . S a k u r a j i m a i n
s p i t e o f l i t t l e r a i n f a l l . They o f t e n
damage b o t h dams a n d c h a n n e l s , a n d a l s o
t h r e a t e n t h e i n h a b i t a n t s of S a k u r a j i m a . I n
t h i s s t u d y , t h e magnitude of t h e a c t u a l
s h e a r i n g f o r c e o f a v o l c a n i c mud f l o w was
r e s e a r c h e d i n o r d e r t o make c l e a r t h e
mechanism o f t h e d e s t r u c t i o n a n d t h e
a b r a s i o n o f a dam o r a c o n c r e t e c h a n n e l i n
t o r r e n t s o f M t . S a k u r a j i m a . The d a t a were
a n a l y z e d by t h e t h e o r i e s o f h y d r a u l i c s a n d
t h e c o l l i s i o n o f a n e l a s t i c b o d y . The
cause of d e s t r u c t i o n and t h e a b r a s i o n of a
dam o r a c o n c r e t e c h a n n e l b y mud f l o w s
c o u l d b e c l a r i f i e d t o some e x t e n t from t h e
r e s u l t s of these surveys.
SEDIMENT YIELD ON M T . SAKURAJIMA
M t . S a k u r a j i m a , which l i e s i n t h e
s o u t h e r n p a r t o f Japan ( F i g . l ) , i s one of
t h e most a c t i v e v o l c a n o e s i n J a p a n . I t i s
-
l p r e s e n t e d a t t h e S u b j e c t Group S 1 . 0 4
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s i n
Managed F o r e s t s , X I X World F o r e s t r y
C o n g r e s s , I n t e r n a t i o n a l Union o f F o r e s t r y
R e s e a r c h O r g a n i z a t i o n s , August 5-11, 1990,
M o n t r e a l , Canada.
2 ~ o s h i n o b uT a n i g u c h i : (1985) 58-2811.
P r o f e s s o r of A g r i c u l t u r e and F o r e s t
S c i e n c e . F a c u l t y of A g r i c u l t u r e , Miyazaki
U n i v e r s i t y , M i y a z a k i 889-21, J a p a n
TOKYO
Fig. 1
Map o f J a p a n
l o c a t e d i n Kagoshima Bay a n d h a s a n a r e a o f
80 km2 a n d c i r c u m f e r e n c e o f 52 k i l o m e t e r s .
T h e r e a r e t h r e e c r a t e r s on M t . S a k u r a j i m a :
K i t a d a k e C r a t e r (1117 m e t e r s a b o v e s e a
l e v e l ) , Nakahake C r a t e r (1060 m e t e r s ) , a n d
Minamidake C r a t e r (1040 meters).
Minamidake C r a t e r i s c u r r e n t l y e r u p t i n g
v i g o r o u s l y . T a b l e 1 shows t h e v o l c a n i c
a c t i v i t i e s of M t . Sakurajima f o r t h e p a s t
20 y e a r s (Osumi P u b l i c Works O f f i c e , 1 9 8 6 ) .
L a t e l y t h e b a r i n g of mountain s l o p e s
h a s b e e n making c o n s p i c u o u s p r o g r e s s on M t .
Sakurajima i n l i n e with t h e vigorous
v o l c a n i c a c t i v i t i e s . The b a r i n g o f t h e
s l o p e s h a s been caused by b o t h t h e e f f e c t
o f f a l l from t h e e r u p t i o n s a n d t h e a c t i o n
o f s u l p h u r g a s from smoke e m i s s i o n s o f t h e
Minamidake C r a t e r . The r e c e d i n g o f
v e g e t a t i o n on t h e s l o p e s i n t h e u p p e r
r e a c h e s o f e a c h t o r r e n t h a s c o n t i n u e d on
M t . Sakurajima, and t h e b a r i n g of t h e
g downwards y e a r b y y e a r . A number o f
g u l l i e s h a v e formed on t h e s l o p e s . T h e s e
s l o p e s h a v e b e e n s u f f e r i n g from r a p i d
e r o s i o n , and t h e y have been producing a
g r e a t amount of s e d i m e n t f o r t h e l a s t 20
y e a r s . F i g . 2 shows a p i c t u r e o f t h e
s l o p e s around t h e Kitadake C r a t e r . There
i s no v e g e t a t i o n i n t h i s a r e a , a n d many
r i l l s a n d s m a l l g u l l i e s h a v e a l r e a d y formed
on t h e s l o p e .
Some o f t h e g e o m o r p h o l o g i c a l f a c t o r s i n
r e f e r e n c e t o mud f l o w s were a n a l y z e d b y
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
Table 1 Volcanic a c t i v i t i e s of M t .
Sakurajima
YSaZ
erupt-
number o f o c c u r a n c e s
smoke
. .
earthquakes
0
1940
1960
1980 year
F i g . 3 Expansion of
gullies
1940
1
1980 year
F i g . 4 I n c r e a s e of
t o t a l length
of g u l l i e s
u s i n g b o t h a s e r i e s of s e r i a l photographs
from 1947 t o 1984 a n d t h e r e p o r t on t h e
s e d i m e n t y i e l d on t h e s l o p e s o f M t .
S a k u r a j i m a (Osumi P u b l i c Works O f f i c e ,
1 9 8 8 ) . T h e s e r e s u l t s a r e shown i n F i g s .
3-6.
F i g . 3 shows t h e e x p a n s i o n o f t h e t o t a l
a r e a of t h e s e g u l l i e s i n t h e 38 y e a r s from
1947 t o 1 9 8 4 . The i n c r e a s e i n t h e i r t o t a l
a r e a i n t h e 26 y e a r s from 1947 t o 1972 i s
l e s s t h a n t h a t i n t h e p e r i o d s i n c e 1974.
V o l c a n i c a c t i v i t y became v e r y v i g o r o u s
a f t e r 1 9 7 4 . T h i s f a c t shows t h a t t h e r e
s h o u l d b e a r e l a t i o n s h i p between t h e number
of mud f l o w s a n d t h e v o l c a n i c a c t i v i t y
s i n c e 1 9 7 4 . The same t e n d e n c y a l s o e x i s t s
i n t h e length of g u l l i e s (Fig. 4 ) . This
proves t h a t t h e g u l l i e s have been
c o n s i d e r a b l y extended, and t h e y have a l s o
e x p a n d e d i n w i d t h by t h e f a i l u r e o f
O+
1940
1980 year
F i g . 5 Change o f g u l l y
width
1940
1960
Fig. 6 Increase i n
number o f
gullies
s i d e w a l l s o v e r t h e l a s t 10 y e a r s ( F i g . 5 ) .
An a v e r a g e r a t e of t h e e x p a n s i o n o f t h e
g u l l i e s i n t h e 20 y e a r s from 1947 was Only
0.13 m/yr.
On t h e o t h e r hand, i t i n c r e a s e d
t o 0 . 7 6 m/yr i n t h e 8 y e a r s from 1966. The
l a t t e r is 5.9 times g r e a t e r t h a n t h e
f o r m e r . However, it h a s d e c r e a s e d s i n c e
1980, b e c a u s e f r e s h g u l l i e s began t o form
on t h e s l o p e s . F i g . 4 shows t h e g r e a t
e x t e n s i o n of g u l l i e s .
The number o f
g u l l i e s i n c r e a s e d c o n s p i c u o u s l y i n t h e 20
y e a r s from 1947 t o 1966 ( F i g . 6 ) . T h i s
means t h a t t h e f o r m a t i o n o f g u l l i e s h a d
a l r e a d y e n d e d d u r i n g t h e s e y e a r s . Most o f
t h e s e d i m e n t y i e l d on M t . S a k u r a j i m a i s
c a u s e d by t h e e x t e n s i o n and t h e expansion
o f g u l l i e s . The v o l u m e t r i c r a t e o f t h e
s e d i m e n t y i e l d by t h e e x t e n s i o n of g u l l i e s
i s 4 1 p e r c e n t o f t h e whole, a n d t h e
e x p a n s i o n o f them i s 59 p e r c e n t .
SURVEYING METHOD
Fig. 2
G u l l i e s on t h e s l o p e of M t .
Sakurajima
USDA Forest Service Gem Tech. Rep. PSW-GTR-130.1991
1y"@
A s u r v e y of t h e s h e a r i n g f o r c e of a
v o l c a n i c mud f l o w a c t i n g on a c h a n n e l
{
MOVABLE
PLATE
SENSOR
PLATE
b e n d i n g moment forms between p l a t e B a n d
t h e w a l l o f c o n c r e t e t o which p l a t e B i s
attached (Fig. 8 ) . This space i s
i n e v i t a b l y f i l l e d u p b y s o i l a n d s a n d which
a r e c o n t a i n e d i n a mud f l o w whenever one
r u n s down on p l a t e A . On a c c o u n t o f t h i s ,
p l a t e B of t h i s meter cannot avoid
i n c r e a s i n g i n d e f l e c t i o n , whenever a
b e n d i n g moment a c t s on t h e p l a t e . Of
c o u r s e , t h i s h a p p e n s on c o n d i t i o n t h a t t h e
deflection is within t h e proportional l i m i t
o f t h e s t r e n g t h o f t h e m a t e r i a l o f which
t h e p l a t e i s made.
SURVEYING RESULTS
Fig. 7
S h e a r i n g stress m e t e r ( t y p e A )
DIRECTION OF
~ i g .8
Shearing stress meter ( t y p e B )
b o t t o m h a s b e e n g o i n g on i n t h e Mochiki
R i v e r s i n c e 1987 u s i n g t h e two k i n d s o f
s h e a r i n g s t r e s s m e t e r s shown i n F i g . 7
( t y p e A) a n d F i g . 8 ( t y p e B ) . No d a t a h a v e
b e e n o b t a i n e d from t h e t y p e A s u r v e y up t o
t h e p r e s e n t , b u t some d a t a h a v e b e e n g o t t e n
I n t h e t y p e B, p l a t e A i s
from t h e t y p e B .
t r a i l e d downstream b y t h e s h e a r i n g f o r c e
a c t i n g on i t s s u r f a c e , a n d p l a t e B i s b e n t
by t h e s h e a r i n g f o r c e . A s a r e s u l t , a
b e n d i n g moment i s g e n e r a t e d i n p l a t e B .
T h e r e s h o u l d , however, b e a b a l a n c e between
t h e s h e a r i n g f o r c e a n d t h e b e n d i n g moment.
A c c o r d i n g l y , t h e s h e a r i n g f o r c e a c t i n g on
p l a t e A ( t h e channel bottom) can be e a s i l y
measured by t h e m a g n i t u d e o f i t s d e f l e c t i o n
b a s e d on t h e t h e o r y o f t h e d e f l e c t i o n o f a
c a n t i l e v e r . The c h a n g e i n s h e a r i n g f o r c e
c a n n o t b e m e a s u r e d e v e r y t i m e by t h i s
method, b u t t h e maximum s h e a r i n g f o r c e c a n
b e e a s i l y measured u s i n g t h i s m e t e r .
When a d e a d l o a d o f 5 6 . 8 k i l o g r a m s was
a p p l i e d t o t h i s s h e a r i n g stress m e t e r ( t y p e
B) f o r t h e c a l i b r a t i o n o f o b s e r v e d v a l u e s ,
t h e a v e r a g e d e f l e c t i o n o f p l a t e B was 8
millimeters.
T h i s m e t e r i s l i m i t e d by t h e
f a c t t h a t p l a t e B c a n n o t r e c o v e r from i t s
d e f l e c t i o n , b e c a u s e a s p a c e c a u s e d by t h e
T a b l e 2 shows t h e v o l u m e t r i c
c o n c e n t r a t i o n o f t h e mud f l o w s a m p l e s
c o l l e c t e d by t h e a u t h o r i n t h e Arimura
R i v e r on J u l y 1 8 , 1987 i n o r d e r t o
i n v e s t i g a t e t h e change o f composition o f a
mud f l o w ( T a n i g u c h i a n d T a k a h a s h i , 1 9 8 9 ) .
The o b s e r v e d v a l u e s o f t h e s h e a r i n g
f o r c e s o f s e v e r a l mud f l o w s a r e shown i n
t a b l e 3 . Some v e l o c i t i e s o f t h e mud f l o w ,
a n d t h e d i a m e t e r s o f t h e s t o n e s i n it a r e
shown i n t a b l e 4 . They were measured on a
v i d e o t a p e r e c o r d e d b y Osumi P u b l i c Works
O f f i c e on September 24, 1 9 8 8 . One h u g e
s t o n e i n t h e mud f l o w i s shown i n F i g . 9.
T h e s e p i c t u r e s were t a k e n from t h a t v i d e o .
F i g . 10 i s a p i c t u r e o f t h e measurement o f
t h e d e f l e c t i o n o f p l a t e B i n t h e Arimura
R i v e r a f t e r t h e o c c u r r e n c e o f t h e mud f l o w
on O c t o b e r 6, 1 9 8 8 . No g r e a t number o f
huge s t o n e s g a t h e r e d t o g e t h e r a t t h e f r o n t
o f t h a t mud f l o w was o b s e r v e d .
Table 2
Grain s i z e d i s t r i b u t i o n and
c o n c e n t r a t i o n o f mud f l o w on J u l y
1 8 , 1987
C o l l e c t i o n Time
LC m i n .
1 5 min.
30 min,
grain diameter
distribution rate
- - - - - - - - ( P C ~ ------)
o v e r 2000 $
840
500
250
37
u n d e r 37
concentration (pct)
density
(g/cm3)
1.0
3.5
5.8
22.2
1.0
3.1
6.9
22.4
2.9
12.9
32.5
32.0
34.3
7.7
2.2
0.2
15.6
1.11
1.25
1.27
USDA Forest Service Gen.Tech.Rep.PSW-GTR-130.1991
Table 3
Observed s h e a r i n g f o r c e s of mud
flows
d a t e observed
shearing force
2.13
0.462
1.402
2.502
Table 4
StMe
river
Arimura
Arimura
Arimura
Mochiki
S t o n e s ' d i a m e t e r s i n t h e mud
f l o w on S e p t e m b e r 2 4 , 1988 a n d
their velocities.
diameter
(cm)
veloc1t.v
m/sec
F i g . 10
Measurement of s h e a r i n g f o r c e o f a
mud f l o w
DISCUSSION
The t y p e B s h e a r i n g s t r e s s m e t e r i s
s t r u c t u r a l l y a k i n d of c a n t i l e v e r .
According t o t h e t h e o r y of c a n t i l e v e r
deflection, t h e r e should be a l i n e a r i t y
between t h e s h e a r i n g s t r e s s (2) a n d t h e
of t h e p l a t e :
maximum d e f l e c t i o n 6
6
2
(1)
If i t i s s u p p o s e d t h a t t h e m a g n i t u d e o f
t h e s h e a r i n g s t r e s s ( Z o ) a l r e a d y known a c t s
on t h e s h e a r p l a n e ( p l a t e A ) , a n d t h a t t h e
d e f l e c t i o n o f p l a t e B i s 60, t h e r e s h o u l d
b e t h e f o l l o w i n g r e l a t i o n between 2, 20 a n d
6 , 60, u s i n g e x p r e s s i o n (1):
z /TO = 6 /60
(2)
The s h e a r i n g s t r e s s m e t e r was t e s t e d b y a
dead l o a d of 56.8 k i l o g r a m s . A s a r e s u l t
o f t h a t , t h e mean v a l u e o f t h e d e f l e c t i o n s
(60) was 8 m i l l i m e t e r s i n t h e l o a d t e s t .
When t h e above v a l u e o f 8 m i l l i m e t e r s i s
s u b s t i t u t e d i n t o e q u a t i o n (21, t h e
following is obtained:
T = 0.357 6
(3)
-
Some d a t a (& 6 . 0 c e n t i m e t e r s , 1 . 3
c e n t i m e t e r s and 4.0 c e n t i m e t e r s i n t h e
Arimura R i v e r mud f l o w which t o o k p l a c e on
S e p t e m b e r 24, 1988, O c t o b e r 6, 1988, a n d
February 17,1989, and 7 . 0 c e n t i m e t e r s i n
t h e Mochiki R i v e r mud f l o w on F e b r u a r y 1 7 ,
1989) were o b t a i n e d . When t h e s e v a l u e s
were s u b s t i t u t e d i n t o e q u a t i o n ( 3 ) , t h e
r e s u l t s o f c o m p u t a t i o n s were shown i n t a b l e
3 above.
Fig. 9
Huge s t o n e i n t h e mud f l o w on
September 2 4
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
I t i s , however, d o u b t f u l w h e t h e r a
l i n e a r i t y between.these s h e a r i n g f o r c e s and
d e f l e c t i o n s of t h e p l a t e might s t r i c t l y
e x i s t i n t h i s case, because t h e s e observed
d e f l e c t i o n s a r e conspicuously l a r g e .
However, s e e i n g t h a t t h e s e d e f l e c t i o n s
began t o occur i n t h e t e s t when t h e a c t i n g
l o a d had gone o v e r 57 kilograms, it was
evident t h a t a shearing force a t l e a s t
g r e a t e r t h a n 0 . 2 9 kgf/cm2 a c t e d on t h e
shear plane.
The s h e a r i n g f o r c e of a mud flow a c t i n g
on a channel bottom can be e x p r e s s e d a s
f o l l o w s , t a k i n g t h e flow model of a mud
flow shown i n F i g . 11 i n t o c o n s i d e r a t i o n :
2 = po g ~ s i n 8
(4)
where po i s t h e d e n s i t y of a mud flow; H i s
i t s water h e i g h t ; and 8 i s t h e a n g l e of t h e
channel s l o p e . When t h e a c t u a l l y observed
v a l u e s of a d e n s i t y of 1 . 2 7 g/cm3 and a
water h e i g h t of 1 . 0 meters i n t h e mud flow
of t h e Arimura River on J u l y 18, 1987 a r e
s u b s t i t u t e d i n t o equation ( 4 ) , t h e shearing
Fig.11 Flow model of a mud flow
s t r e s s ( 2 ) becomes about 9 gf/cm2. The
computed v a l u e from e q u a t i o n ( 4 ) cannot
prove t h a t a l a r g e s h e a r i n g s t r e s s a s g r e a t
2 . 5 kgf/cm2 should occur even i f
a s 0.5
t h e r e i s a v e r y l a r g e s c a l e of a mud f l o w .
Judging from t h a t , it can be i n f e r r e d t h a t
such a l a r g e s h e a r i n g s t r e s s must be caused
by t h e f r i c t i o n between s t o n e s and t h e
channel bottom, because t h e s e s t o n e s a r e
dragged a l o n g t h e channel bottom a t a
r a t h e r h i g h speed.
-
Using t h e a c t u a l s h e a r i n g f o r c e a c t i n g
on t h e channel bottom, t h e s i z e of a s t o n e
c o n t a i n e d i n t h e mud flow which took p l a c e
i n t h e Arimura R i v e r on September 24, 1988
c o u l d be e s t i m a t e d . When it was supposed
t h a t t h e d e n s i t y of a s t o n e was 2 . 7 g/cm3
and i t s f r i c t i o n a l c o e f f i c i e n t was 0 . 7 , t h e
s i z e of a s t o n e c o r r e s p o n d i n g t o t h e above
s h e a r i n g f o r c e of 2 . 1 3 kgf/cm2 was
c a l c u l a t e d a t about 60 c e n t i m e t e r s i n
l e n g t h f o r one s i d e of a cube, o r about 80
c e n t i m e t e r s i n t h e d i a m e t e r of a s p h e r e .
Many s t o n e s c o r r e s p o n d i n g t o such s i z e s
were observed on t h e v i d e o . Judging from
t h a t , it can be seen t h a t t h e c a l c u l a t e d
v a l u e of t h e s i z e of a s t o n e i s p r o p e r
compared w i t h t h e a c t u a l s i z e s . However,
t h e maximum s i z e of a s t o n e i n t h e Arimura
R i v e r mud flow on September 24 was 3.8
m e t e r s . T h i s proves t h a t t h e concept of
s h e a r i n g f o r c e i n t h e c a s e i n which a mud
flow i s r e g a r d e d a s o n l y a f l u i d l i k e water
cannot be used f o r t h e s o l u t i o n of an
a c t u a l problem l i k e t h e a b r a s i o n of a
c o n c r e t e channel bottom.
When a mud flow accompanied by many
s t o n e s flows on a channel bottom, i t s
a b r a s i o n i s v e r y conspicuous, because t h e
s t o n e s a r e dragged a l o n g t h e channel
bottom. A g r e a t f r i c t i o n between t h e
s u r f a c e of t h e channel bottom and s t o n e s i s
generated.
The h y d r a u l i c d r a g f o r c e of a s t o n e ( a
p e r f e c t cube o r s p h e r e ) i n f l u i d can be
expressed a s follows:
F = (1/2) CoPo V2A
(5)
where F i s t h e d r a g f o r c e ; CD i s t h e
c o e f f i c i e n t of t h e d r a g f o r c e ; V i s t h e
r e l a t i v e v e l o c i t y between f l u i d and a
s t o n e ; and A i s t h e a r e a of t h e a p p l i c a t i o n
of t h e d r a g f o r c e . The v a l u e Co became
about 8 from t h e r e s u l t s of t h e
computations on t h e mud flow which t o o k
p l a c e on J u l y 16, 1987 i n t h e Arimura
River.
Supposing t h a t CD was 8, t h e d e n s i t y of
a mud flow was 1.27 g/cm3 ( t h e v a l u e i n
t a b l e 2 ) , t h e s t o n e ' s d i a m e t e r was 3.8
m e t e r s ( t h e maximum d i a m e t e r i n t h e mud
flow on September 24, 1988 i n t h e Arimura
R i v e r ) , and t h e r e l a t i v e v e l o c i t y was 5 . 1
m/sec., t h e d r a g f o r c e of t h e mud flow
c o u l d be e s t i m a t e d a t 50 t o n s by e q u a t i o n
( 5 ) . On t h e o t h e r hand, t h e f r i c t i o n a l
r e s i s t a n c e of a s t o n e on t h e channel bottom
i s estimated a t 40
50 t o n s , u s i n g t h e
v a l u e 0 . 7 6 a s t h e c o e f f i c i e n t of i t s
f r i c t i o n . Judging from t h e above r e s u l t ,
it can be seen t h a t a mud flow w i t h a water
h e i g h t of about 1 meter and a r e l a t i v e
v e l o c i t y of about 5 m/sec can e a s i l y c a r r y
a huge s t o n e a s l a r g e a s 3 meters i n
d i a m e t e r . The g r e a t f r i c t i o n i s caused by
many s t o n e s dragged a l o n g a channel bottom
by a mud f l o w . There i s a n o t h e r r e p o r t
t h a t t h e t e m p e r a t u r e r o s e about 0 . 5
1.5012
i n t h e Mochiki River when a mud flow r a n
down i n t h e channel (Hirano, 1 9 8 9 ) . T h i s
shows t h a t t h e f r i c t i o n a l h e a t s t a t e d above
might have a r e l a t i o n t o t h e f r i c t i o n which
was g e n e r a t e d between t h e c o n c r e t e channel
bottom and t h e s t o n e s .
-
-
A mud flow a l s o has t h e same
It
c h a r a c t e r i s t i c a s a d e b r i s flow.
g r e a t l y v i b r a t e s t h e e a r t h around t h e
s t r e a m when it flows a t a high speed. The
v i b r a t i o n i s caused by t h e c o l l i s i o n of
s t o n e s w i t h t h e c o n c r e t e channel bottom o r
s i d e w a l l s of t h e s t r e a m . There a r e some
r e p o r t s t h a t t h e v i b r a t i o n s caused by
c o l l i s i o n s between huge s t o n e s and t h e
c h a n n e l bottom have a c c e l e r a t e d s l o p e
f a i l u r e s a l o n g t o r r e n t s . This c o l l i s i o n i s
a l s o a n o t h e r important f a c t o r i n t h e
d e s t r u c t i v e damage of dams o r c o n c r e t e
channels i n t o r r e n t s . The v i b r a t i o n caused
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
by t h e c o l l i s i o n of a huge s t o n e i n a mudd e b r i s flow was surveyed on t h e s l o p e s of
M t . Yake i n o r d e r t o e s t i m a t e t h e
occurrence of a s l o p e f a i l u r e when t h e flow
r a n down i n a t o r r e n t . An a c c e l e r a t i o n of
0 . 1 g a l was observed a t a p o i n t 15 meters
from t h e c e n t r e of t h e t o r r e n t i n c r o s s
s e c t i o n (Matsumoto P u b l i c Sabo Works
O f f i c e , 1975) . There might have been a
g r e a t v i b r a t i o n n e a r t h e c e n t r e . This
problem s h o u l d be t a k e n i n t o c o n s i d e r a t i o n
t o p r e v e n t dams o r c h a n n e l s from being
damaged i n t o r r e n t s .
The r e l a t i o n s h i p between t h e s t r e n g t h
of t h e c o n c r e t e of a channel and t h e
a b r a s i o n caused by t h e c o l l i s i o n of s t o n e s
c o n t a i n e d i n a mud flow i s u n c l e a r even
now. The impact f o r c e caused by t h e
c o l l i s i o n of an e l a s t i c body with c o n c r e t e
can be e x p r e s s e d a s f o l l o w s (Okubo, 1 9 6 3 ) :
( a 2 / 2 E ) A l = Wo(S + h)
(6)
where a i s t h e impact s t r e s s p e r u n i t a r e a ;
E i s t h e c o e f f i c i e n t of t h e modulus of
c o n c r e t e ; A i s t h e a r e a of t h e a p p l i c a t i o n
of a f o r c e ; L i s t h e l e n g t h of a body; Wo
i s a dead l o a d S i s t h e f a l l i n g h e i g h t of a
body from a l e v e l ; and h i s t h e compressed
t h i c k n e s s of c o n c r e t e . By s o l v i n g e q u a t i o n
( 6 ) , a i s obtained:
a = (2EWo (S + h) / A 1 ) ' I 2
(7)
On t h e o t h e r hand, a can a l s o be e x p r e s s e d
a s follows:
a= E(X/~)
(8)
By s u b s t i t u t i n g e q u a t i o n ( 8 ) i n t o e q u a t i o n
( 6 ) , a can be s o l v e d :
dl+
a = (Wo/A) (1 +
2SEA/Wol
(9)
When it i s supposed t h a t ho i s t h e
t h i c k n e s s corresponding t o a dead load
( W o ) , ho can be e x p r e s s e d a s f o l l o w s :
ha = W ~ L / A E
(10)
When e q u a t i o n (10) i s s u b s t i t u t e d i n t o
e q u a t i o n ( 9 ) , a can be s o l v e d :
a = (w0/n)(1 +
q
x
(11)
The s t r a i n ( h ) caused by t h e impact fol
of a s t o n e which i s c o n t a i n e d i n a mud
can be s o l v e d , u s i n g e q u a t i o n s ( 8 ) and
(10) :
. \ , I
h= Xo(l +
(12)
The dead l o a d c o r r e s p o n d i n g t o t h e above
s t r a i n can be e s t i m a t e d , u s i n g e q u a t i o n s
(8) and (12) :
~~
(13)
w/w0 = 1 +
When it i s supposed t h a t Do i s t h e a c t u a l
s t o n e ' s diameter, t h e converted diameter
(D), d e f i n e d h e r e a s t h e d i a m e t e r of an
imaginary s t o n e which i s assumed t o be
e q u a l t o t h e impact f o r c e caused by an
a c t u a l stone with t h e diameter (Do) s t a t e d
USDA Forest Service Gen.Tech. Rep. PSW-GTR-130.1991
above, can be c a l c u l a t e d a s f o l l o w s , u s i n g
e q u a t i o n (13) and b o t h e x p r e s s i o n s of W =
~ p , ~ ~ /W 6=, 7tpS~o3/6:
D / D o = (1 +
(14)
where D i s t h e c o n v e r t e d d i a m e t e r d e f i n e d
above; p, i s t h e d e n s i t y of a s t o n e . When
it i s supposed t h a t S i s 10 c e n t i m e t e r s , ha
i s 1 m i l l i m e t e r , and s t o n e ' s d i a m e t e r i s
3 . 8 m e t e r s ( t h e maximum d i a m e t e r i n t h e
Arimura R i v e r mud flow on September 24,
1 9 8 8 ) , t h e d i a m e t e r ( D ) of an imaginary
s t o n e ( t h e c o n v e r t e d d i a m e t e r corresponding
t o t h e impact f o r c e caused by an a c t u a l
s t o n e w i t h a d i a m e t e r of 3 . 8 meters i s
e s t i m a t e d t o be about 9 . 4 m e t e r s . T h i s
means t h a t t h e impact f o r c e has t h e same
e f f e c t a s a huge s t o n e loaded on t h e
I t shows t h a t channel
channel bottom.
works s h o u l d be designed s a f e l y enough t o
p r e v e n t a c o n c r e t e channel from
d e s t r u c t i o n , because a channel may be
a t t a c k e d by a v e r y h i g h impact f o r c e .
I f it i s supposed t h a t b o t h a r e a s of
t h e a p p l i c a t i o n of f o r c e s , t h e dead l o a d
( W O ) and t h e impact l o a d (W), a r e e q u a l , Wo
and W can be e x p r e s s e d a s f o l l o w :
Wv = A a O
(15)
w = Aa
(16)
When e x p r e s s i o n s (15) and (16) a r e s u b s t i t u t e d i n t o equation ( 1 3 ) , t h e following
e q u a t i o n can be o b t a i n e d :
a/ao
= 1
+
(17)
Do i n e q u a t i o n (17) i s t h e s t r e s s by t h e
dead l o a d d e r i v e d from an a c t u a l impact
s t r e s s ( a ) . The s t r e s s ((r) must be w i t h i n
t h e a l l o w a b l e s t r e n g t h of t h e c o n c r e t e . It
i s g e n e r a l l y s a i d t h a t t h e l i m i t of t h e
s t r e n g t h of c o n c r e t e i s about 250 kgf/cm2.
Accordingly, t h e maximum (a) must be about
I f t h e same v a l u e s a s t h e
250 kgf/cm2.
above (hv = 1 m i l l i m e t e r and S = 10
c e n t i m e t e r s ) a r e used h e r e , Go can be
d e r i v e d from e q u a t i o n ( 1 7 ) :
250/00 = 15
.: av = 1 6 .kgf/cm2
When t h e a r e a of t h e a p p l i c a t i o n of a
f o r c e i s about 10 cm2, t h e whole f o r c e
becomes 167 kilograms, and a s t o n e ' s
d i a m e t e r corresponding t o t h i s a l l o w a b l e
f o r c e i s c a l c u l a t e d a t 50 c e n t i m e t e r s .
However, t h e a c t u a l compressed t h i c k n e s s of
t h e c o n c r e t e of a channel must be l e s s t h a n
t h e 1 m i l l i m e t e r assumed above. Then t h e
v a l u e of oo becomes s m a l l e r t h a n 1 6 . 7
kgf /cm2. Accordingly, t h e a l l o w a b l e
d i a m e t e r of a s t o n e i n a mud flow t o
p r e v e n t t h e d e s t r u c t i o n of a c o n c r e t e
channel must be l e s s t h a n 50 c e n t i m e t e r s .
The a b o v e i s a d i s c u s s i o n from t h e
p o i n t o f view o f t h e c o m p r e s s i v e s t r e n g t h
of concrete. Shearing force i s a l s o a very
important f a c t o r i n t h e destruction of a
It i s generally said
concrete channel.
t h a t t h e shearing s t r e n g t h of concrete i s
1/4
1/7 of i t s compressive s t r e n g t h
(Okada a n d Muguruma, 1989) . A c c o r d i n g l y ,
t h e a l l o w a b l e s i z e of a s t o n e should be
e v e n s m a l l e r t h a n 50 c e n t i m e t e r s i n
diameter.
I t can be f o r e s e e n t h a t t h e
destructive action against a concrete
c h a n n e l w i l l i n c r e a s e e v e n more b y d i n t o f
t h e s h e a r i n g f o r c e caused by t h e f r i c t i o n
of s t o n e s w i t h a channel bottom, i n
a d d i t i o n t o t h e c o m p r e s s i v e f o r c e by t h e
i m p a c t . The Osumi P u b l i c Works O f f i c e
began t o c a r r y o u t a s u r v e y of t h e a b r a s i o n
o f t h e c h a n n e l c o n c r e t e i n t h e Mochiki
R i v e r i n 1 9 8 8 . T h a t c o n c r e t e c h a n n e l was
c o n s t r u c t e d t o t h e s t r e n g t h o f 160 k g f / c m 2 .
The m i x i n g p r o p o r t i o n o f t h a t c o n c r e t e i s
shown i n t h e f o l l o w i n g .
-
slump w a t e r
aggregate
f i n e coarse
a d d i t i v e cement
allowable shearing strength of t h e concrete
( 1 5 . 7 kgf/cm2) s t a t e d a b o v e .
CONCLUSION
The r e s u l t s o f s u r v e y s i n t h e Arimura
R i v e r a n d t h e Mochiki R i v e r showed t h a t t h e
a c t u a l s h e a r i n g f o r c e o f a mud f l o w on t h e
s u r f a c e o f a c h a n n e l b o t t o m was a b o u t 0 . 5
2 . 5 kgf/cm2.
According t o t h e t h e o r e t i c a l
c a l c u l a t i o n s , t h e f r i c t i o n a l f o r c e which
s h o u l d b e c a u s e d by a s t o n e o f a b o u t 80
c e n t i m e t e r s i n diameter corresponded t o t h e
f o r c e o f 2 . 1 3 kgf/cm2 i n t h e Arimura R i v e r
mud f l o w on S e p t e m b e r 24, 1 9 8 8 . Such s i z e s
o f s t o n e s c o u l d b e o b s e r v e d on t h e v i d e o .
The i m p a c t f o r c e c a u s e d by huge s t o n e s i n a
mud f l o w was d e r i v e d from t h e t h e o r y o f t h e
c o l l i s i o n o f a n e l a s t i c body, a n d i t p r o v e d
t h a t t h e i m p a c t . f o r c e o f a s t o n e was
s e v e r a l times g r e a t e r t h a n t h e dead l o a d
c a u s e d by t h a t s t o n e . When a s h e a r i n g
s t r e s s o f a b o u t 2 . 5 kgf/cm2 a c t e d on a
c o n c r e t e channel with a compressive
s t r e n g t h o f 110 kgf/cm2, t h e a b r a s i o n o f
t h a t c o n c r e t e was 2 . 5 c e n t i m e t e r s i n d e p t h .
-
REFERENCES
A mud f l o w t o o k p l a c e on O c t o b e r 6,
1988, a week a f t e r t h e c h a n n e l works h a d
b e e n c o m p l e t e d , a n d it a b r a d e d t h e c o n c r e t e
i n t h e s u r v e y s e c t i o n . T h a t mud f l o w c o u l d
n o t b e r e c o r d e d on v i d e o t a p e , b e c a u s e i t
t o o k p l a c e a t n i g h t . The a b r a s i o n o f t h e
c o n c r e t e w a s 2 . 5 c e n t i m e t e r s i n d e p t h . The
r e s u l t o f t h e s t r e n g t h t e s t of t h e c o n c r e t e
r e p o r t e d t h a t t h e s t r e n g t h on t h e 7 t h d a y
a f t e r t h e m i x i n g o f t h a t c o n c r e t e was 110
kgf /cm2.
Taking i n t o c o n s i d e r a t i o n t h e f a c t t h a t
t h e s h e a r i n g s t r e n g t h of c o n c r e t e i s about
1/7 of t h e compressive, t h e a l l o w a b l e
c o m p r e s s i v e s t r e n g t h o f 1 1 0 / kgf/cm2
corresponds t o an allowable shearing
The s h e a r i n g
s t r e n g t h of 1 5 . 7 kgf/cm2.
f o r c e o f t h e mud f l o w which t o o k p l a c e on
t h e Mochiki R i v e r on F e b r u a r y 1 7 , 1989, was
A s t h e mud f l o w on O c t o b e r 6,
2 . 5 kgf/cm2.
1988, c o u l d n o t b e r e c o r d e d on v i d e o t a p e ,
i t s s c a l e was unknown, b u t t h e marks o f t h e
water h e i g h t i n t h e channel a f t e r t h i s flow
n e a r l y e q u a l t o t h e marks o f t h e mud f l o w
on F e b r u a r y 1 7 , 1989, i n t h e same r i v e r .
A s b o t h s c a l e s were a l m o s t e q u a l , t h e v a l u e
o f 2 . 5 kgf/cm2 was s u b s t i t u t e d f o r i t s
shearing force.
It r e s u l t e d i n t h e
calculated value (the allowable shearing
s t r e n g t h o f t h e m a t e r i a l , 1 5 . 7 kgf/cm2)
being l a r g e r t h a n t h e observed ones.
However, i n t h e c a s e i n which s u c h s h e a r i n g
f o r c e a c t s a c t u a l l y on a c h a n n e l b o t t o m a s
a repeated force, t h e shearing force of 2.5
kgf/cm2 i s n o t s m a l l a s compared w i t h t h e
1989. Report o f r e s e a r c h
Hirano, M .
p r o j e c t , G r a n t i n Aid f o r S c i e n t i f i c
R e s e a r c h ; 25 p . ( i n J a p a n e s e ) .
Matsumoto Sabo P u b l i c Works O f f i c e .
1975.
P u b l i c a t i o n o f s u r v e y s o f M t . Yake 7 .
M i n i s t r y o f C o n s t r u c t i o n : 37 p . ( i n
Japanese).
Okada, K . , a n d H . Muguruma. 1989.
E n g i n e e r i n g handbook o f c o n c r e t e .
Tokyo: Heibon-sha Co., 404 p . ( i n
Japanese).
1963. S t r e n g t h of m a t e r i a l .
Okubo, H .
Tokyo: Shokoku-sha C o . ; 40-41 ( i n
Japanese).
Osumi P u b l i c Works O f f i c e .
1982. Report
o f t h e r e s e a r c h work on s e d i m e n t y i e l d
from t h e Kurokami R i v e r . M i n i s t r y of
Construction; 13 p. ( i n Japanese).
Osumi P u b l i c Works O f f i c e .
1 9 8 6 . Sabo i n
volcano Sakurajima. M i n i s t r y of
Construction; 8 p . ( i n Japanese) .
Osumi P u b l i c Works O f f i c e .
1988. Sabo i n
volcano Sakurajima. Ministry of
Construction; 5 p . ( i n Japanese) .
Taniguchi, Y . , and M. Takahashi. 1985.
E x p e r i m e n t a l s t u d y on s e d i m e n t y i e l d
a n d f l u i d i z a t i o n o f s o i l mass i n a n
a r e a o f a c t i v e v o l c a n o . P r s c e e d i n g of
I n t e r n a t i o n a l symposium on E r o s i o n ,
D e b r i s Flow a n d D i s a s t e r
P r e v e n t i o n - T s u k u b a 1 9 8 5 : 133-138.
1989.
Taniguchi, Y . , and M. Takahashi.
P r e d i c t i o n f o r t h e e s c a p e from t h e
s t r i k e o f a v o l c a n i c mud f l o w i n a
t o r r e n t and t h e c h a r a c t e r i s t i c of i t s
movement. J o u r n a l o f t h e J a p a n S o c i e t y
o f E r o s i o n C o n t r o l 4 4 ( 4 ) :26 p . ( i n
Japanese) .
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Research of Wind Erosion Intensity in the Region
of Subotica-Horgos Sands1
Velizar Velasevic and Ljubornir Letic2
3
Abstract: Wind i s a n i m p o r t a n t e r o s i o n a l
p r o c e s s i n t h e a r e a s of steppe-savanna
c l i m a t e i n Europe a s t y p i f i e d b y t h e
Vojvodina p l a i n i n Yugoslavia.
Cultivated
a n d f o r e s t e d p l o t s on t h e S u b o t i c a - H o r g o s
S a n d s were u s e d t o s t u d y a e o l i a n e r o s i o n
p r o c e s s e s . Wind e r o s i o n on t h e c u l t i v a t e d
p l o t was 3-29 t i m e s g r e a t e r t h a n t h a t
o c c u r r i n g on a p l o t p l a n t e d t o f o r e s t
t r e e s . That e r o s i o n r e s u l t s i n important
A practical
l o s s e s o f humus a n d n u t r i e n t s .
e q u a t i o n e s t i m a t i n g wind e r o s i o n from wind
D e f l a t i o n p r o c e s s e s i n t h e zone o f
s t e p p e - s a v a n n a c l i m a t e i n Europe a r e
r e p r e s e n t e d i n t h e l a r g e p l a i n of
V o j v o d i n a , which i s a c o r n f i e l d a n d a
r e g i o n of p a r t i c u l a r importance t o
Y u g o s l a v i a . The u s e o f c o n t e m p o r a r y
a g r i c u l t u r a l engineering, t h e inappropriate
organization of t h e t e r r i t o r y , destruction
o f p r o t e c t i v e g r e e n cover, and o t h e r
unfavorable e f f e c t s l e a d t o t h e i n i t i a t i o n
and development of d e f l a t i o n p r o c e s s e s of
d i f f e r e n t i n t e n s i t i e s . This aspect of s o i l
d e s t r u c t i o n a f f e c t s , f i r s t of a l l ,
a g r i c u l t u r e , w a t e r r e s o u r c e s management,
t r a f f i c , i n f r a s t r u c t u r e , environment, e t c .
The r e g i o n o f V o j v o d i n a i s c h a r a c t e r i z e d b y
h e t e r o g e n e o u s s o i l t y p e s , r a n g i n g from
s a n d s , b l a c k s o i l , chernozem, a n d s m o n i t z a
t o g l e y e d s o i l which, i n g i v e n c l i m a t e
c o n d i t i o n s , a r e d i f f e r e n t l y t h r e a t e n e d by
t h e p r o c e s s o f wind e r o s i o n .
In t h i s paper
w e s h a l l p o i n t o u t t h e r e s e a r c h on wind
e r o s i o n ( s t a r t e d i n 1980) on t h e s o i l s o f
l i g h t mechanical composition ( p o t e n t i a l l y
t h e most t h r e a t e n e d s o i l s ) , on t h e
Subotica-Horgos Sands.
The S u b o t i c a - H o r g o s S a n d s a r e s i t u a t e d
i n t h e North-Northwest p a r t o f V o j v o d i n a
p l a i n between t h e Danube a n d T i s a r i v e r s .
The a v e r a g e l e n g t h o f t h e Sands i s 48 km
a n d t h e a v e r a g e d i a m e t e r i s 5-11 km. The
S a n d s c o v e r a n a r e a a b o u t o f 240 km2.
The V o j v o d i n a p l a i n i s a well-known
o r c h a r d - g r a p e v i n e c o u n t r y , w i t h more t h a n
33 p e r c e n t u n d e r v i n e y a r d s a n d o r c h a r d s ,
a b o u t 20 p e r c e n t f o r e s t s a n d woodlands, a n d
It is
o v e r 34 p e r c e n t u n d e r g r a s s l a n d .
c h a r a c t e r i z e d by m i l d l y u n d u l a t i n g dune
r e l i e f of northwest-southeast direction, a s
w e l l a s by a h i g h l e v e l of underground
w a t e r s , 2 - 8 m . A s t h e s e Sands a r e i n t h e
zone of a r i d c l i m a t e , a t t h e boundary o f
s t e p p e - s a v a n n a a n d s l i g h t woodland
c h a r a c t e r , under t h e i n f l u e n c e o f
p e d o g e n e t i c f a c t o r s , t h e r e can b e
d i s t i n g u i s h e d d i f f e r e n t t y p e s of sand:
g r e y - y e l l o w , brown, b l a c k , b l a c k loamy, a n d
s a l i n e sands with d i f f e r e n t production
capacities.
METHOD OF RESEARCH
A c o m p a r a t i v e method o f s t a t i o n a r y
o b s e r v a t i o n b y wind-gage s t a t i o n s h a s b e e n
a p p l i e d on s p e c i a l l y s e l e c t e d e r o s i o n
p l o t s , o f which o n e , u s e d f o r a g r i c u l t u r a l
production, has n o t been p r o t e c t e d ("U"),
w h i l e t h e o t h e r ("P") h a s been p r o t e c t e d
w i t h f o r e s t p l a n t i n g s , f i g u r e 1.
l p r e s e n t e d a t t h e S u b j e c t Group 5 1 . 0 4
T e c h n i c a l S e s s i o n on Geomorphic H a z a r d s i n
Managed F o r e s t s , X I X World F o r e s t r y
C o n g r e s s , I n t e r n a t i o n a l Union o f F o r e s t r y
R e s e a r c h O r g a n i z a t i o n s , August 5-11, 1990,
M o n t r e a l , Canada.
2 ~ a c u l t yo f F o r e s t r y , U n i v e r s i t y o f
Beograd, Beograd, Y u g o s l a v i a .
3 ~ b s t r a c ts u p p l i e d by S e s s i o n
Chairman.
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
F i g u r e 1 - - ~ x p e r i m e n t a l wind-gage s t a t i o n
records deflation processes.
T a b l e 1. Average monthly a n d a n n u a l d e p o s i t i o n q u a n t i t i e s (En kg m - l )
En
( k g m-l)
Loc."U'
Loc.'P"
( k g m-l)
R e l a t i o n U/P
Jan
Feb
Mar
Apr
May
0.272
0.017
16
0.765
0.026
29
0.504
0.028
18
0.693
0.047
15
0.306
0.053
6
June
0.350
0.038
9
Months
July
0.507
0.040
13
Loc. "U"
and l o c . "Pu
Rug
Sep
Oct
Nov
Dec
En
0.106
0.039
0.136
0.025
5
0.116
0.019
6
0.040
0.014
0.062
0.010
6
3.857
0.356
11
3
3
T a b l e 2 . Average monthly v e l o c i t i e s (m s
a t 0 .O5 m above ground f r e q u e n c i e s ( p c t ) a n d
s t o r m winds ( 1 2 . 3 m s - l ) NW a n d N d i r e c t i o n s .
Parameters
V e l o c i t y (m s - l )
Frequency ( p c t )
F o r c e IK)
Jan
Feb
Mar
Apr
May
8.10
4.32
23.42
4.65
3.08
8.49
8.13
9.01
7.21
16.85
3.00
6.24
4.90
6.23
32.51
2.82
7.89
7.13
5.76
0.77
3.51
-
11.88
2.48
Months
June
July
Auy
Sep
Oct
Nov
Dec
Average
-
Experimental s t a t i o n s record: q u a n t i t y
o f a e o l i a n d e p o s i t i o n , wind f r e q u e n c y a n d
v e l o c i t y , a i r and s o i l temperatures, a i r
and s o i l humidity, e t c . F i e l d d a t a a r e
a n a l y z e d i n o r d e r t o q u a l i f y and q u a n t i f y
t h e deflation process, a s well a s t o define
t h e c o n d i t i o n s of c l i m a t e and r e s i d u a l s o i l
i n which t h e y o c c u r .
RESULTS OF RESEARCH
The a n a l y s i s o f t h e d a t a o b t a i n e d a t
e x p e r i m e n t a l s t a t i o n s "U" a n d "P" h a s
proved s i g n i f i c a n t d i f f e r e n c e s i n t h e
d i s t r i b u t i o n and i n t e n s i t y of d e f l a t o r y
p r o c e s s e s , as w e l l a s i n t h e p a r a m e t e r s o f
c l i m a t e a n d r e s i d u a l s o i l which a f f e c t
them.
The d a t a on t h e a n n u a l i n t e n s i t y o f
wind e r o s i o n , w i t h 2.127-5.490 t km-l p e r
y e a r , emphasize t h a t u n p r o t e c t e d a r e a s
( l o c . "U") o f t h e r e s e a r c h e d r e g i o n a r e
t h r e a t e n e d by e r o s i o n , whereas t h e
p r o t e c t e d a r e a s ( l o c . "P") a r e s u b j e c t e d t o
d e f l a t i o n p r o c e s s e s o f a b o u t 11 t i m e s l o w e r
i n t e n s i t y , r a n g i n g from 0 . 2 4 7 t o 0 . 4 4 4 t
km-l p e r y e a r , a v e r a g e 0.356 t km-l p e r
y e a r ( t a b l e 1 ) . According t o t h e d a t a i n
t a b l e 1, maximum v a l u e s o f wind e r o s i o n
i n t e n s i t y occur i n t h e first half of t h e
y e a r between J a n u a r y and J u l y , amounting t o
a b o u t 80 p e r c e n t t o t a l a n n u a l q u a n t i t y o f
a e o l i a n d e p o s i t i o n , whereas t h e remaining
12 p e r c e n t a r e d e p o s i t e d between August a n d
December.
Therefore i n t h e unprotected a r e a s of
t h e Subotica-Horgos Sands, d e f l a t i o n
p r o c e s s e s o s c i l l a t e w i t h i n c a t e g o r i e s I1
a n d 111, s t a r t i n g from medium i n t e n s i t y
e r o s i o n ( 2 . 0 - 5 . 0 t km-l p e r y e a r ) t o
i n t e n s i v e e r o s i o n ( 5 . 0 - 7 . 0 t km-l p e r
y e a r ) . In t h e protected areas of t h e
Sands, d e f l a t i o n p r o c e s s e s a r e reduced t o
t h e l e v e l o f normal e r o s i o n ( c a t e g o r y I o f
e r o s i o n p r o c e s s e s ) w i t h t h e i n t e n s i t y lower
t h a n 0 . 5 t km-l p e r y e a r .
The d e g r e e o f h a z a r d ( c o m p a r i s o n o f
p r o t e c t e d and u n p r o t e c t e d a r e a s of t h e
Sands) i s i n c l u d e d i n t h e e x p r e s s i o n B =
I e e P / I e e S , a n d r a n g e s between 11 f o r a n n u a l
a n d 1 7 1 f o r d i u r n a l i n t e n s i t i e s o f wind
erosion. This points out t h e s i g n i f i c a n t
d i f f e r e n c e s i n t h e d e g r e e of h a z a r d o f t h e
compared l a n d s , which i s c o n d i t i o n e d b y t h e
b u f f e r i n g e f f e c t o f p r o t e c t i v e p l a n t i n g s on
the deflatory processes i n t h e protected
erosion p l o t s .
The e s t a b l i s h m e n t o f " e r o s i o n a c t i v e "
winds h a s been performed by t h e c r i t e r i o n
o f c r i t i c a l ( i n i t i a l ) v e l o c i t i e s (Vs>Vkr) .
Accordingly, t h e i n i t i a l v e l o c i t y necessary
t o move t h e m i x t u r e of D . Tavankut s a n d s Ds
= 0 . 1 8 mm, i s a b o u t 3 . 0 m s - l a t t h e h e i g h t
of 0 . 0 5 m above g r o u n d . T h i s d e n o t e s
s t o r m y winds ( > 1 2 . 3 m s - l ) a s e r o s i o n
a c t i v e winds.
I n t h e researched region of t h e
P a n n o n i a n P l a i n , b y t h e " M o d i f i e d Method o f
Instrumental Analysis", t h e following
dominant winds h a v e b e e n d i s t i n g u i s h e d : NW
( 1 4 ) and N (16) with t h e degree of
dominance r a n g i n g u p t o 10 t i m e s . Average
m o n t h l y v e l o c i t i e s ( a t 0 . 0 5 m) a n d wind
frequencies a r e presented i n Table 2 .
Stormy winds i n t h e S u b o t i c a - H o r g o s
S a n d s o c c u r 48.96 p e r c e n t i n t h e p e r i o d
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
Table 3 . Average monthly a i r temperatures ( S C ) , p r e c i p i t a t i o n (mm), r e l a t i v e a i r humidity
( p c t ) , and t o t a l s o i l moisture, l o c . "U" and "P"
Climatic
Factors
Loc. Jan
Feb
Air
Temp. OC
nu,, - 0 . 8 7
"P" - 1 . 5 2
-0.54
-0.49
Precip.
(llm)
"Uv 2 8 . 7 8
21.48
VP*
NVP**
3.91
0.41
3.07 -0.04
9.98
9.64
16.64
16.64
3.25
2.91
40.20 47.36
41.62 49.26
499.60
519.04
Relative
"U" 8 1 . 4 5 7 8 . 2 4 6 8 . 9 2 6 4 . 1 9 6 5 . 4 0 6 6 . 7 7 6 7 . 4 9 6 7 . 8 9 7 1 . 8 8 7 2 . 7 6 7 7 . 5 9 8 3 . 0 1
Humidity
"P" 8 8 . 6 6 8 1 . 0 6 7 2 . 5 7 6 8 . 3 1 6 7 . 3 2 7 0 . 4 4 6 9 . 3 4 7 2 . 2 7 7 5 . 7 0 7 7 . 7 3 8 2 . 9 6 8 6 . 5 4
of Air (pct)
Total Soil "U" 3 . 8 2
6.52
2.68
3.36
3.32
2.30
2.42
2.56
2.68
3.96
4.96
7.04
Moisture
"P" 1 5 . 7 8 2 1 . 0 2 1 2 . 6 0
9.56
6.70
6.42
5.70
4.96
7.56 10.88 11.42 1 7 . 8 0
(PCt)
72.13
75.91
67.27
70.56
77.00
81.25
3.80
10.87
2.80
6.80
4.80
14.90
**
Apr
May
June
Montlls
July Aug
Annual
*
Mar
Sep
Oct
6.07 10.01 15.58 1 7 . 6 3 20.16 1 9 . 8 1 16.64 1 0 . 8 8
5.86 10.70 15.00 18.04 19.53 1 8 . 9 1 16.02 10.58
35.42
32.16 54.92
"P" 3 1 . 3 6 2 2 . 8 8 3 7 . 4 8 3 4 . 3 8 5 7 . 4 4
90.30 35.22
88.76 39.66
30.74
25.70
43.18
46.24
39.84
44.26
Nov
Dec
286.52 213.08
292.18 226.86
VP denotes Vegetational Period
NVP denotes Non-Vegetational Period
between 10 a.m. and 3 p.m. A s p e r t h e i r
d u r a t i o n , c a t e g o r y I1 winds (60 - 360 min.)
occur most f r e q u e n t l y i n March and October.
I n a d d i t i o n , it has been observed t h a t
e r o s i o n a l l y a c t i v e a i r c u r r e n t s of NW
d i r e c t i o n ( 1 4 ) a r e more f a v o r a b l e (warmer
and d r i e r a i r ) t o t h e development of
d e f l a t i o n , t h a n t h e winds of N ( 1 6 )
direction.
The degree of nonuniformness of a i r
c u r r e n t s e x p r e s s e d t h r o u g h t h e f a c t o r s of
f o r c e (K) and frequency ( p e r c e n t ) ranges
These v a l u e s f o r NW
between 1 . 0 and 9 . 6 .
( 1 4 ) and N (16) winds o s c i l l a t e much l e s s ,
a v e r a g i n g 3 . 3 3 and 3 . 8 6 ( t a b l e 2 ) which i s
v e r y s i g n i f i c a n t f o r t h e e v a l u a t i o n of t h e
a g g r e s s i v e n e s s of a i r c u r r e n t s .
The a n a l y s i s of d a t a ( t a b l e 3 ) of t h e
hydrometric regime of t h e r e s e a r c h e d
erosion p l o t s points t o the significantly
more humid regime on t h e p r o t e c t e d e r o s i o n
p l o t , which d e c r e a s e s t h e development of
deflatory processes.
The a n a l y s i s of a e o l i a n d e p o s i t ( E n )
and r e s i d u a l s o i l ( O Z ) r e s u l t e d i n s e v e r a l
i n d i c a t o r s of c o n d i t i o n s i n which d e f l a t i o n
p r o c e s s e s o c c u r . The f o l l o w i n g a r e t h e
most important ones :
P a r t i c l e - s i z e composition of t h e
r e s e a r c h e d sands i n d i c a t e s a v e r y " e r o d i b l e
s o i l " . The c o n t e n t of e r o d i b l e p a r t i c l e s
s m a l l e r t h a n 1 mm ( t o t h e depth of 0.05 m )
amounts t o more t h a n 9 9 p e r c e n t , and t h e
c o n d i t i o n of e r o d i b i l i t y i s 40 p e r c e n t of
these particles.
Sand m o i s t u r e (rough d i s p e r s i o n ) i s a
v e r y s i g n i f i c a n t f a c t o r i n t h e group of
s o i l p h y s i c a l p r o p e r t i e s which c o n d i t i o n
t h e "pseudo cohesion" reducing t h e
USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991
development of t h e d e f l a t i o n p r o c e s s . The
c o n t e n t of t o t a l sand m o i s t u r e ( t o t h e
d e p t h of 0.05 m ) on t h e u n p r o t e c t e d a r e a
ranges between 2 . 3 p e r c e n t and 7.0 p e r c e n t ,
and on t h e p r o t e c t e d a r e a it i s 4 . 9 p e r c e n t
t o 21 p e r c e n t ( t a b l e 3 ) . The r e l a t i o n of
m o i s t u r e ( W Z ) and a p p a r e n t cohesion ( c ) i s
d e f i n e d by t h e f u n c t i o n :
and it h a s been e s t a b l i s h e d f o r Wz = 1 - 21
p e r c e n t , with t h e corresponding v a l u e s of
cohesion of up t o c = 6 . 7 9 kN x m-*.
On
t h i s o c c a s i o n it has been observed t h a t
d e f l a t i o n p r o c e s s e s occur a t t h e s o i l
m o i s t u r e below 7 p e r c e n t , which corresponds
t o cohesion below c = 3.0 k N x m-2.
The a n a l y s i s of t h e r e l a t i o n of
chemical c h a r a c t e r i s t i c s of t h e a e o l i a n
d e p o s i t i o n ( E n ) and t h e r e s i d u a l s o i l ( O Z )
p o i n t s t o t h e very s i g n i f i c a n t i n d i c a t i o n
of s o i l f e r t i l i z a t i o n l o s s a f f e c t e d by
I t i s denoted by t h e
d e f l a t i o n processes.
"deflation c o e f f i c i e n t " presented i n t a b l e
4.
Table 4 . The degree of t h e damaging e f f e c t
of d e f l a t i o n p r o c e s s e x p r e s s e d a s
d e f l a t i o n c o e f f i c i e n t mu=En x oZ-l
Number
Nutrients
1
Humu~
2
3
4
5
CaC03
Total N i t ~ o g e n
Readily Available P
Readily Available K
mu = En x 0,-l
5.7 - 16.2
1.1
1.3
3.2
14.0
15.5
20.3
6.4
14.3
-
81
By the research of correlation between
aggressive factors of climate, resistances
of soil particles, and the quantity of
aeolian deposition in the conditions of the
Pannonian Plain, the basic equation of wind
erosion has been developed:
where:
-
Quantity of aeolian
deposition in kg m-l;
A and B - coefficients of regression;
- base of natural logarithms;
e
- air flow in seconds through
Qv
the observed cross section in
m3s-1;
- duration of each aggressive
T
wind in s.
En
The formula is practical, as it is
incomparably easier (with the aid of
analytical evaluations and graphs of input
parameters) to evaluate the erosion
process, which otherwise calls for a rather
complicated procedure of measurements.
more than 90 percent particles smaller than
1 mm) and they can be classified as
category I11 wind erosion hazard (Chepil
and Woodruff 1954) - soils not resistant to
wind erosion, or as (III), category of
intensive erosion (Letic, Lj. 1989) with
5.0 - 7.0 t km-1 per year of deflation.
- Deflation processes occur in the
periods winter - spring (Jan - Apr) and
summer (June - July) and they are caused by
aggressive winds NW (14) and N (16),
velocity above 3.0 m s-l (at 0 .O5 m above
ground) .
- The researched soils are subject to
the accelerated nutrient loss resulting in
fertility loss.
- These researches have a practical
value, as they widen and supplement the
knowledge of the measures of struggle
against the phenomena of deflation, i.e.
the establishment of shelterbelt plantings
(and other measures) in this part of the
Pannonian Plain.
REFERENCES
CONCLUSIONS
By the analysis of data presented in
the paper, it can be concluded as follows:
- In steppe-savanna conditions of the
Pannonian Plain deflation processes
represent a significant factor of soil
destruction. They are factors which have
adverse effects on the quality of the
environment and, in general, on human
activities in the region.
- Light soils (sands) of the SuboticaHorgos Sands are very erodible (containing
Chepil, W.S. and N.P. Woodruff. 1954.
Estimations of wind erodibility of
field surfaces. Journal of Soil and
Water Conservation 9:257-265, 285.
Letic, Lj. 1989. Istrazivanje intenziteta
eoloske erozije na Suboticko-horgoskoj
pescari, Disertacija, Beograd.
Svehlik, R. 1975. Vetrna eroze pudy na
jinovychodni Morave, Sv. 20, C.S.R. ve
ZH. Praha.
Velasevic, V. 1978. Zastita i unapredjenje
suma Suboticko-horgoske pescare,
Studija, Subotica.
U S D A Forest Service Gen. Tech. Rep. PSW-GTR-130.1991
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August 5-11,1990, Montreal, Canada
Proceedings of the IUFRO Technical Session on Geomorphic Hazards in Managed Forests