Applyi g Dendrogeomorphic
Applying
D d g
phi Methods
M th d to
t Determine
D t
i Site
Sit Specific
Sp ifi Annual
A
l Erosion
E i Rates
R t – A Quick
Q i k and
d Cost
C t Effective
Eff ti
Alternative
l
i to Using
i g Erosion
i Pins
i
1 2, PE
1, MS
3
B
Bryan
M Dick
Di k1,2
PE, PH
PH, Ph
Ph.D
DC
Candidate;
did t Ian
I Jewell
J
ll1, JD
JD; Steven
St
Pi 1, MS
Pires
MS; Illona
Ill
P l 2, Ph
Peszlen
Ph.D;
D Andrew
A d
Wil 1; Ron
Wilson
R Johnson
J h
MS; Peter
P t Simon
Si
1AECOM,
AECOM
701 Corporate Center Drive,
Drive Suite 475,
475 Raleigh,
Raleigh NC; 2North Carolina State University,
University 2200 Hillsborough St,
St Raleigh,
Raleigh NC; 3Ann Arbor Technical Services,
Services 290 South Wagner Road,
Road Ann Arbor,
Arbor MI
Riverbank Erosion
Methods – Laboratoryy Analysis
y
The rate
Th
t att which
hi h streambanks
t
b k are eroding,
di g and
d the
th total
t t l annuall quantity
tity off sediment
di
t
q
being entrained from eroding streambanks are of a primary concern for ecological
ecological, water
quality,
qua
y, and
a d sedimentation
sed e a o sstudies.
ud es
St
b k erosion
i is
i responsible
p ibl for
f upwards
p
d off 80% off ttotal
t l sediment
di
t yyield
i ld in
i
• Streambank
some rivers
EPA, 1990)
i
(US EPA
• Where contaminants are bound to riverbank sediments,
sediments erosion
poses a primary means by which contaminated sediments are
transported downstream
• Need methods to quickly calculate erosion rates at specific locations Exposed roots on an
erosive streambank
• Some common methods to calculate annual erosion rates include:
Method
Direct
i
measurement (e.g,
(
erosion pins, bank surveys,
etc )
etc.)
Time
i
trend
d analysis
l i off historic
hi
i
maps/photos
Sedimentological/biological
monitoring
Dendrogeomorphology
B
Benefits
fit off Using
U i Dendrogeomorphic
D d
hi Methods
M th d to
t
D t
Determine
i Site
Sit Specific
S ifi Erosion
E i Rates
R t
Pro
Con
i annuall monitoring
i i
• Requires
• Most commonly used method
• Several years of data needed
• Accurate
• No hindcasting
Gi
l
long‐term
erosion
i rates quickly
i kl • Not as accurate due
d to scale
l
• Gives
• Inexpensive
• Only used for high erosion rates
• Expensive/labor intensive
C
li
d data
d
analysis
l i
• Accurate
• Complicated
• Requires several years of data
• Accurate
• Need exposed tree roots to sample
i l
• Economical
• Weak annual growth ring formation in
• Generate large data sets rapidly
sub‐tropical
b
i l trees will
ill require
i a more
• Great for hindcasting erosion rates
advanced skill set to analyze
G
f forecasting
for
f
i erosion
i rates
• Great
Macroscopic Exposure Indicators
Significant
f
d Cost Savings Over Alternative
l
Time and
Bankk Erosion
Measurement Methods
Analysis of Samples
• Date of exposure identified using macroscopic and
microscopic indicators
Date of
Exposure
Indications of Root Exposure
What is Dendrogeomorphology?
Analysis
y Used
Cut disk of hackberry root (Celtis spp.)
SSpecies
i Type
T
Diffuse‐porous
H d
Hardwoods
d (Maples,
(M l
Cottonwoods,,
Dogwoods Alders,
Dogwoods,
Alders etc)
Ring‐porous
Hardwoods (Elms,
(Elms
Hackberry Ash,
Hackberry,
Ash Oaks,
Oaks
etc)
Cut disk of elm root (Ulmus rubra)
Date of
Exposure
Distinct change from diffuse‐porous
diffuse porous type vessel
arrangement to ring‐porous structure (resembling
tree stem cell anatomy)
BEFORE
O EXPOSURE
OS
AFTER EXPOSURE
OS
•
•
•
•
Avoid the reliance on regional erosion rate curves
Results suggest erosion rate data varies largely on a site to site basis
More accurate representation of erosion rate than using regional erosion rate curves
Quick calculations of annual erosion on specific rivers/streams can be extremely
ccritical
t ca if co
contaminated
ta
ated sed
sediments
e ts are
a ep
present
ese t (to ttrack
ac tthee fate
ate aand
d ttransport
a spo t o
of
contaminants))
• A ggreat metric
i for
f p
prioritizing
i i i i g sites
i along
l g the
h banks
b k off streams
• Create
C t reall world
ld numbers
b to
t establish
t bli h baseline
b li d
data
t to
t monitor
it success off restoration
t ti
projects
j t
Cross
section
of root
sample
p
AFTER EXPOSURE
BEFORE EXPOSURE
P j
Projects
and
d Results
R l
R lt
Results
• Dendrogeomorphology has been tested on several projects and has shown high levels of accuracy in predicting annual erosion rates
• Tree anatomy changes in response to environmental factors
(e.g.,
(e
g , landslide,
a ds de, lakeshore,
a es o e, st
streambank
ea ba aand
d hillslope
s ope eerosion)
os o )
• Change
g reflected
f
in ggrowth rings
g off tree
• Count
C
number
b off rings
i g to find
fi d date
d
off ggeomorphic
phi change
h g
Tree stem
Buffalo Bayou – Houston,
Houston TX
C fid ti l Site
Confidential
Sit – Midwestern
Mid
t
U.S.
US
Annuall Growth
h ring on the
h
cross‐section
cross
section of a tree stem
Exposed Roots
• Unstable channel is causing threats to
infrastructure and increased flood
damage potentials
• Client needs stream specific erosion rate
to provide sediment reduction numbers
associated
assoc
ated with
t ba
bank stab
stabilization
at o eefforts
o ts
• River had several highly erosive streambanks
• Erosion causing sediments to become mobile within the
water system
• Client needed a quick/effective way to quantify erosion
rates at specific locations of banks to track and quantify
sediment
sed
e t flux
u
Riverbank
Collect cluster of samples to get
different ages of exposure
Avg. Erossion
Rate
e (ft//yr)
y = 3E‐06x
3E 06x2.9549
R² = 0.8729
15
20
25
30
35
40
BEHI Score
Exposed roots on a section of the
Ri
River
Eroding streambank on the River
Ero
osio
on R
Rate
e (ftt/yr))
0.100
y = 0.0019e0.1288x
R² = 0.594
0 594
0 010
0.010
C l i
Conclusions
0.001
20
Exposed roots
sampled from
eroding streambank
Expon. (Erosion Rate vs. BEHI Score)
• Client needed to establish an erosion rate
curve to use for prediction of entrainment
at any point along the study reach of Halls
Bayou
1.000
Collectingg roots samples
p
from erodingg streambank
Erosion Rate vs. BEHI Score
Halls Bayou – Houston,
Houston TX
Erosion Rate vs. BEHI Score for Root Samples
25
30
35
40
45
50
Dendrogeomorphic assessments of tree roots provides an effective means for
estimating annual erosion rates on site specific riverbank locations
EEroding
di streambank
b k on Halls
H ll
Bayou
y
BEHI Score
E i R
Erosion
Rate
t vs. BEHI S
Score
E
Expon.
(E
(Erosion
i R
Rate
t vs. BEHI S
Score))
Erosion Rate vs. BEHI Score for Samples on Halls Bayou
Multiple bank variables
measured in a BEHI analysis
y
Samples
p Prepared
p
for Microscopy
py
Results suggest:
• Erosion rate can be estimated from BEHI score where no
direct erosion rate measurements had previously been made
• Strong ability to predict erosion rates (indicated by high R2
values )
Erossion Rate
e (ft/yr)
1.000
R t Sample
Root
S pl Preparation
P p ti
• Stained with safrannin and mounted on glass slides
for microscopic analysis of cellular structure
• Longer
Longer‐exposed
exposed samples may not reflect current susceptibility of bank to erosion
• Difficult to obtain samples on banks with worst and least susceptibility to erosion
• Climactic variations can cause difficulty in analysis, mainly in subtropical geographies
0.010
0 001
0.001
Fi ld Sample
Field
S pl Collection
C ll ti
• “Disks”
Disks cut into small samples (15‐90µm thickness)
P t ti l Disadvantages
Potential
Di d t g to
t Method
M th d
0.100
10
y = 0.0045e0.0805x
R² = 0.7433
0 7433
0.100
0.010
0.001
10
15
20
25
30
35
40
BEHI Scores
Erosion Rate vs.
vs BEHI Score
Sample location
• A
Analyze
l
hi t i trends
historic
t d off bank
b k erosion
i through
th
h bank
b k profile
fil recreation
ti
• Predict
P di t future
f t
migration
i ti off river
i
and
d estimate
ti t mass flux
fl off sediments
di
t
1 000
1.000
Methods
h d – Root Collection
ll i and
d Sample
pl
P
Preparation
i
Hi t i bank
Historic
b k profile
fil
Erodingg streambank on Buffalo
Bayou
Erosion Rate vs.
vs BEHI Score for Samples on Buffalo Bayou
• Select
S l t live,
li healthy,
h lth exposed
d tree
t
roots
t with
ith a 2”
minimum diameter
• Measure distance between root and river bank (1
(1”
minimum)
• Cut samples from bank using a handsaw first marking
the top of the tree root
• Take multiple samples from each tree along vertical
and lateral distribution
• Perform a Bank Erosion Hazard Index (BEHI) analysis
on bank as measurement of erodibilityy
U d
Understand
d Mass
M
Fl off Sediment
Flux
S di
to G
Generate Hi
Historic
i B
Bankk P
Profiles
fil
• To assess/test the accuracy of the dendrogeomorphology erosion rate prediction method
• Allow the ability to predict erosion rates (from erosion rate curve)
How does it work?
Install 20 bank pins/day;
p / y; Minimum
yearly monitoring of pins; Need at
least 3 years of data to see meaningful
t d
trends
Create Site Specific Erosion Rates
How was BEHI used?
Using tree rings to identify dates of changes in land surface
((riverbanks,, hillsides,, lakeshores))
Erosion Pins
Exposed root sampled from an
eroding bank
Response in
R
i Tree
T
A t
Anatomy
Vessel size and arrangement clearly takes on
earlywood and latewood structure
Vessel size
si e decreases while the number of vessels
increases in post‐exposure
post exposure rings
Time Investment
Collection: 20 samples
p p
per day;
y;
Sample preparation time: 10 samples
Root Analysis
per day; Analysis of samples: 15
samples
pl p
per d
dayy
Mi
Microscopic
pi Exposure
E p
IIndicators
di t
• Hardwood species
p
easiest to detect change
g
• Looking
k g ffor visible
bl scarring,
g, root eccentricity,
y, change
h g in
vessell size,
i , change
h g iin vessell arrangement,
g
, change
h g iin
growth
th ring
i width,
idth etc.
t
• Cellular
C ll l response diff
differs b
based
d on species
i and
d ttype:
• Dendrogeomorphology provides a quick and cost effective method for calculating
annual erosion rates
Usingg Dendrogeomorphology
g
p
gy to Quantifyy
Streambank
b k Erosion
• Root analysis provides erosion rate data quicker and with less cost than other
methods
Expon (Erosion Rate vs.
Expon.
vs BEHI Score)
45
50
55
• Dendrogeomorphic
d g
ph assessment presents
p
the
h best
b p
predictor
d
off erosion rates in the
h
absence
b
off erosion
i p
pins
i or bank
b kp
profiles
fil
• Assessments
A
t proven to
t be
b reliable
li bl and
d inexpensive
i
i
• Samples
S
l can be
b collected
ll t d with
ith little
littl time
ti
i
investment
t
t and
d training
t i i
References
United States Environmental Protection Agency.,
g y , 1990. Managing
g g Nonpoint
p
Source
Pollution: Final Report to Congress on Section 319 of the Clean Water Act (Washington
(Washington,
D.C.: US EPA).