BAHAN KAJIAN MANAJEMEN EKOSISTEM
PENANAMAN POHON
MELESTARIKAN
SUMBER MATA AIR
Soemarno - pslp ppsub 2010
1
www.thecottagekey.com/watershed.htm
2
Peran pohon
dalam siklus
air
3
Trees: The Original Multi-taskers
• Provide social,
ecological, and
economic benefits
• Their leaves and
roots clean the air
we breathe and
the water we drink
Their beauty inspires writers and
other artists.
4
• Save Energy
• Improve air
quality
Benefits of Trees in Urban
Areas
• Extend life of
paved surfaces
• Increase traffic
safety
• Increase real
estate values
• Increase
sociological
benefits
• Protect our
water resources
5
All water is part of this cycle
6
Storm Water and the Hydrologic Cycle
• Urbanization
dramatically alters the
hydrologic cycle
– Increases runoff
– Increases flooding
frequency
– Decreases infiltration and
groundwater recharge
• Nationwide impervious
surfaces have increased
by 20% in the past 20
years
7
8
More Trees Means Less
Runoff
Some Statistics
• Fayetteville,
Arkansas: increasing
tree canopy from 2740% reduced their
storm water runoff by
31%
• South Miami
residential study
found that a 21%
existing tree canopy
reduces the storm
water runoff by 15%
For every 5% of tree cover added
to a community, storm water is
reduced by approximately 2%
9
How Do Trees Effect Stormwater?
• Above ground effects:
– Interception,
evaporation and
absorption of
precipitation
• Ground surface
effects:
– Temporary storage
• Below ground effects:
– Infiltration, permeation
and filtration
10
11
Above Ground
Effects
• Intercept rainwater on
leaves, branches and
trunks – slowing its
movement
• Evaporation of some
of this intercepted
precipitation of the
tree surfaces
Absorption of a small portion
into leaves or stems
12
Ground Surface Effects
Leaf litter and
other organic
matter can hold
precipitation and
stemflow on a
site, reducing the
amount and peak
rates of runoff
Roots and trunk bases of mature
trees tend to create hollows and
hummocks on the ground
13
Below Ground Effects
• Organic material from
leaf litter and other
tree detritus tends to
increase infiltration
rates by increasing
pore spaces in soil
• Organic material also
increases the
moisture-holding
capacity of these sites
• Root mats of trees
also tend to break up
most soils further
improving infiltration
and moisture-holding
capacity
14
Below Ground Effects cont
•
•
•
Deep roots tend to
improve the rates of
percolation of water
from upper soil
horizons into lower
substrates
Trees take up water
through their roots that
is eventually transpired
onto leaf surfaces and
evaporated
Tree roots act as
natural pollution filters
(biofilters) using
nitrogen, phosphorus
and potassium
15
EPA’s Tree Canopy
Target Goals
• Set to protect a
community’s green
infrastructure and
maximize the
environmental benefits
• For metropolitan areas
east of the Mississippi
– Average tree cover for all
land use 40%
– Suburban residential
50%
– Urban residential
25%
– Central business districts
15%
16
Complications?
17
Complicating Factors
• Presence of soil
compaction
• Presence of soil textural
discontinuity
– Has the site been
disturbed in the past?
• Management of the ground
surface
– Is litter layer removed?
– Is soil surface exposed
in winter?
– How much of the
surface is like a natural
forest? (number and
size of trees)
18
Water Movement in Soils
• Forces affecting the energy of
soil water
– Matric force (absorption
and capillary)
– Gravity
– Osmotic forces
• Field Capacity is the amount of
water held in the soil after
gravitational water had drained
away
• Movement of water is the soil is
controlled :
– Gravitational forces if
saturated
– Matric forces if unsaturated
19
Soil Factors Influencing Infiltration
• Infiltration is the mode of
entry of all water into the
soil
• Rate of infiltration
determined:
– Initial water content
– Surface permeability
– Internal characteristics
of the soil
• Intensity and duration of
rainfall
• Temperature of soil and
water
20
Soil Factors Influencing
Infiltration cont.
• Microrelief under
trees provides
catchment basins
during heavy rains
• Removal of litter
layer reduces the
infiltration rate
• Forest soils have a
high percentage of
macropores
• The frost type found
in forest soils
promotes infiltration
year-long
Soil compaction reduces
the infiltration rate
21
Importance of the Litter Layer
•
•
•
•
•
•
•
Absorbs several times its
own weight
Breaks the impact of
raindrops
Prevents agitation of the
mineral soil
Discourages formation of
surface crusts
Increases soil biotic
activity
Increases incorporation
of organics
Slows down lateral
movement of water
22
Affect of Micropores in the Soil
• Develop in old root
channels or from
burrows and tunnels
made by insects,
worms or other
animals
• Lead to better soil
structure
• Increases organic
matter incorporation
• Increases percolation
rates and root
penetration
23
Soil Frost Types
• Granular
– Small frost crystals
intermingled with soil
particles
– Found in woodland
soils with litter
– May be more
permeable than
unfrozen soil
• Honeycomb
– Has loose porous
structure
– Found in highly
aggregated soils and
also formed in organic
layers and litter layers
24
Source and fate of water
added to a soil system.
The proportion of the soil
occupied by water and air is
referred to as the pore volume.
The pore volume is generally
constant for a given soil layer
but may be altered by tillage
and compaction. The ratio of
air to water stored in the pores
changes as water is added to
or lost from the soil. Water is
added by rainfall or irrigation.
Water is lost through surface
runoff, evaporation (direct loss
from the soil to the
atmosphere), transpiration
(losses from plant tissue), and
either percolation (seepage
into lower layers) or drainage.
25
Components of Ground
Water Use and Sources
of Recharge
There is a substantial
amount of ground water
recharge from surface
water and ground water
used to irrigate
agricultural crops.
Some of the irrigation
water flowing in unlined
ditches and some of the
water that is applied to
irrigate crops infiltrates
into the soil, percolates
through the root zone
and recharges the
ground water basins
26
Ground water
Ground water occupies the
zone of saturation. Ground
water moves downward
through the soil by percolation
and then toward a stream
channel or large body of water
as seepage. The water table
separates the zone of
saturation from the zone of
aeration.
The water table fluctuates with
moisture conditions, during wet
times the water table will rise
as more pore spaces are
occupied with water. Ground
water is found in aquifers,
bodies of earth material that
have the ability to hold and
transmit water. Aquifers can be
either unconfined or confined.
Unconfined (open) aquifers are
"connected" to the surface
above.
27
Aquifers replenish their supply of water very slowly.
The rate of ground water flow depends on the permeability of the aquifer
and the hydraulic gradient. Permeability is affected by the size and
connectivity of pore spaces. Larger, better connected pore spaces creates
highly permeable earth material. The hydraulic gradient is the difference in
elevation between two points on the water table divided by the horizontal
distance between them.
The rate of ground water flow is expressed by the equation:
Ground water flow rate = permeability X hydraulic gradient
Groundwater flow rates are usually quite slow.
Average ground water flow rate of 15 m per day is common. Highly
permeable materials like gravels can have flow velocities of 125 m per day.
28
Ground water in an
aquifer is under
pressure called
hydrostatic pressure.
Hydrostatic pressure in
a confined aquifer
pushes water upward
when a well is drilled
into the aquifer.
The height to which the
water rises is called the
peizometeric surface. If
the hydrostatic
pressure is great
enough to push the
peizometeric surface
above the elevation of
the surface, water
readily flows out as an
artesian well.
www.uwsp.edu/geo/faculty/ritter/geog101/textb...
29
Following an infiltration event, in
which the entire soil profile becomes
saturated with water (indicated by a
solid vertical line corresponding to a
water saturation of 1.0), water will
drain from the soil profile primarily
under the influence of gravity (i.e., the
pressure gradient is negligible).
Assuming that no additional water
enters the system, the soil water
saturation profile at static equilibrium
(dashed line) will decrease from a
value of 1.0 in the saturated zone
(groundwater and capillary fringe) to
a value corresponding to field
capacity below the root zone. In
effect, the soil water profile is
analogous to a soil water retention
(pressure-saturation) curve. Hence,
the solid and dashed lines represent
the limits in water content (saturation)
between which soil water percolation
occurs in soils overlying an
unconfined aquifer.
www.informaworld.com/smpp/95829679-70617050/c...
30
Water is
recharged to
the groundwater system
by percolation
of water from
precipitation
and then flows
to the stream
through the
ground-water
system.
ga.water.usgs.gov/edu/earthgwdecline.html
31
.
Water pumped
from the groundwater system
causes the water
table to lower
and alters the
direction of
ground-water
movement.
Some water that
flowed to the
stream no longer
does so and
some water may
be drawn in from
the stream into
the ground-water
system, thereby
reducing the
amount of
streamflow.
32
Contaminants
introduced at the
land surface may
infiltrate to the
water table and
flow towards a
point of
discharge, either
the well or the
stream. (Not
shown, but also
important, is the
potential
movement of
contaminants
from the stream
into the groundwater system.)
33
Water-level declines
may affect the
environment for plants
and animals.
For example, plants in
the riparian zone that
grew because of the
close proximity of the
water table to the land
surface may not
survive as the depth to
water increases.
The environment for
fish and other aquatic
species also may be
altered as the stream
level drops.
34
35
The fate of applied water can be
better understood if the total
hydrologic cycle is understood
first. The hydrologic cycle,
illustrated in Figure 1, describes
the movement of water through its
different forms and
locations. Important processes in
the hydrologic cycle are:
1. Evaporation -the transformation
of liquid water into water vapor
from free water surfaces.
2. Precipitation (rain or snow).
3. Runoff -water moving overland
or in a river or stream.
4. Infiltration -the movement of
water into the soil.
5. Percolation -the movement of
water through the soil.
6. Freezing - liquid water turning
into ice
7. Thawing - melting of ice
8. Transpiration - the movement of
water vapor out through
plant/animal tissue surfaces into
36
the atmosphere.
www.forestry.ubc.ca/.../forwady/forwady.htm
37
Forests and the Hydrologic Cycle
The surface water in a stream, lake, or wetland is most commonly precipitation
that has run off the land or flowed through topsoils to subsequently enter the
waterbody. If a surficial aquifer is present and hydraulically connected to a
surface-water body, the aquifer can sustain surface flow by releasing water to it.
In general, a heavy rainfall causes a temporary and relatively rapid increase in
streamflow due to surface runoff. This increased flow is followed by a relatively
slow decline back to baseflow, which is the amount of streamflow derived largely
or entirely from groundwater. During long dry spells, streams with a baseflow
component will keep flowing, whereas streams relying totally on precipitation will
cease flowing.
Generally speaking, a natural, expansive forest environment can enhance and
sustain relationships in the water cycle because there are less human
modifications to interfere with its components. A forested watershed helps
moderate storm flows by increasing infiltration and reducing overland runoff.
Further, a forest helps sustain streamflow by reducing evaporation (e.g., owing to
slightly lower temperatures in shaded areas). Forests can help increase recharge
to aquifers by allowing more precipitation to infiltrate the soil, as opposed to
rapidly running off the land to a downslope area.
38
Implications of Frost Types
• Forests and
prairies
rarely yield
runoff
regardless of
steepness,
even when
frozen
Forested areas provide storm
water protection and protect the
quantity and quality of
groundwater
39
Groundwater –Surface Water Flows
40
Black Earth Creek Study
• Black Earth Creek
receives 80% of its
water from
groundwater
• Main recharge
occurs in spring and
fall
• Recharge from the
agricultural uplands
is highly variable
• Forested slopes are
significant recharge
areas
Wooded hill slopes generate
no significant runoff
41
Effects are
greatest during
the growing
season
Effects are
greatest on sites
whose soils are
relatively
impermeable
Trees and Storm Water: Conclusions
42
The impact of urban trees on hydrology is extremely variable
and complex, in general increases in tree cover and tree size
over a site will result in reduced total runoff amounts and peak
43
runoff rates.
Trees and Storm Water:
•
•
•
Trees have a relatively
greater effect on
smaller storm runoff
amounts than on large
storm events
Surface and belowground effects on
runoff are much more
significant than the
above-ground effects
All of the effects on
runoff are greatest
when urban trees are
large and wellestablished on
undisturbed sites
44
Contact Information:
Mindy Habecker
Dane County UW-Extension 224-3718
Habecker@co.dane.wi.us
45
www.cropscience.org.au/.../1399_shahbazkhan.htm
46
www.ene.gov.on.ca/envision/gp/4329e_1.htm
47
www.aucklandcity.govt.nz/.../hgiapp15.asp
Typical root systems are made up of a
combination of four types of roots:
major lateral roots
sinker roots
woody feeder roots
non-woody feeder roots.
48
49
www.dof.virginia.gov/ur
ban/landscapemanual.shtml
50
51
Tree and
Root System
on Bank of
Darling River,
Kinchega
National
Park,
Outback, New
South Wales,
Australia
52
en.allexperts.com/q/Trees-739/DouglasFir-Roo...
53
www.forestry.ubc.ca/.../forwady/forwady.htm
54
55
www.icsu-scope.org/.../scope51/chapter06.html
A model illustrating fluxes of sulphur in a forest ecosystem
56
Schematic illustration of the biogeochemical processes of
importance in long-term research of a watershed (Swank, 1986).
57
www.aracruz.com.br/show.do?menu=true&id=943...
58
sofia.usgs.gov/publications/posters/challenge/
59
60
www.waterbucket.ca/rm/?sid=33&id=271&type=single
61
Four-Way Collaboration
The Water Balance Model includes a tree
canopy module so that the rainfall
interception benefits of trees in the
urban environment can be quantified. To
populate the module with local data, a
four-way collaboration has been
established under the umbrella of the
Inter-Governmental Partnership (IGP)
that developed the Water Balance
Model. The Greater Vancouver Regional
District and Ministry of Community
Services are providing funding, and the
University of British Columbia and
District of North Vancouver are making
in-kind contributions in carrying out the
applied research project. The District of
North Vancouver is acting on behalf of
the IGP in leading this on-the-ground
initiative.
62
Tree canopy interception is
the process of storing
precipitation temporally in
the canopy and releasing it
slowly to the ground and
back to the atmosphere. It is
an important component of
the water balance, easily
accounting for up to 35% of
gross annual precipitation.
Removing trees will in
general decrease
interception and thus
increase annual runoff and
rainwater runoff. Vegetation
also reduces rainfall
intensity due to the temporal
storage effect.
63
64
wwa.colorado.edu/treeflow/lees/treering.html
SOIL WATER
infiltration & percolation
permeability
porosity
Zone of aeration:
soil water storage
plant uptake &
transpiration
evaporation
throughflow
Water table
Zone of saturation:
groundwater flow
aquifer
65
www.uwsp.edu/geo/faculty/lemke/geog101/lectur...
HYDROLOGIC CYCLE &
WATER BUDGETS
What happens to
precipitation?
Water budget: local scale
examination of the gains,
uses, and losses of water
www.uwsp.edu/geo/faculty/lemke/geog101/lectur...
66
WATER BALANCE
Gains: precipitation
Soil moisture storage
Losses: utilization and
evapotranspiration
actual evapotranspiration (AE)
potential evapotranspiration (PE)
Simple water balance:
moisture abundant environments
P > PE and therefore AE
= PE
moisture limited environments
P < PE and therefore AE <
PE
seasonal moisture environments
67
www.ecologyandsociety.
org/vol3/iss2/art5/
The hydrological
cycle, showing the
repartitioning of
rainfall into vapor and
liquid freshwater flow
(modified from
Jansson et al. 1999).
68
INVISIBLE GREEN WATER VAPOR AND VISIBLE BLUE LIQUID
WATER
It is distinguished between water vapor flows and liquid water flows. In the
literature on water and food production, water vapor and liquid water are
sometimes called green water and blue water, respectively .
Both concepts provide useful tools for the analysis of local, regional, and
global flows in the hydrologic cycle. Liquid (blue) water flow is the total runoff
originating from the partitioning of precipitation at the land surface (forming
surface runoff ) and the partitioning of soil water (forming groundwater
recharge) .
Water vapor (green) is the return flow of water to the atmosphere as
evapotranspiration (ET), which includes transpiration by vegetation and
evaporation from soil, lakes, and water intercepted by canopy surfaces .
We regard ET as the result of the work of the whole ecosystem, including the
resilience it needs for securing the generation of ecosystem services in the
long run.
69
https://www.uwsp.edu/natres/nres743/T
1Eco2.htm
Nutrient cycle
We already know trees rely
on nutrients like
phosphorous and nitrogen
for healthy growth and
reproduction.
Throughout a trees life
stages, they constantly
use and return nutrients to
the soil.
Nutrient cycles regularly
transform nutrients from
the non-living environment
(air, soil, water, rocks) to
the living environment and
then back again
70
Water cycle
Water is constantly
cycling. The water cycle
collects, purifies, and
distributes the world�s
water. Without the water
cycle, life on earth would
be impossible. Trees and
plants are part of this
water cycle.
Transpiration is the
controlled evaporation
process by which plants
lose H2O through the
pores in their leaf
structures. A full-grown
tree can transpire
hundreds of gallons of
water a day during
growing season. 71
https://www.uwsp.edu/natres/nres743/T1Eco2.htm
www.bgky.org/tree/care.php
72
www.fastest-growingtrees.com/articles/10058-...
73
phytosphere.com/vtf/treewater.htm
Water deeply rather
than frequently.
Because most tree
roots are found in the
upper 18 - 24 inches of
the soil, this is the
zone that should be
wetted up in each
irrigation cycle.
Each deep irrigation
will meet a tree's water
needs for between 10
days to 4 weeks
during the hottest part
of the summer,
depending on the tree
species and soil type.
74
www.cmhcschl.gc.ca/en/co/maho/la/la_003
.cfm
Trees require water for
many biological functions,
but the function requiring
the greatest quantity of
water is transpiration .
Transpiration is the
movement of water vapour
from the leaves of plants to
the atmosphere.
The soil in which trees grow
is the reservoir from which
tree roots draw water.
75
www.cmhc-schl.gc.ca/en/co/maho/la/la_003.cfm
As a general rule
of thumb,
management of
trees near
buildings in
sensitive clay soils
should begin no
later than when the
height of the tree
is equal to the
horizontal distance
of the tree to the
building
76
www.flemings.com.au/treefacts_environmental.asp
Tree Facts - Environmental Benefits
Trees intercept and slow storm water,
decreasing the likelihood of flooding and
erosion, and improving water quality
Large trees have a greater benefit in
terms of reducing pollution than small
trees
Trees, shrubs, hedges and grasses
have a positive effect on the
environment by the transpiration of
water and the emission of oxygen by
photosynthesis
Plantings around buildings are a proven
method of reducing the demand for
artificial heating and cooling with a
resultant, and important, lower use of
fossil fuels.
Greenery provides ‘white noise’
reducing the effects of man-made 77
sounds
Air hujan yang jatuh ke
tanah
tidak seluruhnya langsung
mengalir sebagai air
permukaan, tetapi ada
yang terserap oleh tanah.
Peresapan air ke dalam
tanah pada umumnya terjadi
melalui dua
tahapan, yaitu infiltrasi dan
perkolasi.
Infiltrasi adalah gerakan air
menembus permukaan tanah
masuk ke dalam tanah.
Perkolasi adalah
proses penyaringan air
melalui pori-pori halus tanah
sehingga air bisa
meresap ke dalam tanah.
78
Kuantitas air yang mampu diserap
tanah sangat tergantung
beberapa faktor, yaitu: jumlah air
hujan, kondisi fisik tanah seperti
bobot
isi, infiltrasi, porositas dan struktur
tanah, jumlah tumbuh-tumbuhan
serta
lapisan yang tidak dapat ditembus
oleh air. Terbentuknya sumbersumber
air di alam mengalami serangkaian
proses. Air hujan jatuh ke tanah
kemudian meresap ke dalam tanah.
Sebelum mencapai jenuh, air masih
dapat diserap oleh tanah. Sampai di
kedalaman tertentu, air tersebut
tertahan oleh lapisan batu-batuan
(lapisan kedap air), yang
membendung
air sehingga tidak terus meresap ke
bawah sehingga membentuk air
79
tanah.
Secara mudah ilfiltrasi digambarkan seperti disebalah ini. Kalau tanahnya berbutir
kasar dan berpori-pori bagus, maka air akan terserap. Ketika air hujan menjatuhi
tanah lanau yg lebih halus, maka kapasitas ilfiltrasinya berkurang banyak.
Demikian juga ketika air hujan turun tepat diatas lempung, ya lebih sulit lagi
terserap.
80
www.tanindo.com/abdi18/hal
1101.htm
Saat terjadinya hujan, air
dapat masuk ke dalam
tanah (infiltrasi) atau
mengalir di permukaan
tanah (limpasan
permukaan / surface runoff). Air dalam tanah
yang terikat oleh poripori dan mineral tanah,
ada yang dapat
dimanfaatkan oleh
tanaman sebagai air
tersedia, menguap dari
permukaan tanah atau
mengalir di permukaan
atau ke dalam tanah
(perkolasi), dan
tersimpan dalam tanah
sebagai air tanah.
81
Telah diketahui
bahwa Konsep
daur hidrologi DAS
menjelaskan
bahwa air hujan
langsung sampai
ke permukaan
tanah untuk
kemudian terbagi
menjadi air larian,
evaporasi dan air
infiltrasi, yang
kemudian akan
mengalir ke sungai
sebagai debit
aliran.
82
Deskripsi Singkat
Infiltrasi dari segi hidrologi
penting, karena hal ini menandai
peralihan dari air permukaan yang
bergerak cepat ke air tanah yang
bergerak lambat dan air tanah.
Kapasitas infiltrasi suatu tanah
dipengaruhi oleh sifat-sifat fisiknya
dan derajat kemampatannya,
kandungan air dan permebilitas
lapisan bawah permukaan, nisbi
air, dan iklim mikro tanah.
Air yang berinfiltrasi pada sutu
tanah hutan karena pengaruh
gravitasi dan daya tarik kapiler
atau disebabkan juga oleh tekanan
dari pukulan air hujan pada
permukaan tanah.
83
suwitogeografi.blogspot.com/2008_11_08_archiv...
Sirkulasi air yang berpola
siklus itu tidak pernah berhenti
dari atmosfir ke bumi dan
kembali ke atmosfir melalui
kondensasi, presipitasi,
evaporasi, dan
transpirasi.Pemanasan air
samudera oleh sinar matahari
merupakan kunci proses siklus
hidrologi tersebut dapat
berjalan secara kontinu. Air
berevaporasi, kemudian jatuh
sebagai presipitasi dalam
bentuk hujan, salju, hujan batu,
hujan es dan salju (sleet),
hujan gerimis atau kabut. Pada
perjalanan menuju bumi
beberapa presipitasi dapat
berevaporasi kembali ke atas
atau langsung jatuh yang
kemudian diintersepsi oleh
tanaman sebelum mencapai
tanah. Setelah mencapai
tanah, siklus hidrologi terus
bergerak secara kontinu dalam
tiga cara diantaranya melaui
kondensasi, presipitasi,
evaporasi dan transpirasi.
84
A number of
management options
have been tried to
conserve water in
the soil, improve
structural stability
and increase
productivity. The
available
management options
can be grouped into
three categories:
a. Tillage based
systems
b. Organic systems
c. Biological
systems
85
alonashwjis.blogspot.co
m/2009/11/watercycle.html
Precipitation rains
water onto the
ground, after that it
starts to sink in the
ground that is called
infiltration.
86
Infiltrasi/Perkolasi ke
dalam tanah Adalah
Air bergerak ke dalam
tanah melalui celahcelah dan pori-pori
tanah dan batuan
menuju muka air
tanah. Air dapat
bergerak akibat aksi
kapiler atau air dapat
bergerak secara
vertikal atau
horizontal dibawah
permukaan tanah
hingga air tersebut
memasuki kembali
sistem air permukaan
87
Air tanah merupakan air
yang mengisi ronggarongga batuan di bawah
permukaan tanah pada
zone jenuh air.
Kondisi air tanah sangat
beragam dan pada musim
tertentu akan mengalami
perubahan dan faktor
tersebut juga merupakan
faktor cuaca dan iklim
serta faktor radiasi
terestrial.
Radiasi yang masuk pada
tanah pada musim hujan
dan musim kering akan
sangat berbeda dan suhu
yang terjadi juga akan
mengalami perubahana
dengan daya serap tanah
akan berbeda.
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Sebagian dari air tanah
dihisap oleh tumbuhtumbuhan melalui daundaunan lalu menguapkan
airnya ke udara
(transpiration).
Air yang mengalir di atas
permukaan menuju sungai
kemungkinan tertahan di
kolam, selokan dan
sebagainya (surface
detention), ada juga yang
sementara tersimpan di
danau, tetapi kemudian
menguap atau
sebaliknya sebagian air
mengalir di atas permukaan
tanah melalui parit, sungai,
hingga menuju ke laut (
surface run off ), sebagian
lagi infiltrasi ke dasar danaudanau dan bergabung di
dalam tanah sebagi air tanah
yang pada akhirnya ke luar
sebagi mata air. 89
AIR TANAH
Air tanah adalah air yang terdapat dalam pori-pori tanah atau pada celahcelah batuan. Air tanah terbentuk dari air hujan.
Pada saat turun hujan, sebagian titik-titik air meresap ke dalam tanah
(infiltrasi). Air hujan yang masuk itu yang menjadi adangan air tanah. Volume
air yang meresap ke dalam tanah tergantung pada jenis lapisan batuannya.
Berdasarkan kenyataan tersebut terdapat pula dua jenis batuan utama, yaitu
lapisan kedap (impermiable) dan lapisan tanah tidak kedap air (permeable)
Kadar pori lapisan kedap atau tak tembus air sangat kecil, sehingga
kemampuan untuk meneruskan air juga kecil.
Contoh lapisan kedap, yaitu geluh, napal, dan lempung. Sedangkan kadar
pori lapisan tak kedap air atau tembus air cukup besar. Oleh karena itu,
kemampuan untuk meneruskan air juga besar.
Contoh lapisan tembus air, yaitu pasir, padas, krikil dan kapur. Kita akan lihat
bersama gambar lapisan kedap dan lapisan tak kedap pada air tanah di
halaman berikutnya
90
www.aboutcivil.com/hydrol
ogy.html
Water Balance Components
Inflow:
Precipitation
Import defined as water
channeled into a given
area.
Groundwater inflow from
adjoining areas.
Outflow:
Surface runoff outflow
Export defined as water
channeled out of the
same area.
Evaporation
Transpiration
Change in Storage:
This occurs as change in:
Groundwater
Soil moisture
Surface reservoir water and
depression storage
Detention Storage
91
Hydrological Systems
A hydrologic system is as a structure or volume in space, surrounded by a boundary,
that accepts water and other inputs, operates on them internally, and produces them
as outputs.
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aXRlbV9pZD02Mg==
Water supply to
the roots,
infiltration,
runoff,
percolation and
redistribution of
water in a onedimensional
profile are
derived from
hydraulic
characteristics
and moisture
storage capacity
of the soil.
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chapt6.htm
The processes directly
affecting the root zone soil
moisture content can be
defined as:
Infiltration: i.e. transport from
the soil surface into the root
zone;
Evaporation: i.e. the loss of
soil moisture to the
atmosphere;
Plant transpiration: i.e. loss of
water from the interior root
zone;
Percolation: i.e. downward
transport of water from the
root zone to the layer below
the root zone;
Capillary rise: i.e. upward
94
transport into the rooted zone.
Preliminary infiltration
The infiltration rate depends on the available water and the infiltration capacity of
the soil. If the actual surface storage is less then or equal to 0.1 cm, the preliminary
infiltration capacity is simply described as:
Where
INp : Preliminary infiltration rate[cm d-1]
FI : Maximum fraction of rain not infiltrating during time step t[-]
CI : Reduction factor applied to FI as a function of the precipitation intensity[-]
P : Precipitation intensity[cm d-1]
Ie : Effective irrigation[cm d-1]
SSt : Surface storage at time step t [cm]
Dt : Time step[d]
The maximum fraction of rain not infiltrating during time step t, FI can be either set
to a fixed value or assumed to be variable by multiplying FI with a precipitation
dependent reduction factor CI which is maximum for high rainfall and will be
reduced for low rainfall. The user should provide FI. The CI table is included in the
95
model and is assumed to be fixed.
The calculated infiltration rate is preliminary, as the storage capacity of the soil is
not yet taken into account.
If the actual surface storage is more than 0.1 cm, the available water which can
potentially infiltrate, is equal to the water amount on the surface (i.e. supplied via
rainfall/irrigation and depleted via evaporation):
Where
INp : Preliminary infiltration rate[cm d-1]
P : Precipitation intensity[cm d-1
Ie : Effective irrigation[cm d-1]
Ew : Evaporation rate from a shaded water surface[cm d-1]
SS : Surface storage at time step t [cm]
Dt :Time step[d]
However, the infiltration rate is hampered by the soil conductivity and cannot
exceed it. Soil conductivity is soil specific and should be given by the user.
96
Adjusted infiltration
Total water loss from the root zone can now be calculated as the sum of
transpiration, evaporation and percolation. The sum of total water loss and
available pore space in the root zone define the maximum infiltration rate. The
preliminary infiltration rate cannot exceed this value.
The maximum possible infiltration rate is given by:
Where:
INmax :Maximum infiltration rate[cm d-1]
qmax :Soil porosity (maximum soil moisture)[cm3 cm-3]
Qt :Actual soil moisture content[cm3 cm-3]
RD :Actual rooting depth[cm]
Dt
:Time step[d]Ta:Actual transpiration rate[cm d-1
Es :Evaporation rate from a shaded soil surface [cm d-1]
Perc :Percolation rate from root zone to lower zone[cm d-1]
97
PERKOLASI
If the root zone soil moisture content is above field capacity, water percolates to
the lower part of the potentially rootable zone and the subsoil. A clear distinction
is made between percolation from the actual rootzone to the so-called lower zone,
and percolation from the lower zone to the subsoil. The former is called Perc and
the latter is called Loss.
The percolation rate from the rooted zone can be calculated as:
Where
Perc : Percolation rate from the root zone to the lower zone[cm d-1]
Wrz : Soil moisture amount in the root zone [cm]
Wrz,fc Equilibrium soil moisture amount in the root zone [cm]
Dt
: Time step[d]
Ta
: Actual transpiration rate [cm d-1]
Es
: Evaporation rate from a shaded soil surface [cm d-1]
98
The equilibrium soil moisture amount in the root zone can be calculated
as the soil moisture content at field capacity times the depth of the
rooting zone:
Where
Wrz,fc : Equilibrium soil moisture amount in the root zone[cm]
Qfc
: Soil moisture content at field capacity[cm3 cm-3]
RD
: Actual rooting depth[cm]
99
The percolation rate and infiltration rate are limited by the conductivity of the wet
soil, which is soil specific and should be given by the user. Note that the
percolation from the root zone to the lower zone can be limited by the uptake
capacity of the lower zone.
The value calculated is preliminary and the uptake capacity should first be
checked.
The percolation from the lower zone to the subsoil, the so-called Loss, should
take the water amount in the lower zone into account. If the water amount in the
lower zone is less than the equilibrium soil moisture amount, a part of the
percolating water will be retained and the percolation rate will be reduced.
Water loss from the lower end of the maximum root zone can be calculated as:
Where
Loss :Percolation rate from the lower zone to the subsoil[cm d-1]
Perc :Percolation rate from root zone to lower zone (see eq. 6.21)[cm d-1]
Wlz :Soil moisture amount in the lower zone [cm]
Wlz,fc :Equilibrium soil moisture amount in the lower zone [cm]
Dt
:Time step
100
Water loss from the potentially rootable zone, is also limited by the maximum
percolation rate of the subsoil, which is soil specific and should be provided by the
user.
The equilibrium soil moisture amount in the lower zone can be calculated as the soil
moisture content at field capacity times the root zone depth:
Where
Wrz,fc : Equilibrium soil moisture amount in the lower zone[cm]
Qfc :Soil moisture content at field capacity[cm3 cm-3]
RDmax :Maximum rooting depth[cm]
RD :Actual rooting depth[cm]
For rice an additional limit of five percent of the saturated soil conductivity is set to
account for puddling (a rather arbitrary value, which may be easily changed in the
program).
The saturated soil conductivity and is calculated with pF= -1.0 (i.e. a hydraulic head of
0.1 cm). The percolation rate from the lower zone to the sub soil is not to exceed this
value (van Diepen et al., 1988).
The value calculated should be regarded as preliminary; the storage capacity of101
the
receiving layer may become limiting.
The storage capacity of the lower zone, also called the uptake capacity, is
the amount of air plus the loss.
It can de defined as:
Where
UP :Uptake capacity of lower zone[cm d-1]
RDmax :Maximum rooting depth[cm]
RD :Actual rooting depth[cm]
Wlz :Soil moisture amount in lower zone[cm]
Qmax :Soil porosity (maximum soil moisture)[cm3 cm-3]
Dt :Time step[d]
Loss :Percolation rate from the lower zone to the subsoil[cm d-1]
Percolation to the lower part of the potentially rootable zone can not exceed the
uptake capacity of the lower zone. Therefore the percolation rate is set equal to
102
the minimum of the calculated percolation rate and the uptake.
LIMPASAN PERMUKAAN : Surface runoff
Surface runoff is also taken into account by defining a maximum value for surface
storage. If the surface storage exceeds this value the exceeding water amount will
run off. Surface storage at time step t can be calculated as:
Where
SSt : Surface storage at time step t[cm d-1]
P : Precipitation intensity[cm d-1]
Ie : Effective irrigation rate[cm d-1]
Ew : Evaporation rate from a shaded water surface[cm d-1]
IN : Infiltration rate (adjusted)[cm d-1]
Surface runoff can be calculated as:
Where
SRt:Surface runoff at time step t[cm]
SSt:Surface storage at time step t[cm]
SSmax:Maximum surface storage[cm]
SSmax is an environmental specific variable and should be provided by the user.
103
Rates of change and root extension
The rates of change in the water amount in the root and lower zone are calculated straightforward from
the flows found above:
Where
DWrz :Change of the soil moisture amount in the root zone[cm]
DWlz :Change of the soil moisture amount in the lower zone[cm]
Ta :Actual transpiration rate[cm d-1]
Es :Evaporation rate from a shaded soil surface[cm d-1]; IN :Infiltration rate[cm d-1]
Perc :Percolation rate from root zone to lower zone[cm d-1]
Loss :Percolation rate from lower zone to sub soil[cm d-1]; Dt :Time step[d]
Due to extension of the roots into the lower zone, extra soil moisture becomes available, which can be
calculated as:
Where
RDt :Rooting depth at time step t[cm]
RDt-1:Rooting depth at time step t-1[cm]
RDmax:Maximum rooting depth[cm]
Wlz:Soil moisture amount in the lower zone [cm]
DWrz:Change of the soil moisture amount in the root zone[cm]
DWlz:Change of the soil moisture amount in the lower zone[cm]
104
The actual water amount in the root zone and in the lower zone can be calculated
according to:
Where:
Wrz,t : Soil moisture amount in the root zone at time step t[cm]
Wlz,t : Soil moisture amount in the lower zone at time step t[cm]
Wrz,t-1: Soil moisture amount in the root zone at time step t-1[cm]
Wlz,t-1: Soil moisture amount in the lower zone at time step t-1[cm]
DWrz : Rate of change of the soil moisture amount in the root zone[cm]
DWlz : Rate of change of the soil moisture amount in the lower zone[cm]
105
Actual soil moisture content
The actual soil moisture content can now be calculated
according to :
Where
qt : Actual soil moisture content at time step t [cm3 cm-3]
Wrz,t : Soil moisture amount in the root zone at time step t [cm]
RD : Actual rooting depth [cm]
106
www.tutorvista.com/search/effectsof-soil-erosion
Effects of Deforestation
1) Percolation and ground water
recharge has decreased.
2) Floods and drought have become
more frequent. 3) Soil erosion has
increased.
4) Pattern of rainfall has changed. 5)
Land slides and avalanches are on
the increase.
6) Climate has become warmer in
the deforested region due to lack of
humidity added by the plants. 7)
Consumption of CO2 and
production of O2 is adversely
affected.
8) Man has been deprived of the
benefits of trees and animals. 9)
Extinction of many species of plants
and animals, still not discovered by
scientists.
10) Shortage of fuel
107
www.cluin.org/studio/2003phyto/abstr
acts.htm
108
www.worldagroforestry.org/af2/?q=node/122
GenRiver: Generic River model on river flow
Overview of the GenRiver
model; the multiple
subcatchments that make
up the catchment as a whole
can differ in basic soil
properties, land cover
fractions that affect
interception, soil structure
(infiltration rate) and
seasonal pattern of water
use by the vegetation.
The subcatchment will also
typically differ in ‘routing
time' or in the time it takes
the streams and river to
reach the observation point
of main interest
109
Genriver Components
GenRiver model consists of several
sectors, which are related to one
another. Those sectors are:
Water Balance is a main sector that
calculating the input, output, and
storage changes of water in the
systems. Some components which
are in this sector, rainfall,
interception, infiltration,
percolation, soil water, surface
flow, soil discharge, deep
infiltration, ground water area and
base flow
Stream Network is a sector that
estimating the flow of water from
the river to the final outlet. Some
components which are in this
sector, total ttream in flow, routing
time, direct surface flow, delay
surface flow, river flow to final
outlet.
Land Cover ,
Subcatachment Parameter is a sector
stired constant parameters that
control to the changes of water
110
balance, landcover and stream
network.
www.ecy.wa.gov/programs/sea/pubs/9
3-31/chap1.html
111
www.ecolotree.com/applications.html
112