Title: Infiltration, Runoff and Stream flow
1Infiltration, Runoff and Stream flow
- Ali Fares, PhD
- Watershed Hydrology, NREM 691
- UHM-CTAHR-NREM
2Presentation Outline
- Infiltration
- Definition theory
- Green-Ampt, Horton Philip equations
- Infiltration measurement
- Infiltration as affected by
- Soil type
3Infiltration
- Infiltration is the actual rate at which water is
entering the soil at any given time(SCSA, 1976). - Infiltration capacity Maximum rate (LT-1).
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5Measuring infiltration
6Infiltration Characteristics
- Infiltration is influence by
- Rain intensity, - Soil type -Disturbance. - Crust
- Soil cover - etc.
7Soil Type Effects on Infiltration
- Sand soils have the highest infiltration rates
- Clay soils have the lowest infiltration rates.
- High organic matter improves infiltration rates.
8Water Flow in Soil
- The flux density, q, is the rate of water
movement through a medium. - q is a function of ?H and the hydraulic
conductivity of the medium. - ?H H1 H2 is the difference between total
water potential inlet and outlet. - H Pressure head Gravitational head
9DERIVATION OF RICHARDS EQUATION IN RECTANGULAR
COORDINATES
The general continuity equation is Q a
q where Q is the flow rate, volume/time
(L3/T) a is the cross-section area
perpendicular to the flow, (L2) q is the flow
velocity, length/time (L/T)
10FLOW THROUGH POROUS MEDIA
In unsaturated soil the total potential can be
estimated as the sum of the matric potential and
the gravity potential
Since the gravity potential only acts in the
vertical, or z-direction, the total potential, H,
can be replaced by the matric potential, h, in
all terms except the one involving z
11FLOW THROUGH POROUS MEDIA
12From Continuity of mass
Where Q is the volumetric water content and t is
time.
13 Applying the Darcy Law to each velocity term
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15Infiltration Equations
- Green-Ampt (1911)
- i ic b/I
- Where I is cumulative infiltration,
- ic and b are constants.
- There are several other equations
- Horton (1940)
- Philip (1957)
16Hortons Equation
- Assumes K and D are constants (no dependence on
q) - Richards equation reduces to the diffusion
equation dq/dt D d2q/dz2 - Solve the equation for the rate of moisture
diffusion at soil surface f(t) fc (f0 fc)
ekt - k Decay constant T-1
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