1. Infiltration
Reading AH Sec 4.3 to 4.4

2. Infiltration
General
Process of water penetrating from ground into soil
Factors affecting
Condition of soil surface, vegetative cover, soil properties, hydraulic conductivity, antecedent soil moisture
Four zones
Saturated, transmission, wetting, and wetting front
depth
Wetting Zone
Transmission
Zone
Transition Zone
Saturation Zone
Wetting Front q

3. Infiltration Infiltration rate Cumulative infiltration
Rate at which water enters the soil at the surface (in/hr or cm/hr)
Cumulative infiltration
Accumulated depth of water infiltrating during given time period

4. Infiltrometers Single Ring Double Ring

5. Infiltration Methods Horton and Phillips Green – Ampt
Infiltration models developed as approximate solutions of an exact theory (Richard’s Equation)
Green – Ampt
Infiltration model developed from an approximate theory to an exact solution

6. Hortonian Infiltration
Recall Richard’s Equation
Assume K and D are constants, not a function of q or z
Solve for moisture diffusion at surface
f0 initial infiltration rate, fc is constant rate and k is decay constant

7. Hortonian Infiltration

8. Philips Equation Recall Richard’s Equation Solution S – Sorptivity
Assume K and D are functions of q, not z
Solution
Two terms represent effects of
Suction head
Gravity head
S – Sorptivity
Function of soil suction potential
Found from experiment

9. Green – Ampt Infiltration
Ponded Water
Ground Surface
Wetted Zone
Wetting Front
Dry Soil

10. Green – Ampt Infiltration (Cont.)
Ground Surface
Wetted Zone
Wetting Front
Apply finite difference to the derivative, between
Ground surface
Wetting front
Dry Soil

11. Green – Ampt Infiltration (Cont.)
Ground Surface
Wetted Zone
Wetting Front
Dry Soil
Evaluate the constant of integration
Integrate

12. Green – Ampt Infiltration (Cont.)
Ground Surface
Wetted Zone
Wetting Front
Dry Soil
Nonlinear equation, requiring iterative solution.

13. Soil Parameters Green-Ampt model requires
Hydraulic conductivity, Porosity, Wetting Front Suction Head
Effective saturation
Effective porosity

15. Ponding time
Elapsed time between the time rainfall begins and the time water begins to pond on the soil surface (tp)

16. Ponding Time
Potential
Infiltration
Actual Infiltration
Rainfall
Accumulated
Time
Infiltration rate, f
Cumulative
Infiltration, F
Up to the time of ponding, all rainfall has infiltrated (i = rainfall rate)

17. Example
Silty-Loam soil, 30% effective saturation, rainfall 5 cm/hr intensity