Green and Ampt developed an infiltration model based on Darcy’s law. Generally, the governing equation is:
= K(change in potential)/distance
where
-
f is the infiltration rate
-
K is the hydraulic conductivity of the wetted soil part of the profile
-
Lf is the depth of the wetting front
-
tau is the pressure head for wetting at the wetting front
-
d is the depth of ponding of water on the soil surface
By assuming the ponded depth is small enough to be neglected, the equation can be transformed to:
Where
-
F(t) is the cumulative infiltration rate at time t
-
tau is the change in water content across the wetting front
Typical Green Ampt parameters are:
|
Green Ampt Infiltration Parameters (Rawls et all., 1983) |
|
Soil texture |
Total porosity |
Effective porosity |
Pressure head (cm) |
K (cm/hr) |
|
Sand |
0.437 |
0.417 |
4.95 |
11.78 |
|
Loamy sand |
0.437 |
0.401 |
6.13 |
2.99 |
|
Sandy loam |
0.453 |
0.412 |
11.01 |
1.09 |
|
Loam |
0.463 |
0.434 |
8.89 |
0.34 |
|
Silt loam |
0.501 |
0.486 |
16.68 |
0.65 |
|
Sandy clay loam |
0.398 |
0.330 |
21.85 |
0.15 |
|
Clay loam |
0.464 |
0.309 |
20.88 |
0.10 |
|
Silty clay loam |
0.471 |
0.432 |
27.30 |
0.10 |
|
Sandy clay |
0.430 |
0.321 |
23.90 |
0.03 |
|
Silty clay |
0.479 |
0.423 |
29.22 |
0.05 |
|
Clay |
0.475 |
0.385 |
31.63 |
0.03 |