Hydro - Green ampt infiltration equation

Five Principal Assumptions

1) The soil under consideration is homogeneous and stable, implying that macropores and preferential migration pathways should not be considered.

2) The supply of ponded water at the surface is not limited.

3) A distinct and precisely definable wetting front exists, and as water continues to infiltrate, the wetting front advances at the same rate with depth.

4) The capillary suction just below the wetting front is uniform throughout the profile and constant in time during the infiltration event.

5) The soil is uniformly saturated above the wetting front, and the volumetric water contents remain constant above and below the advancing wetting front.

wetting font

the boundary between wet and dry soil during infiltration

Ponding Depth

is the depth of water infiltrated at the time when the ponding starts to happen.

Ponding Time

is the amount of time that elapsed when the ponding starts to happen.

Case 1: i < Ks

The rainfall intensity is less than the maximum downward hydraulic conductivity, meaning that runoff will never occur and all rainfall will infiltrate regardless of the duration.

Case 2: Ks < i < f

The rainfall intensity is greater than the saturated hydraulic conductivity but less than the infiltration rate. The time to ponding varies for different rainfall intensities.

Case 3: i > f

The rainfall intensity is greater than the infiltration rate and runoff can occur.