Development of the Green-Ampt Infiltration Rate Model and Relationship of the GA Model Parameters with Soil Hydraulic Parameters

In the Green-Ampt model, the infiltration rate is indirectly related to time via the intermediate term of cumulative infiltration depth. In the present study, the direct theoretical relationship between the infiltration rate of the GA infiltration model with time is derived and elaborated. A new laboratory method for separate measurement of the GA model parameters is developed and tested via the constant-head infiltration tests on two sandy soil columns considering different values of initial soil water content. Hysteretic soil water characteristic (SWC) curves of studied soils are also measured. Results indicate that the GA model parameters are constant values and independent from the initial soil water content. Hydraulic conductivity $K$, wetting front matric head ${\mathrm{\Psi }}_{\mathrm{f}}$, and water content of wetted zone ${\theta }_{\mathrm{wz}}$ of GA model are separately estimated from proposed method and are found to be respectively equal to saturated hydraulic conductivity $K_{\mathrm{s}}$, water-entry value $h_{\mathrm{w}-\mathrm{e}}$, and saturated water content of the wetting SWC curve ${\theta }_{\mathrm{s}}^{\mathrm{w}}$. By setting $K=K_{\mathrm{s}}$, ${\mathrm{\Psi }}_{\mathrm{f}}=h_{\mathrm{w}-\mathrm{e}}$, and ${\theta }_{\mathrm{wz}}={\theta }_{\mathrm{s}}^{\mathrm{w}}$, the results of the GA model matched reasonably well with the numerical solution of Richards’ equation using HYDRUS-1D and measured data.