Effective Green-Ampt Parameters of Sloping Layered Soils

Abstract:

The Green-Ampt (GA) model has been widely used to estimate infiltration in many field applications due to its physically-based with simplicity and accuracy. The main objectives of this study are to (1) develop a modified Green-Ampt infiltration model for sloping layered soils (GASLS) and (2) investigate effective parameters of Green-Ampt model applicable to large-scale hydrologic and land-atmosphere simulations based on the developed GASLS. The GASLS model has extended the Green-Ampt equation to calculate the infiltration in layered soil profile for different slopes under constant ponding head. The model employs two assumptions: negligible flow caused by downslope component of gravity and instantaneous hydraulic equilibrium at layer interfaces. Cumulative vertical infiltration depth is obtained from GASLS model, which is used to determine the effective parameters and evaluate their performance. Essential in the effective parameters is to capture the infiltration process in the sloping layered soils by an equivalent homogeneous system (i.e. one layer homogeneous soil without sloping). Optimal sets of effective Green-Ampt parameters are determined by minimizing the root mean square errors of cumulative infiltration calculated from the discrepancy between the results from effective parameters and those from the GASLS. Performance of the effective parameters is investigated by comparing to results from the GASLS model using correlation coefficients under various scenarios of different sloping angles, layer formations, and ponding head depths. The effective parameters are also compared to the arithmetic mean, harmonic mean and geometric mean. The ability and potential of the three means as effective parameters in infiltration into sloping layered soils are then examined and discussed.