A MODIFIED GREEN-AMPT MODEL FOR WATER INFILTRATION AND REDISTRIBUTION IN FIELD LAYERED SOILS AT THE ARID REGION OF NORTHWEST CHINA

Water infiltration and redistribution process play a very important role in hydrological cycle in arid region. A physically modified Green-Ampt model (MGAM) was proposed in this study to simulate water infiltration and redistribution in field layered soils. An infiltration and redistribution experiment was conducted in a 280-cm depth soil profile at the Shiyang river basin in arid land of northwest China to test validity of the proposed model. The entire soil profile covered seven distinct soil layers with nonuniform initial water content. In MGAM, a saturation coefficient (smaller than 1) was introduced to account for air entrapment in upper wetted zone. The actual water content and hydraulic conductivity of the wetted zone were equal to the saturated water content and hydraulic conductivity multiplied by the saturation coefficient, respectively. The simulation results of MGAM were compared against those of traditional Green-Ampt model (TGAM) and Richards' equation. It was found that TGAM was unable to describe the infiltration and redistribution process adequately. The Richards' equation provided good simulation results of infiltration rate, accumulative infiltration as well as soil water content redistribution, while it significantly underestimated the wetting front depth. Comparing to TGAM, the MGAM markedly improved infiltration predictions (determination coefficient >0.9), and the simulated water contents in redistribution process by MGAM were satisfactorily close to the measured results (root mean square error < 0.05). Furthermore, the MGAM could better describe the advancing depth of wetting front than Richards' equation. Therefore, it appears that the MGAM presented in this study is a highly effective approach to simulate water infiltration and redistribution in field layered soils.