Modeling water infiltration in a large layered soil column with a modified Green-Ampt model and HYDRUS-1D

A modified Green-Ampt model was developed in this study to describe water infiltration through a 300-cm long and five-layered soil column. In the modified Green-Ampt model, a saturation coefficient was introduced to determine the water content and hydraulic conductivity of the wetted zone. The saturation coefficient was determined by the ratio between measured moisture volume and total saturated moisture volume of the wetted zone, and it should be less than 1. In this experiment, the calculated saturation coefficient was 0.8. The wetting front suction head was determined by Bouwer and Neuman methods. For comparison, the infiltration process was also simulated by traditional Green-Ampt model and HYDRUS-1D code which was based on the Richards equation. It was found that the traditional Green-Ampt model was unable to describe the infiltration process adequately. The HYDRUS-1D provided good simulation results of infiltration rate and accumulative infiltration. However, it was difficult to track the movement of wetting front along the soil profile and the corresponding root mean square error (RMSE) value was up to 57.17cm. For the modified Green-Ampt model with Bouwer method, the RMSE values of simulated infiltration rate, accumulative infiltration and wetting front depth were 2.01E-3cm/min, 1.28 and 8.29cm, respectively, which were much smaller than those of traditional Green-Ampt model and HYDRUS-1D. Moreover, the modified Green-Ampt model with Bouwer method could adequately capture the infiltration rate, the accumulative infiltration and the movement process of wetting front in the large layered soil column. Therefore, it appears that the modified Green-Ampt model presented in this study is a highly effective approach to simulate water infiltration in layered soils.

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