Modeling Infiltration and Runoff with Surface Crust under Unsteady Rainfalls

Abstract

This study develops a new analytical model to simulate the infiltration and runoff with a crust surface. The new model consists of two parts: (1) an infiltration capacity model using a linear rate-moisture relation (RMR) similar to the flux-concentration relation (FCR) for homogeneous soil, but considering the changing saturation over time at the interface and unsaturated flow in the subsoil layer; and (2) an infiltration and runoff model under rainfall events based on the time compression approximation (TCA) using the developed infiltration capacity in part (1). Its performance is evaluated by comparing to the solutions of the Richards equation and two field experiments under different rainfall patterns. Results show that the new model can well predict the infiltration capacity and wetting front profiles with slight underestimation of infiltration. The modeled runoff closely agrees with field measurements. The new model extends the FCR and TCA with the prediction of unsaturated flow. The model can use any form of soil hydraulic model and is computationally stable without numerically solving the Richards equation, which facilitates large-scale predictions of the rainfall-runoff process.