Modeling Surface Runoff on a Semi-Arid Watershed Using a Physically Based Model

Physically based hydrologic models can represent spatial variability of soil hydraulic properties. In this study, a two-dimensional distributed rainfall-runoff model is used to examine runoff on a small (4.4 ha) basin (Lucky Hills 104) in the Walnut Gulch Experimental Watershed, near Tombstone, Arizona. Soil samples were collected across the basin and analyzed for texture. Soil hydraulic parameters were derived using a pedotransfer function. Parameter fields were then generated using a geostatistical approach. The numerical model was run for four rainfall events that generated measured runoff from on-site flumes. The results showed that the geostatistical approach generated parameter fields with significant spatial patterns. Simulated runoff depths were closely correlated to measured depths (relative error ranged from 3–31.9%). Results showed that the Green-Ampt infiltration model underestimated infiltration for multi-peak events. A more realistic infiltration model and more detailed use of spatial variability of hydraulic properties are needed to improve the prediction accuracy.