Comparison of saturation models in complex hillslopes

Hillslopes of natural catchment have a complex geometry. In complex hillslopes, combining different cases of plan shape (convergent, parallel and divergent) and profile curvature (concave, convex and straight) nine different geometries are created. In prediction of the surface and subsurface runoff of catchments based on saturation excess runoff mechanism, the saturated and unsaturated zones of hillslopes must be first separated. Subsurface travel time of hillslope is dependent on saturation attributes. In this research, a new saturation model, called Gamma, was developed to predict the saturated zone length and subsurface travel time in complex hillslopes. An analytical formula was introduced to calculate saturation zone length in Gamma model. Results of Gamma model, namely the saturation zone length and subsurface travel time, were compared with the results given by two other complex saturation models W and Sigma. The results of the three models were relatively close to each other in convergent and parallel hillslopes of different profile curvature type. However, due to the existence of an analytical equation for estimation of saturated zone length in the Gamma model, this model is recommended. It should be noted that for straight divergent and convex divergent hillslopes, the Gamma model is not suitable and Sigma or W model should be used.