A dynamic hillslope response model in a geomorphology based rainfall-runoff model

This paper presents a technique for the determination of a dynamic hillslope instantaneous unit hydrograph (IUH) in concert with a variable saturation excess runoff production model using a grid-based digital elevation model (DEM). The total channel network responsible for routing the runoff produced on the catchment is divided into two parts: the main channel network and the hillslope channel network. The hillslope IUH, which routes water from the hillslopes to the main channel network, is essentially the solution of the linear advection-dispersion routing model weighted by the hillslope travel distance distribution of saturated pixels to the main channel network. The shape of the hillslope travel distance is found to consist of an initial spike, representing saturated pixels on the main channel network, and an exponential decay function for those pixels on the hillslope. However, the proportion of saturated pixels on the main channel network varies with total saturated pixels, causing an inverse change of scale of the spike and the exponential decay part. As the number of saturated pixels changes during a storm event, the hillslope IUH is dynamic. The main channel network IUH is also modelled by the linear advection-dispersion model weighted by the normalized width function of the main channel network. Convolution of the hillslope and main channel network IUHs gives the catchment IUH, which is also dynamically changing with the degree of saturation. It is demonstrated that the direct runoff hydrograph is sensitive to the variation of the degree of saturation within and between storm events.