On the generation of delayed peaks in stream discharge

Abstract Where deep permeable soils overlie impermeable bedrock and where steep hillslopes border a narrow floodplain, subsurface stormflow dominates the hydrograph. In such cases delayed peaks in stream discharge may occur several days after rainfall, providing the major volumetric response and possibly also the highest peak discharge. The general occurrence of such delayed peaks is considered, making reference to field data from two small drainage basins in southwest England, and to the results of computer simulations using a distributed hillslope model. The importance of soil-water convergence into hillslope hollows is stressed. The relative roles of rainfall and antecedent soil moisture in controlling the size and timing of the delayed peak is discussed. The implications of the results for hillslope runoff modelling are briefly considered.