Threshold effects in catchment storm response and the occurrence and magnitude of flood events: implications for flood frequency

摘要

The aim of this paper is to illustrate the effects of selected catchmentstorage thresholds upon runoff behaviour, and specifically their impact uponflood frequency. The analysis is carried out with the use of a stochasticrainfall model, incorporating rainfall variability at intra-event,inter-event and seasonal timescales, as well as infrequent summer tropicalcyclones, coupled with deterministic rainfall-runoff models that incorporaterunoff generation by both saturation excess and subsurface stormflowmechanisms. Changing runoff generation mechanisms (i.e. from subsurface flowto surface runoff) associated with a given threshold (i.e. saturationstorage capacity) is shown to be manifested in the flood frequency curve asa break in slope. It is observed that the inclusion of infrequent summerstorm events increases the temporal frequency occurrence and magnitude ofsurface runoff events, in this way contributing to steeper flood frequencycurves, and an additional break in the slope of the flood frequency curve.The results of this study highlight the importance of thresholds on floodfrequency, and provide insights into the complex interactions betweenrainfall variability and threshold nonlinearities in the rainfall-runoffprocess, which are shown to have a significant impact on the resulting floodfrequency curves.