A multi-scale nested experiment for understanding flood wave generation across four orders of magnitude of catchment area

Abstract

Current understanding of flood response is deficient concerning the variation of flood generation at different spatial scales as a function of spatial and temporal variations in storm rainfall. This study therefore investigates the relationship between rainfall spatial variability and flood response through a multi-scale nested experiment. Hydrological data from an extensive network in the Eden catchment, UK, were collected for a range of flood events over varying scales from 1.1 km2 to 2,286 km2. The data were analysed to show the spatial scale dependency of flood peak and lag time. Peak specific discharge for winter events appears to remain constant with area up to 20–30 km2, corresponding to the main upland headwater catchments, thereafter declining as area increases. The flood response to the convective storms depends on the location of the rainfall and the downstream rates of change of runoff and peak discharge can vary significantly from the winter storm relationships. Particularly for large synoptic storms, average scaling laws for peak discharge have been quantified (exponents ranging between 0.75 and 0.86), illustrating the non-linear nature of the cross-scale variations. Such laws provide a means of linking the headwater catchments with the larger scale at which planners and decision-makers operate.