Characteristics of recent UK flood-producing rainfalls in relation to the Flood Studies Report design event method

Abstract

Weather radar images were used in an investigation of the rainfall events which gave rise to various damaging UK floods in the 1990s. Radar data of sufficient quality were available for seven events from an initial list of 26. The relative temporal and spatial rainfall profiles of each event are displayed and summarised, along with the antecedent catchment wetnesses. Catchment rainfall totals were obtained from daily raingauges. These characteristics are compared with their equivalents in a standard method of flood estimation, the design event method of the Flood Studies Report. The results highlight the complexity of rainfall fields. The wide variety of event characteristics includes some large deviations from their counterparts in the design event. Six of the catchments were modelled with the design event method in order to assess the significance of the deviations in terms of the estimated flood peaks. The rainfall depth and duration and the antecedent catchment wetness were found to have a significant influence within the design event method. The temporal profile was of lesser importance, for most of the events studied.