| Summary: | A simple four parameter conceptual model of catchment response has been developed with the object of modelling only isolated storm events and thus providing a useful tool for flood estimation. Most previous conceptual modelling has been concerned with fitting continuous long-term records in which flood events are small in number. The isolated event model (IEM) is concerned only with such flood events. At its present stage of development, the isolated event model is more suited to steep upland gauged catchments. In essence, the model is fitted to such catchments by using an automatic computer optimisation technique to find those optimum values of the model parameters which enable the model to reproduce existing isolated events to an acceptable degree of accuracy. Design rainstorms may be routed through a fitted model to yield design flood hydrographs. After considerable development work on a sequence of model structures and strategies of optimisation, the IEM4 model has been found acceptable on the proving data used, consisting of 500 events from 21 catchments, and a two stage optimisation strategy has been adopted. A further version of the model, incorporating a number of improvements, was applied exhaustively to individual events from the River Ray catchment. An interesting idea that emerged was the concept of the augmented hydrograph. The latter half of this thesis is devoted to expanding this concept, incorporating evidence from other researchers, and making comparisons with the standard unit hydrograph method of analysis of isolated events.
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