River discharge estimated from river channel dimensions in Britain

Wharton, Geraldene (1989) River discharge estimated from river channel dimensions in Britain. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Estimates of flood discharges are often required at ungauged sites but because such estimates are costly to obtain a considerable amount of research has focussed upon developing techniques of indirect flood estimation. Although a catchment-based approach has often been used, for example in the U.K. Flood Studies Report, an alternative method is to estimate flows at ungauged sites from river channel dimensions. In the last two decades considerable progress has been made, almost entirely in the United States by the U.S. Geological Survey, in relating channel dimensions to flow indices for the purpose of indirect discharge estimation. Success has also been reported for rivers in New Zealand and Piedmont in north western Italy. This thesis considers the extent to which it is possible to produce relationships between flood discharges of particular frequencies and river channel dimensions; relationships that could be used to provide flood discharge estimates for ungauged rivers throughout Britain. A database of channel dimensions and return period flood discharges is assembled from archive and field-surveyed data for a total of 161 river gauging sites in Britain. Channel dimensions of width and cross-sectional area individually account for up to 83% of the variation in the mean annual flood and the inclusion of a width/depth ratio gives a 2-3% improvement in the predictive power of the channel-geometry equations. The results compare favourably with mean annual flood estimates obtained from multivariate catchment-based approaches. Examination of regression residuals revealed that the best estimates (to within 10% of the `true' mean annual flood value) were obtained in the sparsely gauged regions of western upland Britain, where methods of indirect flood estimation are most required. For the estimation of flood discharge characteristics, along natural stretches of river, channel-geometry equations may be used either prior to, or in some cases instead of, equations based on catchment characteristics. A set of guidelines outline the procedures for obtaining flood discharge estimates from river channel dimensions. These guidelines are presented in the concluding chapter.

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