Evaluating hydrometric networks for prediction in ungauged basins: a new methodology and its application to England and Wales

Flow estimates for ungauged catchments are often derived through regionalisation methods, which enable data transfer from a pool of hydrologically similar catchments with existing gauging stations (i.e., pooling-groups). This paper presents a methodology for indexing the utility of gauged catchments within widely used pooling-group methodologies for high and low flow estimation; this methodology is then used as the basis for a network evaluation strategy. The utility of monitoring stations is assessed using catchment properties and a parallel, but independent, appraisal of the quality of gauging station data, which considers hydrometric performance, anthropogenic disturbances and record length. Results from the application of the method to a national network of over 1,100 gauging stations in England and Wales are presented. First, the method is used to appraise the fitness-for-purpose of the network for regionalisation. The method is then used to identify gauges which monitor catchments with high potential for regionalisation, but which are deficient in terms of data quality – where upgrades in hydrometric performance would yield the greatest benefits. Finally, gauging stations with limited value for regionalisation, given the pooling-group criteria employed, are identified. Alongside a wider review of other uses of the network, this analysis could inform a judicious approach to network rationalisation.