Relationships between dynamic response characteristics and physical descriptors of catchments in England and Wales

Abstract

A regionalisation methodology has been applied to catchments in England and Wales enabling estimation of daily flows for any catchment in the region for which physical data and records of rainfall and temperature are available. The rainfall-runoff model IHACRES has been calibrated to 60 catchments to obtain a set of dynamic response characteristics (DRCs) describing the hydrological behaviour within the region. Physical catchment descriptors (PCDs) indexing topography, soil type, climate and land cover were collated and linked to the hydrological model by overlaying catchment boundaries with a geographical information system. Relationships were derived to describe the DRCs in terms of the PCDs so that the model may be used to simulate flow for any catchment in the region, given the driving variables, i.e. rainfall and temperature. In the England and Wales region, rainfall loss parameters have been defined in terms of land use, climate and soil type, whilst hydrograph separation parameters were characterised using topographical and soil variables. The set of DRC–PCD relationships, which were obtained by balancing the dual objectives of hydrological integrity and statistical significance, has been satisfactorily validated on two additional catchments within the region. Analysis of calibration errors was aided by sensitivity tests at one of these catchments in which flow response to variations in DRCs was assessed. Finally, a simple land use scenario demonstrates an application of the methodology in which variation in PCDs may be used to assess the impacts of environmental change.