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Keywords:

  • Land-use management;
  • measurement;
  • modelling;
  • rainfall

Abstract

The current UK guidelines for sustainable drainage systems design [Department of the Environment Food and Rural Affairs/Environment Agency (DEFRA/EA), 2005; Construction Industry Research and Information Association (CIRIA), 2007] require that the design peak flow from a new development should not exceed that which would occur under the pre-development or Greenfield conditions. Although these guidelines are fairly recent documents, the standard methodology for estimating Greenfield flows dates back to the results of studies from the 1970s. The recommendation of the guideline method was not the result of any testing and calibration but rather the assumption that it produced Greenfield flow estimates that were in the order of what would be expected. Experience of Greenfield peak flow estimates using the approved method has shown flows to be very low compared with what would be expected where a detailed knowledge of the site hydrology was available or from observational evidence of flooding events. Recent monitoring of surface run-off and drainage using a 1-min temporal resolution at the Rowden Moor Drainage Experiment at North Wyke Research, Devon, UK has provided an ideal dataset through which to test the current approved methodology for Greenfield flow estimation. The results show that the methods significantly underestimate the Greenfield peak flows.