Stage‐Discharge Functions for Two‐Stage Channels: The Impact of New Research

Research into two-stage channels carried out in the large flood channel facility at Wallingford has shown that the conventional approach to their hydraulics over-estimates their conveyance when in flood. This is because of the interaction between the main channel flow and the slower moving flood plain flows which, traditionally, has been ignored. A new design procedure has therefore been developed allowing for this effect. This has important implications in respect of the stage-discharge functions for rivers and bermed drainage channels, and especially on the extrapolation of observed flows to greater depths. The newly developed hydraulic design method is provided as an Appendix.