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.