Discharge assessment in mobile-bed compound meandering channels

Abstract

Many discharge prediction methods have been developed for compound meandering channels. Most of these methods have been found to produce reasonable results for fixed-bed channels, but the effects of the presence of a mobile main channel bed on discharge assessment have yet to be assessed. Sediment movement increases the complexity of experiments by facilitating the creation of bedforms, which alter flow resistance. The shape characteristics of these bedforms and their associated roughness are known to depend on channel stage and geometry, and to vary with flow conditions. This paper seeks to assess the performance of six discharge assessment methods using the Phase C mobile-bed meandering UK Flood Channel Facility (FCF) overbank flow data. The results show that the accuracy of the different methods depends heavily on the boundary roughness, and the James and Wark (1992) method performed most consistently for the range of floodplain configurations tested. A modification to this method is also presented that is shown to improve the accuracy of the predicted discharges.