A comparative study of capacity and non-capacity models for bed load sediment transport by unsteady flows

摘要

It has long been thought that bed load sediment transport may adapt to capacity instantly, and based on this idea, various capacity models have been developed. While the recent theoretical work on the multiple time scales of fluvial processes have revealed approximate applicability of capacity models for bed load, the extent to which a capacity model differs from a non-capacity model remains to be unraveled. Here, a comparative investigation of capacity and non-capacity models for bed load transport is presented using coupled modelling approach. Field observation data of bed load transport by flash floods are deployed. Corollary to our theoretical analyses of the multiple time scales, the discrepancy between capacity and non-capacity models is discernible only in the immediate vicinity of the inlet boundary. Therefore, capacity models are mostly valid for bed load transport even in unsteady flows.