Nonequilibrium Bedload Transport by Steady Flows

Abstract

The response of a gravel bed reach to imposed steady flows is examined under nonequilibrium conditions, where the bedload inflow is zero. Experimental research to date and general mathematical models for nonequilibrium alluvial conditions are reviewed. An experimental program was designed to examine the transient bed response for different reach lengths. Also, measured nonequilibrium bedload transport rates were compared with comparable local equilibrium capacity rates at selected time intervals and distances for a common mean flow velocity. Differences occurred between nonequilibrium transport rates and comparable equilibrium capacity rates at a maximum near the beginning of the reach but diminishing towards the downstream end of the local scour hole. This spatial variation of the transport rate deficit exists because the flow requires a finite length of bed to erode sufficient bed material to satisfy its equilibrium transport capacity. Consequently, mathematical model performance will be poor in the local scour hole region.