Hu, P.; Tan, L., and He, Z., 0000. Numerical investigation on the adaptation of dam-break flow-induced bed load transport to the capacity regime over a sloping bed.
Knowledge about dam-break flow-induced bed load transport over a sloping bed is widely used to shed light on swash-induced bed load transport over erodible beaches. However, numerical modeling of flows in this configuration has mostly assumed instant sediment adaptation and accordingly ignored the potential lag between bed load and its capacity regime. This paper presents a numerical assessment of the bed load adaptation characteristics in this configuration. Two models are considered: a capacity model that assumes negligible lag and a noncapacity model that uses a sediment adaptation empirical relationship to appreciate the lag. Two experimental dam-break flow events over a fine sand (1.3 mm) bed and a coarse gravel (8.4 mm) bed are numerically simulated. Three estimates are used for the bed friction, five empirical relationships are used for the sediment transport rate at capacity, and five empirical relationships are used for the adaptation length. The following findings are obtained. First, bed friction values calibrated by hydrodynamics do not necessarily represent actual bed resistance better than existing empirical bed friction relationships. Second, given a reasonably well-estimated adaptation length, the noncapacity model can give comparable or better predictions of the sediment transport rate for both fine and coarse sediments, whereas the performance of the capacity model strongly depends on sediment adaptation features.