An experimental investigation has been conducted in a 0.4x 0.4 x 9.0 m laboratory flume to study the sediment transport in unsteady flow. The bed material used was almost uniform gravel (d₅₀ = 4 mm). The instantaneous sediment transport has been measured during the passage of flood waves. Results have shown that, for an equal water depth, the sediment transport rate in the rising branch (accelerating phase) of the hydrograph is larger than the one in the falling branch (decelerating phase). Also, there is a phase shift between the peaks of sediment transport rate, flow rate, and water depth. The main parameters which affect bed sediment transport during rising and recession phase of the hydrograph have been established. Based on 60 different hydrographs and by using multiple variate regression analysis, an empirical equation has been developed to compute the instantaneous sediment transport in unsteady flow. A sensitivity analysis and a verification with available data from literature have been made to assess the validity of the proposed equation. A satisfactory agreement has been found which gives some confidence in the approach.

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