To initiate a fundamental understanding of the complex nature of unsteady sediment transport phenomena, laboratory experiments for two types of non-cohesive material are presented. These experiments were performed in a test flume with semi-circular cross-section. Friction velocity for the transient regime is obtained using the equations of de Saint-Venant, which are rearranged using the kinematic flow principle. Inertia of bed load material and material in suspension causes a time and forme discrepancy between the unsteady friction velocity and transport. Hence the friction velocity obtained with a steady state formula is chosen as basic parameter to setup an instantaneous relationship with transport. A correction for the time lag is clearly a function of the unsteady character of the flow.

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