Semi-empirical model to predict mobile bed evolution in presence of a side overflow

Abstract

Side weirs are a widely used device to control flow processes along a channel or river course. Thelateral loss of water is responsible for the reduction of sediment transport capacity in the main-channel yieldingto aggradation and the formation of a local sediment deposit in the downstream weir alignment. The reducedcross section generates backwater effects and additional contraction and expansion losses. As a consequence, thehead over the side weir rises. Accompanied with supplementary roughness induced by the development of bedforms, the design discharge to be diverted over the weir is increased by this flow-sediment transport interaction.Based on a flume study, a semi-empirical model to predict the length and the global longitudinal shape of theaggraded reach as well as the position and height of the maximum bed elevation is developed. The longitudinalshape is fairly well represented by an adapted Maxwell-type distribution function.