Abstract

Side weirs are a widely used device to control flow processes along a channel or river course. The lateral loss of water is responsible for the reduction of sediment transport capacity in the main-channel yielding to aggradation and the formation of a local sediment deposit in the downstream weir alignment. The reduced cross section generates backwater effects and additional contraction and expansion losses. As a consequence, the design discharge to be diverted over the weir is increased by this flow-sediment transport interaction. The side overflow increase is uncontrolled and might be significant with substantial deviations in the order of 40 %. As a precursor to the analysis of an extensive experimental data set concerning side overflow in presence of a mobile bed, the influence of a fixed obstacle is investigated numerically. The aim of this simultaneous investigation is to get a sensibility of basic principles and fundamental processes taking place at the interaction of a sedimentary deposit with a lateral overflow. The 1D-numerical simulation is focused on the impact of obstacle height, shape and position with respect to side weir location. The investigations reveal considerable influence of the parameters height and position, whereas the obstacle shape seems to be of subordinate importance.

Keywords: Side weir, side overflow, sedimentary deposit, bed morphology, 1D-numerical modelling