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In flood protection engineering, side weirs or overflow dams are used to divert water in a controlled way into flood plains as soon as the discharge capacity of the main-channel is reached. Because of the lateral loss of water, the sediment transport capacity is reduced, resulting in local sediment deposition near the side overflow. Moreover, bed form characteristics such as length, height, steepness, and stoss and lee slope angle are affected by the lateral water withdrawal. Both phenomena are responsible for an increased side overflow intensity compared with plane bed conditions. The results from a systematic flume study show that the shape of observed bed forms is highly three-dimensional and that three distinct regions along the channel axis can be identified. The first one extends from the channel entrance to the upstream weir corner, the second one comprises the reach of the weir, and the third one represents the reach downstream of the weir. The description of bed form shape by approaches from literature shows reasonable agreement with measured bed form geometry. [ABSTRACT FROM AUTHOR]

Side weirs and overtopable levees are widely used to increase flood routing along a channel or river. The lateral loss of water reduces the sediment transport capacity leading to the formation of a local sediment deposit close to the overflow. Since the extent of the morphological bed changes is not known a priori, the design discharge is increased by this flow-sediment transport interaction in an uncontrolled way. Based on a systematic flume study, a semi-empirical model to predict the three-dimensional bed evolution of the aggraded channel reach in the vicinity of the overflow is developed. The shape of the deposit is modelled by an adapted Maxwell-type distribution function. The main input parameters of the model are expressed in terms of dimensionless parameters accounting for main channel and side overflow geometry as well as flow and sediment transport characteristics. The application of the empirical model in numerical flow calculations predicts 90% of the measured overflow. [ABSTRACT FROM AUTHOR]

Side weirs are free overflow regulation and diversion structures commonly encountered in flood protection engineering. The lateral loss of water reduces the bed-load transport capacity in the main channel, leading to local sediment deposition near the side overflow. As a consequence, the design overflow is increased in an uncontrolled way. Since this flow-sediment interaction in such a channel has not been studied so far, systematic flume experiments have been performed. Based on these experiments, a two-dimensional empirical model to describe the longitudinal evolution of the aggraded channel reach near the weir has been developed. In addition, a simple and straightforward approach for direct estimation of the side overflow in presence of bed-load transport has been established. To be generally applicable in engineering practice, all input variables are expressed in terms of dimensionless parameters. Finally, the application of the models is demonstrated in a case study on the Rhone River in Switzerland. [ABSTRACT FROM AUTHOR]