Author(s): B. Rosier; J.-L. Boillat; A. J. Schleiss
Linked Author(s): Anton J. Schleiss
Keywords: Side overflow; Diverted discharge; Sedimentary deposit; Bed forms; Movable bed roughness; Flow Resistance; Alluvial channels
Abstract: In irrigation and flood protection engineering an efficient control and management of flow processes along the channel or river course is required. Lateral side weirs and fuse plugs are a feasible and widely used device to cope with this challenge. They are installed at the wall along the side of the main-channel to divert or spill water over them when the water level in the channel rises above their crest. This lateral loss of water is responsible for the reduction of sediment transport capacity in the main-channel by decreasing the bottom shear stress. This yields to the formation of a local sediment deposit in the weir alignment thus reducing the cross section. Consequently, the upstream water level rises and the head over the side weir as well. In addition with supplementary roughness induced by the development of bed forms, the design discharge to be diverted over the side weir is also increased and sediment transport capacity is further decreased. This interaction between lateral overflow and sediment transport has to be known in order to avoid undesirable consequences. By the help of an experimental setup the physical processes in the main-channel and on the side weir were analyzed systematically confirming the processes mentioned above. Observed dimensions of bed undulations in the presence of a lateral overflow are poorly represented by theory and play a subordinate role regarding increased lateral discharge intensity. Without paying attention to side overflow induced morphological river bed changes, resulting errors in calculating spilled side overflow discharge may be in the order of 40 % .