Study on the channel development in a wide reservoir

摘要

In most reservoirs incisive channels are formed within the widening depositional area (the delta). Understanding this phenomenon is important for the development of an efficient sedimentation control strategy that uses these natural erosion processes to remove the deposits. Laboratory experiments in a wide rectangular flume with an initially flat alluvial bed showed that the location of the channel is determined by the initial flow-pattern, and by the up- and down-stream conditions that control this pattern. In these experiments the channel formed along the left bank although the outflow was positioned on the right bank. Two to three major horizontal eddies developed which force the flow field to support the observed curved channel. This particular behavior could also be reproduced by a two-dimensional (depth-averaged) morphological model of the experiment using the Delft3D modeling system. The simulations indicate that the observed asymmetry in channel position, and sudden switches in channel location can be explained by the sensitivity of this flow pattern to geometry and boundary conditions. Following this verification of the model-approach, a case-study has been carried out for Senbiri reservoir in the Hokkaido region in Japan which shows the characteristic channel pattern as observed in the flume experiment. Two-dimensional simulations indicate that time-dependent control of outflow gates and modification of bend pattern in upstream river reach can be applied to increase erosion of the deposits.