Keywords: horizontal sharp crested weirs, channel bends, control section, flow discharge, performance evaluation, diversion structures, river bends, hydraulic structures, river morphology, erosion, sedimentation, non–uniform flow
Performance evaluation of horizontal sharp crested weirs in a channel bend
In some cases, construction of weirs and diversion structures in river bends is inevitable. There are a number of such hydraulic structures which were installed around the river bend without considering the undesirable effects of these structures on the river morphology which resulted in serious problems like that of erosion, sedimentation and non–symmetrical distribution of flow where water intakes are required on both sides of the river banks. The main hypothesis for uniform flow distribution across the bend and along the weir crest is changing the weir crest profile from horizontal to sloping. Most of times, this criterion is neglected. In this study, performance of horizontal sharp crested weirs in a 90–degree bend channel is discussed. An experimental set up was prepared in which channel width was taken as 1 m with a 9 m straight reach on the upstream with a depth of 60 cm. The results show the non–uniform flow distribution along the bend with non–symmetric distribution of water depth across channel width. Since at present there is no criterion for location of control section in the bend, this study presents new criteria for suitable place of control section of sharp crested weirs in the bendway. It was found that the control section of sharp crested weir in the bendway lies in the range of 2.6 to 3.0 times of hmax. It was also found that the direction of control section is not parallel to weir in the bendway.