Experimental Investigations on Scour Volume Upstream of a Slit Weir

Abstract

The frequent removal of sediment accumulation from reservoirs by dredging requires interruption of power generation. Alternatively, this can be avoided by using a slit weir. In the present study, the impact of sediment nonuniformity, slit weir dimensions, weir slit position, and discharge on the effectiveness of sediment removal was experimentally investigated using a flume with a length of 12m, a width of 0.30m, and a depth of 0.30m. In the flume, a slit weir was tightly fixed at the end of a 2m working section filled with nonuniform sediments up to 110mm. Results showed that using coarser sediment (d50 = 0.70mm) reduces the scour volume by 22-folds compared to finer sediment (d50=0.30mm). This study tested five different slit weir dimensions using two weir slit positions (slit positioned in the center and slit positioned on the side). The maximum scour volume was recorded when the crest level, z of the slit weir, was 0 cm from the mobile bed. The study concluded that a 3-fold increase in discharge corresponds to a 10-fold increase in scour volume regardless of bed material nonuniformity. The existing model for estimating scour volume for uniform sediments was validated using the data of this study, and it was observed that the model predicts the scour volume in nonuniform sediments with sufficient accuracy. Thus, the model can determine the scour volume, and maximum scour depth occurring upstream of a slit weir near a hydropower intake in reservoirs.