Effects of Upstream Weir Slope on Local Scour at Submerged Weirs

Abstract

The variation of upstream slope of a submerged weir could significantly alter the local flow pattern and sediment transport. This paper presents an experimental investigation into local scour at submerged weirs with different upstream weir slope angles. In this study, 62 tests are carried out in a tilting recirculating flume, including 38 tests using coarse sand and 24 tests using fine sand, to investigate the effects of upstream weir slope on the local scour at a submerged weir. The tests of each sand use four weirs with different upstream weir slopes. For clear-water scour, no upstream scour depth is observed at the sloped weirs, and downstream scour depth is independent of the upstream weir slope. For live-bed scour, a flatter upstream weir slope reduces upstream scour depth for both sands. The results for fine sand show that when the slope is gentler than a critical angle α, the effects of upstream weir slope on upstream scour depth are minimized, such that the upstream scour depth no longer decreases with decreasing weir slope angle. The existence of upstream weir slope slightly reduces the downstream scour depth when the sediment is transported as bedload. When the sediment transport mode is suspension load, the downstream scour depth is independent of the weir slope. New predictors for the average scour depth including the effects of upstream weir slope are developed. A relationship between the average and maximum scour depth is also proposed.