Author(s): Wen Zhang; Lu Wang; Binrui Gan; Xingnian Liu
Linked Author(s): Lu Wang, Xingnian Liu
Keywords: Rock weirs; Live-bed scour; Bedforms; Scour depth; Grade-control structures
Abstract: Rock weirs typically placed by loose rocks and span the full width of channel, are eco-friendly grade-control structures (GCSs) commonly built in small and medium-sized rivers (USBR, 2016). A rock weir in rivers can preventing bed degradation, whereas the over-weir flow can cause local scour that can threaten the structure stability. Current studies mainly focus on the clear-water scour at rock weirs (Scurlock et al., 2012), remaining the live-bed scour (e.g. the effect of approach bedforms on the scour depth) at rock weirs are unknow. As such, predictors for accurately estimating the scour depth at rock weirs are far from complete. Experimental tests using sand-water recirculating flume and uniform coarse sand (d50 = 1.17 mm) were conducted to study the live-bed scour at rock weirs. The rock weir was placed by loose rocks (artificial pebbles that have the same shape and density as river pebbles, Zhang et al., 2023) spanning the full width of the flume in a I-shape. A brick foundation was set below the weir. Various combinations of flow intensity, submergence and void ratio were tested in this study. The scour depth at rock weirs was manually read using cameras focused through transparent grid sheet attached to both sides of the flume (Guan et al., 2015). For live-bed scour conditions, scour occurs both upstream and downstream of rock weirs. In response to the periodic motion of the approaching bedforms, the equilibrium scour depth fluctuates around a mean depth (Fig. 1). The equilibrium upstream scour depth increases first and then decreases with increasing flow intensity, decreases with increasing weir height, but is less affected by increasing void ratio. The equilibrium downstream scour depth decreases first and then increases with increasing flow intensity, increases with increasing weir height, and decreases with increasing void ratio. New predictors for both upstream and downstream equilibrium scour depths at rock weirs are proposed for design.
Year: 2023