Impact of Bed Scour on the Length and Stability of Rock Vanes and Bendway Weirs

Abstract

Consequences are presented from flume experiments regarding bed scour at rock vanes and bendway weirs constructed of loose rock placed on sand bed channels. The experiments involved three flow discharges adjusted to replicate approximately the rising limb of a hydrograph and two bed-material sizes (a medium sand and a very coarse sand) subject to live-bed and clearwater scour. Observations show that these structures shortened due to rock dislodgement triggered by relatively modest contraction scour, which undermined the toe of the crest tip of these loose rock structures, causing the tips to become geotechnically unstable. Additionally, flow dislodgment of rock destabilized by tip slope failure further shortened the crest length of these structures and decreased tip slope. Displaced rock partially armored the scour zone and, thereby, affected scour depth and thalweg development. The experiments illustrated thalweg development as flow rate increased. Design dimensions are given for rock vanes and bendway weirs.