Scour depth around flat and sloped crest bendway weirs: a laboratory study

Abstract

ABSTRACTBendway weirs are low stone sills designed to control erosion at the outer bank of river bends, redirecting the current from the outer to the inner bank. Laboratory experiments were conducted in a movable bed channel with three consecutive meandering bends (relative curvature equal to 2) and continuous sediment supply from upstream. The aim of these tests was to study the effects of weir crest slope on maximum scour depth at the weir nose, on point-bar height and on cross-sectional eroded surface area in a meander live-bed. Concrete trapezoidal bendway weirs were constructed at the outer bank of the central bend. The investigated configurations consisted of series (3–5) of weirs characterized by prescribed: inclination angles (60°, 75° and 90°), length ratio (0.2, 0.3 and 0.4), crest slope (0%, 5%, 10% and 20%) discharge ratio (0.8, 1 and 1.2), the same height and the same distance between weir axes. Results showed that the maximum and minimum scour depths at the nose of sloping crest weirs were attained for α = 75° and RL = 0.3, respectively. By increasing the crest slope from 0% to 20%, the scour depth decreased more than three times. In addition, flat weirs appear to be more effective in capturing and redirecting the flow from the outer bank towards the inner bank. Finally, the data set collected during the experimental tests was used to derive an empirical relationship for predicting of maximum scour depth at the weir nose.