Coupled influence of wing geometry and seepage on local scour around spur dikes

Present study experimentally investigates the coupled influence of the wing thickness of a T-shaped spur dike and downward seepage on local scour in an alluvial channel. Two configurations were tested under seepage levels of the main discharge. Bed response was quantified using time evolution of maximum scour depth, post-run bed morphology mapping, and bedform celerity at the upstream and downstream wing edges. The thicker wing consistently produced larger equilibrium scour under different seepage levels. The increased seepage indicates a stronger relative seepage response for the thinner wing despite lower absolute scour. Longitudinal profiles show a more extensive erosion footprint for thicker winged spur, with scour growth occurring mainly for initial time, followed by a slower approach to dynamic equilibrium. These findings provide practical guidance for spur-dike detailing in seepage-affected alluvial rivers by showing how wing thickness and seepage jointly control scour depth, footprint, and time to stabilisation.