Effect of corrugated apron pitch ratio on local scour resistance behind weirs

ABSTRACT Local scour downstream of stilling basins is governed by energetic roller vortices generated within hydraulic jumps. While corrugated aprons are widely used to modify jump behavior, the specific influence of corrugation pitch ratio (S/t) on downstream scour has not been quantified under a discharge-normalized, hydraulically neutral framework. This study experimentally evaluates a flat apron and three corrugated aprons (S/t = 3, 4, and 6) under four clear-water discharges normalised by a critical-flow reference (Qn = Qac/Qcr) to separate hydraulic forcing from geometric modulation. Results show that S/t acts as a primary morphodynamic control by regulating the downstream persistence of coherent roller forcing and, consequently, scour magnitude and extent. Increasing S/t at constant corrugation height shifts turbulence dissipation upstream and produces a monotonic reduction in relative maximum scour depth (Dmax/y1). Scour length (Ls/y1) reaches a minimum at S/t = 4, indicating a depth–extent trade-off at larger pitches while still outperforming the flat apron. Spatial scour patterns further indicate turbulence-inheritance effects rather than roughness magnitude alone. These findings support using S/t as a hydraulically impartial design parameter for sediment-sensitive stilling basins.