Morphological impacts of scour around spur dikes in trapezoidal meandering channels

Abstract Scour around river training structures is a critical concern in meandering channels, as excessive local erosion can threaten structural stability and alter channel morphology. The primary focus of previous studies has been the rectangular cross section and little, or no concentration has been given to trapezoidal section which is close to natural river cross sections. To address this gap, the present experimental study examines the effectiveness of curved spur dikes installed at different locations in trapezoidal meandering channels with sinuosity values of 1.35 and 1.50. Experiments were conducted using uniform sand ( d 50 = 0.87 mm) under subcritical flow conditions with discharges of 0.015 and 0.020 m 3 s −1 . A spur dike of constant length (0.167 m) was installed with varying permeabilities (0%–75%) at five angular positions (0°, 30°, 60°, 90°, and 120°), designated as P 1 through P 5 . Results indicate that channel sinuosity, discharge, dike permeability, and installation angle significantly influence scour depth. The reduction if maximum scour depth was highest when a 50% permeable spur dike was installed at 90° from bend start achieving an efficiency of 54.3% (1.35 sinuosity and 0.015 m 3 s −1 discharge) and 42.4% (1.50 sinuosity and 0.020 m 3 s −1 discharge). This scour reduction is attributed to enhanced redistribution of secondary currents toward the channel centerline. Furthermore, the spur dike oriented towards downstream was found to be more effective in reducing scour compared to upstream-oriented orientation. In addition, a predictive equation was developed to estimate scour depth, demonstrating good performance with a coefficient of determination ( R 2 = 0.854).