Numerical study of overflow hydrodynamics and pressure distribution on a spur dike under tidal bore-like flow

Three-dimensional (3D) numerical simulations of a tidal bore interacting with a trapezoidal, round-headed spur dike were conducted using OpenFOAM under various initial still-water depth conditions ( d 0 ) and incoming flow conditions. Short ( L = 0.3 m) and long ( L = 0.5 m) spur dikes installed in flumes of two different widths: B = 1 m and 2 m, respectively, are tested. Flow dynamics, overflow characteristics, and pressure acting on the spur dike during tidal bore interaction are systematically analyzed and presented. Results show that the overflow discharge ( Q of ) is primarily governed by the water level at the immediate upstream of the spur dike ( h us ), and the overflow discharge is well predicted by Poleni’s overflow equation, with a discharge coefficient of 0.9 [-], despite the presence of local 3D flow effects. 3D pressure variation was observed on the spur dike head, with increasing d 0 resulting in different pressure distribution patterns. Overflow generated significant pressure differences between the upstream and downstream sides of the spur dike. Under emergent conditions, overflow-induced suction pressures at the downstream crest and at the dike head’s crest, when the angular positions of the pressure measured, θ ≥ 90° (with respect to incoming flow direction), with suction intensity increasing with higher discharge and lower submergence ratios ( d₀/h d ; with h d being the spur dike height). These conditions enhance the failure potential and destabilization of armour units at the crest of rubble mound spur dikes. Increased overflow also elevated downstream toe pressures, with the existing still-water depth playing a significant role at higher submergence. Predictive equations for estimating pressures acting on the spur dike are proposed for safer design against extreme impacts.