Geometry of developing and equilibrium scour holes at bridge piers in gravel

Experimental results on scour at circular and square cylinders in uniform gravel under the clear-water scour condition are presented. Nonintrusive, high-resolution topographic measurements of developing and equilibrium scour holes were performed during running experiments with an experimental installation using a laser distance sensor (LDS) and precision step motors. Measurements were taken by the LDS in different azimuthal half-planes with θ = 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 135°, 150°, 165°, and 180° to study the spatio-temporal variation of geometric properties of scour holes. Experiments were conducted over 40 h until equilibrium, with bed shear stress equal to 95% of the critical bed shear stress for the initiation of sediment motion at the undisturbed plane gravel bed having a d50 of 3.25 mm. Results show that scour in gravel progresses more slowly around the square cylinder, where steeper slopes than at the circular cylinder are observed. During experiments the scour slopes do not exceed th...