Modelling local scour in light weight sediment

Investigations on scour at cylindrical piers showed that the scour formula of Chiew that has been developed for sand also applies for scour in sediments that are considerably lighter than sand because his formula implicitely considers sediment properties by the critical flow velocity to which sediment can withstand. It was also shown that the influence of the grain size and of the gradation on scour depth can be used to compensate scale effects, i.e. as scale laws require an exaggeration of mean diameter in the model and thus give way to a lower scour depth this effect is compensated by a steeper gradation of the light weight sediment. The use of light weight sediment in hydraulic models renders possible smaller models and a shorter experimental time.