Physical scale modelling of scour around bridge piers

The feasibility of physical modelling techniques for quantification of prototype bridge pier scour in reduced scale models is investigated through 17 ad hoc designed experiments which were conducted in three flumes with different widths and depths, using three sediments, and two other materials of different size and density. Experiments covered clear-water and live-bed conditions as well as steady state conditions and real hydrographs of limited duration. Results show that the scour process at a bridge pier is controlled by the dimensionless effective flow work, and the dimensionless grain diameter. The time scale depends on the pier diameter, sediment relative density, sediment size, and flow velocity. In very specific cases, perfect similitude between model and prototype is achieved. In common situations however, the relative size of the pier to sediment in the prototype and the model is distorted, introducing scale effects in the model scour, which are shown to be small.