EVALUATION OF SAFETY OF HYDRAULIC STRUCTURES AFFECTED BY MIGRATING PITS

Because it can be carried by flowing water, a sand/gravel pit on the r iver bed could migrate downstream. Consequently, the presence of pits on river beds could pose a safety threat to in-stream hydraulic struct ures such as bridge piers. A pit migration model can be used to predic t progressive changes of pit geometry as it migrates downstream. Howev er, due to the existence of many uncertainties, the maximum pit depth cannot be predicted with certainty. This paper adopted a simple pit mi gration model and evaluated the uncertainty associated with the calcul ated maximum pit depth. Such information is essential for evaluating t he probability that a migrating pit could pose a safety threat to a do wnstream hydraulic structure. Three reliability analysis techniques we re applied and their performances were compared.