Local scour at bridge piers founded in coarse-bed streams

On-site measurements of local scour at bridge piers founded in coarse-bed streams made by several investigators are assembled and used to fit coefficients of a nonlinear model of scour depth. Only measurements at circular cylindrical piers (that is, piers having straight sides, circular ends of equal size, and a constant circular cross section) and other cylindrical round-nosed piers aligned with the approaching streamflow are considered to avoid having to assess the influence of flow alignment and pier shape, factors that are more easily evaluated in small-scale laboratory studies. Model variance is also calculated, which provides a means of generating upper confidence limits of predicted scour depths. As a result, one can estimate margins of safety for appropriate exceedance probabilities needed to design reliable multiple-span bridge crossings of coarse-bed streams.