SCOUR HOLE CHARACTERISTICS BELOW FREE OVERFALL SPILLWAY

摘要

When flow passes over a free overfall spillway, forms a jet. This jet of flow with a high velocity may cause scour at the downstream of spillway. The scour hole characteristics is affected by parameters like discharge intensity, drop height, tail water depth, size of bed material and standard deviation of bed material. In this paper, results of experiments on scour below free overfall spillway for uniform and non-uniform bed materials are presented. It was found that scour hole characteristics (i.e. maximum depth of scour, distance of maximum scour point from spillway, width of scour hole, distance of end of scour hole from spillway and height of ridge formed at the downstream of scour hole) is a function of densimetric Froude number and ratio of drop height to tail water depth. Analysis of experimental data with uniform bed material resulted in equations for estimation of scour hole characteristics. Further correction factors were introduced in order to consider the effect of non-uniformity of bed material.