SCOUR HOLE CHARACTERISTICS BELOW FREE OVERFALL SPILLWAY

1 INTRODUCTION Flow through hydraulic structures often issues in the form of jets. The jet velocities are usually high enough to produce sizable, even dangerous scour hole. The extent of the resulting scour depends on the nature of bed material and flow characteristics. The erosion process is quite complex and depends upon the interaction of hydraulic and morphological factors. Scouring may lead to: endangering the stability of the structure by structural failure or increased seepage, end…

SCOUR HOLE CHARACTERISTICS BELOW FREE OVERFALL SPILLWAY

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.