Investigation of the scour occured at the downstream of cascades

Cascade and stepped spillways have regained popularity over the last decades with the evolution of the roller compacted concrete (RCC) dam construction technique. These hydraulic structures are used for energy dissipation at dam spillway, at conduction line, at aeration of water, at oxygen transfer, at systems of irrigation and stormwater. Advantage of hydraulic structure include ease of construction, reduction of cavitations risk potential, and reduction of the stilling basin dimensions at the downstream dam toe due to significant energy dissipation along the chute.Kinetic energy of water falls down from a specific height transform to dynamic pressure at area to where water jet hits. The main reasons of the scouring are dynamic pressure effect over the base of jet. Falling water drifts material over the bad in a short time and then starts to carve the base. In this time, the distance of scouring to hydraulic structure and depth of scouring can be danger for body and other extra builds stability.The real aim of this study is; investigate the hydraulic characteristics of cascades and determine the effect of different flow conditions and build geometries to scouring hole. Scouring at cascades downstream has been investigated considering different stepped chute base angle, step geometry, stilling basin sill type, downstream water levels and material granulometry parameters. All data of experiment have been discussed with investigating the effect of parameters, which affects the event, over the scouring geometry. At the end of each experiment to determine the scour geometry readings were taken in the directions of x, y, z and the three dimension scour perspective, cross section and contour maps, geometry was drawn using computer program by using these readings. The parameters affected the scour geometry was taken into account for obtaining maximum scour depth and all experimental data were analyzed. Equations for maximum scour depth have been presented.As a result; step geometry, stepped chute base angle and sill type of the stilling basin are very important parameters over the maximum scour depth and scour hole geometry, has been obtained.Keywords: Maximum scour depth, Scour hole geometry, Cascade, Local scour