Experimental Investigation on Local Scour at Downstream of the Inclined Grade Control Structure

In river conservation practices, maintenance of a river bed level especially at under situations where the slopes of bed increases due to different reasons such as sand mining is very important. The inclined grade control structure is one of eco-friendly structures that is applied in order to stabilize rivers beds and banks. One of the important parameters for design of such structures, is estimation of a local scour depth around downstream of the structures. In present study, the effect of different hydraulic and geometric parameters on the maximum scour depth at the downstream of inclined grade control structure was experimentally investigated. Experiments were conducted for slopes of 14 to 33%, unit discharges of 28.4-45.5, tail water depths of 3.5-6 yc and roughness sizes of 4 to 10 mm. Comparison of results of the maximum scour depth for the grade control structure with slope of 33% showed that the tail water depth had direct effect on the scour depth increased from 4.5 to 6 yc, and the maximum scour depth increased by 13 percent. By decreasing the installation bed level to 20 and 14, increasing the tail water had inverse effect on the maximum scour depth in such a way that by increase of the tail water depth from 3.5 to 4.5 yc, average reduction of the maximum scour depth was found to be 9 and 25 percent for slopes of 20 and 14 percent, respectively. Comparison of the results indicated that increasing the roughness of bed caused decrease in the maximum scour depth from 5 to 21 percent within the range of the minimum and maximum roughness.