Laboratory Study on Local Scour at the Downstream of Grade Control Structures with Labyrinth Planform

Grade control structures are commonly used to prevent degradation, increase bank and bed of rivers stability and prevent cross structures failure in rivers. In order to design a safe grade control structures, estimation of local scour depth downstream of these structures is crucial. In this study effect of different parameters on local scour at the downstream of grade control structures with labyrinth planform was experimentally investigated. Different types of rectangular and trapezoidal labyrinth planform weirs were studied. Experimental results showed that labyrinth planform has a high effect on reducing scour depth. It was found that decreasing the length of cycles in trapezoidal weirs decreases the depth of scour while, decreasing the width of cycles in rectangular weirs increases the depth of scour. It was found that by increasing parameter and drop height, depth of scour increases, while increasing tailwater depth decreases the depth of scour and it varied from 2 to 8 percent for labyrinth weirs. Results showed that the scour depth follows an exponential law, dimensional equation for prediction of scour depth is presented. The accuracy of developed equation was examined with the available prototype data.