Experimental investigation on local scour at the downstream of grade control structures with labyrinth planform

Abstract

ABSTRACT Grade control structures are commonly used to prevent degradation, increase bank and bed of rivers stability and prevent cross structures failure in rivers. To safe design grade control structures, estimation of local scour depth downstream of these structures is crucial. In this study, the effects of different parameters on local scour at the downstream of grade control structures with labyrinth planform were investigated experimentally. Different types of rectangular and trapezoidal labyrinth planform weirs were studied. Experimental results showed that the labyrinth planform has a high effect on reducing scour depth. It was found that decreasing the length of cycles in the trapezoidal labyrinth weirs and increasing width of cycles in rectangular weirs causes reduction of the maximum scour depth. Experimental observations and comparison of results showed that trapezoidal labyrinth weirs effectively reduce scouring with an average of 19 percent in comparison with linear weir; moreover, the rectangular labyrinth weir reduces to 10 percent. Furthermore, dimensional equation for prediction of scour depth is derived.