Experimental Investigation of Scour Upstream of a Square Orifice under Constant Head

Orifices are historically used in different hydraulic structures for flow regulation and removal of sediments from reservoirs. The performance of orifices in drawdown flushing to increase the lifetime of dams is vital. Anayiotos et al. [1] performed extensive measurements of the velocity contours upstream of an orifice. They have reported that the shape of the velocity contours at the vicinity of the orifice becomes elliptical. Chanson et al. [2] studied the characteristics of the flow in an orifice under unsteady flow condition. Their measurement were done by means of ADV technique. Bryant et al. [3] conducted experiments to study the flow upstream of a small orifice, a large orifice, an orifice near the free surface, and multiple orifices [3]. Physical and numerical studies were conducted to quantify the scour or sediment removal upstream of orifices under a falling head [4]. One of the most important parameters affecting scour characteristics upstream of the orifices is the shape of the orifices. This paper reports the results of experiments carrie out on the mechanism of scour upstream of square orifices. Velocity profiles before and after the scour process are compared to understand the flow behavior associated with the equilibrium scour conditions.