Experimental Investigation of The Effect of Number and Angle of Anti-Vortex Piers on Submergence Threshold in Square and Circular Morning Glory Spillways

Morning glory spillway, is one of the spillways and used when it is not possible to use any other spillways. With the onset of Submergence and flow Loss, and circulation flows intensify, Spillway performance decrease severely and the height of water in the reservoir increases and Risk of dam damage, caused by the lack of spillway ability of great flow discharge, rises. The increase of the Submergence threshold provide ability of greater flow discharging, without Spillway submergence and its negative consequences. Anti-vortex piers, in addition to correcting circulation and vortexes, may also be effective in increasing the Submergence threshold. To investigate the effect of Anti-vortex piers on submergence threshold, 199 experiments were performed with the physical model on spillways with square and circular inlet section in different modes of number and angle of anti-vortex piers. Results show that in the square spillway, increasing the number (Best mode, 8 piers) or decreasing the angle of Anti-vortex piers (Best mode, 30o), increase the Submergence. In the circular spillway, increasing the number (Best mode, 8 piers) or the angle of Anti-vortex piers (Best mode, 90o), increase the Submergence. At all modes of numbers and angles of piers increasing of submergence threshold in the circular spillway is more than square spillway, But submergence threshold values at all modes in the square spillway is greather. Also, in both spillways the angle of piers more than the number of them affect the submergence threshold.