Effects of Upward Seepage on Depth of Scour Hole Downstream of Free Falling Jets Under Constant Tail Water Depth

Grade control structures are used to control bed erosion in steep small rivers mostly in the mountains. Scour downstream of this structure can lead to failure. Over the past years, the effect of different variables on this phenomena have been studied, however the effect of upward seepage which is common due to head difference of the banks water table or water surface level between the upstream and downstream reaches of a grade control structure has not been studied. In this paper, results of an experimental investigation on the maximum scour depth downstream of a grade control structure with and without upward seepage through bed sediments are presented. Experiments were run for the conditions of free falling jets, over sedimentary beds (median sizes = 1.5, 2.4 and 3.15 mm). Our data for the case of existing upward seepage shows that Dʹ Agostino and Ferro (2004) expression significantly overestimates the scour depth. New finding of this study indicates that with the presence of upward seepage the scour depth decreases significantly which confirms the results of Sarker and Dey (2006) on scour downstream of horizontal jet with no horizontal apron.