Effect of tailwater depth on local scour downstream of horizontal jets

Abstract

In this paper the results of an experimental study on the effect of tailwater depth on the mechanism of scouring downstream of hydraulic jumps is presented. Totally, 53 tests with 12 hours run time were carried out under various tailwater depths ranging from 14.2 to 32.5 cm for 5 different densimetric Froude numbers. The results show that the tailwater depth has a significant role in the scouring process and its effect depends on the magnitude of densimetric Froude numbers. For high values of the Froude number, there is a critical submergence value, where the minimum depth of the scour hole is occurred. An empirical equation is proposed to determine this critical submergence factor. Considering the mechanism of a submerged jet issuing from a sluice gate opening and passing a sudden step, a new approach is proposed to justify the presence of critical submergence factor. Comparing the present results with those of previous studies shows that the length of apron is also an important factor in the scouring process. Non-dimensional graphs are presented to determine the magnitude of scour depth for different tailwater depth and Froude numbers. Finally, it was found that the maximum scour depth and the dune height are more impressible to the variations of the tailwater depth than scour hole length.

Keywords

• local scour
• tailwater depth
• hydraulic jump
• critical submergence factor