Variation of Mean Pressure Around the Chute Blocks of SAF Stilling Basin

Construction of stilling basins downstream of hydraulic structures is a common tool to dissipate the excess energy created by exit supercritical flows from the outlets. The length of the stilling basin and its construction costs are the factors which should closely be considered by designers to select the most economical structure. Saint Anthony Fall (SAF) stilling basin is one of the compact and short length pools which are utilized in downstream of high velocity exit flows. The efficiency of energy dissipation of this type of stilling basins would be too high despite to the short length of the pool which is the consequence of appurtenances encountered with this basin. Generally, to design this stilling pools the average flow characteristics (such as mean velocity, hydrostatic pressure, …)are used which reflects some uncertainties due to presence of high turbulent and fluctuating flow in the reach which is to be considered for careful clarifications. In this research a stilling basin of SAF type has been constructed in a glass walled flume and electronic devices been used to take the precise measurements of actual pressure prevailed around the chute blocks of the basin. The results showed that the mean pressure is not in accordance with hydrostatic distribution and varies inversely with entering supercritical flow and directly with submergence ratio of hydraulic jump formed in the basin. It was also revealed that the variation of mean pressure at different faces of the chute blocks follows a different trend at each face.