Experimental Study of the Maximum Scour Depth Due to Free-Falling Jets at the Downstream of Storage Reservoir

In this study the experimental study was performed to determine the scour hole dimensions due to falling jets at the downstream of storage reservoir. The geometry of the scour hole depend to many parameters such as outflow discharge of gates (Qj), medium diameter of sediment (D50) and the confluence angle of jets at horizontal plane ( . In this study the effect of these parameters were investigated. Water jet falls from pipes with circular section and diameter of 1.25 inch into the downstream pound. The drop height was 95 cm. The downstream pound filled with 20 cm of non-cohesive sediments with medium diameter of 1.7 mm, 3.2 mm and 6.75 mm.  Experiments were carried out with different discharges at the range of 1.32 to 5.14 l/s. The results of this study shows that for all experiments a scour hole created at the downstream of the reservoir and with increasing discharge the scour depth (ds) increased. The sensitive analysis of the proposed general equation showed that when jet discharge, sediment diameter and the confluence angle of jets at horizontal plane (  changed ± 20%, the relative scour depth changed 12.33, 6.23 and 34.03 %, respectively.