Jordan Journal of Civil Engineering

Effects of Chute Block Geometry on the Performance of the USBR II Stilling Basin


Layla Ali; Saleh Khassaf;


Stilling basins are designed to decrease high kinetic energy of flow downstream of spillways. Particularly, the USBR II stilling basin is distinguished by chute blocks fixed at the upstream end and a dented sill near to the downstream end. These accessories allow for the effective dissipation of excess energy. This research investigates the effect of chute block geometry on the hydraulic performance of USBR II stilling basin. Six types of chute blocks were constructed and tested for six incoming Froude Number values. Modified blocks have the same height, width, and upstream edge spacing as standard blocks. The results indicate that chute blocks with stepped side walls are more effective than standard blocks because they increase energy dissipation by 1.47 % and decrease subsequent depth ratio by 3.91 %. Moreover, blocks with gradually increasing spacing lose 0.7% more energy than standard and decrease the sequential depth ratio by 1.91 %. Blocks with prismatic spacing and top surfaces at an angle of 152 degrees relative to the downstream slope of the spillway are less effective than standard blocks, with energy dissipation reduced by 2.73 % and the depth ratio increased by 7.24 %.


Chute Block; Energy Dissipation; Hydraulic Jump; Spillway; Stilling Basins