TYPE III STILLING BASIN

Hydraulic structures such as dams require energy dissipation for their safe operation. Scouring and cavitation are challenges which may arise at the downstream toe of earth dams due to inadequate provision for proper energy dissipation leading to severe damages or total loss of the dam. This study aimed at designing the United States Bureau of Reclamation (USBR) type III basin for energy dissipation downstream of earth dam spillways in Nigeria using Microsoft Excel as computational tool. Microsoft Excel was used in developing the design code governed by a set of algorithms which conformed to USBR standard. The algorithm was used to compute flow data suitable for the formation of hydraulic jump within the USBR type III stilling basin. Various flow conditions with discharges ranging from 10 m3 /s to 110 m3 /s and inflow velocity ranging from 3 m/s to 18 m/s) were simulated at various basin widths ranging from 3 m to 12 m. Acceptable design flows were determined using the Froude numbers that ranged between 4.5 to 9 as the major criterion. The results obtained showed that an increase in velocity led to an increased Froude number for the various basinm widths. At 3 m/s inflow velocity, the mean Fr values were 0.59, 0.85, 1.03 and 1.10 forstilling basins width of 3 m, 6 m, 9 m and 12 m respectively. At 6 m/s the mean Fr valueswere 1.69, 2.38, 2.93 and 3.38. At 9 m/s, mean Fr values were 3.10, 4.34, 5.37 and 6.21. At 12 m/s, the mean Fr values were 4.77, 6.76, 8.82 and 9.47. At 15 m/s, mean Fr values were 6.68, 9.89, 9.89 and 13.36. At 18 m/s mean Fr values were 8.68, 12.42, 15.22 and 17.57. These implied that at increased basin widths, the efficiency of the formation of hydraulic jump improved with higher inflow velocities resulting in shorter basins with more numbers of baffle piers and chute blocks. The results obtained will find relevant application in the preliminary design of the type III stilling basins for earth dams, reservoirs in Nigeria, in accordance with the United States Bureau of Reclamation standard. It will also aid Engineers in the proper control and evacuation of small earth dams while checking erosive effects from the velocity of the evacuated outflow by means of hydraulic jump formation. Furthermore, experimental researches involving physical models are recommended to ascertain more results and facilitate more efficient and economical USBR stillingbasin designs