Author(s): Ubaid Ullah, Muhammad Iqbal, Eric J. Lesleighter, Bronson Mcpherson, Umair Mannan
Linked Author(s): Eric J Lesleighter
Keywords: Hydraulic jump, stilling basins, cavitation, aeration, pressure transients
Abstract:
The Mohmand Dam is a 213 m tall concrete-faced rockfill dam (CFRD) under the design by a consortium of foreign and Pakistani consultants. The dam is constructed on the Swat River in Pakistan. The hydraulics detailing of the project has included large diversion tunnels, one to be converted to a permanent low level outlet works and sediment flushing outlet, and a seven-gated headworks with discharge into a 100 m wide spillway. A strategic component of the hydraulics studies has been large-scale physical model studies carried out by the Irrigation Research Institute, Nandipur, Pakistan. The paper presents the details of the model arrangements, particularly the final arrangement, and describes the hydraulic behaviour of a double hydraulic jump stilling basin facility as a means of breaking down the high heads for better energy dissipation control. While a ski-jump type spillway was considered, the large discharges into rock of relatively modest erosion resistance, with consequent deep and laterally extensive scour, made the selection of the hydraulic jump basins more attractive. The upper basin was designed to operate with a maximum head of about 100 m, and the lower basin was designed to operate with a maximum head of approximately 120 m. The studies considered the discharges up to 25,500 m3 /s. Detailed pressure transducer measurements of transients were made as part of the design of the basins. The chutes utilize a number of aerator steps for aeration of the flows along the chutes and into the stilling basins. The paper describes stilling basins and their effectiveness in handling such high discharges; basins which are generally based on the configuration of the USBR Type III stilling basin, utilizing a variation to the “normal” baffle blocks as a further hedge against cavitation potential. (2609, 71, 313)
Year: 2017