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SANCOLD Conference 2017: USBR Stilling Basins on Steep Slopes, With Ntsonyini Dam As A Case Study

By SD Anderson, DG Cameron-Ellis, HJ Wright ARQ Pty (Ltd), Dams and Hydro, Pretoria, South Africa.

Stephen received third place for best youth publication and presentation at the 2017 SANCOLD conference.

The basic principle behind standardised hydraulic jump energy dissipation structures, e.g. the USBR Type III Stilling Basin, is to reduce the length of the hydraulic jump and contain it within a concrete structure to control erosion. The concept of returning flow to the river through the hydraulic jump, simultaneously dissipating energy, is common to all such structures. However, where the gradient and roughness of the river reach downstream of the dam dictates super-critical flow conditions, such a jump will not, by definition, occur. This phenomenon is discussed and a potential solution is described: ensuring the flow regime downstream of the stilling basin is stable and sub critical so that a hydraulic jump forms in the stilling basin consistently