Physical and numerical model study investigating plunge pool scour at Kariba Dam

Kariba Dam is a 128 m high arch dam located on the border between Zambia and Zimbabwe. The dam has been constructed in the late 1950s and formed at that time the largest man-made lake worldwide. The dam is equipped with 6 flood gates, each about 9 m high by 9 m wide, allowing for a total outflow of about 9000 m3/s. The plunge pool downstream of the dam consists of sound and relatively hard gneiss bedrock and is basically unlined. Nevertheless, frequent outflows generated between 1962 and 1981 have formed an 80 m deep scour hole in the bedrock, which is unprecedented in dam history. As the flood gates are located in the upper part of the dam wall, they operate under relatively low velocities and thus generate plunging jets that impact quite close to the dam foundations. As such, potential regression during further scour formation might approach the dam foundations and should be avoided This paper presents a combined physical-numerical study investigating scour potential at Kariba Dam, performed by a consortium consisting of the Laboratory of Hydraulic Constructions of the Swiss Federal Institute of Technology in Lausanne (EPFL) for the physical modelling and the consulting company AquaVision engineering Ltd. In Ecublens, Switzerland (AVE) for the numerical modelling and for future scour predictions. The paper focuses on the hybrid methodology that has been proposed to assess past and future scour formation in the plunge pool.