Kariba dam on Zambezi river: stabilizing the natural plunge pool

The paper presents the outstanding case history of the development of a deep scour hole downstream of Kariba arch Dam on Zambezi River, since its commissioning in 1959 for hydropower generation, and the reshaping project under development, designed as a remedial measure to stabilize the plunge pool evolution.The history of spilling through its gated spillway 9 000 m3/s capacity is summarized and the consequent deepening of a scour hole in the competent rocks of river bed, under the spillway impact zone, extending now about 80m below mean tail water level is depicted.The reshaping project development has been validated through an original progressive optimization methodology involving in various steps both civil engineering design and up to date hydraulic modelling, both physical and numerical. The reasonably feasible design of these exceptional civil works, while keeping in operation the dam and both powerhouses totalizing 1350 MW, is then described.