oa Civil Engineer in South Africa - Overtopping of dams by surging flow
Several dams in South Africa were overtopped by the unprecedented floods of 1981, now well documented. Stage at the dam wall was, in every case amplified due to surges, waves and their reflections, leading to overestimation of the actual flood peaks. The dams did not fail although stressed beyond their design values. Even an earth dam, although twice severely overtopped, survived - probably because of the short-time duration of the amplified peak loading. Such surges can lead to overstress. The observed flood peaks at several dams were greater than those estimated by slope-area methods from down-river flood marks. These increased discharges ascribable to surge agree with calculated values. The results of theoretical analysis of unsteady-state flood routing and a hydraulic model simulation are presented in the paper.
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