Barrage du Chambon Ouverture de la vidange de fond d'origine

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1. General The concrete gravity dam of Chambon (height : 135 m) was originally equipped with an outlet formed of a 2 meter diameter draw off pipe at altitude 951,50. This facility became inoperative at the beginning of the 1960's because mud clogged up the reservoir, and a new pipe was installed at altitude 959, the old outlet having been obturated by a full plug which could be dynamited, downstream from its guard gate. The reservoir had been drained down to altitude 963 at the beginning of 1980, and was to be drained again the following winter to build a new water intake structure, replace the outlet screen at altitude 959, and build a support for the watertight hood of the dam. At that time, the decision was taken to resume operation of the original bottom outlet. 2.- 3.Recommissioning of the old bottom outlet The following precautions were taken in recommissioning the facility the outlet was opened under a 30 m pressure a powerful clean-water injector was used the gate was opened before the cover was blown up, and the explosion of the plug bolts was synchronised The operation was performed most satisfactorily. The water injection was maintained until the reservoir had been completely emptied. 4. Findings and conclusion The precautions made it possible to solve a problem for which twenty years ago no answer had been found. It is believed that in the future repetition of this operation at judicious by chosen intervals would help prevent renewed fouling of the reservoir by mud.