Pondage device

A pondage device comprising a dam and a downstream improvement arranged downstream of said dam, wherein said dam and said improvement are made of concrete, wherein said pondage device comprises at least one flexible jack interposed between a downstream facing of said dam and an upstream facing of said downstream improvement, said flexible jack comprising an upstream face and a downstream face which are opposite, the at least one flexible jack comprises a chamber inside of which water is stored, this chamber being delimited at least in part by an elastically deformable membrane, this chamber being kept under pressure by pressurization means and wherein the pressurization means of the chamber of said flexible jack comprise at least one line which passes through said dam and which leads at its upstream end on the upstream facing of the dam and which, at its downstream end, is in fluid communication with an interior of the chamber of the flexible jack, so as to provide for the pressurization thereof, so that the hydrostatic pressure at a point located at a given altitude inside said flexible jack is identical to the hydrostatic pressure exerted on the upstream facing of said dam at a given point at the same altitude.