Abstract: The arrangement includes a downstream jack pivotably mounted about an axis in the floor of the dam and a rotating abutment member carried by the wicket for receiving an end of a jack piston rod. The jack is restored to an end angular orientation when the piston rod is moved away from the abutment member. This end angular orientation is determined by the axis joining the end upright position of the abutment member and the end down position of the abutment member. The piston rod of the jack and the abutment member are provided with a coupler for ensuring their engagement. The jack body is fitted with a sealing apparatus pivotably mounted about the same axis in the floor of the dam and out of which the jack body is easily removable.