Construction method for downstream flow guarantee supply in high dam and large reservoir in-situ reconstruction

The invention discloses a construction method for downstream flow conservation and supply for high dam large reservoir original site reconstruction, and belongs to the technical field of water conservancy and hydropower engineering. A barrage is arranged on the downstream of the original site of the old dam, and a reverse regulation reservoir is formed; the barrage comprises an overflow dam section and an ecological gate section; a plurality of gates are respectively arranged on the ecological gate section and the overflow dam section; when the old dam is completely dismantled, a new dam is constructed in a segmented mode at the dam site of the old dam through a segmented cofferdam structure; the part where the cofferdam is not built serves as a flow discharging channel to discharge water to the reverse regulation reservoir, or the built new dam section is used for discharging water to the reverse regulation reservoir; when the old dam is not completely dismantled, the old dam is used as a water retaining str