Optimization study on construction diversion scheme for phase III-First dry season of Dongfengyan navigation-power junction

Abstract This study addresses critical issues in the construction diversion scheme for the Dongfengyan Navigation-Power Junction during the first dry season of Phase III, including significant water surface drop upstream of the spillway, excessive flow velocity, and severe downstream riverbed scouring. To ensure construction safety, a 1:100 scale normal physical model was employed to systematically investigate the hydraulic conditions of the project reach. The results demonstrate that modifying the original design by: (1) reducing the elevation difference between the large right-bank shoal and the spillway floor from 4 m to 2.5 m while flattening the upstream riverbed slope from 1:10 to 1:50 upstream; and (2) expanding the stilling basin downstream of the spillway – effectively mitigated the water surface drop and high-velocity flow near the spillway. Post-optimization measurements under the diversion design flow show: maximum upstream velocity decreased from 8.9 m/s to 4.18 m/s, and maximum downstream velocity reduced from 11.75 m/s to 4.49 m/s. These modifications substantially reduced scouring risks, achieved smoother water surface transitions across the spillway, and significantly enhanced the junction’s discharge capacity.