Impact of the Poyang Lake Hydraulic Project on local hydrodynamic conditions at the confluence section of the Yangtze River mainstream

The Poyang Lake Hydraulic Project is a major water conservancy initiative proposed by Jiangxi Province to address several challenges, including hydrological imbalance during the lakes dry season, water scarcity, and reduced navigability. In recent years, due to the weakening backwater effect from the Yangtze River mainstream, the onset of the dry season in Poyang Lake has advanced, with significantly lower water levels, resulting in ecological degradation, intensified water supply conflicts, and navigation obstructions in the lake region. To regulate the relationship between the river and the lake, enhance water resource carrying capacity during the dry season, and ensure integrated benefits such as water supply, irrigation, and navigation, the Poyang Lake Hydraulic Project was constructed. However, the reservoirs water storage and regulation operations directly influence the outflow, thereby affecting local hydrodynamic conditions at the confluence section of the Yangtze River mainstream. Using a two-dimensional hydrodynamic model, this paper analyzes the impact of the project under unfavorable operating scenarios by examining changes in distributary flow ratios, mainstream belt shifts, and localized flow field variations in relation to the dispatching strategies of the hydraulic project. Model test results indicate that following the construction and operation of the project, the distributary flow ratio at the Zhangjiazhou reach of the river undergoes only minor changes, with an adjustment range within 1.3%, and there is no significant impact on mainstream position or flow velocity. Consequently, the project does not pose any substantial adverse effect on navigability. These findings provide technical support for further research into the impacts on waterways and navigation conditions.