Predicting the Hydrological Impacts of the Poyang Lake Project Using an EFDC Model

Dams have great hydrological impacts on the river system. Poyang Lake, the largest freshwater lake in China, has experienced severe drought over the past decade since the operation of the Three Georges Dam. The Jiangxi Province Government proposed to build a 2.8-km-wide dam with sluice gates across the narrowest part of the channel that links Poyang Lake and Yangtze River, called the Poyang Lake Project (PLP), to solve the problem of drought. The proposal caused concerns about the negative effect of increased water level on wintering birds’ habitat and water quality. But so far, little scientific data have been provided to evaluate the hydrological impacts of the PLP. The aim of this study is to investigate the hydrological impacts of the PLP using a two-dimensional Environmental Fluid Dynamics Code (EFDC) model based on the latest regulation scheme, which will be helpful to evaluate the advantages and disadvantages of the building of PLP. The model was calibrated and verified by comparing model predictions with observed data. A typical dry season between 2006 and 2007 was used as the period to simulate the scenarios with and without the PLP. Simulated results from the EFDC model showed that the increase of water depth mainly occurred in the water channel in the north part of Poyang Lake with the regulated water level set at 10–11 m, and the increased water depth in two national nature reserves was less than 0.1 m, which has little effect on wintering birds’ habitat. However, the benefit of the PLP was limited with this regulated water level and the increased water storage was less than $6.2\times {10}^8{\mathrm{m}}^3$. The increased water storage would double when the lowest water level was set at 12 m, and the bird habitat was still little affected. The existing regulated water level reduced the flow velocity in the northern part of Poyang Lake by approximately 50% and the effect became smaller with distance far away from the PLP. The slowdown of flow velocity would increase the eutrophication risk and the water quality would deteriorate if the regulated water level was set higher. Whether the project should go ahead depends on how to balance the advantages and disadvantages.