Impact of Water Projects on River Flow Regimes and Water Quality in Huai River Basin

Research on the impact of water projects (dams or floodgates) on river hydrology and the surrounding environment is important in river basin management. However, it is a difficult scientific issue due to its complexity. Huai River Basin is a unique region in China with high densities in both population and water projects and is experiencing a serious pollution problem. Based on the extended SWAT model with consideration of dams & floodgates, this paper proposes a quantitative framework to assess the impact of dams & floodgates on the river flow regimes and water quality in the middle and upper reaches of Huai River Basin. The results show that: (1) The dams & floodgates reduced the basin's annual average flow by 2%, in comparison with the scenario of no water projects in the whole basin during 1991-2000, because of the regulation and storage of dams & floodgates. The flow in the non-flood season reduced 5% while the change of flow in the flood season was not acute. The impact of dams & floodgates on the annual flow are different in wet and dry years. In the wet year (1991), the impact of dams & floodgates is not obvious because the gates were opened to control the floods and their main functions are to change the temporal distribution in a year. In the dry year (1999), the flow reduced remarkably in comparison with the flow without dams & floodgates in the basin because the gates were closed in order to meet the water demand. The flow in the flood season increased by 8% whiles the flow in the non-flood season reduced by 12%. (2) There was a certain impact of dams & floodgates on water quality but they were quite different in the different area. It would be changed from the positive effect to the negative effect from the upriver to downstream. The dams & floodgates in the upper reaches played a positive role to improve water quality. But the ones in the middle and lower reaches played a negative role with contribution from 0 to 0.4. However, the contribution of exceeding pollutant discharge was more than 0.6. (3) The joint operation of dams & floodgates to control water quantity and quality will improve the water environment in Huai River Basin, but the key to improve the basin's water environment is pollution control. This research will guide the anti-pollution and the united water quantity and quality assessment of dams & floodgates in Huai River Basin. Moreover it will provide a foundation to achieve the integrated basin management and sustainability of Huai River Basin.