Hanfeng Pre-reservoir Commissioning Time Variation Feature of the Hydrology and Water Quality in Three Gorges Reservoir

Abstract

Hanfeng Pre-reservoir is very rare in the world which is specially designed to reduce the impact of Fluctuating Zone, and it is formed in Hanfeng Lake of Three Gorges reservoir. The Hanfeng Pre-reservoir has many special hydrological characteristics and ecological environment features based on its unique "pre-reservoir" control mode, the wide seasonal wetland of Fluctuating Zone, the huge life pollution and agricultural pollution, and the pressure of huge city and excessive population. HanFeng Lake has a variety of morphological features such as lakes, rivers, and other backwater bay, for the effect of water level regulation in Three Gorges, since the successful commissioning of the Hanfeng Lake pre-dam system in 2015. The change of Hanfeng Lake hydrology and water quality during the commissioning was divided into four periods by combining Hydrological and Morphological Variation characteristics with Water quality indicators time clustering analysis:May to August as T1 (river period); January, March and November to December as T2 (lake period); February, April and September as T3 (water level fluctuation period); October as T4 (algal blooms period) in 2015. Principal component analysis and stepwise regression analysis showed that Eutrophication of Hanfeng Lake was dominated by different dominant components at different times and the water quality index factor which has a significant effect on the Chl-a was also different. Cumulative contribution rates of principal components were 82.93%, 77.61%, 78.32%, 88.40% for each period, respectively. The main water quality indicators of T1 (river period) were DP, TP, SD, pH and the significant influencing index of Chl-a was PC2, so Chl-a was mainly affected by water nitrogen content. The main water quality indicators of T2 (lake period) were TN, DN, DP, TP, NO3--N and the significant influencing index of Chl-a was PC1, so Chl-a was mainly affected by water eutrophication including nitrogen and phosphorus nutrient status. The main water quality indicators of T3 (water level fluctuation period) were SD, NH4+-N, DN, T and the significant influencing index of Chl-a was PC3. so Chl-a was mainly affected by water level fluctuation. The main water quality indicators of T4 (algal blooms period) were TN, DN, DO, NH4+-N, pH, permanganate index, H, NO3--N and the significant influencing index of Chl-a was PC3. so Chl-a was mainly affected by flow rate and hydrodynamic conditions. As mentioned in the review, the frequent and significant water level changes during the commissioning of Hanfeng Lake were the important factors influencing the change of hydrological and water quality characteristics.