Optimization and Effect of Inner Water Diversion and Distribution in the West Lake of Hangzhou

Abstract

West Lake is a world-famous landscape in Hangzhou, listed on the World Heritage list. In 2003, Hangzhou municipal government implemented the project of water diversion project, which diverted 400,000t/d water from Qiantang River into West Lake, thus, improved the overall water quality of West Lake significantly. However, due to the zigzag lakeshore line and the inlake embankment separation, the diverted water could not fully exchange among different regions of the lake, therefore, high concentration region of nutrient and cyanobacteria outbreak risk still existed in some lake bays. On the basis of spatial water quality analysis, this study put forward the internal water diversion and distribution scheme of the West Lake. Total phosphorus (TP) model with Environmental Fluid Dynamic Code (EFDC) was built to study the optimum water diversion quantity and distribution layout. According to the numerical result, the recommended water diversion scale was 70,000t/d, the layout of diversion and distribution recommended was 2 in 3 out . The internal water diversion and distribution project was complemented in October 2015. According to the comparison of water quality before and after the project construction, the improvement rates of TP, TN and Chlorophyll A were 26.0%, 8.9% and 25.9% respectively, and the dead water area was reduced from 35% to 13%, which greatly improved the water environment of the water diversion area.