Feasibility and Optimization of Hydrodynamic Methods to Improve Water Quality in Pinqing Lake

In order to enhance the quality and hydrodynamic conditions of the lagoon water, and to improve the ecological environmental impacts on the coastal lagoon due to weak tidal hydrodynamics, natural conditions restriction and frequent human activities, the second largest lagoon in Asia, Pinqing Lake was studied using a hydrodynamic water quality model based on unstructured grids of the surrounding waters. To develop cost effective approaches for the ecological restoration and development of Pinqing Lake, the hydrodynamic and water quality impacts between the current situation of Pinqing Lake and the 17 modification conditions were analyzed. The results show that the removement of 50% of the breakwater near or offshore (Case 2 and Case 3) or 25% of the sand tongue and part of the crumbling angle (Case 9) can effectively improve the hydrodynamics and water quality of Pinqing Lake at relatively low cost, increase the overall flow rate and tidal volume by 10.42%~32.25% and 1.68%~2.48%, reduce the renewal time of the water body by 21.44%~23.13%, reduce TN and TP concentrations by 9.0%~10.7% and 11.2%~13%. Case 2, Case 3 and Case 9 have their own advantages, but they are not suitable for joint implementation. Therefore, the water dynamics and water quality of Pinqing Lake could be improved by the removement of 50% of the breakwater or by synchronizing the removement of 25% of the sand tongue and a portion of the avalanche angle, or a similar effect could be achieved by a permeable retrofit.