Assessing And Optimizing Water Diversion Schemes For The Demonstration Area Of Gonghu In Taihu Lake Based On Experimentation And Modelling

Eutrophication in lakes is still severe.Taihu Lake,the water source of the important developed area,blue-green algal blooms frequently happened.Beginning at 2002,the diversion from Yangtze River to Taihu Lake project,which transfers water from Yangtze River to Gonghu Lake through Wangyu River,was able to efficiently avoid deteriorating the environment of Taihu Lake.Therefore,the diversion of clean water is an imortant method to improve the environment of Taihu Lake.This research bearing the consideration of the existed ecological remediation studied the optimization of the diversion of clean water,which locates in the demonstrating district for returning fish back to lake in Gonghu Bay.So that an excellent water environment in the demonstrating district can be established and simultaneously more clean water can be introduced to Taihu Lake.In this study,a proportional physical model in accordance with the demonstrating area was established and a research method that combines both on-site experiment and numerical simulation was utilized to evaluate the optimizing results of different diversion modes therefore to provide suggestions for the hydrodynamic diversion methods in the demonstrating area.In June 2014,diversipn experiments were conducted on site to the physical model,where multiple diversion methods were simulated,including diversion from Xuxian harbor,diversion from Dianji harbor and vertically inflowing from Xuxian harbor.Cross section flow field was measured using current meter and this is verified using tracing experiment.The result shows that the diversion effect is not good if the flow is small.On the other hand,diversion by large scale of flow in short time works efficiently for diluting pollution.It is suggested to choose the vertical inflow from Xuxian Harbor as the optimal method.Moreover,diversion from Dianji harbor improves the activity of the water body on the east of the Lake.Based on the primary election among the optimized methods according to diversion experiment results,an ELCOM 3-D hydrodynamic mathematical model was established,which offers a decision making supporting tool for forecast and adjust.Eight different diversion methods were constructed basing on inlet location and inflow scale at the same time when flow field changing condition was simulated according to different situations.An assessing system was established based upon hydrodynamic characteristic index.So that it would be possible to comprehensively assessing the diversion methods and suggestions for diversion in demonstrating area are as following.First,if one single inlet were expected then the vertical inflow from Xuxian harbor should take advantage.Large-scale diversion could efficiently speed up the velocity of water,quickly improve water quality in the whole area and minimize the area of stagnant water.Hence,a higher replacement rate of water body could be achieved.To decide the practical diversion route,more consideration should be given to optimize the arrangement of inlets in Xuxian harbor.Secondly,if multiple inlets were expected then it is suggested to choose vertical inflow in Xuxian harbor and Dianji harbor inlet.Meanwhile,the inflow scale in Dianji harbor should be enlarged.Under this situation,the velocity of water reaches the maximum,the activity of water body is relatively high and the flow field distributes the most uniformly.So that it could be avoided where partially over-fast water harms the growth of aquatic plants.Hence,it is the best diversion method,which integrates with ecological restoration.Therefore,when deciding the diversion method for the demonstrating area in practice,election between different diversion methods should consist with the relevant recovery purpose.In the purpose of fast diluting pollution and improving water quality in the demonstrating area,the diversion method of vertical inflow in Xuxian harbor that utilizes single inlet and large-scale inflow should take precedence.On the other hand,when it aims at using the aquatic plants to recover the demonstrating area and constructing the clean water regeneration engineering,the diversion method of vertical inflow from Xuxian harbor and Dianji harbor should take advantage.