Study On Water Transfer Scheme Of Dishui Lake Water System In Lingang New City

Dishui Lake, located in the centre of Lingang New Town, is an artificial lake of a large scale with an area of 5.6 km² . As the landmark of this new city, Dishui Lake has a diameter of about 2.7 kilometers, an average depth of 3.7m, a maximum depth of 6.2m, and a capacity of 1200-1600 million m . The water environment quality of Dishui lake is critical for the social and economic development of Lingang New City.The flow control structures separate Dishui Lake water system from the river network to the east of Huangpu River, which made it an independent one. Besides, as Dishui Lake lies near the sea, which made it able to achieve water replacement in a short time, water conservancy is an important method to ameliorate the water quality of this water system, based on which, the research of water conservancy of Dishui Lake water system was made. The achievements are shown as follows:(1)Based on the 1D-2D coupling model of Huangpu River, a new part about Dishui Lake system is added, and the river network model in plain area with the character of Lake-river network is also set up, which avoids the problem that the previous research on Dishui Lake only makes an isolated lake model based on unreasonable flux boundary conditions. With this modified model, it becomes possible to make full consideration on the water transfer of the whole water system including both rivers and lake.(2)Based on the developed hydrodynamics model, the simulation of wind-driven flow with wind currents of NW6m/s and SE4m/s is made. It suggests the flow driven by wind is obvious: the average velocity of the water system is 0.04～0.07m/s, and the hydrodynamic conditions brought by NW6m/s is much better than that by SE4m/s. However, the water velocity varied in different parts of the lake, and in some area in shore and in the center of the lake the water velocity is quite low. Therefore, water conservancy is needed to reduce the area with low water velocity, especially in some area in shore.(3) Two kinds of water conservancy, nonsynchronous and synchronous discharge-diversion, were simulated to analyze different combination of discharge-diversion ports for the present water system. According to the amelioration effects of flowing field and water quality, the optimized schedules were provided.The amelioration effect of flowing field and water quality for nonsynchronous diversion for 20h is equal to that of synchronous discharge-diversion for 96h, which means that the concentration of COD_Mn was reduced from 10mg/Lto 8mg/L, while the concentration of chlorophyll was reduced from 15mg/m³ to 11mg/m³. However, the precondition for synchronous discharge-diversion is that a water gate should be set up to guide the inflow into the lake instead of discharged directly through the ring-river.As there is no water gate across the ring-river and vertical-river, the application of synchronous conservancy would brought flow short circuit, the suggestion was made that nonsynchronous conservancy is more suitable at present.In future, after the water gates were constructed across the river, the inflow could be guided to avoid the short circuit to perform synchronous conservancy. For both nonsynchronous and synchronous conservancies, a appropriate schedule of water gates control would be helpful to ameliorate the flowing field in the river, especially for some area new the ports.(4) With the development of Lingang New City, the initial rain water would be an important problem. Aiming at the planned water system, the measures to protect the Dishui Lake from pollution and quick discharge of initial rain water were researched. The suggestion of setting up gates across all vertical rivers was made to separate the polluted river water and achieve quick discharge of polluted water.The simulation showed that provided that Chuhai Gate were open, it would cost about 17～19h for this planning water system to reduce water level from 3.3m to 1.5m, which demonstrated its ability to make quick discharge.Generally, based on this complex river-lake tiding water system, the research on the relationship between water flow and flux boundary conditions are made, and the measures to protect Dishui Lake from initial rain water and optimized schedule for water conservancy were provided.Finally, several suggestions on subsequent research were provided.