| Urban landscape lakes are small-medium sized shallow lakes, usually located in the city and the suburbs and mainly used for sightseeing,they have very important tourism value and environmental significance.However,in recent years due to the rapid development of industry and agriculture in the cities of china,a lot of industrial, agricultural and municipal sewage water flow into urban landscape lakes,the water in the urban landscape lakes have been polluted seriously and become eutrophication.In order to make urban landscape lakes regain vitality,it is not only necessary to take sewage treatment but also innovative hydraulic engineering technology for the lake water quality improvement are urgently required.Replacement by clean water from diversion has been demonstrated to be a great method of water environment management.The West Lake was choosed for this studying.This thesis mainly discussed the methods for West Lake quality improvement,the applications of 2-D hydrodynamic numerical simulation and 3-D hydrodynamic numerical simulation.Mathematical models were constructed respectively by using software Delft-3D and SMS to simulate the West Lake's hydrodynamic environment under various drainage operation conditions.Furthermore,the simualted results given by the models were compared.Various operation conditions of water diversion of Beili Lake as a demonstration project were simulated and calculated using software SMS,the optimal case is suggested.A 3-D mathematical model was constructed by using software Delft-3D to simulate the West Lake's hydrodynamic environment under the action of wind field,especially the the flow field under storm conditions were explored,the formative process of wind-driven current,the case of mixed current and critical wind speed are simulated.The result of the simulation in this thesis showed that the calculations agreed well with the measured data which proved the model is credible.The hydrodynamic environment results of simulation shown that the flow state of Xihu Lake's flow appeared to be inlet and outlet flow if the influences of wind field were ignored,the inlet and outlet flow which was drived by gravity mainly flew along the track of the inlets and outlets in the Xihu Lake.There was hardly any flow difference in vertical profile,most of Xihu Lake's flow velocity was in mm/s magnitude,only the flow velocity at Nan Lake inlet and Yingbo bridge's culvert reached to cm/s magnitude,the flow field mainly depended on the flow distribution of inlets and outlets.As a whole,the flow field could be well simulated by SMS and Delft-3D,the simulation given by software Delft-3D illustrated the stationary flow field was formed faster and the inlet and outlet flow were simulated better,but the flow velocity on some regions which was simulated by software SMS was bigger than the results given by software Delft-3D,for example the flow rate of culvert was more realistic.The results of numerical simulation under the wind field only showed that the steady wind-driven flow field was produced after two hours,there is a compensation current in the vertical direction, the surface layer flow direction was opposite the flow direction at bottom layer.The results of numerical simulation under the stormy wind conditions showed that there were circulation flow in the vertical and horizontal direction and strong longshore current along the SuDi.There should be a critical wind speed when the wind and water diversion affect at the same time,below which the flow feild is controlled by water flows inlet and outlet,as the wind speed increases,the current is graduately dominated by wind. |
