Research On Hydrodynamic Analysis And Related Issues Of Rriver Network In Jiaxing City

In recent years,China has witnessed rapid urbanization and rapid economic growth.But the water environment problems are also more prominent.Jiaxing is facing the same problems.In order to improve the water quality in urban river network,Jiaxing analyses the hydrodynamic of the river network and sthdies engineering measures to enhance hydrodynamic force and other related issues.It is not only necessary but also has the practical application value and certain promotion value.In this paper,the Saint-Venant equations are used to establish mathematical model of river network flow of the Jiaxing city,discrete the equations in time and space by using the Preissmann four-point weighted implicit scheme,and use double relaxation iterative method to solve the unsteady flow of river network.The model is calibrated and verified by field observation data.The established mathematical model is used to study the followings:(1)Under low water level,normal water level and high water level conditions,the hydrodynamic force under a variety of running water scheme for pump gate operation is analyzed based on the average velocity and hysteresis rate of the river network,and the running water schemes are optimized.Under the low water level condition,in the operation which is planed for the whole river network,the river channels of Zhenheligang,Yuehe,Qinghe,Xinchengtang and Yinjiaqiaogang in the urban area are lack of hydrodynamic force.The use of the sub-area dispatching scheme can effectively improve the hydrodynamic force.Under the normal water level condition,the hydrodynamic force of the river network is generally good.But the partial rivers in the urban area are still lack of hydrodynamic force.Under the high water level condition,the hydrodynamic force of the river network is generally good.Opening the Changshuitang north gate partially can improve the hydrodynamic force to some extent.(2)Aiming at the problems of insufficient hydrodynamic force of some river channels in the city,insufficient water diversion flow at low water level,and the influence of tributaries on the water quality of Nanhu during the water diversion process,this paper puts forward four engineering measures to improve the effect of running water in river network.After Pinghutang hub transforms into a two-way pumping station,the hydrodynamic power of the river network is effectively improved unde the low water lever condition.The construction of Yanjinggang pump station can increase the hydrodynamic force of Xinchengtang and Yinjiaqiaogang.The construction of Zhenheligang pump station can increase the velocity sharply.The construction of Nanhu south gate and the west gate can effectively discourage the water of poor quality from flowing into Nanhu.(3)Two emergency water dispatch schemes of the water flow from the main channel on the southwest side to the outlet on the northeast side and the water flow from Changshuitang to the Haiyantang are mainly studied.Under the low water level condition,the flow in and out of Nanhu is relatively small,the effect of the disapatching is unsatisfactory.Under the normal and high water level coditions,the former scheme generates large flow in and out of Nanhu and water can change quickly,but the power utilization is low and the scheme is complicated.The latter scheme results in high power utilization and the scheme is simple,but the flow in and out of Nanhu is relatively small,which will make negative impact on the water environment of the Guanjinggang wetland.