Studies On The Impact Of The Water Abstraction Along The Long River Reach Of Tong Cheng

The Tong Cheng Reach is the lower part of the Yangtze River, where the water abstraction is active and gives impact both on the location of the tidal limit and on that of the tidal current limit. This paper established a two-dimensional flow numerical model with the DSI method to discretize the shallow water equations and then the shooting method to solve the discretized equation group. Owing to the combined function of the runoff and the tide, the validation of the roughness is complicate and the result shows that it changes with the tide ebbing and flooding and is different in different area.The month averaged discharge data was utilized here to determine the characteristic discharge of the runoff and the data of the water abstraction along the Tong Cheng Reach is generalized provided that the amount of water abstraction in every sub reach keeps the same. The established numerical model is used to simulate the impact on the hydrodynamic environment in this reach, especially that on the locations of the tidal limit and the tidal current limit. The distributions of water level, velocity and discharge along this reach are calculated according to different amount of the water abstraction and their impacts on the locations of the tidal limit and the tidal current limit are analyzed. The result shows that if the discharge is very extreme small, water abstracting will lead to:1. Enlarge the flooding discharge while reduce the ebbing discharge2. Keep the net discharge the same to the total amount of the water abstraction3. Displace the locations of the tidal limit and the tidal current limit upward little in spring tide but great in neap tide.4. Enlarge the ebbing velocity in the upper reach and reduce in the down stream.5. Enlarge the flooding velocity and become a little great as the tide upstream and then reduce little by little as the tide upstream further.In a word, the impact of the water abstraction on the hydrodynamic environment of the Tong Cheng Reach is much greater in the spring tide than in the neap tide.