Author(s): Yun Lang; Yingping Zang; Yubao Wo; Lingling Wang
Linked Author(s): Lingling Wang
Keywords: Sanchahe River Gate (SRG); Numerical simulation; Flow pattern passing the gates; River regime; Guide walls
Abstract: The Nanjing Sanchahe River Gate (SRG) locates at the conjunction of the Qinhuai River and the Yangtze River. It can raise the water level in the river reach from Wudingmen to Sanchahe, and then improve the water quality and urban river landscape of Nanjing. Since its completion in 2005, several problems have emerged during normal operations, for instance, the vibration and noise of the sluice gates, the large-scale recirculation zone around the left sluice gate and the deflective flow pattern that affects the discharge capacity of SRG in flood season. Meanwhile, the asymmetric inflow has caused left erosion and right sedimentation in the riverbed. Aiming at these problems, a two dimensional depth-averaged mathematic model is developed in the present research. The computational domain consists of part of the Yangtze River (where there is a combining flow), the Qinhuai River (about 1000 meters) and SRG. An orthogonal curvilinear grid with quadrilateral elements is adopted and the grid number is 182×92. Finite Difference Method for the spatial discretization on staggered grids is used to solve the shallow water equations. Compared to the experimental data, the numerical model is able to faithfully predict the distribution of water level and velocity in the Qinhuai River. While the sluice gates are opened in flood season and the inflow discharge of the Qinhuai River reaches the design discharge of 600 m³/s (the largest inflow discharge) which should undoubtedly lead to asymmetric flow pattern passing the gates, several typical operating conditions with different combinations of the water level and discharge of the Yangtze River were replicated. The results suggest that the operating condition with lower water level and smaller discharge of the Yangtze River should cause the worst flow pattern passing the gates. By then, the large water head between the two sluice gates may threaten the security and stability of the middle-pier at SRG. In general, the flow pattern passing the gates is affected by many factors, such as the water level and discharge of the Yangtze River, the inflow discharge of the Qinhuai River, the river regime and topography in the upstream and downstream of SRG. Under the most unfavorable operating condition, a terrain modification scheme was employed in the present research. It is found that removing the wharf, cofferdams and other water blocking facilities in the upstream of the Qinhuai River could not improve the flow pattern passing the gates, and the large-scale recirculation zone around the left sluice gate still existed. Another scheme to improve the flow pattern passing the gates was to build a guide wall in the upper reach of SRG. Designing the length and the angle down from the river center line, a guide wall, 50 meters away from SRG, as long as the middle-pier at SRG, 5-degree angle down from the river center line was set up. With this guide wall, the flow pattern passing the gates could be improved significantly, and the large-scale recirculation zone around the left sluice gate would be largely reduced.
Year: 2013