Self balancing characteristics and disturbance threshold of open channel water diversion projects
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Abstract:
Open channel water diversion project is important to solve the regional water shortage problems. However, due to the changes in water supply demand along the line and frequent changes in upstream flow during the operation of the project, the water conditions along the line are complex and variable, which can result in fluctuations in the channel water level and affect the stability of the system. As a controlled system with self balancing ability, the open channel water diversion project can withstand a certain degree of external disturbance through its own self balancing ability when not under control, while meeting the conditions of safe operation of the project. Studying the safety threshold and variation law of this disturbance is of great significance for guiding the control gates. A one-dimensional unsteady hydrodynamic model of coupled control gates was developed to simulate potential disturbance scenarios that may arise during engineering operations. The model calculated the changes in water levels in front of the gate under various disturbance intensities. Based on the safety constraints for water levels, we determined the disturbance threshold that the water conveyance system can tolerate under different working conditions. A fast calculation formula was constructed based on the relationship between upstream flow rate, regulating gate opening, and safety disturbance threshold calculation results. It can be endured under different initial working conditions, providing a discrimination basis for whether to enable regulating gate control. The study focuses on four control gates from the inlet cut-off gate of Diaohe aqueduct to the inverted siphon outlet of Qihe in the middle route of the South-to-North Water Transfers Project , as well as the upstream and downstream channels of each control gate. Different initial operating conditions are set for calculation. The results show that the self balancing ability mainly depends on the overcurrent characteristics of the regulating gate. When both the downstream water level and the position of the regulating gate remain unchanged, the disturbance threshold decreases as the upstream boundary flow increases, indicating a reduction in self balancing capability. In contrast, when the upstream flow boundary and downstream water level are held constant, an increase in the gate opening leads to a higher disturbance threshold, thereby enhancing the self balancing ability. The average error between the constructed fast calculation formula and the model calculation results is less than 0.7 m3/s. The self balancing ability and safety disturbance threshold of the canal pool are closely related to the overcurrent characteristics of the regulating gate, which is mainly influenced by the water level difference before and after the gate, as well as the gate opening. The larger the gate opening and the initial water level difference, the higher the safety disturbance threshold, and the greater the disturbance amount that the canal pool can withstand. This study is applicable to other canal sections of the South-to-North Water Transfers Project and can provide support for scheduling decisions in water transfer projects.
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