Hydraulic response of synchronous and intermittent closing of gates on Beijing-Shijiazhuang section in the Middle Route of the South-to-North Water Transfers Project
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Abstract:
The Middle Route of the South-to-North Water Transfers Project was structured with interconnected canal pools, divided by regulating gates. During emergency situations, the synchronous operation approach was commonly adopted to shift the channel's operation from a normal water level regime to an equal-volume operation by simultaneously closing gates. This swift change in channel flow dynamics due to the abrupt hydraulic transition proved highly effective in emergency management. However, research efforts at that time focused solely on continuous gate closures, neglecting the study of hydraulic response characteristics stemming from sequential intermittent gate closures in small steps. Exploring these responses was anticipated to provide guidance for emergency gate closure strategies to effectively prevent water levels from surpassing safety thresholds.Building on the synchronization principle, the study targeted the canal pools between the Cihe gate and the Shahebei gate within the Beijing-Shijiazhuang section of the Middle Route Project. Employing the Saint-Venant equations, a one-dimensional simulation model was constructed to simulate non-uniform transient flow in open channels. This model compared the hydraulic response characteristics between sequential intermittent gate closures and continuous closures, and it simulated various hydraulic responses under different intermittent closure patterns. The analysis aimed to assess the impacts of different closure initiation times, the frequency of closures, and the duration of closures on the peak water levels upstream of the gates and the duration of hydraulic oscillations.Simulation outcomes demonstrated that, with an equal total closure time, sequential intermittent gate closures considerably reduced peak water levels and hydraulic oscillation amplitudes compared to continuous closures. These closures substantially shortened the time required for stability, allowing the canal pools to rapidly regain stability. Peak water levels upstream of the gates initially declined and then increased as the closure initiation time was adjusted. Conversely, the stability duration of hydraulic oscillations decreased as the closure initiation time was altered. Initiating intermittent closures as precipitation waves approached downstream gates facilitated a reduction in water levels during the closure period, slowing the buildup of water resulting from gate closure. This action effectively minimized peak water levels upstream while significantly reducing the required duration for stability. The increased frequency of intermittent closures led to higher peak water levels upstream and reduced the rate of water level reduction. Yet, it notably reduced the duration of hydraulic oscillations. Despite slightly prolonging the stability time needed for upstream water levels, concentrating closures maximized the utilization of precipitation waves, achieving the most substantial reduction in upstream water levels. Both peak water levels and the duration of hydraulic oscillations initially decreased and then increased with longer closure durations. Closure duration directly influenced the duration of action for precipitation waves and gate closure speed. Optimal closure duration, slightly less than half of the total closure time, resulted in the highest reduction rates of peak water levels and shorter stability times.The hydraulic response characteristics of sequential intermittent gate closures were closely associated with water wave dynamics, primarily influenced by canal pool dimensions, depth, and flow velocity. Setting a single intermittent closure as precipitation waves approached downstream gates, with a duration slightly less than half of the total closure time, maximized water reduction and shortened stability time. These findings, derived from the Cihe gate to Shahebei gate canal segment, were deemed broadly applicable to other segments within the Middle Route Project.
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