Winter dispatch strategies for Beijing-Shijiazhuang Section of the Middle Route of South-to-North Water Transfer Project
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Abstract:
The Middle Route of South-to-North Water Transfer Project is a great longdistance water transfer project that solves the problem of the uneven spatial distribution of water resources in China.It crosses three climatic zones.The ice conditions are complex and changeable in the winter.If the operation method is inappropriate,it is easy to cause ice damage,which may even block the main channel and cause water supply interruption.Ice clogging is the main ice damage in the Middle Route of SouthtoNorth Water Transfers Project during transferring water in the winter.The occurrence and development of ice clogging are related to hydraulic,thermal,and frozen factors.Therefore,the control of influencing factors to ice clogging,such as water depth and flow velocity,is vital to reduce the occurrence probability of ice clogging disaster and guarantee the water supply security for the project transferring water in the winter. The channel between Fenzhuang River Regulator and Nanjuma River Regulator was taken as a case study,since it has a greater risk of ice damage in the Middle Route of South-to-North Water Transfers Project.Firstly,based on the theories of hydrodynamics,thermodynamics,and ice hydraulics,a loosely coupled thermodynamic-hydraulic-ice mechanics ice evolution numerical model is established.The model is calibrated and verified with the observational data of the winter ice thickness from 2010 to 2011 and the measured water level and water temperature data in the winter of from 2014 to 2019.Secondly,the forming conditions and influencing factors of ice clogging were comprehensively considered,and different combinations of water depth,flow velocity,and temperature were setup according to the actual operation of the canal after the formal operation and historical temperature changes and ice conditions changes.Thirdly,based on the above research,the changes in ice conditions were quantitatively analyzed under different combination of scenarios,and ice clogging were found out under different water depths,flow rates,and water temperature changes.The indexes of flow velocity control and air temperature early warning were determined,and a scheduling strategy was proposed to ensure the safety of water transfer in the study canal in the winter.Finally,the combined scenarios of water depth,flow velocity,and temperature that were most likely to occur in ice clogging were used to verify the scheduling strategy. The results show that:the ice evolution numerical model meets the accuracy requirements for the simulation results of the ice condition related factors such as water level,water temperature,and ice cover thickness in the study canal,and can more accurately reflect the ice condition changes in the study canal in the winter and can be used in analyzing and researching on the characteristics of ice clogging changes and scheduling strategy in the winter.The ice clogging shows different variation characteristics under different hydraulic and thermal conditions.For example:when the water depth is less than 4.0 m,the high flow rate is prone to ice clogging and the thickness of ice clogging is small;when the water depth is equal or greater than 4.0 m,the low flow rate is prone to ice clogging and the thickness of ice clogging is large;when the negative accumulated temperature is equal or less than -150 ℃,the risk probability of ice clogging is high.The velocity control index and air temperature early warning index of water transfer in the winter is determined,and based on this,the scheduling strategy to ensure the safety of water supply in the winter of the Middle Route of South-to-North Water Transfer Project is put forward,which is normal water transfer when the negative accumulated temperature is greater than -150 ℃,the flow rate is maintained at 0.2 m/s when the negative accumulated temperature is less than -150 ℃ and the water depth is less than 4.0 m,and the flow rate is maintained at 0.6 m/s when the negative accumulated temperature is less than -150 ℃ and the water depth is equal and greater than 4.0 m;after the implementation of the winter scheduling strategy,the risk probability of ice clogging in the combination scenario most likely to occur decreased from 4.054% and 2.225% to 0.001%,respectively,which significantly reduced the probability of ice clogging and effectively guaranteed the water supply security in the ice period. Based on the construction of the ice evolution numerical model,the different combined working conditions are set up,the influence of hydraulic and thermal factors on ice condition changes are quantitatively analyzed,and a set of scheduling strategies that can significantly reduce the risk of ice jams are farmulated.The results provide certain references for the actual dispatch of the Middle Route of South-to-North Water Transfer Project in the winter,which is of great significance for ensuring the water supply security in the winter.
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