Empirical estimation of water conveyance flow loss in Liangji canal section of the South-to-North Water Transfer Eastern Route Project
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Abstract:
The South-to-North Water Transfer Project is the world's largest inter-basin water transfer project, and its main purpose is to alleviate the serious shortage of water resources in northern China. The main task is to reasonably determine the amount of water transfer, water transfer process and the scope of water transfer. Since its operation, the project has effectively alleviated the current situation of water shortage in northern China and promoted social and economic development. The accuracy of the water transfer efficiency affects the accuracy of the scheduling scheme, and the water transfer loss is an important index reflecting the water transfer efficiency. However, in the operation of the project, due to internal and external factors, there is a difference between the actual water transmission loss and the designed water transmission loss, so it is important to reasonably determine the water transmission loss to achieve accurate scheduling.The calculation accuracy of water conveyance loss has an important impact on the scheduling and configuration of water transfer projects. The traditional Kostiakov empirical formula is of certain value, which can not fully reflect the dynamic characteristics of the change of water transmission loss along the river when it is applied to the unlined river reaches with large geological changes. To overcome the limitations of the traditional Kostiakov empirical formula, it was improved with the integral method and the generalized reduced gradient method. The Liangji canal section of the eastern route of the South-to-North Water Transfer Project was taken as an example, and the field data from 2013 to 2019 were used to calibrate the parameters in the improved Kostiakov empirical formula. Considering that the Liangji canal section is susceptible to spring irrigation during the operation, the field data from 2019 to 2020 and 2020 to 2021 were used, which was significantly affected by spring irrigation to verify the improved Kostiakov empirical formula. To overcome the limitations of the traditional formula, the average relative error between the calculated results and the measured values before and after the empirical formula showed improvement and it varies greatly. From 2019 to 2020, the average relative error after improvement was reduced from 27.26% of the original formula to 7.9%, and from 11.72% to 6.84% in 2020-2021. The calculation error of Kostiakov's empirical formula method in 2019-2020 was relatively large because the Liangji canal section was greatly affected by spring irrigation and the water level was higher during the scheduling period. The calculation error was generally affected by spring irrigation from 2020 to 2021, and the calculation error was reduced. While the settlement result of the improved Kostiakov empirical formula was relatively stable, overcoming the limitation that the original formula was greatly affected by hydraulic factors in the application process, improving the calculation accuracy of water loss, and ensuring the reliability of the calculation results.The improved method overcomes the limitations of the original formula in the actual application of the water transmission loss as a value per unit length and the application range of the parameters in the original formula is not accurate enough, improves the calculation accuracy of the water transmission loss, and fully reflects the superiority of the dynamic change characteristics of the water transmission loss along the course. Improving the Kostiakov empirical formula improves the accuracy and reliability of calculations before the improvement. For the unlined and large differences in engineering geology of the water transmission line, the improved Kostiakov empirical formula method has good applicability, according to the specific characteristics of the water transmission trunk configuration parameters, can be generalized and applied to other canal sections of the water transfer project, and can further study the water transmission loss under different seasons and different water transfer scenarios of the typical canal section, explore the mechanism and factors of dynamic change of multi-scenario water transport, which is conducive to accurate water transfer and improve the efficiency of the project.
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