Study on the effect of water level at different time scales on the calculation accuracy of annual storage variation of shallow groundwater

Abstract: 【Objective】In order to explore the influence of water levels at different time scales on the calculation accuracy of regional shallow groundwater storage variations, including moment, daily average, monthly average, and annual average water levels, 【Methods】the grid method and Thiessen polygon method were used to compare the difference of groundwater storage variations calculated by various scales water levels in Handan Plain in 2019. 【Results】The research shows that using water level at the same time scale, the storage variations calculated by the grid method and Thiessen polygon method are relatively close with the maximum difference of 11.4 million cubic meters. When using water levels at different time scales, both methods show the greatest deviation between the monthly average water levels and the hourly water levels, with a difference of 72.7 million cubic meters for the grid method and 61.1 million cubic meters for the Thiessen polygon method. And the deviation is random. Although the difference of calculating results between the annual average water levels and hourly water levels is small with a difference of 1.5 million cubic meters, there is also randomness in the degree of approximation. For the grid method, the storage variations calculated using the annual average levels, with a maximum difference of 1.1 million cubic meters. For water levels at other scales, the accuracy of the grid method will increase as the grid size decreases. when the grid size is smaller than 1 km, the accuracy of the grid method is higher than that of the Thiessen polygon method. However, when using the grid of Thiessen polygon, or when the size of regular grid is close to the average area of the Thiessen polygon partition, the accuracy of the Thiessen polygon method is higher. 【Conclusion】The research can provide theoretical and methodological support for the rational use of water levels at different time scales, which can improve the accuracy of calculating storage variation. Finally, it will help accurately evaluate the effect of groundwater overexploitation control.