Monitoring, evaluation and prediction of ground deformation in the groundwater level drop area of Jiansanjiang area, Sanjiang plain

The amount of groundwater exploitation in the Sanjiang Plain has increased significantly with the rapid expansion of rice planting scale; in addition, the water level in 2021 was 5~12 m lower than that in 1980.Whether it causes ground deformation and land subsidence has become a social concern.In this study, the present situation, development trend and risk of ground deformation of groundwater depression cone in Jiansanjiang reclamation area of Sanjiang plain has been analyzed and studied by using second-order leveling method and analogy method.The results showed that the vertical deformation of the surface was generally small(maximum-18.00 mm, average change rate-4.6 mm/a)by the comparison of the continuous three-period measurement data of 50 second-class leveling points in the study area from the year 2019 to 2021.It has been predicted that the depth of the water level in the center of the groundwater level depression funnel can be reduced from 19.88 m in 2021 to about 25 m in 2040.With the dual lithologic structure of ' upper clay and lower sand ' in the study area, the strata drained by the groundwater level drop was located in the shallow upper part and the thickness was limited.The amount of land subsidence was still small; the degree of geological disaster development was weak and the risk was small.This study was not only reponse to social concerns, but also a foundation for further researches.