Objectives Land subsidence caused by long-term over-exploitation of groundwater is one of major problems in Beijing. Since the opening of the South-to-North Water Transfer Project, the problem of water shortage in Beijing has been greatly alleviated, and the pressure of land subsidence has been reduced to a certain extent.
Methods In order to analyze the development of land subsidence after the start of the South-to-North Water Transfer in Beijing, ascending and descending time-series interferometric synthetic aperture radar (InSAR) technique is used to monitor land subsidence in Beijing. First, the mean deformation velocity and cumulative deformation in line of sight in Beijing from January 2015 to December 2020 is obtained by the small baseline subset InSAR. Second, the robust least square fitting method is used to fuse the deformation results of the lifting rail, after that the global positioning system monitoring data are compared with the fusion results of lifting rail. Finally, the variation trend between the deformation results obtained by the robust least quadratic fitting and groundwater data is analyzed.
Results The deformation results show that the center of Beijing is basically stable and the deformation distribution is not uniform. The maximum ascending annual deformation velocity and the maximum ascending cumulative deformation amount reach -134 mm/a and -697 mm respectively. The maximum descending annual deformation velocity and the maximum descending cumulative deformation amount reach -135 mm/a and -734 mm respectively. And the fusion results obtained by the least square fitting method has reliability and accuracy.
Conclusions The subsidence rate in Beijing shows a decreasing trend with the gradual increase of groundwater level. In general, the middle route of South-to-North Water Transfer Project has alleviated the expansion trend of land subsidence in Beijing to a certain extent.
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