Spatiotemporal Evolution Of Land Subsidence And Mechanism Discussion In The Yellow River Delta, China

Ground deformation measurements can be conducted through leveling as well as globalpositing system (GPS) and synthetic aperture radar (SAR)-based interferometry. Given its simpleoperation and high precision, leveling remains widely used as the traditional method formonitoring land subsidence in many cities and is also employed to calibrate or verify themeasurement accuracy of GPS or Interferometric SAR. In this paper, spatiotemporal evolution ofland subsidence in the Yellow River Delta is described quantitatively by the use of levelingduring2002–2008in contrast with subsidence information obtained by the use of topographicmaps and InSAR technology in existing studies. In view of the qualitative analysis of landsubsidence mechanism such as tectonic movement, the natural consolidation of sediment and sealevel rise et al. in the Yellow River Delta in previous researches, groundwater exploitation widelyregarded as the key factor for land subsidence has not been futher studied in the Yellow RiverDelta. Therefore, the spatial coupling relationship is analysed between the groundwaterdepression cones and land subsidence funnels in this paper. Integrated with hydrogeology,engineering geology, and soil mechanics theory, compression of geological engineering stratumsin different depth is estimated and then focused on the mechanism of land subsidence induced bydeep groundwater exploitation. This will be helpful for constructing the mathematic model ofland subsidence and for providing decision support for the sustainable development of theYellow River Delta efficient ecological economic zone.The results show that many parts of Guangrao County and Dongying District have been inoverexploitation with the large amplitude fluctuations of groundwater level. Several deepgroundwater depression cones were primarily centered in Guangrao County, Daozhuang, Shikou and Shengli Towns, where deep groundwater level decline rate is2–3m/years, and the depthranges from50to60m. There existed a significant linear positive correlation betweengroundwater level and elevation in the center of the deep groundwater depression cone, with thecorrelation coefficient of0.92. Obviously, overexploitation of deep groundwater is the mostessential factor to land subsidence. By estimate, the compression of the second and third clayeyaquitards is36–63mm and98–138mm, respectively. Aquitard compression with a thickness ofapproximately300m is two to four times as much as the corresponding aquifers. The thirdclayey compression layer (third aquitard) contributes approximately47.6–57.1%of the totalsubsidence and has become the primary contributing layer of subsidence. In addition, the impactof groundwater exploitation, engineering and construction, oil and gas exploitation, regionaltectonic movement, natural consolidation of sediment and sea level rise on land subsidence in theYellow River Delta has been analysed，respectively. Correspondingly, it is estimated that thecontribution ratio of the six factors to land subsidence is about28:4:2:3:2:1in Dongying Districtand Guangrao Country Where groundwater exploitation contributes70%of total subsidence.Finally, some control measures against land subsidence are proposed according to the harm inthe he Yellow River Delta.