Abstract
Lanzhou New District is the first and largest national-level new district in the Loess Plateau region of China. Large-scale land creation and rapid utilization of the land surface for construction has induced various magnitudes of land subsidence in the region, which is posing an increasing threat to the built environment and quality of life. In this study, the spatial and temporal evolution of surface subsidence in Lanzhou New District was assessed using Persistent Scatterer Interferometric Synthetic Aperture radar (PSInSAR) to process the ENVISAT SAR images from 2003–2010, and the Small Baseline Subset (SBAS) InSAR to process the Sentinel-1A images from 2015–2016. We found that the land subsidence exhibits distinct spatiotemporal patterns in the study region. The spatial pattern of land subsidence has evidently extended from the major urban zone to the land creation region. Significant subsidence of 0–55 mm/year was detected between 2015 and 2016 in the land creation and urbanization area where either zero or minor subsidence of 0–17.2 mm/year was recorded between 2003 and 2010. The change in the spatiotemporal pattern appears to be dominated mainly by the spatial heterogeneity of land creation and urban expansion. The spatial associations of subsidence suggest a clear geological control, in terms of the presence of compressible sedimentary deposits; however, subsidence and groundwater fluctuations are weakly correlated. We infer that the processes of land creation and rapid urban construction are responsible for determining subsidence over the region, and the local geological conditions, including lithology and the thickness of the compressible layer, control the magnitude of the subsidence process. However, anthropogenic activities, especially related to land creation, have more significant impacts on the detected subsidence than other factors. In addition, the higher collapsibility and compressibility of the loess deposits in the land creation region may be the underlying mechanism of macro-subsidence in Lanzhou New District. Our results provide a useful reference for land creation, urban planning and subsidence mitigation in the Loess Plateau region, where the large-scale process of bulldozing mountains and valley infilling to create level areas for city construction is either underway or forthcoming.
Highlights
Urbanization has become an irreversible global trend [1,2], and the limited supply of available land is an important impediment for rapid urbanization, especially in the case of cities in upland areas such as the Loess Plateau in China; examples are the cities of Lanzhou and Yan’an
We infer that the processes of land creation and rapid urban construction are responsible for determining subsidence over the region, and the local geological conditions, including lithology and the thickness of the compressible layer, control the magnitude of the subsidence process
48 pairs of interferograms images were generated for the persistent scatter interferometry (PSI) analysis (FigIunreth3ea)p, arensdenatcosthuedreyn, c4e8cpoaefirfiscioefntinotfe0r.f7e5rowgarasmusseidmtoagmesaiwntearien cgoennfeirdaetnecde fionrththeegePnSeIraatnioanlyosifs (Fhiigguhrequ3aa)li,taynddisapclaocheemreennctes.cFooerffitchieenStBoAfS0.c7a5lcwulaastiuosne,dtwtoomthariensthaoinldcsoonffi2d1e0ncme ianndthe18g0endearyastiwoneroef huigshedqufoarlittyhedissppaltaicaelmanedntste. mFoprotrhael bSBasAeSlincea,lcruelsapteiocnti,vtewlyo,otfo21d0ermivaensdur1f8a0ceddayisspwlaecreemuesnetd rates in line-of-sight (LOS) across the LZND
Summary
Urbanization has become an irreversible global trend [1,2], and the limited supply of available land is an important impediment for rapid urbanization, especially in the case of cities in upland areas such as the Loess Plateau in China; examples are the cities of Lanzhou and Yan’an. There is a severe shortage of available land for urban development in the region, and local governments have resorted to removing the tops of many high loess mountains to fill the adjacent valleys to create flat land for construction—a process of land creation. There is a strenuous debate underway regarding the environmental impacts of land creation [4,5], with the major concern that large-scale land creation may cause severe land subsidence This subsidence poses a major threat to urban construction with the possibility of substantial damage to the urban infrastructure, including buildings, railroads and highways, and increasing the risk of flooding and accelerated erosion along land fissures [6]
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