Analysis Of Impacts Of Anthropogenic Causation On Land Subsidence In The Yellow River Delta

Due to the movement of modern tectonic plates, natural consolidation andcompaction of sediments, and frequent human activities, there are land subsidenceand sea level rising in the Yellow River Delta (YRD), which makes it an area ofserious land subsidence. Of all the factors, human activities are especially important.There are two kinds of human activities, which lead to the land subsidence in theYRD. One kind is the engineering construction, including high buildings,underground construction of cities, construction of sea walls, dams and habours, andso on. The other kind is the excessive extraction of underground fluids, including thatof the underground water, oil, gas, and so on.The present paper investigates three regions of land subsidence, which are mainlyinduced by urban construction, oil exploitation, and construction of sea walls anddams, respectively. For that purpose, we collect the leveling data in the years of1990and1999for Dongying District, topographical maps of the YRD with a scale of1:50000surveyed in1980and1995, and the borehole data in2002in Zone One of thecoastal embankment of GuDong oil zone.With use of the leveling data, the present work calculates the elevation changesbetween1990and1999in the Dongying District, produce digital elevation models(DEMs) with softwares of geographical information system (GIS), and conductspatial analysis. Using the topographical maps of the YRD surveyed in1980and1995,respectively, we produce DEMs, and analyze the spatial correspondence between theoil zones of GuDong and ShengLi Oil Field and regions of land subsidence. At last,making use of the borehole data, we compute the quantities of natural consolidationand compaction of sediments, and estimate the contribution of the construction of theGuDong sea wall to the land subsidence. 1. Urban construction. From1990to1999, all leveling points in DongyingDistrict showed land subsidence. The maximum land subsidence occurred around theShengLi Oil Field, where the urban constructions were much earlier and faster. At thesame time, the annual average subsidence rate during the two periods of from1956to1967and from1980to1995were obtained using the topographical maps of the YRDwith a scale of1:50000surveyed in1956,1967,1980and1995. The analysis furthersupports that the urban constructions induce significant land subsidence.2. Oil exploitation. In1980, though the coastal regions in GuDong Oil Fieldshowed land uplift, there were still large regions that had land subsidence. In1995,the region of land subsidence in GuDong Oil Field was larger than that in1980. InShengLi Oil Field, the oil exploitation was stronger, the area of land subsidence waslarger, and the accumulative land subsidence quantity was much bigger. The aboveresults indicate that oil exploitation could produce significant land subsidence.3. Construction of the GuDong sea wall. In regions around the GuDong seawall, the subsidence rate induced by the sea wall was about42.5mm/a when it wasbuilt up and decreased with time. From2000to2007, the subsidence rate induced bythe sea wall was about7.4mm/a, comparable with8.0mm/a induced by all otherfactors; the total subsidence rate was about15.4mm/a. The results approve that theconstruction of sea wall could result in strong land subsidence.At last, we analyze the characteristics of the three kinds of human activities,which lead to land subsidence in the YRD as shown above, including their influenceregions, time and strength of operation.