Study On Quaternary Hydrogeology Conditions In Northern Zhoushan Sea Area

Zhoushan Islands, China’s largest coastal islands, located in eastern HangzhouBay, south-eastern Yangtze estuary, north-western East China Sea continental shelf, istourism, port and fishing city composed of many islands. Shengsi Islands is located inthe northern Zhoushan sea area. But due to limitations of natural conditions and theexisting technical conditions, islands far away from the mainland, difficult waterdiversion and water transfer in land, too high seawater desalination cost, the islandfresh water resources are scarce on the islands, an important factor in restricting localeconomic and social development. To, the discovery of the submarine freshwaterresources point to a new directions for solving the condition of fresh water shortages.From the1980s and1990s, the related units, in northern Zhoushan sea area, havelaunched investigations and feasibility studies of submarine freshwater resources,which included hydrogeology geophysical, hydrogeological drilling, pumping test.They provide a certain amount of paleoenvironmental evolution, the basis ofstratigraphy and hydrogeology for finding submarine freshwater resources. At present,a breakthrough that fresh water has been made,however, the hydrogeology surveydegree is still low and the control level is relatively poor, the accurate structure ofsubmarine Quaternary stratigraphy, ancient river distribution, aquifer structure,storage regularity of submarine of submarine groundwater are not been mastered, theideal freshwater aquifer is not been found and the work do not achieve the desiredresults, so it is still necessary to carry out more in the workload of furtherinvestigation research work.To solve freshwater shortage and the above problems in shengsi, in2009,Qingdao institute of marine geology carried out the program of ‘The Survey andEvaluation of Submarine Freshwater Resources in Zhoushan, Zhejiang’. According tothe2009high-resolution single-channel seismic data and previous research,preliminary results has been obtained: Basic identification of Quaternary stratigraphystructure in northern Zhoushan sea area, stratigraphic thickness variation, distributionof paleochanne in the early and mid-late Early Pleistocene;A comparative analysis ofregional hydrogeological conditions work, in northern Zhoushan sea area and Shanghai, is basically completed. There are five confined aquifers in northernZhoushan sea area; the fourth confined aquifer, which contrasts to the fourth confinedaquifer in Shanghai, is the main study object; The rich area of submarine freshwaterresource, which is mainly distributed in the study area to remove the islands and thenearby region, is the west of northern north Zhoushan sea which is the north of theQiantang River mouth, the north of Shengsi Islands and Well ShengsiⅡandnortheastern of Shengsi sea area, where the thickness of the fourth confined aquifer ofterrestrial formation is from30to50meter. The deposition depression, located inwestern the Rugged Islands and Qushan Island, shoud also be as a focus for lookingfor the rich area of submarine freshwater.Because of little experience and the limitation of existing technologies andmeans, in northern Zhoushan sea area, there is part of the single-channel seismicsurveys，marine geology holes and the hydro-geological holes, but entire Quaternarystudy (especially Early and Middle Pleistocene) is difficult to proceed, which is thesedimentary sequence, depositional environment, stratigraphic spatial distribution, thestructure of the aquifer system and the distribution of palaeochannel in the period.And the contrast of the strata and aquifer with adjacent land areas is still very weak,its understanding are to be further deepened.