| Hangzhou Bay New Area lies in the Yuci Coastal plain.Influenced by several transgression and retreats during the period from the early Pleistocene to the Holocene,the water of the plain in various water bodies area is mainly salt water,and the fresh water bodies is only distributed in the Ⅱ confined aquifer.That’s to say,fresh water and salt water coexist in this area,but the fresh water resources in the area are extremely scarce.Hangzhou Bay New Area is a state-level economic and technological development area.The water demand increases gradually with the rapid development of social economy in the region,leading to the unreasonable mining of freshwater bodies enormously in the area.Resulting to some geological environmental problems such as land subsidence and freshwater salinization,besides,a regional landing funnel has formed in this area.Those results not only seriously threaten the safety of regional freshwater resources,but also hinder the development of local economic and social development.Taking the local government’s planning requirements,the population size and different emergency time of the area,the study has adopted nine emergency mining exploiting cases for three different emergency levels.Besides,the author has predicted and evaluated the negative effects of water capacity,water quality evolution and geological environment caused by groundwater exploitation employing different numerical models.And the researchresults indicates:(1)The type of groundwater hydrochemistry in the study area is affected by TDS.With the increase of TDS content in groundwater,the main anions in groundwater in this area evolve from HCO3-to Cl-,and the main cations evolve from Ca2+ and Mg2+ to Na+.Combined with hydrogeological conditions,hydrochemical evolution characteristics and the distribution characteristics of groundwater 2H,18O,3H,and get the result that the hydraulic connection of each aquifer is not closely related.The diving water is mainly supplemented by atmospheric precipitation and surface water,and drains mainly by evaporation.The confined water is not subject to modern water supply,mainly by lateral runoff;(2)The deep underground freshwater in the study area formed between 3.0～17.9ka.B.P,based on the dating of 3H and 14C,and detecting the salt water formation time was between 10.6～15.6ka.B.P(in late Pleistocene).It is speculated that the underground freshwater system is buried in the continental sedimentary water.In the later transgression(mainly the late-sea transgression),due to the direct infiltration in the upstream and cutting infiltration in the downstream,it will—shield"the original part of the good area.The result of sedimentation of fresh water enveloping-storage";since fresh water has no recharge source,indicating that there is no renewability;(3)According to the requirements of groundwater planning,considering the water demand of the population in the area,the control of water level and mining time,the author proposed different exploitation plan under different emergency levels.Based on hydrogeological data,the author established a three-dimensional geological structure model of the study area by GMS pre-processing.Then the MODFLOW,MT3DMS and SUB modules were used to assign and solve the parameters of groundwater flow,solute transport and ground subsidence,and gives prediction to the groundwater falling funnel,salty water interface evolution and land subsidence caused by mining in different emergency levels.Overall,the more amount of the mining and the deeper mining is the greater the impact is.The maximum depth of the water level for continuous mining for grades Ⅰ,Ⅱ,and Ⅲ is 38.5 meters,24 meters,and 18.5 meters,respectively,and the area of the landing funnel is 53.755km2,33.026km2,25.273km2,the width of salt water intrusion is 931,585m,413m,ground subsidence is up to 60～61mm,40～41mm,26～27mm,respectively.The recovery time of grade I water level is more than three years,and grade Ⅱ and have basically recovered in a year or so. |
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