Study On A Long Sequence Of Groundwater Level Dynamic In Tianjin

Tianjin,which is situated along the downstream of the Hai River,is the largest coastal open city in Northern China.The groundwater in Tianjin is of great significance for the socio-economic development.However,years of over exploitation of groundwater takes a large amount of groundwater storage,which caused lots of environmental geological problems such as the sustained decline of groundwater table and ground subsidence,thus,seriously affected the sustainable development of the economy and society.Study on the dynamic variation of groundwater level in Tianjin can make it understood that how the groundwater level in different aquifers changes and what is the quantitative relationship between groundwater exploitation and groundwater level.It also can be the basis of decision making for rational exploitation and utilization of deep groundwater resources.On the basis of understanding the history and development of groundwater level dynamic simulation and groundwater level numerical simulation at home and abroad,the author built the groundwater dynamic and numerical model with the long-term meteorological and water level information in Tianjin to analyze the dynamic change and predict the variation trend of the groundwater level.Conclusions are as follows:The results of time sequence model show that: the groundwater level is generally declining from the year 1980 to now.First,the change of water level in the second layer is gentle;second,the groundwater level of the third and fourth layers decreases the fastest in the early stage of the simulation period and slowly after 2000.The declining speed of groundwater level in each observation wells is past 1m/year before 2000,the declining speed of water level in well xiqing11 even reached 1.96m/year.However,the declining speed of water level is less than 1m/year after 2000 in each well of the third layer,and it even rebounds in well hangu1.The declining speed is less than 0.6m/year in each well of the forth layer;third,through the forecasting model,the water level of the fourth layer will fall continually and the fall speed is fast.The results of the numerical model show that: first,the average fall rate of the groundwater level of the second layer is less than that of the third and the fourth layer during the simulation period: the rate of the second layer is less than 0.5m/year and that of the third and the fourth layer is about 0.9m/year,even reaches 1.65m/year;second,the exploitation of the second layer is of a larger amount while the drop of water level is smaller than the third and fourth layer and the reason is that the water in the second layer has a close contact with the unconfined aquifer which makes it get much more recharge and difficult to drop;third,the author also simulated the ground subsidence in Tianjin,and got the result that subsidence in different degree will take place under the effect of water level decline and aquifer lithology,in addition,the subsidence of the second and the third layer is bigger;fourth,the prediction of the water level trend shows that the water level changes gentle,and water level declines no more in most areas.The results above can provide reference for the groundwater level control in the study area and provide the basis for the utilization of groundwater resources.