Study On Numerical Simulation Of Land Subsidence And Its Application

Overexploitation of groundwater unbalances groundwater in water quantity,salinity and soil dynamics. New balance will be achieved through a series ofresponses from aquifer system including changes of water levels, water quantity,water quality and water table characteristics. Such changes may result in catastrophicgeologic transformations, among which land subsidence is typical and universal.Based on observed data from the study area of Tanggu district in Tianjin, a BP neuralnetwork model is established to predict possible land subsidence due to exploitationof groundwater. Advices on land subsidence control are provided.Spatial cluster and standard deviation analysis are employed during theoptimization of land subsidence monitoring network. Annual volumetric extractionfrom different confined aquifer in both urban and rural area is introduced as modelinput, while land subsidence rate of optimized monitoring points is defined as modeloutput. The modeling results are proofed to be statistically significant whichguarantees the explanation ability of the model, and the contour map of model outputsfit reasonably well with the spatial characteristics of land subsidence in the study area.According to model estimation, the average background land subsidence rate ofTanggu district is 9.47 mm/ a. Land subsidence of monitoring points respondsbasically the same to variation of extraction from certain aquifer. The significance ofcontribution of aquifers to land subsidence descends in order of the Ⅳ,Ⅲ,Ⅴ,Ⅱconfined aquifer. Land subsidence trend to deteriorate with the increase in overallexploitation, which plays a more important part in land subsidence process than theplane allocation of exploitation. When hypothetic yield of groundwater meets8. 46× 10~6m~3/a, 1 .69× 10~7m~3/a and 2 .70× 10~7/m~3a, the corresponding estimatedaverage land subsidence rate is 16.8 mm/ a, 30.9 mm/ a and 45.7 mm/ a respectively.In order to control the fate of land subsidence and make good use of therenew-ability of confined groundwater, suggestions such as: compacting overallextraction, exploitation reallocation among aquifers, strengthening hydrogeologicsurvey, saving water and searching for substitute sources are concluded.