MODFLOW-based Numerical Simulation Of Groundwater Flow In Xigaze City Of Tibet,China

For a long time,groundwater was the only water supply source in the urban area of Xigaze,Tibet.In recent years,with the development of local tourism and population growth,the amount of groundwater extraction has also increased.At the same time,a series of wetland degradation problems have occurred in the surrounding areas of the urban area.According to the urban plan of Shigatse City,the groundwater extraction volume will reach 19 million m~3 by 2030.In order to influence the expansion of groundwater in the study area that may be caused by the expansion of exploitation,MODFLOW has been used to establish a numerical model of groundwater flow in the study area.In the process of actual modeling based on the data of the study area,using the 36th(January 2015-December 2017)high score No.2 remote sensing data,27 points were evenly arranged in the surface water body,and according to the Shigatse on the Nianchu River The hydrological station performs fitting analysis and assigns the inverted water level to the model as a given head boundary.The boundary of the piedmont is divided into 6 sections using water resources zoning,and then the specific size of the given flow is determined using the rainfall and water catchment area in combination with the water level of the borehole in the front of the mountain;The water level-flow response curve of the automatic monitoring well is used to obtain the rainfall infiltration coefficient,and the Tyson polygon is used to partition.According to the established numerical model of groundwater flow in Shigatse.The actual water level of observation wells in the study area was used to correct and verify the model,and a sensitivity analysis of the model parameters was carried out.It was found that the permeability coefficient was the most sensitive to the simulation results.Three mining scenarios were further set up,and the calibrated numerical model was used to predict the groundwater flow field under the condition of gradually expanding groundwater exploitation in the study area.The results showed that the Nanjiao Water Plant was closed and the Beijiao Water Plant was used to draw water.After the water intake was gradually increased from 15.16 million m~3 to 18.76 million m~3,the replenishment of groundwater by the Zebra River dropped sharply from 18.653 million m~3 to 6.686 million m~3,and at the same time,the Yajiang and Nianchu rivers were recharged by the original groundwater It was converted to surface water to recharge groundwater,and the total recharge amount was also reduced from 26.474 million m~3 to 22.024 million m~3.According to the actual needs of Shigatse City,it is proposed that the construction should meet the standby water source.On the one hand,the amount of groundwater needs to be reduced by mining surface water to reduce the damage to the ecological environment.On the other hand,water supply from multiple sources can reduce the pollution of groundwater.The impact of extreme conditions on people 's lives.