Study On Assessment And Sustainable Utilization Of Groundwater Resources In Yanji City

With the rapid development of city and living standards, the demand of water isincreasing. So the status of groundwater in water exploitation is rising, and thesustainable utilization of groundwater becomes an important guarantee of urbandevelopment. The main water source of YanJi city is Wudaohe and Yanhe reservoirs.But for the increasing demand of water and the capacity limitation of reservoirs,groundwater becomes essential spare resources for urban water supply. So the studyon resources evaluation and sustainable utilization of groundwater in Yanji city is ofsignificant importance.This paper chooses the planned urban area of Yanji city as the study area, whichcontains the whole Yanji basin. The area of the study area is87.81km2, and itincludes the most part of Buerhatong river and Yanji and Chaoyang rivers which arethe tributaries of Buerhatong river. The target aquifer can be generalized intoquaternary unconsolidated rock pore water and the cretaceous clastic rock pore fissurewater. The former is unconfined water, and the latter is confined water. Between themis the aquitard made of upper cretaceous Longjing group of powder sandstone andmudstone.Unconsolidated rock pore water locates at the discharge area of the groundwaterflow system. The main recharge of it is precipitation infiltration and lateral flow. Themain discharge of it is evaporation, lateral flow and exploitation. The main rechargeof cretaceous clastic rock pore fissure water is leakage and lateral flow and the maindischarge of it is lateral flow, springs and artificial extraction.According to the result of2012Yanji municipal hydrogeologic survey ofgeologic survey assessment of Yanlongtu area and the corresponding meteorologicalhydrological data, groundwater budget of the study area has been calculated. Theresult shows that the total amount of groundwater recharge is1001.38×104m3/a in2012,and that the total amount of groundwater recharge is844.81×104m3/a.Groundwater is in a state of positive balance. Based on the calculation of waterbalance we can easily get the allowable withdrawal is547.48×104m3/a. A groundwater numerical model was established by Visual MODFLOW. Basedon identification and verification, fitting points which error less than1m accountedfor92.7%and87.03%respectively. Water head fitting of the model is in goodcondition. The water dynamic of the study area could be simulate and predict on it.On the basic of current situation and future demand of water supply in Yanji City,the groundwater level of the study area was simulated and predicted in differentmining conditions. It was shown that the current mine layout is not reasonable, on thecondition of annual average rainfall, current pumping is greater than the allowablewithdrawal and groundwater is overexploited. When the withdrawal increasing by3%along with the demand of water supply, the water level will be in significant decliningtrend, and the sustainable use of groundwater resources could not be guaranteed. Amore rational exploitation layout is carried out on the control principle that thegroundwater level decline of the phreatic is less than1/3of the thickness of theaquifer, and the groundwater level decline of the confined aquifer is not exceed theceiling. Based on the exploitation layout, the groundwater allowable withdrawal is446.67×104m3/a. On the situation of the surface water supply system is in emergency,to meet the demand of water supply, the groundwater extraction could be used forabout165days. Along with the increasing demand for urban water supply, in2020,the groundwater could guarantee the water supply for about95days in emergencysituation, and about90days in2030.