Development Of A Numerical Model Of Regional Groundwater Flow And Its Application To The North China Plain

The North China Plain (NCP), an important economic core and agricultural base in thenorth part of China, takes groundwater as the major water supply. As economy booms, this areahas been facing serious water shortage. Meanwhile, long-term excessive groundwater pumpingthere also results in some environmental problems including continuous water level decline,land subsidence, etc. Therefore, it is necessary to develop a numerical model of regionalgroundwater flow system for the NCP, which could be used to accurately evaluate the amountof groundwater resources and provide scientific support for reasonable groundwaterexploitation in the NCP.To improve operating efficiency and data processing capability of groundwater model ofthe NCP, this study started with the groundwater flow modeling program–MODFLOW.Because the MODFLOW has a disadvantage in processing input data as the format of rechargeor discharge rate. The existing RCH procedure was improved and a new procedure RAW wasdeveloped aiming to solve this problem. Performance of the improved RCH procedure and theRAW procedure were tested by an idealized groundwater model. The test results indicated thatthe improved RCH procedure and the RAW procedure could greatly improve the efficiency ofdata input and data reading of MODFLOW. The RAW procedure could also process the inputdata of different aquifer layers as the format of recharge or discharge rate. In addition, amethod of inverting groundwater withdrawal was proposed in the study and correspondinggroundwater withdrawal inversion procedure was schemed so as to accurately represent currentgroundwater exploitation in the NCP.The numerical model of regional groundwater flow of the NCP in the study wasdeveloped on the basis of the original groundwater model of the NCP, using the improvedMODFLOW. The size of the model grid was1000×1000m2, which is16times smaller than theoriginal one. Moreover, the simulation period was prolonged as2001-2010instead of2002-2003. After preliminarily calibrating the established model by fitting the observedgroundwater flow field with the simulated ones in shallow layers and deep layers respectively,the groundwater withdrawal of the NPC was inverted using the proposed inversion method in combination with the observed groundwater level date during2001-2008. The outcomeshowed that the inverted average groundwater withdrawal was234.36108m3per year.Meanwhile, the established model obtained a better fitting of groundwater flow fields and ofhydrograph by putting the inverted groundwater withdrawal date into the model. Finally,according to the simulation results and groundwater budget analysis of2001-2010, this studyassessed the average annual groundwater recharge and safe yield of the NCP. The evaluationresults indicated that the average recharge of the shallow aquifer was242.07108m3per yearand the safe yield of groundwater for NCP was191.51×108m3per year during2001-2010.