Characteristics Of Large Regional Groundwater Modeling And The Applied FEFLOW Technique

Recently, groundwater resource assessment is no more completely limited to localareas,instead more and more hydrogeologists have been attaching importance to theresearch on large regional groundwater system. The large regional groundwater model canbe distinguished from other types of relatively small flow models in several aspects: spatialmeasure of model, disposal of model data, edition of meshes, application purpose of model,modeling rules and etc. In comparison to small regional flow models, characteristics of largeregional groundwater flow model are discussed in this dissertation based on the groundwatermodeling of the North China Plain.On foundation of the detailed analysis of geology and hydrogeology conditions inNorth China plain, hydrogeologic conceptual model and groundwater flow model arerespectively built and then, the flow model is computed by finite element method which isembedded in FEFLOW (Finite Element subsurface Flow system) software. By using thecomputation model, the evaluation and analysis of annual average groundwater recharge andsafe yield are done separately. Following this, the prediction model in current pumpingcondition is built to estimate the groundwater flow direction, so as to provide a necessaryfoundation for the practice of South-North diversion project. Finally, features of largeregional groundwater flow model and the applied skills of FELFOW software are concludedin detail, so as to provide technical support for regional water resource assessment work inthe future.The results of model indicates that during simulation periods 2002-2003 in the upperaquifer total groundwater recharge is 449.75×108m3, total discharge is 490.41×108m3 On theother hand, total groundwater recharge of deep confined aquifer is 38.39×108m3, totaldischarge is 61.00×108m3. In sum, annual average total groundwater recharge of study areais 239.46×108m3/a, and safe yield is 256.67×108m3/a. The prediction model indicates thattotal cumulative recharge is 2765.59×108m3, and the total discharge approaches3194.60×108m3. During the prediction period water level in upper aquifer descends atdifferent rate in the whole plain.Large regional groundwater system generally consists of different geomorphologicunits, due to the complexity of groundwater system, there exist so obvious differences whencompared with the groundwater system in small scale areas in the objective of modeling,hydrogeologic structure, flow fields, and computation of various recharge and discharge. Asa result, the rules of modeling of the two types are accordingly different. Here FEFLOW isused to do the modeling, the integral components of which are interactive graphics, a GISinterface, data regionalization, visualization tools and powerful numeric techniques etc, byusing these skills to solve the partition of aquifers, generation of meshes, interpolation ofdiscrete nodes, conversion of data, computation of regional balance, assigning of boundaryconditions etc, can make up the deficiency of FEFLOW and apparently improve theefficiency to do groundwater modeling and therefore make FEFLOW more suitable to buildgroundwater model of large-scale areas.