The Study And Application Of Two Levels Ghost-node Local Grid Refinement Technique Based On MODFLOW2005

In more than seventy percent of the north China plain area, the shortage of recharge and long term over extraction of groundwater, lead to a sharp drop in groundwater resources, land subsidence and other environmental geological disasters, has become the bottleneck of restricting the sustainable development. In 2014, the middle route of South-to-North Water Diversion Project began running, it will gradually improve water structure of the north China plain, provides conditions for groundwater recharge and self-restraint. Numerical model of groundwater is an important tool of evaluation and management of groundwater resources. In the regional groundwater flow model, it can improve the simulation precision of the partial key areas to refine he grid in water resources site and drawdown cone or recharge area.On the basis of learning and contrast of Share-node and Ghost-node local grid refinement technology based on MODFLOW2005, take the groundwater flow model of the alluvial-pluvial fan of the Hutuo River as an real example, establish a local grid refinement model that region and site coupled with LGR-GN method and make a contest to the model established whit LGR-SN method. Identified a way to establish a two levels refined region-site coupled model,that is a method which include one-way coupling and LGR-GN two-way coupling method : establish a transition model in the affected area of artificial as the child model to regional model and a parent model to the field model, in this way, we can couple the region model and field model.In the numerical simulation of groundwater flow process, the refinement effect difference of two methods of LGR effect is very small, LGR-SN has an advantage on interpolation precision, LGR-GN has an advantage on source sink term superior treatment especially on planar ones; processing to each grid of drilling hole in grid refinement area has little effect on the simulation running time, just takes up the space is significantly larger.The two levels grid refinement method defined by this paper that take the recharge affected area as the transition model area and make a time- varied head boundary, is proved correct. the transition boundary does not affected by grid refinement, can control the injection of transition boundary effect; the amplitude of water level simulated by Regional model coupling field model is more close to reality, the water dome is more apparent, and in practice,field model area is small and conditions is simple, the increasing work content is not much, the greater proportion refinement method achieved by the two levels grid refinement can be used for future regional multiple region local grid refinement; simulated by region and field coupling model,after continue 7 years’ injection,the water level is higher 1.04 m than that without recharge condition at most, impact is less than 0.5 m to the site boundaries, the effect is less than 0.1 m to transition model’s boundary; Local well irrigation have little impact on regional flow field, a lot of arrangement and irrigation facilities is needed in the territory for groundwater recharge work for a long time, thus to realize the recovery of regional underground water level and to ease the trend of groundwater over exploitation.