Abstract:

Reading and writing precipitation and well data are all based on each grid in the existing MODFLOW. So building regional groundwater flow numerical models with refined spatial and temporal discretization often involves storing and reading large quantities of well and precipitation data. However, the storage requirement can be prohibitive and the program efficiency can be quite low. To address this problem, we have modified the existing package RCH and also developed a new package named RAW (recharge and well), which is based on the existing packages in MODFLOW. The improved MODFLOW program can only read values of every subarea and the subarea number of each grid which is stored in the RCH or RAW file, and then allocates the values to corresponding grids. With the RAW package, the area recharge and discharge could occur in all layers. Therefore, it could be used to simulate the source and sink term, like groundwater exploitation and agricultural irrigation return. The correctness has been verified and the efficiency has been tested through simulating a theoretical groundwater flow model and a real North China Plain model respectively. Compared with the traditional method of storing data, the size of RCH and RAW file decreases 1/145 and 1/255 respectively, and the time ratio for reading data is 7.46.

Key words: MODFLOW, RCH, RAW, large-scale groundwater simulation, North China Plain