Program Optimization For Numerical Simulation Of Groundwater Flow In Large-scale Area Based On MODFLOW

The numerical simulation of groundwater flow is an important method ofevaluating the groundwater resource. However, with the demand for groundwaterflow numerical model accuracy, groundwater flow numerical model with refinedspatial and temporal discretization is often required. Building large-scale areagroundwater flow numerical model with refined spatial discretization often involvesstoring and reading large quantities of data.In this dissertation, we analysed the principle, methods, structure and programprocess of the MODFLOW. We also discussed the input and output files formatand the procedure of processing model data in detail. The storage requirement couldbe prohibitive and the program efficiency could be quite low, while usingMODFLOW to build large-scale area groundwater flow numerical model. Inaddition, the procedure of processing model data is very complicated. To addressthis problem, we have modified the existing packages RCH and EVT, anddeveloped a new package named RAW (recharge and well), which is used to dealwith the area-feature source and sink terms. The three packages as mentionedabove, read values of every subarea and the subarea number of each grid which isstored in corresponding input files, and then allocates the values to correspondinggrids. Therefore the data processing method of these packages are all based onevery subarea.The performance of the improved MODFLOW program is tested by an idealgroundwater flow model. The North China Plain groundwater flow model is buildbased on the improved MODFLOW program. The RCH package and EVT packageare used to deal with the precipitation recharge and the evaporation, respectively.Area-featured source and sink terms(include the river) are all handled by the RAWpackage. Compared with the traditional method, the size of RCH and RAW file isonly2.00MB and2.81MB,and the time ratio for reading data is16.77and12.34,respectively. Compared with the WEL package, the time ratio for reading data ofRAW package is40.59.The RAW package can deal with many area-feature source and sink termsseparately, at the meanwhile output the balance data respectively. Therefore, theimproved MODFLOW is extremely effective in the field of compressing data,accelerating the program and simplifying the data processing procedure. The RAW package could be used to simulate the source and sink terms, like area-featuredgroundwater exploitation and agricultural irrigation infiltration and thus expandedsimulation function of MODFLOW.