Water Resources of the United States

*A Data Input Program (MFI) for the U.S. Geological Survey Modular Finite-Difference Ground-Water Flow Model*

U.S. Geological Survey Water-Resources Investigations Report 94-468

Those already familiar with MODFLOW or those who carefully examine the MODFLOW and MODPATH input instructions will notice that the MFI data screens do not directly include all parameters required for MODFLOW and MODPATH. This is because MFI calculates some parameters either by assumption or from other requested information. Table 2 lists the parameters that are calculated by some method other than direct data entry.

Table 2. Parameters that MFI calculates (PostScript file of Table 2)

--------------------------------------------------------------------------OptionParameterHow Calculated-------------------------------------------------------------------------- BAS IAPART 0 if LAYAVG (Goode and Appel, 1992) is not 30; 1 if LAYAVG is 30. BAS ISTRT 0 when drawdown is not calculated; 1 when drawdown is calculated. BAS IUNIT Unit numbers for files are automatically selected. BAS NPER User specified when transient; 1 when steady state. BAS PERLEN User specified when transient; 1.0 when steady state. BAS NSTP User specified when transient; 1 when steady state. BAS TSMULT User specified when transient; 1.0 when steady state. BAS ITMUNI User specified when transient; set to "UNDEFINED" when steady state. BCF ISS Determined from the "Steady State/Transient" option specified in the Miscellaneous input screen for the Basic Package; 0 if transient, and 1 if steady state. BCF IBCFCB Determined from data entered in Output Control screens. RIV ITMP Determined by counting the reaches entered by the user. RIV MXRIVR Determined by looking at the number of reaches used in each stress period and finding the maximum number. RIV IRIVCB Determined from data entered in Output Control screens. WEL ITMP Determined by counting the wells entered by the user. WEL MXWELL Determined by looking at the number of wells used in each stress period and finding the maximum number. WEL IWELCB Determined from data entered in Output Control screens. DRN ITMP Determined by counting the drains entered by the user. DRN MXDRN Determined by looking at the number of drains used in each stress period and finding the maximum number. DRN IDRNCB Determined from data entered in Output Control screens. GHB ITMP Determined by counting the boundaries entered by the user. GHB MXBND Determined by looking at the number of boundaries used in each stress period and finding the maximum number. GHB IGHBCB Determined from data entered in Output Control screens. RCH INRECH -1 if RECH array is reused from previous stress period; otherwise 0. RCH INIRCH -1 if IRCH array is reused from previous stress period; otherwise 0. RCH IRCHCB Determined from data entered in Output Control screens. EVT INIEVT -1 if IEVT array is reused from previous stress period; otherwise 0. EVT INEVTR -1 if EVTR array is reused from previous stress period; otherwise 0. EVT INEXDP -1 if EXDP array is reused from previous stress period; otherwise 0. EVT INSURF -1 if SURF array is reused from previous stress period; otherwise 0. EVT IEVTCB Determined from data entered in Output Control screens. SIP NPARM Always 5. SIP IPCALC 0 if WSEED is not 0; 1 if WSEED is 0. PCG NPCOND Always 1. PCG NBPOL Always 2. PCG IPCGCD Always 0. Output IHEDUN 0 if head is not saved. If head is saved, unit number is automatically selected. Output IDDNUN 0 if drawdown is not saved. If drawdown is saved, unit number is automatically selected. Output INCODE Determined from data entered in Output Control screens. Output IHDDFL Determined from data entered in Output Control screens. Output IBUDFL Determined from data entered in Output Control screens. Output ICBCFL Determined from data entered in Output Control screens. Output Hdpr Determined from data entered in Output Control screens. Output Ddpr Determined from data entered in Output Control screens. Output Hdsv Determined from data entered in Output Control screens. Output Ddsv Determined from data entered in Output Control screens. Modpath IGRID Always 0. Modpath NCBL Calculated by counting the number of layers for which NCON (the confining bed code) is not 0. Modpath TOP For layers below the top layer, TOP is defined as the BOT of the layer above when there is no confining layer above; otherwise TOP is either user defined or the elevation of the water table. --------------------------------------------------------------------------

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