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RECHARGE PACKAGE

RECHARGE PACKAGE. The Recharge Package is designed to simulate areally distributed recharge to the groundwater system. Application of irrigation water to farm acreage, and precipitation are two processes that can result in areally distributed recharge.

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RECHARGE PACKAGE

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  1. RECHARGE PACKAGE • The Recharge Package is designed to simulate areally distributed recharge to the groundwater system. • Application of irrigation water to farm acreage, and precipitation are two processes that can result in areally distributed recharge. • Like the Well Package, the Recharge Package assumes a recharge that is head independent. • The head independent assumption implies irrigated crops take no water from the water table. RCH6

  2. RECHARGE PACKAGE • Recharge (or discharge) is entered as a recharge flux [L/t]—common units are in inches/hour, feet/year, or mm/s • MODFLOW converts the recharge flux to a volumetric flow rateby multiplying by an appropriate area. If QRij is the recharge flow rate applied to the model at a horizontal cell location(i,j), Iij is the recharge flux applicable, and DELRj×DELCi is horizontal surface are of the cell, then, QRij = Iij × DELRj×DELCi RCH6

  3. RECHARGE PACKAGE • The recharge, QRij, is applied to a single cell within the vertical column of cells located at (i,j) • Recharge enters the groundwater system at its top; however, the vertical position of the top of the system may vary with horizontal location and with time. • If the ability to apply recharge to more than one cell in a vertical column of cells is required, use the Well Package RCH6

  4. RECHARGE PACKAGE • Three options for specifying the cell in each vertical column of cells that receives the recharge has been implemented. Option1—Application of the recharge to model layer 1. Option2—Application of the recharge to any cell in the vertical column as specified by layer numbers contained in a two-dimensional array IRCHij Option3—Application of the recharge to the uppermost active cell in the vertical column, provided there is no constant head cell above it in the column. RCH6

  5. RECHARGE PACKAGE • Consider the distribution of active, constant head and no-flow cells shown in the cross-section (figure a). • Option 1 is used, only recharge to the layer is permitted, and only to those active cells (figure b) a b RCH6

  6. RECHARGE PACKAGE • Option 2 is used, and a IRECH array is specified. However, the modeler has incorrectly specified recharge to four inactive nodes (enclosed in circle). Only the Xed cells will receive recharge. Option 2 would have worked if a proper IRECH had be specified. RCH6

  7. RECHARGE PACKAGE • Option 3 is used, recharge enters the uppermost active cell in each vertical column, except where constant head cells are present. RCH6

  8. RECHARGE PACKAGE For single layer systems or multiple layered systems where there are no lower layer outcropping, Option 1 is sufficient if the user assigns zero recharge to non-areas of recharge. For multiple layered systems with outcropping use Option 2 or 3. Option 2 requires more computer memory, which now days is not a factor. Recharge Area Layer 1 Recharge Areas Layer 1 Layer 2 RCH6

  9. RECHARGE PACKAGE • The Crop Irrigation Requirement (CIR) is the consumptive use requirement minus the effective precipitation. • The Farm Delivery Requirement (FDR) is the CIR divided by the irrigation efficiency, • Typical irrigation efficiencies are 70% for sprinkler irrigation systems and 50% for gravity fed systems. • The difference between the FDR and the CIR, adjusted for some evaporative losses, is the potential recharge to the groundwater system. RCH6

  10. RECHARGE PACKAGE NPRCH—is the number of recharge parameters. NRCHOP—is the recharge option code. NRCHOP=1, recharge is only to the top grid layer. NRCHOP=2, vertical distribution of recharge specified in layer variable IRCH. NRCHOP=3, is applied to the highest active cell in each vertical column (Note: a constant-head node intercepts recharge an prevents deeper infiltration) RCH6

  11. RECHARGE PACKAGE IRCHCB—is a flag and a unit number. IRCHCB > 0, the unit number to which cell-by-cell terms will be written whenSAVE BUDGETor a non-zero value ofICBCFLis specified in output control. IRCHCB ≤ 0, cell-by-cell flow terms will not be written. PARNAM—isthe name of aparameter. This name can consist of 1 to 10 characters, and is not case specific. PARTYP—is parameter type. There is only one parameter type for theRCHPackage—therecharge flux, RCH. RCH6

  12. RECHARGE PACKAGE Parval—is the parameter value. NCLU—isthe number of clusters required to define a parameter. Each repetition of Item 4 is a cluster. There is usually only one cluster used to define a RCH parameter, but it is acceptable to have more. Mltarr—is the name of the multiplier array to be used to define cell values that are determined by parameters. The name NONE means that there is no multiplier array, and the cell value will be set to Parval. RCH6

  13. RECHARGE PACKAGE Zonarr—is the name of the zone array to be used to define cell values that are associated with a parameters. The name ALL means that there is no zone array, and all cells in the layer are associated with the parameter. IZ—is up to ten zone numbers (specified by spaces) the define the cells that are associated with a parameter. These values are not used if Zonarr is specified as ALL. Values can be negative, but not zero. The end of line, a zero value, or a non-numeric entry terminates the list of values. RCH6

  14. RECHARGE PACKAGE INRECH—is the recharge flux (RECH) read flag whose function depends on whether or not parameters are being used. If no parameters are being used(NPRCH=0) INRECH≥0, a layer variable of recharge fluxes, RECH, is read INRECH<0, the recharge fluxes from the preceding stress period is reused. RCH6

  15. RECHARGE PACKAGE If parameters are used (NPRCH>0) INRECH>0, INRECH is the number of parameters that will be used to define RECH in the current stress period. Item 7 defines the names of the parameters. INRECH<0, recharge parameters from the preceding stress period are used. INRECH=0 is not allowed because when parameters are used, at least one parameter must be specified each stress period. RCH6

  16. RECHARGE PACKAGE INIRCH—is the IRCH read flag, which is only read if NRCHOP=2 INIRCH≥0, a layer variable of layer numbers (IRCH) is read. INIRCH<0, the variable IRCH from preceding stress period is used. RECH—is the recharge flux [L/t]. Read only if INRECH≥0 and if NPRCH=0. Pname—is the name of the parameter the will be used to define the RECH variable in the current stress period. Read INRECH values if NPRCH>0 and INRECH>0. RCH6

  17. RECHARGE PACKAGE IRCHPF—is an optional format code for printing the RECH variable after it has been defined by parameters. The format codes are the same as those used in the U2DREL array reading utility module. IRCH—is the layer number variable that defines the layer in each vertical column where recharge is applied. Read only if NRCHOP=2 and if INIRCH≥0. RCH6

  18. RECHARGE PACKAGE No Parameters Option 1 Option 2 RCH6

  19. RECHARGE PACKAGE Parameters Zone File RCH6

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