Transcript recharge package - Numerical Modelling of Ground

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
1
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
2
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
3
RECHARGE PACKAGE
•
Three options for specifying the cell in each vertical
column of cells that receives the recharge has been
implemented.
Option 1—Application of the recharge to model layer 1.
Option 2—Application of the recharge to any cell in the vertical
column as specified by layer numbers contained in a twodimensional array IRCHij
Option 3—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
4
RECHARGE PACKAGE
• Consider the distribution
of active, constant head
and no-flow cells shown in
the cross-section (figure
a).
a
• Option 1 is used, only
recharge to the layer is
permitted, and only to
those active cells (figure
b)
b
RCH6
5
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
6
RECHARGE PACKAGE
• Option 3 is used,
recharge enters the
uppermost active cell
in each vertical
column, except where
constant head cells
are present.
RCH6
7
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
8
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,
CIR
FDR 
Farm 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
9
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
10
RECHARGE PACKAGE
IRCHCB—is a flag and a unit number.
IRCHCB > 0, the unit number to
which cell-by-cell terms will be
written when SAVE BUDGET or a
non-zero value of ICBCFL is
specified in output control.
IRCHCB ≤ 0, cell-by-cell flow terms
will not be written.
PARNAM—is the name of a
parameter. 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 the
RCH Package—the recharge flux,
RCH.
RCH6
11
RECHARGE PACKAGE
Parval—is the parameter value.
NCLU—is the 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
12
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
13
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
14
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
15
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
16
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
17
RECHARGE PACKAGE
No Parameters
Option 1
Option 2
RCH6
18
RECHARGE PACKAGE
Parameters
Zone File
RCH6
19