Changes to SFR2, LAK7, and UZF Packages for MODFLOW-2005, version 1.12.00

Changes to SFR2, UZF1, and LAK7 for MODFLOW version 1.12.00 is based 
on MODFLOW-NWT version 1.1.2. Changes made to MODFLOW-NWT are described 
in the release notes; users are encouraged to review those release notes 
in addition to the notes provided below. 

This release provides support for the new transport model called 
MT3D-USGS. Changes to MODFLOW to support MT3D-USGS were made to the 
source file lmt8.f. These changes include writing output for the 
UZF, SFR2, and LAK7 Packages that is required for simulating transport 
in the unsaturated zone, streams, and lakes. Refer to the MT3D-USGS 
documentation report for details (Bedekar, V., Morway, E.D., 
Langevin, C.D., Tonkin, M.T., 2015, MT3D-USGS version 1: a U.S. 
Geological Survey release of MT3DMS updated with new and expanded 
transport capabilities for MODFLOW: U.S. Geological Survey Techniques 
and Methods 6-A53, variously paginated).

SFR2: 
(1) The input format for specifying character-variable options has 
changed. Rather than specifying character-variable options in a 
single line in a particular order, each character-variable option 
is specified on a separate line in any order. If additional input 
is required along with the character-variable option, then this value 
is specified on the same line as the character-variable option 
separated by one or more spaces. For the new input format, options should
be proceeded with the "OPTIONS" specification and followed by the "END"
specification. Characters can be specified as upper or lower case. 
Previous input formats for SFR2 are supported.  See 
Updated_SFR2_input_instructions_MF2005.pdf input file details.

(2) Other changes: Some variables in the SFR2 Package were 
initialized; some variables were changed to arrays for use in 
MT3D-USGS; and an access violation was fixed.  A bug was fixed to 
avoid a memory-allocation error that occurred when using the tabfile 
option for models with more tabfiles than stream segments. Also, an 
uninitialized variable was initialized.

UZF2:
(1) Some variables in the UZF Package for calculating runoff were 
initialized; a minor bug was corrected that relates to simulating 
unsaturated-zone flow beneath lakes; and a floating-point exception 
was fixed.

(2) A new function was added for simulating groundwater 
evapotranspiration (ET). This function simulates a constant ET rate 
over the extinction depth rather than linearly reducing ET as 
groundwater head decreases. The ET is smoothly reduced to zero using 
the same polynomial function used to reduce pumping in drying cells 
(Niswonger and others, 2011). ET is smoothly reduced as groundwater 
head drops to the extinction depth. The smoothing interval is 
specified as a factor of the extinction depth.

(3) New Options were added to UZF1 to allow the hydraulic conductivity 
used to calculate rejected infiltration and surface leakage to be 
different than the vertical hydraulic conductivity of the unsaturated 
zone (VKS). 

(4) The input format for specifying character-variable options has 
changed. Rather than specifying character-variable options in a single 
line in a particular order, each character-variable option is specified 
on a separate line in any order. If additional input is required along 
with the character-variable option, then this value is specified on the 
same line as the character-variable option separated by one or more 
spaces.  For this new input format, options should be proceeded with 
the "OPTIONS" specification and followed by the "END" specification. 
Letters can be specified as upper or lower case. Previous input 
formats for UZF1 are supported.

Optional character variables for UZF1 in any order:

[OPTIONS]
[SPECIFYTHTR] 
[SPECIFYTHTI] 
[NOSURFLEAK] 
[SPECIFYSURFK] 
[REJECTSURFK] 
[SEEPSURFK] 
[ETSQUARE smoothfact]
[NETFLUX unitrech unitdis]  
[END]

Definitions of new variables:

SPECIFYSURFK -- An optional character variable. When SPECIFYSURFK 
is specified, the variable SURFK is specified in Data Set 4b.

REJECTSURFK -- An optional character variable. When REJECTSURFK is 
specified, variable SURFK instead of VKS is used to calculate rejected 
infiltration. REJECTSURFK is included only if SPECIFYSURFK is included.
              
SEEPSURFK -- An optional character variable. When SEEPSURFK is specified, 
variable SURFK instead of VKS is used to calculate surface leakage. 
SEEPSURFK is included only if SPECIFYSURFK is included.

ETSQUARE -- An optional character variable. When ETSQUARE is specified, 
groundwater ET is simulated using a constant potential ET rate, and is 
smoothed over a specified smoothing interval. This option is 
recommended only when using the NWT solver.

smoothfact --  An optional real variable specified if ETSQUARE is 
specified. For example, if the interval factor (smoothfact) is specified 
as smoothfact =0.1 (recommended value), then the smoothing interval will 
be calculated as: SMOOTHINT = 0.1*EXTDP and  is applied over the range 
for groundwater head (h): 

  h < CELTOP-EXTDP,     ET is zero;
  CELTOP-EXTDP < h < CELTOP-EXTDP+SMOOTHINT,     ET is smoothed; and
  CELTOP-EXTDP+SMOOTHINT < h,      ET is equal to potential ET.
               
NETFLUX -- An optional character variable. When NETFLUX is specified, 
the sum of recharge (units of cubic length per time) and the sum of 
discharge (units of cubic length per time) is written to separate 
unformatted files using module UBDSV3. Unitrech and Unitdis are the 
unit numbers to which these values are written when SAVE BUDGET is 
specified in Output Control. Values written to Unitrech are the sum 
of recharge values for the UZF, SFR2, and LAK Packages, and values 
written to Unitdis are the sum of discharge values for the UZF, SFR2, 
and LAK Packages. Values are averaged over the period between output 
times.

Data Set 4B:

[SURFK (NCOL, NROW)] -- U2DREL

SURFK -- An optional array of positive real values used to define 
the hydraulic conductivity (units of length per time). SURFK is 
used for calculating the rejected infiltration and/or surface 
leakage. If SURFK is set greater than VKS, then it is set equal 
to VKS.


(5) Bug fixes 

First corrected in MODFLOW-NWT version 1.0.9 07/01/2014
A bug was fixed to correct the applied infiltration 
rate as printed to the UZF1 gage output file summed over the entire 
model. Previous versions did not include applied infiltration rates 
in excess of VKS. This bug did not affect calculations or solutions 
made by UZF, rather only the values for applied infiltration written 
to UZF1 gage output summed over the entire model were affected.

First corrected in MODFLOW-NWT version 1.0.8 09/24/2013
A bug was fixed to allow the vertical hydraulic conductivity to be 
read when IUZFOPT=-1; that is, when unsaturated-zone storage is 
ignored and infiltrated water is added directly to the water table. 

The maximum root depth was reduced from extending through 99% of 
the cell thickness to 90% of the cell thickness. This improves 
convergence for models where the root depth extends to the bottom 
of the cell.

Initialization was added for a few variables and checks were added 
for divide by zero.

LAK:
(1) Some variables were changed to arrays in order to save data for 
MT3D-USGS. A minor bug was corrected that relates to simulating 
unsaturated-zone flow beneath lakes.

(2) Bug fixes

First corrected in MODFLOW-NWT version 1.0.9 07/01/2014
Fixed compact budget for outputting lake seepage. A small change 
was made that sets layer indices for calculating lakebed conductance.

First corrected in MODFLOW-NWT version 1.0.8 09/24/2013
A bug was fixed to correctly print lake seepage to unformatted 
budget files. This bug affects models with lake cells that are 
surrounded by inactive groundwater cells in the same lake.

____________________________________________________________________________

Changes to SFR2, LAK7, UZF, and GAG Packages for MODFLOW-2005, version 1.10.0

SFR2:
Modifications were made to check for streambed altitudes set below the cell
bottom to which the reach is connected.  Some code was commented out that
supports options not documented. The package specific version of LAYTYP was
replaced with the global variable LAYHDT. Some variable initialization was
moved outside IF blocks to be sure of initialization in the read and prepare
subroutine.  Some redundant code was removed in formulate subroutine. A
calculation for stream reach seepage was added to formulate and budget
subroutines for certain cases when seepage was not set. Some variables
were set for zero inflow in the subroutine trans_route.

UZF2:
The package specific version of LAYTYP was replaced with the global variable
LAYHDT. Some work arrays were allocated as single dimension instead of a
double dimension. Previously, when the extinction depth (EXTDP) for ET was
set to zero it was reset to 1. Now, it is left as zero and ET for these cells
is set to inactive. Some of the unsaturated flow budget information that is
printed to UZF1 GAGE files was modified to correct some inconsistencies in
budget items.

LAK:
A bug was found that affects simulations that use the Hydrologic-Unit Flow
(HUF) Package (Anderman and Hill, 2000). The Lake Package has been modified
to compute effective lake-aquifer conductance solely on the basis of the
user-specified value of lakebed leakance; aquifer hydraulic conductivities
are not used in this calculation.  An appropriate informational message is
now printed after the lakebed conductances are written to the main output
file.  There have also been several minor changes to format statements to
improve the information content of the output file.

SEE FILE Lake3_Input_Modified.pdf for the revised input instructions.

GAG:
The variable that stores lake seepage into the unsaturated zone was changed
to correctly reflect this value.
____________________________________________________________________________


The following text describes changes that were made to the SFR2, LAK7, and
UZF1 Packages for the release of MODFLOW-2005, version 1.9.

Unsaturated-Zone Flow Package

Unsaturated-Flow Package (gwf2uzf1.f and gwfuzfmodule.f): 

A change was made to increase the internal check made by UZF of the ratio of ROOTDEPTH to the 
thickness of the cell from 0.90 to 0.99. Fixed memory out-of-bounds bug for array BOTM when IUZFBND 
was specified as less than zero. This problem was fixed by taking the absolute value of IUZFBND 
when used to access arrays.

Added deallocate statements for the variables CHECKTIME, MORE and LAYNUM. The default value for  
SURFDEP was changed. In prior versions of UZF1, if the value for SURFDEP was specified as 0, it 
was reset internally to 1.0. In this new version of UZF1, SURFDEP is reset to 1.0x10-6. This change 
could affect simulated results if the value of SURDFEP was specified as 0 in the input file.
 
Three new options were added to this package to allow specification of the residual water content 
(THTR), to provide the option of specifying initial water content (THTI) for simulations that 
begin with a steady-state recharge period, and to turn off calculation of surface leakage. 
These changes were made for the following reasons. 

THTR originally was calculated internally by the UZF Package on the basis of the difference between the 
saturated water content (THTS) and the specific yield (SY) of the aquifer receiving recharge (Niswonger 
and others, 2006). However,the ability to specify THTR can be useful for some applications in which the 
maximum storage in the unsaturated zone (THTS-THTR)is different than the instantaneous drainage from the 
aquifer (SY). For these cases, specifying THTR based on external calculations provides greater 
flexibility for parameterizing the unsaturated zone. The option to specify THTR is activated using the 
key word SPECIFYTHTR. This key word is input on line 1a of the revised UZF1 input file (see revised 
input instructions below). Values for THTR are input following the variable THTS (see below).

Originally, THTI was not specified for simulations that included both a steady-state and one or more 
transient stress periods. For this case, THTI was calculated internally by the code on the basis of the 
steady-state infiltration rate and the unsaturated-zone hydraulic properties (FINF, FKS, EPS, THTS, and 
THTR). However, in well-drained soils, the steady-state recharge rate corresponds to an initial water 
content that is too large for coarse sediments. Consequently, drainage from the unsaturated zone during 
the first transient stress period could result in an unrealistically large recharge rate. Additionally, 
the head dependency on recharge that does not occur during steady-state stress periods but that can 
occur during transient stress periods can cause a sudden increase in recharge during the transition 
between these stress periods. For these circumstances it is more realistic to specify the initial water 
content for the first transient stress period that follows a steady-state stress period. The option to 
specify THTI in simulations that include both steady-state and one or more transient stress periods is 
activated using the key word SPECIFYTHTI. This key word is input on line 1a of the UZF1 input file, and 
follows the key word SPECIFYTHTR if SPECIFYTHTR is specified. Values for THTI are input following 
variable THTR if it is input; otherwise, THTI follows THTS (see below). 

UZF1 simulates surface leakage in the uppermost active cell if groundwater head is greater
than the top of this cell. Surface leakage is a nonlinear boundary condition that can slow model  
convergence, and in some cases it is beneficial to inactive this boundary condition. Surface leakage  
is inactivated by the key word NOSURFLEAK that is specified on line 1a of the UZF1 input 
file. This key word is specified following the key word SPECIFYTHTI (if SPECIFYTHTI is specified). 
If the key word NOSURFLEAK is specified then water will not be removed from the uppermost active cell 
when groundwater head rises above the top of this cell. 

Modified input instructions for the UZF1 input file for specifying optional key words

0. Data: [#Text]		(As in previous versions of the code)

1a. Data: [SPECIFYTHTR] [SPECIFYTHTI] [NOSURFLEAK]

SPECIFYTHTR 	key word for specifying optional input variable THTR. 
SPECIFYTHTI 	key word for specifying optional input variable THTI.
NOSURFLEAK 	key word for inactivating calculation of surface leakage.

Note that the keywords must be entered in the order shown. For example, if keywords SPECIFYTHTR and 
NOSURFLEAK are specified, then SPECIFYTHTR must precede NOSURFLEAK. Alternatively, if only SPECIFYTHTI  
is specified, then the other two keywords should not be specified.

1b. Data: NUZTOP IUZFOPT IRUNFLG IETFLG IUZFCB1 IUZFCB2 NTRAIL2 NSETS2 NUZGAG SURFDEP NUZTOP		
   (As in previous versions of the code)

Items 2-5:  As in previous versions of the code.

6a. Data:  THTS (NCOL, NROW) -- U2DREL
Refer to UZF1 documentation report (Niswonger and other, 2006) for definition of THTS.

6b. Data: [THTR (NCOL, NROW)] -- U2DREL
THTR 	An array of positive real values used to define the residual water content for each vertical 
column of cells in units of volume of water to total volume (L3L-3). THTR is the irreducible water 
content and the unsaturated water content cannot drain to water contents less than THTR. This variable 
is not included unless the key word SPECIFYTHTR is specified.

7. Data: [THTI (NCOL, NROW)] -- U2DREL
Refer to UZF1 documentation report (Niswonger and others, 2006) for definition of THTI. This variable is 
not included for simulations with a steady-state stress period unless the key word SPECIFYTHTI is 
specified.

Items 8-16: As in previous versions of the code.

Streamflow-Routing Package (gwf2sfr7.f and gwfsfrmodule.f):
 
Several updates were made to the SFR2 Package, which are described here. The major
changes are described first, and smaller modifications are described at the end of this
section.

Four modifications were made to the SFR2 Package that affect Item 1 of the input file.

Previous versions of Item 1 had the following data entries:
1. Data: NSTRM NSS NSFRPAR NPARSEG CONST DLEAK ISTCB1 ISTCB2
{ISFROPT} {NSTRAIL} {ISUZN} {NSFRSETS} {IRTFLG} {NUMTIM}
{WEIGHT} {FLWTOL}

The revised input structure for Item 1 is as follows:
1a. Data: {REACHINPUT TRANSROUTE}
1b. Data: {TABFILES NUMTAB MAXVAL}
1c. Data: NSTRM NSS NSFRPAR NPARSEG CONST DLEAK ISTCB1 ISTCB2
{ISFROPT} {NSTRAIL} {ISUZN} {NSFRSETS} {IRTFLG} {NUMTIM}
{WEIGHT} {FLWTOL} {IFACE}

The two new (optional) keyword variables in Item 1a were added to change the method for 
invoking the options to specify streambed properties by reach or to simulate unsaturated flow
beneath streams (REACHINPUT), and to simulate transient streamflow routing (TRANSROUTE).
Previous versions of SFR2 had used an approach in which a negative value was specified for
input variable NSTRM to invoke these options. In the new approach, the user specifies keywords
REACHINPUT and (or) TRANSROUTE as Item 1a. The previous method of specifying a negative value
for NSTRM is still supported in the new code; however, users are encouraged to use the key
word option for developing new models. The definitions of REACHINPUT and TRANSROUTE, and the  
revised definition of NSTRM, are as follows:

REACHINPUT An optional character variable that is a flag to change the default format for
entering reach and segment data input and to simulate unsaturated flow beneath streams. When
REACHINPUT is specified, optional variable ISFROPT must be specified in item 1c; optional 
variables NSTRAIL, ISUZN, and NSFRSETS also must be specified if ISFROPT>0.

TRANSROUTE An optional character variable that is a flag to indicate that transient streamflow
routing is active. When TRANSROUTE is specified, optional variables IRTFLG, NUMTIM, WEIGHT,
and FLWTOL also must be specified in Item 1c. 

NSTRM An integer value equal to the number of stream reaches (finite-difference cells) that are 
active during the simulation. Specifying a negative value for NSTRM is equivelent to specifying 
the key word REACHINPUT.

An updated, complete version of the SFR2 input instructions is  with the MODFLOW-2005 version 1.9 
release (file SFR2_for_MF2005_v1.9.pdf). Input data specified using the previous input structure   
for SFR will be compatible with the updated version. Item 1b was added to allow users to specify 
inflows of water to the first reach of stream segments to be read from files that are external to
the SFR2 main input file. Reading specified flow rates from external files allows the user to 
specify flows that change for each time step, rather than for each stress period. The specified 
flows must be positive (a negative value for flow can not be specified using an external inflow file).
When flows are specified using these files, any flows specified in Item 4a with variable FLOW are 
ignored. The external files that contain the specified flows are referred to as tabular flow files.
Each tabular file consists of two columns of input that are read using free format: TIME and
INFLOW. Time is the point in the simulation when the flow is specified for the segment; INFLOW is
the specified flow, in units of length cubed per time. The units for TIME and INFLOW should be
consistent with those specified for variables ITMUNI and LENUNI in the MODFLOW Discretization 
File. Times listed in the tabular flow file do not need to correspond to the beginning of 
If the beginnings of the MODFLOW time steps fall MODFLOW time steps. between times listed in the
tabular flow file, then the specified inflow is calculated using a timeweighted average of specified
flows within the MODFLOW time step. Times can be listed in the tabular flow file either more 
frequently or less frequently than the MODFLOW time steps. The option for reading tabular flow
files is invoked using the keyword TABFILES, as shown above for Item 1b. Keyword TABFILES is 
followed by two integer variables, NUMTAB and MAXVAL. The definitions of these variables are:

TABFILES An optional character variable that is a flag to indicate that inflows to one or more
stream segments will be specified with tabular flow files.

NUMTAB An integer value equal to the number of tabular inflow files that will be read if TABFILES
is specified. A separate input file is required for each segment that receives specified flow.
Thus, the maximum value of NUMTAB that can be specified is equal to the total number of segments
specified with variable NSS in Item 1c. The name (Fname) and unit number (Nunit) of each tabular 
file must be specified in the MODFLOW-2005 Name File using file type (Ftype) DATA.

MAXVAL An integer value equal to the largest number of rows of specified inflows for any of the
tabular flow files. MAXVAL is used for memory allocation. For example, if there are two tabular 
inflow files and the files contain 100 and 200 flow values, respectively, then MAXVAL would be 
specified as 200.

IFACE is an optional keyword that indicates that an IFACE value will be read for each reach and
written to the budget file so that MODPATH can track particles to an exit face (or from an entry
face) of a stream cell.  If "IFACE" is found at the end of record 1c, then IFACE values are read
from the end of each item 2 record.

If TABFILES is specified, then the following variables must be specified for the first stress 
period only after the segment information has been specified (that is, new item 4f). One line of 
entry is needed for each stream segment for which a time series of flows will be specified (that
is, repeat the following line NUMTAB times):

Data: SEGNUM NUMVAL IUNIT

The definitions of these variables are:

SEGNUM An integer value equal to the segment number to which the specified inflows will be applied.

NUMVAL An integer value equal to the number of rows in the tabular flow file. Each flow file may 
contain a different number of rows, but the number of rows in any file cannot exceed MAXVAL specified 
in data Item 1b.

IUNIT An integer value equal to the unit number of the tabular inflow file. IUNIT must match the unit 
number for the file specified in the Name File.

Refer to updated, complete version of the SFR2 input instructions for the MODFLOW-2005 version 1.9 
release (file SFR2_for_MF2005_v1.9.pdf) for example SFR2 input instructions that include specified
segment inflows and the key-word input options.

Another major modification was made to add a smoothing function for the calculation of wetted channel  
area when the SFR2 input variable ICALC is set to 1 (constant stream width). In previous versions of 
the package, a discontinuity could form if the stream channel became dry during the outer iteration of  
a time step, because stream width would oscillate between the specified value and zero. To avoid such  
conditions, a smoothing function was used in SFR2 to smooth the transition between the constant (specified) 
stream width and a zero stream width over the interval between zero depth and 1.0x10-5 (units defined on  
the basis of the DIS file input variable LENUNI). Smoothing is applied automatically if ICALC=1 and the 
stream depth is between zero and 1.0x10-5 and users should refer to the calculated stream depths to 
determine if smoothing was applied to a particular reach in a simulation. SFR2 smoothes the constant-
to-zero-width transition using the same smoothing function that is used by the WEL Package to decrease 
specified pumping rates to zero when unconfined cells are dry in MODFLOW-NWT (see Niswonger and others, 
2011, p. 14). 
 
Modifications were made to correct the effects of lakes inundating stream cells. Seepage in inundated 
stream cells was not being set to zero in the budget routine. This change could affect mass-balance 
errors for models that include lakes that grow and inundate stream cells.

Modifications were made to correct a bug that occurred when the specific yield specified in the 
Block-Centered Flow (BCF7) Package was used for calculating the residual water content for the 
unsaturated zone beneath streams. Changes were made such that the code searches through model layers 
to find the corresponding layer that stores the specific yield for the case when the BCF7 input variable 
LAYCON is 2 or 3.

A change was made to fix the way stream information was being written to the LIST file. 


Lake Package (gwf2lak7.f)

A major change was to add the option for the user to specify the lake bathymetry information directly through 
exteral text files. If the optional key word TABLEINPUT is specified on the first line of the Lake 
package input file then the program reads values of lake stage, volume, and area from external lake 
bathymetry text files. The unit number of the external text file for each lake is read from the end 
of item 3, following the variable STAGES or the optional variables SSMN and SSMX, if they are specified. 
Additionally, the file type, unit number, and file name must be specified in the MODFLOW Name file if 
TABLEINPUT is specified. See revised input instructions below for more details. Each lake bathymetry input
file must contain 151 lines with values of lake stage and the corresponding lake volume, and area in each line.
Values are read in as free format, either as space or comma delimited. See example input file excerpt below.
Seepage between lakes and groundwater is calculated on cell-by-cell basis using the area of cells inundated
by the lake, and not the lake surface area specified with the external lake bathymetry file.

Corrected two bugs. The first caused the package to incorrectly set the uppermost active cell beneath a lake 
cell to NLAY. The second occurred in the calculation of outflow to a stream for specified outflow diversions; 
the lake stage was not being set correctly.

A format statement was modified to allow proper printout of the number of dry lake cells to the main 
Listing file. This change does not affect simulation results.

Modified input instructions for the LAK7 input file for specifying the optional key word TABLEINPUT for 
specifying lake bathymetry information

0. Data: [#Text]		(As in previous versions of the code)

1a. Data: [TABLEINPUT]

TABLEINPUT 	optional key word for specifying lake bathymetry information using external text files. 

1b. Data: NLAKES ILKCB		 (As in previous versions of the code)

Item 2:  As in previous versions of the code.

3. Data:  STAGES [SSMN] [SSMX] [IUNITLAKTAB]

This data set should consist of 1 line for each lake, where line 1 includes data for lake 1, and line n 
includes data for lake n. There must be exactly NLAKES lines of data. See Merritt and Konikow (2000) 
for more information about variables STAGES, SSMN, and SSMX. A value must be specified for each lake 
if the key word TABLEINPUT is specified in item 1a (that is, if TABLEINPUT is specified then all
lakes must have their bathymetry specified through external text files).

Items 4-9: As in previous versions of the code.
# Example input for specifying lake bathymetry information using external 
# text files using key word option TABLEINPUT
TABLEINPUT                             Item 1a: KEY WORD
         1         0                   Item 1b: NLAKES,ILKCB
      0.00        50     0.001         Item 2:  THETA,NSSITER,SSCNCR     
     110.0     100.0     170.0   22    Item 3:  STAGES,SSMN,SSMX,IUNITLAKTAB
The rest of the file is unchanged from the original version.

The lake bathymetry input file has been assigned IUNIT 22 and Fname lak1b_bath.txt in the Name File:

data            22  lak1b_bath.txt

File lak1b_bath.txt must have exactly 151 lines of data, and each line contains the stage, volume,
and surface area, respectively. Comment lines are not supported. The first five are:
 
   9.70000E+01   0.00000E+00   2.25000E+06
   9.96867E+01   6.04500E+06   2.25000E+06
   1.02373E+02   1.20900E+07   2.25000E+06
   1.05060E+02   1.81350E+07   2.25000E+06
   1.07747E+02   3.49267E+07   6.25000E+06

The lake stage, volume, and surface area are echoed to the MODFLOW-2005 LIST file.


References

Markstrom, S.L., Niswonger, R.G., Regan, R.S., Prudic, D.E., and Barlow, P.M., 2008, GSFLOWCoupled 
ground-water and surface-water flow model based on the integration of the Precipitation-Runoff Modeling 
System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005): U.S. Geological Survey Techniques 
and Methods 6-D1, 240 p.

Merritt, M.L., and Konikow, L.F., 2000, Documentation of a computer program to simulate lake-aquifer 
interaction using the MODFLOW ground-water flow model and the MOC3D solute-transport model: U.S. 
Geological Survey Water-Resources Investigations Report 00-4167, 146 p.

Niswonger, R.G., Panday, Sorab, and Ibaraki, Motomu, 2011, MODFLOW-NWT, A Newton formulation for 
MODFLOW-2005: U.S. Geological Survey Techniques and Methods 6-A37, 44 p.

Niswonger, R.G., and Prudic, D.E., 2005, Documentation of the Streamflow-Routing (SFR2) Package to 
include unsaturated flow beneath streamsA modification to SFR1: U.S. Geological Survey Techniques 
and Methods 6-A13, 62 p.

Niswonger, R.G., Prudic, D.E., and Regan, R.S., 2006, Documentation of the Unsaturated-Zone Flow (UZF1) 
Package for modeling unsaturated flow between the land surface and the water table with MODFLOW-2005: 
U.S. Geological Survey Techniques and Methods 6-A19, 62 p.
