GAGE - Gage Package

Abbreviation in Name file

GAGE

Purpose

Lakes and streams can be designated as having gaging stations located on them. For each such designated lake or stream, the time and a variety of other information will be written to a separate output file after each time step (and each transport time increment) to facilitate graphical postprocessing of the calculated data.

Documentation

•	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.

•	Prudic, D.E., Konikow, L.F., and Banta, E.R., 2004, A new stream-flow routing (SFR1) package to simulate stream-aquifer interaction with MODFLOW-2000: U.S. Geological Survey Open-File Report 2004-1042, 95 p.

•	Niswonger, R.G. and Prudic, D.E., 2005, Documentation of the Streamflow-Routing (SFR2) Package to include unsaturated flow beneath streams--A modification to SFR1: U.S. Geological Survey Techniques and Methods, Book 6, Chap. A13, 47 p.

•	Combined_gage_input_instructions.pdf

•	Gage7_input_instructions.pdf

•	Gage_input_instructions.pdf

Related Packages

Lake (LAK) package

Streamflow-Routing (SFR) package

Supported in

•	MODFLOW-2000

•	MODFLOW-2005

•	MODFLOW-LGR

•	MODFLOW-CFP

•	MODFLOW-NWT

•	MODFLOW-OWHM

Input Instructions

Stream Gaging (Monitoring) Station File (GAGE)

Cells of the model grid can be designated as “stream gaging station” locations. At each designated cell (or stream reach), the time, stage, streamflow out of that reach, the streambed seepage, unsaturated storage, change in unsaturated storage, and groundwater recharge will be written to a separate output file to facilitate model output evaluation and graphical post processing of the calculated data. Several options are available to print additional information. The input file for specifying gaging station locations is read if the file type (Ftype) “GAGE” is included in the MODFLOW name file. The output file will contain two header lines that provide relevant information (the text will be contained within quotes).

For each simulation, if GAGE Package is used:

Data Set 1

NUMGAGE Number of gaging stations

For each gaging station:

Data Set 2 must include exactly NUMGAGE lines (or records) of data. If NUMGAGE > 1, it is permissible to interleaf in Data Set 2 records for stream gaging stations (according to the format specified in the documentation for the Stream Package) with records for gages on lakes. Data lines (records) within Data Set 2 can be listed in any arbitrary order.

If the gage is on a lake

Data Set 2a

LAKE UNIT [OUTTYPE]

LAKE Negative value of the lake number of the lake where the gage is located.

•

The Gage Package can also be used in conjunction with the Stream Flow Routing (SFR) Package to specify the location of a gaging station on a stream. Therefore, to guarantee that the code can distinguish between input for lakes and that for stream locations, lake numbers are specified as their negative value.

UNIT Unit number for output file. Specify negative value of unit number to invoke reading of optional parameter OUTTYPE for listing additional information for lakes.

•	The user should specify a unique unit number for each gaging station and match those unit numbers to DATA file types and file names in the MODFLOW name file (Harbaugh and McDonald, 1996b).

OUTTYPE Code for type of expanded listing desired in output file:

0.	Use standard default listing of time, stage, volume, and concentration.

•

Default values plus all inflows to and outflows from lake (as volumes during time increment), total lake conductance, and time-step budget error (percent). Computed runoff from UZF and lake infiltration to UZF is added whenever the UZF Package is active in MODFLOW-2005 and MODFLOW-LGR. (The UZF Package is not available in MODFLOW-2000.)

•

•	Default values plus changes in lake stage, lake volume, and solute concentrations, and cumulative lake budget error (percent).

3.	All of the above except time-step budget error.

Time, lake stage, lake volume, solute concentration, and rate of change of lake volume, as well as volumetric rates for all inflows to and outflows from lakes (L3/T), total lake conductance (L2/T), and time-step budget error. Volumetric rates of computed runoff from UZF and lake infiltration to UZF is added whenever the UZF Package is active in MODFLOW-2005, MODFLOW-CFP, MODFLOW-NWT, and MODFLOW-LGR.

Total lake conductance (OUTTYPE options 1 and 3 for a lake gaging station) is the sum of the conductances of each seepage interface for each lake. Changes in lake stage, volume, and solute concentrations (OUTTYPE options 2 or 3) are listed as incremental changes from previous time increment and as cumulative change since start of simulation.Volumetric rates for option 4 are expressed in units of volume per time during a time step increment. Versions of the GAGE Package since 2006 for MODFLOW-2000 and MODFLOW-2005 had listed groundwater inflows and outflows as volumetric flow rates and listed the other values as volumes per time step for options 1 and 3.

Note 1: A unique unit number must be specified for each stream gaging station and the MODFLOW name file (see Harbaugh and others, 2000, p. 42-44) must specify the file for each unit. The file type in the name file must be “DATA”.

Note 2: If the LAK3 Package is also active, a gaging station may be placed on a lake. In this case, only two required variables and one optional variable are read. The first variable should be the negative value of the lake number and the second is the unit number for the output. The original description of the Gage Package (Merritt and Konikow, 2000, p. 57) did not include additional print options listed for OUTTYPE. For a gaging station on a lake, a minus sign on the unit number is a flag indicating that OUTTYPE for a lake will be read.

Note 3: Data Set 2 must include exactly NUMGAGE lines (records) of data. If NUMGAGE > 1, it is permissible to interleaf the Item 2 lines for stream gaging stations with lines for lake gages. Data lines (records) within Item 2 can be listed in any arbitrary order.

Note 5: Unsaturated flow is not simulated beneath lakes.

If the gage is on a stream

Data Set 2b

GAGESEG GAGERCH UNIT OUTTYPE

GAGESEG An integer value that is the stream segment number where gage is located.

GAGERCH An integer value that is the stream reach number where gage is located.

UNIT An integer value that is the unit number of output file for this gage.

OUTTYPE An integer value that is a flag for type of expanded listing desired in output file:

•	0 Use standard default listing of time, stage, outflow, and solute concentration.

•	1 Default values plus depth, width, and flow at midpoint.

•	2 Default values plus streambed conductance for the reach, head difference across streambed, and hydraulic gradient across streambed.

•	3 Default values plus solute load in stream (if GWT is active).

•	4 All of the above.

•	5 Use for diversions to provide a listing of time, stage, flow diverted, maximum assigned diversion rate, flow at end of upstream segment prior to diversion, solute concentration, and solute load.

•	6 Used for unsaturated flow routing to provide a listing of time, stage, groundwater head, streambed seepage, change in unsaturated storage, and recharge.

•

7 Used for unsaturated flow routing to provide a listing of time and the unsaturated water content profile beneath the stream. Two profiles are printed. The first is the volume average water content of ISUZN unsaturated cells beneath a stream reach. The second profile is the volume averaged water content beneath the low flow channel only. If ISUZN =1 then both water content profiles will be the same.

•	8 Use for unsaturated flow to provide a listing of time and the following budget components summed over all stream reaches: stream loss; stream gain; infiltration into the unsaturated zone; change of storage in the unsaturated zone; recharge; and storage in the unsaturated zone.

Note 4: Solute is not routed through the unsaturated zone. For this reason, solute routing between streams and ground water cannot be simulated when using the unsaturated flow option in SFR2.

Note: Although a stream segment and reach number are required inputs for a stream gaging station, any active segment and reach number can be specified when OUTTYPE is 8 (recommend using segment 1, reach 1). No information specific to the specified reach is printed when this OUTTYPE option is selected.

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