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Online Guide to MODFLOW-2005

Abbreviation in Name file

LAK

Purpose

The Lake package is used to simulate lakes.  Unlike the Reservoir package, the head in the lakes can rise and fall due to interaction with groundwater or with streams simulated with the SFR package.

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. (PDF version)

readme_LAK.pdf

readme_LAK3.pdf

LAK_SFR_UZF_updates_MF2005.txt

Lake3_Input_Modified.pdf

Release.txt for MODFLOW-NWT

Related Packages

Gage package

Head-Dependent Flux Boundary packages

Reservoir package

Supported in

MODFLOW-2000

MODFLOW-2005

MODFLOW-LGR

MODFLOW-CFP

MODFLOW-NWT

MODFLOW-OWHM

Other Notes

Rejected recharge in the UZF package can be routed to lakes in the  LAK package.

The vertical flow from or to a lake is calculated incorrectly when the HUF package is used. This bug is present in MODFLOW-2005 version 1.9.1 and in all earlier versions. This bug has been fixed in MODFLOW-NWT version 1.7 and MODFLOW-2005 version 1.10.

Compared to the explicit method of updating lake stage, the semi-implicit and fully-implicit methods require more iterations, more run time, and tighter convergence criteria to minimize the percent discrepancy in the aquifer water budget. Between 500 and 1000 iterations may be required.

MODFLOW Name File

The simulation of the interaction of lakes with the aquifer is activated by including a record in the MODFLOW name file using the file type (Ftype) “LAK” to indicate that such calculations are to be made in the model and to specify the related input data file. The user can optionally specify that lake stages are to be written using the Gage Package by including a record in the MODFLOW name file using the file type (Ftype) “GAGE” that specifies the selected input data file identifying the lakes.

Lake Package Input Data

Input for the Lake Package is read from the unit specified in the MODFLOW name file. The input consists of nine separate data sets, each consisting of one or more records, as described in detail below. These data are used to specify information about the physical geometry of the lakes, hydraulic properties of the lakebeds, and the degree of hydraulic stress originating from atmospheric and anthropogenic sources, as well as specifying certain output control parameters. Spatial and temporal units of input data specifications should be consistent with other data input for the MODFLOW run.

In the following section, parameters are indicated as being optional by their enclosure in brackets. All input variables are read using free formats, unless specifically indicated otherwise. In free format, variables are separated by one or more spaces, or by a comma and, optionally, one or more spaces. It is important to note that, in free format, blank spaces are not read as zeroes and a blank field cannot be used to set a parameter value to zero.

For Each Simulation:

Data Set 1a

 

Data Set 1b

NLAKES ILKCB

If data are being read using the fixed format mode, then each field should be entered using I10 format.

Data Set 2

THETA [NSSITR SSCNCR] [SURFDEPTH]

If data are being read using the fixed format mode, then the data should be entered using format (F10.4,I10,F10.4).

For the First Stress Period Only:

Data Set 3


MODFLOW-2005, MODFLOW-NWT, MODFLOW-OWHM

STAGES [SSMN SSMX] [IUNITTAB] [CLAKE(1)..........CLAKE(NSOL)]

This data set should consist of one 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.

If data are being read using the fixed format mode, then each field should be entered using F10.4 format.

For Each Stress Period:

Data Set 4

ITMP ITMP1 LWRT

If data are being read using the fixed format mode, then each field should be entered using I10 format.

Lake definition data are restricted to cells for which IBOUND and WETDRY values have been set to zero.

If ITMP > 0 read lake definition data (records 5-7, and, optionally, records 8 and 9).

Data Set 5

LKARR(NCOL,NROW)

A NCOL by NROW array is read for each layer in the grid by MODFLOW module U2DINT.

Data Set 6

BDLKNC(NCOL,NROW)

A NCOL by NROW array is read for each layer in the grid by MODFLOW module U2DREL.

Data Set 7

NSLMS

If data are being read using the fixed format mode, then NSLMS should be entered using format I5.

If ITMP > 0 and NSLMS > 0:

A pair of records (records 8a and 8b) is read for each multiple-lake system, i.e., NSLMS pairs of records. However, IC = 0 will terminate the input.

Data Set 8a

IC ISUB(1) ISUB(2) ............ ISUB(IC)

If data are being read using the fixed format mode, then each field of Record 8a should be entered using I5 format

Data Set 8b

SILLVT(2) ............. SILLVT(IC)

If data are being read using the fixed format mode, then each field of Record 8b should be entered using F10.4 format

If ITMP1 0

At least one of the above records will be read for each lake; i.e., NLAKES records, or sets of records, will be read. If MODFLOW is being run, only the first record is read. If MOC3D or GWT is being run, a set of two or more records will be read for each lake (see next  note).

If record 9b is included because solute transport is being simulated, then 9b should consist of one record (line) for each solute; each record must contain two or three values; and there must be as many records as the number of solutes being simulated (NSOL). The order of records must be that all necessary lines for 9b are listed for a given lake before line 9a for the next lake. For example, if the Lake Package is representing three lakes and the solute transport package is representing two solutes, then the order of data for Record 9 would be 9a, 9b, 9b, 9a, 9b, 9b, 9a, 9b, and 9b.

Data Set 9a

PRCPLK EVAPLK RNF WTHDRW [SSMN] [SSMX]

Data Set 9b

If solute transport is also being simulated (Ftype “CONC” exists), then for each solute the following data are read:

CPPT(NSOL) CRNF(NSOL) [CAUG(NSOL)]

If data are being read using the fixed format mode, then each field should be entered using F10.4 format.

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