IBS - Interbed-Storage Package

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Abbreviation in Name file

IBS

Purpose

The Interbed-Storage package is used to simulate compaction of low-permeability interbeds within layers.

Documentation

Leake, S.A., and Prudic, D.E., 1991, Documentation of a computer program to simulate aquifer-system compaction using the modular finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water- Resources Investigations, book 6, chap. A2, 68 p.

Related Packages

Subsidence package

SWT Subsidence and Aquifer-System Compaction Package

Supported in

•MODFLOW-2000

•MODFLOW-2005

•MODFLOW-LGR

•MODFLOW-CFP

•MODFLOW-NWT

•MODFLOW-OWHM

Other Notes

•The Interbed Storage Package can not be used in the same model with the Subsidence and Aquifer-System Compaction (SUB) package.

•Data Set 8 is only read for transient stress periods. (See Ss/tr.)

•The UZF package does not take into account changes in the land surface due to subsidence.

See the Frequently Asked Questions for information on how to read data from binary files generated by MODFLOW.

Input Instructions

Input for the Interbed-Storage Package is read from a file that is specified with "IBS" as the file type listed in the name file.

FOR EACH SIMULATION

Data Set 1

IIBSCB IIBSOC

Format: I10 I10

IIBSCB is a flag and unit number.

•If IIBSCB > 0, it is the unit number on which cell-by-cell flow terms will be recorded whenever ICBCFL is set or "Save Budget" is specified in the Output Control Option (see McDonald and Harbaugh, 1988, chap. 4, p. 14-15).

•If IIBSCB ≤ 0, cell-by-cell flow terms will not be recorded.

IIBSOC is a flag for selecting output control for each time step.

•If IIBSOC > 0, output control will be read each time step for printing and recording subsidence (total compaction of all layers with interbed storage), and compaction and preconsolidation head for all layers with interbed storage.

•If IIBSOC ≤ 0, subsidence will be printed at the end of each stress period using format (10Gll.4). Compaction and preconsolidation head will not be printed and subsidence, compaction, and preconsoiidation head will not be recorded.

Data Set 2

IBQ(NLAY) (Maximum of 999 layers in MODFLOW-2000; no fixed limit on the number of layers in MODFLOW-2005, MODFLOW-CFP, MODFLOW-NWT, MODFLOW-OWHM and MODFLOW-LGR)

Format: 4012 (If there are 40 or fewer layers, use one record; otherwise, use multiple records)

IBQ is an indicator to specify which model layers have interbed storage.

•If IBQ(K) > 0, model layer K has interbed storage.

•If IBQ(K) ≤ 0, model layer K does not have interbed storage.

 

The following four arrays are needed to specify the material properties and initial compaction of model layers having interbed storage as indicated in the IBQ array. The four arrays are first read for the uppermost layer with interbed storage, and then continuing downward to lower layers with interbed storage.

FOR EACH LAYER WITH IBQ CODE GREATER THAN ZERO

Data Set 3

HC(NCOL,NROW) Module: UZDREL

HC is an array specifying the preconsolidation head or preconsolidation stress in terms of head in the aquifer. Preconsolidation head is the previous minimum head value in the aquifer. For any model cells in which specified HC is greater than the corresponding value of starting head (see McDonald and Harbaugh, 1988, chap. 4, p. 9-12), value of HC will be set to that of starting head.

Data Set 4

Sfe(NCOL,NROW) Module: UZDREL

Sfe is an array specifying the dimensionless elastic storage factor for interbeds present in model layer. The storage factor may be estimated as the sum of the products of elastic skeletal specific storage and thickness of all interbeds in a model layer.

Data Set 5

Sfv(NCOL,NROW) Module: UZDREL

Sfv is an array specifying the dimensionless inelastic storage factor for interbeds present in model layer. The storage factor may be estimated as the sum of the products of inelastic skeletal specific storage and thickness of all interbeds in a model layer.

Data Set 6

COM(NCOL,NROW) Module: UZDREL

Com is an array specifying the starting compaction in each layer with interbed storage. Compaction values computed by the package are added to values in this array so that printed or stored values of compaction and land subsidence may include previous components. Values in this array do not affect calculations of storage changes or resulting compaction. For simulations in which output values are to reflect compaction and subsidence since the start of the simulation, enter zero values for all elements of this array.

IF IIBSOC IS GREATER THAN ZERO

Data Set 7

ISUBFM ICOMFM IHCFM ISUBUN ICOMUN IHCUN

Format: 110 110 110 110 110 110

ISUBFM is a code for the format in which subsidence will be printed.

Format codes have the same meaning for subsidence, compaction, and preconsolidation head and are the same as codes specified by McDonald and Harbaugh (1988, chap. 4, p. 14-15) for printing head and drawdown. A positive code selects their wrap format and a negative code selects their strip format. The absolute value of the code specifies the printout format as follows:

Code

Format

0

(10G11.4)

1

(11G10.3)

2

(9G13.6)

3

(15F7.1)

4

(15F7.2)

5

(15F7.3)

6

(15F7.4)

7

(20F5.0)

8

(20F5.1)

9

(20F5.2)

10

(20F5.3)

11

(20F5.4)

12

(10G11.4)

ICOMFM is a code for the format in which compaction will be printed.

Format codes have the same meaning for subsidence, compaction, and preconsolidation head and are the same as codes specified by McDonald and Harbaugh (1988, chap. 4, p. 14-15) for printing head and drawdown. A positive code selects their wrap format and a negative code selects their strip format. The absolute value of the code specifies the printout format as follows:

Code

Format

0

(10G11.4)

1

(11G10.3)

2

(9G13.6)

3

(15F7.1)

4

(15F7.2)

5

(15F7.3)

6

(15F7.4)

7

(20F5.0)

8

(20F5.1)

9

(20F5.2)

10

(20F5.3)

11

(20F5.4)

12

(10G11.4)

IHCFM is a code for the format in which preconsolidation head will be printed.

Format codes have the same meaning for subsidence, compaction, and preconsolidation head and are the same as codes specified by McDonald and Harbaugh (1988, chap. 4, p. 14-15) for printing head and drawdown. A positive code selects their wrap format and a negative code selects their strip format. The absolute value of the code specifies the printout format as follows:

Code

Format

0

(10G11.4)

1

(11G10.3)

2

(9G13.6)

3

(15F7.1)

4

(15F7.2)

5

(15F7.3)

6

(15F7.4)

7

(20F5.0)

8

(20F5.1)

9

(20F5.2)

10

(20F5.3)

11

(20F5.4)

12

(10G11.4)

ISUBUN is the unit number to which subsidence arrays will be written if they are saved on disk.

ICOMUN is the unit number to which compaction arrays will be written if they are saved on disk.

IHCUN is the unit number to which preconsolidation head arrays will be written if they are saved on disk.

FOR EACH TIME STEP

IF IIBSOC IS GREATER THAN ZERO and Ss/tr indicates that this is a transient stress period.

Data Set 8

ISUBPR ICOMPR IHCPR ISUBSV ICOMSV IHCSV

Format: 110 110 110 110 110 110

ISUBPR is the output flag for subsidence printout.

•If ISUBPR ≤ 0, subsidence is not printed.

•If ISUBPR > 0, subsidence is printed.

ICOMPR is the output flag for compaction printout.

•If ICOMPR ≤ 0, compaction is not printed.

•If ICOMPR > 0, compaction is printed for each layer with interbed storage.

IHCPR is the output flag for preconsolidation head printout.

•If IHCPR ≤ 0, preconsolidation head is not printed.

•If IHCPR > 0, preconsolidation head is printed for each layer with interbed storage.

ISUBSV is the output flag for saving subsidence in an unformatted disk file.

•If ISUBSV ≤ 0, subsidence is not saved.

•If ISUBSV > 0, subsidence is saved.

ICOMSV is the output flag for saving compaction in an unformatted disk file.

•If ICOMSV ≤ 0, compaction is not saved.

•If ICOMSV > 0, compaction is saved for each layer with interbed storage.

IHCSV is the output flag for saving preconsolidation head in an unformatted disk file.

If IHCSV ≤ 0, preconsolidation head is not saved.

If IHCSV > 0, preconsolidation head is saved for each layer with interbed storage.