| MODFLOW |
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| Pre-processing |
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MODFLOW Commands |
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Building a MODFLOW Model |
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Map to MODFLOW |
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Calibration |
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Packages Supported in GMS |
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Saving a MODFLOW Simulation |
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Importing MODFLOW Files |
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Unsupported MODFLOW Features |
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Run MODFLOW |
| Post-processing |
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MODFLOW Display Options |
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MODFLOW Post-Processing Viewing Options |
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Reading a MODFLOW Simulation |
| Tutorials |
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| Packages |
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| Flow: |
BCF6, HUF, LPF, UPW |
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| Solvers: |
DE4, GMG, NWT, PCG,
PCGN, LMG, SIP, SOR,
SMS |
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| Other: |
BAS6, BFH, CHD1, CLN,
DRN1, DRT1, EVT1, ETS1,
GAGE, GHB1, GNC, HFB1,
HUF, LAK3, MNW1, MNW2,
OUT1, RCH1, RIV1, SFR2,
STR1, SUB1, SWI2, WEL1,
UZF1 |
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The STR and SFR packages are used to simulate the interaction between surficial streams and the groundwater. These packages are somewhat similar to the River package in that water can move from the stream to the aquifer or from the aquifer to the stream depending on the relative differences in the stream stage and the water table elevations. However, unlike the River package, flow is routed through the stream. For the STR package, simple channel hydraulics and Manning's equation are used to compute the stage in the stream. The SFR package has more sophisticated hydraulics and routing options.
Stream Network
When either the STR or SFR package is used, a complete, ordered stream network must be defined as shown in the following figure.
A stream network is composed of reaches and segments. A reach is the portion of a stream that lies inside a single cell. A single cell may contain multiple reaches. A segment is a group of reaches that forms one section of the stream. The reaches within a segment are always numbered from upstream to downstream. The segments should also be numbered from upstream to downstream.
The incoming flowrate may only be defined for the topmost segments (segments 1, 4, and 6 in the above figure) and is typically entered as a positive value to represent the amount of flow in the stream channel. Flow is then routed and combined to get the incoming flowrate for the other segments. An exception to this is a diversion such as the canal at segment #2 in the above figure. In this case the flowrate into the diversion should be specified. The flow to the diversion would be subtracted from the flow coming out of segment #1 and whatever is left over would be routed to segment #3.
Defining Streams
Unlike other packages in GMS, a stream network cannot be created by selecting cells in the grid and manually assigning values to the cells. Due to the complex nature of the input and the requirement that the data be ordered in a specific fashion, a stream network can only be created using a series of Stream Arcs in the Map module. The cell-by-cell values are automatically created and properly ordered when the Map -> MODFLOW command is selected.
There are some restrictions on the STR and SFR conceptual models:
- STR and SFR stream arcs cannot both exist in the same coverage because of the stream numbering issues.
- All STR (or SFR) arcs must be in one coverage. You cannot use two or more coverages to represent your stream network.
- SFR - All downstream streams must be diversions except for one. The variable OUTSEG is the segment number of the downstream segment that is not a diversion.
- SFR - If the current segment has the diversion flag set then IUPSEG is the id of the upstream segment.
Set Arc Directions From Stream Data
Right-clicking on a coverage containing STR streams shows a Set Arc Directions From Stream Data menu item. This operation will cause all stream arcs to point downhill based on the elevation of the top of the river sediments as defined at the nodes.
STR Package
In the input file for the STR package, each reach is assigned the following values:
- stage (typically starting stage)
- conductance factor (multipled by the conductance during parameter estimation)
- Elevation of the bottom of the streambed
- Elevation of the top of the streambed
Each segment is assigned the following values:
- incoming flow (for top segments and diversions)
- IDs of tributaries (upstream segments)
- ID of upstream segment (for diversions only)
When Manning's equation is used to route the flow through the network, the stream channels are assumed to have a rectangular cross section.
When the Map -> MODFLOW command is selected, GMS automatically does the following: classifies all of the cells beneath the streams as reaches, builds segments, numbers the reaches and segments, and assigns the appropriate values to the reaches and segments. These values defined at the nodes are linearly interpolated across the arcs when the model is converted. The slope assigned to reaches is computed by dividing the difference in the streambed top elevations at the ends of the arc by the arc length multiplied by the sinuosity factor.
The STR Package Dialog
Once the Map -> MODFLOW command is selected and the stream data have been assigned to the grid cells, the data can be viewed and some of the input values can be edited using the Stream Package dialog. The options for the Stream Package dialog include:
Calculate Stage
- The Calculate stage toggle is used to specify whether the Stream package should compute the stages (specified stages are initial values only) or whether the specified stages should be used directly.
SFR Package
Support for the SFR2 package was added at GMS version 7.0.
The SFR Package Dialog
Once the Map -> MODFLOW command is selected and the stream data have been assigned to the grid cells, the data can be viewed and some of the input values can be edited using the SFR Package dialog. Stream segments and reaches cannot be created in the SFR Package dialog - creation can only be done via the Map -> MODFLOW command. The SFR Package dialog has two spreadsheets, one showing stream segments and one showing stream reaches. For a further explanation of the columns in each spreadsheet you can refer to the Online Guide to MODFLOW.
ISTCB2 info
The ISTCB2 info combo box controls the ISTCB2 flag in the SFR file. This flag can be used to tell MODFLOW to output lots of stream related data such as the flow in and out of each stream reach. There are three choices:
- Don't save
- No extra information will be saved. The standard information specified by the ISTCB1 flag will still be saved if the Save cell by cell flow terms to *.ccf file is on in the Output Control dialog.
- Save to CCF file
- The information will be saved to the CCF file. If this option is chosen, the standard information specified by the ISTCB1 flag will NOT be written to the CCF file. So, you can get the ISTCB1 info or the ISTCB2 info, but not both. This is because if both are specified, MODFLOW merges the info in the CCF file in a way that is difficult to read. However, the ISTCB2 info also includes the ISTCB1 info, so nothing is lost.
- Save to .istcb2 text file
- MODFLOW will write a text file with the same prefix as all the other files but with a .istcb2 extension. This text file will be displayed in the MODFLOW Solution in the Project Explorer when the solution is imported.
