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Twin Cities Metropolitan Area Groundwater Flow Model (Metro Model)

As part of a regional water supply planning effort, the Metropolitan Council (Council) is constructing a Twin Cities metropolitan area groundwater flow model (Metro Model) with the cooperation of Barr Engineering Company, a technical workgroup (meeting materials) and other stakeholders. This modeling effort builds upon the Minnesota Pollution Control Agency’s (MPCA’s) 2000 Metro Model.

 

The new Metro Model will help Council staff and stakeholders assess current and projected groundwater withdrawals, future water availability, and to identify alternatives in areas facing possible future water supply limitations. Specifically, the model will help answer questions such as:

 

  • What is the likely maximum pumping capacity of a proposed wellfield or well?
  • What will drawdown be from a proposed well or wellfield, and what existing wells might be impacted?
  • What will groundwater levels be in the future, given projected water demand?
  • How will pumping affect important ecological resources such as calcareous fens and trout streams?
  • How might land use and development patterns affect recharge and groundwater levels?

 

The Council will make the Metro Model and supporting datasets available to the public for water supply management, protection, research and other applications in the metropolitan area. The Council intends to update and to perform routine maintenance on the model, to ensure that it is available with up-to-date information for ongoing planning and other applications.

 

What is a groundwater model?

Groundwater models are tools that improve our understanding of aquifer behavior. A numerical groundwater flow model, such as the one being constructed for the Twin Cities Metropolitan Area, is the mathematical representation of aquifers in a computer. Using specially developed software code, the computer models the behavior of aquifers over time by applying the basic laws of physics governing groundwater flow to the physical boundaries of the aquifer, recharge, pumping, interaction with rivers, or other phenomenon.

 

Metropolitan Council’s Metro Model vs. Minnesota Pollution Control Agency’s Metro Model

The Council's Metro Model, like the Minnesota Pollution Control Agency’s (MPCA’s) Metro Model, will be a coarse, regional-scale, multi-aquifer groundwater flow model of the seven-county metropolitan area for use in both the public and private sectors.

 

The most notable difference between the Council's Metro Model and the MPCA's Metro Model is the use of the finite difference MODFLOW code instead of Multi-Layer Analytical Element Mode (MLAEM) codel. Other differences include the development of additional model layers to reflect our improved understanding of hydraulic variability and characteristics within geologic units, and use of an automated inverse optimization method for model calibration.

 

Which aquifers will be modeled?

All of the major aquifers of the seven-county metropolitan area will be modeled. These aquifers include: (1) Glacial Drift/Recent Alluvium, (2) St. Peter Sandstone, (3) Prairie du Chien Group, (4) Jordan Sandstone, (5) St. Lawrence Formation, (6) Upper Franconia Formation, (7) Ironton-Galesville Sandstones, (8) Eau Claire Formation, and (9) Mt. Simon-Hinckley Sandstones.

 

See Metropolitan Area Aquifer Map (pdf 8KB)

 

Datasets

Datasets are still under development and should not be considered final. Data was last updated on March 3, 2008.

If you have comments or questions about these data, please contact Lanya Ross at lanya.ross@metc.state.mn or 651-602-1803.

 

Important caveats regarding GMS versions of the model:

  • The current version of GMS only supports MODFLOW-2000.  The Groundwater Vistas model was converted from MODFLOW 96 to MODFLOW 2000. 
  • GMS does not support the ability to force convergence if the convergence criteria are met for a given number of iterations.  When using the PCG solver with resaturation capability turned on, this often becomes necessary as the model will not fully converge.  If you run the GMS version out to 20 iterations, you should get essentially the same solution.
  • GMS will not automatically calculate the leakance needed for the BCF package.  So, if changes are made to the model (i.e. the K of a given zone is changed) leakance needs to be manually calculated.  This can be a very tedious task.  Therefore, a second GMS version was created using the LPF package instead of the BCF package.  When using the LFP package, it is not necessary to calculate the leakance term.

 

  • Subregional Models

 

 

 

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