MODFLOW General

1
MODFLOW

• What is it and what does it do?
• What are the required inputs?
• What are the outputs?
• Who runs and maintains it?
• Resources requirements to generate useful output?

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MODFLOW

• What is it and what does it do?
• Modular finite-difference flow model
• Program that solves the groundwater flow equation
• Describes 3-D groundwater flow in a porous media
• Used to simulate the flow of groundwater through
  aquifers.

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Discretizing 1
Springs
Well
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Discretizing 4
5
Discretizing 6
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Boundaries
Upper Deschutes Basin Model Grid with Boundary
Conditions
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MODFLOW

• General requirements for groundwater flow models
• Physical Framework
• Geologic map, Topographic map, thickness of
  aquifer and confining beds, etc
• Hydrogeologic Framework
• Head maps for all aquifers, well hydrographs,
  aquifer properties, spatial/temporal distribution
  of flux, etc
• Adapted from Anderson and Woessner

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MODFLOW

• What are the required inputs?
• Physical properties of the modeled system.
• Geometry (conceptual model and grid design)
• Boundary Conditions
• Internal Properties (hydraulic conductivity
  storativity, etc)
• Sources/Sinks (recharge, streams, wells, etc)

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K value zones (layers 1 2)
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Recharge
Average Annual Recharge, 1993-1995
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Wells
Wells included in the Simulation
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MODFLOW

• What are the outputs?
• Hydraulic head distribution.
• Flux distribution.

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Conceptual Model


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MODFLOW

• Who runs and maintains it?
• Developed by USGS.
• Software is public domain. Open source (anyone
  can modify source code).
• Periodic upgrades/releases by USGS. (4 since
  release in early 1980s.
• Numerous commercial interfaces available.
• The Upper Deschutes model (a specific application
  of MODFLOW) is available from USGS and OWRD.

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MODFLOW

• Resource Requirements?
• Scope of the project.
• Availability of hydrologic data.
• Geologic knowledge.
• Conceptual understanding of the hydrology.
• Accuracy requirements.
• Deschutes hydrologic study (gt5 years)
• Subsequent simulations (weeks).

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MODFLOW

• Other thoughts on MODFLOW.
• Very useful in proving the conceptual
  understanding of an areas hydrology.
• Very useful in providing new hydrologic insights.
• If calibrated properly, very useful as a
  predictive tool.

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Redmond Well Simulation Model Layer 2
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Canal Lining Simulation
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MODFLOW

• Other thoughts on MODFLOW.
• Interpret model results in context of model
  accuracy, scale, and hydrologic understanding.
• Interpret model results in context of other data
  sets (e.g., chemistry data).
• Understand model processes (algorithms) in
  context of how well the model simulates a
  specific area.
• http//wwwbrr.cr.usgs.gov/projects/GW_ModUncert/hi
  ll_tiedeman_book/