CEGR 4145 5145 Groundwater Resources Engineering

1
CEGR 4145 / 5145 Groundwater Resources
Engineering

• Groundwater Modeling (Ch. 13)
• Physical Scale Models
• Analog Models
• Mathematical Models
• Excel-based modeling
• Visual MODFLOW

2
Reasons for Modeling

• Explain observed aquifer behavior
• Predict response in future, under various
  stresses
• Primary GW models
• Groundwater flow
• Solute flow
• Heat flow
• Aquifer deformation

3
GW Flow and Solute Transport

• Models based on equations to describe
• Porous Media
• Fractured Media
• Saturated Zone
• Unsaturated Zone

4
Data Requirements

• GW Flow
• Physical dimensions, strata thicknesses, boundary
  conditions, formation constants (T, K and S),
  recharge, head distribution, etc.
• Solute Transport
• In addition to GW flow data, effective porosity,
  aquifer dispersivity, fluid density variability,
  contaminant source and strength, soil reactivity
  (distribution coefficients), etc.

5
Model Calibration and Verification

• For GW Flow models, a primary goal is often to
  develop the potentiometric surface for a given
  area
• This model is calibrated against known values
  of head (from an observation well). Aquifer
  properties are adjusted.
• Matching the model-predicted values of head to
  those previously produced (or in the future) in
  response to a transient event provides
  verification

6
Mathematical Model Types

• Finite Difference (Fig. 13.1, 13.2 text)
• Real geometry is discretized into grid nodes
• Finite Element (Fig. 13.5 text)
• Real geometry is discretized into elements
• In either case, the governing differential
  equations can be simplified

7
Governing Equations

• Conservation of Energy, Darcys Law in 3D.(pages
  125-128)
• Equation 4.42, p. 128 (unsteady state)
• Laplaces Equation, (Eq. 4.43, steady state)
• Finite Difference Notation Solution is much
  simplerEq. 13.1, p. 521 (without recharge)
• Function of head and distance
• Boundary Conditions-Known Head or Known Flow

8
GW Models

• Excel-based Modeling (Ex., p. 531)
• Visual MODFLOW
• MODFLOW, the code is from the USGS
• Waterloo Hydrogeologic makes it easier to work
  with
• Generally working with an accepted model is
  better than developing a new one, particularly
  from a regulatory perspective