Dr. James M. MartinHayden

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Dr. James M. Martin-Hayden Associate Professor
[phone] Jhayden_at_Geology.UToledo.edu
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Ground Water Flow Modeling

• A Powerful Tool
• for furthering our understanding of
  hydrogeological systems

• Importance of understanding ground water flow
  models
• Construct accurate representations of
  hydrogeological systems
• Understand the interrelationships between
  elements of systems
• Efficiently develop a sound mathematical
  representation
• Make reasonable assumptions and simplifications
  (a necessity)
• Understand the limitations of the mathematical
  representation
• Understand the limitations of the interpretation
  of the results

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3-D Darcys Law (cont.)

• Horizontal and Vertical Hydraulic Gradients

• Horizontal Component, in field applications
• Represented as a single vector perpendicular to
  flow lines
• Approximated using a 3 point problem or a
  contour map of the piezometric surface
  (horizontal component only)

Ds385m
0.0104

• Vertical component
• Often taken as positive downward
• Can be approximated using a well nest

Dh4.00m
hs 291.26m
hd 290.74
Dh0.52m
Dz-5.84m
Vz
Finite difference approximation
-0.0890 m
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Introduction to Ground Water Flow Modeling

• Predicting heads (and flows) and
• Approximating parameters

• Solutions to the flow equations
• Most ground water flow models are solutions of
  some form of the ground water flow equation

• The partial differential equation needs to be
  solved to calculate head as a function of
  position and time, i.e., hf(x,y,z,t)

• e.g., unidirectional, steady-state flow within a
  confined aquifer

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Flow Modeling (cont.)

• Limitations of Analytical Models
• Closed form models are well suited to the
  characterization of bulk parameters
• However, the flexibility of forward modeling is
  limited due to simplifying assumptions
• Homogeneity, Isotropy, simple geometry, simple
  initial conditions
• Geology is inherently complex
• Heterogeneous, anisotropic, complex geometry,
  complex conditions

• This complexity calls for a more
• powerful solution to the flow equation ?
  Numerical modeling

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Finite Difference Modeling (cont.)

• 3-D Finite Difference Models
• Requires vertical discretization (or layering) of
  model

K1
K2
K3
K4
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Case Study

• An unconfined sand aquifer in northwest Ohio
• Conceptual Model

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Groundwater Sampling
An Overview

• Boreholes our primary method of collecting
  subsurface data
• Geological data does not change much, but

Water Table

• Groundwater geochemistry is always changing

• Enter, groundwater monitoring wells
• screen sediments out and allow groundwater in to
  be sampled
• provide continuous access to the subsurface
  (i.e. allow groundwater monitoring)