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Interdisciplinary Modeling of Aquatic Ecosystems Curriculum Development Workshop July 18, 2005 Groundwater Flow and Tran PowerPoint Presentation
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Interdisciplinary Modeling of Aquatic Ecosystems Curriculum Development Workshop July 18, 2005 Groundwater Flow and Transport Modeling. Greg Pohll Division of Hydrologic Sciences Desert Research Institute. July 18, 2005. Outline. Why model? What are models? Groundwater modeling protocol

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Interdisciplinary Modeling of Aquatic Ecosystems Curriculum Development WorkshopJuly 18, 2005Groundwater Flow and Transport Modeling

Greg Pohll

Division of Hydrologic Sciences

Desert Research Institute

July 18, 2005

outline
Outline
  • Why model?
  • What are models?
  • Groundwater modeling protocol
  • Governing equations
  • Input/output data
  • Model scales
  • Uncertainty
  • Interdisciplinary issues
  • Modeling difficulties
  • Modeling options

July 18, 2005

why model
Why Model?
  • Prediction
    • Solve management problems
      • When will contaminated groundwater move off site
      • How much water can be pumped
  • Interpretation
    • Data synthesis
    • Studying system dynamics
  • Hypothesis testing
    • Testing new theories and conceptual models

July 18, 2005

what is a model
What is a Model?
  • A model is anything that represents an approximation of a field situation
  • Models include:
    • Mathematical models
      • Numerical
      • Analytical
    • Physical models
      • Sand tank
  • A model is a simplified version of a real system and the phenomena that take place within it

July 18, 2005

modeling protocol
Modeling Protocol

Define Purpose

Collect Field Data

Conceptual Model

Mathematical Model

Numerical or Analytical

Write or Choose Code

No

Verify Code

Yes

Model Design

Field Data

Calibration

No

Verification

Yes

Prediction/Sensitivity Analysis

Presentation of Results

Collect Field Data

Postaudit

July 18, 2005

governing equations
Governing Equations
  • Flow Model
  • Transport Model

Fluid continuity

Storage

Sources/sinks

First Order

Decay

Source/

Sink

Sorption

Matrix

Diffusion

Advection

Dispersion

July 18, 2005

input output data
Input/Output Data
  • Flow model input data requirements
    • Defining hydrostratigraphic units
    • Fluid sources (e.g. recharge, interbasin flow)
    • Fluid Sinks (e.g. ET, pumping)
    • Boundary conditions (e.g. specified flow, specified head, head-dependent)
    • Model grid geometry
    • Time stepping information
    • Hydraulic Parameters
    • Initial hydraulic head distribution

July 18, 2005

input output data1
Input/Output Data
  • Flow model output
    • Hydraulic head values over space and time
    • Groundwater fluxes over space and time

July 18, 2005

input output data2
Input/Output Data
  • Transport model input requirements
    • Fluid velocities
    • Initial distribution of contaminants
    • Sources and sinks for contaminants
    • Boundary conditions
    • Dispersion coefficients
    • Effective porosity
    • Decay and/or reaction coefficients
    • Contaminant loading functions

July 18, 2005

input output data3
Input/Output Data
  • Transport model output
    • Contaminant concentrations over space and time
    • Contaminant breakthrough curves at specified locations

July 18, 2005

model scales
Model Scales
  • Groundwater flow and transport models span scales from the sub-centimeter to 100’s of kilometers

July 18, 2005

model uncertainty
Model Uncertainty
  • Predictions made by groundwater flow and transport model are inherently uncertain
  • The uncertainty stems from numerous sources
    • Conceptual model errors
    • Lack of information on the spatial and temporal variability
    • Errors due to inaccurate boundary condition specification
    • Numerical solvers can impart errors, especially for transport solutions
    • Parametric uncertainty in model input parameters

July 18, 2005

model uncertainty1

Input Parameter PDF

Model

Prediction PDF

Model Uncertainty
  • Since model uncertainty always exists modelers should strive to quantify it impact on model predictions
  • Methods typically used to quantify uncertainty include:
    • Taylor’s series approximations (e.g. first order second moment techniques)
    • Monte Carlo analysis
    • Statistical evaluation of spatial variability in input parameters
    • Bayesian techniques

July 18, 2005

interdisciplinary issues
Interdisciplinary Issues
  • As groundwater models become more and more complex, so does the need for integrated modeling teams and models
  • Some of the disciplines that are typically required to effectively build complex models include:
    • Geochemists
    • Geologists
    • Surface water hydrologists
    • Statisticians
    • Ecologists
    • Biologists
    • Soil scientists
    • Heath physicists

July 18, 2005

interdisciplinary issues1
Interdisciplinary Issues
  • Groundwater models are beginning to be coupled to other types of models to investigate various types of problems
    • Surface/subsurface models (e.g. GSFLOW, MIKE-SHE)
    • Flow and geochemical reaction models (e.g. FEHM, PHREEQC)
    • Risk assessment

July 18, 2005

modeling difficulties
Modeling Difficulties
  • Defining a purpose and associated objectives
  • Estimating groundwater recharge
  • Assigning boundary conditions
  • Calibrating
  • Estimating the source term for transport models

July 18, 2005