subsurface hydrology
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Subsurface Hydrology. Unsaturated Zone. Water table. Saturated Zone . R = P - ET - RO. ET. ET. P. RO. E. R. R / P = ?. Water Table. Groundwater. Processes we might want to model Groundwater flow calculate both heads and flow

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subsurface hydrology
Subsurface Hydrology

Unsaturated Zone

Water table

Saturated Zone

slide2

R = P - ET - RO

ET

ET

P

RO

E

R

R / P = ?

Water Table

Groundwater

slide3

Processes we might want to model

  • Groundwater flow
  • calculate both heads and flow
  • Solute transport – requires information on flow (velocities)
  • calculate concentrations

v = K I / n

Darcy’s law

slide4

Conceptual Model

A descriptive representation

of a groundwater system that incorporates an interpretation of the geological & hydrological conditions. Generally includes information about the water budget.

slide5

Toth Problem

Water Table

Groundwater

divide

Groundwater

divide

AQUIFER

Impermeable Rock

Steady state system: inflow equals outflow

slide6

Types of Models

  • Physical (e.g., sand tank)
  • Analog (electric analog, Hele-Shaw)
  • Mathematical
slide9

Types of Models

  • Physical (e.g., sand tank)
  • Analog (electric analog, Hele-Shaw)
  • Mathematical
slide10

Components of a Mathematical Model

  • Governing Equation (Darcy’s law + water balance eqn) with head (h) as the dependent variable
  • Boundary Conditions
  • Initial conditions (for transient problems)
slide11

Toth Problem

Water Table

Groundwater

divide

Groundwater

divide

AQUIFER

Impermeable Rock

Steady state system: inflow equals outflow

slide12

Toth Problem

Water Table

Groundwater

divide

Groundwater

divide

Laplace Equation

Impermeable Rock

2D, steady state

slide13

Types of Solutions of Mathematical Models

  • Analytical Solutions: h= f(x,y,z,t)
  • (example: Theis eqn.)
  • Numerical Solutions
  • Finite difference methods
  • Finite element methods
  • Analytic Element Methods (AEM)
slide14

Topo-Drive

Finite element model of a version of the Toth Problem for regional flow in cross section.

slide15

Finite difference models

  • may be solved using:
  • a computer program or code (e.g., a FORTRAN program)
  • a spreadsheet (e.g., EXCEL)
slide16

MODFLOW

  •  a computer code that solves a groundwater flow model using finite difference techniques
  • Several versions available
  • MODFLOW 88
  • MODFLOW 96
  • MODFLOW 2000
  • MODFLOW 2005
slide17

Steps in Groundwater Modeling

  • 1. Model Design
  • Calibration (History matching)
  • Prediction (of heads)
slide18

Define Purpose

Conceptual Model

Field Data

Mathematical Model

Numerical Method-Computer Code

Model Design

Grid, Boundary and Initial Conditions, Parameterization

Calibration and Sensitivity Analyses

Predictive Simulation

Presentation of Results

Postaudit

slide19

Define Purpose

Conceptual Model

Field Data

Mathematical Model

Numerical Method-Computer Code

Model Design

Grid, Boundary and Initial Conditions, Parameterization

Calibration and Sensitivity Analyses

Predictive Simulation

Presentation of Results

Postaudit

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