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Final Project I. Calibration Drawdown Prediction Particle Tracking Presentation of Results. Final Project. Particle Tracking. FLOW NETS. The streamfunction, . (from Hornberger et al., 1998). (from Hornberger et al., 1998). A flow net consists of equipotential lines and streamlines .

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Presentation Transcript
slide1

Final Project

  • I. Calibration
  • Drawdown Prediction
  • Particle Tracking
  • Presentation of Results
slide4

FLOW NETS

The streamfunction, 

(from Hornberger et al., 1998)

slide5

(from Hornberger et al., 1998)

A flow net consists of equipotential lines and streamlines.

slide6

Particle Tracking

(used to trace flow lines)

distance = velocity x time

slide7

Particle Tracking

(used to trace flow lines)

Groundwater flow model

MODFLOW

Note: need to input

effective porosity, ne

Darcy’s law

v = KI / ne

Particle tracking code

MODPATH,

Path3D

slide8

Particle tracking simulates advection of

contaminant “particles”.

Transport models (e.g., MT3D) simulate

advection, dispersion and chemical reactions.

Retardation caused by linear adsorption reactions

can be simulated using particle tracking, since

the velocity can be adjusted: vc = v/Rd

Rd is the retardation coefficient.

slide9

Steps in Particle Tracking

  • Need to interpolate velocities from nodal
  • point values since particle tracking is done
  • in a continuous coordinate system.
  • Need to track the movement of the particles
  • in the computed velocity field.
slide10

Interpolation Schemes

  • Linear (MODPATH, Path3D)
  • Bilinear
  • Reverse distance (FLOWPATH)
slide11

Tracking

distance = velocity x time

dx/dt = vx

dx = vx dt

slide12

Tracking Schemes

Semianalytical (MODPATH)

Euler (FLOWPATH)

Runge Kutta (Path3D)

Taylor Series (WHPA)

slide13

Profile Models

(e.g., the Toth Problem)

h = c x + zo

z

x

z

x

slide14

Profile Models

  • The profile should be oriented parallel to flow.
  • Axisymmetric profiles (useful to simulate pumping)
  • Slice orientation and layer orientation
slide15

Layer Orientation

Profile – unconfined aquifer

2D confined aquifer

for homogeneous, anisotropic aquifers

 We can simulate a profile by

using 1 confined layer in MODFLOW.

slide16

Problem 6.1a

Specified head cells

Active cells

MODFLOW computes fluxes between specified head cells and active cells.

MODFLOW does not compute fluxes between specified head cells; you need to compute those manually.

slide17

Qp= Q1 + Q2

Q2

Q1

active cells with injection wells

Active cells

In problem 6.1b, you use injection wells to simulate

recharge to the profile. Calculate the injection rate

as the net flux into each of the cells in the top row.

slide18

Problem Set 6 illustrates:

  • Use of a confined MODFLOW layer to simulate an
  • unconfined aquifer in profile view.
  • Procedure for switching from specified head
  • to specified flux boundary conditions.
slide19

Problems dealing with the water table

  • In a profile model or a 3D model, the water table
  • typically forms the upper boundary of the model.
  • In transient problems the water table fluctuates and the
  • position of the water table is unknown.
  • MODFLOW
  • utilizes the Dupuit assumptions
  • to calculate the water table in unconfined layers.
  • Recharge typically occurs to the top active cell.
slide20

Alternatives to MODFLOW for water table problems

Finite element codes with deformable elements allow

the element to deform as the water table moves.

Codes that incorporate the unsaturated zone.

slide21

Models that incorporate the unsaturated zone

solve for the position of the water table by locating

where pressure head (hp) equals zero.

h = z + hp = z + p/g

Total head = elevation head + pressure head

2D USGS codes for flow in partially saturated media

(unsaturated zone and saturated zone)

VS2DTI (for water and solutes)

VS2DHI (for water and heat)

Other codes include: SUTRA, HYDRUS and many others.

slide22

infiltration

Possible seepage face

Example problem

run with VS2D

Infiltration into

a cross section

with a slope

low K

layer

perched water

Pressure

head = 0

defines

the water

table