Groundwater Modeling Assignment 3

1
Groundwater Modeling Assignment 3

• Model Sensitivity Analysis

2
Example

• No-flow boundaries north south
• Constant-head boundaries west east sides
• Layer 1 (Upper) Unconfined sandy gravel aquifer
• Kh 100 m/day (assumed)
• Kv 10 m/day (assumed)
• n 0.15 (porosity)
• Layer 2 (Lower) Confined silty sand aquifer
• Kh 10 m/day (assumed)
• Kv 1 m/day (assumed)
• n 0.15 (porosity)

3
Model Information

• 30 rows 30 columns
• Row spacing 20 m
• Column spacing 20 m
• 2 Layers
• Top of Layer 1 10 m
• Bottom of Layer 1 -3 m
• Bottom of Layer 2 -8 m
• Column 1, Layers 1 and 2, Constant Head Boundary
  9 m
• Column 30, Layers 1 and 2, Constant Head Boundary
  8 m
• Initial Heads 0 ft for both layers 1 and 2
• Recharge Top layer only

4
Model Information (Continued)

• Create a transient model for this example
• Use 12 stress periods, one for each day for 12
  days
• Layer 1
• Q 0 m3/d for stress periods 1, 2, and 3
• Q -159840 m3/d for stress periods 4 - 12
• Layer 2
• Q 0 m3/d in stress periods 1, 2 and 3
• Q -1296 m3/d in periods 4 12
• Storage
• Ss 0.0001, Sy 0.15, Porosity 0.15
• Leakance 864 m/day

5
Target Data

• The table shows the measured heads in the aquifer
  at the indicated model cell locations

6
Target Data
NOTE Not EVERY day is included!
Layer 1
Layer 2
7
Assignment

• Develop a MODFLOW model for the 2-layer aquifer
  system
• Use the target values of head and Sensitivity
  Analysis to determine the hydraulic conductivity
  of both aquifer layers

8
Procedure

• See class handout for
• Thursday Feb. 21, 2008
• Start on Slide 12
• www.ce.utexas.edu/prof/mckinney/ce374l/Overheads/1
  0-MODFLOW.pdf

Adapted from Chiang, W-H and W. Kinzelbach,
Processing Modflow A Simulation System For
Modeling Groundwater Flow and Pollution, 1996
9
Create a New Model

• Start the GV program
• Select File --gt New
• Enter basic information about the model
• 30 rows 30 columns
• Row spacing 20 m
• Column spacing 20 m
• Top of Layer 1 10 m
• Bottom of Layer 1 -3 m
• Bottom of Layer 2 -8 m

Press
10
Model Grid
Elevation 10 m
Elevation -3 m
Elevation -8
11
Layer 1 Top (Ground) Elevation

• Select Props ? Top Elevation

Increase layer number to 2
Bottom Layer
Top Layer
12
Add Constant Head Boundary Conditions

• Select Layer 1
• Select BCs ? Constant Head Boundary
• Select BCs ? Insert ? Window
• Hold left Mouse button and Drag cursor through
  cells in Column 1
• Set value to 9 m

Constant Head Boundary Cells (h 9 m)
Top Layer - 1
13
Repeat for Boundary in Column 30

• Select Layer 1
• Select BCs ? Constant Head Boundary
• Select BCs ? Insert ? Window
• Hold left Mouse button and Drag cursor through
  cells in Column 30
• Set value to 8 m

Constant Head Boundary Cells (h 8 m)
Top Layer - 1
14
Repeat for Layer 2

• Select Layer 2
• Select BCs ? Constant Head Boundary
• Select BCs ? Insert ? Window
• Hold left Mouse button and Drag cursor through
  cells in Columns 1 and 30
• Set value to 9 and 8 m

Constant Head Boundary Cells (h 8 m)
Bottom Layer - 2
15
Edit Database - Hydraulic Conductivity

• Select Properties ? Hydraulic Conductivity
• Select Property Values ? Database
• Set up 2 zones
• 1 Upper Layer Kh 100 m/dayKv 10 m/day
• 2 Lower Layer Kh 10 m/dayKv 1 m/day
• Click OK

16
Assign Conductivity Values to Layers

• Select Layer 1
• Select Props ? Hydraulic Conductivity
• Select Props ? Set Value or Zone ? Window
• Start in upper right-hand corner and drag to
  select all cells in grid
• Click OK
• Select Zone Number 1
• Click OK
• Repeat for Layer 2, but assign it zone number 2

17
Add Well Boundary Conditions

• Select Layer 1
• Select BCs ? Well
• Select BCs ? Insert ? Single Cell
• Use cursor to click on cell at Row 15, Column 25
• Enter Flow Rate in Well
• Layer 1
• Q 0 m3/d for stress periods 1, 2, and 3
• Q -159840 m3/d for stress periods 4 - 12
• Layer 2
• Q 0 m3/d in stress periods 1, 2 and 3
• Q -1296 m3/d in periods 4 12
• Select OK

18
Target Locations

• The table shows the measured heads in the aquifer
  at the indicated model cell locations

19
Target Data
NOTE Not EVERY day is included!
Layer 1
Layer 2
20
Add Target Location

• Select Add-gtTargets from the main menu.

T1L1
21
Target Data

• Enter Target Data

22
Create MODFLOW Dataset

• Save your model
• you know how to do this

23
Run Simulation

• Select Calculator button
• Would you like to process the results? Select
  Yes
• Select Cell-by-cell flows

24
Results
25
Set Display Options

• Select Plot ? What to display
• Select Display Color Flood of Head
• Select Display Legend
• Select OK

26
Set Legend Options

• Select Plot ? Legend ? Options
• Select Contents
• Select Color Flood Scale
• Select Dry Cells
• Select Title
• Select Title Font 10 bold
• Select Text Font 10
• Select OK

27
Results
28
Target Results
29
GV Automatic Sensitivity Analysis

• Select Model-gtAuto Sensitivity-gtOptions
• Select Well Discharge as the parameter to vary
• Keep the default of Zone number 1 and change the
  number of simulations from 5 to 11.
• Click on the Multipliers button
• Enter the values 0.5, 0.6, 0.7, 0.8, 0.9, 1.0,
  1.1, 1.2, 1.3, 1.4, and 1.5 for simulations 1
  through 11, respectively

30
Scripting Sensitivity Analysis

• Evaluate multiple parameters (i.e., Q1 and Q2 in
  layers 1, and 2)
• Run the automatic sensitivity analysis from a
  script file generated by GV
• Select New Script button
• GV will prompt for a file name. Use default
  name.
• Make sure to place the file in the working
  directory (\...\work)

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Scripting Sensitivity Analysis

• GV asks for a range of zones
• Enter 1 for the minimum zone and 2 for the
  maximum zone
• Again, use zones 1 to 2 on the next dialog
• Select the Run from Script File button
• Select browse next to the output file name and
  place it in the same directory as the sensitivity
  script file.
• Click OK

32
Running Sensitivity Analysis

• Select Models-gtAuto Sensitivity-gtRun Analysis
• MODFLOW will flash on your screen numerous times
• After the last simulation a dialog will ask
  whether you would like to see the results.
• Select Yes
• Choose squared residuals

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View Sensitivity Results

• Select Plot ? Sensitivity Analysis ? Plot
  Scripted Results
• Select file autosens.OUT
• Select Sum of Squared Residuals

34
Results Sensitivity AnalysisRound 1
35
View Residual Statistics

• View calibration statistics
• Select Plot-gtCalibration-gtStatistics/Plots
• Select head as the type of targets
• Click the Statistics button
• Residual sum of squares m2

36
Plot Residuals

• Click Plot Observed vs. Simulated button.
• Ideally the plot shown should be a straight line
  oriented at a 45-degree angle.
• In that case, the observed value should equal the
  simulated value.