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Groundwater Modeling 3: Transient Models
Daene C. McKinney, Professor The University of Texas Austin
Eusebio Ingol Blanco, Teaching Assistant
Remember Your Old Model?
• Find the file that you used for the example model from the previous class
• Or recreate it by reviewing the overhead slides from that assignment.
Example • Boundaries
– North & South: No-flow
– East & West: Constant-head
• Layer 1 – unconfined (13 m) – Kh = 5x10-3 m/s; Kv = 5x10-4 m/s
– Porosity = 0.25
• Layer 2 – confined (5 m) – Kh = 1x10-3 m/s; Kv = 1x10-4 m/s
– Porosity = 0.25
No-flow Boundary
No-flow Boundary
Con
sta
nt H
ea
d B
ou
nd
ary
(h =
9 m
)
Co
nsta
nt H
ea
d B
ou
nd
ary
(h
= 8
m)
Pumping Well
60
0 m
600 m Adapted from Chiang, W-H and W. Kinzelbach, Processing Modflow: A
Simulation System For Modeling Groundwater Flow and Pollution, 1996
Pumping Well
Layer 1
Layer 2
5
13
10 m
-3 m
-8 m
N
Results – Remember?
To get contours of water
table, check this box
Always check the box for
Cell-by-Cell flow
Transient Groundwater Models
• Transient models simulate changes over time – Necessary when boundary conditions vary with time (e.g., pumping
rates, recharge, river stage, etc.)
• Stress period: – Period of time during which boundary conditions are constant
– Stress periods can have multiple time steps
– Boundary conditions can change at the beginning of a stress period
Stress period
Time Steps
Stress period
Time Steps
Stress period
Time Steps
Time
Pumping and boundary
conditions can change e.g., one month
e.g., one day
Transient Model
• Convert you steady-state model to a transient model
• Open your model
• Select: Model MODFLOW Package Options
• Select: Basic Package Tab
• Uncheck: Steady-State checkbox
• Enter: Number of stress periods = 12
• Select: Days
• Select: OK
• Do you want to copy data? Select: Yes
• Do you want to set up stress periods? Select: Yes
Stress Periods • Use 12 stress periods, one for each day for 12 days
• Enter – Length of each stress period (= 1 day)
– Number of time steps (= 1)
– Time step multiplier (= 1.0)
Pumping Conditions
• Select: Layer 1
• Select: BC Well
• Select: BC Modify Layer
• Uncheck: “Steady-state Boundary Condition”
• Press: “Transient Data”
Uncheck this box
Press this button
Pumping Conditions • Change the pumping rates from “m3/sec” to “m3/day”
• Enter: Starting and Ending Stress Period Numbers
• Enter: Q = 0 m3/d for stress periods 1, 2, and 3
• Enter: Q = -159,840 m3/d for stress periods 4 - 12
• Repeat for layer 2: Q = 0 m3/d in stress periods 1, 2 and 3; Q = -1296 m3/d in periods 4 - 12
Hydraulic Conductivity • Change the hydraulic
conductivity values from “m/sec” to “m/day”
• Select: Props – Hydraulic Conductivity
• Select: Props – Property Values – Database
• Enter:
– Zone 1: • Kx = 432 m/d • Ky = 432 m/d • Kz = 43.2 m/d
– Zone 2: • Kx = 86.4 m/d • Ky = 86.4 m/d • Kz = 8.64 m/d
Storage/Porosity
• Select: Props – Storage/Porosity
• Select: Props – Property Values – Database
• Enter:
– Zone 1 and Zone 2:
• Ss = 0.0001
• Sy = 0.15
• Porosity = 0.15
Leakance
• Select: Props – Leakance
• Select: Props – Property Values – Database
• Enter: – Zone 1 and Zone 2:
• Leakance = 864 m/day
Monitoring Wells • Select: AE Well
• Select: Row 15, Column 24
• Select: Top layer = 1, and Bottom Layer = 2
• Change: Pumping rate = 0.0
• Check box: Monitor Head/Concentration vs. Time
• Select: Well Name button
– Enter MW-1
• Select: OK
Add another
Monitoting Well
(MW-2) in cell
(15, 18)
Model with Monitoring Wells
Run Simulation • Select: Calculator button
• Would you like to process the results? Select: Yes
• Select: Cell-by-cell flows
Switching Between Time Steps
• There are several options that allow switching between time steps in a transient run:
– Import Results (Plot->Import Results) Ctrl+Shift+I
– Next Time Step (Plot->Next Time Step) Ctrl+Shift+N
– Previous Time Step (Plot->Previous Time Step) Ctrl+Shift+P
• Selecting the next time step will bring in the next set of heads, drawdowns, and cell-by-cell flows
Results – Stress Period 12