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Groundwater Modeling – 3 Transient Models

Groundwater Modeling – 3 Transient Models. Groundwater Hydraulics Daene C. McKinney. 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 .

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Groundwater Modeling – 3 Transient Models

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  1. Groundwater Modeling – 3Transient Models Groundwater Hydraulics Daene C. McKinney

  2. 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. • See file: 07_Groundwater_Modeling_2.pptx

  3. Example Pumping Well Layer 1 10 m • 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 13 Layer 2 -3 m 5 -8 m No-flow Boundary N Pumping Well Constant Head Boundary (h = 9 m) Constant Head Boundary (h = 8 m) 600 m No-flow Boundary Adapted from Chiang, W-H and W. Kinzelbach, Processing Modflow: A Simulation System For Modeling Groundwater Flow and Pollution, 1996 600 m

  4. Results – Remember? To get contours of water table, check this box Always check the box for Cell-by-Cell flow

  5. 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 e.g., one day Time Steps Time Steps Time Steps Time Stress period Stress period Stress period e.g., one month Pumping and boundary conditions can change

  6. 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

  7. 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)

  8. 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

  9. 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

  10. 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

  11. 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

  12. Leakance • Select: Props – Leakance • Select: Props – Property Values – Database • Enter: • Zone 1 and Zone 2: • Leakance = 864 m/day

  13. 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)

  14. Model with Monitoring Wells

  15. Run Simulation • Select: Calculator button • Would you like to process the results? Select: Yes • Select: Cell-by-cell flows

  16. 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

  17. Results – Stress Period 12

  18. Monitoring Wells Row 7 Column 9 • Select: Plot – Hydrograph - Monitoring Well • Select: Your Monitoring Wells Row 2 Column 9

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