1. Groundwater Modeling – 3 Transient 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 Boundaries – North & South: No-flow – East & West: Constant-head Layer 1 – unconfined (13 m) – K h = 5x10 -3 m/s; K v = 5x10 -4 m/s – Porosity = 0.25 Layer 2 – confined (5 m) – K h = 1x10 -3 m/s; K v = 1x10 -4 m/s – Porosity = 0.25 No-flow Boundary Constant Head Boundary (h = 9 m) Constant Head Boundary (h = 8 m) Pumping Well 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

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 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

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 “m 3 /sec” to “m 3 /day” Enter: Starting and Ending Stress Period Numbers Enter: Q = 0 m 3 /d for stress periods 1, 2, and 3 Enter: Q = -159,840 m 3 /d for stress periods 4 - 12 Repeat for layer 2:Q = 0 m 3 /d in stress periods 1, 2 and 3; Q = -1296 m 3 /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: S s = 0.0001 S y = 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 Select: Plot – Hydrograph - Monitoring Well Select: Your Monitoring Wells Row 7 Column 9 Row 2 Column 9