Welcome to San Diego!

First we'll set up the GNOME model to explore the effect of tides by starting spills at two different times in the tidal cycle, once at the beginning of a flood tide and once at the beginning of the ebb tide. Then we'll see the effect of the wind and look at the uncertainty in the predictions.

1. Start up GNOME.

2. Choose the San Diego Bay location file.

3. Set up the model as follows for the flood tide case:
   • Start Date: January 19, 2000
   • Start Time: 1500 (beginning of the flood tide)
   • Model Run Duration: 1 Day
   • Wind: Constant, 0
   • Oil spill: Create a linear source of oil extending from 117^o 13.55'W to 117^o 16.5'W along 32^o 39.5'N. To do this, simply click anywhere on the water area on the map. In the Spill Information window that opens you can enter the exact latitude and longitude of the starting point and end point of the spill. Set the type of pollutant to non-weathering and the amount to 1000 barrels.

   • Run the model. Observe if there are any beach impacts and where the oil goes.

   • Save your settings as a Location File Save (LFS) by choosing Save from the GNOME File menu.

4. Next, run the model for the ebb tide case:

   The settings are the same, except the start time of the spill (and the model). Change the spill start time to January 19, 2000 at 0740 by double-clicking on the non-weathering 1000 barrels under Spills in the left-hand frame. You will be prompted to change the model start time to match the spill start time.

   Question 1: Are tides important in San Diego Bay? How does the tide affect where the oil goes?

5. Next we'll look at how the wind affects the results.

   Rerun the previous scenario at flood tide (1500), but add a 15-knot wind from the NW.
   Hint: To change the wind in your model, double-click Wind in the Summary List and then enter the wind speed and direction in the window, or click in the wind rose.

   Question 2: Does the wind have a significant effect? How do the oil's trajectory and beach impacts change from the scenario without any wind?

6. All predictions are inherently uncertain. The "minimum regret" solution in GNOME takes into account uncertainties in the wind, horizontal mixing, and currents. In this final case, you will use the minimum regret solution to see the range of solutions for where the oil spill might go.

   In this case, set a point source in the middle of San Diego Bay. Set a start time of 0720 and run for 2 hours. First run the model with no wind and then with a 25-knot wind from each of the cardinal directions, N,S,E, and W.

   Hint: to remove the old linear spill, select its description (Non-weathering, 1000 barrels) in the Summary List. Under the Item menu, select Delete. Then use the spill tool to add the point source spill.

   Question 3: Briefly discuss the difference between the "best guess" (black) and the "minimum regret" (red) trajectories for these cases. Do you think this type of information might be useful?

   Hint: Zoom into your spill area to see more details.