Narragansett Bay exercise

Welcome to Narragansett Bay!

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.

Start up GNOME.
Choose the Narragansett Bay location file.
Set up the model as follows for the ebb tide case:
- Start Date: March 26, 2001
- Start Time: 0910 (beginning of the ebb tide)
- Model Run Duration: 1 Day
- Wind: Constant, 0
- Oil spill: Place a point source spill at 41^o 38'N, 71^o 23'W (west of Prudence Island). 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 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.
Next, run the model for the flood tide case:
The settings are the same, except the start time of the spill (and the model). Change the spill start time to March 26, 2001 at 1440 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 Narragansett Bay? How does the tide affect where the oil goes?
Next we'll look at how the wind affects the results.
Rerun the previous scenario at flood tide, but add a 10-knot wind from the WSW.
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 shoreline impacts change from the scenario without any wind?
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.
Rerun the flood tide case above, with the minimum regret solution included (wind at 10 knots from the WSW, start time 1440). Use the "zoom" button to zoom in on the area of the spill.
Question 3: Briefly discuss the difference between the "best guess" (black) and the "minimum regret" (red) trajectories for this case. Do you think this type of information might be useful?