Strait of Juan de Fuca Example Problems

Try out these examples to learn the basics of modeling oil spills in the Strait of Juan de Fuca. Explore how winds, current reversals, and changing tides can affect the trajectories of oil slicks. In addition, you’ll see how model and observation limitations can be overcome by considering both the “Best Estimate” and the “Uncertainty” solutions. This knowledge will help you in designing your own GNOME model runs.

Example 1.

On July 13, 2001, a vessel traveling the inbound lane of the Strait of Juan de Fuca begins to leak medium crude while transiting from 48° 20’N, 124° 20’W to 48° 14’N, 124°W. The release occurs at 0930 and the oil continues to leak over a two-hour period.

Try the following conditions to see how the current reversal and wind can affect the trajectory:

(a) Conditions at the entrance to the strait: normal; no wind.

(b) Current reversal (mild to strong); no wind.

(c) A 10-knot east wind with either of the above cases.

Begin by selecting the Strait of Juan de Fuca Location File which will launch the Wizard to guide you through setting up the scenario. Use the information in the following table to set up the intial scenario as you advance through the Wizard.

Start time:	July 13, 2001 at 0930.
Model duration:	2 days.
Uncertainty:	Not included.
Strait entrance conditions:	Normal
Wind:	No wind (constant at 0 knots).
Spill type:	Continuous.
Time of Release:	Same as model start time.
Spill Duration:	2 hours.
Amount released:	1000 barrels.
Pollutant type:	Non-weathering.
Start Position:	48° 20’N, 124° 20’W.
End Position	48° 14’N, 124°W.

Once you have run the model for all three cases examine the differences in beach impacts between the two spills. To more easily visualize the difference between the spill impacts, you could take a screenshot of the map at the end of each model run.

How do the beach impacts differ in each case? How does the trajectory change?

Tips:

1. If you only want to change one spill parameter, like the wind in Case (b), there is no need to reload the Location File and step through the Wizard. Instead, use the buttons on the Menu Bar to switch from Map View to Setup View. In Setup View there are various panels which allow you to edit the model setup. In the Wind panel, click on the edit (pencil) icon next to the wind entry (named “Wind #1 unless you specified a different name in the Wizard). Here you can change the wind direction and speed. (For a constant wind, the Date & Time Field is not important as the same values will be applied at all model times.) You may want to read the help available about conventions for entering wind data - these are available by clicking on the question mark icon at the top of the form.

2. To change the current reversal conditions, but keep all other model settings the same, click on the edit (pencil) icon next to the current entry named “Surface Reversal Current”. The Reference Point Value is set to 0 for Normal, .1 for Mild Reversal, .35 for Moderate Reversal, and .5 for Strong Reversal.

Answer:

(a) Conditions at the entrance to the strait: normal; no wind.

The spill travels west along the strait; very little of the oil beaches.

(b) Current reversal (mild to strong); no wind.

As the current reversal increases, the spill is carried further east. Beach impacts are minimal.

(c) A 10-knot east wind with any of the previous cases.

The wind causes the oil in each scenario to beach more quickly and more extensively on the north coast of Washington.

Example 2

Set a spill at the mouth of Admiralty Inlet (48° 11.35’N, 122° 48.87’W) at 0200 on July 22, 2001, with a light (10-knot) wind from the east. Choose normal conditions at the entrance to the strait. Run trajectories with the “Uncertainty” solution for a 2-day spill simulation first with a light product (gasoline), then with a heavy product (e.g. IFO).

Compare the differences in risk to Dungeness Spit (approximately 48° 10’N, 123° 8’W) from the two different products.

Tips:

1. To start over and relaunch the Wizard, select Select a Location File from the New pulldown menu.

2. To include the “Uncertainty” solution, click the box “Include uncertainty in particle transport” in the Model Settings form.

3. Choose the Instantaneous Spill option this time. Use the ADIOS Oil Database link to open the ADIOS oil database. From the database interface select an oil that corresponds to a gasoline. It doesn’t matter which exact oil you select, as long as it has the label ‘Gasoline’. Download the oil and load the file into WebGNOME using the load oil drop box.

3. To change the oil type without “starting over”, switch to the Setup View page.

Answer:

Heavier oils remain in the environment longer than lighter, refined products. Beach impacts from the heavy oil spill are much more extensive around Dungeness Spit than for the gasoline spill, most of which evaporated and dispersed. (To view the mass balance for a scenario, switch to the Fate View.)

Example 2b

Can you change the wind to make the beach impacts more extensive?

Answer:

Any wind with a southerly component will certainly increase beach impacts. You just need one strong enough to beach the gasoline spill quickly.

Example 2c

Try starting the heavy oil spill at a different part of the tide cycle. Move the start time to 1130. Change the wind conditions back to a 10-knot wind from the east.

How do beach impacts change? Where is the uncertainty?

Tip:

When you change the start time of the spill, you will likely want to change both the spill start time and the model start time. If you change the spill start time first, WebGNOME will automatically prompt you to change the model start time to match the spill start time. So it is a good idea to always change the spill start time first.

Answer:

More oil beaches in the spill that occurs at 1130 than in the 0200 spill (about 31% compared with about 14%, respectively). WebGNOME’s “Uncertainty” solution takes into account uncertainty in wind, horizontal mixing, and currents. Areas that are oiled after this spill include regions of Dungeness Spit, the western shoreline of Sequim Bay, Protection Island, and Port Townsend.