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Oil Spill Risk Analysis Model (OSRAM)
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Information to Be Used In Oil Spill Response Plans
A Notice to Lessees, Operators, and Pipeline Right-Of-Way Holders (NTL) was
effective on October 26, 2006
(NTL
2006-G21) that provides additional guidance on the
review and update of Oil Spill Response Plans (OSRP), recognizes the National
Incident Management System, adds a new Section 22 to OSRP’s regarding
prevention measures for facilities located in State
waters, updates regulatory citations, and makes a few minor
technical amendments.
This web site contains tables providing the conditional probability results
of the most up-to-date trajectory simulations and instructions for the operator. These tables
are available in the following document:
Ji, Zhen-Gang, Walter R. Johnson, Charles F. Marshall, and Eileen M. Lear.
2004. Oil-Spill Risk Analysis: Contingency Planning Statistics for Gulf of
Mexico OCS Activities. OCS
Report 2004-026, Herndon, VA: U.S. Dept. of the Interior, Minerals
Management Service, Environmental Division.
This document is available online at
http://www.mms.gov/itd/pubs/2004/2004-026.pdf.
In the future, please check this website for any updated OSRA model information and
instructions when preparing future updates of OSRP's.
What are Oil-Spill Trajectory Simulations?
Oil spill trajectory simulations are generated by MMS to be used to estimate
spill risk. The MMS uses a numerical computer model that simulates the likely
trajectory of a surface slick, represented as a point launched from locations
projected onto a gridded area. For more information on the trajectory model,
called the OSRA (oil spill risk analysis) model, see Ji et al. (2002; Smith et
al, 1982; and LaBelle and Anderson, 1985). The point’s trajectory simulates a
spill’s movement on the surface of water by using modeled ocean current and wind
fields. The model uses temporally and spatially varying, numerically computed
ocean currents and winds.
The model tabulates the number of times that each trajectory moves across or
touches a location (contact) occupied by polygons mapped on the gridded surface.
These polygons represent locations of various environmental features or
shoreline segments. The OSRA model compiles the number of contacts to each
feature that result from the modeled trajectory simulations from all of the
launch points for a specific launch area, discussed below. Each trajectory was
allowed to continue for as long as 30 days and contacts within 3, 10 and 30 days
were compiled. However, if the hypothetical spill contacted shoreline sooner
than 30 days after the start of the spill, the spill trajectory was terminated,
and the contact was recorded.
What are Conditional Probabilities of Contact?
The probability of contact to an environmental feature is calculated by
dividing the number of contacts by the number of trajectories started within
each launch area. The output from these trajectories provides information on the
likely trajectory of a spill by wind and current transport, should one occur and
persist for the time modeled in the simulations. The probability that an oil
spill will contact a specific location within a given time of travel from a
certain location or spill point is provided in the attached tables.
These
probabilities are termed conditional probabilities, the condition being that a
spill is assumed to have occurred and persist for the time period modeled.
TABLES OF PROBABILITIES
What are the onshore areas I must identify?
The onshore areas that must be identified are counties and parishes.
All Gulf of Mexico
coastal counties and parishes must be listed that can be potentially contacted (i.e., have
a probability greater than 0.5% that they will be contacted) by an oil spill starting at
the determined worst case discharge locations.
The probability tables (see above) show the
parishes/counties having a probability of contact.
How can I find the launch area where my lease or facility is located?
If you do not know the launch area(s) where your lease or facility is
located, we have included an Excel file listing Lease Block Areas, Blocks within
each Lease Block Area, and the launch area for each block.
If the facility in your nearshore worst case response scenario is located in
state offshore waters, choose launch area for the nearest block in the OCS.
OSRA Launch Areas by Block
(Excel spreadsheet - August 2008)
What time frame should I use?
Three time frames (within 3, 10, or 30 days), are provided in
the probability
tables. The time frame that you choose should best represent the likely time
period that the hypothetical oil slick would persist on the surface of the water
based on what you know about how quickly it will weather.
Climatological wind and ocean estimates are available for your
use in oil weathering calculations.
For questions, please contact
Erin O'Reilly at (504) 736-1759, or (alternate)
Rusty Wright at (504) 736-2529.
Other
OSRA Information
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