Risk modeling

Modeling oil spill risk in Washington waters

The modeling framework is a long-term asset for Ecology to analyze oil spill risks and the potential effectiveness of oil spill prevention, preparedness, and response strategies. We consulted with Tribes and stakeholders to develop modeling assumptions and scenarios, and to periodically update the model.

Ecology used the model to complete two analyses, as directed by the Legislature:

• A quantitative assessment of whether an emergency response towing vessel (ERTV) serving Haro Strait, Boundary Pass, Rosario Strait, and connected navigable waterways will reduce oil spill risk.
• An analysis of tug escorts for oil tankers, articulated tug barges, and towed oil barges to be completed with the Washington State Board of Pilotage Commissioners.

Our model

Marine transportation systems are complex. As a result, it can be difficult to compare the relative benefits of different safety measures just by analyzing historical data. A modeling approach helps us leverage our knowledge about the past into insights about what might happen in the future.

In developing our model, we focused on creating a flexible model framework that can be responsive to a wide array of possible oil spill risk related questions. The model is structured as a series of modules, each of which deals with an element of determining oil spill risk:

• Vessel Movement Module simulates vessel movements.
• Vessel Accident Module evaluates situations for their potential for accidents.
• Momentum and Drift Module plots drift trajectories for simulated ships that lose propulsion.
• Vessel Rescue Analysis Module evaluates the potential for vessels to avoid a grounding by regaining propulsion after losing it, anchoring, or tug rescue.
• Oil Spill Risk Module generates oil related risk metrics for each simulated incident.

For future analyses, we can use some or all of these modules, or we may need to develop additional tools to meet the specific needs of the analysis.

Why it matters

More than 20 billion gallons of crude oil and refined petroleum products are transported through Washington each year by vessel, pipeline, and rail. A major spill in Washington waters could have severe consequences to the environment, economy, public health, and cultural and historical resources.

Our modeling capability allows us to consider current and future oil spills risks, and the potential effectiveness of safety measures.

Board of Pilotage Commissioners rule effects assessment and model update

Under RCW 88.46.260, by October 1, 2028, and at least every 10 years thereafter, the Board of Pilotage Commissioners and Ecology must determine whether updates to the 2025 tug escort rules are necessary. To support decision-making in 2028, the Board of Pilotage Commissioners and Ecology will assess the rule, as outlined in RCW 88.46.260. The RCW requires that the assessment: 

• Must include an analysis of the effects of the rule on vessel traffic patterns and oil spill risks in the Salish Sea, 
• Must include an analysis of whether experienced or forecasted changes to vessel traffic patterns or oil spill risk necessitate an update to the rule,   
• Must include modeling from Ecology’s risk model,   
• Must include consultation with the USCG and potentially affected federally recognized Tribes,  
• May include vessel traffic data, vessel accident and incident data such as incidents where tug escorts or an emergency response towing vessel acted to reduce spill risks.  

Ecology and the Board of Pilotage Commissioners are in the early stages of preparing for this assessment and associated updates to the model. More information, including public input opportunities and materials, will be posted here when available.