Risk modeling

Vessels and state ferry in Puget Sound.

Vessels and state ferry in Puget Sound.

We are developing a quantitative model to assess current and potential future risks of oil spills in Washington waters.​


Modeling oil spill risk in Washington waters

This model is part of a package of measures passed by the Legislature in 2019 to reduce the risk of oil spills and protect Southern Resident Killer Whales.

The model will be a long-term asset for Ecology to analyze oil spill risks and the potential effectiveness of oil spill prevention, preparedness, and response strategies. As part of this work, we are consulting with tribes and stakeholders to develop modeling assumptions and scenarios, and to periodically update the model.

The Legislature directed Ecology to use the model to complete two assessments:

  • 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.

Reports on the results of these first two assessments are due to the Legislature by Sept. 1, 2023.


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 will help us leverage our knowledge about the past into insights about what might happen in the future.


To build the model, we will use existing knowledge and data on vessel behavior, including historical frequency of incidents and accidents. Once the model is built, we can test future scenarios against that historical backdrop to provide insight into oil spill risk in different scenarios.

Our approach

We are developing a flexible model framework to make sure that our model is able to tackle a wide array of possible oil spill risk related questions. To do this, we are breaking down our modeling approach into a series of modules. Each module will deal with an element of determining oil spill risk.

  • Vessel Movement Module will model vessel movements.
  • Vessel Encounter Module will measure and evaluate relationships between each vessel and shore and other vessels.
  • Vessel Accident Module will evaluate situations for their potential for accidents.
  • Oil Outflow Module will estimate spills from simulated accidents.

Each one of these modules contains many components that work together to meet the needs of the module and the output of each module feeds into the next. To learn more about our modeling approach, and the role of each individual module, please see our focus sheet on this topic. 

The output of this model will be the quantity, type, and location of simulated oil spills generated by the model. This output may be a sufficient representation of consequence to meet the needs of many analysis projects. However, when a specific risk analysis requires additional consideration of potential consequences, these model outputs will be available to form the inputs to other analytical techniques, as needed.

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 new modeling capability will provide tools to consider current and future oil spills risks, and the potential effectiveness of safety measures.