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 very 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.

Model components

Our modeling project is in the beginning phases, and many aspects of the model have yet to be decided. However, certain components are common to many marine transportation models:

  • Information about the local waterway
    • Depth of the water
    • Frequency of low visibility conditions
    • Local tidal currents
  • Information about the vessels operating in the area
    • Type
    • Size
    • Routing
    • Cargo and fuel capacity
  •  Incident or accident likelihood
    • Historical rates for accidents like collisions and groundings
    • Historical rates for incidents like loss of propulsion or near misses
  • Estimated spill volume
    • Oil outflow based on things like vessel design, fuel tank location, type of accident, etc.

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.