Salish Sea Model

The Salish Sea Model is a powerful computer tool that simulates hydrodynamic and water quality processes to improve our understanding of how nutrients affect water quality in Puget Sound, the Strait of Georgia, and the Strait of Juan de Fuca.

The model was developed by Pacific Northwest National Laboratory (PNNL) in collaboration with scientists within our Environmental Assessment Program. We have invested several years of time and research into the model and are using it to guide management actions that are needed to protect water quality in Puget Sound.

Four maps of the Salish Sea model with grid lines extending around the coastlines from Canada to Oregon, mapping out the Salish Sea. — The Salish Sea Model domain and intermediate scale model grid (A) in Greater Puget Sound (B), northern Puget Sound (C), and South Sound (D).

Model description

The Salish Sea Model is a powerful three-dimensional computer tool that simulates hydrodynamic and water quality processes in the Salish Sea, including Puget Sound. It is a scientific and engineering tool to guide management actions to protect water quality. The model can run scenarios to evaluate the relative effect of current, anthropogenic, and potential future nutrient loads on dissolved oxygen in the Salish Sea.

The model domain includes all of Puget Sound, the Strait of Juan de Fuca, and the Strait of Georgia, as well as the continental shelf off the coast of Washington state and Vancouver Island. The model also includes inputs from 193 rivers and streams and 101 point sources — including 90 municipal wastewater treatment plants and 11 industrial facilities — in the US and Canada.

The model grid is represented with triangular cells, showing smaller triangles with higher resolution in the inlets, bays, and narrower regions of Puget Sound, and larger traingles with coarser resolution in the northern straits. It has 10 vertical layers, thinner at the surface and thicker at depth. The model currently includes the following simulated features:

Hydrodynamics — Circulation, currents, water temperature, and salinity using an unstructured grid under the Finite Volume Coastal Ocean Model (FVCOM) framework.
Water quality — Includes a total of 19 state variables, two species of algae, dissolved and particulate carbon, as well as nutrients, using biogeochemical water quality kinetics from the integrated compartment model (ICM).
Sediment diagenesis — Fluxes of nitrogen, phosphorus, and carbon between the sediment and water column.
Acidification — pH, aragonite saturation state, and related carbonate system parameters.

Why do we need a model

Scientists use computer models to represent natural processes and predict responses to changes or management actions. The Salish Sea Model allows us to run virtual experiments on water quality that we can't do in real life.

For example, we can use the Salish Sea Model to assess how water quality might change under different scenarios, such as the effect on dissolved oxygen levels due to either an increase in wastewater effluent flows from population growth or a decrease in human nutrient loading from rivers entering the Salish Sea. We compare model results from different scenarios to help policymakers identify what actions can improve or protect water quality.

We use the Salish Sea Model to answer the following key questions:

What are the relative impacts on dissolved oxygen and pH levels from human nutrient loads, Pacific Ocean conditions, and climate change?
How are human sources of nutrients from local and regional sources impacting water quality?
How much do we need to reduce local and regional human sources of nutrients to meet dissolved oxygen water quality standards in the U.S. portions of the Salish Sea?

Model results

We have created interactive web maps that summarize Salish Sea Model results for each major phase of work. The maps allow users to see model-predicted dissolved oxygen levels under current conditions, and hypothetical nutrient reduction scenarios:

Web map: Optimization Scenarios Phase 1 (2021)
Web map: Bounding Scenarios (2019)

The table below outlines the work that has been done to date and includes related publications. The model has now been calibrated to water quality conditions in 2000, 2006, 2008 and 2014. Also note that previous publications and reports have referred to this model as the "Puget Sound Dissolved Oxygen Model" and the "Puget Sound Georgia Basin Model."

Year	Publication	Reference/Link
2025	Puget Sound Nutrient Source Reduction Project Volume 2: Model Updates and Optimization Scenarios Phase 2	Figueroa-Kaminsky et al.
2021	Technical Memorandum: Puget Sound Nutrient Source Reduction Project — Optimization Scenarios Phase 1	Ahmed et al., 2021
2019	Puget Sound Nutrient Source Reduction Project Volume 1: Model Updates & Bounding Scenarios	Ahmed et al., 2019
2018	Quality Assurance Project Plan: Salish Sea Model Applications	McCarthy, S., 2018
2018	Simulation of Response to Climate Change and Sea Level Rise Scenarios (PNNL)	Khangaonkar et al., 2018
2017	"Assessment of circulation and inter-basin transport in the Salish Sea including Johnstone Strait and Discovery Islands pathways" from Ocean Modeling	Khangaonkar, et al, 2017
2017	Addition of Sediment Diagenesis Module to the Salish Sea model	Pelletier et al., 2017
2015	Quality Assurance Project Plan: Salish Sea Dissolved Oxygen Modeling Approach: Sediment-Water Interactions	Roberts et al., 2015
2014	Approach for Simulating Acidification and the Carbon Cycle in the Salish Sea to Distinguish Regional Source Impacts	Long et al., 2014
2014	Sound and the Straits Dissolved Oxygen Assessment: Impacts of Current and Future Human Nitrogen Sources and Climate Change through 2070 (Note: this version of the model did not include sediment diagenesis	Roberts et al., 2014
2012	Simulation of annual biogeochemical cycles of nutrient balance, phytoplankton bloom(s), and DO in Puget Sound using an unstructured grid model	Khangaonkar et. al., 2012
2012	Puget Sound Dissolved Oxygen Modeling Study: Development of an Intermediate Scale Water Quality Model	Khangaonkar et. al., 2012
2011	Development of nutrient loading estimates from point and nonpoint sources into the Salish Sea.	Mohamedali et al., 2011
2010	Puget Sound Dissolved Oxygen Modeling Study: Development of an Intermediate Scale Hydrodynamic Model	Yang et al., 2010
2009	Quality Assurance Project Plan for Puget Sound Dissolved Oxygen Modeling Study	Sackmann, 2009

Future modeling work

Through each phase of work, we update and refine the model based on code updates, availability of more recent data and/or better data, and in response to feedback from scientific peer reviews. To date, we have primarily applied the model to study the effects of nutrient pollution on oxygen levels in Puget Sound. However, the model has the potential for ongoing and future applications, such as:

Continued evaluation of the effect of eutrophication and human impacts on water quality in Puget Sound.
Modeling of historical natural conditions in the Salish Sea.
Refined-scale modeling for more localized studies in specific inlets of Puget Sound when near-shore data are available to address current model limitations in these regions.
Continued and consistent updates to the models’ watersheds and wastewater inputs to reflect more recent years as needed to answer policy questions.
Evaluating the effect of future climate change on water quality, in collaboration with other scientific groups in the region to acquire the necessary hydrologic and meteorological inputs reflective of climate change for our region.

Contact information

Cristiana Figueroa-Kaminsky
Environmental Engineer
c.figueroa-kaminsky@ecy.wa.gov
360-764-9936