Explicit quantification of residence and flushing times in the Salish Sea using a sub-basin scale shoreline resolving model

Journal Article · Sat Aug 13 00:00:00 EDT 2022 · Estuarine Coastal and Shelf Science

DOI:https://doi.org/10.1016/j.ecss.2022.108022· OSTI ID:1888561

Premathilake, Lakshitha ^[1]; Khangaonkar, Tarang P. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Washington, Tacoma, WA (United States)

The Salish Sea, located in the Pacific Northwest region of North America has complex currents and circulation features distributed over numerous interconnected deep basins with islands. Increased risk of exposure to oil spills and untreated wastewater from maritime emergencies and treatment plant failures have led to a need for quantifying residence and flushing characteristics at a sub-basin scale using a shoreline resolving hydrodynamic model. An unstructured grid model of the Salish Sea was developed using FVCOM with a ≈75-100m shoreline resolution. In addition to 7 tides and 23 salinity and temperature monitoring stations, an extensive currents data set from 135 stations collected over a span of three years was used for skill assessment and validation. Explicit forward computations were then conducted to define and quantify residence and flushing times in various sub-basins of interest using (a) Lagrangian particles and (b) Numerical/virtual dye experiments. The results in most basins show expected seasonal variability with longer flushing time associated with summer lower tides and lower freshwater inflows. However, contrary to expectation, flushing time is significantly longer in wintertime in large fjord-like basins such as Hood Canal (≈138 days), likely due to increased stratification and reduced mixing. The flushing time for the Puget Sound region of the Salish Sea is ≈115 days, while Georgia Basin is 240 days when analyzed as stand-alone basins with zero background concentrations. When examined as part of the flushing of the entire Puget Sound filled with virtual dye, the compounded flushing times for embedded sub-basins can be significantly longer in order of magnitudes and largely dictated by the flushing time of Puget Sound. The computed residence and flushing time scales tabulated over 36 sub-basins provide an improved understanding of water renewal in the system, informing pollution management actions.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1888561
• Report Number(s): PNNL-SA-176901
• Journal Information: Estuarine Coastal and Shelf Science, Journal Name: Estuarine Coastal and Shelf Science Vol. 276; ISSN 0272-7714
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Currents
Flushing time
Model skill assessment
Residence time
Salish sea
Tidal ellipses
Tides