Connecting the sound to the shelf: a numerical modeling study of estuarine exchange flow in the Salish Sea Dave Sutherland 1 Parker MacCready 1, Neil Banas 2 1 School of Oceanography, UW 2 Applied Physics Laboratory, UW CERF, Portland, OR, November 2009

Connecting the sound to the shelf: a numerical modeling study of estuarine exchange flow in the Salish Sea Acknowledgments: PRISM (Jeff Richey) Barb Hickey, Amy MacFadyen, David Darr (UW) WA DOE All data sources PRISM Puget Sound Regional Synthesis Model

The Salish Sea Strait of Georgia Strait of Juan de Fuca Puget Sound Columbia River Vancouver Island coastal WA, OR 400 m

The Straits Strait of Juan de Fuca 100 km long, 20 km wide, 200 m deep ~0.2 Sv exchange flow significant spring/neap variability, seasonal variability, and tidal rectification (see Martin and MacCready, 2009) (Collias et al., 1974) Strait of Georgia Fraser River: mean ~7500 m 3 /s, large seasonal variability intense mixing in SJI’s and sill regions, more stratified in basins significant spring/neap variability (Masson and Cummins, 2000) Salinity, July

Puget Sound Skagit 2 largest rivers (~75% of Puget Sound mean ~1000 m 3 /s) Tacoma Narrows Admiralty Inlet Deception Pass Hood Canal Snohomish 5 km Main Basin South Sound Whidbey Basin

Puget Sound exchange flow Salinity, July Puget Sound series of reaches (basins) connected by shallow sills 0.04 Sv exchange flow ~1000 m 3 /s river input large seasonal and spring/neap variability residence times: range from 5-70 days (cm/s) 150 m Main Basin Hood Canal

Hypothesis : Puget Sound, SJdF, and the SoG are characterized by quiescent reaches (e.g. Main Basin) and turbulent sill regions (e.g. AInlet) river sill Construct realistic hindcast simulations for in Puget Sound and greater Salish Sea region Puget Sound resolution ~200 m coastal resolution ~2 km use best available forcing (rivers, meteorological, boundary) Tool : realistic ROMS numerical model setup of the Salish Sea to investigate patterns of exchange flow on varied time and space scales (Ebbesmeyer and Barnes, 1980; Cokelet and Stewart, 1985)

Model Set-up Parameters - stretched, spherical grid with 25 vertical levels,  b = 0.6 and  s = 5 - k-  version of GLS turbulence closure - horizontal diffusivity = 0.5 m 2 s -1 - quadratic bottom friction, C d = h min = 4 m, r max ~ 0.7, no wet/dry Forcing Boundaries - Radiation and nudging at southern and western boundaries (NCOM-CCS) Atmosphere - Bulk fluxes from hourly fields from the MM5 regional forecast model Rivers - 19 rivers, daily time series (USGS) Tides - 8 constituents calculated from TPXO7.1 global tide model

Model validation Whidbey Basin mid Strait of Georgia JEMS SJDF ROMS OBS Mooring time-series outside Columbia CTD profiles

Patterns of exchange flow JdF-E JdF-mid JdF-W SoG-N SoG-mid SoG-S AI-N,S MB SS WB HC AI-N (May-July mean) “in-estuary” “out-estuary” |U e | ~ 20,000 m 3 /s net U e ~ 500 m 3 /s

Patterns of exchange flow JdF-E JdF-mid JdF-W SoG-N SoG-mid SoG-S AI-N,S MB SS WB HC AI-N (May-July mean) “in-estuary” “out-estuary” AI-S

Patterns of exchange flow JdF-E JdF-mid JdF-W SoG-N SoG-mid SoG-S AI-N,S MB SS WB HC MB-N (May-July mean) “in-estuary” “out-estuary” MB-mid MB-S

Patterns of exchange flow JdF SoG AI SOG-N “in-estuary” “out estuary” SOG-mid SOG-S AI-N “in-estuary” AI-S “out estuary” JdF-E “in-estuary” “out estuary” JdF-mid JdF-W |U e | ~ 130,000 m 3 /s net U e ~ 6000 m 3 /s |U e | ~ 80,000 m 3 /s net U e ~ 5000 m 3 /s |U e | ~ 20,000 m 3 /s net U e ~ 500 m 3 /s Strait of Juan de FucaStrait of GeorgiaAdmiralty Inlet

Variability of exchange flow at Adm. Inlet river discharge (m 3 /s) N/S winds (m/s) depth mean current (m/s) exchange flow (1000 m 3 /s) “out-estuary” “in-estuary” SkagitSnohomish

Conclusions Development underway of realistic, high resolution simulations of Puget Sound and the surrounding coastal ocean Patterns of exchange flow are useful in characterizing estuarine regions in the Salish Sea and will lead to quantitative comparisons in the future (