Connecting the sound to the shelf:

a numerical modeling study of estuarine exchange flow

in the Salish Sea

Dave Sutherland1

Parker MacCready1, Neil Banas2

1 School of Oceanography, UW2 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 SeaAcknowledgments:PRISM (Jeff Richey)

Barb Hickey, Amy MacFadyen, David Darr (UW)

WA DOE

All data sources

PRISMPuget 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 m3/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, JulySalinity, July

Puget Sound

Skagit2 largest rivers (~75% of Puget Sound mean ~1000 m3/s)

Tacoma Narrows

Admiralty Inlet

Deception Pass

Hood Canal

Snohomish

5 km

Main Basin

SouthSound

WhidbeyBasin

Puget Sound

exchange flow

Salinity, July

Puget Sound

• series of reaches (basins) connected by shallow sills• 0.04 Sv exchange flow• ~1000 m3/s river input• large seasonal and spring/neap variability• residence times: range from 5-70 days

(cm/s)

150

m

MainBasin

HoodCanal

Hypothesis: Puget Sound, SJdF, and the SoG are characterized by quiescent reaches (e.g. Main Basin) and turbulent sill regions (e.g. AInlet)

river river

sill

• Construct realistic hindcast simulations for 1998-2008 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-upParameters- stretched, spherical grid with 25 vertical levels, b = 0.6 and s = 5- k- version of GLS turbulence closure- horizontal diffusivity = 0.5 m2 s-1

- quadratic bottom friction, Cd = 0.003- hmin = 4 m, rmax ~ 0.7, no wet/dry

ForcingBoundaries - 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 Basinmid Straitof Georgia

JEMSSJDF

ROMSOBS

Mooring time-series outside Columbia

CTD profiles

Patterns of exchange flow

JdF-EJdF-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”

|Ue| ~ 20,000 m3/snet Ue ~ 500 m3/s

Patterns of exchange flow

JdF-EJdF-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-EJdF-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-midMB-S

Patterns of exchange flow JdF

SoG

AI

SOG-N

“in-estuary”

“outestuary”SOG-mid

SOG-S

AI-N

“in-estuary”

AI-S

“outestuary”JdF-E

“in-estuary”

“outestuary”JdF-mid

JdF-W

|Ue| ~ 130,000 m3/snet Ue ~ 6000 m3/s

|Ue| ~ 80,000 m3/snet Ue ~ 5000 m3/s

|Ue| ~ 20,000 m3/snet Ue ~ 500 m3/s

Strait of Juan de Fuca Strait of Georgia Admiralty Inlet

Variability of exchange flow at Adm. Inlet

riverdischarge(m3/s)

N/S winds(m/s)

depth meancurrent (m/s)

exchange flow(1000 m3/s)

“out-estuary”“in-estuary”

Skagit Snohomish

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

(http://faculty.washington.edu/dsuth/MoSSea/)