Circulation in Narragansett Bay: Water flow & mixing Transport of chemical-biological material...

Circulation in Narragansett Bay:

Water flow & mixing

Transport of chemical-biological material

Exchange between sub-regions of Bay

Motivation: Episodic hypoxia in NB & Developing management tools for the

Bay ecosystem

National Capitol Columns at the United States National Arboretum in Washington, D.C.

CHRP Coupled Ecological Modeling (GEMBox - ROMS Model)

Fundamental Column:

Detailed understanding of physical processes

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• Physical Drivers:– Tides– Winds– River discharge– Density differences

http://www.geo.brown.edu/georesearch/insomniacs

Role of physical processes in the health of the Bay


• Out with the bad





• Out with the bad

• In with the good


Circulation in Narragansett Bay:

3 Basic Methods

Hydrographic data (currents, density)

Numerical Modeling (ROMS : ( Regional Ocean Modeling System)

Physical - Laboratory Modeling

Physics: Observations

Acoustic Doppler Current Profilers

Bottom mounted Ship mounted / underway

Data coverage:Excellent temporalPoor Spatial

Data coverage:Good spatialPoor Temporal

Tilt Current Meters : (tilt proportional to water velocity)

Buoyant cylinder

Flexible membraneMooring weight

Water flow

Initial Conditions

Forcing Conditions

Output

Shallow Water EquationsMomentum balance x & y directions:u + vu – fv = + Fu + Du t xv + vv + fu = + Fv + Dv t yPotential temperature and salinity :T + vT = FT + DT

t S + v S = FS + DS

t The equation of state:= (T, S, P) Vertical momentum: = - gz o

Continuity equation:u + v + w = 0x y z

Numerical Model

ROMS Model

Regional Ocean Modeling System

Fluid Dynamics Laboratory Models (a.k.a analog models)

Fall, 2008 at GFD Lab, Australian National University: .

Developed flume tank to represent the upper Providence River

Lab models provide excellent check against numerical modelsS

hipp

ing

Cha

nnel

Shipping Channel

Edg

ewoo

d S

hoal

Edgewood Shoal

Port Edgewood

Save the Bay

Hurricane Barrier

Save the Bay

Circulation in Narragansett Bay: 3 Basic Methods

Lots of great students!!

Bridget Sullivan (1st developed SCRUM, then ROMS)

William Deleo (data at Bay Mouth, detailed study of Mt. Hope Bay)

Kurt Rosenberger (data at Bay Mouth and in Rhode Island Sound)

Deanna Bergondo (develop ROMS model/data for Providence River, initial CHRP proposal)

Justin Rogers (ROMS, Mid-Bay Data )

Nicole LaSota (ROMS Prov. River dye dispersion study)

Anna Pfeiffer-Herbert (Detailed data RIS, mouth, Greenwich Bay, Bay-Shelf Exchange)

Christelle Balt (Greenwich Bay & Prov. River Data, ROMS flushing exeriments, Mixing schemes)

Circulation in Narragansett Bay: 3 Basic Methods

Lots of great students

Heaps of excellent support

















NB

GB

PR

MHB

RIS

1999-2001

RI Sea Grant

Quick summary:









NB

GB

PR

MHB

RIS

99-01

Narragansett Bay Commission

2001-2005









NB

GB

PR

MHB

RIS

99-01

Narragansett Bay Commission

& CHRP award, 2006 2005

2006









NB

GB

PR

MHB

RIS

99-01

Narragansett Bay CommissionRI Sea Grant& CHRP award, 2007 2005

2006

2007









NB

GB

PR

MHB

RIS 2008

99-01

RI Sea Grant & CHRP award, 2008

2005

2006

2007









NB

GB

PR

MHB

RIS 2008

99-01

RI Sea Grant &CHRP award, 2009

Most ambitious physical sampling survey ever…..

Focus on key CHRP Dye Boxes

2005

2006

2007

2009

RIS-NB Model Domain(Rogers, 2008)

Full Bay Model Domain

Providence River Model

Data tell a physical story……..

Circulation and Transport in Upper Circulation and Transport in Upper Narragansett BayNarragansett Bay

Justin RogersJustin RogersMS Thesis,08MS Thesis,08

Data Example

West Passage (Tidal flows)

East Passage Channel (Tidal flows)

Fast in,

Faster out

North - IN Surf.

Bot.

Decimal Day in 2006 (summer)

Slow in,

Slowerout

North - IN

Examples what these data look like:




Data tell a physical story……..over lots of different scales (different forcing)

Residual (de-tided) Flow

Surface

Bottom

On-average…southward

West Passage

Residual (de-tided) Flow

Surface

Bottom

On-average…southward

On-average…northward

West Passage

East Passage Channel

Physical Story of the Bay, by Residual Q. Data

Water enters eastern EP

Dominant re-supply up EP

Outflow through WP*

-------------------------------------------------

Enhance: Eastward winds

Southward winds Northward, then Southward winds

Stall/reverse: Northwestward winds stall / reverse

?

We have a very good idea about deep intrusionswhere they come from, what drives them, and their thermal advection

Steady Re-supply up East Passage

Enhanced by: Eastward winds

Southward winds Northward, then Southward winds

? Bottom Temperature @ ADCP

Deep EP




Data tell a physical story….

Data always limited in space and/or time…..

Models extend us towards full physical story of the Bay, all places, for all time






Models extend us towards a full physical story of the Bay, all places, for all time

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Models….do we trust them?

do the data and model wiggles match?

ROMS Modeling for Narragansett Bay is built on years of GSO student efforts

Bergondo: Providence River model

Rogers: Bay - Rhode Island Sound Model

Rogers, Ullman, Balt: Full Narragansett Bay Model




ROMS Modeling for Narragansett Bay is built on years of GSO student efforts

Bergondo: Providence River model

Rogers: Bay - Rhode Island Sound Model

Rogers, Ullman, Balt: Full Narragansett Bay Model




2006 wind, runoff, air conditions

Tides, mouth forced by large model

15 terrain-following vertical coordinates

<50 meter horizontal grids

Models match instantaneous (tidal) flows/heights very well

Data ( R) vs Model (B) Tidal response

Skill = .98

Skill = .97

Skill = .98

Wat

er L

evel

Decimal Day, 2006

Validation using fixed- point data

VARIABLE SKILL

Surface Temperature

0.98

Surface Salinity 0.94

Bottom Temperature

0.79

Bottom Salinity 0.76

2006

From C. Balt,09

ROMS Assessment : Quantitative comparisons with fixed station data

Tide heights: Skill >0.95 // Velocity fields: Skill 0.8 - 0.9 // T,S: Skill 0.75-0.98

Actual forcing data

ROMS Model

Time series model output at buoy locations

Statistical metrics: Skill = 0 poorSkill = 1 perfect

+ Time series buoy data






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does the model predict the gross character shown in data?

Modeled upper bay transport: Vertically integrated along N. Prudence Line

--- Zero wind

Summer 2006 forcing, except winds


--- Zero wind--- Northward wind GYRE STALLS


--- Zero wind--- Northward wind GYRE STALLS

--- Southwestward wind GYRE ENHANCED

Patterns match 06-09 ADCP data

OUT

IN







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does the model predict the gross character shown in data?

Quasi-trusted models….how can we use them?


Key Management Issue: The role of flushing dynamics as the root of chronic water quality problems?

Out with the Bad

Flushing Time using Fraction of Water Method (assume complete mixing)

Simple estimates: ~4 days

Simple estimates: ~10 days

Flushing processes may be more complex…….

Greenwich Bay:

Rogers thesis models using ROMS show longer times

Future: Test model predictions with dense current meter network

Providence River:

NBC data & Fluid Dynamics Lab Models suggest longer times

Future: Test predictions using dense current meter network


Greenwich Bay:



Providence River:



CHRP models must represent flushing accurately

Providence River flushing may not follow simple estimates

Models & Data Suggest a Bimodel Residence Time

Edgewood shoals

channelNBC

Save the Bay

EYC

Fluid Dynamics Laboratory Models (a.k.a analog models)

Fall, 2008 at GFD Lab, Australian National University: .

Developed flume tank to represent the Providence River

Model includes shipping channel & the Edgewood Shoals

Parameters: river flow , NBC discharge, tides : (no winds)

Shi

ppin

g C

hann

el

Shipping Channel

Edg

ewoo

d S

hoal

Edgewood Shoal

Port Edgewood

Save the Bay

Hurricane Barrier

Save the Bay

We have modified a 3 meter long flume tank at the Fluid Dynamics Lab of the Australian National University to represent the Providence River-Fields Point-Edgewood region of the estuary.

NBCNBC

PortEdgewood

PortEdgewood

BroadShoalBroad

Shoal

Channel

Channel

66 cm (1000m)

Z= 2cm 33 cm

(400 m)

Scaling:

Re#= 105

Scale on runoff prism and tidal prism : 30 CMS = 7 liters/min1 tide cycle = 20 seconds

NB

C

Bro

adS

hoal

Channel

Relevance to Water Quality Models

Lab Models: small physics that numerical models can’t represent

Do small scale processes influence exchange & mixing between shoal and channel & overall water quality?

NB

C

Bro

adS

hoal

Channel

Movies: no wind/density forcing

1. 30 CMS (7liters/min), no tide (2 CMS NBC Fields Pt).

2. 2 CMS runoff, 1.5 meter tide

3. 30 CMS & 1 meter tide (late addition of 2 CMS NBC outfall)

NB

C

Bro

adS

hoal

Channel

Small scale eddies: tilted/sheared

Vertical & horizontal structure to shoal-channel exchange:

>15 days: shoal bottom water retention

Surface floaters rapid exchange, but recycle

Do small scale processes influence exchange & mixing? YES

Lab Models: Discharge, no tide

Eddies 10-50 meters

Spring tide only, no runoff: Mid-shoal surface off in 4 cycles (2 days)Mid-shoal deep >> 10 cycles (5 days)Inside shoal >> 10 cycles (5 days)

Do small scale processes influence exchange & mixing? YES

Combined 30 CMS runoff & 1m tide: flushing ~5 cyclesTwo exchange modes

1. tilted-stretched eddies

Combined 30 CMS runoff & 1m tide: flushing ~5 cyclesTwo exchange modes

1. tilted-stretched eddies2. late flood, eastward plumes

Conclusions:

Lab models show:

two modes of shoal-channel exchangedeformed eddies at shoal-channel interfacetides & runoff drive off-shoal plumes

strong vertical flow structures, deep shoal water isolation

flushing times of 5-20 tide cycles

Mixed basin model for Narragansett Bay is not appropriate

NBC outfall on shoals increases flushing by factor of 3

x

x

Tilt Current Meters: 1) Gyre vorticity / shape vs. environmental forcing

2) Small scale eddy field at channel-shoal intersection

x

Testing Model Predictions


Greenwich Bay:



Providence River:



No wind NNE-ward wind

Retention in Greenwich Bay: Wind mattersPosition of floats after 10 days of simulation after float cloud introduced,

J.M. Rogers

No sea breeze

Applied sea breeze

summer 2006

Movies of Greenwich Bay Flushing: Narraganset Bay-RIS ROMS model.Summer 2006 tides & density fields

1) 2006 Runoff, no wind

2) 2006 Runoff, northwestward wind


Retention in Greenwich Bay: Wind mattersResidual flows are predicted to be distinctly in the two cases.

J.M. Rogers

No sea breeze

Applied sea breeze

summer 2006


Retention in Greenwich Bay: Wind mattersResidual flows are predicted to be distinctly in the two cases.

J.M. Rogers

No sea breeze

Applied sea breeze

summer 2006

Test with data


Greenwich Bay:



Providence River:





Greenwich Bay:



Providence River:




CHRP Coupled Eco-model

Fundamental Column:

Detailed understanding of physical processes

Circulation in Narragansett Bay: Water flow & mixing Transport of chemical-biological material...

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