10 January 2016
Waves, Wakes and Water Clarity: Understanding Physical Drivers of Seagrass Distribution in Coastal Waters
Mark Fonseca, Ph.D.CSA Ocean Sciences Inc.
Amit Malhotra, MSc., GISPGeohorizons
Problems and Solutions – Physical Drivers of Seagrass Landscape Dynamics
Likely Physical Drivers
• Wind Waves
• Vessel Wakes
• Spatial and Temporal Light Availability
Tools Highlights
• WEMo – Wave exposure model (+ higher order tools)
• BoMo – Boat wake model (method)
• OWMo – Optical water quality model (method)
Opportunities and Issues
• Applications
• Average Conditions versus Extreme Events
• Traction
Wind waves and currents influence seagrass landscapes across hydrodynamic gradients
3More Patchiness + More Frequent Spatial Change
Increasing Tidal Currents and/or Wave Energy
Recomputed from Fonseca and Bell, 1998
Tipping point? Wind waves and cover
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Wave forecasting tools
• SWAN – Complex model to compute waves generated by wind and swells– Wave propagation; refraction, diffraction and dissipation (shoaling, whitecapping, bottom
friction, vegetation, breaking and turbulent flow)– Complex and time consuming computations– Well reviewed by scientific community
• DELFT3D – 3D model which includes SWAN along with modules for sediment transport and water
quality– Complex and time consuming computations– Well reviewed by scientific community
• WEMo – wave modeling for ecologists
– Simplified model to compute local wind waves - not swells– Wave propagation and dissipation (shoaling, white capping, bottom friction and breaking)– Module for forecasting sediment initiation of motion– Does not explicitly compute refraction / diffraction – Easier to run and less computationally intensive– Verified– Few publications
Application
• We have tools
• We have theory
• Can we apply this concept to mitigation?
Application: NC Bonner Bridge Mitigation
Reduce wave energy on patchy seagrass beds
Facilitate bed coalescence
Increase cover per unit area seafloor
WEMo wave reduction + seagrass response
Pet. or all wind obs. by direction
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CSA Dcaan Sciancaa Inc.
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Wave break installation – NC (Jan. 2017)
CSA Dcaan Sciancaa Inc.
Vessel Wakes – Marine Corps Base Camp Lejeune
CSA Dcaan Sciancaa Inc.
:oo9-10':'7 Cocwlu.C~k . F\orids
Shoreline Change in the :>lew River Estuary, North Carolina: Rates and Consequences
Camlyn Currint *, ~cnn)' fr.l\'is\ l..i.o;a Co...,<~r t BaronH, Amit \1alhotrat , and Mar k forL..cca * ' NOAA National Ocean Sel"\oioe
C.:·ntcr for Coastal Fi3htri'lll & Hab1ta: F~arch
.Uaufort, NC 28516., US.A.
'cSA O::can ScicocH :nc. Stuart. FL 34007, l'.SA.
'National Park Sorvi:e Scrutheut C.:u:t Nc:wnrt
Athtns, GA 30605, U.S.A_
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Nort."' Carolina: Ra:t<11 and ro~u~noos_ J,urtUJlQf~td. P.~eewcli, 31($), 1069---1077. Coconut Cr-wt ( Florida). ISSN 0749--0006.
AtrW ph (!tccraphy li'IU UJod l(•dttenninGrU.elof8 h<Wiinechu1p in tMNawRiver 111l1111.ryf~f'.E\ l\od1 Caro&na.from 1S56 to2004. TheN!tE llt-.oNiine "'!lldigitizo:t frorn atri.d j1'\ot£p'aph.J tilken m 1956, l!ieS, and 2004. andsh>n:line IYJ» Wall d(;((lrtni!'l&<ll by J!'(Ufld·tru!hl-og the tnlin'l &htraline by IID.lO l:oot ia 2XH .\tfjor &l'loH!line lype ea:c~\11 ib:!ludOO go;.Q.I:lpf~YeJt (fi%!if kU!),taft manih(21 *). ~ira(.d OOnlt (53\i),atd modifi«lthardened ( 19'it ~. Gn:uld-Uul.hi-lg proW:I.-rl adiD!ionald<-taill o>n relie~ a.arsh sptcietl oxnr~>o&i~CJI, and structure type. A poirU UJ&i, m(!-p-Jir.t rat.ta ppn:a:h W!JI UMd ID rr.-ure &honlifle change n::te ($Cil ) at &J m in tervs lll f<r the puicda 1~9, 1989-2001, and l !ll6-2004. ~~a.ol'lllltivewavt e:.~ (lm'eJ wu modeled f<r o,;a,c__'\ inUI'\'a.l using loeol i»th)'l'il~ ud wiad data A~r• S('R 8(ri)M all 'htf'(lir~ l)'p:l tu the entm.~ pwiod M •gtd fro!r~ -2.3to ~l .J ny 1, Wllh am ron Sf1Rof-0.3my--.l. This trarula~toar. St'(l.ftli'I ~Of....., J3mbranyo>ivl'fl~~rtht 48-~ill'p:!ri>drover00b)'t.hig n.._dy.'tb~m-:.st: n~~g&&.ive ,.....,, ag~ sen ~.p-..__._tor;t {!,._..._,) <J~Xutn.! .Jo . .., u.:vo:-g~rakd -.I..U.aoot ba.ul.. ~w•d"ll<b (-o.aJ o y ' ). Chanl!" f.lo,g m ..,.,_l &honlirt.ea(..0.18M! 1) "-AAiower t.b.9.11 alor.gMldimrlnt banks, and na n-<Mt fringingnw-;;h Ul~)tiat.ed ...-ilh Mldil'l'o(!l'lt Mn~ shorelillet l!lignificattl) rtodU'OO hlll'..k ('ll'(aioo . l\bdt~ R\-\-E valuu w-e~ po..~it lw~!y oolT't'liat:ed wih ~r.'l only in lhe hiJhtllt "-'I.VHnergyllettiJigt. ErOOoo (/lltdimmtba.'lks00relir.esprovidefl aron11trwli~&81imat.e of 1 ~.660 m3 ofaf!dinlert ea:hyear toth"enUU), o;.ith I'IUlt!lheAI!ian conltlb\;.brt;: up1DarladJiUonal l9Xlm' y-1
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INTRODUCTIOl\" shcreline change t-.lne rocused m oceanfront bmches, there
Marine Corps Base Camp Lejeune
• Continuous wave recording
• 6 Hz
• 18 months
• Measured all passing vessels
BOAT WAKE MODEL (BoMo)Boat Wake Model
V Hull [0·711) V Hul (7-1611) V Hull [16-30m)
DD Sailboat Ferryboat _j
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CSA Dcaan Sciancaa Inc.
Hull Characteristics
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length ( m ): \II etted \II ater line ( m~ Total \II ater line( m~
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Beam (m): Draft (m):
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Displacement (tonne~ Note: 1 tonne = 1 000 kgs 1 tonne = 2204.6 lbs 1 short ton = 2000 lbs
Enter Density of water or use defaut 1027kglm3
0.61
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m/s Average speed of boat I~ '----------'
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Tipping point between wind wave and boat wake dominance
Comparing Wind Waves and Boat Wakes
New River ·
CSA Dcaan Sciancaa Inc.
Percentage of boat wakes exceeding wind waves
• 0.20-0.24
0 0.25-0.36
0.37-0.52
0 0.53-0.75
• 0.76- 1.00
Atlantic Ocean
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Boat wakes and their influence o n erosion in 1he Atlantic Intracoastal Waterway,
North Carolina
• Predicts geography of seagrass light requirements
• Informs ‘what if’ and cost-benefit questions for exploring management alternatives (scenario gaming)
• Link with wave tools for geospatial water quality forecasts
• Best application requires calibration (field assessment)
OWMo + GUI
Optical Water Quality Model (OWMo) + Graphical User Interface (GUI)
• Slide CHL and/or TSS to see new potential habitat
• Set a depth or acreage target and see required CHL and TSS levels
OWMo – GUI interface
Works Forwards & Backwards
Seagrass suitable area at default CHL and
TSS values
1.50 m contour
(default depth)
1.75 m contour
1.50 m contour
(default depth)
Change in seagrass suitable area after
reducing CHL 10% and TSS 30%
New
extent
(gain)Original
extent
SUMMARY - FORECASTING TOOLS
• Wind waves – programs forecasting wind waves and sediment movement SWAN
Delft3D
WEMo
• BoMo - forecast boat wake waves, sediment motion
• OWMo – forecast light availability using bathymetry and selective spectral attenuation
OPPORTUNITIES
• Restoration site selection
• Seagrass cover manipulation
• Shoreline management
• Sediment resuspension forecasts
• Vessel traffic management
ISSUES TO CONSIDER
• Not much traction with ecologists
– Historical absence of ecologist-friendly tools
– Physical assessments not taught
• Correct forecasts? Average conditions vs Extremes
– Extent
– Resolution
– Duration
– Intensity
– Return interval (1/frequency)
– Sequence
Questions?
Waves, Wakes and Water Clarity: Understanding Physical Drivers of Seagrass Distribution in Coastal Waters
Mark Fonseca, Ph.D.CSA Ocean Sciences Inc.
Amit Malhotra, MSc., GISPGeohorizons
Questions?
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