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Chapter 8: Barrier Systems

•General Description of Morphology

•Distribution & Coastal Setting

•Barrier Types

•Evolution (Prograding, Retrograding, or Aggrading)

•Barrier Stratigraphy

•LI Barrier System

Physical Description

•Wave built accumulations of sand

•Waves and Winds sustain their evolution

•Linear features, parallel to coast

•Occur in groups or chains

Barrier Systems BeachBarrier Interior

Landward Margin

Beach: dynamic, evolution dependant on winds, waves and tides

Barrier Interior: sand dunes, dune lines, vegetated beach ridges, brackish ponds.

Landward Margin: intertidalsand/mud flats, salt marsh, overwash splays, transitions into bay, lagoon or tidal creek

Distribution and Coastal Setting

•Comprise ~15% of the worlds coastline

•Found on every continent (except Antarctica), geologic-climatologic setting

•Amero-trailing edge coasts

•Mid-low latitudes, micro-meso tidal environments

Barrier Distribution

Microtidal: < 2 m

Mesotidal: 2 – 4 m

Macrotidal: > 4 m

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Amero-Trailing Edge Coasts

Sediment supply

Shelf width

US east coast

barrier chains extend 3100 km

Slow erosion Appalachian Mnts

Gulf coast (1600 km)

Marginal Sea & Collision Coasts

Sediment supply is low (short steep rivers)

Shelves tend to be narrow (high wave energy)

Sediment is often transported to ocean basins

Afro-Neo Trailing Edge Coasts

Lack of sediment

Lack of organized drainage

Types of Barriers

Barrier Spits

Recurved spits

Stony Brook Harbor, Long Beach

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Spit Formation

Tombolos

Georgica Pond, NY

Welded Barriers

Barrier Island

NOTES

•Barrier chains are aligned parallel to the coast

•Most have formed in a regime of slow eustaticsea-level rise

•They are separated from the mainland by shallow lagoons, marshes, and/or tidal flats

•Tidal inlets separate individual barriers along a chain

•They formed during periods of sand abundance

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Offshore bar theory (de Beaumont, Johnson)

Spit accretion theory (Gilbert, Fisher)

Submergence theory (McGee, Hoyt)

Barrier Island Formation Spit Accretion Theory

Shinnecock Inlet, 1938

Spit Accretion Theory Spit Accretion Fire Island Inlet

Prograding Barriers: building/migrating seaward

Any mechanism that forms a continuous feature along the barrier that acts as a nucleus for dune ridge development

Retrograding Barriers - bar island rollover

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Dauphin Island Hurricane Ivan, September 2004

Aggrading Barriers: Barrier systems is stationary, keeps up with rising sea level Barrier Stratigraphy

Layering or sequencing of sedimentary deposits

Bluff Erosion

Offshore Glacially Deposited Sand Ridges, Relict Ebb Shoals

Sources of Sand For Littoral Transport

2 m

Tide Dominated &

Riverine

Wave Dominated

Mixed Energy

Gravel

Sand

Barrier Island

Cliff or Bluff Coast

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Maximum Amount of Material Derived From Bluff Erosion

•Historic estimates 81,100 yd3/yr to 132,100 yd3/yr

•The bluffs at Montauk Point are receding at 1 ft/yr

•This recession rate has been well documented due to endangerment of the historic Montauk Light House constructed in 1796.

•Analysis of the bluff composition and historic rates of recession have determined Montauk (Ronkonkoma Moraine) bluffs could not account for all of the material contained within the littoral system.

•Based on sieve analysis data

•63-percent of the size fraction (by weight) is similar in composition (fine to medium sand) to the barrier beaches to the west

•Littoral Transport reaches a maximum rate of 463,015 to 601,657 yd3/yr at Democrat Point (Fire Island Inlet)

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Calculated Recession Rates for Montauk Bluffs

McCormic & Pilkey1796 – 199676,065253,5501.000.30Kana, 19951955 – 1979132,100253,5501.560.47USACE, 199539,000253,5500.460.14Rosati et al, 19991983 – 199586,600253,5501.020.31Rosati et al, 19991979 – 199581,100253,5500.950.29

yd3/yryd2ft3/yrm2/yr

ReferenceYearsLit. Cont.SARecession Rate

Atlantic Coast of New York Monitoring Program

Seasonal Profiles 1995 through 2004

Measured Recession Rates and Littoral Drift Contribution for Montauk Bluffs

3411754151Total0.97Average608296540.810.91M43567090004.451.30M4291614530.620.31M41

190030151.200.20M4072511500.402.00M39

11034175147.801.90M38166326401.200.83M37612797253.200.32M35

Littoral Volume yd3/yr

Integrated Volume yd3/yr

Vol. Change yd3/ft/yr

Recession Rate ft/yr

ACNYMP Station

6 to 29 % of Longshore transport at Fire Island Inlet.

The Flandrian Transgression

•Current sea level rise which began approximately 18-19,000 years ago (during latest Pleistocene time and continuing progressivelyduring Holocene time to the present).

•This rise in sea level is directly related to the melting of continental polar and mountain piedmont glaciers.

•During the "climax" of the Wisconsin glacial advance (lowstand) sea level was anywhere between 70 to 150 meters below its current level

•Shelf Break = the outer edge of the continental shelf

Shoreline Retreat During The Flandrian Transgression

-50 m -40 m -30 m

-20 m -10 m 0 m

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•30 kilometer wide band of sand ridges on the middle continental shelf represent a broad band of degraded and submerged barrier islands formed between 14,000 and 8,000 years before present (Stubblefield, et al. 1983)

•Shelf currents are actively reworking the barrier sands into ridges

•It has been in the last 4000-6000 years that the majority of modern coastal barrier islands and tidal wetlands have developed.

109,868 to 517,948 yd3/yr of sediment may be coming from offshore, however the exact mechanism for the material transport into the littoral zone has not been determined (Schwab et al., 1999)

Additional Metropolitan Beach Composition

Wave driven transport and

winnowing

River and Raritan Bay Sediments

Raritan Bay Sediments