1Chapter 8: Barrier Systems•General Description of Morphology•Distribution & Coastal Setting•Barrier Types•Evolution (Prograding, Retrograding, or Aggrading)•Barrier Stratigraphy•LI Barrier SystemPhysical Description•Wave built accumulations of sand•Waves and Winds sustain their evolution •Linear features, parallel to coast•Occur in groups or chainsBarrier SystemsBeachBarrier InteriorLandward MarginBeach: dynamic, evolution dependant on winds, waves and tidesBarrier 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 creekDistribution 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 DistributionMicrotidal: < 2 mMesotidal: 2 – 4 mMacrotidal: > 4 m2Amero-Trailing Edge CoastsSediment supply Shelf widthUS east coastbarrier chains extend 3100 kmSlow erosion Appalachian MntsGulf coast (1600 km)Marginal Sea & Collision CoastsSediment supply is low (short steep rivers) Shelves tend to be narrow (high wave energy)Sediment is often transported to ocean basinsAfro-Neo Trailing Edge CoastsLack of sedimentLack of organized drainageTypes of BarriersBarrier SpitsRecurved spitsStony Brook Harbor, Long Beach3Spit FormationTombolosGeorgica Pond, NYWelded BarriersBarrier IslandNOTES •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 abundance4Offshore bar theory (de Beaumont, Johnson)Spit accretion theory (Gilbert, Fisher)Submergence theory (McGee, Hoyt)Barrier Island Formation Spit Accretion TheoryShinnecock Inlet, 1938Spit Accretion TheorySpit Accretion Fire Island InletPrograding Barriers: building/migrating seawardAny mechanism that forms a continuous feature along the barrier that acts as a nucleus for dune ridge developmentRetrograding Barriers - bar island rollover5Dauphin Island Hurricane Ivan, September 2004Aggrading Barriers: Barrier systems is stationary, keeps up with rising sea levelBarrier StratigraphyLayering or sequencing of sedimentary depositsBluff ErosionOffshore Glacially Deposited Sand Ridges, Relict Ebb ShoalsSources of Sand For Littoral Transport 2 mTide Dominated &RiverineWave DominatedMixed EnergyGravelSandBarrier IslandCliff or Bluff Coast6Maximum 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)7Calculated Recession Rates for Montauk BluffsMcCormic & 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 – 199581,100253,5500.950.29yd3/yryd2ft3/yrm2/yrReferenceYearsLit. Cont.SARecession RateAtlantic Coast of New York Monitoring ProgramSeasonal Profiles 1995 through 2004Measured Recession Rates and Littoral Drift Contribution for Montauk Bluffs3411754151Total0.97Average608296540.810.91M43567090004.451.30M4291614530.620.31M41190030151.200.20M4072511500.402.00M3911034175147.801.90M38166326401.200.83M37612797253.200.32M35Littoral Volume yd3/yrIntegrated Volume yd3/yrVol. Change yd3/ft/yrRecession Rate ft/yrACNYMP Station6 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 shelfShoreline Retreat During The Flandrian Transgression -50 m -40 m -30 m-20 m-10 m0 m8•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 CompositionWave driven transport and winnowingRiver and Raritan Bay SedimentsRaritan Bay