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UW ESS 230 - Reading Material

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Reading MaterialSlide 2Slide 3Slide 4Slide 5Terminology for Coastal EnvironmentSlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Transitions as waves approach shorelineSlide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Impacts of winter stormsSlide 24Coastal BarriersSlide 26Slide 27Formation of Barrier IslandsSlide 29Slide 30Slide 31Reading MaterialOn reserve in:Ocean-Fisheries library (Oceanography Teaching Building)Through the following web site:https://eres.lib.washington.edu/eres/coursepage.aspx?cid=4291&page=docs\\Type in your UW Net ID when prompted and accept the Copyright statement.“Inshore oceanography”, Anikouchine and Sternberg – “The World Ocean, Prentice-HallBEACH PROCESSES AND COASTAL ENVIRONMENTSCOASTAL FEATURESCross sectionMap viewTerminology for Coastal EnvironmentBeach – extending from MLLW to dunes/clifShoreline – where land and ocean meetSpit – linear extension of shoreline, due to accumulation of sedimentBarrier – spit or island seaward of land, usually ~parallel to trend of landBars and troughs – seabed features in surf zoneBerm – relatively flat region of beach, behind shorelineForeshore – seaward sloping surface, located seaward of bermBackshore – berm and dunesInlet/washover – means to transport beach sediment landward,due to tides and storms (respectively)Longshore (littoral) drift or transport – water and sediment movement parallel to beachFactors afecting formation of wind wavesDuration wind blowsWind speedDistance over which wind blows (fetch)Terminology for Describing WavesT = wave period = time between two wave crests passing a pointIn deep water, wave speed increases with wavelengthTherefore, waves sort themselves as they travel from source area;waves with large wavelength reach beach first = swellChanging Wave Character from Source to Surf confused sea single wave shape pointed wave crest Wave shape Wave characteristics change with long travel distance, because waves sort themselvesWaves in deep waterWater molecules move in closed circular orbitsDiameter of orbit decreases with depth below water surfaceNo motion at a water depth >1/2 wavelength of wave = wave baseWaves in shallow water(water depth <1/2 wavelength)Water molecules move in elliptical orbitsAt seabed, water (and sediment) moves back and forthThere is an asymmetry with more transport under crest than trough, causing net movement in the direction of the waves – i.e., toward shoreWaves approaching a straight shorelineIn shallow water, wave speed decreases as water depth decreaseswaves travel progressively slower as depth decreases,therefore crests bend = wave refractionRay = perpendicular to wave crest wave crestWaves Approaching an Irregular Shorelinewave rays = perpendicular to wave crestspaths of rays indicate that waves: focus energy on headland, eroding it and defocus energy in embayments, causing sediment depositionTransitions as waves approach shoreline1) Waves feel bottom at wave base (1/2 wavelength), ~10-50 meters depth2) Seabed is eroded, mud moves seaward in suspension, sand moves as bedload back-and-forth with net drift toward shore3) Wave speed decreases as water depth decreases (wave refraction)4) Wave height increases, wavelength decreases5) Crest becomes progressively steeper – ratio of wave height to wave length (H/L) becomes large6) At H/L ratio > 1/7, wave becomes unstable and breaks = surf7) Water moves up foreshore as swash, and back down as backwashTypes of Breaking WavesLargely dependent on steepness of seabed, which is related to grain sizespilling breakers are found on fine sand beaches (e.g., southern Washington coast beaches)plunging and surging breakers are found on coarse sand and gravel beaches (e.g., northern Washington coast beaches)Rip CurrentsRip currents are the primary mechanism for returning water through surf zone, and are the most dangerous for swimmersAlso broad, weak flow near seabed = undertowBeach TerminologyLongshore or Littoral DriftWaves break at angle to shore, which causes swash at angle to shoreBackwash follows gravity down foreshoreNet efect is water and sediment transport along shoreBeach growth during swash and backwashSwash – flow up foreshore after wave breakstransport all water and much sediment, but water percolates into permeable beach sandBackwash - less water and sediment flow with backwashTherefore, beach builds up to uniform level, creating the bermSummer Beach GrowthImpacts of winter stormsStorms bring strong winds and larger wavesStrong winds push ocean water against coast = storm surgeLarger waves erode beach sediment (i.e., erode fairweather berm)Sediment goes to:build bars ofshorebuild higher berm (storm berm)washes through dunes forming washover depositsSediment stored in ofshore bars is transported back slowly by waves during fairweather (due to crest/trough asymmetry and net drift shoreward)Processes create cycle of summer/winter beach profilesSummer/Winter Beach ProfilesSummer: wider berm little sediment in barsWinter: summer berm gone; higher berm possible much sediment in barsCoastal BarriersSpits and barrier islandsCommon for trailing-edge margins gentle gradientslittle tectonic uplift/subsidenceStretch along most of US Atlantic and Gulf coastssouthern Washington coast(protecting Willapa Bay and Grays Harbor)Landward migration is common todaydue to sea-level riseSeaward growth can occur near fluvial sediment sourcesFormation of spitLongshore transport is dominant mechanismTidal flux in/out of embayment creates inletBarrier IslandsTidal inlets at both endsElevation depends on sand supply and winds forming dunes – typically <10 mLow barrier islands can experience washover during stormsLength of island depends on amount of water that must enter/leave lagoon with tides (= tidal prism)Formation of Barrier IslandsSpit elongation – Extension of spit becomes too long to allow inlet to transport all water between tides, and a new inlet forms, changing a spit into an islandBar submergence – Old dune or topographic high is surrounded by water as sea level rises.Bar emergence – During strong storm, waves create a large bar ofshore, which becomes island when storm surge subsidesSpit ElongationLongshore transport causes spit extensionFlow in and out of lagoon cannot occur entirely with changing tides.Diferent water levels on the two sides of spit cause a new inlet to form – usually


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UW ESS 230 - Reading Material

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