1Coastal Geomorphology & Coastal DynamicsSpring 2007Field Trip ScheduleMontaukSaturday March 31thSunday April 15th Saturday April 28thChapter 6: WavesChapter 6: WavesWave properties, propagation, particle motionTypes of WavesDistribution & Transfer of EnergyTsunamis, Standing WavesWave Generated CurrentsCoastal Engineering Manual: Coastal Hydrodynamics (Part II )Water Wave Mechanics (Part 2 - Chapter 1)Meteorology and Wave Climate (Part 2 - Chapter 2)Estimation of Nearshore Waves (Part 2 - Chapter 3)Surf Zone Hydrodynamics (Part 2 - Chapter 4)Hydrodynamics of Tidal Inlets (Part 2 - Chapter 6)Wave Generation and PropagationNearshore Transformation and BreakingWave Form PropertiesLinear Wave EquationHeight and AmplitudeWave NumberRadian FrequencyPeriod Classification2Wave Data: is often reported or presented as a spectrum. Wave energy is a proxy for wave heightWave NomenclatureWave Field are usually described by three variables:H:height sometimes reported as Hsig or HrmsHsig = average of 1/3 largest waves recoded or observedHrms = square root (of the average of the sum ((of all the waves recorded or observed )squared)T: periodα:angle, either geographic angle with respect to north or incident wave angle with respect to shore normal. Similar to wind the direction is relative to where the wave is coming fromWave GenerationWind Speed: velocity at which the wind is blowingFetch: distance over which the wind is blowingDuration: length of time wind blows over a given area (fetch)Fully Developed Sea StateFetch LimitationWsWave Field Observations, Forecasts and HindcastsNomogramsfetchWind SpeedNDBC Telemetry BuoysNAVY WAM (Wave Amplitude Model)Wave speed or celerityDispersion Relationship: relates wave celerity to period, wavelength, and water depth Deep water wave speed is a function of period only Shallow water wave speed is constrained by water depth In deep water wavelength is a function of period. In shallow water it is a function of period and water depth, and must be solved iteratively. Linear Wave Theory (H/L is small)3Dispersion* Waves with longer period move fasterWave SuperpositionForced wave Water Particle MotionFrom deep- to shallow-Wave Transformation NearshoreBeach FaceBreak PointBermShoal ZoneStepWave Shoaling: transformation of the wave form due to interaction with bathymetry (intermediate – shallow water)H: increases up to breakingT: remains constantL: decreasesC: decreases4Breaker Height IndexBreak Point: point at which wave form becomes unstable and breaks (water particles at the crest travel much faster/farther than water particles in the trough)Breaker Index ~= 0.78Note: Rough estimates of breaking wave height and depth can be calculated from deep water wave parameters (ie buoy measurementsBreaker ClassificationBreaker ClassificationSurf Similarity Parameter ~ Irribarren NumberBeach Slope Deep Water Wave LengthDeep Water Wave HeightWave Setup & SetdownWave Refraction: changes in the direction of wave propagation due to along crest variations in wave speedWave Rays: lines drawn perpendicular to the crest of the wave in the direction of wave propagationWave RefractionParallel Contours: refraction results in wave rays approaching normal to shoreline = (wave crests parallel to shoreline (a))Submarine Ridge: focusing of wave energy toward the ridge (b)Submarine Canyon: spreading of wave energy throughout the depression (c)Headland: focusing of wave energy (d)Ebb-Shoal:(a)(c)(b)(d)5Wave Diffraction: bending of wave crests (changes in direction) due to along crest gradients in wave heightWave DiffractionWave Generated Currents6SeichesCreated By:WindTsunamisTidal Resonance Potential MechanismsGeologic EventsVertical fault movementMass wasting eventsubmarine landslidescollapsing volcanoesMeteor Impacthttp://walrus.wr.usgs.gov/tsunami/sumatraEQ/tectonics.htmlThe Dec 26, 2004 M=9.0 Sumatra earthquake occurred along a subduction zone in which the India and Australia plates to the west are being subducted beneath the Sunda plate and Burma microplateto the east. TsunamisSatellite altimeters450 mph in deep waterSatellite images of a coastal village in Banda Aceh, Indonesiahttp://en.wikipedia.org/wiki/Image:Tsunami-2hrs.jpghttp://www.seed.slb.com/en/scictr/watch/living_planet/tsunami.htmWave TheoriesComplexityRange of ApplicationWave Theories7Sediment TransportShearing forces and turbulence exerted on the sand grains by the overlying fluid are responsible for the movement of sedimentSediment Transport Sediment can be transported in three distinct modes1. Suspended Load: material is transported up into the water column and advected by currents (both wave and tide driven)2. Bed Load: material is rolled/moved along the bottom without being suspended. Sand bars and bed forms are transported as bed load3. Saltation: material is bounced along the bedGrain Size – Velocity