Daily tidal fluctuations(actually a little more than 24 hours)Most areas have semidiurnalfluctuations, with two nearly equal high and low tides each daySome areas have diurnalfluctuations, with one high and one low each dayOther areas have mixed semidiurnal fluctuations, with two highs and two lows of unequal elevationCause of TidesGravitational attraction of moon/sun creates bulge of ocean waterCentrifugal force creates second bulgeEarth rotates through both bulges in ~24 hours, causing two high and two low tides each dayMonthly fluctuations in tidesOver ~28 days, orientation of moon and sun changes with respect to EarthThis causes two periods of large tidal range (spring tides) and two periods of small tidal range (neap tides) each monthWhy we have monthly changes in tidesGravitational attraction from moon and sun pull water toward themThis creates two bulgesAs the Earth rotates through these bulges each day, locations experience changing sea levelOver a ~28-day period, the orientation of the moon and sun change, creating different tidal ranges through monthSpring tide = large differencesNeap tide = small differencesTidal range(vertical difference between high and low tide)Macro > 4 m Meso = 2-4 m Micro <2 mLocal differences in geometry of seabed can increase or decrease tidal rangeLagoonal environmentsIntertidal environments (between high and low tide) surround lagoonThey trap and accumulate sediment, filling lagoonTidal-flat sedimentationMud transported as suspended load accumulates on high flatSand transported as bedload accumulates on low flatUpward growth ultimately controlled by rate of sea-level riseAsymmetry between flood and ebb currentsFrictional interaction with seabed commonly causes flood current to be strongerThis results in more sediment being transported into the lagoon and onto the tidal flats, enhancing accumulationMarsh vegetationMany niches develop, depending on many variables, e.g.,: salt and soaking tolerance, and current velocityVegetation helps to baffle flow, reduce tidal current velocity, and enhance sediment accumulationMangrove vegetationMangrove distributionFound in warm, tropical settingsOcean circulation extends latitudinal distribution on west sides of ocean basins, and reduces distribution on east sidesSediment Budget for Beaches and CoastsSediment Sources:Longshore drift (local source)Cliff erosionRiversBiogenic shellsContinental shelfSediment Losses:DunesLagoon (washover, tidal inlets)Submarine canyons (unusual)Longshore drift (local sink)Prograding shoreline, building seawardRequires sediment supply to exceed processes leading toward landward movement of shoreline.Rivers are most common supply mechanism(example from east Texas coastline, downstream of Mississippi supply)Prograding beach ridgesImpact of Groins to ShorelineDeposit sediment on upcurrent side, erode beach on downcurrent sideDeflects longshoretransport farther offshoreJetty entrapment of sedimentSediment trapped on upstream side, due to longshore transportLoss of sediment causes erosion on downstream side, to resupplylongshore transport systemSimilar to entrapment associated with groins, but on larger scalegroinsHuman Beach
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