Wave Erosion

Wavesandcoastalprocesses

Factorsinfluencinpthe rate and locationof processes in coastalenvironments:

processes: Atmospheric

Geological factors:

- Windspeedanddirection.

- Rocktype(soft/hard).

- Precipitation/ frostetc.

- Rockstructureandanyweaknesses.

Marinefactors:

Humanfactors:

- Wavestrengthandtype.

- Coastal defences.

- Waveenergy.

- Beach nourishment.

- Waverefraction.

Howdoesa waveformandbreak?

t. Windblowsoverthe surfacecreating a transferof frictionandenergywhichcauses a wave to develop. Thesizeof the wavedepends of the fetch(howfar the windhastravelled), wind strength, speedandduration. 2. Frictionbetweenthe windandthe watersurfacecauses waterparticles to beginto rotate. 3. Dueto frictionwith the seabed;the wavebeginsto slowdownat the base. 4. Thewavebecomes steeperuntilthe waveheightto wavelengthratiois 1:7.Thewavewill thenbreakasit becomes unstable andtopplesover.

Wavefeaturesandterminologv: Crest: The highestpoint of a wave.

Through: The lowest point of a wave.

Waveheieht: ls the distancebetweencrestand trough.

Wavelength: ls the distancebetweentwo successive crests.

Wavefrequency: The numberof waverper minute.

Waveperiod: ls the time takenfor a wave to travelthroughone wave length.

Wavesteepness: ls the ratio of the wave heightto wave length.

Wave Base: Thisis the depthbelowwhichthere is no rotationalmovement.

HangTen

Destructive and constructive waves: Destructive waves: a

Highenergywaves.

a

Backwashis greaterthan the swash.

a

Highfrequencywave (10-12per min)

a

Shortwavelength.

a

Createdby localisedwindsand storms.

a

Steepbeachprofile,erosionalwaves. Highwaves(greaterthan 1m)

a

Constructivewaves: a

Low energywaves.

a

Swashis greaterthan the backwash.

a

Low frequencywaves(6-8per min)

a

Longwavelength(up to 100m)

a

Createdby the swell.

a

Fairlyflat, gentle beachprofile.

a

Low flat waves(lessthan 1m)

Waverefraction: Wherewavesmeetan irregular coastline theyarerefracted whichmeansthat theybecome parallel increasingly to thecoastline: Where a headlandseparatestwo baysas eachwave crestnearsthe coastit tendsto drag into shallowwater nearto a headlandor indeedany shallowwater. Thenthe crestin deeperwater movesforwardwhile that in shallowwater is retarded(by frictionaldrag)causingthe waveto bend. The longshorecurrentscarrysedimentawayfrom the headland.