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Beaches. What is a beach?. Area along coast where sediment accumulates. Coastal zones begin when waves interact with seafloor. Beaches Shoreline Divisions. Littoral zone. Part of coast that stretches from land plants to where waves start to break. Shoreface. Permanently covered by water.

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What is a beach
What is a beach?

  • Area along coast where sediment accumulates

  • Coastal zones begin when waves interact with seafloor


Beaches shoreline divisions
BeachesShoreline Divisions

  • Littoral zone

  • Part of coast that stretches from land plants to where waves start to break

  • Shoreface

  • Permanently covered by water

  • Foreshore

  • Exposed at low tide and covered at high tide

  • Backshore

  • above mean high tide – only affected by storms


Beaches shoreline divisions1
BeachesShoreline Divisions

Divided by wave action:

  • Breaker zone

  • Where waves become unstable and break

  • Surf zone

  • Shallower waves move up beach face

  • Swash zone

  • alternately covered by “swash” and uncovered by “backwash”


Beaches sediment profile
BeachesSediment Profile

  • Berm

  • Flat-top ridge of backshore

  • Berm crest

  • High point on a beach

  • Beach face

  • Sloping portion of the beach

  • Longshore bars

  • In winter, sediment from berm is transported below breaker zone


Beaches types

Quartz

wide

Cobble

Pink sand

narrow

sand

Black sand

Shell

BeachesTypes

  • Shape and structure

  • Composition

  • Size

  • Color


Beaches summer and winter

winter

summer

BeachesSummer and Winter

  • Summer

  • Winter

  • Gentle waves

  • Erosive storm waves

  • Carry sand to shore but too weak to carry back to sea

  • Sand carried seaward to offshore sandbars

  • Wide, sandy beach

  • Narrow, rocky beach


Beach processes refraction
Beach ProcessesRefraction

  • Wave crests approach shore at an angle

  • Slows over shallow water

  • Wave bends

  • Wave rays travel perpendicular to wave crest

  • Energy focused on headlands  erosion


Beach processes rip currents
Beach ProcessesRip Currents

  • Incoming waves create underwater sandbar close to shore

  • Waves cause sandbar to collapse

  • Excess water is pushed through gap

  • Creates a strong, narrow current away from shore


Beach processes longshore current and transport
Beach ProcessesLongshore Current and Transport

  • Longshore current moves parallel to shore

  • Longshore transport moves sediment along shore by LS current

  • Zig-zag motion has an overall net transport

  • Swash moves sediment onto beach at an angle

  • Backwash moves sediment down perpendicular to shore


Beach dynamics deposition and erosion

Sandy shore

Rocky shore

Beach DynamicsDeposition and Erosion

  • Deposition

  • Accumulation of sediment

  • Coasts build out by waves and currents

  • Erosion

  • Little incoming sand, usually no major river

  • Sediment is removed

  • Reshaping of coastline by wave action


Beaches depositional features
BeachesDepositional Features

  • Longshore current deposits sand in a line downcurrent

  • Sand spits

  • Bay mouth bars

  • When a sand spit closes off a bay

  • Barrier island

  • Long sand island enclosing a bay or lagoon


Beaches erosional features
BeachesErosional Features

  • Arches

  • Weaker rocks erode

Stack

Arch

  • Stacks

  • Offshore column formed from collapsed arch

  • Tombolo

  • Sand bar connecting to a rock or offshore outcrop

Tombolo


Beaches erosional features1

Cliff

Wave cut bench

BeachesErosional Features

  • Wave cut bench

  • Cliff

  • Cliff bottom attacked by waves

  • Waves undercut cliff to form wave cut notch

  • Overhanging rock collapse

  • As cliff retreats, area of flat rock exposed


Beaches erosional features2
BeachesErosional Features

  • Marine terrace

  • If sea level lowers or land uplifted, wave cut bench becomes marine terrace


Beaches human impacts
BeachesHuman Impacts

  • Parallel concrete structures

  • Absorbs wave energy

  • Sea walls

  • Actually promotes erosion

  • Groins

  • Wall perpendicular to shore

  • Stops erosion

  • Erodes downcurrent side

  • Jetties

  • Designed to maintain navigation routes

  • Erosion and deposition

  • Breakwaters

  • Wall parallel to shore

  • Reduce wave energy

  • Interrupts beach drift


Beaches human intervention

Miami Beach

after

before

BeachesHuman intervention

  • Beach nourishment

  • Import sand into coastal areas

  • Dredging

  • Underwater excavation to clear waterways


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