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Beaches

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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Beaches

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  1. Beaches

  2. What is a beach? • Area along coast where sediment accumulates • Coastal zones begin when waves interact with seafloor

  3. 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

  4. 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”

  5. 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

  6. Quartz wide Cobble Pink sand narrow sand Black sand Shell BeachesTypes • Shape and structure • Composition • Size • Color

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. BeachesErosional Features • Marine terrace • If sea level lowers or land uplifted, wave cut bench becomes marine terrace

  16. 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

  17. Miami Beach after before BeachesHuman intervention • Beach nourishment • Import sand into coastal areas • Dredging • Underwater excavation to clear waterways

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