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Coasts, Beaches and Shorelines

Jurassic Coast, England (SW)

“Coast”

“Coast” and “Shore”

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Coast and Shore• Shore - between low tide and highest

elevation affected by storm waves• Coast - from shore to farthest inland

ocean features

Coast and Shore

• What are ocean features?

Shoreline and Beach• Shore: backshore, foreshore,

nearshore, offshore– Berm, beach face, longshore bar,

longshore trough• Coast – not necessarily effected by

wave action

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Beach

• Actively changing• Composition

– What is locally available?• Coral and carbonate sand in the Bahamas• Lithogenous sediment in Louisiana, Gulf Coast• Lava in Hawaii

• Shape– Determined by composition and energy (waves, tides)

• Fine sand, more gentle slope• Coarse material, steeper slope

Beach

• Coarse Grain – steep slope

Alaska

Beach

• Fine Grain – gentle slope

Puerto Rico

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Swash Zone of the Beach

• Swash and backwash– Sediments moved up and down beach

face– Smaller, low energy waves move sand

up beach face (depositional to berm)• Summertime beach

– Larger, high energy waves move sand off shore (erosive to berm)• Wintertime beach

Sand Movement parallel to Beaches

• Longshore current

Sand Movement parallel to Beaches

• Longshore current– Longshore drift or transport– Parallel to shore– Increasing strength

• More wave energy• Higher wave frequency• Steeper beach• Greater angle

– Southward along both U.S. coasts (most of the time)

– Main sediment transport along coasts

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Rip “Tide”

• Localized currents return swash zone water to deeper water

Rip Current

• Location determined by bathymetry built by swash and longshore drift

Shore Types• Erosional Beaches

– Evident of local sea level fall– Erosion and transport offshore

• Depositional Beaches– Gradually subsiding coast lines– Large sediment source elsewhere

• Both erosion and deposition happen on both types of beach!

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Beach Erosion and Deposition

Erosional Beaches

Depositional BeachBarrier Islands

Bay mouth bar

Sand spit

Tombolo

Lagoon

River Deltas

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Beach Features

Beach Features

http://www.shorebirdworld.org/fromthefield/FLsurvey.htm

Beach Features

http://www.cografyaogretmeni.org/galeri/details.php?image_id=22

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Beach Features

http://www.cografyaogretmeni.org/galeri/details.php?image_id=22

Beach Features

http://www.etribes.com/node/36793

Beach Features

http://verseguru.com/media/?gallery/state=South%20Ari%20Atolhttp://geology.uprm.edu/Morelock/morphol.htm

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Seasonal Beach Features

• Stormier (winter) beaches take sand offshore – sandbars

• Gentler slope in summer (calm weather)

Coastline Types

• Deltas– Delivery of lithogenous sediment from river

systems “bends” lithosphere, creates space– Sedimentation keeps pace with sea level

Deltas

• Why do deltas only form where large rivers intersect the oceans? Why not where every river enters the ocean?

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Fjords

• Fjords– Valleys carved by glaciers– Filled by rising sea level

Mangrove Coasts

• Vegetation stabilized coasts in the tropics• Sedimentation within the roots of large

expanses of mangroves

Barrier Islands

• Temperate latitudes, passive margins

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Coastal Classification

Barrier Island Beaches

• Progression response to sea level

1887 1996

Barrier Island Beaches

• Recreationally important• Building on barrier islands has increased• How do we protect these investments?

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Beach Restoration and Protection

• Maintain deposition– Sediment source

• What happens when nearby rivers are dammed?

• Prevent or slow erosion– Steady state is desirable

• What structures intensify beach erosion?• What about rising sea level?

Beach Barrier Management

• Beach groins

Beach Barrier Management

• Jetties and groins

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Beach Barrier Management

• Breakwater

Beach Barrier Management

• Breakwater and dredge system

Beach Barrier Management

• Seawall

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Key Concepts

• Beach classification• Beach movement• Sea level rise• Protection of barrier islands

– Natural systems or resorts?