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
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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 Beach
Barrier 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%20Atol
http://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
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Beach classification
Beach movement
Sea level rise
Protection of barrier islands
– Natural systems or resorts?
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