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The Beach and Nearshore Environment PowerPoint PPT Presentation


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The Beach and Nearshore Environment. Sources of Sand. Sand, Gravel, Pebble, Cobble Quartz Volcanic Carbonate. Nearshore Features. Depositional Coasts Dunes Beach Face Berm Beach sediment Erosional Coasts Headlands Sea Cliffs, Sea Stacks, Sea Arches and Sea Caves

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The Beach and Nearshore Environment

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The beach and nearshore environment l.jpg

The Beach and NearshoreEnvironment


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Sources of Sand

Sand, Gravel, Pebble, Cobble

Quartz

Volcanic

Carbonate


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Nearshore Features

Depositional Coasts

  • Dunes

  • Beach Face

  • Berm

  • Beach sediment

    Erosional Coasts

  • Headlands

  • Sea Cliffs, Sea Stacks, Sea Arches and Sea Caves

  • Wave-Cut marine Terraces


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/Dune or Seawall

Foreshore

Intertidal

Area

Ridge &

Runnel

Beachface

Usually 2 sand bars innermost 30-50m from shoreline


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Berms and Dunes

  • Over time, sand builds up at the far reach of the waves forming a high called a Berm.

  • Storm surges wash over the berm and deposit sediment on the landward dipping surface.

  • They can also erode the berm.

  • Wind commonly reworks this sand to form coastal dunes.

  • These dunes are similar to those in arid environments, but due to the proximity of the ocean, they are commonly more moist, and vegetation is common.

  • The vegetation stabilizes the dunes reducing their migration as well as disrupts stratification in them.


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RIDGE & RUNNEL SYSTEM

Paignton Beach, 2001. A sandy beach with ridge and runnel morphology on the low gradient lower foreshore occupies the broad bay between Roundham Head and Hollicombe. (http://www.scopac.org.uk)


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The tidal range on this beach is about 10 m, and it has very small waves because it is protected on one side by a spit and the other by a grove of mangroves that extends into the water. A view of the shore-ward end of the spit also shows the slope of the beach face where waves break at high tide. (Dawn [email protected])


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Note series of bars and swales that parallel the beach front, as seen during low tide


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Two sets of ripples cross to form an interference pattern. Ripple sets represent swash and backwash of waves on the beach front.


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Beach Profile

  • The profile of many beaches vary seasonally as a result of wave processes and sediment transport

  • Summer beaches exhibit gently sloping profiles with offshore sand bars

  • During winter larger more powerful waves redistribute offshore sand and erose the beach producing a steeper profile


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DUNES


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BERM


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STORM BERMS

Each storm berm has a steeper lower slope and flatter upper slope. There are at least five storm deposits preserved here. (http://www.maine.gov/doc/nrimc/mgs/explore/marine/facts/sep00-5.htm)


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(Barcelona Field Studies Centre)


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Longshore Drift of Sediment

  • Longshore Drift

    • Swash/Backwash

  • Spit

  • Baymouth Bar

  • Tombolo


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Barrier Spits

  • Beaches that are attached at one end to their source of sediment are called Simple spits if they consist of a narrow finger of sand with a single dune ridge that elongates in the downdrift direction.

  • Double spits can form if drift transports sand in two directions across and inlet, or if a baymouth barrier is cut by a tidal channel.

  • Wave refraction at the end of a spit will transport sand to form a recurvedspit.

  • Complex spits form when a plentiful supply of sediment is transported by both ocean and bay currents. Multiple lines of dunes can be formed by wind transport of sand across the spit.


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Complex Spit

Simple Spit

Double Spit


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Bay Barriers

  • Continuous barrier beaches that close off the entrance to a bay.

  • In the upper reaches of a bay the bayheadbarrier protects lagoon or marshland.

  • Barriers that connect headlands together along the outer reaches of an embayment are called baymouth barriers.


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