Chapter 11: The Coast: Beaches and Shoreline Processes

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Chapter 11 The Coast Beaches and Shoreline
Processes
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Coastal region

• Shore between low tide and highest elevation
  affected by storm waves
• Coast from shore to farthest inland ocean features

Fig. 11-1
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Beach

• Actively changing
• Shore backshore, foreshore, nearshore, offshore
• Berm, beach face, longshore bar, longshore trough

Fig. 11-1
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Beach composition and shape

• Locally available material
• Coarser sediment
• Beach steeper
• Finer sediment
• Beach more gentle

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Sand movement

• Swash and backwash
• Sediments moved up and down beach face
• Smaller, low energy waves sand moved up beach
  face
• Summertime beach
• Larger, high energy waves sand moved off shore
• Wintertime beach

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Sand movement

• Longshore current
• Longshore drift or transport
• Parallel to shore
• Increasing strength
• More wave energy
• Higher wave frequency
• Steeper beach
• Greater angle

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• Longshore current main way sediments moved along
  coasts
• Southward along both U.S. coasts most of the time

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Erosional-type shore

• Headlands eroded
• Sea arches
• Sea stacks
• Wave-cut cliffs
• Sea caves
• Tectonically active coasts
• Example Pacific coast U.S.

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Depositional-type shores

• Sediments re-distributed by ocean processes
• Typical in tectonically passive areas

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Depositional features

• Spit
• Tombolo
• Bay barrier or baymouth bar

Fig. 11-7
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Barrier islands

• Ocean beach
• Dune
• Barrier flat
• High salt marsh
• Low salt marsh
• Lagoon
• Rising sea level pushes barrier island landward

Fig. 11-10
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Deltas
FIG. 11.11b

• Rivers deposit sediment at coast
• If more fluvial influence than ocean influence
• Birds foot delta
• If more ocean influence than river influence
• Arcuate delta

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Shepard classification of coasts

• Primary
• Geologically youthful
• Controlled by non-marine processes
• Examples
• Drowned river or glacial valleys
• Volcanic coasts
• Coasts shaped by recent tectonic movements

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• Secondary coasts
• Geologically mature
• Controlled by marine processes
• Tectonically passive
• Examples
• Straightened coasts
• Coral reefs
• Marsh grass

Fig. 11-13f
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Emergent coasts

• Uplift or sea level drops
• Once marine is now land
• Marine terraces
• Stranded beach deposits

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Submergent coasts

• Subsidence or sea level rises
• Once land (or shallower) is now underwater (or
  deeper)
• Drowned beach deposits
• Drowned river/glacial valleys
• Submerged dunes

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Tectonic and isostatic changes

• Tectonic uplift and subsidence
• Larger scale major parts of continents
• Smaller scale local deformation
• Isostatic adjustments to loading
• Sediments or ice
• Regional and local effects
• Affect sea level

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Eustatic changes in sea level

• Global
• Changes in spreading rates of ocean floor
• Changes in ice volumes
• Changes in ocean temperature
• Global warming
• Sea level rises
• Ice melts, ocean warmer

Fig. 11-15
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Atlantic coast of U.S.

• Mainly submergent
• Barrier islands
• Glaciers shaped some shorelines
• Eroding coasts
• Subsidence in most areas

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Gulf coast of U.S.

• Mainly submergent
• Barrier islands
• Mississippi delta
• High rates of erosion
• Tectonic subsidence

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Pacific coast of U.S.

• Mainly emergent
• Less erosion
• Mainly rocky shoreline
• Dams on rivers beach starvation
• Tectonically active

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U.S. coastal erosion, deposition
Fig. 11-17
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Hard stabilization

• Groin and groin field
• Perpendicular to shore
• Traps sand between groins
• Interrupts longshore current
• Jetty similar
• Built to protect harbor entrance
• Sand on upcurrent side

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• Breakwater
• Parallel to shore
• Offshore
• Deposition behind breakwater

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• Seawall
• Built on beach
• Parallel to beach
• Erosion enhanced seaward of wall
• Seawall destroyed
• Beach narrowed

Fig. 11-25
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Alternatives to hard stabilization

• Limit construction near shore
• Relocate businesses/homes destroyed by wave
  erosion

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End of Chapter 11 The Coast Beaches and
Shoreline Processes