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P. Overview. Coastal region constantly changes Primarily due to waves Erosion Deposition Many people live in coastal regions 80% of people in U.S. live within easy access of coast. P. Coastal Processes. Wave Refraction and the Longshore Current Convergence and Divergence of Wave Energy

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overview

P

Overview
  • Coastal region constantly changes
  • Primarily due to waves
    • Erosion
    • Deposition
  • Many people live in coastal regions
    • 80% of people in U.S. live within easy access of coast
coastal processes

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Coastal Processes
  • Wave Refraction and the Longshore Current
  • Convergence and Divergence of Wave Energy
  • Sediment Cells
  • Sediment Budget
  • Grain Size and Beach Slope
slide3

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Fig. 10-1

slide4

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Fig. 10.3b

composition of beaches

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Composition of beaches
  • Locally available material
  • May be coarse or fine
    • Boulders from local cliffs
    • Sand from rivers
    • Mud from rivers
  • Significant biologic material at tropical beaches
    • Example, Coral reef material
longshore current
Longshore current

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  • Wave refraction causes water and sand to move parallel to shore
  • Zigzag motion in surf zone
  • Longshore current
  • Longshore transport
longshore transport

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Longshore transport
  • Millions of tons of sediment moved yearly
  • Direction of transport changes due to wave approach
  • In general, sediment transported southward along Atlantic and Pacific coasts of U.S.
slide9

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Wave Refraction

slide12

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Convergence

Divergence

slide13

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Lower energy,

sand settles out

beach compartments
Beach compartments

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  • Rivers supply sediment
  • Beach
  • Offshore submarine canyons “drain” sediments from beach
slide16

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Fig. 10.12

slide20

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Winter

Summer

slide21

10_02a

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Summer

slide22

10_02b

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Winter

changing sea level
Changing sea level

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  • Local tectonic processes
    • Example, Pacific Coast of U.S. and active plate margin
    • Isostatic adjustments
      • Ice-loading
  • Global (eustatic) changes in sea level
    • Changes in sea floor spreading rates
    • Lake buildup or destruction
    • Ice volume changes
eustatic changes in sea level

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Eustatic changes in sea level
  • Ice build up (glaciation)
  • Ice melting (deglaciation)
  • Thermal contraction and expansion of
  • seawater
  • About 120 m (400 ft) change in sea level
slide29

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Fig. 10.15

global warming and changing sea level

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Global warming and changing sea level
  • About 0.6oC (1.1oF) warmer over last 130 years
  • Sea level rose 10-15 cm (4-10 in) over past 100 years
  • If global warming continues, higher sea level

Fig. 10.15

slide31

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.37 cm/yr

or

7.5” in 50 years

.25 cm/yr

or

5” in 50 years

alternatives to hard stabilization

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Alternatives to hard stabilization
  • Construction restrictions
    • Limit building near shorelines
    • National Flood Insurance Program encouraged construction
  • Beach replenishment
    • Sand added to beach/longshore current
alternatives to hard stabilization33
Alternatives to hard stabilization

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  • Relocation
    • Move structures rather than protect them in areas of erosion

Fig. 10B

portrait of a coast video
Portrait of a Coast Video
  • Repeated coastal damage
  • Once every 4 years on average
  • Seawall rebuilt once every 2 years on average
  • Rising sea level (1 foot/ 100 years)
  • Seasonal changes in beaches
  • Buildings and other man-made structures restrict beach mobility