Coastal processes

1. 1
Coastal Processes and Hazards
About 75% of the US population lives in coastal areas. Impacts from
coastal hazards can be substantial. The source of the hazards
includes several “non-geologic” processes such as:
Golden Gate Bridge data set
Tropical cyclones - high winds (100+ km/hr)
- flooding from intense precipitation
- storm surges
Tidal floods – storm surges coinciding with tidal peaks
Tsunami’s – seismic sea waves

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Margins
Structure of the ocean margins
Passive margin
There are two general ocean margins – passive and active margins – both
are related to plate tectonics
The geologic hazards vary according to the continental margins

3. 3
Coastal Geology
Structure of the ocean margins
Active Margins
Components of the active margin

4. 4
Coastal Geology
All coasts are divided into natural compartments called littoral cells. Each
cell contains a complete cycle of sedimentation including sources,
transport paths, and sinks.
Active margin
The Littoral Cell
www.surfrider.org/structures/images/canyons.jpg

5. 5
Coastal Geology
The presence of sand on any particular beach depends on the transport of
sand within the cell. When structures such as dams or harbors
interfere with sand transport, downcoast beaches will erode.
Therefore, the littoral cell and its budget of sediment are essential
planning tools for regional and coastal management.
Active margin
The Littoral Cell

6. 6
Coastal Geology
Structure of the ocean margins
Summer versus winter beaches
Active margin
Beaches

7. 7
Coastal Processes and Hazards
Coastal hazards that arise along the different margins include:
Golden Gate Bridge data set
• Erosion – due to wave action and fluctuating sea levels
• Deposition – from littoral transport

8. 8
Perceptions and adjustment to hazards
Golden Gate Bridge data set
More and more the question is becoming:
do we continue to subsidize development in risky coastal areas?
From 1978 to 1982, $43 million dollars in federal flood insurance was paid
in damage claims to barrier-island residents, which far exceeded the
premiums they paid.
It is becoming increasingly obvious that the most sensible thing to do with
many such structures is to abandon the costly and ultimately doomed
efforts to protect or maintain them, and simply leave these areas in
their dynamic, natural, rapidly changing state, most often as
underdeveloped recreation areas.

9. 9
Perceptions and adjustments to hazards
From a philosophical perspective:
Golden Gate Bridge data set
1. Coastal erosion is a natural process rather than a natural
hazard; erosion problems occur when people build structures in
the coastal zone.
2. Any shoreline construction causes change.
3. Engineering structures designed to protect a beach may
eventually destroy it.

10. 10
Coastal Processes and Hazards
From a philosophical perspective:
Golden Gate Bridge data set
4. Stabilization of the coastal zone through engineering structures
protects the property of relatively few people at a larger general
expense to the public.
5. Once constructed, shoreline engineering structures produce a
trend in coastal development that is difficult if not impossible to
reverse.

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End

12. 12
Erosion
Golden Gate Bridge data set
• Sea level has risen 15 – 20 cm during the last century.
www.wildwildweather.com/forecastblog/wp-conte

13. 13
Emerging
shorelines
Changing sea levels over time produce emerging shorelines. Tectonic
uplift also causes land to slowly emerging from the sea.

14. 14
Submerging
shorelines
Changing sea levels over time
produce submergent
shorelines.

15. 15
Erosion
Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.

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Erosion
Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.
Wave erosion – force
is concentrated on
headlands,
resulting in
excessive erosion.
Called wave
refraction and
results from wave
“drag” on ocean
floor.

17. 17
Erosion
Effects of waves
Waves are a powerful force. Can cause severe erosion problems along
coastal areas.

18. 18
Erosional Landforms – winter, 1989

19. 19
Erosional Landforms – February, 1990

20. 20
Erosional Landforms – February, 1991

21. 21
Erosional Landforms – February, 1993

22. 22
Erosional Landforms – March, 1999

23. 23
Erosion
El Nino conditions produce more extreme wave conditions
Warmer than normal
waters produce warm
air masses that hold
lots of rain and
produce severe storms
and waves.

24. 24
Erosion
El Nino conditions produce more extreme wave conditions
Normal wind and water
motion

25. 25
Erosion
El Nino conditions produce more extreme wave conditions
El Nino wind and water
motion

26. 26
Deposition
Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.
Wave deposition –
waves spread out
here, have less
energy.
Longshore drift
moves sand as a
sheet along the
coastline.

27. 27
Deposition
Sand transportation – is a natural process but has also been affected by
humans.
Groins – encourage deposition in
desired locale.

28. 28
Deposition
Sand transportation – is a natural process but has also been affected by
humans.
Jetties – designed
to keep river
channels from
filling in and
relocating due
to sand
deposition.

29. 29
Deposition
Sand transportation – is a natural process but has also been affected by
humans.
breakwaters –
designed to
protect and
encourage
harbor
development.

30. 30
Deposition
Sand transportation – is a natural process but has also been affected by
humans.
Man-made
structures in
action.

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Links

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