1. Coastal Erosion

2. Wave Formation
Energy transferred from one water particle to another in orbits
Causes the wave form to move
Called orbital wave
Occur between two fluid media
Progressive waves – waveform moves forward

4. Wave Types Wavelength determines the size of the orbits
Water depth determines the shape of the orbits
Two broad categories
Deep-water Waves
Shallow-water Waves

5. Wave Formation Wind blows Tiny ripples form on water surface
Side of ripples increases surface area
More wind = more waves

6. Wave Formation Factors Affecting Wave Development
Wind Strength – wind speed
Wind Duration – how long the wind blows
Fetch – distance wind is blowing without a change in direction

7. Wave train moves towards shore
Circular motion of water molecules is interrupted
Wave slows as water becomes more shallow
Wave becomes too high for its wavelength
Water now moving faster than the wave
Wave breaks
Forms the surf

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9. Refraction = bending of waves
Reflection = bouncing back of waves
Diffraction = radiating outward of waves

10. Beach
Thurman Essentials of Oceanography 6/e
Beach = a zone of loose particles that covers a shore. Includes the backshore, foreshore & offshore

11. Shore: seaward lowest tide to waves influence on land
Thurman Essentials of Oceanography 6/e
Shore: seaward lowest tide to waves influence on land

12. Backshore: submerged during highest tide,strong storms
offshore
nearshore
backshore
foreshore
Thurman Essentials of Oceanography 6/e
Backshore: submerged during highest tide,strong storms
Foreshore: extends past low tide
Nearshore: from the low-tide shoreline to the low-tide breaker line
Offshore: low tide to limit of wave reworking

13. Beaches classified by:
Shape & structure
Size of materials

14. Beaches classified by:
Shells
Cabo, Baja Mexico
Beaches classified by:
Shape & structure
Size of materials
Composition
Basalt
Waianapanapa, Maui
Olivine
Guam
Coral
Huahini, Tahiti
Minerals (quartz, feldspar, hornblend)
Ventura, California

15. Beaches classified by:
White Sand Beach Sand Key, Florida
© Sonjia Leyva
Beaches classified by:
Shape & structure
Size of materials
Composition
Color
Black Sand Beach, Hawai’i
Green Sand Beach
Papakolea, Hawai’i
Harbour Island: “Harbour Island is most renowned for its pale pink sand beaches some 3 plus miles long and 50 to 100 feet wide - considered one of the very best beaches in the Bahamas. The sand is a composition of bits of coral, broken shells, minute rocks and calcium carbonate from tiny marine invertebrates. The pink color comes from tiny microscopic shelled animals known as Foraminifera. This animal has a bright pink or red shell full of holes through which it extends a footing, called "pseudopodia", which it uses to attach itself and feed. These animals live on the underside of the reefs, on the sea floors, beneath rocks and in caves. They are washed up on shore as a result of waves or fish who knock them loose as they feed on them. Foraminifera are among the most abundant single cell organisms in the ocean and play a significant role in the environment. Snorkeling and swimming are made safe and easy by outlying reefs. These reefs provide large areas of relatively calm and shallow waters. ” From:
Pink Sand Beach
Harbour Island, Bermuda

16. Sediment Sources Rivers and Streams
Eroding beach cliffs – 5 – 10% of beach sand
Sand from the seafloor immediately offshore

17. Longshore Drift: Longshore Current:
sediment on beach moves in zig-zag fashion via swash/backwash
Longshore Current:
current moves down beach, caused by waves hitting beach at angle
Flows parallel to the shore
Transports sediments down the coast
Moves substantially more sediment than beach drift
Earth: An Introduction to Physical Geology, 7e - Tarbuck & Lutgens
A longshore current, caused by refracting waves, moves water in a zigzag fashion along the shoreline. This causes a net movement of sand grains, also in a zigzag fashion, from upstream to downstream ends. After Tarbuck, E. J., and Lutgens, F. K., The Earth: An Introduction to Physical Geology, 4th Ed. (Fig. 14.8), Macmillan Publishing Company, 1993

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19. Littoral Cells cycle of sediment transport along shore
sediment to beach
along beach
back to sea
cycle part of littoral cell
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

20. Longshore Drift and Submarine Canyons

21. Beach Processes Processes Equilibrium Erosion Deposition
Wave impact and pressure
Deposition
Rivers, cliff erosion, longshore drift
Equilibrium
material brought in = material removed

22. Summer & Winter Beaches

23. A B
This beach north of Point Reyes, California, was eroded by waves during the
1997 El Niño event; in (a) much of the sand has been removed (October 1997), but in (b) it has
been naturally rebuilt by April 1998.

24. Threats to the Sand Supply
Flood control dams
Sand & Gravel Quarries
Southern California has 77
Paved river channels
Seawalls and riprap

25. Coastal Erosion Natural factors are very important in most areas
Width of the beach
Amount of wave energy
Nature of the rock present
Humans have become very important at changing erosion rates

26. Coastal Erosion
Dams

27. Coastal Erosion
Sea Walls
Accelerate the erosion of adjacent property

28. Coastal Erosion
Groins
Jetties
Breakwaters

29. Coastal Stabilization Structures
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30. Longshore drift and groin erosion – 9/23/2002
N     W     Image 4066     Mon Sep 23 14:08:   Sunset Blvd.
Longshore drift and groin erosion – 9/23/2002
Sunset Boulevard at PCH; Gladstone's Restaurant in foreground (blue bldg)

31. N     W     Image 8284     Wed Oct 30 11:34:   Left - Marina Del Rey Harbor Entrance, Middle - Ballona Creek, Right - Toes Beach
Jetties, Marina – 10/30/2002
Left - Marina Del Rey Harbor Entrance, Middle - Ballona Creek, Right - Toes Beach

32. Coastal Erosion Breakwaters Santa Monica breakwater
Attached to the coast
Requires continuous dredging
350,000 m3/yr

33. Coastal Erosion Alternatives to hard stabilization
Beach nourishment by adding sand to the beach system
Relocating buildings away from beach
Returning to “natural” channels

34. Stabilizing The Shore Characteristics Of U.S. Coasts
The Pacific Coast - An actively rising margin where indications of recent tectonic activity can be observed.
The Atlantic Coast - A passive margin on the trailing position of the North American plate.
The Gulf Coast - A passive margin with smaller waves and tidal range

35. Stabilizing The Shore Active Coastlines (The Pacific Coast)
Characterized by relatively narrow beaches backed by steep cliffs and mountain ranges
Problems:
Sediment for beaches is interrupted by dams and reservoirs
Development along cliffs and beaches

36. Features of an Active Coastline

37. graphic by USGS

38. graphics by USGS

39. Coastal Erosion from El Niño Winter Storms
Cabrillo State Beach, California
October, 1997
April, 1998

40. Coastal Erosion from El Niño Winter Storms
Fort Stevens State Park, Oregon
October, 1997
April, 1998

41. Coastal Erosion from El Niño Winter Storms
Agate Beach, Oregon
October, 1997
April, 1998

42. March 1998
Beach erosion and cliff collapse endangered homes in Pacifica (south of San Francisco) in March Collapsed parts of houses litter the base of the cliff. (b) Taken from the same viewpoint as (a) in December 2003, this photo shows that the seven homes nearest the camera are gone. Only two of the original ten houses remain, and one of these sold in 2004 for $450,000!

43. December 2003
Beach erosion and cliff collapse endangered homes in Pacifica (south of San Francisco) in March Collapsed parts of houses litter the base of the cliff. (b) Taken from the same viewpoint as (a) in December 2003, this photo shows that the seven homes nearest the camera are gone. Only two of the original ten houses remain, and one of these sold in 2004 for $450,000!

44. Stabilizing The Shore Passive Coastlines (Atlantic and Gulf Coasts)
Development:
occurs mainly on barrier islands
has taken place more rapidly than our understanding of barrier island dynamics
North Myrtle Beach, South Carolina

45. Features of a Passive Coastline

46. Barrier Islands Built of sand dunes Vegetation: Grows in summer
Erodes in winter
Vegetation:
Stabilizes dunes
Prevents erosion
Sand dunes Sand Key, Florida
© Sonjia Leyva

48. Passive Coastline Problems
Erosion caused by
Human development
Storms

49. Florida Beach Erosion
©  Beaches & Shores Resource Center Florida State University (

50. Belleair Beach, Sand Key, Florida
©  Beaches & Shores Resource Center Florida State University (

51. South Amelia Island, Florida
©  Beaches & Shores Resource Center Florida State University (

52. Barrier Island Erosion

53. A
Shoreward migration of beach at North Topsail Beach, North Carolina, is well shown by a series of three views of the same area. (a) Use the colorful condominiums in the upper left here as a reference and note those in the center of the photo taken after Hurricane Bertha on July 16, (b) This is the same location following Hurricane Fran on September 7, Finally, (c) shows the same location after Hurricane Bonnie on August 28, Note that the series of photos spans only about two years. Source: Natural Hazards & Disasters 1/e, Hyndman & Hyndman

54. B
Shoreward migration of beach at North Topsail Beach, North Carolina, is well shown by a series of three views of the same area. (a) Use the colorful condominiums in the upper left here as a reference and note those in the center of the photo taken after Hurricane Bertha on July 16, (b) This is the same location following Hurricane Fran on September 7, Finally, (c) shows the same location after Hurricane Bonnie on August 28, Note that the series of photos spans only about two years. Source: Natural Hazards & Disasters 1/e, Hyndman & Hyndman

55. C
Shoreward migration of beach at North Topsail Beach, North Carolina, is well shown by a series of three views of the same area. (a) Use the colorful condominiums in the upper left here as a reference and note those in the center of the photo taken after Hurricane Bertha on July 16, (b) This is the same location following Hurricane Fran on September 7, Finally, (c) shows the same location after Hurricane Bonnie on August 28, Note that the series of photos spans only about two years. Source: Natural Hazards & Disasters 1/e, Hyndman & Hyndman

56.
Oblique aerial photographs taken on Topsail Island, North Carolina before and after Hurricane Fran in The yellow arrows point out the same buildings in both photos. Note the destroyed buildings, the overwash, and the damaged road in the post-storm photo on the right.

57. ~ End ~