Coastal Hazards

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Coastal Hazards

• Chapter 9
• Melinda Balk Jennifer Lowney

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Tsunami damage from 1946
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What if
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Hurricane Andrew August 1992
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Huge waves swamp this lighthouse at the entrance
to the harbor at Les Sables d'Olone (France) on
the Bay of Biscay on November 6, 2000.
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The French Storm
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A couple watches huge waves break along Point
Lobos as a fierce winter storm bears down.
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Surf pounds Peggotty Beach, Massachusetts
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Violent wave overtopping occurs when waves break
against sea walls in Great Britain.
Would you stand here?
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Scientists are compiling the first detailed map
of Britain's receding coastline. (2001)
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Rapid coastal erosion caused by block failures at
Key Point, Yukon.
(July, 1987)
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Coastal flooding in Bangladesh
.In Texas
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Flood in China, 2002
Indonesian Flood, 2002
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Most Serious Coastal Hazards
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Tropical cyclones
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Tropical Cyclones

• Typhoons in the Pacific
• Hurricanes in the Atlantic
• Wind speeds greater than 100 km/hr
• Wind blows in a large spiral around the eye (calm
  center)

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Facts

• Between 8 degrees north and 15 degrees south of
  the equator
• Warm surface water temperatures

• US Hurricanes
• Begin as thunderstorms in Africa
• Move west and north and gain energy from warm
  ocean waters

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Hurricane Info

• Storms that become hurricanes are monitored from
  satellites and planes

• Hazards
• High Winds
• Flooding (causes the most damage for property and
  people)
• Storm Surges are major rises in ocean levels (10
  meters)

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Flood Facts

• - Nine out of ten "Presidential Disaster
  Declarations"
• Flood waters move fast enough to roll boulders,
  tear out trees, and
• obliterate bridges
• Flooding has killed more than 10,000 people since
  1900. Property
• damage from flooding totals over 1 billion
  each year in the United
• States.
• -The average automobile can easily be swept away
  in just two feet of water.
• - Floods are most likely to occur in spring due
  to snow melt and rains.

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What would happen if the ocean rose one meter?

• http//archive.abcnews.go.com/sections/us/global_c
  oast1008/

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Never attempt this!
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Hurricane Andrew (1992)

• Costliest in US history
• Over 20 billion dollars in damage
• 250,000 homeless
• More than 100,000 buildings damaged, including
  the hurricane center

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Costliest
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Deadliest
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Most Intense
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Waves

• Size depends on
• Velocity of the Wind
• (Greater the velocity, the greater the wave)
• Time period (duration) that wind blows
• Distance (fetch) that the wind blows across the
  water. (The longer the fetch, the greater the
  wave)

• Wave form
• Wave height (difference in height between the low
  and the high)
• Wave length (distance between successive peaks)
• Wave period (time in seconds between successive
  waves to pass a point)

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Swells

• The wave groups generated by storms far at sea.
• If we can predict the velocity and height of the
  waves, we can estimate when waves with a
  particular erosive ability can strike the
  shoreline.
• When waves enter shallow water, wave period
  remains constant, wave length and velocity
  decrease and height increases.
• When water depth wave height, waves break

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Tsunamis

• What causes a tsunami?
• Usually the result of a sudden rise or fall of a
  section of the earth's crust under or near the
  ocean.
• Tsunami waves can also be created by volcanic
  activity and landslides occurring above or below
  the sea surface.

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Tsunami Waves

• When these waves approach shore, the speed of the
  wave decreases as they begin to "feel" the
  bottom.  It is at this time that the height of
  the wave drastically increases.  As the waves
  strike shore they may inundate low-lying coastal
  areas resulting in mass destruction and in many
  instances loss of life.

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Beach Composition Formation

• Loose material like sand or gravel
• Accumulates by wave action at the shoreline
• Made from shells, coral, volcanic rock (depends
  on the geography)

• Various areas of beach (top down)
• Berms
• Beach face
• Swash zone
• Surf zone
• Breaker zone

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Littoral Transport of Beach

• Waves can cause drifting of sand and beach
  materials

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Homes destroyed by coastal erosion
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How close should we build to the water?
(Rhode Island)
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Coastal Erosion

• Erosion and the Economy More than 100,000 state
  residents and tens of thousands of out-of-state
  tourists use Rhode Islands beaches each summer,
  bringing millions of dollars in revenue.

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Coastal Erosion

• Property located along Rhode Islands coast
  represents an enormous investment. It has been
  estimated that if a 100-year storm had occurred
  in 1989, losses of properties in the coastal
  floodplain would have exceeded 280 million.
  Losses would be even higher today, due to both
  sea-level rise and to additional construction
  since 1989.

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• Rhode Island's Changing Coast
• The majority of Rhode Islands south shore is
  eroding over the long term, with an average
  annual rate of retreat of 1 to 2 feet.
• Exposed sandy shores can recede by as much as 30
  feet in a single severe hurricane.
• If sea level continues to rise by 1 foot per
  centuryas is actually being measured at
  Newportall of Rhode Islands low-lying coastal
  areas (76 percent of the shoreline) could be
  adversely affected.

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Coastal Erosion

• Natural, continuous process
• Predictable
• We spend lots of money trying to control it

• 75 of the US lives near the coast
• We have interfered with material flow of sand
  from inland areas by building dams that trap sand
• This causes beaches to be deprived of sediment
  and erode

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Seacliff Erosion

• Result of natural processes
• Storms
• Cyclones
• Marine life that destroys rocks (mollusks)
• Weather (waves)
• Rain

• Human Activities
• Urbanization
• Recreation

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Controlling Erosion

• Cannot be completely controlled
• Natural process!

• Spend money
• Seawalls (reflect waves)
• Groin fields (trap sand)
• Breakwaters (break up large waves)
• Jetties (wave protection, prevents movement and
  settling of sediments)
• These control erosion of a coast but can
  contribute to erosion of their immediate area

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Jetties
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Seawall
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Breakwaters
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Groins
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Erosion Waterfall Formation

• http//earthsci.terc.edu/content/visualizations/es
  1305/es1305page01.cfm?chapter_novisualization

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Human Activity Coastal Erosion

• Humans like to live near water
• Causes coastal disturbances
• Increases erosion rate
• Eventually, this can potentially cause millions
  and billions in damage
• Some do not see erosion as a problem

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In The Classroom

• As mentioned earlier, people that have their
  property destroyed can have their homes rebuilt
  in the same location. Should we continue to
  allow this?
• Debate the benefits and consequences of using
  engineering structures to decrease the rate of
  erosion. Should we use more natural means?

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Classroom Extension

• Fieldtrip to a beach
• Examine beach composition
• Vegetation surround the beach
• Other structures present that influence erosion
  rates
• Human factors local developments, recreation,
  etc.

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Interdisciplinary

• Math Estimate the impact of waves on a local
  shore by using wave velocity, height, and
  distance between waves
• English Write a letter to a local government
  official explaining your opinion on the
  conditions of local beaches and what should be
  done to preserve them.
• Art Make observations and inferences of an area
  and draw a picture showing the same area after it
  has experienced a severe coastal hazard.

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Final Thought

• How do you make people consider erosion (a
  problem that is constantly occurring) as a
  serious coastal threat when there are more
  immediate and devastating coastal hazards?