Transcript California`s Changing Coastline - Cal State LA

California’s Changing Coastline
California Coast—Overview
Pedro Ramirez, Steve LaDochy, William Patzert
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~ 950 miles (86%) of state’s 1,120
miles of coastline are eroding.
Eroding sea cliffs comprise 72% of
coast
Less than 10 miles have no dry
sand beach at high tide.
About 150 miles gaining sand or
stable.
Erosion rates generally range from
0-42cm/year
– But variable. Point Año Nuevo
averages 9 ft/yr retreat rate.
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1.4 meter sea level rise will put
480,000 people at risk of a 100
year flood
– will accelerate erosion, resulting in
a loss of 41 square miles (over
26,000 acres) of California’s coast
by 2100
http://www.beachapedia.org/State_of_the_Beach/State_Reports/CA/Beach_Eros
ion#cite_ref-2
California Climate Change Center
NASA
Southern California Coast
Factors Influencing Coastal Erosion
• Sea Level Change
– Governed mostly by
• Changing Climate
• Tectonics
• Natural Variability in
Oceans
• Storminess
• Humans
– Petroleum and
Groundwater
Extraction
Tide Gauge Observations
150
3.2 mm/year
100
2.0 mm/year
MSL (mm)
50
~ 8 inches
(20 cm)
0.8 mm/year
0
= 16,000 cubic miles!!!
(67,000
cubic km)
Average Rate ~
1.8 mm/year
-50
-100
1880
1900
1920
1940
Year
1960
1980
2000
[Church and White, 2006]
Sea Level Rise Resource
Projected San Francisco Inundation
FIGURE 1.2 Expected inundation of low-lying areas, including the San Francisco
International Airport (center), in the San Francisco Bay Area with a 40 cm rise in
sea level (light blue shading). SOURCE: Bay Conservation and Development
Commission, <http://www.bcdc.ca.gov/planning/climate_change/index_map.shtml>.
Local/Regional Sea Level Changes
• Ocean Circulation
– El Nino-Southern
Oscillation
• El Nino = warm waters
= increased sea level
• Related low pressure
and w-sw winds raise
levels
• Levels rise up to 50 cm
for some months
– Storms
• increase sea level up to
several hours
1995 El Nino storm, Malibu, Reed Saxon /
AP
Sediment Compaction
• Land subsidence with
water/petroleum
withdrawal, sea level
rise
USGS
Factors Influencing Coastal Erosion
• Geology
– Lithologies
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Hard or Soft
Weathering
Fracturing
Faults
– Presence or Absence of
beach
– Landslides
• Storminess
• Development
• Coastal Modification
Landslides in Southern California
Coastal Armoring to Save Coast
• Cliffs armored with revetments
or seawalls to slow erosion
• 10% of California coastline is
armored
• 33%of coastline in Ventura,
Los Angeles, Orange, and San
Diego Counties armored
• Yet coastal damage has
increased due to
– Development and several El
Nino events
• Seawall/Revetments
temporary
– Rising sea level and wave
heights will overtopp
Capitola
NOAA
Beaches
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More storms narrow beaches
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Reduced sand supplies result in
erosion
500 dams reduced sediment
supply to California coast by 25%
– 28 dams & 150 debris basins
in southern California in 8
watersheds have impounded
more than 4 million m3/yr of
sand
– About 152 million m3 of sand
would have been deliverd to
beaches in California since
1885
.2 +-0.4 m short term erosion rate
Longer term rate is 2 +-0.1 m/yr
net accretion
– Accretion from large volumes
of seds added to rivers
– Coastal engineering and
beach nourishment
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Malibu’s “sandbagged” Broad Beach. The oncewide sand strip, swept away by waves and rising
seas.
Resources
• Earth System Science Education Alliance (ESSEA) educational
module: Sea Level Change/Coastal Inundation. Grades 7-12.
Includes resources and lesson plans (investigations) on coastal
erosion, environmental impacts of sea level rise.
– http://essea.strategies.org/module.php?module_id=142
• COSEE -Thermal expansion & sea level rise activity, grades 5-9
– http://cosee.umaine.edu/cfuser/resources/tr_sea_level.pdf
• Changing Planet: Sea Level Rising hands-on activity, map & data
interpretation for grades 6-10
– http://www.windows2universe.org/teacher_resources/sea_level_
rise.html
• NASA climate time machine. Interactive tool showing effects on
coastlines with varying sea level rises for Gulf, E. coast, other global
sites. Click on sea level rise.
– http://climate.nasa.gov/ClimateTimeMachine/climateTimeMachin
e.cfm
(Habel and Armstrong 1977)
http://www.ppic.org/content/pubs/report/R_1108GMR.pdf
Cliff and Bluff Erosion
• Mostly episodic
– Blocks fall due to
rainfall, large
waves during high
sea level or tides,
earthquakes
– Then little erosion
– Mountainous areas
erosion through
landslides/rock falls
FIGURE 6.2 Large-scale landsliding along the Humboldt County, California,
coast at Centerville. SOURCE: Copyright 2002-2012 Kenneth & Gabrielle
Adelman, California Coastal Records Project,<www.Californiacoastline.org>.