Geology, Weather Affect Erosion Rates on Regions of California Coast
Royal Palm Beach, Fla. — The
shoreline and seaside cliffs in California are eroding at increasing rates,
especially in the short term, and a variety of causes—from El Nĩno to
geology—may be involved.
About 40% of California
beaches are eroding in the long term—defined as 120 years—and that number
increases to 66% in the short term—or last 25 years—according to a new study by
the U.S. Geological Survey (USGS) that’s highlighted in the Journal of
Coastal Research.
In
their article on the USGS analysis, “Rates
and Trends of Coastal Change in California and the Regional Behavior of the
Beach and Cliff System,” Cheryl J. Hapke, Dave
Reid, and Bruce Richmond examine the spatial relationship between shoreline
change and cliff retreat on a regional scale.
The
USGS research found that higher rates of cliff retreat correspond with lower
rates of shoreline erosion on high-relief coasts, while low- to moderate-relief
coastal areas typically are areas with high shoreline change and high cliff
retreat. This reflects a strong relationship between the features and geology of
the coast and how they affect beaches or cliffs.
For
the research, the California coast was divided into three areas: Northern,
Central, and Southern. Overall, Northern California coasts are a bit more rugged
and steep with high-energy waves, while the more urbanized Southern California
coast is home to lower-energy waves.
“In
general, the cliff-retreat rates are highest in Central and Northern California,
with the exception of the San Diego region in Southern California. Rates of
shoreline change are highest in Central California,” the authors write. “There
is a distinct trend of decreasing coastal cliff-retreat rates from north to
south, with relatively uniform cliff retreat in the southern part of the
state.”
Central California is the
most diverse region with developed terraces and coastal bluffs, plus pocket and
linear beaches, according to the authors: “Numerous seawalls and revetments
exist along this stretch of coast, especially in more heavily developed areas.
These structures, built in response to cliff erosion … act to reduce the rate of
cliff retreat, although they may have negative impacts.”
And
while it has the longest stretches of linear beaches, “the Southern California
coastline … is the most heavily affected by human development and engineering
structures in the state,” according to the article. “Many of the portions of the
coast that are backed by cliffs have coastal protection structures, which have
likely affected the rates of cliff retreat and thus contribute to Southern
California having the lowest average retreat rates in the state.”
Cliff-retreat rates appear to
be most influenced by geology, with erosion rates higher in focused headland
areas where wave energy typically is high. Other factors that may affect erosion
include seasonal weather patterns such as El Nĩno, which brings above-average
rainfall and larger waves; coastline areas with large, deep-seated landslides;
and ocean facilities such as harbors and ports that affect sediment
flow.
The
researchers found the highest long-term accretion rates near coastal engineering
structures, beach nourishment sites, and areas with high sediment supply from
large rivers. The increase in long- and short-term erosion “implies that erosion
hazards have increased in California, especially from the 1950s-70s to the late
1990s.”
With
recent environmental changes such as global warming and rising sea levels, the
USGS study serves as an important resource for future management of coastlines,
according to the article.
“As
interest and concern about impacts of global sea-level rise on the world’s
coastline continue to increase, a fundamental understanding of past behavior of
coastal systems … is critical to future planning and management,” write Hapke,
Reid, and Richmond.
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The
full article is available at www.allenpress.com/pdf/COAS_25.3_603_615.pdf
July 1, 2009
Geology, Weather Affect Erosion Rates on Regions of California Coast
Royal Palm Beach, Fla. — The
shoreline and seaside cliffs in California are eroding at increasing rates,
especially in the short term, and a variety of causes—from El Nĩno to
geology—may be involved.
About 40% of California
beaches are eroding in the long term—defined as 120 years—and that number
increases to 66% in the short term—or last 25 years—according to a new study by
the U.S. Geological Survey (USGS) that’s highlighted in the Journal of
Coastal Research.
In
their article on the USGS analysis, “Rates
and Trends of Coastal Change in California and the Regional Behavior of the
Beach and Cliff System,” Cheryl J. Hapke, Dave
Reid, and Bruce Richmond examine the spatial relationship between shoreline
change and cliff retreat on a regional scale.
The
USGS research found that higher rates of cliff retreat correspond with lower
rates of shoreline erosion on high-relief coasts, while low- to moderate-relief
coastal areas typically are areas with high shoreline change and high cliff
retreat. This reflects a strong relationship between the features and geology of
the coast and how they affect beaches or cliffs.
For
the research, the California coast was divided into three areas: Northern,
Central, and Southern. Overall, Northern California coasts are a bit more rugged
and steep with high-energy waves, while the more urbanized Southern California
coast is home to lower-energy waves.
“In
general, the cliff-retreat rates are highest in Central and Northern California,
with the exception of the San Diego region in Southern California. Rates of
shoreline change are highest in Central California,” the authors write. “There
is a distinct trend of decreasing coastal cliff-retreat rates from north to
south, with relatively uniform cliff retreat in the southern part of the
state.”
Central California is the
most diverse region with developed terraces and coastal bluffs, plus pocket and
linear beaches, according to the authors: “Numerous seawalls and revetments
exist along this stretch of coast, especially in more heavily developed areas.
These structures, built in response to cliff erosion … act to reduce the rate of
cliff retreat, although they may have negative impacts.”
And
while it has the longest stretches of linear beaches, “the Southern California
coastline … is the most heavily affected by human development and engineering
structures in the state,” according to the article. “Many of the portions of the
coast that are backed by cliffs have coastal protection structures, which have
likely affected the rates of cliff retreat and thus contribute to Southern
California having the lowest average retreat rates in the state.”
Cliff-retreat rates appear to
be most influenced by geology, with erosion rates higher in focused headland
areas where wave energy typically is high. Other factors that may affect erosion
include seasonal weather patterns such as El Nĩno, which brings above-average
rainfall and larger waves; coastline areas with large, deep-seated landslides;
and ocean facilities such as harbors and ports that affect sediment
flow.
The
researchers found the highest long-term accretion rates near coastal engineering
structures, beach nourishment sites, and areas with high sediment supply from
large rivers. The increase in long- and short-term erosion “implies that erosion
hazards have increased in California, especially from the 1950s-70s to the late
1990s.”
With
recent environmental changes such as global warming and rising sea levels, the
USGS study serves as an important resource for future management of coastlines,
according to the article.
“As
interest and concern about impacts of global sea-level rise on the world’s
coastline continue to increase, a fundamental understanding of past behavior of
coastal systems … is critical to future planning and management,” write Hapke,
Reid, and Richmond.
The
full article is available at www.allenpress.com/pdf/COAS_25.3_603_615.pdf