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Cliff Erosion Creates Most Sand on Beaches, Study Says

Seawalls, which decrease corrosion, may inhibit the creation of sand, researchers believe.

October 13, 2005|Sara Lin | Times Staff Writer

The gradual erosion of Southern California's majestic coastal bluffs contribute a far greater amount of beach sand than previously thought, according to a university study that may arm environmentalists with a weapon in fighting oceanfront development.

The report, unveiled Wednesday by UC San Diego researchers, studied the craggy shoreline from Dana Point to La Jolla and concluded that as much as 68% of the region's beach sand comes from the coastal bluffs and cliffs, which have been steadily developed over the years.

Many of the area's bluffs and promontories are protected by seawalls that have been constructed to prevent the ocean from chewing away at the hillside. But, the study indicates, seawalls may actually reduce an important seashore ingredient -- sand.

The loss of sand is an important issue along the California coastline, where beach cities spend millions of dollars replacing sand that has been swept away.

The study was immediately challenged by coastal engineers and seawall advocates who argued that, ultimately, it might be easier to replace beach sand than allow cliff erosion to go unchecked.

The findings stand in stark contrast to a long-held assumption that most beach sand comes from rivers and other tributaries that drain into the sea.

Environmentalists cheered the report, citing it as further proof that seawalls are a detriment to sandy beaches.

State law currently allows beachfront property owners to protect their homes from erosion with seawalls, large boulders and other means of holding back the sea.

"I hope it raises the bar to qualify for a seawall," said Chad Nelsen, environmental director for the Surfrider Foundation, an environmental group that has sued developers to stop seawalls.

The report gives ammunition to environmentalists who believe that property owners whose homes are threatened should retreat from coastal bluff areas rather than fight nature. Areas with long-standing erosion problems include north San Diego County, Santa Cruz and Pacifica, south of San Francisco.

But critics say this study doesn't change the seawall debate. Eroding bluffs make up a bigger percentage of beach sand simply because the region's urbanized rivers carry less sediment, said David Skelly, a coastal engineer who designs seawalls. The study was also done over a very dry six-year period ending in 2004, which meant there was less rainfall to carry sediment down rivers.

"I think everybody's accepted the fact that we built too close to the shoreline," Skelly said. "But if it isn't the first row of houses, then it's the next row of houses" that could be affected by erosion, he said. "Somewhere down the line, we're going to have to stop erosion, and it'll be easier to keep building beaches than to allow the land to erode."

Gail Steel, who lives atop a Solana Beach bluff where two seawalls hold back the ocean, said it was easy for environmentalists to say people should give up on the coast.

"If their homes were in jeopardy, I think they would think differently," she said. "I'm all for beaches, believe me -- any one of us who [lives near] the ocean are for beaches. I'm all for having sand and paying whatever it takes to get it here."

In the past, scientists assumed that beaches were largely nourished by sediment-laden rivers dumping into the Pacific. The natural erosion of coastal cliffs was thought to provide only 10% to 15% of the sand, said Scott Ashford, one of the study's authors. Ashford, an associate professor of geotechnical engineering at UC San Diego, and graduate student Adam Young used laser scans to measure erosion from 1998 to 2004 along a 50-mile stretch of coastline between Dana Point and La Jolla.

They concluded that beachfront cliffs provided 68% of the area's beach sand. Rivers and gullies provided 14 and 18%, respectively, they said.

Researchers say that although the study focused on parts of Orange and San Diego counties, the results indicate that coastal experts still don't understand beaches very well and that other bluff areas might deserve a closer look.

"It does suggest that sand held back by coastal armoring is relatively more important than we thought a year ago," said Mark Johnsson, staff geologist for the California Coastal Commission, which must approve requests to build seawalls.

Although the findings don't affect the law that allows oceanfront homeowners the right to protect their property from erosion, Johnsson said, the findings could help change what homeowners might be required to do to be allowed to build seawalls.



Sands of time

A new report says eroding oceanfront bluffs are a primary source of sand in San Diego County and that protective sea walls prevent erosion that is needed to replenish beaches. Earlier studies said cliff erosion accounted for only 10 to 15% of beach sand.


Source of sand deposits

Sea cliffs 68%

Gullies 18%

Rivers 14%


Sandy beaches

San Onofre bluffs produced the most sand in the study area -- 40,500 cubic meters -- from April 1998 to April 2004.

Sand eroded from sea cliffs, annual figures, in cubic meters

Area: Amount

San Onofre: 40,500

Camp Pendleton: 2,900

Carlsbad: 3,200

Leucadia: 4,700

Cardiff: 4,600

Solana Beach: 6,200

Del Mar: 3,700

Torrey Pines: 11,100


Friend or foe?

Sea walls vary in shape, size and composition -- including rows of telephone poles and stacks of boulder-filled metal cages. Common along the state's coast:

Concrete sea wall: Protects bluff during high tide

Beach: Exposed during low tide

Sources: UC San Diego; California Coastal Commission; Scripps Institution of Oceanography

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