Bluff erosion primary source, studies show

By Terry Rodgers

October 13, 2005

CHARLIE NEUMAN / Union-Tribune
Homes on South Sierra Avenue in Solana Beach sit atop eroding bluffs above Fletcher Cove Beach Park. Two new studies by scientists at UCSD found that erosion of Southern California’s sea cliffs is the primary source of the region’s beach sand.

UCSD scientists have completed two studies showing that cliff erosion produces far more sand for local beaches than previously estimated.

A six-year study by engineering professor Scott Ashford and graduate student Adam Young found that bluff erosion accounted for 68 percent of the fresh sand that nature provides to the county’s eroding beaches.

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A second study by geology professor Neal Driscoll and graduate student Jennifer Haas used a “mineralogical fingerprinting” technique to compare grains of sand on local beaches with the types of sand found in bluffs and rivers, and from material dredged offshore.

Driscoll and Haas concluded that 50 percent of the sand came from erosion of the bluffs, also known as sea cliffs.

The combined studies were released yesterday. They rebut the conventional wisdom often heard at public hearings that cliff erosion accounts for only 10 percent to 15 percent of the sand that nature supplies to local beaches.

The findings immediately rekindled the debate over sea walls, the “armoring” of the coastline that has pitted private-property owners against opponents of such walls.

“This is huge for us,” said Marco Gonzalez of the San Diego chapter of the Surfrider Foundation, which views erosion as a natural process necessary to maintain sandy beaches. “It spotlights the true impact of sea walls, which are a bad long-term solution to the effects of sea-level rise and the natural processes of erosion.”

But Walter Crampton, a coastal engineer who represents oceanfront property owners, said the studies merely reinforce previous scientific estimates of how natural processes contribute sand to the beaches.

CHARLIE NEUMAN / Union-Tribune
UCSD scientists Neal Driscoll (left) and Scott Ashford shared their findings on where local beaches get their sand with former Solana Beach Mayor Margaret Schlesinger.
“All it does is reaffirm everything we’ve said in the last five years,” Crampton said. “Everything is the same.”

Leslie Ewing, a staff engineer for the state Coastal Commission, applauded the UCSD scientists for using “cutting-edge science and technology.”

However, Ewing said the new findings are unlikely to trigger major changes in coastal policy, including a 10-year-old fee the commission charges residents who want to build sea walls.

Ashford and Young were able to more precisely calculate the amount of bluff erosion by comparing three-dimensional images made from a laser scanning device called LYDAR, an acronym for “light detection and ranging.”

The same type of scanners was used to measure the crater after debris was cleared from the World Trade Center disaster in September 2001. It is also employed by forensics teams to calculate the spray from bomb blasts.

Ashford agreed with other scientists that the amount of sand being supplied from eroding bluffs ““ the study estimated it at 76,000 cubic yards annually along about 50 miles of shoreline ““ is probably far less than what is needed to stabilize beaches that are already too narrow.

The U.S. Army Corps of Engineers recently issued a report saying that to stop further erosion of the cliffs, 825,000 cubic yards of sand needs to be placed on the beaches in Encinitas and an additional 450,000 cubic yards in Solana Beach.

Terry Rodgers: (619) 542-4566;