A new study unveiled last week that concluded that most of the sand on North County beaches comes from eroding sea cliffs is being assessed by environmentalists as a new weapon, and by bluff-top homeowners as nonsense.

"We think it's a dramatic piece of support for our position that sea walls cause damage to the beach," said Marco Gonzalez, a well-known attorney for the Surfrider Foundation, a nonprofit beach-access advocacy group —— an environmentalist.

"We think it's pure hogwash," countered Paul Santina, president of the Beach and Bluff Conservancy a nonprofit group of bluff-top homeowners in Solana Beach.

The study, titled "Quantifying Sea Cliff Sediment Contributions," was released Wednesday by the Jacobs School of Engineering at UC San Diego.

Written by graduate student Adam Young and engineering professor Scott Ashford, the survey estimated that 68 percent of the sand currently on local beaches came from the erosion of sea cliffs.

The study's conclusion, which measured coastal cliff erosion rates from 1998 through 2004, is much different from previous studies.

For example, a study performed by coastal researchers at UC Santa Barbara and published in 2003 found that only about 10 percent to 12 percent of sand on North County beaches came from cliff erosion.

Young and Ashford said that unlike previous coastal erosion studies, they used new technology to measure the rate of sea cliff erosion. Rather than comparing aerial photographs of bluffs over time, they said, a special airborne laser measuring device was used to take two precise pictures of the bluffs from Dana Point in Orange County south to La Jolla.

They said a computer program was then used to compare the differences between the 2004 and 1998 data.

The comparison found that bluffs in different coastal cities eroded at different rates, they said. For example, the bluffs in San Onofre and Solana Beach were found to retreat an average of 5 inches over the six-year period, while bluffs in Leucadia and on Camp Pendleton registered a 2.2-inch average loss annually.

Ashford said the difference was in the extreme precision that laser measurement allows.

"We can get the volume much more accurately than anyone was ever able to before," Ashford said.

Ashford and Young cautioned that their study was conducted during a relatively dry period on the California coast. There were few large storms that could have carried large amounts of sand onto the beach from rivers and streams. They also noted that the six-year study period is very short, especially compared to other studies that use aerial photographs and other measurements dating to the 1930s and 1940s.

"It's important to keep in mind that this was a short-term study," Young said. "More work need is to be done to figure out what the long-term effect is."

The erosion debate

Though the scientists said their conclusions are only preliminary, both sides of the coastal erosion debate are already considering its implications on coastal management policy.

Gonzalez, an attorney who currently has a lawsuit against the city of Solana Beach for its sea wall permitting policies, said Friday that the study will be useful in court at the local level when arguing that anyone who builds or maintains a sea wall must compensate the public for sand that would otherwise end up on the beach.

"We won't hesitate for a minute," Gonzalez said.

Santina, on the other hand, said he and other bluff-top homeowners believe that the Young and Ashford study can be shot full of holes by their own coastal experts.

"We believe our experts can rebut their study quite readily," Santina said.

He added that the Beach and Bluff Conservancy sees no reason, based on the new study, to change its position, expressed on its Web site, that rivers and streams, not coastal bluffs, contribute the majority of beach sand as long as they are not bisected by dams and dredged by sand miners before the grains can make it to the coast.

"We've destroyed the natural sources of beach sand, and that's why there is nothing there now and the cliffs are collapsing," Santina said.

Different viewpoints

Gary Griggs, a professor of earth science and director of the Institute of Marine Sciences at UC Santa Barbara, and then-graduate student Kiki Runyan, published a research paper of their own on the subject in 2003.

It was their paper that estimated coastal bluffs contributed only about 12 percent to North County beaches rather than the 18 percent estimated by Young and Ashford.

Griggs said Friday that he agreed wholeheartedly with the study's use of lasers to measure bluff erosion. But he added that the study's short time period makes it carry less weight.

"I don't question their work at all," Griggs said. "However, a short period can be problematic in coming to conclusions."

Griggs noted that, while erosion rates are generally reported to the public in averages, they often do not happen that way in nature.

"Though you may say that the average retreat rate is a foot per year, we don't see that exactly," Griggs said. "We may see 10 feet in one year and nothing the next year. That's why it's important to have a long study period."

Griggs also noted that the Young and Ashford study uses old data to help estimate the amount of quality sand that made it onto the beach. He explained that the material that makes up each bluff face varies, meaning that erosion in some areas will contribute more useable sand than others.

The Ashford and Young study relies on solid borings done by other studies through the years and does not have the same level of sampling that the laser measurement does.

"Your total study is only as good as the lowest quality available data that went into it," Griggs said.

It is also unclear exactly what effect the new study will have on coastal policy.

Lee McEachern, district regional supervisor for the California Coastal Commission, said the study will not directly affect the "sand mitigation" fees that are tacked onto any sea wall permit. He said current fees estimate the amount of sand that the retreating bluff would contribute if the sea wall was not in place, then force homeowners to pay the public for that sand that is lost.

"That's good information to have, but it does not change our sand mitigation fee at all," he said.

However, McEachern added that more precise methods of measuring bluff erosion, such as the laser measurements used by Young and Ashford, could end up influencing the Coastal Commission's understanding of natural bluff retreat rates and hence the amount of money that individual sea wall builders have to pay.

"If the erosion rate is actually slower, then they would pay less. If it's faster, then obviously they would have to pay more," McEachern said.

Contact staff writer Paul Sisson at (760) 901-4087 or psisson@nctimes.com.