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Case of the Vanishing Coastline : Beaches in Retreat as Man, Nature Take Their Toll

May 09, 1991|CHRIS AHRENS

North County shrinks some days and grows on others.

It is usually a slow, nearly imperceptible change. Each day varying amounts of sand move north or south, in shore or off shore, causing subtle differences in the mass of real estate here.

Sometimes the changes are abrupt, like they were on March 25 in Encinitas when a large portion of the bluff collapsed, taking a retaining wall, wooden stairs and part of a walkway with it.

It's the latest, but not the most dramatic example of bluff failure in North County. In the early '40s, the Golden Lotus Temple belonging to Self Realization Fellowship on the Cardiff/Encinitas border at Swami's slid down the cliff.

Sandstone bluffs are typical along the North County coast. They fail when the top of the bluff becomes too heavy for its base, or when cracks allow large chunks of soil to loosen.

The greatest protection against bluff failure is a wide, sandy beach.

But wide, sandy beaches--once the norm in North County and a great natural attraction for residents and tourists--are disappearing.

The beaches have been in retreat for a number of years. Some beaches have become narrow; others are now covered with cobblestones rather than sand.

The beaches are victims of changing weather patterns and of human-engineered changes to the landscape.

A number of those studying the changing coastline predict that without significant intervention--by people or by nature--sandy beaches in North County may be endangered in as little as five years.

Beach sand is measured in plots known as littoral cells, which are stretches of coast with a rocky headland and source of sand at one end and a submarine canyon that catches sand at the other.

The Oceanside littoral cell stretches from Dana Point in Orange County to the La Jolla Submarine Canyon, and moves hundreds of thousands of cubic yards of sand around each year.

Sand is lost in the winter when the swell direction is normally from the north. Much of that sand returns in the summer when the swells move in the opposite direction. But some of the sand moved south in winter is washed into the underwater depths of Scripps and La Jolla canyons, from which it does not return.

The shifting of sand into offshore canyons has amounted to at least a 14-million-cubic-yard net loss over the last 50 years, according to David Skelly, a coast engineer for Scripps Institution of Oceanography. "The sand in those canyons is about 3 to 4 miles thick. We will continue to loose sand. The cliffs will erode further. Unless we do something, there won't be a beach in North County in five years."

New sand for the nourishment of beaches is generated primarily from two sources--rivers and cliffs. Day after day, the two sources deliver small amounts of new sand; during periods of heavy flooding in the past, large amounts of new sand have been deposited.

The erosive process is as old as the earth itself. But in relatively recent times, it has been disrupted.

The rivers have been dammed and mined; the flow in and out of lagoons has been blocked by roads and other development, and bluffs have been protected as valuable real estate. All of those actions have decreased the flow of sand and hindered the ability of the beaches to replenish themselves naturally.

Not all beaches have been depleted. The Oceanside area beaches still have a fair amount of sand, as do those in Solana Beach and Del Mar.

"I've seen about 2 feet (of sand) a night being deposited in Solana Beach recently," said Andy O'Leary, captain of the Solana Beach Lifeguards. "Unfortunately, that does not seem to be the case from Seaside Reef and points south. There, the entire beach is gone, and there are cobbles in its place.

"I think that this is going to create a large strain on the beaches with sand this year. Everyone will be coming to the beaches that have sand on them."

The presence of beach cobbles in North County is nothing new. The beaches between Oceanside and San Diego were primary sources of cobbles for grinding in California from 1919 to 1949. Ponto Beach in South Carlsbad was mined as a major source of the stones. Many of the streets in San Diego were built from beach cobbles gathered in the Del Mar area.

But since the early 1980s, the amount of beach dominated by the cobble has been increasing.

The cobbles wash ashore as the amount of sand on the beach decreases. The area starting at South Carlsbad and stretching to Solana Beach is now heavily cobbled.

At Encinitas, the beach known as Stone Steps is among those that have shifted from sand to cobble.

Beach cobbles are piled up against the cliff and at the foot of the stairway that allows access to the beach from the bluff. Like most public access stairs in the area, these have had to be rebuilt at the base several times because of the battering they take from waves and cobble.

Two decades ago, people played volleyball in the sand at Stone Steps.

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