Science/Medicine : Shifting Sands : <i> California beaches are disappearing under relentless forces of nature and the unwitting hand of man.</i>
From Santa Barbara to San Ysidro, Southern California’s beaches are disappearing.
They won’t be gone tomorrow but they are indeed vanishing under the relentless forces of nature and the unwitting hand of man.
Beach erosion has been going on forever--wherever land and sea meet. Unfortunately, what is happening in Southern California mirrors an accelerated worldwide problem along the narrow coastal strips, where more than half the world’s people live.
In the contiguous United States, at least 20% of the 10,000-mile coastline is under siege from the sea, according to estimates. Southern California beaches may be eroding as much as 10 feet a year. The loss isn’t always visible, except after disastrous storms such as those of the 1982-83 winter, because Southland beaches are artificially rebuilt and stabilized. But over time, perhaps within 50 years, the result will be smaller beaches than we know today.
Two major factors cause beach erosion--people and natural forces.
People have no control, of course, over the fact that sea level, worldwide, has been rising since the Ice Age. “Although they disagree about the cause,” says Orrin Pilkey, a marine geologist at Duke University, “most geologists agree, despite measuring difficulties, that sea level is generally on the increase.” In Southern California, the increase may total as much as eight inches a year.
The nature of the Southland’s coast may be at least partly responsible.
As explained by Douglas Inman, director of the Center for Coastal Studies at the Scripps Institution of Oceanography in La Jolla, the West Coast is a “collision coast,” characterized by a steep, narrow continental shelf bordered by deep basins and ocean trenches. Submarine canyons--there are six off Southern California--cut across the shelves and enter deep water. The shoreline is often rugged and backed by sea cliffs and coastal mountain ranges where earthquakes and volcanic activity are common.
Under the theory of “plate tectonics,” Inman explains, if the Pacific sea floor plate is shoved upward in relationship to the continental plate--even over millions of years--this could at least partly account for sea level increase. Another factor is glacial melting that adds to the oceans’ water supply.
Old-time residents of Encinitas in San Diego County, for instance, may remember 5th Street on turn-of-the-century subdivision maps. The road was laid out on the rim of sea cliffs, intended to give home buyers a spectacular ocean view. As the rising sea has continued to erode the cliffs, 5th Street has disappeared.
People, too, cause beach erosion. By tampering with nature, humans interfere with beach-building pro-cesses, and erosion inevitably follows. Once replenished naturally, even after the severest winter storms, beaches are sometimes robbed of their new sand by devices intended to prevent such losses.
Southern California beaches owe their existence to two major sources of sand. One is littoral drift. This occurs when surf-dislodged sand particles are carried along by offshore currents to beaches farther downcoast. The sand eventually tumbles into offshore submarine canyons for which the Southland is geologically noted. The La Jolla Underwater Canyon is an example: Most of the southeast-moving sand carried off Oceanside’s beaches between Dana Point and La Jolla eventually winds up on the floor of this yawning offshore trench.
The sand thus lost to the canyons, historically, was replaced naturally by the second major source of sand--almost identical amounts washed down Southland rivers, creeks and streams, especially during the flood stage.
Beginning early in this century, however, Southern California’s rivers, including two flowing through Oceanside, were dammed one by one, choking off sediment flowing toward the coast. Two dams east of Oceanside now block about half the sand that once replenished the beaches.
Coastal construction has also taken its toll on littoral drift--sand carried by winds and currents from one beach downcoast to the next, and finally into the offshore canyons. The principal culprits have been breakwaters, jetties, groins and seawalls, built to protect harbors or beachfront homes.
Ironically, scientists now know that many of these structures, through a kind of chain reaction, have actually accelerated the rate of erosion.
“First, they limit the sand available to downcoast beaches,” Inman says, “and when erosion becomes imminent, they invariably require more protective structures that may cause further damage to the beach.”
During the 1982-83 winter, perhaps the most severe in 50 years, Oceanside beaches alone lost 1 million cubic yards of sand. Replacement cost: $3.5 million.
Fifteen times since 1957, the city has had to dredge its harbor, built for military use in 1942 and later expanded to accommodate pleasure craft. Three times, the system of breakwater, jetties and groins protecting the harbor and beaches at Oceanside has been modified. The beaches still starve, the harbor still shoals.
Most of the coastal construction that apparently contributes to beach decay--harbors, seaside subdivisions, recreational facilities--occurred between the mid-1940s and the mid-1970s. There were relatively mild winters with low rainfall, moderate winds and stable climate in this time. But the Southland may be entering a cycle of severe weather that will last about 30 years.
“We now appear to be entering a period of more variable climate with more extreme weather events,” Inman says. “This could have a marked effect on beach erosion.”
Other than merely surrendering to the sea (which has been seriously suggested), what can be done to save the Southland’s coastline?
First, there are what might be called “quick fixes,” almost anything that will blunt the ocean’s assault. Long Beach tried planting artificial seaweed just offshore. Tetrapods--huge solid structures resembling children’s jacks--have been used. Del Mar once piled old junk cars on the beach during a heavy storm.
For long-range solutions, engineers and scientists have historically divided themselves into two schools of thought.
Engineers, as exemplified by the Army Corps of Engineers, empowered by Congress in 1930 to help save the country’s beaches, tend to view the ocean as an enemy and its coast encroachment as an invasion. The Corps has been inclined historically to build barriers against the “enemy.” They work, at least for a time, but while they solve one problem they often cause others.
Built after a hurricane in 1900 that killed 6,000 people, Galveston’s seawall has ensured the city’s safety in future storms--at the expense of its once-fine beach.
But, increasingly, erosion-plagued communities are enlisting the help of scientists whose “holistic” approach is to better understand the natural processes affecting beaches, and then plan strategy in concert with that, rather than by fighting nature. Scientists view an eroded beach as just one part of a larger problem, and this may explain why Inman insists that erosion planning must consider entire coastal sections rather than specific beaches.
The Corps relies heavily on shoreline models on which it can realistically duplicate beach behavior. Inman prefers on-the-spot studies to models. His staff has devised many scientific tools, including computers, to learn more about Southern California beach behavior.
Oceanside recently completed construction on an experimental, $5.6-million, sand-bypass system, recommended by Inman, which the city feels is a cutting-edge example of the “work with nature” theory. Presently undergoing a shakedown, the system is designed both to keep the Oceanside harbor free of silting and to continuously replenish eroded downcoast beaches.
Two jet pumps, each of which can scoop up 100 cubic yards of sand an hour, have been installed 25 feet below the harbor bottom, sending sand to the beaches through a 14-inch pipeline. Additional pumps can be put in service for about $8 million.
There’s a final alternative to saving the beaches. Horrifying though it may be to anyone who has invested in beach property.
Instead of fighting the sea, some say, humans could do nothing at all.
Such a proposal was submitted in 1982 to President Reagan by shoreline geologists at the Skidway Institute of Oceanography in Savannah, Ga. And in the 1970s, the National Park Service did adopt a modified version of the idea for some of the coastal land it administers.
Doubtless Southern Californians won’t let their Malibus and La Jollas fall into the sea, at least for a long time. But for the moment, nature may have the upper hand.
“The tides and waves breaking on the world’s shorelines cannot be tamed,” Duke’s Orrin Pilkey argues, “even with all the energy and materials that the continents can supply.”
How California Beaches Erode And What Can Be Done About It AT LEFT: How natural and man-made factors are combining to strip California’s beaches of sand. Other factors affecting erosion include a rising sea level, a constantly changing sea floor and increasingly harsh winters. BELOW: Some of the solutions coastal communities are considering. LITTORAL DRIFT Sand dislodged from a beach by the surf is carried by offshore currents to beaches further “downcoast.” The sand eventually tumbles into offshore submarine canyons for which Southern California is geologically noted. DAMS AND SILT Damming rivers has altered a natural sand replacement formula, choking the flow of sediments toward the coast. Engineers say it is possible to design dams that would allow more sediment through--but the cost would be prohibitive. COASTAL CONSTRUCTION Scientists say that construction of breakwaters and jetties built to protect harbors or homes actually has accelerated erosion. They limit the flow of sand downcoast--sand builds up along the seaward walls--and harbors trap sand and shoal. SAND BYPASS SYSTEM Oceanside, working with the Army Corps of Engineers, has installed a series of jet pumps in the harbor to move silt and built-up sand to a pipeline along the beach: (A) A mobile unit with a crane collects built-up sand and pipes it from the seaward side of the harbor to a breakwater pumphouse. (B) Water pressure directs sand particles to underground jet pumps which move the sand from beneath the harbor. (C) The breakwater pumphouse pushes the sand through a shoreline pipeline. (D) Sand is discharged periodically along the two miles of pipeline. SLOWING THE WAVES Both on shore and in the water, communities are trying to save the beaches by dissipating wave strength. Among the ideas in use: (1) Artificial seaweed, like that “planted” by Long Beach. Plants are divided into several four-foot-long, finger-like fronds and anchored to the ocean bottom by plastic tubes. (2) Longard tubes are sausage-like tubes about 660 feet long, six feet in diameter, filled with sand and placed on beaches to protect threatened homes. (3) Tetrapods--resembling giant children’s jacks--break the force of incoming waves, but allow water and sand to pass through. (4) Artificial reefs and floating breakwaters, some made from bundles of old tires. Del Mar residents once parked junk cars on the beach and left them there until a 1978 storm ended.
