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On the BEACH : Shifting Sands, Foul Water and Other Man-Made Follies Threaten Our Coast

June 24, 1990|CHARLES PERRY | Charles Perry is a free-lance writer. His last story for this magazine was "O, Happy Days! When We Were Very Young."

For the last year, Oceanside has been trying a new approach. The federally funded sand bypass system pipes the sand a mile down the coast around a breakwater that otherwise interrupts the flow of sand. The system can move 1,200 cubic yards of sand a day--when it's running. Once the pipe has sucked up enough sand to create a crater in the harbor, the process is stalled until more sand flows into the crater. In the next phase, perforated pipes will be used in the harbor bottom to keep sand circulating.

To appreciate how difficult it is to tame Southern California's beaches, one must consider the powerful forces at play. North of Santa Barbara County, there are scarcely any wide, sandy beaches like those in Santa Monica and Manhattan Beach. Beyond Point Conception, the coast is rocky, and tiny pocket beaches that tend to lose their sand in winter storms are the rule. In Southern California, though, the bluffs are mostly soft shale and sandstone, and 85% are said to be actively eroding. Horrifying as that must be to cliff dwellers, those smooth, eroding bluffs help create Southern California's long, photogenic beaches.

The mildness of our waves is due to the uniqueness of our geography. At Point Conception, the coast turns almost 90 degrees east for 60 miles, paralleling the mountains of the Transverse Range, which continue out at sea as the Channel Islands. Point Conception and the islands take the brunt of the waves' force that would otherwise strip the beaches of sand.

However, this leaves the waves nothing to do but move sand down the coast. In a single day, on average, 770 cubic yards of sand--about 100 dump-truck loads--pass a given point. The absence of natural barriers in our coastline allows sand to move quite a distance: Grains of sand at Hermosa Beach may have originated near Point Dume.

Before humans started interfering, our rivers brought new sand to the beaches. Some was freshly eroded rock material from the mountains, but most was old sediment making up the plains. (Much of the Southern California coast is old sea bottom; the Los Angeles Basin is a mile deep with sediment.) But due to the climate, our rivers don't flow regularly. They alternate between droughts lasting sometimes years and occasional but devastating floods, brought on by violent winter storms.

Years ago, flooding took place with a vengeance in the Los Angeles Basin, which is so wide and flat that no natural river channels exist. The Los Angeles, San Gabriel and Santa Ana rivers were wild in the most dangerous sense. Not only would we never know when there would be water in them or how much there'd be, after a flood, we could never tell what course the water would take. Until the flood of 1824, for instance, the Los Angeles River emptied into the sea near Marina del Rey by way of Ballona Creek. Before 1867, the San Gabriel River joined the Los Angeles River at Dominguez Gap in Long Beach.

Beginning in the '30s, vast flood-control projects were built. Rivers were dammed. Permanent channels were chosen and lined with concrete so that we would never again be at the mercy of the rivers. This may have made the population explosion of Southern California possible, but floodwaters could no longer bring sand to the beach. "The rule of thumb that everybody quotes," says Reinhart Flick of the California Department of Boating and Waterways, "is that roughly half the natural sand supply has been cut off."

That sand can longer reach the beach has created yet another complication: It is estimated that an average of 800,000 cubic yards of sediment have entered San Gabriel Dam every year for the past half-century. When a dam fills up, it can no longer function.

Couldn't we just take the sand from behind the dams and send it to the sea? Not practical, says David Potter of the Hydraulic Division of the L.A. County Department of Public Works. Forcing sediment through the sluice gates would require a tremendous amount of water--essentially, a flood. Potter has also looked into the possibility of building slurry pipelines: The price came to $5 million a mile just for the pipe. To move sand to the beach from the San Gabriel Dam, which is just one of five dams on the San Gabriel River, would mean a 40-mile pipeline. Trucking also is too expensive, except for dams closer to the coast.

But the problem of the dams' filling up may solve itself. Ancient deposits of sand and gravel being mined in Irwindale will eventually run out, perhaps in the next decade, and cleaning out dams may go from being an expense to being a money-maker. Already, one dam in Pasadena sells sand and gravel.

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