Flood Controls : CHANNELING THE LOS ANGELES RIVER

Dry but for a trickle most of the year, Southern California’s concrete spider web of flood control channels turns into a churning torrent of chocolate colored water during heavy rains.

The channels--begun in response to disastrous flooding in 1914--are designed to move vast quantities of water out to sea as quickly and efficiently as possible. Decidedly ugly, their function is more important than their form.

Some have called channelization of the area’s natural waterways a concrete straitjacket that causes more problems than it solves by destroying the natural environment and creating gigantic flumes in which half a dozen people are swept to their deaths every year.

Long before the channels were built, Southern California was plagued by flooding. Runoff from the San Gabriel Mountains--some of the steepest and most unstable in the world--would gush down across the alluvial plains of the San Fernando Valley and Los Angeles, washing away whatever stood in its way.

Floods were unpredictable. Twice in the 1800s the Los Angeles River drastically changed its course during heavy rains.

THE SYSTEM

The 4,000-square-mile Los Angeles Basin is protected by a network of flood control channels that carries most runoff water to the ocean.

DANGEROUS WATERS

Water in the channels can move at speeds of up to 45 miles per hour. At just 25 miles per hour, fighting the water is equivalent to a 350-pound bench press.

Part of the reason for the speed is the steepness of the channels’ course. In just over 50 miles the Los Angeles River drops 800 feet to the ocean--or almost 16 feet per mile. By contrast, the Mississippi River drops 800 feet over 2,300 miles--or about four inches per mile.

Another reason is that the channels are designed straight and with few obstructions to speed the water through. That makes rescues even more difficult because there is little to grab on to.

In heavy rains, the chanels are dangerous places. A dry channel can swell to capacity in minutes. Once trapped in the current, few people make it out alive. After Woodland Hills teen-ager Adam Bischoff was swept to his death in 1992, efforts were made to improve water rescue techniques. All firetrucks and most police cars now are equipped with life vests and other rescue gear.

HOW IT WORKS

Channel Facts:

* Open channels: 450 miles in Los Angeles County

* Storm drains: 4,000 miles of drains

* Dams: 20 major dams

* Los Angeles River: The river can move 146,000 cubic feet of water per second. The powerfulColorado River moves only 30,000 cubic feet per second.

Rainfall

Water from mountain streams and canyons flows into catch basins

Raising the Walls

Flood control officials from Los Angeles County and the Army Corps of Engineers want to expand the river’s capacity by heightening the channel’s walls. Critics of the plan say it would further degrade the environment.

Paving the Rivers

Although most of the channel network is paved along the bottom, about 22% of the Los Angeles River and 66% of the San Gabriel River are unpaved. The reason has to do with soil conditions. In some spots, river bottom is left exposed so water can percolate into underground aquifers. In others--such as along the Los Angeles River through Glendale--high water tables would crack concrete bottoms.

CHANGING CHANNELS

* Seeking thrills: Although driving in the channels is forbidden, bus drivers train there and Hollywood has long been attracted to them for cinematic car chases. Perhaps the most famous recent film to be shot in Valley channels was “Terminator II: Judgement Day,” in which Arnold Schwarzenegger flees on motorcycle from a killer cyborg.

* Traffic flow: In 1990, Assemblyman Richard Katz (D-Sylmar) proposed turning sections of the Los Angeles River into a freeway that could be used during dry months. The idea was legitimized by the Los Angeles Transportation Commission, but ridiculed by environmentalists and others who want the river restored to a more natural state.

* Natural progression: Environmentalists want the river to become more accessible to Los Angeles residents by creating parks and bikeways along its length. Some also want to create collecting ponds to capture rainwater to recharge aquifers.

*

1815: Severe flooding changes the course of the river, switching the outflow from Long Beach to Ballona Creek.

1825: Flooding again changes the course of the river, this time reverting it back to the original outflow.

1905-1913: $22-million Los Angeles Aqueduct system constructed to bring water from the Owens Valley.

1914: Flooding causes $10 million in property damage. Flood control district formed.

1915: Flood control bill signed by governor, and county develops plans to prevent future flooding.

1917: County approves $4.45 million bond issue to begin work on flood control network.

1928: More than 400 die when San Francisquito Dam, part of Los Angeles City’s aqueduct system, fails.

1934: Floods in La Crescenta kill 40 and sweep away 483 homes.

1936: Army Corps of Engineers charged with flood control.

1938: Flooding kills 113 and causes $45 million damage.

1941: Congress approves $230-million flood control project in Los Angeles County.

Sources: Army Corps of Engineers, Los Angeles County Department of Public Works, Los Angeles Times research

Researched by AARON CURTISS / Los Angeles Times.