As the rainy season draws near, city and county fire departments are gearing up as usual for swift-water rescues. Throughout the year, each department's swift-water team undergoes training for rescuing victims from the county's waterways. An average of six drownings a year occur in the county's more than 600 miles of flood-control channels.
The 52-mile Los Angeles River is just one part of the flood-control system. Los Angeles County has 470 miles of open channels, 2,400 miles of covered storm drains, 123 debris basins and 20 dams.
The natural river was prone to flooding, and a devastating flood in 1938, prompted the U.S. Army Corps of Engineers to line the river with concrete and build Sepulveda Dam. Now only about 13 miles of river is unpaved. Some stretches overgrown with vegetation are being cleared by the Department of Public Works and U.S. Army Corps of Engineers, in preparation for what many expect to be a heavy rainy season.
Because of the area's topography, water moves quickly down the steep mountains that surround the basin, filling the river and its diversion channels. When that happens and someone falls in a channel, the city and county fire department swift-water rescue teams must respond quickly.
Los Angeles River
When flowing, the L.A. River's water is mostly runoff from mountains and springs. The river isn't meant for recreation--it's a concrete channel designed to move water out of the Valley and down to the ocean.
The Los Angeles River drops about 800 feet in just over 50 miles--a slope much greater than the Mississippi River, which descends 1,600 feet over its 2,300-mile course.
Slower-moving water along shore circulates with water in middle in a circular motion, which is why a victim is often pulled to the middle and has difficulty getting back to shore.
Strainers are obstructions such as rocks, trees, or even furniture or fencing, which water flows through but a victim or rescuer can get caught in. Strainers also cause currents of different speeds and directions.
Water along shore and bottom is slowed by friction, while friction-free water in the center moves faster.
Angle of channel walls varies from 30 degrees to 90 degrees. Low-head dams are vertical walls along stretches where there is a drop in elevation. These are especially dangerous because of the "hydraulic" effect caused when the current reverses and recirculates over the same area. Firefighters call low-head dams "death traps" or "drowning machines" because it is nearly impossible for a victim to escape.
For most of its 52 miles, the Los Angeles River is a concrete channel with sloped walls, which are difficult for rescue victims to hold onto. A few sections of river are natural bottom. The width of the river averages 30 feet to 60 feet; it is 500 feet wide--its maximum--at its mouth at Long Beach.
A typical Fire Department response on "high-hazard" days--when 2 inches of rain has fallen in the mountains or 1/2 inch in the L.A. Basin--consists of two helicopters, three engine companies, two task forces, a battalion chief, division chief and two swift-water teams. About 85% of swift-water rescues are land-based, meaning the rescuer does not get into the water.
* "Tension diagonal line" is a rope extended diagonally across water and anchored on opposite banks at water level for victim to grab onto.
* Throw bag contains 70 feet of floatable rope and is thrown to victim.
* Rescue sling or inflated fire hose is dropped into water, usually at a bridge, to be grabbed by victim as he or she floats by.
* Rescue rocket shoots 500 feet of line at 45% angle to victim.Pike pole with D-shaped handles is extended for victim to reach.
Contact rescue involves firefighter entering water for rescue. Rescuer is tethered to other rescuers on-shore, pulls victim to shore or onto floating rescue board.
Helicopter lowers rescuer, who attaches harness to victim, who is raised out of water and onto land; rescuer is pulled back onto chopper.
Watercraft are sometimes used to reach victim, who is pulled onto flotation board towed behind.
Hypothermia weakens muscles and slows heart rate, which may stop if body temperature falls below 90 degrees. The L.A. River averages about 50 degrees in the winter. Below is a chart estimating how much useful work a rescuer can accomplish at varying temperatures and how long it takes to become unconscious:
Temperature: 40 degrees
Useful work: 7.5 minutes
Unconscious: 30 minutes
Temperature: 50 degrees
Useful work: 15 minutes
Unconscious: 1 hour
Temperature: 60 degrees
Useful work: 30 minutes
Unconscious: 2 hours
* Inflatable vest: whistle, knife, strobe light
* Gore-Tex dry suit
* Dive booties (fins in water)
\o7 Sources: Los Angeles City and County Fire Departments; U.S. Army Corps of Engineers\f7
Researched by JULIE SHEER / Los Angeles Times