It’s No Inner Tube in the San Gabriel River--It’s a 100-Foot-Long, Inflatable Dam

The dam on the San Gabriel River in Pico Rivera looks a bit like a rubber inner tube, probably because that’s pretty close to what it is. The inflatable rubber dam, which is about 9 1/2 feet high and 100 feet long, is one of three recently sold in the United States by Bridgestone Corp., a $3-billion Japanese manufacturer of tires and other rubber products.

Yasushi Uzawa, a Bridgestone salesman who was in Los Angeles last week, claims that inflatable rubber dams have lots of advantages over the far more common steel-and-concrete variety. For one thing, says Uzawa, in the event of a flood, the dams are easy to open--all you have to do is let the air out. Then the balloon-like dam, which is anchored to a concrete base, neatly collapses and rests on the river bed. It takes only 20 minutes to mechanically blow it up again. And, Uzawa says the rubber dams should last for 30 years.

The Bridgestone model is one of three rubber dams in the region known as the San Gabriel spreading ground. The other two dams were sold to the Los Angeles County Public Works Department by Bridgestone’s biggest domestic competitor, N. M. Imbertson & Associates, a Burbank engineering firm. Its founder, Norman Imbertson, held the now-expired patent on the method of keeping the rubber tube in place by sealing it to a concrete base on the riverbed. His company has installed most of the 300 inflatable dams located in the United States.

Uzawa believes that the biggest markets for the rubber models will be for flood control, irrigation and recreation. The dams in the San Gabriel spreading ground, for example, divert water from the river to the surrounding river basin. Richard Ostrow, assistant division engineer for the Los Angeles County Public Works water conservation division, explained that the diverted water percolates through the soil and replenishes the underground water table.

However, Norman Tabor, N. M. Imbertson vice president, says the most popular place to use for the rubber dams is underground. The dams are used in sewer systems in older cities such as Cleveland and Detroit to divert to a sewage treatment plant the polluted water that would otherwise flow into a nearby river.

Uzawa says the rubber dams don’t work in every situation. Since they aren’t more than 10 feet high, they won’t replace such giants as the 550-foot Grand Coulee, located on Washington state’s Columbia River. And, though they can withstand raging currents and the pounding of boulders and debris, they aren’t vandal-proof. A bullet puncture will cause the dam to leak but not blow out, says Uzawa. That is because the air pressure inside the dam is low--one-third the air pressure of a car tire. Such holes can be easily patched, he added.