First Steps. Inflatable dams will be placed within foundations to impound spreading basins. (Photo courtesy of Los Angeles Dept. of Water and Power)

Completion is scheduled by year’s end for two inflatable rubber dams being installed for Los Angeles-based Water Replenishment District of Southern California. The dams are expected to save $1 million worth of water each year that would otherwise have to be purchased. Despite a jump of more than 50% over the original estimate, the district maintains that the $6.4-million project still is cost-effective.

G.B. Cook Inc., Azusa, Calif., poured the 23-ft x 443-ft foundations on the San Gabriel River in July and then bolted the vandal-proof ceramic-chip bladder in place. The sites were chosen because the spreading grounds behind them were porous enough to allow water to seep into the ground. The contractor is now installing 40-horsepower air compressors that can blow 870 cu ft per minute to fill the 8-ft-high, 442-ft-long dam in as little as 20 minutes. The dam can be deflated just as quickly if a storm becomes too large to contain.

The project–the county’s 12th and 13th of this type–was originally estimated at $4.2 million, but permitting delays and increased steel and concrete prices added more than $1 million, says Ken Zimmer, civil engineer for Los Angeles County. The dams alone cost $1.5 million each.

Ted Johnson, chief hydrogeologist for the Water Replenishment District, says the increase was worthwhile because the water being captured in the spreading grounds to drain to the aquifer for potable use later would otherwise go to the ocean. As much as 3,600 acre-ft of water with a market value of about $354 per acre-ft, could be saved annually. Since costs were shared by the County of Los Angeles and offset by state grants, Johnson estimates the replenishment district’s investment could be recouped in two years with savings every year thereafter.

If the project works as the agency hopes, more dams may follow, Johnson says.