Eroding Concrete in Tunnel Postpones Testing of Seven Oaks Dam; Overall Safety Called OK

Testing at Seven Oaks Dam east of Highland was halted Wednesday when concrete in an outlet channel eroded while a torrent of water was being deliberately unleashed into the Santa Ana River.

The Army Corps of Engineers said the damage was minor and did not undermine the safety of the dam.

“The dam itself is sound,” corps spokeswoman Jennie Salas said.

This year’s record rainfall provided enough storm water to allow the Corps of Engineers to test -- for the first time -- the dam’s ability to release water stored in the reservoir. The dam is a crucial part of the flood-control system that protects more than 3 million people in San Bernardino, Riverside and Orange counties.

Federal engineers had hoped to gradually increase the amount of water released over a two-day period. On Wednesday, engineers opened a release gate, unleashing 2,500 cubic feet of water per second into a concrete and rock-lined pool on the floor of the Santa Ana River.

But shortly after noon, federal officials discovered that a 30-by-30-foot section of patched concrete flooring in the 1,600-foot-long outlet tunnel had eroded. The testing was halted to allow engineers to evaluate the damage and consider ways to make repairs. Then testing will resume.

The dam, which stands 550 feet above the riverbed, is the sixth tallest in the nation. The reservoir behind the dam has a capacity of 145,000 acre-feet of water, or more than 47 billion gallons. Most of the water runs down from the San Bernardino Mountains.

During the recent four-year drought, the reservoir was well below capacity. The record rainfall over the last year has raised the reservoir level to 43,000 acre-feet of water, or 14 billion gallons. The extra water allowed engineers to test the pressure-release gates for the first time.

Most of the water released Wednesday will run along the Santa Ana River to the Prado Dam before being diverted to underground aquifers for storage and use, later, as residential drinking water.