Thursday, February 09, 2006

Nimibus Flood Gate Opens Accidentally

This story, in Tuesday’s Bee, was a shocker. An electrical malfunction on one of the 18 gates at Nimbus, caused the gate to open for 30 minutes causing the water level to rise in the river by over 5 feet.

At that rate, had each gate opened the river could have risen by, (this can’t possibly be right) 90 feet in thirty minutes??? Of course, Lake Nimbus only holds so much water, the level it would drop to after which no more would flow out through the gates, and several other factors, would surely preclude this happening….(right?) but it did happen with one gate, and for thirty minutes the gate stayed wide-open…scary!

Here is an excerpt.

Dam's failed sensor caused water gush
By Jim Downing -- Bee Staff WriterPublished 2:15 am PST Tuesday, February 7, 2006

A loose electrical connection caused the malfunction in a Nimbus Dam gate Saturday, abruptly raising water levels in the lower American River by nearly 5 1/2 feet, a Bureau of Reclamation official said Monday.

Vibrations from water passing through the dam's gates appear to have shaken the connection loose, according to bureau spokesman Jeff McCracken. It was the first serious malfunction in the gate control system, which was installed about two years ago, he said.

The problem occurred at 1 p.m. Saturday as four of the dam's 18 gates were being opened slightly to increase the flow of water below the dam from 5,500 to 7,000 cubic feet per second, he said.

The malfunction caused one of the gates to fully open, increasing the flow to about 20,000 cfs and sending anglers downstream hurrying for higher ground.

"When you raise the gates there's a sensor that's supposed to kick in" and stop the gates from opening beyond a set point, McCracken said. When the sensor failed, one of the gates continued to open, he said.

According to a U.S. Geological Survey chart, a flow increase from 5,500 cfs to 20,000 cfs raises the river's average depth from 7.2 feet to 12.7 feet.

The gate remained open for about 30 minutes before an operator closed it using a manual override switch on top of the dam, McCracken said. "