Calero and Guadalupe dams are in deep doodoo should the earth underneath them start shaking and rolling, officials said this week.
A Santa Clara Valley Water District study has found that both dams are subject to significant damage if a major earthquake were to occur.
The dams have been subject to storage restrictions based on earlier similar findings, according to district spokesman Marty Grimes.
As a result of the new findings, the district has voluntarily decreased the amount of water the dams can hold to 25 feet below their crest. The new operating restrictions are now subject to approval by the state Division of Safety of Dams (DSOD), Grimes explained.
Calero has been under a storage restriction of 20 feet below the dam’s crest since January of 2011, when preliminary data indicated the presence of alluvium—gravel and sand from the underlying creek bed—under the downstream dam embankment. The condition could make the dam vulnerable to damage during a major earthquake, Grimes added.
The additional 5-foot restriction would reduce the available storage capacity by 1,136 acre-feet, he said.
Guadalupe has been under a storage restriction of 14 feet below the dam’s crest since October of 2006. The additional 11-foot restriction would reduce the available storage capacity by 1,003 acre-feet.
The district expects to initiate a capital project to study possible remedial options for the dams, but it's not known how much it will cost.
The district is the largest water services provider in Santa Clara County providing flood protection services to about 1.8 million residents.