MORGAN HILL
In response to a study released earlier this month that said Anderson Dam could fail in the event of a major earthquake, the Santa Clara Valley Water District approved funding further studies up to a cost of $3.5 million.
The district’s board of directors voted unanimously in favor of the more detailed seismic stability studies which will be contracted with AMEC Geomatrix at its regular meeting Jan. 13.
On Jan. 5, the district released the results of a preliminary seismic study of the dam which holds back Anderson Lake, which is east of Morgan Hill and is the largest of ten reservoirs owned by the district. That study said that, based on the content of borings into the earthen dam, the dam could fail if an earthquake of magnitude 7.2 occurs on the Calaveras Fault, which runs directly underneath the reservoir.
In a worst-case scenario, models by district engineers show that a failure of the dam if the reservoir were full could put downtown Morgan Hill underneath 35 feet of water, and Gilroy under 14 feet of water.
The district’s initial response to that study was to keep the reservoir’s water level at or below 87 percent of its capacity, minimizing the amount of water that could spill over the top of the dam if an earthquake happened. However, the California Division of Safety of Dams restricted the water level even further, keeping it at about 70 percent capacity, or about 40 feet below the crest of the dam.
Anderson Lake is currently about 63 percent of its capacity of 90,000 acre-feet.
City of Morgan Hill officials had hoped the district would ensure the water level stayed lower than they had initially planned, but were pleased the division enacted further restrictions.
The in-depth seismic studies could take up to two years to complete, according to discussion at the meeting.
