A new study shows that Anderson Dam could collapse in a major earthquake. It is also the largest dam located Santa Clara County holding 90,000 acre-feet of water when full, which is more than the other nine reservoirs in the county combined.
The new study points to an area of the dam's foundation that contains sand and gravel, which could liquefy in a big quake. Most of the dams foundation was scraped down to bedrock when the dam was built in 1950.
Though the dam which sits on the Calaveras Fault was designed to with stand earthquakes when it was built it was not designed to withstand what is being called the maximum credible earthquake.
According to the study the dam would likely not collapse suddenly or completely but, if completely full, could slump and begin to erode away from the top, giving people a day or so to evacuate, according to Dave Hook, an engineering unit manager for dam safety with the water district.
In the worst case, a complete failure of Anderson Dam could send a wall of water 35 feet high into downtown Morgan Hill within 14 minutes, and eight feet deep into San Jose within three hours, under state emergency scenarios.
More studies are being conducted on the dam since the new findings have been discovered and are being watched carefully by local officials.