Update: Evacuations lifted after inspectors say Tuolumne County dam is safe
All evacuation advisories have been lifted in a Twain Harte neighborhood after cracks were found near a small dam, the Tuolumne County Sheriff’s Department said.
Deputy Niccoli Sandelin said the California Department of Safety of Dams inspected the dam on Twain Harte Lake and determined it was “structurally sound and clear for continued use.”
Twain Harte Lake Association will continue with draining water from the lake and monitoring the dam.
The cracks happened in natural granite next to the small manmade structure, causing a sound known to happen when rock exfoliates.
“Reports of a loud ‘explosion’ noise at the Twain Harte Lake Dam sent first responders to investigate,” the department wrote in a post on its Facebook page just after noon Thursday. “The result was the discovery of some cracks to the dam.”
The department later clarified that the cracks were in the granite. The lake is used in summer for swimming.
Authorities issued evacuation advisories for the areas of Good Shepherd Drive and Lucky Strike Trail in Upper Crystal Falls. An advisory means residents should be prepared to leave if ordered to do so.
About 1:30 p.m., additional evacuation advisories were made to include “all areas east of the Sullivan Creek Bridge along the creek.”
The 1:30 update also said the investigation has determined the noise heard was likely the rock at the dam cracking. There was no sign of any explosive devices or explosions in the area, it said.
A sheriff’s spokesman did not have immediate information about how many people are affected.
“Emergency personnel are still working to determine the full impact of the damage at Twain Harte Lake to the dam itself and surrounding infrastructure,” said a news release issued at 12:08 p.m. “For overall safety, the public is asked to avoid Twain Harte Lake area where first responders are staging.”
At 12:56 p.m., the sheriff’s office warned area residents that water will be released from the lake, “which will create a rise in water levels downstream.”
“Please remain calm.”
The private lake, owned by the Twain Harte Lake Association, has roughly 142 acre-feet of capacity and is 20 to 25 feet deep, according to the Office of Emergency Services.
Other agencies responding to the incident include the Tuolumne Utilities District, Cal Fire, the California Office of Emergency Services, the California Division of Dam Safety and PG&E.
The discovery comes as the area is experiencing heavy snow, rain and wind. The National Weather Service issued a storm warning early Thursday that goes through Dec. 26.
This story was originally published December 23, 2021 at 12:52 PM.
