June residents eye high country dams as runoff season approaches; SCE says dams are safe

Wendilyn Grasseschi
Times Reporter

Far above June Lake in the high Sierra backcountry, three reservoirs created by three different dams perch in the glacier-carved Rush Creek drainage.
Owned and operated by Southern California Edison, Waugh Lake, Gem Lake and Agnew Lake dams (in order of descending elevation) have formed three lakes, which hold back the waters of Rush Creek until it plunges down to the community of June Lake via a spectacular waterfall at the west edge of town.
The reservoirs are used as a place to store water and for electric power for the company’s Rush Creek Powerhouse, located below the dams.
June Lake and Mono County residents have known about and lived with the reservoirs perched far above them for about a century – all three were built between 1916 and 1925. Southern California Edison even has an “Emergency Action Plan” in place as required by its FERC licensing process, should an emergency arise.
None have and for the most part, the dams are out of sight and out of mind for most people, most of the time.
This year however, expectations for an epic, snowmelt runoff, along with this winter’s very public failure of the Oroville Dam spillway (the dam was not damaged, only the spillway) has sparked rumors and anxiety about dams across the state, including the three dams above June Lake.
One additional issue that might have sparked the concern about the three Rush Creek dams is that the three dams are the only SCE dams which are required by state and federal decree to restrict water levels to a certain maximum level due to the potential for earthquakes in the area.
That said, the dams are designed to handle California earthquakes, SCE said, and, they will be able to withstand the influx of snowmelt water later this season.
“First and foremost, we want you to know there has been no increased risk to the community this year (compared to other years) relative to earthquakes,” said Rudy Gonzales, public information specialist with SCE. “The dams are structurally safe.” He noted that SCE is in the process of asking for a temporary waiver for these “seismic restrictions” in one lake, Waugh Lake, in order to accommodate the influx of water but he also said SCE has added other mitigation measures to make sure that even in the unlikely event that an earthquake did occur during this high runoff period, the dam would be safe.
He noted that the dams have withstood “hundreds of earthquakes” during their lifetime and are designed to withstand strong earthquakes.
The Times talked with SCE officials Tuesday to find out if the dams can safely handle the coming runoff, and what the agency plans to do should problems arise.
The bottom line, according to SCE, is as noted, the dams are structurally safe; second, the dams are monitored 24/7; and three, there are a series of extensive, flood-mitigation measures underway now, all of which will be fully in place before peak runoff occurs this summer.
“Second, there is a strong, ongoing monitoring and mitigation program in place for all three dams,” Gonzales said.
“We have measurement tools that we use and we inspect the dams every month, as well as we do an annual inspection,” said Gonzales.
The dam sites are also monitored electronically.
“We use on-site electronic monitoring, with the data sent via radio to a control station in Bishop, where the incoming information is monitored 24 hours a day, seven days a week,” he said.
Third, along with these routine practices and routine flooding control devices and measures, this year SCE is taking proactive steps to get ahead of the expected, possibly record snowmelt runoff, he said.
That peak is expected to hit from June to August in a roughly 40-day period, he said.
“Waugh Lake will be at its maximum capacity then,” he said. “The excess water will flow to Gem Lake, then to Agnew Lake. We will use release valves to keep Gem at minimum levels, then flow the water into Agnew Lake, then allow it to flow through the Rush Creek system to the powerhouse. We will station personnel on site once runoff season begins at Gem and at the Rush Meadows dam (Agnew Lake dam) in order to watch and keep on top of the piping, to keep it safe. Remote cameras will also be installed at the dams and we will also deploy several large, individual pumps into Agnew Lake to add to our backup capacity, should the need arise,” he said.
Should an emergency arise, SCE already has plans in place to work closely with the Mono County Sheriff’s Office and other emergency responders, he said.
In addition, SCE and Mono County will be doing a “tabletop exercise” late this month that simulates a flooding incident, he said.
The power company also has plans to do more community outreach during the next several months, as well as stay in close contact with all emergency personnel in the area, he said.