Dredging deadline
TUD enters final push to begin Phoenix Lake restoration next year with millions in grant funding on the line
After over a decade of work and nearly $2 million spent, Tuolumne Utilities District hopes to break ground by spring or summer next year on a long proposed project to improve the storage capacity and water quality in Phoenix Lake reservoir.
The district’s Board of Directors voted 5-0 this week to spend an additional $99,935 from the project’s total budget of nearly $6.4 million on additional costs associated with obtaining a permit from the U.S. Army Corps of Engineers to begin construction.
District officials say obtaining the permit by the end of this year is critical because they’re at risk of losing a $3.5 million grant for construction from the California Department of Water Resources if the project is not completed by the end of next year.
“In all honesty, this project has to get built,” Erik Johnson, district engineer, told the board at the meeting on Tuesday. “It has to get built with the funding we have available, otherwise we risk losing the faith of the public.”
Sediment flowing into the man-made lake, which was formed by a dam on Sullivan Creek in 1854, has reduced its maximum storage capacity by nearly 30 percent from 850 to 600 acre-feet of water.
Unnaturally high rates of soil ero
sion due to development in the 25-acre watershed that drains into the reservoir is cited as one of the reasons for the rapid buildup of sediment.
The project would dredge the sediment to restore the additional 250 acre-feet of water storage. An acre-foot of water, or roughly 326,000 gallons, is often cited as being roughly equivalent to the amount used by one to three households on average per year.
A sediment forebay would also be constructed near the intake to allow for the periodic removal of sediment before it enters the main body of the lake, while berms would be strategically placed to improve the circulation of water in zones that are currently stagnant.
Any aesthetic or recreational improvements to the lake wouldn’t benefit the general public because the access is restricted mostly to the private homes that surround it, as evidenced by the numerous “no trespassing” signs posted along its shoreline.
However, TUD officials say the project is important because the lake is a key part of the water system that serves thousands of ratepayers in the City of Sonora, East Sonora, Jamestown, Mono Village, and Scenic View, in addition to the principal business and commercial districts in the county.
“I think the county and others have talked about public recreation on that lake, but that is really beyond the scope of this project,” said Ed Pattison, general manager of TUD. “It’s surrounded by private property… We would have to exercise eminent domain or buy it, but who’s going to pay for that?”
Pattison said the public will benefit from the project through increased water storage and reliability, improved taste and odor, and emergency water supplies.
One of the overarching concerns facing TUD is its reliance on a vulnerable wooden flume in the fire-prone Stanislaus River Canyon that moves water from upstream reservoirs to the rest of the district’s system and ultimately the taps of residents throughout the county.
Phoenix Lake would become the district’s main emergency water source if the flume burned.
The amount the reservoir can currently store would last an estimated 90 days, but the dredging project would increase that by about an additional 30 days.
The build-up of sediment over the years has also caused problems with water quality due to increased temperatures that promote the growth of vegetation in the lake, complicating the treatment process.
“Our core message is it’s a water supply, water quality project,” Pattison said.
Work on improving the lake began in 2004 when citizens formed a task force that spent six years researching options before producing a final report in 2010, which prompted the district to seek funding for studying and developing a project based on the group’s suggestions.
The Sierra Nevada Conservancy provided a $100,000 in 2011 for the district to develop a plan for restoring the lake, which helped it secure two additional state grants in 2014 and 2015 totaling $5.1 million for engineering design, environmental work, permitting and construction.
More than $1.7 million has been spent on the project up to this point, with TUD pledging to commit a total of $1.2 million to the overall cost through the completion of construction.