In 2023, Hell Hole Reservoir spilled uncontrolled as water exceeded the spillway’s fixed elevation. PCWA’s upgrades will add crest gates, increasing storage and allowing for controlled releases to better manage supply and environmental flows. Photo courtesy of Placer County Water Agency

AUBURN, CA (MPG) - At its Thursday Feb. 13 meeting, the Placer County Water Agency (PCWA) Board of Directors approved a $5.8 million contract for the Hell Hole seasonal storage increase project, adding to the capacity of the Hell Hole Reservoir so it can store more water during wetter winters.

“This is a crucial and timely adaptation of local resources for Placer County residents, in the near and long-term future,” said PCWA Board Chair Robert Dugan. “By increasing the size of an existing reservoir, more water during wet winters can be saved for summer use without the cost of building a new reservoir.”

Storage at Hell Hole Reservoir will increase by approximately 7,600 acre-feet, enough water to supply more than 10,000 households in Placer County. The contract was awarded to K.W. Emerson, Inc. of San Andreas.

Increasing the capacity of Hell Hole also has other benefits. A direct outgrowth from PCWA’s Middle Fork Project relicensing effort, this project will allow greater control of water in wetter years and provide environmental benefits to aquatic species in the Rubicon River through pulse flows and increased instream flows. Water then can be recovered at the Agency’s American River Pump Station and Folsom Reservoir, located about 40 miles downstream of Hell Hole Dam.

To be completed in time for winter 2027, the total project cost is anticipated to be just over $10 million, funded by energy sales from the Middle Fork Project hydroelectric power generation.

The project focuses on improvements to the Hell Hole Dam spillway. The existing spillway is currently “unregulated”—it spills whenever surface water elevation exceeds 4,630 feet, the elevation of the dam’s overflow weir – and thus, PCWA cannot control spill timing, duration, or flow rate as a result.

Each winter, snowfall blankets the Sierras, eventually melting and flowing into reservoirs like Hell Hole, pictured here. By increasing its storage capacity by 7,600 acre-feet—more than 2.4 billion gallons—PCWA is ensuring that more of this criticalwater supply is captured and available when it’s needed. Photo courtesy of Placer County Water Agency

The spillway modifications will include the installation of 18 pneumatically controlled crest gates to allow the control of potential flow as well as increasing the elevation of the weir by 3 feet to 4,633 feet.  Besides offering control of the spillway, the construction increases the reservoir’s capacity by about 7,600 acre-feet – more than 2.4 billion gallons.

In other business, the board approved the next steps for the Aeolia Drive Sewer and Water Replacement Project by approving a cooperative agreement between PCWA and the City of Auburn for the project’s design and construction. PCWA’s portion is estimated to be $700,000.

Along Aeolia Drive, aging steel water mains will be replaced at the same time that the City of Auburn upgrades 1,320 linear feet of sewer pipes, increasing reliability for both systems. Work is expected to start during Spring 2025.

About PCWA Placer County Water Agency (PCWA) is the primary water resource agency for Placer County, California, with a broad range of responsibilities including water resource planning and management, retail and wholesale supply of drinking water and irrigation water, and production of hydroelectric energy.