USACE prepares fill plan for Isabella Lake as construction wraps up

U.S. Army Corps of Engineers Sacramento District
Published Feb. 3, 2023
Updated: Feb. 3, 2023

The U.S. Army Corps of Engineers Sacramento District is preparing to request a deviation from the operating restriction at the Isabella Dam in Lake Isabella, California, to implement a plan to fill the lake up to its pre-construction volume of 568,000 acre-feet, or gross pool, when sufficient precipitation and snowpack occur.

The lake has been restricted to 361,000 acre-feet since dam safety issues were identified in 2006. Since the dam’s construction in 1953, USACE has limited the lake’s volume to 170,000 acre-feet in the winter (Nov. 1 to Jan. 31) for both flood conservation space and to accommodate runoff from the Sierra Nevada snowpack in the spring.

(See “Isabella Lake Reservoir Water Levels” table below.)

“Our goal is to have the Fill Plan and Deviation Request approved by USACE leadership before April 1, 2023,” said Mike Ruthford, a Lead Engineer with the South Pacific Division Dam Safety Production Center. “This would allow us to proceed with reservoir filling and project monitoring above the operating restriction and potentially up to gross pool depending on snowpack volume.”

The deviation request, when approved, would grant the district a temporary exemption to the operating restriction of 361,000 acre-feet, so USACE engineers can monitor dam performance and validate the dam safety work conducted during the Isabella Dam Safety Modification Project.

“The operating restriction won’t be permanently removed until the Fill Plan has been successfully executed and USACE officially changes the dam’s safety rating,” said David Serafini, a Senior Engineer with the USACE Dam Safety Modification Mandatory Center of Expertise.

However, the plan to fill the lake is heavily dependent on snowpack. Snowpack levels are currently above normal, but uncertainty remains.

“The Fill Plan sets reservoir filling rate targets, but since we can’t control snowmelt volume, we will have to make adjustments in real time,” said Ruthford. “We will coordinate these adjustments with downstream water users as we’ve always done.”

The Sacramento District will continue to provide updates, including photos and video, from Isabella Lake as dam safety construction wraps up. To stay up to date on the project, please visit Photos and video are regularly posted to Facebook and Twitter at the links below.

Completed in 1953, Isabella Dam is located approximately 40 miles northeast of Bakersfield. The reservoir is impounded by two earthen dams on the Kern River and Hot Springs Valley. Today, Isabella Lake and its dams reduce flood risk for Bakersfield and the surrounding region and is a primary water source for water users throughout Kern County. The Isabella Lake Dam Safety Modification Project addressed overtopping, seismic and seepage issues identified with Isabella Lake’s Main and Auxiliary dams to reduce the likelihood of dam failure. Construction of the dam modifications began in 2017, and the project achieved substantial completion in 2022.

Isabella Lake Reservoir Water Levels

Water Level



Gross Pool

568,000 acre-feet

Maximum water level under normal (non-flood) conditions. USACE will attempt to raise the lake to gross pool starting April 1, 2023.

Restricted Pool

361,000 acre-feet

Maximum water level allowed during the Isabella Dam Safety Modification Project. This operating restriction has been in place since 2006.

Flood Conservation Pool

170,000 acre-feet

Maximum water level allowed from Nov. 1 to Jan. 31 every year (regardless of construction). This is to accommodate snowpack runoff from the southern Sierra Nevada and guard against downstream flooding.



Jeremy Croft

Release no. 23-006