Corps identifies selected Isabella Lake Dam modernization plan

Public Affairs Office
Published Nov. 19, 2012

SACRAMENTO, Calif. (Nov. 13, 2012) – The year was 1953.

It began with the inauguration of Dwight D. Eisenhower as President of the United States; IBM unveiled its first commercially available scientific computer – the 701 – larger than many of today’s office cubicles; and by March, Jonas Salk had announced his polio vaccine.

It was also in March of 1953 that the new Isabella Lake main and auxiliary dams were completed after five years of construction, and began serving Kern County and the surrounding cities with flood risk management, irrigation and hydroelectric use.

Nearly 60 years later, they continue to serve those purposes, having helped prevent flooding in downstream communities at least 18 times. But today, Isabella Lake’s dams need an upgrade. A Corps-wide survey of its dams in 2005 put Isabella Lake Dam near the top of its list of highest at-risk dams. The Corps identified significant hydrologic, seismic and seepage issues.   

Both dams lack the filters and drains now understood to be necessary for safely dealing with the seepage that is normal to earthen dams like Isabella’s; the auxiliary dam sits on an active earthquake fault; and the current spillway is too small to safely route the amount of water we know now could come Isabella’s way in a rare, massive storm.

The Corps’ Sacramento District began studying how to address those problems and modernize the dams in 2006. In November 2012, after six years of study, the district presented its solution.

The selected plan will raise the height of both dams by approximately16 feet; add drainage and filters to help maintain the integrity of the dams; and construct a new emergency spillway to work with the smaller spillway already in place. Additionally, the Borel Canal, which runs through the auxiliary dam, will be realigned around the dam, and about one mile each of highways 155 and 178 will be relocated to accommodate the higher dam elevation.

While the dams will be raised nearly two stories, it won’t be to store additional water.

“The purpose of raising the dams is to temporarily store more water in the reservoir only when very large, very rare storm events occur,” said Mike Ruthford, technical lead for the Isabella Lake Dam project.

Together, the modifications efficiently address each of the problems facing the dam, while minimizing the project’s impact to the communities that surround it.

“We’ve studied many alternatives to arrive at the best solution for the dam and the public,” said John Menniti, Isabella Lake Dam project manager. “We’ve determined this to be the best solution.”

Public input helped shape the solution. A total of 435 comments from residents, businesses and agencies helped develop and refine the Corps’ preferred plan, providing additional knowledge, history and potential environmental concerns to project staff.

“It is very beneficial to have local and community input on the project,” Menniti said.

One of the major concerns expressed throughout the course of the study is that the communities in the Kern River Valley would be significantly impacted by a reduced lake level for extended periods. As a result, the plan calls for the in-water work requiring a lower lake elevation to be completed during fall and winter 2020, wrapping up before spring 2021 to help avoid lower lake levels during the peak recreation season. The lake levels are naturally lower during the winter months.

“There will be some short-term inconveniences, but the whole project will be greatly improved from a safety standpoint upon completion,” Menniti said.

The Corps released the project’s final environmental impact statement in October 2012. Once the plan is approved by Corps headquarters, expected in December, the project will enter the design phase and is scheduled to begin construction in October 2014. The first task planned would be to complete the relocation of highways 155 and 178, and, with completion of the project scheduled in February 2022.