Whittier Narrows Dam Safety Modification Project

Background

Whittier Narrows Dam was constructed in 1957 by the U.S. Army Corps of Engineers as a flood-risk management project and is located 11 miles east of downtown Los Angeles. The dam provides flood-risk reduction to more than 1.2 million people.

Following Hurricane Katrina, the Corps dramatically overhauled its process for prioritizing dam and levee evaluations and modifications to better account for potential impacts to the population protected by the structures. The Whittier Narrows Dam Safety Modification Study was subsequently initiated to evaluate the risk to the population, which extends from Pico Rivera to Long Beach.

In May 2016, the Corps placed Whittier Narrows Dam in the agency’s highest risk category, “very high urgency,” when it became clear three potential failure modes threatened the downstream population: the premature opening of the San Gabriel River Spillway gates, erosion resulting from water piping through the foundation of the earthen dam and overtopping during an extreme flood. 

The Modification Project

Whittier Narrows Arial View

The Whittier Narrows Dam Safety Modification Study was completed in June 2019. The project went into the design phase in October 2019. 

Modification of the San Gabriel River Spillway gates, which was one of the biggest factors driving the dam’s reclassification rating change, was completed in December 2020. Utility contracts were awarded in late summer 2021 and construction contracts for the dam modification are anticipated to be awarded in 2022.

The modifications to prevent the earthen dam from eroding or failing if overtopped include placing soil cement on the crest and downstream slope of the embankment and improving the seepage control system with features like trench drains and graded filter/drainage blankets.

Legg Lake

The recommended plan reduces project risk to below individual and societal risk guidelines by addressing the two actionable failure modes: backward erosion piping and overtopping. The features are currently contained within four contracts:

• Contract 1: Utility Relocations near San Gabriel River
• Contract 2: Environmental Commitments
• Contract 3: Crest and downstream slope hardening, trench drain, parapet walls, Rosemead Boulevard road modification, relocation/protection of about 20 utilities
• Contract 4: Lincoln Avenue road raise and shift, relocation/protection of up to 31 utilities.

 

For detailed physical data visit the Reservoir Regulation pageAdditional information on Whittier Narrows Dam and Reservoir can be found in the Whittier Narrows Basin Master Plan.

 


 

How this will affect the surrounding community

Maintenance Activities
 

The remainder of the dam safety project is anticipated the have the following impacts during major construction, which is slated for 2025-2029:

 

TRAFFIC CHANGES

  • Lincoln Avenue
  • Rosemead Boulevard

TEMPORARY

  • Noise, vibration, dust
  • Impacts to bike riders, horse riders, walkers

CLOSURE OF

  • Streamland Park 
  • Golf Course 
  • Sports Arena Drive 
  • Bicentennial Park

The Corps also engages in routine maintenance activities within the operational areas of the reservoir year round to maintain the operational capacity of the project. As congressionally appropriated funding allows, the Corps works to upgrade aging structures and systems. Annual maintenance activities at U.S. Army Corps of Engineers operated dams include grading of access roads, vegetation removal and an annual safety inspection. In addition, the control house, gates, and all mechanical and electrical equipment are checked at each dam to make sure they are functioning in accordance with the Dam Operations Manual. Graffiti removal, clearing of debris and sediment, and additional repairs are regularly performed to maintain the facility. 


Review Upcoming Proposed Actions

To review public notices on our upcoming proposed maintenance activities please visit the Public Notice postings page or click the “Public Notice” link found in the navigational side bar.


Questions, Concerns, Comments?

Let us know by filling out the comment form or click the “Contact” button in the navigation bar and choose Asset Management (Real Estate | Recreation) or Asset Management (Facility Operations | Maintenance) as the recipient.


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