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VIDEO: What community members can expect during the modification project

NEW: Draft Supplemental Environmental Assessment and Draft 404(b)(1) Analysis NOW AVAILABLE for public review and comments

The U.S. Army Corps of Engineers announces availability of the Draft Supplemental Environmental Assessment and Draft 404(b)(1) Analysis for public review and comments. The SEA supplements the 2019 Environmental Impact Statement for the Whittier Narrows Dam Safety Modification Project. Additional engineering investigations initiated after completion of the EIS necessitated the below changes to the project.

The Whittier Narrows Dam Safety Modification Project SEA and supporting materials can be reviewed at:


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 and work has begun to address deficiencies identified. Issues with the San Gabriel River Spillway gates have been addressed, which was one of the biggest factors driving the dam’s risk the public. The remaining work is 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.

Minor construction started in 2021, and larger construction contracts for the dam modification are anticipated to be awarded in 2025 following completion of design work.  Major work is anticipated to take between four and five years to complete.

Legg LakeFor 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:



  • Lincoln Avenue
  • Rosemead Boulevard


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


  • 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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