Army Corps outlines Whittier Narrows Dam safety overhaul, warns of local closures and summer town hall

The Army Corps of Engineers told the Montebello City Council on June 10 that it has fully funded a major safety and modification project at Whittier Narrows Dam intended to extend the structure's service life and reduce catastrophic flood risk. Aaron Smith, speaking for the Corps' dam safety program, said the project's scope includes a downstream drainage system and a stepped concrete armor to protect the dam from erosion and rare overtopping events.

Smith said the Corps is proceeding because, while catastrophic storms of the magnitude that would threaten the dam are unlikely in any single year, the consequences would be severe. "This dam was built over 70 years ago," he said. "We're going to install a large French drain at the downstream end of the dam that will relieve pressure and block sands from eroding, and we'll put a stepped concrete armor on the downstream face to dissipate energy if water goes over the crest." He added the design is a tried‑and‑true solution the Corps has used on other high‑risk dams.

Why it matters: the Corps told council members the modifications are intended to reduce the chance of foundation erosion and to prevent the sort of backward erosion that would allow a catastrophic release of impounded water. The Corps estimated the watershed and infrastructure protected by Whittier Narrows extends well beyond Montebello and could have national significance in a worst‑case failure scenario.

Construction timing and local impacts: the Corps said a contract was awarded in March and that construction could start as early as October and as late as December. The work requires staging and working areas that will be closed to the public. Corps staff said most construction will occur during business hours Monday through Friday to limit nighttime disturbance, but some night work is expected for utility and alignment shifts.

Local roads and trails: Smith cited two road segments that cannot be armored without changing the road profile: Lincoln Boulevard and the highway crossing (State Route 19/Rosemead Boulevard). The Corps said it will raise those crossings so they will not be overtopped in future extreme events; that will require temporary traffic realignments, narrower lanes and occasional night closures for shifts. Several trails and equestrian routes across the dam will be closed during construction; the county is planning restoration once the work is complete. The Corps also announced the permanent closure of Rooks Road, a municipal cut‑through adjacent to a sports arena, because it is incompatible with the long‑term dam modifications.

Parks and public spaces: portions of Streamland Park and a nearby golf course will be closed during the work to allow installation of the French drain in the toe of the dam; the Corps said both will be reopened when work concludes. Corps staff said the site will be secured with temporary fencing and on‑site security during construction.

Coordination and questions from council: Council members pressed the Corps and city staff on how Lincoln Boulevard projects (including a recently awarded Clean California grant and other local improvements) would be coordinated to avoid duplication or loss of city investments. City staff (Caesar) told council the city has been engaged with the Corps and other utilities for more than a year and will continue to coordinate relocations, lane shifts and scheduling. When Council asked whether trails or youth engagement opportunities could be built into outreach, the Corps said it had discussed possible school tours and would work with the El Rancho Unified School District and local partners.

Public outreach: the Corps said it plans a town hall at Montebello Senior Center on June 30 and will maintain a project website and regular office hours for community updates.

What's next: construction staging and periodic closures will begin once permits and other preconstruction work are complete; the Corps reiterated it designed the work to maintain safety during construction and to limit but not eliminate nearby impacts. The city and the Corps will continue to coordinate on lane shifts, trail closures and grants that could overlap with the work.

Source: Presentation and Q&A at the Montebello City Council meeting, Aaron Smith, Army Corps of Engineers (Whittier Narrows Dam safety program).