USACE Identified Restoration Sites

During their preliminary study of Arroyo Seco ecosystem restoration (2005-2017), the U.S. Army Corps of Engineers identified nine potential restoration sites within the lower portion of the watershed. These sites were selected to represent a diverse range of conditions found in the 11-mile reach extending from the Angeles National Forest border to the confluence with the Los Angeles River.

The specific restoration sites are:

Site 1 – Hahamongna Area: A roughly 208-acre site located within Hahamongna Watershed Park in Pasadena, characterized by a broad sediment plain and a diverse matrix of native scrub and riparian habitats.

Site 2 – Flint Wash: An approximate seven-acre area encompassing a 3,200-foot segment of Flint Wash, an unimproved channel that joins the Arroyo Seco just upstream of Devil's Gate Dam.

Site 3 – 210 Freeway near Oak Grove Drive: A 21-acre segment downstream of Devil's Gate Dam containing some of the only natural stream bottom found in the lower reach, supported by water released from production tunnels.

Site 4 – Brookside Area: A 276-acre reach that bisects the Brookside Golf Course and passes the Rose Bowl; it currently features a large, trapezoidal concrete-lined channel with minimal natural habitat.

Site 5 – Lower Arroyo Seco Park: A roughly 106-acre site in Pasadena's Lower Arroyo Park where the main channel is concrete-lined, but is flanked by established low-flow alternative streams with riparian habitat.

Site 6 – South Pasadena Island: A 69-acre undeveloped, isolated area situated between the SR-110 and the Arroyo Seco channel, supporting annual grassland and oak woodland communities.

Site 7 – Arroyo Seco through Los Angeles: A 76-acre, 3.4-mile segment stretching from York Boulevard to the I-5, which is currently fully channelized and tightly constrained by urban development.

Site 8 – Sycamore Grove Park: An eight-acre public park in northeast Los Angeles where the original stream bottom was filled, and the North Branch tributary is currently confined to a storm drain.

Site 9 – Rainbow Canyon: A 5.8-acre undeveloped hillside woodland park owned by the Santa Monica Mountains Conservancy, featuring a remnant stream bottom that is currently disconnected from surface flows.

These sites were evaluated for their potential to provide ecosystem restoration benefits, such as removing fish passage barriers, eradicating invasive species, and restoring native riparian and wetland habitats.