Arroyo Seco Ecosystem
Restoration Program
Frequently Asked Questions

1. Why is the Corps of Engineers involved?

Most people are aware of the U.S. Army Corps of Engineers’ flood control programs, but the Corps also manages one of the largest federal environmental missions: restoring degraded ecosystems; constructing sustainable facilities; regulating waterways; managing natural resources; and, cleaning up contaminated sites from past military activities.

USACE works in partnership with other federal and state agencies, non-governmental organizations and academic institutions to find innovative solutions to challenges that affect everyone – sustainability, climate change, endangered species, environmental cleanup, ecosystem restoration and more.

The Corps is jointly conducting the Arroyo Seco Ecosystem Program with local sponsors. The lead local sponsor is the County of Los Angeles Department of Public Works, and other local sponsors include the Cities of Los Angeles, South Pasadena, Pasadena and La Canada Flintridge, as well as the Arroyo Seco Foundation.

2. Will the restoration affect future flooding?

This Corps of Engineers’ is the national flood control agency and has a mandate to ensure that programs like the Arroyo Seco Ecosystem Restoration Program will not adversely affect flood conditions in any way. That means that the Arroyo program will provide at least as much flood capacity as is currently established and probably will improve flood protection in several areas.

3. Decision-making process? Public input?

The Corps is now working with the local sponsors to compile a package of restoration alternatives that will be the basis for the final AS Ecosystem Restoration program. The program will go through a rigorous review by the Corps’ leadership that will take about two years for approval. A full federal environmental review of the alternatives will be conducted during which the local agencies and the public will be able to provide input. If the program is approved by the Corps, congressional authorization will be sought and eventually federal funding as a major source of support for the program. Implementation of the program is likely to take five to twenty years.

4. What is the Corps’ goal?

The Corps’ goal is primarily ecosystem restoration and the restoration of natural processes in the Arroyo Seco Canyon, while maintaining flood protection. This includes stream and habitat restoration, improved conditions for fish and wildlife, and the conservation and enhancement of natural resources. Other goals, such as recreational opportunity, can be included in the project footprint.

5. Why leave out Hahamongna?

The Corps’ alternatives do not include restoration improvements in the Hahamongna basin because of the County’s sediment management program for Devil’s Gate Dam. In addition the Hahamongna basin has not been channelized and currently has good conditions or a natural stream-based restoration.

6. Will the plan affect recreational opportunities?

The restoration programs promises to dramatically improve nature-based recreation, such as hiking, bird-watching and natural appreciation along the entire stretch of the Arroyo Seco River. It will provide access to the stream and green space areas of the Arroyo, especially if cities adopt the principles of Arroyo River Parks, integrating the stream into local parks and the parks into the stream.

Some current active recreational programs, such as golf and archery and related parking facilities, may have to be modified to accommodate the stream and habitat restoration program.

ASF believes recreational uses and parking should be accommodated where possible, but priority should be given to ecosystem restoration.

7. Which alternatives does ASF recommend?

ASF supports the Corps’ primary goal of ecosystem restoration, which should be the guiding principle for the Arroyo Seco restoration program. We support the most comprehensive, science-based program feasible and urge local agencies and residents to think big about the possibility of a living stream flowing through the Arroyo again.

8. How many acres will be restored?

The habitat benefits and acreage restored depend upon the final program elements that have not yet been determined. The various alternatives can produce as much as 136 acres of restored riparian (streamzone) habitat.

9. Related to Los Angeles River restoration?

The Corps of Engineers is also conducting a massive $1.4 billion river restoration program with the City of Los Angeles, which includes a key project at the Confluence of the Arroyo Seco with the LA River. The Arroyo Seco Ecosystem Program will extend the activities and benefits of that program up the Arroyo Seco all the way to the San Gabriel Mountains.

Since the Arroyo Seco is a major tributary of the Los Angeles River, the Arroyo Seco program will provide tremendously beneficial habitat and wildlife enhancements to the Los Angeles River program. Recognizing this, the City of Los Angeles is a local sponsor of the Arroyo Seco since five miles of the stream flow through the communities of Highland Park, Hermon, Montecito Heights, Mount Washington, Cypress Park and Lincoln Heights to join the Los Angeles River near Elysian Park and Dodger Stadium.

10. What are the main restoration techniques?

  • Flood Plain Benching – full stream restoration; flood channel removal

  • Low-Flow Stream – a natural bottom stream near the existing or modified flood channel

  • RCB with Low-Flow Stream – A natural bottom stream flowing through the arroyo with an overflow buried concrete box culvert

  • Pools – ponds or wetlands that provide good conditions for fish and aquatic species

Arroyo Seco Foundation, 570 W. Avenue 26 #450, Los Angeles, CA 90065-1011
PO Box 91622, Pasadena, CA 91109-1622 (323) 405-7326 info@arroyoseco.org