Los Angeles River Fish Passage and

Habitat Structures Design

Channelization has decreased plant and wildlife diversity and quality in the Los Angeles (LA) River, disconnected the river from its floodplain and important ecological areas, and dramatically changed the river’s appearance and function. Significant funding in recent years has been earmarked for improving ecosystem benefits and recreation opportunities in the LA River, while maintaining existing levels of flood risk management. Consistent with these efforts, Stillwater Sciences is leading an integrated design team to develop channel modifications for a 4.8-mile reach of the LA River through downtown LA, including engineering design, CEQA/NEPA compliance, and permitting. In addition, Stillwater scientists performed a watershed-wide limiting factors analysis for steelhead to improve and synthesize our current understanding and support future restoration prioritization.

The Los Angeles River Fish Passage and Habitat Structures Design project will enhance migration corridors to the LA River soft-bottom reaches and upper tributaries to support native fish habitat needs at all life stages. The design will rely on existing and new hydraulic modeling that has demonstrated that current depth and velocity conditions are fish passage barriers at nearly all flows. Alternatives will be evaluated using criteria that will include flood capacity and steelhead passage, as well as other criteria proposed by stakeholders. 

Stillwater Sciences is leading the integrated design team in developing 60%-level designs for the channel modifications, performing the watershed-wide limiting factors analysis, and preparation of the environmental permitting. Stillwater is conducting an evaluation of existing information and lead coordination with the relevant permitting agencies and landowners through the congested downtown LA River corridor. Stillwater is advancing design concepts studied by the Bureau of Reclamation (BoR) that evaluated ecosystem features in urban flood control channels, particularly for steelhead migration and habitat. The Stillwater Sciences-led integrated design team, which includes the BoR, will perform hydraulic modeling to evaluate the low-flow flood control channel modifications ability to meet both steelhead passage and flood control criteria. The evaluation of designs will include criteria identified by relevant agencies during the initial outreach stage and through collection of existing information. The selected design will be advanced to the 60% level including design drawings, a basis of design report, and a preliminary Engineer’s Opinion of Probable Cost.

This project is supported by the City of Los Angeles Mayor’s Office, and is connected to the U.S. Army Corps of Engineers, Los Angeles District (USACE) 2016 LA River Ecosystem Restoration reach, known as the “Area with Restoration Benefits and Opportunities for Revitalization” (ARBOR) reach. The project also links to other biodiversity projects within the City of Los Angeles, the LA River watershed, and its upper tributaries (Arroyo Seco and Tujunga watersheds), and is consistent with the Los Angeles River Revitalization Master Plan (LARRMP). While focused on providing fish passage and habitat structures to address limiting factors to steelhead trout and other native fish, the project also addresses watershed-wide data gaps and opportunities to promote future projects and address other limiting factors to steelhead recovery from coast to crest.

Learn more about this project at the Council for Watershed Health’s website.


Stillwater's work on the LA River was recently featured in the LA Times.
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Los Angeles, California
Council for Watershed Health and City of Los Angeles
Wendy Katagi
  • U.S. Bureau of Reclamation (USBOR)
  • Southern California Coastal Water Research Project (SCCWRP)
  • National Marine Fisheries Service (NMFS), U.S. Army Corps of Engineers (USACE)
  • County of Los Angeles, California Department of Fish and Wildlife (CDFW)
  • U.S. Fish and Wildlife Service (USFWS)
  • Regional Water Quality Control Board (RWQCB)
  • Arroyo Seco Foundation (ASF)
  • Friends of the Los Angeles River (FoLAR)
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