Tujunga Wash Greenway and Stream Restoration Project

Challenge

The Greenway was part of the Los Angeles River and Tujunga Wash Master Plan. While the initial goal was to create habitat, the project objectives quickly grew to include restoring some of the wash’s natural functions along the side of the flood control channel. Challenges during the design process included determining a strategy to restore natural stream function despite the environmental damage inflicted during channelization, and addressing community concerns given the close proximity of private homes to the channel. These concerns included liability and safety issues, such as the lack of visibility due to overgrown shrubs, which prolonged the permitting process.

Solution

Some of the wash’s natural functions were restored by creating a naturalized streambed, fed by an upstream diversion of up to 325,000 gallons of water per day from the flood control channel. This allows for natural filtration and infiltration after rain events. Community and safety concerns were addressed through public outreach and strategic timing of the construction to coincide with the dry season (April 15 - October 15). Five community meetings were held to get input from the neighborhood. To address concerns regarding vagrancy and vandalism, an 8-foot high fence was installed along some properties, as well as a new iron gateway that both marks the entrance to the Greenway and can be locked as a safety precaution. To increase visibility and reduce perceived threats, the maintenance team periodically limbs-up overgrown shrubs and trees.

• The 1.2-mile long, 50- to 60-ft wide Greenway creates 15 acres of riparian habitat through Los Angeles’ urban fabric, replacing a formerly barren right of way. Urban habitat patches such as this, directly impact species conservation and survival, as well as residents’ access to wildlife.
• Water to feed the re-created stream environment is diverted from 2 miles upstream of the greenway headworks through a gravity-fed pipe.
• 10-ft wide trails line both sides of the concrete channel. On the western bank, 85% of the trails are permeable, made of decomposed granite. These 2.4 miles of off-street, multi-use trails provide opportunities for recreation in a car-dominated neighborhood and connect to the regional trail network and bike routes.
• The site was divided into 8 geomorphic and ecological areas, with specific plant palettes for each area. 1,100 trees and 18,000 shrubs and vines were planted along either side of the wash – all 100% California native. Trees include walnut, laurel, ash, cottonwood, live oak, and willow species. 
• Interpretive signage educates the public about the Greenway’s water filtration and infiltration benefits.

• Ongoing education and outreach are necessary since the stream changes seasonally, and users need to understand what to expect regarding the look and odor of the natural system.
• In man-made streambeds, it is imperative to be able to remove sediment efficiently. To maintain intended infiltration rates, the top layer of silt needs to be periodically removed and the soil scored.

• The initial goal of this project was to create habitat in an urban settting. The wider impacts of the streambed project and its ability to influence and catalyze subsequent projects were not foreseen. Had the greenway been considered as a prototype, formal evaluation and data collection procedures could have been established, which would help to measure impact and improve future designs. 

• Real-time environmental monitoring is necessary for projects like this. Without any data, it is difficult to make habitat management decisions or to optimize the hydrological performance.

Project Team

Project Partners: Los Angeles County Flood Control District, Mountains Recreation and Conservation Authority, Los Angeles County Department of Public Works
Lead Agency and Designer: Mountains Recreation and Conservation Authority, Santa Monica Mountains Conservancy
Engineering: Los Angeles County Department of Public Works Flood Control District
Construction Management: Mountains Recreation and Conservation Authority, Los Angeles County Flood Control District
Construction: Los Angeles Conservation Corps, Powell Construction, Terra Form, W. A. Rasic Construction Company

Role of the Landscape Architect

The Mountains Recreation and Conservation Authority initiated the project with the Los Angeles County Department of Public Works, gathered funding from a variety of local and state sources, designed the landscape, created and bid on construction documents, installed the project, and continues to oversee the on-going monitoring and maintenance.