Making the Most of Small Spaces

Two flood-control projects have collateral benefits

Lining rivers with reinforced concrete has been a common way to prevent flooding. It has allowed cities to grow virtually to the edges of the channels, sometimes within a few feet. But it has also led to unintended consequences through the years.

On rainy days in Los Angeles County, for example, up to 10 billion gallons of water can flow from storm drains into the channelized river system, out onto beaches, and into the Pacific Ocean, according to California’s State Water Resources Control Board. On dry days, the amount can be about 100 million gallons. The water carries vast amounts of trash, oil, chemicals, and other pollutants with it.

The Los Angeles River is on California’s 303(d) list, with three promulgated total maximum daily loads (TMDLs) for trash, nutrients, and metals, according to the Los Angeles County Department of Public Works. The 303(d) list identifies impaired waters that exceed, or are expected to exceed, the maximum allowable amount of a single pollutant in a body of water.

And as development has increased, so have impervious surfaces. In the San Fernando Valley, these force stormwater into storm drains instead of allowing it to infiltrate into the San Fernando Valley Groundwater Basin and help supply the area’s chronic need for water.

According to The River Project, a non-profit organization that advocates for the protection of the county’s natural resources and for the responsible management of its watersheds, before the city was developed and the river system channelized, only about 8% of the area’s rainfall ended up in the ocean. Today, nearly 80% does.

Photo: LA County Department of Public Works

Construction of underground treatment units

Within the last 20 years or so, community leaders, elected officials, public agencies, concerned citizens, and environmental groups have been searching for ways to protect the watershed from floods and, at the same time, solve the problems created by the channel system. They have been transforming neglected lots and paved easements into pocket parks landscaped with native plants and linking the parks with bicycle and footpaths. In Sun Valley, an area within the San Fernando Valley with the worst of both worlds—impervious surfaces and no storm drain system at all—they created a massive infiltration system under a public park.

The Tujunga Wash Greenway and Stream Restoration Project and the Sun Valley Park Project are two exciting and very different projects that have been completed recently in the county. They’re on a small scale because of the amount of development in both areas, but their principles can be replicated any number of times for a large-scale effect.

Although neither project is related to the Los Angeles River’s TMDL problems, they help indirectly, says Vik Bapna, manager of the Los Angeles River and Harbors Watershed for the County of Los Angeles Department of Public Works, who has worked on both projects. If water doesn’t reach the river, he says, neither do the pollutants it carries.

The projects also provide water and create beauty for their communities.

“Both projects meet community needs,” he says. “I think it’s of great value to bring anything to the community that they can enjoy.”

Sun Valley Park Multiuse Project
While the Sun Valley and the Tujunga watersheds are low-lying, highly urbanized and industrial areas south of the Hansen Dam, their stormwater situations have been completely different. Before the park project, Sun Valley’s 4.4-square-mile (2,800-acre) watershed had no stormwater drainage system at all.

“At its iconic intersection at San Fernando and Tuxford, even a light rain would cause serious flooding,” says Rebecca Drayse, director of TreePeople’s Natural Urban Systems Group and part of the team that helped Los Angeles County develop a watershed management plan for Sun Valley. Instead of infiltrating into the aquifer, the stormwater—and the pollutants it carried—would find their way to the Los Angeles River system.

Photo: TreePeople

Swale at southern end of park, landscaped with native plants. Stormwater filters through the swale into an aquifer.

The watershed has sandy soil and a large number of gravel pits, as well as open areas such as easements, public parks, and schoolyards, all of which have tremendous potential for recharge, Drayse says. These pervious surfaces were the keys to the watershed plan and to its pilot project at Sun Valley Park.

The Los Angeles County Department of Public Works conceptualized, designed, and built the project. Stormwater flows into catch basins at the northern end of Sun Valley Park, then through underground treatment units and infiltration basins and into the aquifer. At the southern end of the park, stormwater flows through swales into the aquifer.

In an average year, the facility puts approximately 30 acre-feet of water in the groundwater from the surrounding neighborhoods, says Bapna. That’s almost 10 million gallons.

Construction began in 2004 and ended in 2006, he says. The total cost of the project was $7.1 million.

History. Development in the area had caused the watershed’s flooding and stormwater pollution problems, Drayse says, and the question was how to solve the problems given that development. In 1998, the Sun Valley Watershed Stakeholders Group, which includes TreePeople; local businesses; the school district; federal, state, and local agencies; and property owners, held its first meeting. The group discussed solutions and asked whether it was possible to retain stormwater runoff to increase the groundwater supply.

TreePeople had been working on a number of multipurpose capture projects in Los Angeles to demonstrate their viability, Drayse says. In the late 1990s, the group installed a cistern, a drywell, a vegetated swale, and depressed lawn areas on one single-family property. Working together, these features are capable of capturing the rain from a 2-inch storm. Some is stored in the cistern and the rest soaks into the ground within 72 hours. 

The solution to Sun Valley’s stormwater problems, TreePeople believed, was not to build yet another storm drain system, but instead to make “lots of little changes.”

Feasibility studies showed that an existing park could gain recreational improvements as well as solve the flooding problem, capture stormwater, and recharge the aquifer, she says. They also determined that there were enough pervious spaces in the watershed for numerous projects that could eventually increase local groundwater supplies and reduce the area’s need for imported water.

“That’s why the county and TreePeople received grants from the CALFED Bay-Delta Program,” says Drayse, who managed TreePeople’s involvement. The program is a collaboration among state and federal agencies to improve California’s water supply and the ecology of the San Francisco Bay/Sacramento-San Joaquin River Delta.

With the help of its stakeholders, the county developed the watershed management plan, Drayse says. It includes more than a dozen projects. The first to be built was the Sun Valley Park Multiuse Project.

The Project. The project itself wasn’t complicated, Drayse says. “It was just thinking about things differently, working in a different way than government often has. ‘The way we’ve always done it’ hasn’t worked and has had unforeseen consequences.”

Photos: LA County Department of Public Works

The Tujunga Wash before work was started

At the northern, upstream side of the 23-acre park, water flows into 13 catch basins, Bapna says. From there, pipes lead through a series of three underground treatment units. One unit is designed to extract metals. The other two are hydrodynamic separators, which are installed in parallel. Both take out oil, trash, grease, and suspended solids.

The water is tested 10 feet below ground to be sure it’s within acceptable standards, then piped into one of two underground infiltration basins. These floorless concrete structures allow the treated water to soak into the ground. They cover about 1.5 acres under the park.

At the southern end of the park, a different system has been used, Bapna says. Reverse-grade piping in the curbs sends water runoff to swales at the edge of the park. Stormwater filters through the swales, which have native landscaping, directly into the aquifer.

In addition, the park has new aboveground amenities, says Drayse, including a new soccer field, new turf for existing baseball fields, and sports lighting.

Stakeholder Groups. A large part of the work was getting agreements, funding, and logistics in place, Drayse says.

The County of Los Angeles Department of Public Works Flood Control District (DPW) funded $1.6 million toward the development of the watershed plan, Bapna says. The district designed and built the project and will maintain those parts of it that lie outside the park. The DPW has also committed to providing approximately $42 million to the project.

The DPW hadn’t worked on a park before, he says. One of the lessons the organization learned was that every park has its own charter, and every project has to meet the charter’s terms: “It was just a matter of making sure we didn’t do things that didn’t meet the charter.”

The State Water Resources Control Board provided a $220,000 Clean Beaches Initiative grant. This grant focuses on reducing health risks and increasing public access to clean beaches and is funded by California’s Proposition 13.

CALFED awarded the DPW a $430,000 grant for the development of the watershed management plan. It considers the project a model that could reduce Southern California’s dependence on imported water, some of which is imported from the Bay-Delta.

CALFED also gave TreePeople $350,000 for its education and outreach programs, which included quarterly newsletters, community meetings, and classroom materials for Sun Valley students.

The City of Los Angeles Bureau of Sanitation maintains the water treatment system, and the city’s Recreation and Parks Department maintains the park’s aboveground amenities, according to information from the county.

TreePeople contributed a $473,000 Murray-Hayden grant (Proposition 12 money that funds parks and recreation projects in underserved communities). The grant funded the recreational enhancements and signage that tells park visitors about the stormwater facility.

“Our contribution was the improvement of the ball fields, soccer lighting, and the educational signage,” Drayse says. Those were important pieces of the project, and the county’s funds could be used only on flood control and stormwater management. TreePeople also performed a tree audit to assess opportunities to plant more trees in the area around the park.

Community members were united in wanting to solve the flooding problem, but they did have some concerns. The main one was to get the project done quickly, because the work affected recreation in the park. Two ball fields were affected during construction, Bapna says.

“During the development of the plan there was a lot of outreach,” he says. “Stakeholders met as much as once a month.” They still meet on a quarterly basis.

Results. The project is a great asset, Bapna says. One immediate result has been community beautification. Other results will take some time to come in, probably at least five years.

“It’s a great place to evaluate different technologies,” he says. “We’re doing testing to see how the treatment BMPs work. Based on the BMSs [building management systems] in place, we believe it should be very clean.”

The Tujunga Wash Greenway and Stream Restoration Project
The Tujunga Wash runs south from the Hansen Dam, across the San Fernando Valley, to the Los Angeles River just north of the Santa Monica Mountains, 9 miles away.

Photo: LA County Department of Public Works

Brett Gate at the Victory Blvd. (south) entrance to park

Before it was lined with concrete, the wash was dry most of the year, although some water did flow underground at times, Bapna says. On rainy days, stormwater overflowed its banks and spread across the Tujunga Watershed, eventually percolating into the San Fernando Valley aquifer.

The aquifer used to provide water for most of the San Fernando Valley, says Elizabeth Jordan, project manager for the Mountains Recreation and Conservation Authority (MRCA), a local government public entity whose mission is to preserve and manage local open spaces and wildlife habitat. But as the area was developed, the flooding and erosion became a problem. The Army Corps of Engineers channelized the wash in the early 1950s.

“Very little water penetrates now,” Jordan says. Instead, it—and the pollutants it carries—flow into the Los Angeles River and out to the ocean. In addition, San Fernando Valley residents have to import their water.

History. Two people at MRCA began looking at ways to keep water out of the channel and allow it to infiltrate into the aquifer around 1993 or 1994, says Jordan, who became project manager in 2001.

In the late 1990s, Los Angeles County was doing the same, Bapna says. The county got together with the MRCA and came up with an ingenious design: a stream that runs a mile along the west bank of the channel. At its northern, upstream end, a half-mile-long pipe connects the channel to the stream. At its southern end, any water that hasn’t infiltrated flows directly back into the channel. Water also infiltrates through the sandy soils landscaped with native plants on the easements on both sides of the channel.

Photos: LA County Department of Pubic Works

A close-up of the stream (top). The drain at the southern end of the stream at Victory Blvd. (bottom).

“The stream can take up to 25 cubic feet of water out of the channel per second,” Jordan says. That’s as much as 325,000 gallons of water a day. Once it’s recharged, it can supply water to 760 families of four for a year.

The water will be good quality, too, says Bapna. “The groundwater in this area is about 200 feet below the surface, and the deeper it is, the better for removing pollutants.”

The project cost $7 million and was finished in fall 2007.

How It Works. The project runs from Vanowen Street to Oxnard Street in the community of Valley Glen. At the northern end, water flows out of the channel through a grate that keeps trash out, then into a pipe that leads to the stream, Jordan says.

A gate regulates the amount of water flowing into the stream. In the summer it will be wide open, but it was closed during the first heavy rains of the 2007–2008 winter season. Operators are taking a cautious approach, Jordan says, and will do some calibration tests. The stream will handle surface runoff year round.

The water flows downstream for half a mile inside the pipe and spills into the new, mile-long streambed, which is lined with stones and native plants. Over the course of the stream’s slightly meandering mile, water filters through rocks, plant roots, and the sandy soil into the aquifer.

“We were basically trying to mimic what the wash would be if it wasn’t concreted,” says Bapna.

Near the beginning of the stream, water flows through a low stone structure, which keeps much of the sediment from the channel out of the stream. A huge amount of sediment comes in, Jordan says, especially during the first rains of the season. Some sediment has widened and slowed the flow of the stream in places. The MRCA will clean it out periodically, but she doesn’t expect the stream to return to its pristine form.

“It’s acting like a stream,” she says. “It’s changing itself.”

The stream is interrupted once, where it reaches a headwall and enters a pipe that takes it under a street. It becomes a stream again on the other side of the street and ends at a grate. Water that hasn’t infiltrated at this point will flow back into the channel cleaner than when it entered the stream, Jordan says.

At this point, the world’s largest mural, 13 feet high and almost half a mile long, graces the channel. “The Great Wall of Los Angeles” was painted in 1974 by artist Judy Baca and hundreds of at-risk youth, and is in the process of being restored.

Stakeholder Groups. The various stakeholder groups in the project had different interests, Bapna says, but mostly were concerned with what could be done and how much was possible to provide the most benefit. “The land is limited,” he says. “The goal was to provide multiple benefits.”

While the Army Corps of Engineers built the channel itself, the Los Angeles County Department of Public Works Flood Control District owns and maintains the right of way all along the channel, including the 9 acres in this project, Jordan says.

The county provided $1.5 million to build the stream and install the landscaping, which took about a year and a half. It also gave the MRCA $3 million in a Proposition A Parks and Recreation bond to restore open spaces.

According to information from the county, the state, and the MRCA, the State of California Resources Agency awarded the DPW a $1.9 million Proposition 12 grant to plant native vegetation, provide public access, and develop paths and rest areas, as well as to install irrigation and interpretive signage on the easements. The California Department of Water Resources provided the MRCA with a Proposition 13 grant of $525,000 to provide riparian habitat and recreational access.

When work began on removing the asphalt paving on the easements, workers discovered unexpected obstacles underground: huge pipes and chunks of asphalt up to 20 feet in diameter. They took out what they could, Jordan says, but they had to leave some of the pipes and the asphalt in the ground.

Both easements were landscaped with native plants. They feature hiking and bike paths and, on the east side, a grassy area with shaded picnic tables and interpretive displays. Workers also installed custom wrought iron gates at the entrance to the picnic area, which take it from an ordinary walking path to something that is much more of an addition to the community, Jordan says.

“The county really went far and beyond what it usually does,” she says. “We did the same.”

The MRCA’s landscape department designed the landscaping on the two 60-foot-wide easements. Because the project is part of the LA River Master Plan, the MRCA followed its planting plan and also made sure to maintain flood control access. The MRCA will maintain the stream and the landscaping, which includes clearing out invasive plants.

The Valley Glen Community Council was also involved. This was the first project of its kind in a very urban setting, Bapna says. One of the challenges in carrying it out was that the easements back onto a large number of homes.

“We had, I believe, at least four or five big meetings and got very good input from the community. Part of the discussion early on was that the community was a little apprehensive that new people would be in their backyards.”

Community members were taken to other project sites and shown how they functioned, he says. That relieved many people, and in addition, the project was mitigated by building 8-foot-high fences along the property lines.

“It’s always good to get buy-in from the community,” says Bapna. “The biggest thing is to have the community working with you.”

The River Project undertook a comprehensive study of the Tujunga Watershed, and provided input at the stakeholders’ meetings.

Results. A lot more people are using the easement and are happy about it being there, Bapna says.

“It’s a great resource. Instead of looking at a channel, you’re looking at a picturesque opportunity where you can walk and stroll. I think we’ve brought a jewel back into the community.”

The Tujunga Wash is just a small step, says Jordan. Already the Army Corps of Engineers is talking about doing the same thing farther up the channel.

“It’s important to use leftover urban spaces like these,” she says.

Author's Bio: Janet Aird is a California writer specializing in agricultural and landscaping topics.