As revitalization efforts reach a new stage on major sections of the Los Angeles River, including the creation of a new park at Taylor Yard, an old railroad station, a team of architects, landscape architects, and civil engineers are building off of the approved 2007 Los Angeles River revitalization master plan and 1996 county master plan guiding city, county, and Army Corps of Engineers work. The team comprised of Gehry Partners, OLIN, and Geosyntec — who are now working “pro-bono” and claim to have volunteered $3 million in time — is undertaking a multi-year, “data-driven” research effort to better understand the trade-offs involved in greening the concrete culverts that now define the Los Angeles River in much of its 51-mile span. Mayor Eric Garcetti and the non-profit River LA, formerly known as the Los Angeles River Revitalization Corporation, have lent support to Gehry’s new planning effort.
At a session at the ASLA Annual Meeting in Los Angeles, civil engineer Mark Hanna, Geosyntec, explained that the Los Angeles River is highly variable in its outflow, which makes it dangerous. In 2007, some 48,000 acre feet of water flowed out of the mouth of the river, while just two earlier, there had been 950,000 acre feet. “The variation is extreme.”
Along the course of the channelized river, there are different zones designed by the Army Corps of Engineers to move water rapidly through or hold it. “The channel morphs — there are culverts and also reservoirs. There are narrow box culverts and wider trapezoidal ones. There is a ‘soft bottom reach.’ And then the river widens out as it reaches the estuary by the sea.”
However, Hanna cautioned, even with all the engineering, there are still flood risks. The Los Angeles River was originally channeled because it used to meander and spread wide across the flat flood plain, damaging properties and even claiming more than a hundred lives. The current system has been designed to handle the 100-year storm in most parts, but there are still around 3,300 homes at risk if that level of storm hits the city.
While there are plans underway to return more ecological function to the river zone, there are more calls to make the actual concrete culverts green. “There’s 2,000 acres of open space that is now hot and unwelcoming.”
The problem is any greenery added to the culverts “create friction and therefore slows water down.” Hanna said replacing all the culverts with natural systems would in turn require widening the river by five times, an impossibility given communities now line the concrete channel. Greening the culverts without widening could then in effect create a major flood risk.
“Just adding trees to the banks would reduce flood capacity by 60 percent; turf, grasses and shrubs along the bottom of the culvert would reduce by 45 percent; just grasses, 25 percent; trees in the middle band alone, 20 percent; and grass along the middle stretch, 5 percent,” explained Hanna.
For Richard Jackson, former head of environmental health for Centers for Disease Control and Prevention, and professor at University of California at Los Angeles, adding more green is the goal, but not at the cost of future flood deaths. Still, he wants to see a revitalized river become a positive change agent, instead of a contributor to health problems, as it is now.
Using California’s EnviroScreen, a tool he helped develop, he found those communities “most at risk of severe health problems are near the river.” High levels of asthma and obesity are co-located along the river because many of the communities near the river lack parks, access to healthy foods, and are also near pollutant-spewing highways and freeways.
Richard Roark, ASLA, a partner at landscape architecture firm OLIN, also wants to see a new Los Angeles River creating a healthy environment for both people and wildlife. “If restoring the ecological function of the Los Angeles River costs $100 million a mile, at a total cost of $5 billion, think about what it could be preventing in terms of healthcare costs.” Indeed, Jackson estimated the total public health costs of a poor environment in Los Angeles to be around $25 billion.
Roark called for using “designed ecologies” to improve the quality of life for the communities near the river, by creating fresh air and cleaner water and wildlife habitat. But he cautioned that “we can’t think about restoring the river to its original form; we can’t free it. Within the urban matrix, we have to control it.” Roark also called for a green infrastructure network in the neighborhoods surrounding the river and its primary tributaries.
When landscape architects in the audience questioned why the team didn’t look more closely at distributed options that could make greening the entire river a viable option — including more upland green infrastructure, including reforestation; using structural soils to slow down and store water; or building underground channels to convey water — Hanna cautioned that the models show these systems would help with regular storm events, but not the 100 year storm the culverts are designed to handle.
Still, many of the landscape architects called for much bolder thinking and a renewed effort, given the LA River now functions as “a giant urinal.”