The United States Environmental Protection Agency's top water official, Joel Beauvais, was in the Bay Area recently for a tour of the Oro Loma Sanitary District's wastewater treatment plant in San Lorenzo.
The slope of the horizontal levee was planted in sections so that the team will be able to try out different combinations of soil types and native plants to determine which mix is the most effective at filtering wastewater.
By Bill Picture
Published: April, 2016
The “horizontal levee,” as it’s being called, is designed to mimic the slope of a naturally occurring wetland, and can be built for roughly half the cost of a traditional levee. After his tour, Beauvais said that the idea is a “feasible” solution to a problem that scientists say is inevitable; and he commended the team behind the project for thinking outside the box.
“This is just the kind of innovation we will need to put into practice if we are to protect airports, roads, wastewater treatment plants, and homes in low-lying communities,” Beauvais said.
The scientific community points to climate change as the reason for sea-level rise. Research shows that all around the globe, the sea level has risen about 7.5 inches over the last 150 years. Scientists believe that pace will quicken over the next 50 years, with sea levels in the Bay Area expected to rise another five to 24 inches by 2050, and 17 to 66 inches by 2100.
For communities likes the ones ringing the Bay, where billions of dollars’ worth of homes, businesses and vital infrastructure have been built near what is now the water’s edge, those extra feet of water could spell disaster.
But what is it?
Until now, engineers approached keeping rising water at bay much the same way we all think of keeping away an unwanted visitor—put up a high wall to keep it out. The problem is, lone-standing levees can be breached, as Hurricane Katrina showed us. So being the forward-thinking and eco-minded region that the Bay Area is, it’s no surprise that when charged with the job of shore protection, the local team came up with a more natural and holistic approach to flood control.
The need for a better alternative to the Bay Area’s traditional levees was first realized in 2005, when a major storm swept through the region and sent large waves crashing right over the top of existing levees and sea walls. The Hayward Area Shoreline Protection Association knew this storm was just a taste of things to come, and that rising sea levels would soon again have water lapping at the doors of Bay Area communities.
So they hired environmental planning firm Environmental Science Associates (ESA) to evaluate the risks posed by projected sea-level rise and come up with some ideas for addressing it. Together with coastal ecologist Peter Baye, the team came up with the idea for a sloped terrace or “ecotone slope” that would sit at the foot of a traditionally built levee and slow water down before it reached the levee. Made up of layers of gravel and mud, the slope would be planted with vegetation to absorb waves like the ones generated by the 2005 storm.
The entire team behind the project eventually grew to include Oro Loma Sanitary District, East Bay Dischargers Authority, San Francisco Estuary Partnership, Jeremy Lowe, ESA, Peter Baye, Whitley Burchett and Associates, Engineering Research Center for Reinventing the Nation’s Urban Water Infrastructure (ReNUWit), UC Berkeley, the Bay Institute and Save the Bay.
Baye explained to reporters last year, at an event celebrating the completion of construction of the horizontal levee: “What we’re building is not technically a levee, but a sloping terrace or ramp against a levee. If you can create a really wide rough levee, it will slow waves down; and maybe you can actually build a smaller levee.”
Realizing the potential of the idea, Oro Loma Sanitary District offered up vacant land adjacent to its wastewater treatment plant, whose position at the edge of the San Francisco Bay makes it vulnerable to sea level rise, to give it a try. That location prompted the addition of another exciting element.
Upstream from the gently sloping 400-foot by 200-foot planted terrace will sit a new two-acre wetland basin designed to store wastewater during wet weather, when heavy rains can overwhelm treatment facilities like the one at Oro Loma. The basin will also provide a much-needed habitat for wetland-loving animal species.
By law, wastewater must be treated twice before it’s discharged. During a storm, wastewater could be treated once and then held in the wetland basin until rainfall subsides and the water could be routed back to the facility for a second treatment. This would allow the facility to more efficiently treat higher volumes of incoming wastewater.
While the wastewater was held in the wetland basin, the plants and bacteria there would break down contaminants and remove nutrients that cause algal growth in the Bay; so the water would actually be cleaner when it returns to the facility for its second treatment. Many of the contaminants and nutrients removed during the natural biological processes that occur in wetland areas are resistant to conventional treatment methods.
That’s what really piqued the interest of Beauvais, because part of the EPA’s comprehensive strategy for responding to sea-level rise has been working with communities to ensure that drinking water and wastewater infrastructure are prepared for the punches that climate change is expected to throw. “Protecting this infrastructure is essential to protecting water quality,” he said.
Making the case
The slope itself has been planted, but the wetland basin is not scheduled to be completed until October. When it’s done, the basin will begin receiving wastewater that’s already been treated twice. After passing through the wetland basin, the water will trickle down through the slope’s sub-layers, which will filter out the treatment-resistant contaminants and nutrients, to irrigate the vegetation planted there. Until then, the plants will receive water from a nearby well.
The slope was planted in sections so that the team will be able to try out different combinations of soil types and native plants to determine which mix is the most effective at filtering wastewater. The water will be monitored at various points along its trip from the treatment plant to the foot of the ecotone slope to gauge how effective the natural filtration processes are at removing Bay-unfriendly materials. If these processes prove effective, the ecotone slope could someday be connected directly to the Bay. Until then, however, the water will be collected at the bottom of the slope and returned to the treatment plant.
Beauvais described what he saw during at Oro Loma as a “combination levee and treatment wetland.” “It’s an outdoor laboratory that will build the science needed to inform how we can effectively ‘scale up’ green infrastructure to adapt to rising tides,” he said. “It starts with the ‘wetlands restoration as part of flood protection’ approach and then takes it one step further. We need to keep thinking like that.”
"It’s one of the few projects that I’ve worked on where there’s been absolute unanimity about the value of trying it out,” said Ora Loma General Manager Jason Warner. “In fact, it may be the only one. Of course we still have to run the science and make sure it works; but we’re all confident, and very excited.”
For more about the Oro Loma Wet Weather Equalization & Ecotone Slope Demonstration Project, visit oroloma.org/horizontal-levee-project.
