A “Horizontal Levee” is a re-imagining of how a levee looks and what it can do. Instead of a vertical wall to protect against storm surges, a horizontal levee uses vegetation on a gentle slope to break waves. The ecosystems that live on horizontal levees can thrive while helping to further process waste water from treatment plants.
This project turned a degraded, diked bayland into an outdoor laboratory. Here, construction crews created two things: first, a two-acre wetland basin that can both remove nutrients from wastewater and provide extra wet weather storage capacity; and second, on one side of the basin, the experimental levee. Wastewater that has already undergone secondary treatment passes first across the surface of the basin and treatment wetland, and second through the levee and down into the sub-layers of 1.4 acres of the experimental habitat slope. The idea is that the combination of treatment wetlands and surface and sub-surface filtering processes, will support native plants and purify the water enough so that one day this kind of system can be directly connected to the edge of the Bay. Meanwhile, the new treatment wetland and basin is also designed to store up to eight million gallons of enhanced primary treated wastewater during a storm or peak flow event.
For more a more in depth overview, read the Oro Loma Experimental Levee brochure
Key water quality monitoring findings reveal several key components. First, the Oro Loma Horizontal Levee significantly removes wastewater-derived contaminants while providing valuable habitat. Some contaminants that were found to be removed were nitrogen, phosphate and pharmaceuticals. Second, contaminant removal was influenced by hydrology more than other design and operational parameters. Subsurface flow is the key! Finally, that nitrogen was removed by microbial processing within the horizontal levee design.