Oro Loma Pilot Project – Horizontal Levee

A re-imagining of how a levee looks and what it can do to address flood risk and water quality concerns while providing critical ecosystem benefits.

Project At a Glance

The Horizontal Levee Concept – A Solution for a Region Facing:
  • Flood risk from sea rise
  • Water quality concerns in the Bay
  • At-risk key habitat on the Bay’s edge
  • Traditional levees maintenance costs

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. For more a more in depth overview, read the Oro Loma and Castro Valley Sanitary Districts to Test Pilot Levee brochure

This project advances the following Estuary Blueprint goals and actions

Habitats and Living Resources
Water Quality and Quantity

Action 14

A New Type of Levee

For a New Set of Challenges

The National Research Council projects a rise in sea level for San Francisco Bay of 5-24 inches by 2050 and 17-66 inches by 2100. In addition, the National Oceanic and Atmospheric Administration lists the Bay Area as one of the top ten most vulnerable metropolitan regions in the country. To prepare for more flooding and wet weather, the Oro Loma Sanitary District and the Castro Valley Sanitary District hired consultants Philip Williams and Associates (now ESA) to examine the threat in more depth. The result is one of the Bay Area’s first multi-agency, multi-jurisdictional planning efforts around sea level rise. ESA and Peter Baye designed a new type of levee mimicking the natural slope from historic wetlands into upland areas. If planted with sedges and grasses, and irrigated with treated wastewater, this wedge of habitat, built alongside the new levee, could slow down waves, resist floods, and protect infrastructure and homes in the Bay Area flats. When the Oro Loma Sanitary District offered a a 10-acre field adjacent to its wastewater treatment and purification plant in San Lorenzo, in order to test ecotone slope concept, support for the project grew.

New Water Treatment Methods

In Testing

Currently in construction, the project will turn a degraded, diked bayland into an outdoor laboratory. Here, construction crews will create 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 will pass 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 newly designed habitats, 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. More information available on the Oro Loma Sanitary District website.

Testing New Water Treatment Methods