The Tide Rises

Abstract

David Sedlak, an environmental engineering professor at the University of California– Berkeley, stands on a levee near San Francisco Bay’s eastern shore. Manmade embankments extend for many miles, lining much of the bay’s edge, but Sedlak, a lean, intense guy, is fired up about this newly built one. Instead of the usual barren concrete, the bayward face of the levee slopes gently beneath a dense growth of native wetland plants. From muddy clumps of roots and rhizomes placed here only a year ago, the plants have sprouted into a lush palette of green, from the deep dark of Baltic rush to the bright tones of creeping wild rye. Sedlak is part of a bold experiment. If it succeeds, the project may reshape the East Bay shoreline, restoring a vast acreage of lost tidal wetlands that will be nourished by treated wastewater. The hope is that vegetated levees (the official moniker for the concept is the Horizontal Levee) will save money and energy, recycle treated sewage to create habitat, and help the urbanized East Bay adapt to rising sea levels. Conventional levees form steep concrete or earthen walls that armor roads and buildings against the bay’s powerful waves. The Horizontal Levee is a lovely contrast, a compressed version of a natural habitat long missing from the shoreline. The transition zones, or ecotones, between land and bay were biologically rich places that once hosted a diversity of native plants and animals. Since the Bay Area was settled, wetlands have been diked off from both the open bay and the surrounding land. Between 1800 and 1998, 92 percent of tidal marshes were lost to diking and filling. “In San Francisco Bay, we’ve separated the contacts between the terrestrial and the tidal,” explains Peter Baye, a consulting ecologist whose deep knowledge of remnant natural wetlands acts as guideline for the creation of the Horizontal Levee. Habitats that once formed a continuous gradient from dry land to salt marsh have been boxed off, separated by dikes. The disappearance of what ecologists call the “back end” of tidal marshes has been a significant loss.