By Linda Hunter, Executive Director
In a tiny building on Crissy Field, sits the oldest working tidal gauge in the United States.
Thanks to the constant monitoring provided by this hard working data gatherer, we know that the water is rising in the Bay, and it is rising fairly rapidly due to melting glaciers and warming waters around the globe. In fact, the tides in the Bay have risen eight inches since 1900 and are projected to rise another 14 inches by 2050–and a whopping 55 inches by 2100.
San Francisco, like New Orleans, used to be protected from tidal surges by natural tidal marshes and healthy underwater ecosystems. However, during the last 150 years, the majority of SF Bay marsh has been filled, drained, or replaced with levees and rip rap. As Bay Area scientists gauge the impact that rising sea levels will have on our shoreline, it seems clear that restoring natural ecosystems is an effective way to mitigate the inevitable tidal surges brought about by climate change.
Last week, the Bay Institute presented their new study, The Horizontal Levee, Nature’s Low Cost Defense against Sea Level Rise, to a rapt audience at the Aquarium of the Bay. Local scientists have determined that tidal marshes can significantly reduce the destructive power of storm surges. These horizontal levees incorporate a brackish marsh as a buffer to the tidal marsh, freshwater swales, and a much lower berm or wall at the land’s edge. This four-part defense system imitates nature’s own design, and thus is an ecologically sound protection to storm surges. Plus, it is significantly less expensive to create natural systems rather than to build additional large-scale infrastructure such as the levees, dams, and seawalls that currently adorn our Bay shores.
We have found that oyster reefs can play an important role in addressing the challenges our Bay faces because of rising sea levels. Last year’s Bubbles and Bivalves keynote speaker Paul Greenberg wrote a piece for the New York Times on the eve of Superstorm Sandy called An Oyster in the Storm. In his piece, Paul laments the loss of native oysters that once numbered in the trillions and played a critical role in stabilizing the shoreline from Washington to Boston…
“Just as corals protect tropical islands, these oyster beds created undulation and contour on the harbor bottom that broke up wave action before it could pound the shore with its full force. Beds closer to shore clarified the water through their assiduous filtration (a single oyster can filter as much as 50 gallons of water a day); this allowed marsh grasses to grow, which in turn held the shores together with their extensive root structure.”
Paul points out that it is certain that Sandy was not just a fluke–storms like this will continue to be a part of our new, emerging climate. We at The Watershed Project could not agree more. Natural infrastructure along shorelines is a critical component of a healthy watershed and will also be a key player in the climate change adaptation toolkit.
If you would like to get involved in building up natural shoreline defense systems, please consider joining our native oyster restoration efforts along Point Pinole Regional Shoreline.