Land-Use Planning in an Era of Rising Seas

Photo by Marc Smith

Sea level rise is here, and it is going to get worse. Recent projections show a strong likelihood that the Bay Area will experience at least 6 – 12 inches of sea level rise by 2030, about two feet by 2050, and three to six feet by the end of the century. This will put all of us at risk; even those with homes not directly impacted will suffer if the highways they drive on or the wastewater plants that treat their sewage are flooded out.

Of course, we must continue efforts to reduce carbon emissions to avoid even worse consequences. But our region must also plan for a “new normal,” a normal with more floods and coastal erosion. How should we do this?

First, it’s not enough to merely protect existing development – we must also begin to change our behavior with regard to how we grow our communities. Our past patterns of growth have resulted in over $24 billion of development at risk from sea level rise in San Mateo County alone. Instead of continuing with business as usual, we need to start restricting development in areas where flooding and bluff collapse are likely.

Second, we must look to nature-based solutions to protect existing development. Traditional “hard” levees are less effective than solutions that work with nature instead of against it. But we need to start taking action now – before the slow-moving catastrophe of climate change catches up with us.

Committee for Green Foothills’ knowledge of local land use and planning issues gives us a unique perspective into this question. We are tackling this crisis head-on and educating elected representatives and the public about this threat. Please help us spread this message so our region can plan for rising seas in an environmentally sound manner.

Bayside and Coastside – Two Different Worlds

The effects of sea level rise, and the adaptation measures needed, will be very different by the Bay as opposed to the coast. Along the Bayside, where the land typically slopes down gently towards the water, the primary concern is flooding. Several areas that were once mudflats or tidal marsh and were filled for development several decades ago already experience flooding during yearly king tides (peak high tides that occur in December and January). During king tides, these paved former wetlands are below sea level. That means that the seawater doesn’t even need to wash over the tops of levees to cause flooding – it backs up through the storm drains. Other low-lying areas are subject to flooding from creeks overflowing during heavy storms. Those areas can be expected to flood more often and more severely because higher sea levels mean the creeks can’t drain into the Bay.

On the Coastside, although there are some creeks and streams that experience bad flooding, the primary problem is bluff erosion. While bluff erosion is episodic, some bluffs in Pacifica have collapsed and retreated by as much as four feet per year in recent years, in some cases leaving buildings perched precariously on the edges of cliffs. The rate of bluff erosion is highly variable and difficult to predict along the coast; rocky promontories are relatively resistant to erosion, but the coastal terrace bluffs interspersed among them are unstable and erodible.

The iconic coastal beaches are also at risk as higher sea levels and increasing wave action wash away the sand. Beach erosion has always occurred, but in past times the sand was replenished by sediment that washed down the hills through the creeks. Now, with

many creeks dammed or otherwise altered, that source of new sediment is greatly diminished. Sand replenishment can be artificially done, but it is an expensive and continual process.

Stop “Business As Usual” Development

We have built homes and businesses, wastewater treatment plants, and landfills in areas that are right at sea level, areas that tides formerly inundated regularly. These places will be the first to flood as sea levels rise. On the coast, the lure of beachfront views and a mistaken belief in the stability of bluff tops have resulted in many neighborhoods now perched on the edges of cliffs.

It’s time to rethink our ideas about where development should go. Recent natural disasters, such as the California wildfires and hurricanes in the Southeast, have made the point that when flooding occurs, the economic and societal consequences are far higher if the flooded area is densely developed. And yet, cities are still approving more and denser development in the path of sea level rise. This must stop. We must locate new development, including essential public infrastructure, well away from areas threatened by sea level rise.

With Nature, Not Against It

Many of the best and most cost-effective adaptation measures involve environmental restoration – working with nature instead of against it. One local example is the effort already underway to restore many former Bay wetlands that were converted to salt ponds a century ago. These salt pond restoration projects are the ideal site for “horizontal levees” – long, sloping tidal marshlands that provide sufficient protection against storm surges to allow the engineered levees behind them to be lower than would otherwise be required, reducing costs. And there are additional salt ponds – namely, in Redwood City on the Cargill site – that could be restored just as easily.

On the coast, nature-based solutions are less easily available. However, we must face the fact that hardening the shore with riprap (rocks piled up along the shore) is not a long-term

solution. Armoring the coast with riprap changes the pattern of sand movement along the shore and restricts the natural ability of the beach to move inland, resulting in the eventual loss of the beach. Furthermore, this can worsen erosion on neighboring properties as the waves deflected from the armored areas strike adjacent unprotected areas – causing both beaches and bluffs to erode more quickly.

The Bay Area can survive the worst impacts of sea level rise if we plan ahead and plan wisely. That means taking steps now to create natural infrastructure for flood protection and reducing our risk by limiting future development in vulnerable areas. Committee for Green Foothills is working with local, state, and regional agencies to educate the public and help craft sustainable approaches to these challenges. Please stand with us as we advocate for cities to follow this path in the coming years.

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