Rising seas, algae blooms threaten coast
There’s never a dull moment when it comes to the Bay Area’s coastline.
This week, scientists expect the king tides, some of the highest tides of the year, to hit our shores. These tides, which occur every winter and can measure up to 7 feet high, have the potential to flood coastal neighborhoods and are expected to last several days. And while king tides occur naturally and are not an effect of climate change, they do provide a preview of what Bay Area residents can expect as sea levels continue to rise.
Already, climate change has caused the Bay Area’s water level to rise about 8 inches in the past 200 years and experts predict that the level could rise an additional 6 inches by 2030 and as much as 7 feet by 2100. That kind of rise is likely to cause hundreds of billions of dollars in damage to infrastructure and property, and potentially drown vital marsh habitat. But Bay Area regional agencies recently estimated that armoring the Bay Area’s shorelines against sea level rise would cost about $110 billion.
Meanwhile excess nutrients in the Bay, mostly from treated wastewater, have brought massive algae blooms to our coastal waters the past two summers, leaving untold numbers of dead fish in their wake. And while the summer 2023 bloom was far smaller and less severe than the one that occurred in 2022, experts are worried that the excess nutrients, coupled with climate change and alterations in freshwater flows, are setting the stage for more harmful algal blooms in the future. Wastewater agencies are paying careful attention to this problem, but upgrading treatment plants for additional nutrient removal by installing energy-intensive treatment technologies will cost upward of $12 billion.
So what can the Bay Area do to protect it coastlines from rising sea levels and our waters from future algal blooms that is actually cost-effective? Nature may have the answer.
Over the past decade, Bay Area water agencies and researchers have been working to come up with a low-cost, nature-based solution to address nutrient management and sea level rise. Their answer: horizontal levees.
Instead of a vertical wall to protect against storm surges, Horizontal levees couple traditional levees with a gentle, vegetated slope leading down towards the Bay in order to protect communities from sea-level rise while also removing nutrients from the water. The slope can be built with local materials like dredged sediment overlain by native plants. A buried layer of gravel and sand within the horizontal levee conveys treated wastewater underneath the soil while wetland plants can extend their roots into the permeable layer to get water.
A demonstration of a horizontal levee at the Oro Loma Sanitary District in the East Bay has proven that microbes living in the levee’s sand and gravel remove nutrients, pesticides and pharmaceuticals that otherwise would be discharged to the Bay. According to scientists involved in the project, the levee removes over 97% of nitrates and antibiotics in the wastewater. Moreover, because horizontal levees generate marsh-like conditions with plants and sediment on the Bay-side slope, they are also able to reduce wave energy as natural marshes do — meaning the levee doesn’t need to be built as tall as a traditional one. According to a report by the Bay Institute, horizontal levees can protect communities from sea-level rise at just 60% of the cost of a traditional levee.
So why haven’t horizontal levees been installed around the Bay yet? Institutional barriers.
It is nearly impossible to get permits to build a horizontal levee today. 1970’s-era regulations designed to protect the Bay from pollution and development make the installation of multi-benefit, naturebased solutions like horizontal levees very difficult because these regulations were written with older technologies and practices in mind. Also, because there is not one institution responsible for both flood control and water quality improvement, projects like horizontal levees that provide multiple benefits are more difficult to prioritize in the planning process and require coordination and collaboration between agencies that may not have historically worked together.
These institutional challenges are significant, but they are not insurmountable. Elected officials, champions within public agencies, and interested residents can advocate for the policy changes needed to make horizontal levees a reality.
The serious risks and costs that sea level rise and harmful algal blooms pose to Bay Area communities, require us to leverage bold multi-benefit strategies like horizontal levees. We can’t afford to wait any longer.