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Melting ice, rising water

Salt marsh solution to rising water

Before 1850, the surface of San Francisco/San Pablo Bay was at least eight inches lower and surrounded by 196,000 acres of tidal marshlands.

Today, according to the Bay Institute, just 16,000 acres of marshland remain, and the level of the bay is rising at an accelerating pace.

Estimates compiled by the National Academy of Sciences conclude that, if the pace of climate change and global warming continues at its present rate, along the ocean interface with Northern California – including the circumference of San Francisco Bay – water levels will rise between 16 inches and 4.6 feet by the end of this century.

The consequences of that scenario, according to an analysis by the Pacific Institute prepared for three state agencies, would be 480,000 people and nearly $100 billion in coastal property placed at substantially increased risk.

And that doesn’t include the remaining wetlands and the critical ecosystems they support.

Bringing climate change to the front (or back) door of Sonoma, the year-2100 scenario has Highway 37 mostly underwater and parts of Arnold Drive inundated; the Schellville Airport would become a marina and high water would close parts of Ramal Road.

But sea level rise isn’t responsible for the loss of most of the bay’s once-massive wetland habitat. Beginning shortly after the Gold Rush in 1849, the avalanche of humanity that descended on California began dredging, diking and filling almost every available level acre around the bay, first for agriculture and later to create an enormous array of salt evaporation ponds.

The consequences impacted countless kinds of flora and fauna, driving some species toward extinction and reducing the natural nursery that cloistered both plants and animals.

What most profoundly shifted the dynamic balance of the bay was the creation of endless levies ringing the newly productive farmland to keep the encroaching seawater out. The San Francisco Bay-Delta system has nearly 3,000 miles of levees, a system almost twice as long as the one built by the Dutch to hold back the North Sea. But when you build levees, the land behind them inevitably sinks as the moisture is drained away and years of farming compact the soil.

Stand on the levee encircling the Tolay Creek Lagoon, a 60-acre tidal pool just across Highway 37 from Sonoma Raceway at Sears Point, and you can see a dramatic example of levee-induced subsidence. When the incoming tide floods the Tolay Lagoon, the water level is a good 10 feet higher than the surface of the farmland on the other side of the levee. Much of the seaward strip of land separating highway 37 from the open waters of San Pablo Bay has been dredged, drained and planted with hay and other crops. On the inland side of the highway, thousands of acres of former marshland have been replaced with hay fields. The elevation disparities are startling when observers stop to study them, indicating an intricate and ultimately static system of plumbing.

But the Tolay Lagoon is also a harbinger of change and the model for a major restoration project all along the top of San Pablo Bay that is designed not only to bring the bay marshland back to life, but to serve as a biological buffer to the rising level of the sea.

The lagoon is situated on the tail of Tolay Creek, which is now connected to the bay by a restored stream channel dredged through three miles of silt. Now the bay pulses in and out of the lagoon, gradually transforming it from farmland into a living marsh.

On a January morning, Marc Holmes, Bay Restoration Program Director for the Bay Institute, surveyed the lagoon and called it “a perfect small example of what’s planned all over the bay.”

What’s planned along 1,500 acres bordering Highway 37 is a carefully engineered reconstruction of roadside levees to create more gradual transition zones between flooded areas and future marshland. Meanwhile, levee breeching will gradually allow equilibrium to re-establish between former salt ponds and once-drained acreage. With channels connecting to tidal pulses, water will begin to naturally circulate again and, following a century of hydrological stagnation, the whole area will become dynamic and alive.

Don Brubaker, with the U.S. Fish and Wildlife Service, who is North Bay Sub-Complex Manager for the project, explained that, “When you enhance the habitat the endangered species move in quickly.” High on the endangered list for the Sonoma marshland restoration, is the salt marsh harvest mouse and the California clapper rail, a bird dangerously close to the edge of extinction. “We’re an endangered species refuge,” added Brubaker. “We’re planning to farm clapper rails and harvest mice.”

Asked why the fate of obscure animals most people will never even see should matter, Brubaker responded, “Where do you start? The salt marsh harvest mouse and the clapper rail take to the same kind of habitat as the fish we like to eat for dinner. John Muir said, ‘When you pick up the tongue of the trailer you learn it’s hitched to everything in the universe.’ Hopefully, we’ll bring in more waterfowl.”

Holmes stepped into the conversation to add, “The obscure creatures are indicators. When they’re healthy, we’re healthy. When they start dying off, then we’re in danger. We may not understand how that comes back to us, but it does come back to us. The purpose is not to save the obscure little creatures. The purpose is to protect the whole ecosystem.”

Homes added that saltmarshes “used to be giant carbon sinks. Forget the harvest mouse. Restoring the marsh adds structural protection on the one hand, and it takes carbon out of the atmosphere as well.”

Part of the win-win design in the restoration work being done at the edge of the bay is a design philosophy the Bay Institute is calling “the horizontal levee.”

It is contrasted to typical engineered and reinforced levees commonly found in projects designed by the U.S. Army Corps of Engineers because the Bay Institute plan calls for a series of natural features in transitional steps from the water up to dry land. The sequence runs from mudflats, through tidal marsh, brackish marsh, a freshwater swale and, ultimately, an impermeable berm.

But the marshes that are encouraged to take root are self-maintaining and keep pace with sea level rise, with help from sediment dredged from flood-control channels.

It is, in short, a natural system that, at least in principle, will restore thousands of acres of historic marsh habitat while providing highly effective protection against destructive storm surges and rising sea levels, by dramatically expanding the capacity of the environment to absorb water.

The final bonus: according to the Bay Institute’s analysis, a horizontal levee system could provide protection almost equal to classic, engineered and “armored” levees, at about half the cost, while simultaneously protecting endangered species.

The restoration project along Highway 37 is set for completion by January of 2014, at which point levee breeches will open up new channels for canoes and kayaks to explore the marshlands adjacent to Dutchman’s Slough.

For more information on the horizontal levee plan, go to bay.org.