Bay area sinking

[Botnst]

That sinking feeling

If Cargill's legacy made the salt ponds inhospitable for many forms of wildlife, the salt ponds had the opposite effect on promoting growth in Bayside communities. Millions of residents have settled into homes and offices on dry land protected from flooding hazards by a system of levees that are in some areas nearly a century old.

In the meantime, much of the land has sunk beneath them.

Parts of the South Bay near San Jose have subsided by as much as 14 feet because of groundwater extraction starting in the 1930s. Places such as the Google headquarters and Moffett Field in Mountain View only exist because of the levees protecting the shoreline from incoming tides, according to Stewart.

That's why Phase 1 of the South Bay Salt Pond Restoration Project will only affect areas that don't present flood control problems — all the crucial levees will stay in place until new ones are built closer to the shoreline to raise or replace them.

That also accounts for the $1 billion price. Planning, building, and maintaining levees is notoriously expensive. In 2007, taxpayers spent $2 million just to maintain levees around the Bay for habitat value and flood control.

The Army Corps of Engineers isn't expected to present a new design for local flood protection for at least another decade. When they do, most of the cost will be borne by flood control districts that represent the Santa Clara Valley and Alameda County respectively.

San Mateo County, however, has yet to come up with a funding source for its levees at Ravenswood and elsewhere. That could eventually become a major problem, especially considering Ravenswood Point is the most exposed portion of all the salt ponds in the Bay Area. On a map, it sticks out like a fist into the Bay. Keeping those levees intact will cost a lot of money.

"It's flat as a pancake out there. If those levees don't hold up, the water could come in there and top Bayfront Expressway," warned Steve Ritchie, executive program manager for the restoration project. "It's a good reason to make sure we do something sooner than later."

Facing down a flood

There's another good reason to try to speed up the process: sea level rise. Scientists have predicted the oceans could rise by as much as one meter, or 3.3 feet, in the next 90 years. If the water comes in more quickly than that or in the form of a New Orleans-type epic flood event, it could overtop some levees and utterly thwart the benefits the wetlands officials are working so hard to create.

"If sea level rise starts to occur too fast, we will end up with large areas of mud flat and open water and we will have lost the opportunity for tidal marsh. By then we'll be building flood walls as opposed to a levee-wetlands combination," said Ritchie.

An area of transition between open water and dry land, tidal marsh has more hidden benefits than any inventor could have imagined. Its spongy surface, filled with plant life, actually absorbs storm surges and deflects the pressure of wave action, removing the need for levees the size of castle walls.

Tidal marshes are one of the most productive ecosystems on Earth, producing plant material to absorb carbon from the air at a rate scientists say rivals that of trees. Saltwater tidal zones, like the ones around the Bay, also do not emit high levels of methane (a potent greenhouse gas) like freshwater marshes — so there's no risk of further polluting the atmosphere.

Wetlands solve water pollution by binding to pollutants, such as nitrogen, phosphorous, and even oil and heavy metals, and breaking them down over time before they are buried in the sediment.

"I had a friend who used to refer to (tidal marshes) as the lungs of the Bay, breathing in and out," said Ritchie.

Walking along a levee at Ravenswood that will be closed to the public when construction begins next month, Stewart said locals have so far failed to grasp that this site and a handful of others will be part of "the next big thing" for the coming decade — an enterprise so ambitious in its proportions that other cities around the world with the potential for similar projects will be watching to see what happens.

More than anything, he would like to see locals begin to bridge the disconnect between their notion of nature and the rich diversity of life taking shape in the salt ponds they pass every day on their way to work.

"They go to Yosemite, they go to other parts of the Bay Area for nature," said Stewart. "This project is all about changing that."

more at: http://www.mercurynews.com/ci_11226457