Régulièrement submergée par les inondations, Alviso, une bourgade de la Baie de San Francisco, s’interroge sur les solutions pour échapper à ce sort funeste. Avec les menaces concernant l’élévation du niveau de la mer en raison du changement climatique, c’est toute la Silicon Valley, berceau de l’histoire informatique du 20 ème siècle, qui pourrait être inquiétée. Ainsi que le signale cet article en anglais, diffusé par le plus important site écologique américain, Climatewire : Silicon Valley threatened by flood.
For one town at the southern tip of the San Francisco Bay, Alviso, San Jose (Calif.), water has been the enemy for many years. With climate change predicted to increase sea levels, some fear there and in Silicon Valley generally the water at some point could be unstoppable.
Floods have struck repeatedly in Alviso, a San Jose neighborhood of about 2,000 people. Lying about 8 feet below sea level, it’s been inundated when nearby rivers overflowed during rainstorms, with water rising so high it filled up homes and destroyed businesses.
« Without this levee that we’re standing on, twice a day Alviso would be underwater, » John Bourgeois, executive project manager with the California Coastal Conservancy, said recently from the top of a dirt barricade at the outskirts of town.
A losing battle
« We’re already fighting a losing battle, » Bourgeois said. « We’re already below sea level. So it’s only making it worse. The longer we wait, the harder it gets to fix the problem. »
The Army Corps of Engineers, Fish and Wildlife Service, California Coastal Conservancy and Santa Clara Valley Water District now are working to win approval and funding for levees, restored wetlands and other protections in Alviso.
3 to 10 effet below sea level
The changes would be among the first climate adaptation measures in Silicon Valley. The region is particularly vulnerable, experts said, because much of it is located 3 to 10 feet below sea level.
Home to world-famous technology companies, the area is just beginning to study what moves are needed to defend against a rising tide and other threats.
From 16 to 65 inches
Scientists say sea levels on California’s West Coast could climb as much as 16 inches by midcentury and 65 inches by 2100. Storms are expected to intensify and occur more often. Both in the future would imperil businesses and homes near San Francisco Bay.
Alviso was picked to go first in the region because « the human element here, they’re most at risk, » Bourgeois said. « People who attend our meetings, their homes have been flooded three times in their lifetime, up to their roof flooded, » Bourgeois added. « It’s very personal. »
Levees must be replaced
… It soon became obvious that it would take years before any solutions could be put into place.
To protect Alviso as well as nearby neighborhoods, the alliance of local, state and federal officials wants to build engineered levees that could withstand strong storms and handle a certain amount of sea level rise.
Levees already exist here, as they do in other parts of Silicon Valley, but they weren’t engineered or built properly. Instead, they were pushed into place when businesses cleared land for ponds to harvest salt.
Built by the salt company
« The salt company built all these levees to keep water in the pond for salt evaporation, » Eric Mruz, manager of the Don Edwards San Francisco Bay National Wildlife Refuge, said recently as he drove near one of the barriers. « It was never intended to withstand flooding. »
The alliance focused on Alviso also would allow the tides back in and restore the marshes in the area. Wetlands can adapt to sea level rise, Bourgeois said, because natural sediments will build up and the elevation will increase. It won’t happen quickly, however. « It’s a multiyear if not decades-long process to do that, » he said.
Right now, however, there’s only funding for a $6 million feasibility study. Congress would have to approve the levees and restoration work, then allocate money for the effort. Authorization would have to come in a Water Resources Development Act bill .
Though they are supposed to happen every two years, the last one to pass was in 2007. »We could be into a holding pattern waiting for a water resource development act to pass, » Kendall said.
Living only upstairs
Alviso already is so prone to water inundation that any new home built here must either be constructed on top of an elevated mound or have two stories with no living on the first floor…
Ramiro Espinoza, 54, and his family live in a one-story triplex close to the water. He grew up in Alviso and was there for previous floods. His parents’ home had tile floors and cement walls so there was minimal damage, he said.
A good flood insurance
As for future floods, « That’s why you have to have flood insurance to live in this area, » Espinoza said. It’s also worth the risk, he said, because homes are inexpensive in Alviso. In 1983, his father bought the triplex his family lives in for $35,000.
Other parts of Alviso resemble a ghost town, with numerous abandoned buildings. They include homes and businesses like the historic Bayside Canning Co. Yellow caution tape is wrapped around its walls, which are still adorned with paintings of a drawbridge and sailboats.
Abandoning town debated
Early in its analysis, the Army Corps said it looked at the option of instead abandoning Alviso and relocating residents. That would cost $500 million because Silicon Valley real estate is so expensive, Bourgeois said.
Under federal rules, relocated people would have to be moved into homes that are similar to their current one in size. And replacement values can’t be discounted because those people live in a floodplain. In addition, there’s a nearby water treatment plant that serves 1 million people, he said.
A better choice
Building new levees is a better choice economically, said Mark Bierman, economics section chief in the Army Corps’ San Francisco office.
« It’s a relatively small area, » he said. « There’s high ground on both sides of Alviso. If you construct levees that tie into that high ground, you can for a relatively small price tag significantly reduce the risk to the community and beyond for a very long time. »
In addition, there’s greater importance to the work in Alviso, Bourgeois said. « This is sort of the case study for all of the other areas that are going to have to go through this process, » Bourgeois said. « This is going to be the template for flood protection in other parts of the Bay. »
Anne C. Mulkern, E&E reporter, ClimateWire: Friday, December 21, 2012 (Environment & Energy Publishing, LLC), pour le « lecrapaud.fr ».