Be very careful where you build the seawall

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Recall As a kid on the beach, build a fence around your sand castle. If you design these fortifications correctly, the tide will flood into your kingdom and flow through your kingdom before the walls are finally eroded away. By redirecting the rising water, you could have saved your castle-at least for a while.

Think bigger now. Imagine that you are an urban planner in an area threatened by rising sea levels, and you have spent a lot of money to build a suitable seawall. When the tide comes, the wall is stabilized, saving you billions of dollars in property damage. but: Ho ho ho. Like the waves you once redirected around your sand castle, rising water hits the walls and flows into the communities on either side of you. You saved your residents, but endangered others.

The new model shows how disastrous this wayward water phenomenon can be in the San Francisco Bay Area, where sea levels may rise 7 feet in the next 80 yearsAnne Guerry, chief strategy officer and chief scientist of the Natural Capital Project at Stanford University, said: “These rising water levels put millions of people and billions of dollars in buildings at risk,” she co-authored paper Describe the research.Published in the journal this week Proceedings of the National Academy of Sciences. “A new feature of this work is that people don’t necessarily think about how communities, such as the Bay Area, connect with each other through these shared waters,” she continued.

Guerry and her colleagues modeled the coastline by dividing the coastline into multiple parts based on geological and other characteristics. Then they used a hydrological model to show where the rising water would flow if a seawall was set on a given part of the coastline. Basically, they imagined what would happen if the residents of an area decided to protect themselves without fully considering the resulting hydrology. “The water must flow somewhere,” Gary said. “We found it would eventually flow into other communities, making their flooding worse. ”

They also combined economic models to calculate how much damage this would cause. For example, they estimate that if the local government builds a wall around San Jose, the South Bay city, it will flood other communities with rerouted water equivalent to 14,400 Olympic-sized swimming pools. San Jose will be saved, but the nearby Redwood City and other communities will be messed up. Guerry said: “This is equivalent to a high tide in the spring, the water level is naturally highest, causing additional flood damage of 723 million US dollars.” “This is just building a large seawall in a small part of the bay.” And this exceeds 700 million US dollars. The figure does not consider the potential damage to the ecosystem and fisheries, so this figure is conservative.

The extra water pushed back by the walls of San Jose will even accumulate over the entire bay, 50 miles north of Napa and Sonoma. The damage will also be reversed: If the coasts of Napa and Sonoma are fenced off, the South Bay will suffer tens of millions of dollars in damage.

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This is not good news, considering that humans have the habit of building large cities along the coast, and now city planners must do this Fortify, And seawalls are usually the best defense. The author of this paper pointed out that by 2100, the United States alone is expected to spend 300 billion U.S. dollars on supporting coastlines to prevent sea level rise and greater waves caused by storms. More powerful Due to climate change. Legislators must consider as soon as possible whether to spend $26 billion to quarantine the surrounding area of ​​Houston. Jakarta also needs to build a huge seawall, but it cannot be in the land below it Stop sinking.

So far, policymakers have assumed Laura Feinstein, director of sustainability and resilience policy at SPUR, a non-profit public policy organization in the Bay Area, said that seawalls may have a negative impact on nearby communities, but this new study provides potential harm digital. (She was not involved in this research.) “This is a truly quantitative and rigorous proof of what people have always said about sea level rise, that the area is either sinking or swimming together,” she said. “If a region invests resources to protect its coastline, it will only exacerbate the sea level rise of its neighboring countries.”

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