“The Bay Area has so much burdensome underground from military use, from the tech boom in Silicon Valley – they left a lot of bad stuff,” said Kris May, a coastal engineer and climate scientist who founded the Pathways Climate Institute . “And what often happens is that we build low-income houses in these areas after they have been refurbished. But they still leave some contamination in the soil, and these regulations were not based on a rising water table. “
Now the water table is rising. And in doing so, it saturates the soil and releases pollutants such as benzene. These chemicals are very volatile and can easily get through sewers and into homes as gases.
This is the effect of the rise in groundwater on only one system – sewage. But it could affect many more. Buried electrical lines that are not properly sealed will be short-circuited; Foundations will begin to lift under the pressure. Some fear that seismic faults could even come under pressure.
How water finds a way
To protect themselves from rising sea levels, cities resort to the same tools they have used for centuries: levees and levees. Boston has proposed a 175 mile sea wall called the Sea Gates Project. Miami has a proposal for a $ 6 billion, 20-foot seawall. New York has proposed its own $ 119 billion six-mile project called the New York Harbor Storm-Surge Barrier. Homeowners from Florida to California are putting up barriers to keep the ocean out. But the fundamental problem with all of these interventions is the same: a dike holds back the sea, not the groundwater.
If the subsoil is relatively impermeable, in some areas it is possible to build dams or dykes that will slow down the rise of the groundwater. But then other problems remain. Remember that water moves towards the ocean. A barrier that prevents groundwater from rising with sea level will also prevent rainwater from, for example, recent rains from flowing into the sea.
“If you don’t let the water run off into the sea, you basically have to pump it over the wall. And that’s essentially what the Netherlands has been doing for several centuries, ”says Rozell of Stony Brook. But that, too, can create problems because so many of the places that these sea walls work so hard – much of Lower Manhattan, large parts of San Francisco, and Boston – are built on wetlands, landfills, or both. “If they pump, the land will sink,” says Hill.
And even if cities were willing to take such a path, not every place can. “There are many conditions where you can pump all day and the water table won’t go down,” says Fletcher of the University of Hawaii.
Remember, groundwater is water that enters the spaces or pores in the sediment. In some places, such as Miami, “the pores are so large that you just suck in water from the mouth of the ocean,” says Fletcher. “You can pump as much as you want, and it just keeps coming out of an endless body of water” – the sea.
