How rising groundwater caused by climate change is destroying coastal communities | MIT Technology Review

2021-12-13 19:41:56 By : Ms. Zoe Zhang

Higher sea levels will push up the groundwater level, leading to floods, pollution and all kinds of invisible chaos.

Fae Saulenas does not need your sympathy. 

Solinas and her 46-year-old daughter, Lauren, spent last winter—their new winter—in a house without a stove in Saugus, Massachusetts. Saulenas is over 70 years old. Lauren suffered from brain damage in the womb, quadriplegia, blindness, epilepsy and other disabilities. In winter, it is not uncommon for Saugus’ nighttime temperatures to drop to more than ten degrees Celsius. Without heating, the two cannot survive for long, so without a stove, they rely on space heaters. But in February alone, its electricity cost reached $750, and it only heated one bedroom.

Solenas told this story not to arouse sympathy, but as a warning. She said that the groundwater level is rising-seeping into gas pipes and corroding the furnace from the inside out. This is what happened to her. She wants you to know that if you live anywhere near the coast—even one, two, or three miles away—the water might rush towards you.

For things you may never have heard of, rising groundwater poses a real and potentially catastrophic threat to our infrastructure. The road will be eroded from below; the septic tank system will not drain; the seawall will keep the ocean out, but it will stop the seeping water and cause more flooding. Home foundations will rupture; sewers will flow back and toxic gases may leak into people’s homes. 

Saugus is a small town about 10 miles northeast of Boston. On the map, water is one of its characteristics, and the Saugus River and its tributaries meander through towns and through marshes to the Atlantic Ocean. Among the salt marshes separated from the Atlantic Ocean by the Revere Beach Peninsula, Solenas bought her house in 1975. 

Given the proximity to the ocean, the source of her recent predicament seems obvious: rising sea levels. Since 1950, the sea level in this area has risen by 8 inches, and this change is not linear. The sea level now rises faster than the previous generation—about one inch every eight years. But the water that keeps Saulenas in the cold does not come from the sea, at least not directly from the sea.

Her problem started in 2018, when she lost the natural gas and thus the heat due to water entering the underground main. This is a problem that will continue intermittently for several years. Water will enter the gas main, and her utility, the national grid, will be forced to shut down the gas. Then, the State Grid will try to find the source of the water, repair the leak, and then pump the water out. 

State Grid officials did not disclose the source of the problem. But Saulenas believes that the culprit is groundwater.

Even under normal conditions, the cast iron pipes that make up about one-third of the infrastructure of the Massachusetts State Grid are prone to rust and corrosion. She believes that these pipes, which were once comfortably above the groundwater level, will be intermittently submerged during seasonal high tides, which basically pushes up the groundwater. She believed that high groundwater infiltrated the gas main, flooded her gas meter, and eventually corroded her stove. 

"The problem is big. We seriously underestimated the flood problem." 

Kristina Hill, an associate professor at the University of California, Berkeley, agreed, and Solenas contacted her for answers. "She asked me, is this caused by sea level rise? Obviously, the answer is yes," Hill said. 

Hill is one of many researchers trying to get the public and policymakers to take the risks of rising groundwater seriously. Unlike rising sea levels where the danger is obvious, rising groundwater has never been noticed. Hydrologists are aware of this problem, and this problem is everywhere in academic research, but it has not yet surfaced significantly outside these bubbles. The latest edition of the National Climate Assessment released in 2018 only briefly mentions groundwater rise; many states and regions climate adaptation plans, and even flood maps do not include it.

A 2021 study by Cities magazine found that when coastal cities conduct climate vulnerability assessments, they rarely consider rising groundwater. "They mainly talk about sea level rise and storm surges," said Daniel Rozell, an engineer and scientist affiliated with Stony Brook University, the author of the 2021 paper. "But there are not too many questions about what happens to groundwater."

The impact on existing infrastructure and planned climate adaptation can be catastrophic. Repair work that is not planned for groundwater rise will become useless. The multi-billion dollar infrastructure will need to be upgraded. It may affect an area much larger than the area captured on most flood maps. A 2012 study conducted by researchers at the University of Hawaii included groundwater as a flood risk factor and found that across the country, the threatened area is more than twice as high as the area at risk due to sea level rise alone.

Hill said that any "land is really flat, geology is [the] loose material, coastal areas where water can easily pass through," is "a place that can really be a problem." This includes places like Miami, It also includes Oakland in California and Brooklyn in New York. Silicon Valley communities like Mountain View are vulnerable to rising groundwater, as is Washington, DC. Worldwide, the threatened areas include parts of northwestern Europe and the coastal areas of the United Kingdom, Africa, South America, and Southeast Asia. 

"The problem is big," Hill said. "We underestimated the flood problem."

And because of the way groundwater flows, people at risk may not know it until it's too late. "One of the most important things about groundwater is that the groundwater level rises before the surface is submerged," Rozelle said. In other words, long before the sea hits our front door, we will experience groundwater flooding. 

Rising sea levels may cause groundwater to rise, which seems puzzling. At first glance, the two seem to have nothing to do with each other, but in fact the connection is very simple. It has been overlooked for a long time, reflecting our tendency to solve problems that we can easily see.

To understand this connection, we must first understand groundwater. The water buried in underground sediments starts from surface water, just like rain or snow, and eventually seeps into the ground. A layer of saturated soil lies below a layer of unsaturated soil; the boundary between the two is the so-called groundwater level. In many coastal areas, this layer of saturated soil may be several meters thick, above the salt water from the ocean. As sea levels rise, groundwater is pushed up because salt water is denser than fresh water. 

This is not the only way to connect the ocean and groundwater. 

"Groundwater usually flows to the sea," Rozelle said. "Along the coast, there is what they call a submarine groundwater discharge. If you go to the beach at low tide, you may even notice it. If you stand in the water, you may feel very cold water at the edge of the sand. That is. It is groundwater that keeps flowing into the ocean." 

Therefore, any protection measures aimed at preventing sea level rise must also consider how to let the groundwater flow out.

"It has the power to affect millions of people, but no one is paying attention." 

It can be said that researchers at the University of Hawaii Kolja Rotzoll and Chip Fletcher published the first large-scale study in a well-known scientific journal in Nature in 2012, which looked at the impact of sea level rise on groundwater levels. This study follows a report by researchers from the U.S. Geological Survey and Yale University that studied the changes in groundwater along the coast of New Haven, Connecticut, as sea levels rise. In both cases, the researchers found that both will rise in unison. 

"We checked the records of the oil wells and found that the groundwater level in the coastal areas rose and fell with the tides," Fletcher said. "So we realize that there is a direct connection between the ocean and the groundwater level. As climate change causes the ocean to rise, the groundwater level will rise and eventually flood the land. So we will have all these wetlands around urbanized areas and roads, where we I don't really want them. It turns out that this is a form of sea level rise, and in many areas it is more destructive than people usually think of ocean crossing the coastline and flooding."

We have already seen the effect. 

When discussing groundwater rise with experts, it is often mentioned that it is more complicated and difficult to adapt than sea level rise. Any solution to one aspect of the problem may cause a cascade in other aspects. For example, something as simple as hygiene. Generally, in most parts of the United States, when you flush the toilet, one of three things will happen, depending on where you live: flushing to a cesspool, septic system, or sewer. However, rising groundwater poses increasing challenges for all three. 

The cesspool is essentially a concrete cylinder with an open bottom and perforated sides. Josh Stanbro, the senior policy director of the Honolulu City Council, said that especially in coastal areas, the cesspools that should have been dry are constantly being flooded. He did not serve as the city’s chief resilience officer until January of last year. "They are a bit always wet now," he said. Microorganisms can survive because they are wet, and because there is more water around them, they can leach out.

Honolulu is not the only city with this problem. Miami-Dade County is also facing similar problems with septic tanks. In theory, septic tanks provide a layer of filtration that is not available in sewage tanks. But to filter, the system requires a layer of soil two feet deep, which shrinks as the groundwater level rises. Already 56% of county systems are regularly damaged during storms. It is estimated that by 2040, this number will rise to 64%. A failed septic tank system can contaminate the local aquifer that the community relies on for drinking. 

One solution is to move households and businesses that currently use septic tanks or sewage tank systems to sewers. In Miami-Dade County, the estimated cost of this transition is $2.3 billion. 

Kristina Hill of Berkeley warned that the sewer system is not a panacea. "Most U.S. sewer pipes, including sanitary and rainwater pipes, usually break because we have performed such poor maintenance. We are like an international joke," she said. "People started showing slides on how bad the American system is at civil engineering conferences in Europe to relax the audience." Those broken sewer pipes let in groundwater. In places like New York City and Boston, they have a so-called joint sewer system, where rainwater and untreated sewage are mixed together, so there is less space in the pipeline. This is why, as groundwater rises, places like the Jamaica Bay community in New York City will end up with liquid from rainwater drains at high tide. 

Newer cities often have systems where rainwater enters one pipeline and sewage enters another pipeline. But if the pipe is filled with groundwater when it rains, the rainwater will still have nowhere to go. So in both cases, according to Hill, you will get more floods. 

There is another way that rising groundwater can turn our sanitation system into a killer. 

"In the Bay Area, due to military use and the technological boom in Silicon Valley, there is a lot of legacy pollution underground - it leaves a lot of nasty things," said Kris May, a coastal engineer and climate scientist who founded the Pathways Climate Institute. "And it often happens that after we have resettled low-income houses in these areas, they will still leave a certain amount of pollutants underground, and these regulations are based on non-rising groundwater levels."

The water table is now rising. When it does so, it saturates the soil and releases pollutants such as benzene. These chemicals are extremely volatile, and as gases, they can easily enter the home through the sewer. 

This is the effect of rising groundwater on a system-sewage. But it may affect more. Buried wires that are not properly sealed will short-circuit; the foundation will start to rise from pressure. Some people worry that the earthquake fault may even be stressed. 

To protect themselves from rising sea levels, cities are turning to the same tools they have used for centuries: dams and seawalls. Boston proposed a 175-mile seawall called the Haimen Project. Miami proposes to build a $6 billion, 20-foot-high seawall. New York proposed its own $119 billion, 6-mile project called the New York Harbor Storm Surge Barrier. Homeowners from Florida to California are setting up barriers to prevent the ocean from entering. But the fundamental problem with all these interventions is the same: the sea wall blocks the sea, not the groundwater.

In some areas, if the underlying ground is relatively impermeable, sea dikes or flood dikes can be built to slow the rise of groundwater. But then you will encounter other problems. Recall that the water flows to the ocean. A barrier that prevents groundwater from rising with sea level will also prevent rainwater, such as the recent rain from flowing into the sea. 

"If you don't let the water flow into the ocean, then you basically have to pump it through the wall. This is basically what the Netherlands has been doing for centuries," said Rozell of Stony Brook. But it also creates problems, because many of the places these seawalls are trying to save—most of Lower Manhattan, most of San Francisco and Boston—are built in wetlands, landfills, or both. Of. "If they pump water, the land will sink," Hill said. 

Even if the city is willing to follow this path, it may not be possible everywhere. Fletcher of the University of Hawaii said: “In many cases, you can pump water all day and the groundwater level will not drop.” 

Recall that groundwater is water that enters spaces or pores in sediments. In some places, such as Miami, “the pores are so big that you can only suck in water from the mouth of the river from the ocean,” Fletcher said. "You can pump water as you like, it just keeps pouring in from the endless body of water"-the sea.

Planners often ignore this problem. In 2009, the low-lying island nation of Maldives held the world's first underwater cabinet meeting to draw attention to the long-standing hazards of climate-polluting countries such as the United States due to climate inaction. The message is clear: you are drowning us. Today, the country is already dealing with the consequences of rising sea levels and is integrating its outer island communities into a new island called Hulhumalé. It is designed to withstand rising sea levels. However, the project did not consider the rise in groundwater levels.

"They don't understand that the groundwater level will rise as the sea level rises," Fletcher said. If the sea level rises another two feet-some estimate this will happen in 2040-most of this brand new island will be uninhabitable wetlands.

When he explained this to the lead designer of the project, “He just stared at me—he couldn't speak. It was as if he couldn't understand what I was talking about,” Fletcher said. "They spent billions of dollars on this, but they didn't build it high enough."

At least in one place, you can see people estimating the rise of the groundwater level in near real time. The Strawbery Banke Museum is located in Portsmouth, New Hampshire, near the banks of the Piscataqua River and just a few miles from the Atlantic Ocean. These buildings have been preserved, allowing us to see the past three centuries, but they also give us a glimpse of the future. Some buildings, including the second oldest house in the city, are being flooded from below. 

"We got these super tides, high tides, and the water level was two feet higher than typical. So we started to see this water flowing into our basement," Rodney D., Director of Facilities and Environmental Sustainability at Strawbery Banke Rodney D. Rowland said when visiting the museum in late September. When you squat in a basement where the ceiling is too low for most adults to stand, it is easy to see water marks left by groundwater intrusion in the past. 

The museum has adopted a two-pronged approach. The first element is to educate the public. Rowland said: "One of the exciting things we are going to add is a kiosk, which is connected to sensors placed on the ground around the museum." "They will track the movement of groundwater, [plus] salinity, temperature, Water level. This way visitors will see water under their feet."

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But museums also need to protect buildings. Now, this goal must be balanced with the fight to prevent the water level from rising. In one of the houses, “we decided to eliminate the so-called summer kitchen,” Roland said. "There is a fireplace there, and they cook in the summer. We took it out and put it in a granite block." They had to do this because the old fireplace is like a candle wick, sucking water from the basement into the rest of the structure part.

"So now the rest of the chimneys are preserved," he added. "Water can't pass through that. But we have lost that period of history. This will be a constant battle, how much we will lose to save everything we can."   

In some ways, Roland is lucky. His state of New Hampshire was at least aware of the risk of rising groundwater and included it in the plan. But New Hampshire is an exception. Many other states with wider coastlines will have to face this problem in the next few years, because this invisible risk threatens not only buildings but also lives. 

Less than 50 miles from the Saugus coast, Fae Saulenas plans to go to higher terrain-but not without making some noise. She wrote to legislators, State Grid and the press, trying to draw people's attention to this issue. "Groundwater is really important to me. It is important to me not only because it profoundly affects my life, but also because I think it has the power to affect millions of people," she said. "And no one is ready, and no one pays attention."

Kendra Pierre-Louis is a senior climate reporter for the Gimlet/Spotify podcast "How to Save the Planet".

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