AFTER THE STORM: Rescue workers and a group of Houston residents wait for emergency crews in the wake of Hurricane Harvey in August 2017.

ALYSSA SCHUKAR/THE NEW YORK TIMES/REDUX

STANDARDS:

NGSS: Core Idea: ETS1.C    

CCSS: Reading Informational Text: 8    

TEKS: 7.8A, 8.11D, E.9E, ESS.11E

Holding Back the Floods

After one of the worst hurricane seasons on record, what can the U.S. learn from countries with centuries of experience managing floods?

ESSENTIAL QUESTION: Why might collaboration be important when it comes to solving large engineering problems?

JIM MCMAHON/MAPMAN®

Last August, Hurricane Harvey barreled into the Texas coast. In just a few days, the storm dumped more than 1.2 meters (4 feet) of rain on Houston, America’s fourth most-populous city, and surrounding areas. It set a new record for rainfall from a single storm and led to widespread flooding. Dozens of people died. Tens of thousands had to evacuate, with many still unable to return to their flood-damaged homes.

Like Hurricane Sandy, which hit the Northeast five years earlier, and Hurricane Katrina, which devastated the Gulf Coast in 2005, Harvey demonstrated how vulnerable U.S. coastal communities are to flooding. More than 120 million Americans—nearly 40 percent—live in a coastal county. And that population is growing rapidly.

Scientists believe climate change could bring even more intense flooding to the U.S. Warming temperatures and shifting global climate patterns are not only raising sea levels but could also potentially cause more extreme storms. As a result, U.S. coastal communities are looking for ways to prepare for the future (see Fighting Floods Worldwide). They’re gathering data locally and collaborating with experts around the world to identify the best strategies to keep people and essential facilities above water.

Last August, Hurricane Harvey slammed into the Texas coast. Houston, the city with the fourth largest population in America, was in its path. In just a few days, the storm dumped more than 1.2 meters (4 feet) of rain on Houston and areas around it. It set a new record for rainfall from a single storm. This caused widespread flooding. Dozens of people died. Tens of thousands had to evacuate, and many still can’t return to their flood-damaged homes.

Hurricane Sandy hit the Northeast five years earlier, and Hurricane Katrina pounded the Gulf Coast in 2005. Like these storms, Harvey showed how much danger U.S. coastal communities face from flooding. More than 120 million Americans—almost 40 percent—live in a coastal county. And that number is growing quickly.

Scientists believe climate change could bring even worse flooding to the U.S. Warming temperatures and changing global climate patterns are raising sea levels. They could also cause more extreme storms. So U.S. coastal communities are looking for ways to prepare (see Fighting Floods Worldwide). They’re gathering data at home and working with experts around the world. Their goal: Figure out the best ways to keep people and important facilities above water.

KEEPING A COUNTRY DRY

Perhaps no country on Earth has as much experience protecting against floods as the Netherlands. About a third of the small European nation’s land is below sea level—and much of that area would be underwater if not for centuries of expert engineering. “Flood protection is a huge part of our history and culture,” says Harold van Waveren, a senior adviser for the Dutch government’s flood-prevention agency. “Without it, our country wouldn’t exist.”

Van Waveren lives near Amsterdam at a depth of 5 m (16 ft) below sea level in a polder—an area surrounded by walls, called dikes, that keep water out. The country has nearly 3,500 polders, protected by 40,000 kilometers (25,000 miles) of dikes and dams.

The Netherlands is a small nation in Europe. It may have more experience with flood protection than any other country. About a third of its land is below sea level. Much of that area would be underwater, but expert engineering keeps it dry. “Flood protection is a huge part of our history and culture,” says Harold van Waveren. He’s a senior adviser for the Dutch government’s flood-prevention agency. “Without it, our country wouldn’t exist.”

Van Waveren lives near Amsterdam. His home is 5 m (16 ft) below sea level in a polder. That’s an area surrounded by dikes. These walls keep water out. The country has nearly 3,500 polders, and 40,000 kilometers (25,000 miles) of dikes and dams protect them.

GEORGE STEINMETZ/GETTY IMAGES

FLOATING COMPLEX: These houses in Amsterdam can rise and fall with changing water levels.

Flood protections have continued to evolve since Dutch farmers built the first dikes a thousand years ago. A major storm in 1953 that flooded the southwest Netherlands and killed 1,800 people motivated the country to build the massive Delta Works. This project constructed new barriers and dams to protect against storm surges—increases in sea level due to wind and air pressure changes during storms. The project also included channels called sluices, which drain excess water during floods.

The crown jewel of the Delta Works is the Maeslantkering (MAHS-lawnt-keh-ring), a giant barrier completed in 1997 that protects Rotterdam, one of the world’s busiest ports, from the sea. Ships must enter and exit the port, so building a permanent barrier that blocked the sea wouldn’t work. Instead, the government decided on a huge gate that remains open most of the time and swings shut during storms (see The Netherlands’ Giant Sea Gates).

Dutch farmers built the first dikes a thousand years ago. Flood protections have evolved since then. In 1953, a major storm flooded the southwest Netherlands and killed 1,800 people. This prompted the country to build the huge Delta Works. The project included new barriers and dams to protect against storm surges. These rises in sea level come from wind and air pressure changes during storms. The project also included channels called sluices. They drain excess water during floods.

The crown jewel of the Delta Works is the Maeslantkering (MAHS-lawnt-keh-ring). This giant barrier was finished in 1997. It protects Rotterdam, one of the world’s busiest ports, from the sea. Ships must enter and exit the port. So a fixed barrier that blocked the sea wouldn’t work. Instead, the government chose a huge gate that usually stays open. It swings shut during storms (see The Netherlands’ Giant Sea Gates).

ROOM FOR THE RIVER

The Maeslantkering successfully held back the sea during a 2007 storm. But storm surges aren’t the Netherlands’ only flood threats: In 1995, dikes surrounding the narrow Waal River nearly failed during heavy rains, threatening the city of Nijmegen (NYE-may-ken). Some 200,000 people evacuated. “That led to a big change in our strategy,” says van Waveren. “Until then, we thought we could manage nature and have it do as we wanted. But we realized nature is sometimes stronger than we are. We had to stop fighting it and find ways to work with it.”

Current flood protection strategies in the Netherlands focus on allowing nature to safely take its course during floods. Workers are restoring and protecting coastal lands like beaches, marshes, and dunes, which provide natural buffers against storms.

A storm struck in 2007, and the Maeslantkering held back the sea. But storm surges aren’t the Netherlands’ only flood threats. In 1995, heavy rains fell. Dikes around the narrow Waal River almost failed. The city of Nijmegen (NYE-may-ken) was in danger, and some 200,000 people evacuated. “That led to a big change in our strategy,” says van Waveren. “Until then, we thought we could manage nature and have it do as we wanted. But we realized nature is sometimes stronger than we are. We had to stop fighting it and find ways to work with it.”

Now flood protection methods in the Netherlands have a new focus. They allow nature to safely take its course during floods. Workers are fixing and protecting coastal lands like beaches, marshes, and dunes. These areas are natural barriers against storms.

TELNOV OLEKSII/SHUTTERSTOCK

BOOSTING DEFENSES: Workers in the Netherlands strengthen a dike to prepare for higher waters.

At more than 30 sites around the country, engineers are also creating additional places where water can go. The city of Nijmegen is part of this program, which is called Room for the River. There, workers recently built an extra channel so river water can flow around the city when the level rises. Low-lying areas are being turned into parks, gardens, sports fields, and other amenities that can act as reservoirs for floodwaters in emergencies without harming people or infrastructure. Builders are also moving dikes farther from the river to create additional space for floodwaters.

Engineers are also working at more than 30 sites around the country. They’re creating extra places for water to go. The city of Nijmegen is part of this program, which is called Room for the River. Recently, workers built an extra channel there. It lets river water flow around the city. Low-lying areas are being turned into parks, gardens, sports fields, and other features. They can hold floodwaters in emergencies. Builders are also moving dikes farther from the river. This makes more space for floodwaters.

BRINGING IT HOME

On the coast of Texas, the U.S. Army Corps of Engineers (USACE) is investigating similar plans to combat storm surges. “The biggest element we’re considering is a large gate structure in the Houston-Galveston area that could be closed if a storm is coming,” says Sharon Tirpak, who is overseeing the study. One possible design resembles the Maeslantkering. “If it’s chosen, it would be one of the largest structures in the world,” she says.

The U.S. Army Corps of Engineers (USACE) is looking at similar plans. They need to protect against storm surges on the coast of Texas. Sharon Tirpak is running the study. “The biggest element we’re considering is a large gate structure in the Houston-Galveston area that could be closed if a storm is coming,” she says. One possible plan looks like the Maeslantkering. “If it’s chosen, it would be one of the largest structures in the world,” she says.

For storms like Harvey that dump massive amounts of rain, a sea gate would do little to stop flooding. So the Texas study is also evaluating how natural features like wetlands could help absorb heavy rains. The fact that so much of Houston is covered in concrete is one reason it flooded so badly, says Henk Ovink, the Dutch special envoy for water affairs. His job is to share Dutch expertise in flood management with countries around the world. Restoring native prairies and wetlands, which can soak up water, could help protect Texas and other areas against future floods.

A team from USACE recently visited the Netherlands to tour Dutch coastal defenses. And Dutch flood engineers came to the U.S. to compare methods for evaluating the stability of levees—our version of dikes.

Ovink says the challenges ahead represent an opportunity for coastal communities to come together to innovate. “In the form of rising seas and storms, water gives a tangible meaning to climate change that we have to prepare for,” he says. “But we can do this. It doesn’t have to be something we fear.”

Storms like Harvey dump huge amounts of rain. A sea gate wouldn’t stop that kind of flooding. So the Texas study is also looking at natural features like wetlands. It’s figuring out how these could help soak up heavy rains. Much of Houston is covered in concrete. That’s one reason it flooded so badly, says Henk Ovink. He’s the Dutch special envoy for water affairs. His job is to share Dutch knowledge and skill in flood management with countries around the world. Native prairies and wetlands can soak up water. Restoring them could help protect Texas and other areas against future floods.

Not long ago, a team from USACE visited the Netherlands to see Dutch coastal defenses. And Dutch flood engineers came to the U.S. to meet with engineers here. They compared ways of checking the strength of levees. Those are our versions of dikes.

Challenges lie ahead. But Ovink says they are an opportunity. Coastal communities can come together to find new ideas. “In the form of rising seas and storms, water gives a tangible meaning to climate change that we have to prepare for,” he says. “But we can do this. It doesn’t have to be something we fear.”

CORE QUESTION: Explain why a sea gate alone might not be enough to protect Texas from future floods.

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