A wall is meant to guard Washington D.C. from flooding. Will it withstand Florence?

As Hurricane Florence looms off the East Coast of the United States, a system of barriers stands ready to guard downtown Washington, D.C., from a 100-year-flood.

The system of berms and sandbags has existed in some form for decades, and is intended to prevent sudden floods from the Potomac or Tidal Basin. But after Hurricane Katrina, inspectors found the system lacking.

“The reality is that after Hurricane Katrina, there was understandable increased scrutiny of levee systems during inspections across the country and with the increased scrutiny the Corps determined that the closure structure as it was then was unreliable for reducing flood risk from the Potomac River and gave the system an unacceptable rating,” a spokesperson for the Army Corps of Engineers told McClatchy.

Over the next few years, engineers developed improvements in the system to address the problems. Now, Hurricane Florence could be the first major storm to give those improvements a trial-by-fire, ABC 7 reported.

Hurricane Florence, a Category 4 storm as of Tuesday afternoon, is expected to pummel the Carolinas later this week, and is predicted to make landfall sometime between Thursday and Friday. The governor of South Carolina has ordered evacuations for much of the east coast of the state as Georgia prepared to accept fleeing residents.

But the storm could also threaten parts of Virginia and the D.C. area, depending on how the system moves in the coming days. On Tuesday, officials in the District declared a state of emergency.

A worst-case scenario has Florence making landfall between South Carolina and North Carolina’s Outer Banks islands, then moving north and pushing a storm surge up the Potomac River, according to the Washington Post.

Combined with a city already soaked from a wet summer, it could be a disaster scenario, said Jim Lee, a local meteorologist, according to the paper.

Certainly we’re primed,” Lee said, according to the Post. “Even if we’re on the northern fringe [of the storm], we’re going to have flooding issues. We’re sitting on a powder keg.”

So what would happen if the storm brought major flooding to the nation’s capital? One of the first lines of defense is a system of little-known levees and berms called the Potomac Park Levee System.

There probably aren’t 10 people in Washington who even know this levee exists,” University of Maryland disaster and national-security expert Gerald Galloway said in 2017, according to Rolling Stone.

The system includes sections of decades-old 12-foot-high earthen berms near the Washington Monument that connect to the newer concrete 17th Street levee, which began construction in 2011 and was completed in 2014, according to a news release.

The levee looks like a sturdy stone wall, but it crosses over a major road, which means there is a large gap in protection most of the time. Plans call for engineers to quickly move in when there is a flood threat, close the road and plug the gap with a series of blocks which slide into place, forming a quick, temporary barrier.

The wall, when fully assembled, is designed to handle a flooding event with water levels as high 700,000 cubic feet per second, according to the Army Corps of Engineers.

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Part of the levee system under construction. Army Corps of Engineers

“The levee can be installed in about four hours,” a National Parks Service spokesperson said in 2015, when the city was being threatened by Hurricane Joaquin, according to WTOP. “It would be activated based on … the predicted flood peak versus the number of days before the arrival of the flood.”

Crews have rehearsed how they would assemble the wall quickly, but in the chaos of a storm, the process could become complicated and difficult, disaster experts said, according to Rolling Stone.

Hurricane Florence could be the first real test the levee system has had since its installation, and it’s unclear how well it will perform in disaster situations, said Bilal Ayyub, a professor in the Department of Civil and Environmental Engineering at the University of Maryland, according to Fox 5 DC.

“The flooding will continue where the levee is and then that could affect the Washington Monument,” he said, according to the station. “It could get to the [National] Mall. It could actually get all the way to the backyards of almost the White House.”

A prime concern, he told the station, was that the flooding could go around the levee and flow into the National Mall.

For now, the DC area is watching and preparing. Officials were expecting massive rain and power outages, as well as flooding in certain areas they were paying close attention to, the Washington Post reported.

In a statement, Mayor Muriel Bowser encouraged residents to monitor emergency stations and to stock up their emergency kits of food, medicine and other supplies.

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