BGuthrie Photos: DC -- Natl Mall area -- 17th Street Levee (Floodwall)

DC -- Natl Mall area -- 17th Street Levee (Floodwall):

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Description of Pictures: The DC Historical Society Annual Conference talked about this. I had never noticed it before. From https://www.ncpc.gov/DocumentDepot/LeveeFactSheet.pdf
Following significant regional storm events, the Potomac River sometimes overflows its banks. As a result of several floods that extended all the way to Pennsylvania Avenue, Congress directed the construction of a levee system on the National Mall. The current levee, in place since the late 1930s, includes an earthen berm that runs parallel to the Lincoln Memorial Refl ecting Pool. It requires construction of a temporary closure of sandbags, Jersey barriers, and an earthen dam across 17th Street when river flood conditions are imminent. Post-Katrina federal standards require that a more reliable levee system be in place. Until levee improvements are completed, major federal and private sector offices, cultural institutions, and critical infrastructure in downtown Washington are at risk of river flooding. In addition, flood maps issued by the Federal Emergency Management Agency (FEMA) now show much of this area within the 100-year floodplain. This triggers new flood-related review requirements for federal and private development proposals, and as a result, private property owners are required to purchase flood insurance.

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Copyrights: All pictures were taken by amateur photographer Bruce Guthrie (me!) who retains copyright on them. Free for non-commercial use with attribution. See the [Creative Commons] definition of what this means. "Photos (c) Bruce Guthrie" is fine for attribution. (Commercial use folks including AI scrapers can of course contact me.) Feel free to use in publications and pages with attribution but you don't have permission to sell the photos themselves. A free copy of any printed publication using any photographs is requested. Descriptive text, if any, is from a mixture of sources, quite frequently from signs at the location or from official web sites; copyrights, if any, are retained by their original owners.

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[1] MALLFW_161207_01_STITCH.JPG

[2] MALLFW_161207_04_STITCH.JPG

[3] MALLFW_161207_07.JPG	[4] MALLFW_161207_16.JPG	[5] MALLFW_161207_18.JPG
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Description of Subject Matter: Seen This Wall By The Washington Monument? That’s the Potomac Park Levee
Elliot Carter
These stone walls by the Washington Monument aren’t a part of any memorial or historic structure. They’re a temporary dam that can span 17th street and hold back a 100-year flood. The 17th street dam is the newest part of the 80-year-old Potomac Park levee.
Washington's Federal Triangle neighborhood is uniquely vulnerable to flooding. First – the area is built on low lying land; if the river crests East Potomac Park it would quickly rush downhill and inundate the cross streets off Constitution Avenue. The second threat comes from rain runoff - Federal Triangle is the lowest point in a drainage basin stretching from the ballpark to Fort Totten.
The stakes are even higher because of what’s in those Federal Triangle buildings. Flood damage to the National Archives, EPA, IRS and Department of Justice could be devastating.
The original Potomac Park Levee was a temporary structure built by the Civilian Conservation Corps during a flood in 1936 to keep rising waters from reaching downtown. That weather event spurred Congress to authorize the construction of a larger earthen barrier and make the levee permanent. The Army Corps of Engineers completed the project in 1939. Most people walking along the sloping footpaths around the tidal basin don't realize that they're standing on manmade berms that were carefully laid out to prevent a watery disaster.
17th Street was the only gap in the levee - a deliberate but foolish engineering decision. Building in a gap offered two advantages. First it provided a pleasant even grade for automobile drivers traveling North-South. In the event of flood conditions, the plan called for a hastily built sandbag wall to plug the gap.
The 17th Street gap offered a second benefit of centralizing the risk of a flood, so during a storm engineers could focus their efforts on a single preplanned fail-safe, rather than fighting the waters at a thousand different locations along the levee.
Unfortunately, in the case of the flood of 1937, 1942, 1972, and 2006 that wasn’t good enough.
Washington finally moved to address the issue in 2011 and began construction of the present day stone and cement structure. The gap in the center can be filled in with posts and panels that are capable of holding back waters up to 19 feet above sea level. They’re stored ready to go on trucks in Bladensburg and can be assembled in a few hours. The crews practice once a year to keep up their readiness and check the equipment.

The above was from https://architectofthecapital.org/posts/2016/12/4/potomac-park-levee
Atlas Obscura Description: Potomac Park Flood Levee
This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

These stone walls by the Washington Monument aren’t a part of any memorial or historic structure. They’re part of a temporary dam that can span 17th Street and hold back a 100-year flood. The dam is the newest part of the 80-year-old Potomac Park levee.
Washington’s Federal Triangle neighborhood is uniquely vulnerable to flooding. First, the area is built on low lying land; if the river crests East Potomac Park it would quickly rush downhill and inundate the cross streets off Constitution Avenue. The second threat comes from rain runoff; Federal Triangle is the lowest point in a drainage basin stretching from the ballpark to Fort Totten.
The stakes are even higher because of what’s in those Federal Triangle buildings. Flood damage to the National Archives, EPA, IRS and Department of Justice could be devastating.
The original Potomac Park Levee was a temporary structure built during a flood in 1936 to keep rising waters from reaching downtown. That weather event spurred Congress to authorize the construction of a larger earthen barrier and make the levee permanent. The Army Corps of Engineers completed the project in 1939. Most people walking along the sloping footpaths around the tidal basin don’t realize that they’re standing on manmade berms that were carefully laid out to prevent a watery disaster.
17th Street was the only gap in the levee—a deliberate but foolish engineering decision. The gap provided a pleasant even grade for automobile drivers traveling north to south, and it centralized the risk of a flood, so during a storm engineers could focus their efforts on a single preplanned fail-safe rather than fighting the waters at a thousand different locations along the levee.
In the event of flood conditions, the plan called for a hastily built sandbag wall to plug the gap. Unfortunately, in the case of the floods of 1937, 1942, 1972, and 2006, that wasn’t good enough.
Washington finally moved to address the issue with construction of the present-day stone and cement structure. The gap in the center can be filled in with posts and panels that are capable of holding back waters up to 19 feet above sea level. They’re stored ready to go on trucks in Bladensburg and can be assembled in a few hours. The crews practice once a year to keep up their readiness and check the equipment.

The above was from https://www.atlasobscura.com/places/potomac-park-flood-levee
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