A wall on the Mall protects against a long shot

By Michael E. Ruane
Tuesday, November 16, 2010

Eighty thousand cubic yards of dirt. Thirty steel girders. An eight-foot-high concrete wall.

All to hold back floodwaters that may, or may not, surge across the Mall in the next century or so.

But in the apocalyptic, post-Hurricane Katrina world, no chances can be taken.

So government officials announced Monday morning that work is about to start on a $9 million flood-control project that will alter the landscape of the Mall west of the Washington Monument to protect it, and part of Washington, from potential catastrophe.

The project will create a levee that would be erected across 17th Street below Constitution Avenue in the event of a huge flood.

It calls for the construction of large earthen berms, using tons of dirt, and the eight-foot walls on both sides of 17th Street.

It also will require engineers to sink a series of caissons 30 feet deep into the surface of 17th Street, where girders could be placed to support temporary panels to block floodwater.

Work is to begin next month and conclude next summer.

The project aims to protect large sections of downtown Washington from extensive river flooding, and to keep those sections from being declared a flood zone, which could require property owners to buy flood insurance. Such insurance runs about $1,500 a year, officials said.

The project is the result of the Federal Emergency Management Agency's nationwide review of flood zone maps after Hurricane Katrina devastated New Orleans and parts of the Gulf Coast in 2005.

When FEMA reviewed the District's flood zones, it concluded that existing plans to use sandbags and jersey barriers to block floodwaters flowing north on 17th Street from the Potomac River and the Tidal Basin were inadequate.

FEMA foresaw a scenario in which a flood could inundate a huge crescent of downtown Washington from 17th Street and Constitution Avenue east to the Capitol and south toward Fort McNair.

And it proposed placing the area - including Federal Triangle, the east end of the Mall, and several Smithsonian museums - in the 100-year flood zone unless a better flood-prevention system was devised.

"It became necessary for us to finally protect this Mall with [something] other than sandbags," D.C. Del. Eleanor Holmes Norton (D) said at Monday's announcement.

Working together, the District, the Army Corps of Engineers, the National Park Service and other agencies came up with the idea for a robust flood barrier at a "choke point" on 17th Street.

It is called a "post and panel" system, officials said. In the event of a flood, girders would be erected temporarily and eight-foot-tall aluminum panels assembled between the girders to block the surging water.

The system will first require the sinking of about 30 caissons into the ground across 17th Street and its shoulders, where the girders will be set up. "You've got 10 on the roadway and about an equal number on each side," said Steve Garbarino, the Corps of Engineers' project manager for flood protection in the Washington area.

The posts and panels will be stored on a special tractor-trailer at a National Park Service facility in the District until needed. The caissons will be covered when not in use, officials said.

"This city does not flood that fast," said Steve Lorenzetti, the National Park Service's deputy superintendent of the National Mall and Memorial Parks. "We'll have 24 to 48 hours of notice."

The post and panel system - about 140 feet long - will be augmented by a permanent eight-foot-high concrete, stone-covered wall on either side of 17th Street, and by the earthen berms on either side to link the walls to high ground.

"They've got to bring a lot of dirt in here," Garbarino said, as he stood after a news briefing on the Washington Monument grounds, just east of 17th Street. "This whole area has got to be built up."

Although the project is deemed necessary, Norton expressed some dismay.

"I regret that, however minor, any structure is on this land," she said. "The notion of breaking this landscape is really heartbreaking to me and should be to all who value what the Mall stands for. But . . . there was nothing else to do."

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