The Potomac River flooded after a weekend of heavy rains, and by Monday the river had risen up to 12 feet.

Normally floodwalls are raised to protect Washington Harbour, the restaurant and office complex on the waterfront. The modern floodwalls were part of the original construction, and have been used successfully dozens of times since they were built in 1986.

But this time, a section of the wall wasn’t raised early enough. Muddy water gushed into the Harbour complex, which is conveniently shaped like a crescent bowl.

A week later on Earth Day, the Harbour is still closed as a clean-up crew deals with the effects of Mother Nature.

Of course, this all got me thinking about historic floods in the District.

The capital is located on a tidal river after all, and is subject to the whims of nature – everything from hurricanes coming from the east to melting snows coming from the west.

While I was conducting a tour a few years back, one of the drivers joked with my group about the District’s “Great Flood,” pointing to the line of discoloration that runs about a quarter of the way up the Washington Monument.

Luckily, the waters of the Potomac have never gone that high. But there have been more than ten significant floods in D.C.’s history: 1889, 1924, 1936, 1942, 1969, 1972 (Hurricane Agnes), 1985, 1996, 2001, 2003 (Hurricane Isabel), and 2006.

A photo from June 2, 1889, shows Pennsylvania Avenue looking more like the Potomac River, with waters reaching 12.5 feet above flood stage.

LIFE Magazine documents a great wartime flood in the District, when water came up to the very steps of the Lincoln Memorial and the newly built Jefferson Memorial.

Those two memorials actually sit on land that used to be under water, until the 1901 McMillan Plan called for using landfill to extend the National Mall to the west, and build the Tidal Basin to the south.

Most tourists at these sites don’t realize that they’re walking on reclaimed land, which now constitutes the lowest elevation in the District.

Recently, this area has experienced more and more flooding during high tides and storms. Water regularly flows over the crumbling stone sea wall of the Tidal Basin, sometimes coming right up to the trunks of the famous cherry trees.

Congress recognized the potential for disaster as early as the 1936 flood, and authorized the Army Corps of Engineers to build a levee to protect the city from major flooding. You can still see parts of the Potomac Park Levee today – a long earthen hill built north of the Reflecting Pool, from the Lincoln Memorial to the Washington Monument. Much of it was actually built from the dirt extracted to create the Reflecting Pool.

Unfortunately parts of it were removed during World War II to construct a building for – ironically enough – the Navy.

Washington again flooded in 1942, causing Congress to authorize a repair of the levee. But it never fully funded the plan, and the improvements were never completed.

The plan required that several temporary barriers – much like the floodwalls in Washington Harbour – be built during flooding along north-south roads which constituted gaps in the levee, like 23^rd and 17^th Streets.

If the gap in 17^th Street was left open during a major flood event, the water would flow from the Ellipse, just south of the White House lawn, into the downtown area known as Federal Triangle. It would continue through a crescent-shaped, low-lying area extending all the way to the base of Capitol Hill, and down to Fort McNair in Southwest Washington.

All this sound familiar? In New Orleans, it was the 17^th Street Canal levee that was breached during Hurricane Katrina, causing massive flooding to the Crescent City.

The District’s potential flood zone would also sound familiar to Nineteenth Century Washingtonians. It follows the exact same course of what was once a city canal, and before that, a major tributary of the Potomac River called Tiber Creek. The waterway and the canal were submerged in the late 1800s when Constitution Avenue was built above it.

But because of its past life under water, this area is still susceptible to flooding – and not just from the rising of the Potomac. After several days of summer storms in 2006, buildings like the Commerce Department, Justice Department, IRS, and National Archives were all submerged. Luckily the Declaration of Independence and the Constitution were spared water damage.

After Hurricane Katrina, the Federal Emergency Management Agency reviewed levees nationwide, and determined that Washington’s were inadequate. Emergency plans to use sandbags and jersey barriers to stop up the 17^th gap didn’t quite cut it, and FEMA threatened to declare much of the Federal Triangle area a flood zone unless improvements were made.

A modern floodwall was planned for 17^th Street by the Army Corps of Engineers, and construction began last fall. It includes creating a system of girders on the street that could hold temporary panels to form a dam.

These would connect to permanent, eight-foot stone walls built on the Mall on either side of the street. Additional earthen mounds will also be built to complete the levee and block the water’s route.

The project is slated to be finished later this year.

Once it’s built, it should ensure that Tiber Creek remains a thing of the past.