I recall from my elementary school history books that Washington DC was built on donated marsh land that the contributing states deemed almost worthless.
Why doesn’t it have a constant flood problem like New Orleans? I know NO has pumps that removes drainage water and that helps after normal rains. What did the designers do in DC?
Yes, another Sandy inspired thread. I’m wondering if the Capital bldg and White House will get soggy in the next day or two.
DC actually HAS flooded several times. This NCPC PowerPoint presentation shows the effects of that flooding and the flood control measures that have been put in place in response to it. (Warning: PDF!)
Awesome answer jayjay. Thanks.
This is why I visit the sdmb for answers to tough questions. 
New Orleans is officially below sea level (minus eight feet), sitting atop an alluvial fan that is forever sinking, in a geographic location prone to flooding storms. OTOH, the lowest official elevation for DC is one foot above sea level, with its highest point 410 feet above sea level.
Some parts, like Georgetown & the Tidal Basin, have been flooded before and by Sandy. Any location near sea level will get flooded in a strong storm.
Yep. There are actually some sort of flood gates at Georgetown Harbour (a commercial area, lots of restaurants and nightlife, right on the Potomac).
Old Town Alexandria (the coastal / touristy area), which is right across the river from parts of DC, gets flooded periodically as well.
I don’t know if either area had much trouble this time around, haven’t looked for news of it.