Blossomania! Originally uploaded by Payton Chung
Sure, living by the water has its highlights — like being able to walk out your front door to views like these — but I can’t help but worry about the impact of sea level rise on my neighborhood. Luckily, I suppose, I live a few meters above sea level; Washington’s park-lined waterfront allows a substantial buffer against the encroaching high tides.
The EPA’s Rising Sea site offers state-by-state reports on adaptation plans for sea level rise. For the District, the reports indicate that there is a high likelihood of further shore protection for already armored shorelines, like the ones nearest me. A hybrid approach may be taken for currently natural shorelines, like those along the Anacostia River.
Ultimately, the answer may be akin to the tidal gates that have kept the Tidal Basin relatively clean for over a century: a tidal barrier akin to the Thames Barrier, the IHNC under construction outside New Orleans, or one contemplated for New York Harbor. I found a 1963 Army Corps publication on hurricane preparedness (pp. 16-17 of this PDF) that modeled the 15-foot storm surge protection that could be afforded by a mechanical tidal barrier. Their proposed location for the barrier was between Marshall Hall, Maryland and Mason Neck, Virginia. Incidentally, the Marshall and Washington families used to run a little ferry across the river there — but protecting the city named after Mr. Washington might ultimately trump his lifelong dream of improving the Potomac’s navigability.
[2017 update: a Bisnow article mentions proposals for storm surge barriers in Boston, Houston, and New York harbors.]
west north 
ABC’s Bill Blakemore points out that Saint Petersburg, Russia has dammed the Gulf of Finland. Closer to home, in the 1960s Providence built a hurricane barrier across its estuary, capable of turning away 20-foot storm surges.
An examination of local elevation maps finds that one or two strategically placed dams across the Potomac could protect the city up to over 100′ of sea level rise. Only a few other coastal-plain cities worldwide can make a similar claim, and that degree of SLR would threaten even inland cities like Beijing and Burlington, Vermont.
Leon Krier’s sketches of a reimagined, water-filled Mall show another way to accommodate slightly higher sea levels — as well as allowing continued growth of museums, filling in around today’s existing buildings and taming the over-scaled spaces of Burnham’s Mall.