This week on Now and a Long Time Ago, GM visits in with the great flood of 1972. The old photo comes courtesy of the fantastic Old Time DC Facebook page.
The photo is of lower Wisconsin Ave. after Hurricane Agnes blew through. This spring hurricane was the costliest hurricane in history until Hurricane Frederick passed it in 1979.
From the photo, you can see that the Potomac flooded right up to the bottom of Wisconsin. By comparison, as heavy as Sandy was, the Potomac water levels remained several feet below cresting the waterfront, let alone lapping up to Wisconsin.
As for the built environment, you can see a couple changes. The Whitehurst looks mostly the same, although historic lamps were added at some point. The incinerator that would eventually be torn down and turned into the Four Seasons/movie theater was still there.
Additionally, it looks like Wisconsin Avenue was concrete, not asphalt (curiously Reservoir Rd. east of Wisconsin still is concrete, does anyone know why?)
Finally, on one of the old lamp posts on the right, you can see the old street light signs that used to adorn Georgetown’s lamp posts:
The Georgetown Metropolitan 
Several edits. The incinerator was not torn down, most of the building still exists, incorporated into the Ritz Carlton hotel. And it is the Ritz, not the Four Seasons. The Four Seasons occupies the site of the former Washington Gas Light Co. garage.
I don’t know why the concrete on the Wisconsin Ave hill was covered with asphalt; however, I remember the hill being slippery when wet, and vehicles (including a fire truck) wound up where the soon-to-be-dedicated Percy Plaza now is
Thanks for the corrections Walter! I always get the Ritz and the Four Seasons mixed up.