One of the smartest things the Army Corps of Engineers ever did

In the 1970s, the Corps abandoned plans for a massive series of levees and flood-control dams along the Charles River and instead bought up or acquired easements to 8,100 acres of land along the river from Millis to Boston. The land acts like a sponge - absorbing large amounts of water during heavy rains and the releasing it slowly afterward, reducing the amount of flooding in built up areas - such as Cambridge and the Back Bay. Not only does it work (in conjuction with giant pumps installed at the New Charles River Dam at the river's mouth), it cost 10% of the levee/dam plan.

You can get a good view of the plan in action from the top of Millennium Park in West Roxbury (Ed. note: Only an idiot, or a Universal Hub editor, will go to the top in the middle of a nor'easter), built into a curve on the Charles. There's flood-control land on either side, including Cutler Park, which, while marshy, does not usually look like a lake.

• Charles River Valley Natural Storage Area.
• Water Resources and the Urban Environment, Lower Charles River Watershed, Massachusetts, 1630-2005