Why the Charles doesn't seem to flood as much as other rivers

Natural flood control in action this afternoon along the Charles River near Milliennium Park in West Roxbury.

Part of the reason you're not hearing much about flooding along the Charles is simply because a lot more rain fell up near the Merrimack than around the Charles. But part of it might also have to do with a decision made by the Army Corps of Engineers in the 1970s.

Until the '70s, the federal and state governments used classic engineering techniques to try to reduce flooding in the Charles - they built a dam at the mouth and some mega-pumps to pump water from the river into the harbor. And the Corps came up with a $100-million proposal to build levees and flood-control dams along the middle Charles. But the Corps abandoned that plan in favor of something more unusual: It began buying up or acquiring easements to some 8,100 acres of low-lying riverbank land from the Medfield/Millis line to the Dedham/Boston line - and then just let the land sit there.

The idea was that the various parcels of land would act as giant natural sponges during floods, absorbing vast amounts of water quickly, then releasing it slowly as the river receded. And it seems to work. During heavy rain (or the spring thaw), the Medfield/Millis border becomes a large lake - but since nobody lives on the Corps land, nobody has to be evacuated, either. You can see similar flood control in action from the top of Millennium Park in West Roxbury - or even across from the northbound side of Rte. 128 just past Great Plain Avenue.

Acquiring the land cost $10 million - or 10% of what the government had originally expected to spend on manmade structures.

• Charles River Valley Natural Storage Area
• Charles River Watershed Association
• Water Resources and the Urban Environment, Lower Charles River Watershed, Massachusetts, 1630-2005 (via Charles Swift)
• Charles River at Mother Brook flow information