CRWA in the News

Taking on Water
If it seems like devastating floods are more common each spring, they are. We have no one but ourselves to blame.

By Jeremy Miller  

Boston Globe, Sunday, May 6, 2007

The storms that dropped more than a foot of rain in 24 hours on northeastern Massachusetts last May are not likely to fade from memory, or the record books, any time soon. After the deluge, parts of Lawrence and Lowell were under 5 feet of water, and sections of downtown Peabody sat under more than twice that much. Tons of raw sewage sluiced from municipal sewer systems into regional waterways. More than 4,000 residents in 17 communities throughout Middlesex, Essex, and Suffolk counties fled the rising flood waters. Just more than $70 million in state and federal aid poured in to finance the recovery and repair of nearly 11,000 damaged households and businesses.

These were the dreaded "100-year floods," a designation applied to a defined area of land with a 1-in-100 chance of experiencing a flood of this magnitude in a single year. It serves as a key guideline for the design and maintenance of flood defenses, as well as zoning and home insurance premiums.

But many in the Boston engineering community say our 100-year flood boundaries are dangerously outdated. They point to Peabody and its perennial downtown floods. Richard Carnevale, Peabody’s public services director, says his town has experienced five so-called 100-year events in the last 10 years. It doesn’t take an actuary to see something’s amiss here. The odds of five 100-year floods in the span of a decade, says Tufts environmental civil engineering professor Richard Vogel, is about 1 in 40 million. Serious repeat floods aren’t unique to Peabody. In the last decade, Massachusetts saw six federal states of emergency related to flooding – all involving one or more of the state’s most populous and built-up eastern counties.

Vogel says our flood designations don’t account for one critical variable: urban development. In natural settings, rainwater soaks into the earth, eventually percolating into aquifers deep underground. But in the concrete terrain of modern cities, rainfall is funneled unnaturally – over roads, roofs, streets, and parking lots – into storm sewers. As the water discharges rapidly back into river systems, the waterways often can’t handle the excess burden. "We treat water the way we treat garbage. We throw it away into our sewers," says Robert Zimmerman, executive director of the nonprofit Charles River Watershed Association.

An area’s chance of flooding increases with each developed acre. A landmark 1968 US Geological Survey study found that urbanized areas are three times as likely to experience floods as they were before they were developed. Vogel and colleagues have found that the next time a 100-year flood strikes the Aberjona River, near Winchester, it could bring four times as much water as one would have brought in the 1940s, due mainly to "increased land development." According to data gathered from 1991 to 1999 by the Metro Area Planning Commission, metro Boston loses about 7 acres daily to new development.

Add climate change to the picture, and it’s even gloomier. While there is some disagreement over long-term projections, several climate models, including one by University of New Hampshire climate scientist Cameron Wake, predict increased frequency of "extreme rainfall events" in New England. Even so, a laser focus on climate change will not help us solve flood problems derived from our love of concrete, culverts, and elaborate storm sewers.

We can reduce our risk, say Vogel and Zimmerman, by redesigning our cities to function within the parameters of nature. That means using low-impact building techniques that reduce the amount of impervious surface, thereby decreasing the rate at which rainwater is funneled back into local waterways.

Nature was heeded with the creation in the 1970s of the Charles River Natural Valley Storage Area, a series of protected wetlands in the suburbs west of Boston. This 8,000-acre tract acts as a sponge during heavy rainstorms, allowing water to percolate back into aquifers and leaving space for the river to overrun its banks without damaging residential and business property. The proof of its effectiveness seems to be the 100-year flood that did not happen on the Charles. Though rainfall totals were comparable throughout Eastern Massachusetts, the Charles was largely able to resist the rapid rise that the Merrimack, Ipswich, and Saugus rivers experienced last May.

While the threat of shifting weather patterns and global warming dominates our environmental outlook, it’s important we don’t neglect the key factor driving our flood risk: sprawl.

Jeremy Miller is a New Jersey-based freelance writer. Send comments to magazine@globe.com.