A year ago this week, record rainfalls and overflowing rivers temporarily transformed this region into a strange, watery world.

From the Eightmile River in Lyme to the Yantic in Norwich, the Quinebaug and the Pachaug in Griswold, Whitford Brook in Old Mystic and the Wood-Pawcatuck rivers watershed on both sides of the Connecticut-Rhode Island border, watercourses swelled onto roadways, overtopped dams, undermined bridges, invaded garages and forced evacuations of some neighborhoods.

Overfilled by record rainfalls, groundwater stores normally sequestered deep within the earth rose to swamp septic systems and basement furnaces. Fortunately, there were no deaths.

While much of the cleanup was completed months ago, there is still visible evidence of the floods in the two closed bridges awaiting repairs in Washington County, R.I., in the badly eroded section of River Road in Old Mystic and the missing span to North Stonington's village center.

Not only did the flood of 2010 have a major impact on the region, but experts say it holds important lessons for wise community planners and residents.

"This was an extreme event, but it certainly fits into the patterns of climate change," said Professor Thomas Boving, hydrologist in the College of Environmental and Life Sciences at the University of Rhode Island who recently completed an analysis of the flood and, as a Hope Valley, R.I., resident, was affected by it. "It should serve as a warning that these types of events are much more likely to occur more frequently. It will probably happen again."

What is now recognized as this region's worst flooding in decades extended to all of Rhode Island and southeastern Massachusetts. In New London County and neighboring Washington County, R.I., it left affected residents to clean up a mess of mud, debris and damage and wade through repair bills, government assistance applications and insurance claims.

In the Westerly neighborhood off Pound Road, Ed and Cindy Morrone are still rebuilding parts of their flood-damaged home overlooking Chapman Pond, replacing a destroyed cement patio and stairs with a wooden deck and new staircase. They also lost a basement boiler. Floodwaters surrounded the neighborhood, leaving it inaccessible except by the small boats residents used to cross the pond. While some residents of "Chapman Island" evacuated, others stayed to make do with generator power and share what they had. Floodwaters didn't recede for days.

"It took over a week," Ed Morrone recalled. "I stayed here, helping everybody else. It brought everybody in the neighborhood closer in a time of emergency."

Open space limited damage

While homeowners focused on personal losses, local and state governments tackled infrastructure repairs and awaited federal assistance, and began considering the long-term implications of how to plan for future floods. As bad as it was in this region, though, it would have been much worse if there had been fewer forests, fields and open spaces to hold floodwaters. In eastern Rhode Island, with more pavement to channel the downpours directly into rivers and streams, damage was greater.

"We would have seen as much damage here as they did in Cranston if we had as much pavement," said Christopher Fox, executive director of the Wood-Pawcatuck Watershed Association. "The take-home message is that man does not have control over the environment, no matter how much you're lulled into a false sense of security."

An important part of the association's mission, he said, is to monitor development in the 300-square-mile watershed, which extends into four Connecticut border towns, and the flood certainly provides a strong argument for working to keep the area rural.

The U.S. Geological Survey, using data from gauges in streams, has deemed the deluge of 2010 a 100-year flood in southeastern Connecticut, and a 200- to 500-year flood in Washington County. That means that, based on the historical record, it was a flood of a rarity and magnitude that has only a 1 percent chance of happening in Connecticut in any given year, and a 0.2 percent to 0.5 percent chance of recurring in any year in that part of Rhode Island. At some of the 10 stream gauges in the area, it set new records for the height and volume of water measured.

"It was a pretty incredible flood," said Andrew Waite, hydrologist with the USGS office in Northborough, Mass., which is in charge of stream gauges in Rhode Island. "Some of our gauges were overwhelmed (during the flood), but this one did continue to work."

The gauge he was referring to is on the Pawcatuck River at Wood River Junction, R.I., next to a bridge over Route 91. On Tuesday, as he conducted routine checking of the instruments and flow measurements, he recalled the scene a year ago: The bridge and highway were submerged, and waders were required to reach the gauge. A pencil line on the wall about 3½ feet from the floor inside the concrete gauge house marks the water height.

In the days after the flood, he and USGS colleagues from the Massachusetts and Connecticut offices, along with Army Corps of Engineers staff, attached dozens of small green discs and other reminders at high water marks on trees, walls, bridges and signs over hundreds of miles throughout the flooded area. The marks serve as the historical flood record and will be used for flood mapping projects.

"We were out in full force for a solid month surveying the area," Waite said.

Field work during and after the floods is also used to validate - or revise - Federal Emergency Management Agency flood maps, said Elizabeth Ahearn, hydrologist and surface water specialist at the Connecticut USGS office in East Hartford.

Areas shown on these maps as being flood prone are required to carry flood insurance. The field work also provides the basis of flood calculations developed for rivers and streams where there are no gauges.

Phil Zarriello, surface water specialist for the USGS, said the high-water marking and flood data collection are useful for decisions about wetlands preservation, roads, drainage, bridge height, culvert size and intensity of development appropriate for particular areas. Keeping flood information up to date, he believes, is particularly critical now as climate conditions are in flux, and past patterns can't be relied upon as guides for the future.

"We're dealing with a moving target," he said.

More '100-year floods' expected

Three research reports published over the last two years, the most recent released just as the floods were occurring, document trends for heavier, more intense precipitation and more frequent flooding in the northern latitudes.

The phenomenon results, the research authors say, from warming due to climate change. That causes the atmosphere to hold more water vapor and energizes hydrological cycles.

Mathias Collins, hydrologist with the National Oceanic and Atmospheric Administration, noted a significant uptick in flood events in New England since 1970.

A report from the University of New Hampshire describes increases both in yearly rainfall totals across the region and for more of that rainfall to come during intense storms. Coupled with more development over the last 60 years, flooding and flood risk have also increased, the report said.

"Requirements for how and where we build our homes, businesses, roads, wastewater treatment plants, power lines and other structure need to be re-evaluated," the report concludes. "The problem with increasing frequency and intensity of extreme precipitation is that the 100-year flood is now occurring much more frequently. ... Future increases in extreme precipitation are very likely."

Like other municipal officials in the flood-affected region, Steve Hartford, town manager of Westerly, said last year's experience will have a lasting impact. Even as immediate needs for flood damage repairs continue - Canal Street and its drainage structures need to be redesigned and rebuilt, some local businesses haven't fully recovered, and the location of the public works garage and transfer station that were under water for days during the flood are being re-examined - the town is also taking a longer view.

"There's a greater urgency to take a look at the whole area along the (Pawcatuck) river, and consider how development can be better managed," Hartford said. "There's definitely a concern, now that people understand the risks of being in a low-lying area."

j.benson@theday.com

HOW HIGH DID THE WATER GET?

Peak water heights during 2010 floods at U.S. Geological Survey stream gauges in the Wood-Pawcatuck rivers watershed and southeastern Connecticut.

Pawcatuck River at Westerly:Peak height during 2010 flood: 15.4 feetPrevious peak: 15 feet, 1938

Pawcatuck River at Wood River Junction:Peak height during 2010 flood: 11.16 feetPrevious peak: 10.3 feet, 19382

Pendleton Hill Brook, North Stonington:Peak height during 2010 flood: 7.6 feetPrevious peak: 6.73 feet, 1982

Quinebaug River, Jewett City:Peak height during 2010 flood: 23.3 feetPrevious peak: 29 feet, 1955

Yantic River, Norwich:Peak height during 2010 flood: 13.2 feetPrevious peak: 14.9 feet, 1982

East branch of Eightmile River, Lyme:Peak height during 2010 flood: 7.2 feetPrevious peak: 10.22 feet, 1982

Eightmile River at North Plain, Lyme:Peak height during 2010 flood: 7.8 feetPrevious peak: 11.1 feet, 1982

HOW MUCH RAIN?*• March 2010 precipitation: 16.34 inches (wettest March in 116-year record)• Average monthly precipitation: 3.87 inches• Average March precipitation:4.43 inches• Number of heavy rainstorms from March 16 to 30, 2010: 4• Total rainfall in February and March 2010: 25.4 inches• Average annual precipitation total: 46.45 inches*Figures for Washington County, R.I.; figures similar for New London County

Source: Prof. Thomas Boving, University of Rhode Island; National Weather Service

BY THE NUMBERS2010 flood in New London County and Washington County, R.I.• Applications approved for individuals and households for FEMA assistance:New London County: 2,480Washington County: 4,981• FEMA funds approved for individuals and households:New London County: $3.6 millionWashington County: $7.7 million• Number of residences impacted:New London County: 4,228Washington County: 25,943• Number of businesses impacted:New London County: 279Washington County: 718• Total impact estimate:New London County: $5.3 millionWashington County: $37.1 million

Source: Federal Emergency Management Agency