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After flood damage, Suncook River project almost complete

  • The Suncook flows south near the Epsom traffic circle. GEOFF FORESTER—Monitor staff

  • A bridge carries Route 4 over the Suncook River in Epsom. Adjustments have been made to the river banks to prevent future flooding. GEOFF FORESTER / Monitor staff

  • The fallen trees and damage from past floods can still be seen along the Suncook River in Epsom near the traffic circle. GEOFF FORESTER—Monitor staff

  • Area where river breached into sand pit. The water in old riverbed is running backwards on right on the Suncook River in Epsom GEOFF FORESTER—Monitor staff

  • Part of the overflow flooding from the Suncook River in Epsom. GEOFF FORESTER—Monitor staff

  • An excavator places sandbags down on the rock dam to divert the Suncook River to avert another flood like the Mother’s Day flood in 2006. GEOFF FORESTER—Monitor staff

  • Uprooted trees line the Suncook River about a quarter mile south of the Route 4 bridge just east of the Epsom traffic circle. The tree roots are undercut from the river flow and then they fall into the river. (GEOFF FORESTER / Monitor staff) GEOFF FORESTER—Monitor staff



Monitor staff
Saturday, April 07, 2018

One of the most unusual environmental repair projects in New Hampshire, the reconstruction of the Suncook River in Epsom after it was rerouted by the Mothers Day floods of 2006, is just about complete despite the best efforts of winter weather.

“They began in October and worked right through February, until that nasty cold snap locked everything up – diesel engines weren’t turning over,” said Steve Landry, supervisor of the Watershed Assistance Section of the state Department of Environmental Services. “They had to shut down for a while.”

The main goal of the roughly $3 million project is to prevent future floods from moving the riverbed and undermining the bridge that carries Route 4 over the Suncook River just east of the Epsom traffic circle. Replacing the bridge with a bigger, stronger version would have cost as much as $15 million, Landry said.

The bridge became a concern after huge floods around Mothers Day in 2006 caused the river to cut through the neck of an oxbow downriver, or south, of the bridge. This created a new channel, leaving two other channels dry that went around Bear Island, which is no longer an island, as well as two small dams.

This process, known as an avulsion, is unusual in the geology of New Hampshire. This was the biggest change in a river channel ever recorded in the state. 

“There’s been a ton of interest in the site. … We had groups request tours during construction,” Landry said. At least one college class and two river-oriented environmental groups toured the project.

People were concerned that more floods would continue to eat away at the river banks, eventually undermining the bridge’s footings. This is a particular issue along this stretch of the Suncook River because many of the banks are sandy and vulnerable to erosion; in fact, the river broke into a sandpit during the flooding.

Perhaps the most impressive part of the project, although the least visible, is designed to prevent the banks from eroding too much.

“Forty-foot lengths of sheet piling were driven vertically down under the cornfield and on the west side (of the river). They’re all out of sight, covered by 3 feet of topsoil,” said Landry. “It’s a secondary defense in case the downstream area should catastrophically fail – that will be the failsafe measure for the Route 4 bridge.”

More visible are the 4- to 6-foot boulders set on the banks to hold them in place.

Virtually all the work near the bridge is done, except for some clean-up of the work site and planting of “literally thousands of plants, shrubs, small trees at the top of both banks,” Landry said.

Downriver from the bridge, more work needs to be done fortifying the east bank of the Suncook. Downriver, the west bank is forest with no cropland or buildings that would be endangered if the riverbank shifted, so little work is being done on that side.

“We feel it is not going to aggressively migrate to the west. But we’re going to have to keep an eye on it,” Landry said.

If all goes as planned, the project should be complete by June.

The 2006 flood happened after a huge low-pressure system stalled over New England and dropped more than 8 inches of rain on Concord in the largest three-day precipitation total ever recorded in the city.

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)