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WALPOLE, N.H. — In October, it will be 16 years since 50 acres of water busted through a clogged culvert in Alstead, N.H., destroying 26 houses and killing four people on its way to the Connecticut River.

“The water was 70 feet deep at the plugged culvert,” said Perley Lund, standing in a field near where the Cold River meets the Connecticut River, just east of Route 12 in Walpole. “The road agent and the chief of police did a great job saving lives, but we still lost four.”

On a recent summer day it was hard to believe the intensity of the rushing water and the amount of debris it must have carried with it back then, as the water is now barely two feet deep and 20 feet across the rocky river bed.

On both sides of the Cold River, the Connecticut River Conservancy and the New Hampshire Association of Conservation Districts have been overseeing a $500,000 project to reinforce the banks of the river.

Heavy equipment is being used to drive pilings into the river banks and lay down uprooted trees with their roots facing the water.

The work is not intended as flood prevention, but can help keep fertile cropland from being washed away during high water events.

“The root balls take the energy of the high water and the ice,” said Ron Rhodes, director of restoration projects for the CRC. “Instead of the erosive force being on the soil, it’s hitting the wood.”

Bill Fosher, the lead conservation planner for the NHACD, said the system acts like “a shock absorber.”

“It’s designed to take the force of the water, dissipate it and let the water keep flowing,” he said. “And it also creates habitat for fish and places for birds to sit and hunt fish.”

Historically, rip-rap, rocky material placed at the sites of erosion, has been used, but that doesn’t slow the water down, said Fosher. In fact, he said, it speeds it up.

“Which just moves the problem downstream,” he said.

The land on both sides of the Cold River is incredibly fertile, said Lund.

“This has a soil potential index of 100, meaning it doesn’t need any fertilizer,” he said.

“This is some of the best farmland in the United States of America,” said Fosher. “You could go to Iowa and not find anything better than what you have here.”

The project is meant to keep the farmland from washing away into the river, eventually making its way to Long Island Sound.

“For me, as a soil conservation person, seeing the river wash away big chunks of this every spring and into the summer ... it doesn’t sit well,” said Fosher.

“Without this work, we would lose this field,” said Lund.

Each particle of soil that washes away carries with it nitrogen and phosphorous, said Fosher.

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“Phosphorous is a huge problem for freshwater environments and nitrogen is a huge problem for saltwater environments,” he said.

The project on the Cold River is just one of 58 projects along 180 miles of rivers in New Hampshire, Vermont and Massachusetts, designed to help reduce erosion, runoff, and excess nitrogen, which causes low dissolved oxygen levels that threaten fish and other aquatic organisms.

Projects included planting trees and shrubs along rivers on agricultural lands to slow runoff and filter pollutants from water before it enters rivers, berm and dam removals that restore natural river flows and decrease erosion during floods, and streambank stabilization work that helps keep soil in place rather than polluting rivers.

The work is expensive; projects are paid for with grants, donations and landowner contributions cobbled together. The largest source of money comes from the USDA’s Regional Conservation Partnership Program through a grant to the Connecticut Council on Soil and Water Conservation, aimed at reducing pollution in the Connecticut River and Long Island Sound.

The fields along the Cold River are used to grow corn silage for a dairy herd and vegetables for sale at Pete’s Farmstand in Walpole. Right now, the disturbed land has been seeded with a cover crop, but in the fall, volunteers will come in and plant trees and shrubs to help stabilize the banks and keep protect them from rainstorms like the region saw in July.

“This is the nervous part for us,” said Rhodes. “If an Irene-type event was to hit in the middle of the work or just as we’re done ... we need Mother Nature to give us time to help the land heal and to get the roots growing.”

Nicolas Miller, of Field Geology Services, specializes in stream restoration.

“We were contacted by the Natural Resources Conservation Service, which had been working with the farmer on the persistent problem of bank erosion and losing agricultural land,” said Miller.

Miller surveyed the work area and designed a project proposal that included harvesting local trees with intact root balls.

“The vertical piles are driven 15 feet into the stream bed,” said Miller. “Those provide scour protection and anchor points for the structure and root wads.”

Sand and gravel deposition around the root balls will help rebuild the banks, he said, while plantings are given time to root and take hold.

“The root balls and trees will start rotting and falling apart,” said Miller. “Maybe 30 years, when all the trees and shrubs have provided long-term stability.”

The CRC will monitor the area for the next three to five years to make sure the reinforced banks are holding and the plantings are taking root.

“The cover crop will help,” said Fosher. “But until the trees grow and get established ... that’s what really holds the banks in place.”

A site on the Cold River, in Walpole, N.H., that was five years in the making to help restore the riverbed.

The federal funding, which CRC matched dollar for dollar with other grants and private donations, was used to complete engineering designs, restoration plans, and permitting necessary for project implementation.

CRC worked over the five-year grant period to help local landowners sign up for USDA NRCS programs that helped fund implementation of the restoration projects. CRC was able to secure additional grant funds to help reduce or eliminate landowner out of pocket expenses.

Bob Audette can be contacted at raudette@reformer.com.