Project Title: Warren Brook and Cold River Salmonid Habitat Restoration (FFS #R5UB)

State: New Hampshire

Project Description:Five years after a devastating flood along Warren Brook in Alstead, New Hampshire, the U.S. Fish and Wildlife Service (Service) allocated $242,000 in American Recovery and Reinvestment Act (Recovery Act) funds to help the town stabilize a portion of the area along the brook. Stream and floodplain terrain has been restored along 900 linear feet of Warren Brook to protect against future bank erosion and provide habitat for fish and wildlife.

In October 2005, torrential rains poured over the small southern New Hampshire town, unleashing at least seven inches of precipitation in two days. Floodwaters furiously rushed down Warren Brook, taking with it sediment, rocks and sticks until the debris clogged a 12-foot culvert under the Cooper Hill Road embankment. With nowhere to go, the floodwaters rose high enough to crest the 30-foot-tall embankment. Within a half hour this spontaneously created “dam” gave way, sending a massive flood into the low-lying terrain on the other side.

This portion of Warren Brook, which flows into the Cold River, was a meandering waterway before the storm. Its natural bends served important ecological purposes. The flood destroyed the traditional path of the water, leaving a straight-flowing stream in return.

John Magee, fish habitat biologist at the New Hampshire Department of Fish and Game, said that the brook’s natural bends were vital to the stability of its channel. Eroding sediment gets deposited further downstream in a straightened waterway, and rivers become even more susceptible to bank erosion.

Along with altering the brook’s shape, the flood swept away rocks and fallen trees from the streambed that were needed to maintain the “roughness” of the water. The choppy nature of typical river water is the result of having these submerged objects to break up the flow. Rocks, trees, and other objects that add to the roughness provide cover for fish and help stabilize the stream banks.

Magee likened the flow to a “Slip ‘N Slide,” with the water rushing downstream, uninterrupted. The project added trees and boulders to the stream in an attempt to restore the roughness and lure fish back. The floodplain was also restored to reduce any future erosion problems and the pre-flood terrain of the brook was also restored. This will result in the natural retention of water in the channel and floodplain during annual floods.

Magee said that if nature were left to do this on its own, it may take over a decade for trees to begin growing again in the floodplain area, and perhaps another 70 years before those trees begin to fall in to the water. This Recovery Act project served to jumpstart that process.
The flood essentially eliminated fish populations in the area, but past experience suggests that, “the long term prognosis is very good,” according to Magee. When similar repairs were made to another part of the brook in 2007, fish began to populate the area in less than a year.

This restoration project was completed in October 2010.

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Originally posted 03/31/2010
Page Completed 05/05/2011