The Suncook River in Epsom, NH abruptly changed course in 2006 as a result of spring storms and flooding. This avulsion caused the abandonment of two river channels west of Bear Island and created a new, shorter, and steeper channel to the east. The Suncook River is continuing to adjust to its shorter channel length by migrating laterally (moving from side to side) and incising (cutting down deeper into the river bed). The lateral migration of the Suncook River to the east combined with the incision has triggered similar responses in both the Little Suncook River and Leighton Brook as they continue to adjust to the changes on the Suncook River.
One of the major concerns stemming from the avulsion is upstream erosion in the vicinity of the Route 4 Bridge and the stream crossings under Black Hall Road in Epsom. When the Suncook River changed course, the slope of the river became steeper at the avulsion site and large amounts of loose sediment were washed downstream. As a result, another form of erosion called headcutting began to occur and gradually move upstream from the avulsion site. This is a natural process that happens as a river attempts to restore its equilibrium relative to slope, length, erosion rates and sediment transport. However, if left unchecked, such headcutting may introduce increased vulnerability to important infrastructure such as the Route 4 Bridge east of the Epsom traffic circle and the stream crossings under Black Hall Road.The New Hampshire Department of Environmental Services (NHDES)is coordinating a multi-agency led project to develop designs and permits for the protection of critical infrastructure located on the Suncook River, Leighton Brook and the Little Suncook River. This project will prepare the necessary work scope and budget to proceed with construction.
Fieldwork for the geophysical survey and geomorphic assessment began in 2011 and will conclude during the spring of 2012. NHDES anticipates that the construction of stabilization measures on the Suncook River and Leighton Brook will occur in 2013. Design and permitting for this project were made possible through a grant from the Federal Emergency Management Agency and the New Hampshire Department of Safety. A significant percentage of funding for construction activities was secured through a special capital appropriation made by the New Hampshire Legislature in 2011.
Resources:
Technical Memos:
Inter-Fluve Technical Memo: Basis of Design 30% Complete, December 2011
Inter-Fluve 30% Complete Design Sheets, December 2011
Click image above to view 2011 topographic
survey points for the Suncook River
stabilization study.
NHDES Update on the Suncook River Design and Permitting Project, July 2011
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