River Flooding and Erosion: Public Safety and Property Protection Concerns

New Hampshire's most frequent and damaging natural hazard is flooding from heavy rains and severe storm events. Rivers and streams carry flood waters, and are often the source of damage to roads, property, and the existing landscape. River channels are more vulnerable in certain areas than others to serious erosion. In extreme cases, entire river banks can breach, causing the river to change course. The Suncook River experienced this kind of abrupt channel change, or avulsion, in 2006 in Epsom.

The New Hampshire Geological Survey (NHGS), a division of the Department of Environmental Services, established a program to assess the vulnerability of the state's rivers to bank destabilization and erosion. This program is called the Fluvial Erosion and Geologic Hazards Program. NHGS staff undertake detailed mapping and field-based assessments along every portion of a river to analyze the channel and bank characteristics. Special attention is given to bridges and culverts, which are often particularly prone to flood and erosion damage, causing washouts and damage to property.

Ultimately, a set of maps and data are produced which show the degree of vulnerability at each point along the river, and the areas of the river valley most likely to be affected by erosion. Such maps can be valuable tools for hazard mitigation planning, flood evacuation strategies, and other public safety and property protection efforts.  A fluvial erosion hazard study has been commissioned for the Suncook River in 2012. NHGS staff and contractors will conduct fieldwork during the summer months to assess the river along its entire length. Personnel will be out walking the length of the river to take measurements and conduct bank and culvert assessments.

Resources:

NHGS Update on Suncook River Fluvial Erosion Hazard Assessment (July 2011)

NHGS Fluvial Erosion Hazards and Geomorphic Assessment Program (Fact Sheet)