TAMING A CHANGED RIVER: A STATE GEOLOGICAL SURVEY’S ROLE IN COLLABORATION FOR PROJECT SUCCESS

As part of the Department of Environmental Services (DES), the New Hampshire Geological Survey (NHGS) serves the state through provision of its in-house geoscience expertise and data collection activities to address applied problems. A primary role of NHGS is to provide its expertise to the DES Water Division. To fulfill that role, NHGS works with contractors to collect and analyze the data necessary to support the many applied water-resource issues that the Water Division is charged with managing. One such issue centers on the Suncook River in Epsom, New Hampshire, which underwent an avulsion in 2006. After the avulsion, the river length was reduced by 0.5 miles in the vicinity of the avulsion, leading to increased sedimentation downstream and an upstream- migrating headcut. The migrating headcut continues to pose potential public safety ramifications to the crossing of Route 4, a key thoroughfare between Concord and the Seacoast region. DES Water Division personnel were charged with engaging a project to protect this infrastructure using techniques to stabilize the headcut. A complicating factor at this location is the sandy composition of the Suncook Rivers’ adjacent floodplain, necessitating geological surveys to ascertain depth to bedrock or other hard substrate in order to inform the designs of the headcut stabilization. NHGS, working with a contractor, performed a geophysical survey using seismic refraction to provide reliable data regarding the character and elevation of soil and rock formation and the composition of the floodplain under the surface, and worked to provide the results to a second contractor tasked with designing the stabilization project. In this presentation, we will present an overview of the Suncook River avulsion and its potential impacts to the road crossing, outline the results of the geophysical survey and its implications for the design phase of the in-channel stabilization project for protection of the Route 4 bridge.