TWO DECADES OF COLLABORATIVE LANDSLIDE RESEARCH IN VERMONT

Over the last 24 years the Vermont Geological Survey (VGS) and Norwich University have undertaken a series of studies to map existing landslides (LS), understand their causes, and predict locations of future LS. VGS has worked with the Vermont Emergency Management Division, regional planning commissions, towns, and citizens to incorporate LS hazards in town and regional plans and to mitigate the impacts on the built and natural environments.

A large LS in Jeffersonville prompted the VGS to begin these studies. The VGS investigation led directly to the first FEMA-funded buyout of a property due to an erosion hazard issue in VT (the first of many). From 1999 on, VGS has worked with the Vermont Rivers Program (VRP) to assess riverine erosion hazards as a component of the VRP Stream Geomorphic Assessment (SGA) Protocols. This work has clearly shown the close link between fluvial toe erosion and landslide activity. A study of rockfall and debris flow hazards in Smugglers Notch was completed in 2009.

Following Tropical Storm Irene in 2011, the team assessed the geomorphic impacts, including bank erosion, lateral and vertical channel shifts, floodplain erosion and deposition, reactivation of alluvial fans and LS, and initiation of new LS.

VGS completed a Landslide Protocol in 2013. This includes a database, a procedure for LS inventories, and ideas on modeling existing LS and potentially unstable slopes. This became part of the State Hazard Mitigation Plan. Inventories have been completed for 5 of 14 counties in VT. The Report a Landslide web tool allows citizens to report LS and view locations of over 3,000 LS. It includes sites identified in the LS inventories, surficial mapping and SGA projects and is continually updated.

Since 2019 the team has included the University of Vermont and VT Agency of Transportation. Work includes detailed investigations of the >200,000 m³ 2019 landslide at Cotton Brook in Waterbury, monitoring at Smugglers Notch, and slope stability studies at two flood control dams. New techniques include use of LiDAR, photogrammetry from drones, and survey-grade GPS. The creation of 3D point clouds and digital models enables us to measure the dimensions and orientations of features, calculate volume change, and quantify change over time. This allows us to make predictions to inform hazard mitigation efforts.