MAPPING AND ANALYSIS OF MELTWATER EROSION MARKS IN BEDROCK AT BAILEY’S RAVINE, CT. USING TERRESTRIAL LASER SCANNING DATA

This study examines large meltwater erosion marks (up 3m high) present in garnet-mica-schist (Scotland Fm.) along a ~350m reach of Bailey’s Brook, North Franklin, CT. Similar marks occur on the slopes of several valley sides in Eastern Connecticut and have been used to map the locations of meltwater channels. Current discharge and channel size for Bailey’s Brook, a small first order stream, is grossly undersized when compared with paleoflow associated with meltwater marks. This study relies on survey data collected with total stations and a VX Spatial Station that is capable of terrestrial laser scanning (TLS). This includes ~10 valley cross-sections, a lengthwise profile, and a ~60,000 point cloud collected from 6 instrument positions along the modern channel. In general, the stream flows across ~6 small bedrock escarpments, ~2-4m high, resulting in distinct knickpoints in the long profile. These escarpments constricted meltwater resulting in larger erosion marks where flow incised through the escarpments. TLS data were analyzed using Trimble Real Works Advanced software by segmenting and refining point-clouds to remove vegetation so that bedrock surfaces could be analyzed. TIN based meshes constructed from point clouds were refined, slightly smoothed, and extraneous peaks removed. Meshes were textured with generated VX imagery and in some cases retextured with higher quality DLSR imagery so that individual erosion mark boundaries could be easily recognized. Point-clouds were then segmented to create datasets for eac­h meltwater erosion mark (form). Individual form clouds were analyzed geometrically, defining coordinate systems (frames) based on a best-fit plane to the form-cloud. Form-clouds were exported as object files for analysis using geometric mesh-editing software. Although data analysis is ongoing, the goal is to quantify these erosion forms to determine whether they can be distinguished from similar looking features developed in modern rivers.