MAPPING CHANNEL CHANGES IN GLACIAL AND LEGACY SEDIMENT REACHES OF THE SOUTH RIVER

The effects from both Pleistocene glaciation and historic land use change are visible throughout New England today, and continue to impact the region’s watersheds. The South River in western Massachusetts is an upland setting with hillslopes mantled by till, and glacial deltas provide evidence that one or more lakes once filled the valley. The quantity, size, and location of sediment available for transport in the watershed is influenced by these deposits. During the 18^th-19^th centuries, European settlement included the construction of approximately 30 mill dams along the river, coinciding with widespread regional deforestation. Sediment eroded from the landscape as a result of human activity was deposited in valley bottoms behind these mill dams, and much of this persists as legacy deposits. The banks of the South River are primarily composed of glacial and legacy sediments. We hypothesize that erosion in the watershed over the past ~100 years is primarily from legacy sediment deposits. In this study, we used aerial photographs from 1940 and 2013 to delineate channel banks and calculate changes in channel width following methods in Galster et al. (2008), in order to determine areas of widening or narrowing and changes in sinuosity, comparing reaches with banks composed of legacy and glacial sediment. We also used recent LiDAR digital elevation models from 2012 and 2015. Preliminary results indicate that legacy sediment reaches are experiencing the most migration and changes in width (in some areas up to 10 m) in comparison with those confined by glacial deposits. Ongoing analyses of channel changes will allow us to quantify 20^th century erosion and evaluate the response of the landscape to glaciation and 17^th-19^th century land use changes.