UPLAND SEDIMENT YIELD AND THE IMPORTANCE OF SUSPENDED SEDIMENT IN A NEW ENGLAND WATERSHED

The delivery of sediment from upland watersheds remains an outstanding issue in geomorphology and watershed management. The controls on the transfer and storage of sediment play important roles in the ecological functioning of upland streams and in the potential for contaminant transport throughout watersheds. What has made empirical assessments of the controls on upland sediment yield difficult has been the dearth of field locations that would allow for direct measurements of the various components of sediment load. Here, we leverage the unique history of Birch Brook, a small (<3m width) forested stream in the Taconic Mountains of Massachusetts, to examine both the nature of sediment yield and the role of extreme precipitation events. As a component of USDA management in the early 20^th century, low-head weirs were constructed along Birch Brook. Bed load trapped by the South Branch weir has been annually measured since 1986. Turbidity sensor measurements have also provided estimates of suspended sediment flux since 2016, which we use to calculate annual suspended sediment load. Together, the data provide a glimpse into the annual variability of sediment yield while repeat high-resolution LiDAR flown in the latter part of the study period, 2015 and 2020, allows identification of potential sediment sources and comparison to annual fluxes in that period. These data contribute to our understanding of the interplay between hydrology and hillslope processes in forested mountain watersheds and highlight the role of increasingly-frequent hydrological extremes in sediment supply and transport.