MONITORING CHANNEL AND WOODY DEBRIS DAM CONFIGURATIONS IN SILVER CREEK, NY

The interplay of sediment movement and large woody debris in streams is a very common interaction in the forested areas of New York. Documentation of the interaction to present however, has been somewhat limited. We report here the results of total station and structure from motion surveys of a woody debris dam in a low order perennial stream in Otsego County New York. The surveys were conducted by students in a geologic field data collection course at SUNY Oneonta taken over a period of time from 2010 to 2015.We surveyed ground control points for most of the surveys, which permit us to tie all of the surveys together in GIS and document decimeter scale changes in ground surface elevation. Longitudinal channel profiles reveal the migration of a knickpoint as the dam began to fail in 2013-2014. Photographs taken since 2007 reveal large changes in the channel character and damming capability of the debris. The total station surveys reveal some of the changes in bed elevation, but miss much of the richness of channel changes. In 2015 we conducted a photogrammetric structure from motion (SfM) survey to capture more of the changes. The high fidelity of the SfM elevation data permit nearly complete reconstruction of the channel conditions, including cobble and pebble grain size measurements. Dimensions of the woody debris can be reconstructed, and we anticipate monitoring changes to the dam on a detailed basis moving forward. We expect our work to provide better constraints on life span of woody debris dams, on the quantity and caliber of sediment movement in local streams, on habitat stability, and the linkage between channel aggradation/degradation and mass movements from adjacent hillslopes. Changes in bed and debris configuration happen rapidly enough that shorter term monitoring is warranted.