SUSTAINABILITY ANALYSIS AND SEDIMENTATION IN THE LOWER RESERVOIR ONEONTA, NY; A DRAINED PERSPECTIVE

Reservoirs behind dams stymie natural sediment transport and encourage sediment accumulation, which decreases the volume and life expectancy of drinking water reservoirs. The present study focuses on the sustainability of Wilber Lake and the Lower Reservoir, the drinking water sources for Oneonta, New York. A Hummingbird Helix 9 equipped with CHIRP sonar (455 kHz, 800 kHz) coupled with ReefMaster software was used as a low-cost means of evaluating sedimentation in reservoirs. Sonar data was used to produce bathymetric, hardness maps, subsurface profiles, and volumes of sediment and water. In August of 2019 the Lower Reservoir was drained to make improvements to the dam to meet Department of Environmental Conservation (DEC) 500-year flood regulations. While drained sediment coring using manual and Vibracore techniques, soil profiling, drone imagery, and 3D SfM modeling was completed to augment CHIRP sonar data collected.

Based on several measurements in the down scan sonar profiles, it was determined that the average sediment thickness above a gravel layer is ~ 2 m. In the sonar profile the gravel layer was reflected and interpreted to be indicative of a migrating delta associated with previous draining of the reservoir. Coring operations revealed a max recovery of 101 cm interrupted by the gravel layer. Recovery rates with the Vibracoring were poor with an average recovery rate of 68%. To mitigate this issue a ~ 1.5 m soil profile of the channel banks was collected. Exposed banks along the channel revealed alternating layers of silty clay, mixed organics, and gravel. These observations indicate that sedimentation is driven by spring and fall high precipitation flow events from Oneonta Creek into the Lower Reservoir. Drone imagery captured a month apart was converted into 3D SfM models and was used to create channel profiles to evaluate channel evolution and volume. Calculated total water volume of ~ 46,822.27 m³ for the Lower Reservoir and ~ 1,667,720.1 m³ for Wilber Lake. Approximately ~ 27,213 m³ of sediment has been deposited in the Lower Reservoir from the Oneonta Creek inlet and ~ 101,131.7 m³ of sediment has been deposited in Wilber Lake.