BATHYMETRIC MAPPING AND INITIAL SUB-BOTTOM PROFILING OF THE LOWER RESERVOIR OF ONEONTA CREEK, NY, USING HIGH-FREQUENCY SIDE SCAN SONAR

Bathymetric and sub-bottom profiling on lakes and reservoirs provides critical information regarding the hydrology, water depth, volume, lake or reservoir sedimentation, sediment layering, and estimates sediment properties along sonar transects. These data can provide information on reservoir functionality, life span, and derivation of erosion and sedimentation rates of catchments.

This study uses High Frequency CHIRP SONAR produced by a Hummingbird Side Scan Unit^© coupled with ReefMaster^© software to produce bathymetric and bottom feature maps of the Lower Reservoir of the city of Oneonta, NY. The unit provides DownScan, side scan, and ground penetrating sonar data. Side Scan data revealed objects on the bottom of the Lake in high resolution. DownScan provides bathymetric data for mapping as well as ground penetrating data revealing sediment thickness and type.

Lake volume, bathymetric maps, bottom hardness and bottom composition maps and cross-sections were produced. The sonar reflection data was used to interpret sediment thickness. Rocky or silty areas of lake bottom were mapped. These maps show that the rocky areas of the lake are at the northern end and the silty areas are at the southern end. Sediment thickness in the rocky northern portion is ~60cm and in the silty southern portion is ~ 6m. The lower strong reflection is interpreted to represent the original lake bottom and used to calculate water and sediment volumes. The volume estimate of the lake is 37,328.7 m³. Sonar reflection data provided an estimate of the pre-sedimentation volume of 68,042.3 m³ and a bathymetric map of the Lower Reservoir. An estimated 30713.6 m³ of water volume has been lost from sedimentation. To recover lost reservoir space, the municipality is considering the options of sediment flushing or dredging to increase capacity. Other municipalities have the same issue and if all release sediment from reservoirs there could be potentially harmful effects on the Chesapeake Bay ecosystem.