APPLICATION OF GPR, GEOSPATIAL AND GEOCHEMICAL TECHNIQUES TO DETERMINE SEDIMENT ORIGIN AND ACCUMULATION PATTERNS IN KELLER RESERVOIR, CLINTON COUNTY, PA

The Keller Reservoir in Clinton County, PA, serves as a source of drinking water supply for 19,500 subscribers. The reservoir is fed by McElhattan Creek and East Kammerdiner Creek. Over 90% of the land cover of the watershed constitutes deciduous forest and 7% is agricultural landuse. These creeks carry a substantial amount of sediment with surface run-off during high precipitation events. Sediment accumulation poses a problem by decreasing water storage in man-made reservoirs and increasing cost to the water filtration plant. The following methodologies and workflow were used: 1) application of ArcSWAT model to quantify the impact of land management practices on surface run-off and hotspots of sediment yield in the study area, collection of sediment samples from locations of high sediment yield, analysis of sediment samples using XRF to determine their elemental composition, comparison of geochemical signature of sediment samples to those collected from the reservoir; and 2) carrying out a GPR survey to measure the bathymetry and the sediment deposit in the reservoir using a 100MHz antenna with a sub-metric GPS system all placed in an inflatable boat powered by an electric trolling motor. The results of XRF analysis indicate that the geochemical signature of the sediments collected from the reservoir closely resembles those collected from agricultural fields. GPR generated contour maps with bathymetry and sub-bathymetry show areas of heavy sediment accumulation. A 3D-bathymetry model was also constructed to calculate the volume of water in the reservoir and the volume of sediment and accumulation patterns. The water volume was estimated to be 247,474.15 m³ and the sediment deposition to be 311,359.27 m³. This showed that the Keller Reservoir has lost about 56% of its storage capacity since inception.