FUSION OF DISPARATE DATASETS IN QUANTIFYING RESERVOIR SEDIMENTATION

Sediment has been identified by the US Environmental Protection Agency (USEPA) as a leading non-point source of water quality impairment in U.S. lakes and streams. Intense development pressures are a leading factor in increasing sedimentation to waterbodies throughout the nation, including Beaver Reservoir of northwest Arkansas. Several recent, locally discontinuous studies on Beaver Reservoir have identified areas of substantial sediment deposition along with elevated levels of certain trace elements sequestered in the sediment. Advances in dual-frequency echo-sounding currently allow researchers to generate high-resolution, geographically referenced datasets of lake sediment thicknesses. In this study of three coves of Beaver Reservoir in Northwest Arkansas, a high frequency acoustic (200 kHz) signal was used to generate bathymetric (depth) data in conjunction with a low frequency (28 kHz) signal to penetrate in-situ sediment so as to reveal the underlying bedrock surface. These geophysical data were dynamically integrated with GPS location information on a laptop computer to produce high-resolution output that was then imported into a GIS. In addition to these data, uncharacteristically low lake levels allowed exceptional access to areas normally inundated but inaccessible by boat. Sediment probing was performed in these regions using a standard probe in conjunction with a GPS unit and survey-grade laser rangefinder. Finally, historic pre-impoundment topographic maps were digitized to create a high-resolution pre-impoundment surface from which the echo-derived and probing data could be assessed. The fusion of the four datasets allowed precise sediment volume calculations to be performed along with validation of the derived surfaces. Comparisons were performed between the digitized historic map with the present day sediment surface as defined by the laser survey and high-frequency bathymetry, along with comparing the sediment volume derived from the echo-laser/probe survey to volumes estimated from the historic map to the present sediment surface. Results of the study are providing a better understanding of sediment fates within each watershed, and as part of a larger study will further define the impact of development pressures on sedimentation and water quality.