ACOUSTIC IMAGING OF SUBMERGED TOPOGRAPHY, MASS WASTING FEATURES, AND SUBMERGED CULTURAL RESOURCES IN BEAVER LAKE, NORTHWEST ARKANSAS

Beaver Lake is a 28,000-acre reservoir completed in 1966 to provide flood control on the White River, hydroelectric power, drinking water, and recreation in northwest Arkansas. No detailed surveys of lake bathymetry or sedimentation had been conducted since impoundment 37 years ago. This study reports results of dual frequency (28 and 200 kHz) echo sounder and side-scan sonar surveys of upper Beaver Lake in Benton and Washington Counties, Arkansas. The side-scan sonar system was modified to permit high-resolution acoustic imaging of submerged, near-vertical to vertical cliff faces along the lake margins. Side-scan sonar imagery was merged with precision echo sounder data to derive three-dimensional visualizations of pre-impoundment topography. These images were compared to orthorectified pre-impoundment aerial photographs draped on digital terrain models derived from pre-impoundment topographic maps using geographic information system software. Examples of side-scan sonar images from Beaver Lake will be presented showing submerged rock cliffs, details of cliff-face geology and geomorphology showing limestone layering, solution-enlarged fractures, submerged ledges, and features related to post-impoundment mass wasting of cliff-faces (small slumps, rockslides, large limestone blocks derived from rock falls, and spalled rock surfaces). Images of submerged cultural resources within the former White River valley were also obtained on side-scan sonar records. Submerged cultural resources observed on side-scan sonar were correlated with pre-impoundment aerial photographs, providing a novel method for identifying and assessing the preservation state of cultural features within the reservoir basin.