Underwater Acoustic Survey, High Definition Laser Scanning, Structural Monitoring
Designed by the Louisiana Department of Transportation and Development, Office of Public Works, D’Arbonne Dam’s construction was completed in 1961.
In 2007, Fenstermaker conducted a structural monitoring and underwater inspection to provide a comprehensive surface model and high resolution topographic model of the as-found condition of the dam structure and the water bottom approach and egress. The team also conducted a visual safety inspection of the dam system.
The field work only took a total of four days. Surveys were performed on sunny days with temperatures varying from high 30°F to mid-70°F. The lake’s pool stage was below the spillway’s crest. Heavy vegetation on the embankment crown was removed, allowing accessibility from the peak to the water’s edge.
In order to establish geodetic control, one deep-rod monument and one 5/8 rod with aluminum cap benchmark were set at opposite ends of the concrete structure. The HDS survey was executed using a combination of the Leica Scanstation I and Leica HDS 6000 Scanner to perform scans from 40 different scan positions.
A proprietary Fenstermaker remote sensing system was utilized for the Underwater Acoustic Imaging and Profiling, which is based on a Kongsberg Mesotech MS1000 system. This system was used to visualize the underwater component of the dam system, and the same instrumentation was used to generate the underwater dam structure and surface topography and the surrounding water bottom topography.
A comprehensive surface scan was needed to note irregularities in the overall structure. Above-water laser scanning was utilized to survey the structural components and adjacent areas of the dam. Underwater acoustic scanning was used to survey underwater structural components of the dam and adjacent water bottoms. Both data sets were collected under the same environmental conditions. When assimilated and integrated, they were compiled for an accurate, comprehensive as-found model of the spillway system. These determinations were utilized to deduce and report conclusions and recommendations for maintaining structural integrity and safe operation.