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As part of the initial plan development to replace the Route 634 (Hardy Road) bridge over Smith Mountain Lake located at the Bedford and Franklin County line, a Virginia Department of Transportation hydrographic survey team will use sonar to map the lake bottom beneath the bridge.  The survey is scheduled for Tuesday, May 15 and Wednesday, May 16.
The subaqueous data collected from the hydrographic survey will be used to produce 3-D color contour maps, sonar images and elevations of the lake bottom.  These maps will help designers to see the lake floor under the bridge as they begin drawing up plans for a replacement. 
During the survey, a boat will crisscross Smith Mountain Lake beneath the bridge and allow a Hampton-Roads-based, VDOT team to use side-scan sonar with a global positioning system (GPS) to collect the data.
VDOT has used this technology to survey beneath structures on the eastern shore of Virginia, and last summer, VDOT first used side-scan sonar in southwestern Virginia as part of a survey beneath the Interstate 81 bridge over the New River in Montgomery County.
The side-scan sonar and GPS combination allows for a wider scan area than traditional sonar that scans only straight down.  In addition, this technology will generate much more accurate images, reduce the scan time and make the images available sooner than scanning with traditional sonar.
Work to design a new bridge to replace the Hardy Ford bridge is in the very early stages.  The project, estimated at $4.6 million, tentatively is scheduled to be advertised for construction bids in summer of 2016.