Mapping SML 

By Jerry Hale

                Area property owners and vacationers who’ve tried to sketch the route to their Lake retreats for visiting family and friends know how tough it can be to get it right. Now just imagine trying to precisely map Smith Mountain Lake’s bottom contours and establish an up-to-date record of the ever-changing structures that dot her shorelines. Daunting tasks when you’re dealing with well over 500 miles of shoreline, several hundred coves and creeks, and water depths that plunge to over 200 feet.    

                Lake custodian AEP faces these challenges as it seeks to renew its license with the Federal Energy Regulatory Commission (FERC) to continue operating the Smith Mountain Project — part of a 7-year effort to prepare the application for a new license, file it with FERC, and work through all the necessary reviews, revisions and approvals.

                Observant Lakers may have noticed a closed-cabin “SURVEY” boat making methodical passes over SML waters beginning in the fall of 2005 and continuing through last February. Aboard the 23-foot vessel were three crew members – engineers and technicians from Ocean Surveys, Inc., the contractor hired for its bathymetric expertise. 

                With a Reson Multibeam receiver and related SONAR equipment inside the boat’s cabin, the crew gathered data to enable precise analysis of the underwater contours of both SML and Leesville Lakes. Each pass of the 240-beam SONAR array covered a swath of bottom 3.46 times the operational depth of the water. For example, in 100 feet of water, each pass mapped a swath 346 feet wide. Computers recorded the collected bottom data for subsequent use in creating a bathymetry – or bottom contour – map.

                To precisely record underwater contours, both GPS and land-based references are required, explained Brady Todd, Civil Engineering Surveyor at AEP’s Dolan Civil Lab, who shepherded the project. “A total of 17 reference stations were established — a rather extensive network, but necessary since the Lake’s mountainous shores often can limit the range of the GPS base station radio transmitters.” Some reference points had to be located on private property, “…with the permission and gracious assistance of area land owners.”

                This was the first time since the Lake’s flooding 40 years ago that AEP has conducted such a bottom contour survey. Project cost was significant – $740,000 – but the work will enable precise reporting of data required by FERC for the relicensing process.   

                The survey work spanned SML from the Rt. 834 bridge across the Blackwater to Back Creek on the Roanoke, where Bedford and Franklin counties meet. Data collected will be compared to topographic maps of the area before the Lake was flooded to get precise readings on silting and other environmental issues. The bottom contour data also helps develop the water volume estimates required for FERC relicensing.

                The deepest point found on SML was 205 feet, down near the dam; at Leesville Reservoir has 66 feet of water behind its dam. Total water volume in the two lakes runs 53.88 billion gallons – give or take a few – which would weigh 3.36 trillion pounds and require, well, a whole lot of plastic to bottle and sell at the Westlake Kroger. 

                It’s yet to be determined how, whether or when the survey data will find its way onto boating charts of SML. “No real surprises were found,” Todd summarized. “The original river and tributary channels are still intact. There is sedimentation in some areas, and many of the valley’s original stands of trees are evident. The old Rt. 122 bridge is still intact.”

                While the survey crew’s focus was on the Lake’s bottom contours and composition, they did not fail to notice the charms of the area.

                “Boating these lakes gave us first-hand exposure to their beauty and serenity, as well as to the outstanding character of the local citizens who provided excellent support for our efforts,” said Jeffrey Gardner, Sr., Geophysical/Oceanographic Project Manager for Ocean Surveys, Inc. “Our time in Southwest Virginia was a welcome departure from the hustle and bustle of the major seaports and commercialized areas we are accustomed to working.”