DELINEATING SUBSURFACE PATHWAYS FOR WATER LOSS FROM MOUNTAIN LAKE, GILES COUNTY, VA

Mountain Lake, located in Giles County, is one of two naturally formed lakes in Virginia, and is a unique hydrologic feature in the unglaciated portions of the southern Appalachian Mountains. The lake has a documented history of severe water level fluctuation, reducing its aesthetic appeal to patrons of the historic Mountain Lake Hotel and the adjacent wilderness area. A recent mass balance study documented hydrogeologic controls on the lake and estimated annual net outflow from the lake to be approximately 1.4 x 10⁶ m³. There are several unanswered questions about where water exits the lake and possible geologic controls on these flow paths. This study applies hydrologic, geophysical, and geochemical methods to address these questions. Continuous lake level monitoring and side scanning sonar are being used to quantify lake volume changes over time. Electrical resistivity profiles of the dry lake bed will be used to identify possible subsurface pathways for water to exit the lake. A dye trace study, currently in progress, will help delineate subterranean pathways for water exiting the lake. Results from this study will be combined with those from previous studies to evaluate possible methods of lake level management.