SUB-BOTTOM SURVEYS OF SINKHOLE LAKES
NEAR VALDOSTA, GA
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Recently, Canadian colleague Robert Gilbert (Queen's University, Kingston, Ontario, Canada) and I surveyed several sinkhole lakes south of Valdosta near Lake Park, GA. to investigate the potential for surface water - groundwater interactions. Our work focussed on surveying the thickness of sediment in these lakes using sub-bottom acoustic techniques. A brief description of this work is given at the bottom of this page. 
 
Twin lakes Balboa (left) and Ponce de Leon (right) with Long Pond and Ocean Pond in the background (left side). Sub-bottom acoustic surveys were conducted in all of these lakes, plus Lake Louise. Only records from Lake Balbo (opposing image) were successful in penetrating the lake bed. 

 

Areal view of Lake Balboa, Lake Park, GA.
Areal view of Lake Ponce de Leon, Lake Park, GA.
 
 
  
Sub-bottom acoustic record for Lake Balboa with corresponding interpretation. Research is ongoing.
Surveying the Thickness of Sediment Within Sinkhole Lakes Near Valdosta
(new collaborative work with R. Gilbert)
In Lowndes county water well records suggest that surface water is most directly connected to the subsurface groundwater supply through sinkholes in the bed of the Withlacoochie River north of town, and through sinkhole lakes south of Valdosta (Krause, 1979; McConnell and Hacke, 1993). Although many, if not most, lakes in southern Lowndes County are sinkhole lakes not all are well connected to the underlying groundwater system. This is because thick accumulations of impermeable mud in the bottoms of some lakes prevents lake water from seeping downward into the underlying aquifer. Thus, the degree to which surface water connects to groundwater system within these lakes depends in large part on the depth to bedrock (where the main aquifer is located), and the thickness of fine-grained lake mud and underlying sediment that overlies bedrock.  Interestingly, these parameters have not been measured beneath any sinkhole lakes in Lowndes County.  

It is difficult to measure the thickness of lake sediment and depth to bedrock beneath sinkhole lakes. Direct measurements are possible by recovering core from the lake-bed. Coring, however, is very time consuming, only determines sediment thickness at a single point, and almost certainly cannot penetrate completely to bedrock (at least with the equipment available at VSU). An alternative approach is to measure these parameters indirectly by conducting a series of acoustic surveys.  

Several such surveys were conducted between December 29, 1998 and January 3, 1999 using a 3.5 kHz sub-bottom profiling system made available through collaboration with Dr. Robert Gilbert (Department of Geography, Queen’s University, Kingston, Ontario, Canada). Most lakes (Long Pond, Ponce De Leon, Ocean Pond, Lake Louise) proved to have bottom sediments that were too hard to allow the acoustic energy to penetrate. However, we were successful in obtaining up to 25 m of sub-bottom penetration at Lake Balboa. A preliminary interpretation (adjacent) identifies stratigraphic layers in the surrounding Miccosukee Formation which are truncated by the throat of the sinkhole that underlies the lake. Analysis of these data is ongoing.