INJECTING GEOLOGY INTO PUBLIC POLICY THROUGH A SINKHOLE

Lake Jackson, located in northern Leon County, Florida, is a 4,000 acre karst basin lake situated within a 27,000 acre closed drainage basin. It is a popular bass fishing lake and recreation area for local residents. Extensive development has occurred around the lake in the past 30 years and has had a detrimental effect on the water quality. Runoff introduced significant amounts of sediment to the basin. Numerous sinkholes occur in the lakebed linking the lake directly to the underlying Floridan aquifer system. Historical records indicate that the lake drains into sinks approximately every 25 years. Drought conditions during 1998 and 1999 caused the water level within the lake and the aquifer to drop, culminating in a spectacular drainage event on September 16, 1999 where a large portion of Lake Jackson disappeared down Porter Hole Sink. Prior to the final drawdown, Florida Geological Survey (FGS) geologists examined the lake and determined that a sink hole had opened in the southern lake area. Geologists observed the last stages of the lake’s disappearance and began an investigation of the sink. Subsurface excursions eventually reach nearly 50 feet below the lake bottom in small caves in the top of the aquifer. The explorations afforded the opportunity to take governmental officials and employees, and citizens on a tour of the sink hole and show them, up close and personally, the connection between the lake and the aquifer. This was further demonstrated by drilling six cores on the dry lake bottom. The FGS took advantage of this event to educate public officials and citizens on the vulnerability of our ground-water resources to the influences of development. The information gained from the investigation and the interaction with public officials and private citizens is being utilized to provide better protection for the region’s lakes and the groundwater.