A REMOTE SENSING AND GIS STUDY OF LONG TERM WATER MASS BALANCE—LAKE JACKSON, FLORIDA

Lake Jackson is a large (1600 ha), shallow lake (<4m) located near Tallahassee, Florida. In the 1950’s the lake became nationally renowned for its bass fishing and aquatic waterfowl, but rapid urbanization of the lake’s watershed in the 1970’s led to degradation of the lake habitat. The lake has recently undergone a multimillion-dollar rejuvenation program. Remote sensing and GIS studies are being used to evaluate the hydrometerologic controls of lake dynamics, including lake hyposometry, volume and surface area, distribution of karst-related features, variation in the permeability of lake bed sediments and underlying clastic and carbonate units, underlying aquifer levels, and the micrometeorology of the lake watershed.

The lake has no surface outlets but is drained by two major sinks. Direct precipitation (128 cm/yr) is the dominant source of water inflow for the lake, plus periodic storm water runoff into the lake from the local watershed. Evaporation (~116 cm/yr) and lake bottom leakage are the only mechanisms that regulate lake level. Departures from the tight budget between inflow and outflow can produce major changes in lake level over short periods of time. These changes include periodic disappearance of the lake during drought and major flooding of the lake during periods of high rainfall. During a recent severe drought (1998-2000) the lake level dropped rapidly and the eastern portion of the lake emptied through Porter Hole Sink in September 1999. The southwestern portion of the lake slowly drained into Lime Sink and by August 2000 only a small remnant of the lake basin contained water. While the lake bed was dry, approximately 1.2 million cubic meters of muck and lake sediments were removed from the eastern portion of the lake basin as part of the lake rejuvenation project.

A hypsometric map of the lake, produced using air photos of the lake taken at different elevation stages, combined with ground-based leveling and GPS surveying indicate that the lake must be treated as a complex system, composed of at least four separate basins. Preliminary evaluation of variations in lake level, rainfall, and evaporation suggest that sinkhole-related drainage is a very important factor in regulating the lake's surface elevation, even when open sinkhole drainage is not occurring.