By Can Denizman May 1998
This study represents an application of Geographic Information Systems to examine the morphometric and spatial distribution of karstic depressions and the factors controlling the karst development in the Lower Suwannee River basin. Because of the generally unconfined or semiconfined hydrogeologic conditions of the Floridan aquifer system, the Lower Suwannee River basin presents an extraordinary set of karst features illustrating a complex evolutionary history. Analysis of the morphometric and spatial distribution parameters of karstic depressions reveals that the Florida karst is represented by broad, shallow depressions with an average density of 6.07 depressions/km2 and an average pitting index of 14.5. A simple morphoclimatic classification of karst landforms is precluded by the great variation of morphometric and spatial distribution parameters of karstic depressions within the Lower Suwannee River basin.
Comparison of morphometric and spatial distribution parameters of depressions with geologic and hydrogeologic factors such as potentiometric level fluctuation of the Floridan aquifer system, thickness of the overburden material above the Floridan aquifer system, depth to water table, soil type, and the vadose zone lithology suggests that all of the factors examined in this study affect the morphometric characteristics and spatial distribution of karstic depressions. Analysis of depression major axis orientations does not show a structural control on the karst development.
Application of the mass flux technique to available data indicates that the best estimate of the net karstic dissolution rate in the Lower Suwannee River basin is 40 m3/km2/year. This is equal to a denudation rate of 40 mm/1000 years.
Morphometric and spatial distribution characteristics of karstic depressions suggest that the last phase of the post-Miocene karstic evolution within the Lower Suwannee River basin has been controlled by the lower sea-level stands of the Pleistocene. As interglacial seas of the Pleistocene retreated, marine terraces were formed by sequential sea-level lowstands and the time period of subaerial exposure diminished towards the sea. Consequently, geomorphologically younger karst landforms formed as the elevation of marine terraces decreased. This evolutionary pattern of karst landforms has resulted in the development of more frequent and/or larger and more complex depressions at higher elevations.