Baseline Hydrology of the Chickasawhatchee Swamp

Research Team: David W. Hicks (Scientist) and Brian Clayton (Monitoring Technician)

The Upper Floridan aquifer underlies parts of Georgia, Alabama, South Carolina, and all of Florida, and is one of the most productive aquifer systems in the U.S. In the Dougherty Plain area of southwestern Georgia, the carbonate aquifer is at or near land surface and receives recharge directly, or indirectly, from an average annual precipitation of about 52 inches. The Chickasawhatchee Swamp is a mosaic of uplands and wetlands and is believed to function both as a groundwater recharge area and as a groundwater discharge area for the Upper Floridan aquifer. In the wetlands, the shallow aquifer is overlain by poorly drained alluvial soils. However, the uplands are covered with moderate- to well-drained soils. In some areas erosion has removed the overburden and the carbonate rocks that comprise the aquifer are exposed.

According to Theis (1957), there are two possible recharge/discharge scenarios that must be considered in groundwater recharge areas. The first condition is that the potential recharge rate may be so large that during wet seasons, or above normal precipitation cycles the rate at which water can flow laterally through the aquifer may be exceeded. When this condition exists the aquifer essentially becomes over-full and available recharge is rejected which results in the water table standing at or near land surface in the recharge area. There may be permanent or seasonal springs in low places discharging the excess water, or there may be wetlands or other forms of vegetation drawing water from the zone of saturation and transpiring the excess. The second condition is that the possible rate of recharge may be less than the rate at which the Upper Floridan aquifer can transmit the water away. The recharge rate in this case is governed by (1) the rate at which potential recharge water is made available through precipitation or streamflow, or (2) by the vertical hydraulic conductivity of the soil which controls the rate that captured rainfall can move vertically downward to the water table and escape evaporation and plant transpiration. Because the physical properties that control the vertical hydraulic conductivity of the soil are essentially not variable, then the only variable is the rate of potential recharge (rainfall). Thus, the same area can function as both a recharge and discharge area as a result of variable climatic conditions.

In order to develop an understanding of the role the Chickasawhatchee Swamp plays in the hydrology and water quality of the Upper Floridan aquifer and the area streams, it is necessary to develop an aquatic budget. The capacity of the swamp to store water is controlled by the surface contours of the landscape, the permeability and capacity of the subsurface soils, the geology, and the groundwater conditions. In the areas proximate to the Chickasawhatchee Swamp, agricultural pumping may also have an important bearing on the hydroperiod.

Following are specific elements of the study:

Collect synoptic water-level measurements during periods that reflect annual low and high aquifer conditions (spring and fall) to construct maps depicting the aquifer surface which will be used to estimate the directions of groundwater flow.
Install stream-gaging stations on Kiokee and Chickasawhatchee Creeks in the vicinity of Georgia Highway 62 upstream of the Swamp. Gaging stations are currently operating at four sites in, or near the Swamp (Pachitla, Chickasawhatchee, and Ichawaynochaway (middle and lower)). Streamflow data will be used to develop a general water budget, and to provide information for computing loads in the steams.
Install monitor wells at multiple sites in the Chickasawhatchee Swamp; both in the Upper Floridan aquifer and at selected locations in the unconfined water-table aquifer and equip with continuous water-level recorders to provide information on the season fluctuations in groundwater levels in response to climatic and anthropogenic influences, and to provide groundwater samples for analysis.
Install atmospheric monitors (rainfall) at two sites in the Swamp (at the upstream stream-gaging stations. An atmospheric station is currently operating downstream) to provide a measure of the rainfall frequency and volume.
Install wetland-water regime continuous stage monitors at two sites in the Swamp to evaluate the groundwater and surface-water connection.
Conduct single-well aquifer response tests to determine the hydraulic characteristics of the aquifer to be used in conjunction with the aquifer maps in estimating the rate of groundwater flow under a range of hydraulic head relations.
Develop project database.

Research in progress, publications forthcoming.

Funded by: The Joseph W. Jones Ecological Research Center