STUDY AREA DETERMINATION

The original Surface Basin study area was provided to us by the Ichetucknee Springs Water Quality working group. It was based on a map of the surface water basin boundaries developed by the Suwannee Water Management District. While this boundary was significant in determining the surface hydrological features that effect the watershed, we sought to create a boundary area that would also incorporate the effects of the subsurface hydrological conditions that could have an impact the the springs. We also used an area consisting of three counties for sections of our study to derive the role of regional influences on our study.

The Ichetucknee Springs consists of areas that are formed from water flow through a limestone rock layer which causes erosion to the limestone and creates a network of underwater caverns and water flow conduits, also known as a KARST geology. These conduits are fed from several sources. One of these sources consists of a lower aquifer system known as the FLORIDIAN AQUIFER. This is a deep water source that flows from the southern sections of the Appalachian mountains of northern Georgia down through the state of Florida, and out into the Gulf of Mexico and the Atlantic Ocean. This aquifer provides a fresh water source to many rivers, lakes, and springs along the way. Springs are areas where the surface geology is thin enough for the pressure from the aquifer flow to raise the aquifer waters to ground surface levels. The long filtering process that is created from this long distance flow helps to provide the springs with its excellent water quality.

However, these deep sources are only one of several water sources that feed the springs. Another source is local surface water sources that drain into the surface aquifer. A network of lakes, rivers, and streams contribute to the springs by flowing through the area and draining into lakes or sinkholes that are connected to the springs through underground conduits formed in karstic geologic environments, or by flowing directly into the Ichetucknee river basin. Alligator Lake, some 14 miles north of the springs, in Lake City Fl., is thought to be a feature which contributes to the underground water flow. It is known to drain almost completely of water several times a year, and is flushed into the karst network below, which is believed to be connected with the karst hydrological network, that feeds into the spring.

A recent study of Rose Creek Sinkhole, four miles north east of the springs, found a direct link from the sinkhole to the Spring head of Ichetucknee Springs. Through the use of dye traces and underwater cave dives they were able to establish this link. The dye distributed in the sinkhole was collected eight days later at the spring head. Studies like this are being conducted to map out the subsurface network of water flow and the karst geological structures.

The understanding of the role of this network of sources which feed the springs is key to developing a plan to protect the water quality and quantity of the Ichetucknee Springs. Our consultation with a local hydrogeologist led us to explore a geological feature called the poteniometric surface. This surface shows the direction of flow patterns below the geologic surface level. This helped us to incorporate the effects of the sub-surface hydrological conditions that could have an impact the the springs.

Another factor which helped us determine our study boundary was the evaluation of the "confinenment layers". This is the amount of surface soil that rests on top of the base geologic rock structures, which in our area is mostly limestone. This confinement layer is important because it plays a key role in filtering pollutants from the water which flows into the aquifer. Water percolates through this soil, or confinement layer, and eventually into the subsurface geology or aquifer. The areas that have a thinner soil layer will ultimately have little effect filtering pollutants before the water reaches the aquifer. This process is known as the aquifer recharge rate. On the other hand, areas which have a thicker soil or confinement layer will have a better chance to filter pollutants contained in the water before they reach the aquifer.quality.

The Cody Scarp is a rock shelf that begins just to the north east of Lake City and slopes towards the south west of Columbia County, and towards the Ichetucknee Springs. As it slopes, the confinement layer decreases in thickness, becoming as thin as only a few feet in depth above the karst geology. Surface activity within this area would have a more direct impact to the water flowing below and pose a more serious risk to the water quality.

These three hydrological sources for the springs allowed us to expand our study area to incorporate areas we considered as relevant to understanding the subsurface hydrological patterns that were playing a role in the water quality and quantity of the Ichetucknee Springs. This new HYDROLOGICAL BOUNDARY area would incorporate the original surface basin area and aspects of the poteniometric and aquifer containment features. The Agriculture and Conservation groups of our study would use this hydrological boundary to define the limits of their study as it would best serve to confront the issues for their group on the impact to the springs. The Urban group would look at urban development from the three county area to better illustrate and incorporate urban growth across the study area. Their site specific portions would use the hydrological boundary to define the limits for their more detailed urban design strategies. The Growth Model group would look at the three county area to determine a wider range of growth pressures and distribution in and around the hydrological study area.

STUDY AREA OVERVIEW - 1992 True Color TM Satellite Image