This Earthcache will introduce you to two very different but closely-related things. First, an inexhaustible Spring that is the original namesake of the City of Chickamauga. Then, a nearby wetlands, fed by this Spring, which is also located and protected entirely within the city limits. Read on, and enjoy ...
“Crawfish Springs” is the original name given to the Town of Chickamauga, in acknowledgement of the perennial source of water that is to be found here. These waters have been pivotal to hundreds of years of human history – as the foundations of a community, and as an instrument of human mercy in times of terrible war.
The wetlands, several hundred acres in size, occupy an area of land that is supplied by the drainage waters of this and several other Springs, yet not directly along the path of the exit stream. They represent a fragile ecosystem that is sustained by a flow of fresh water that, even though it ebbs and flows from one season to the next, never ends and never will.
The rocks exposed in Walker County originated as sediments on the floor of a shallow inland sea. The oldest rocks were formed about 450 million years ago and are characterized by the fossilized shells of saltwater creatures. Plant fossils are abundant in the younger rocks, deposited about 225 million years ago. Cycles of uplift and erosion occurred many times, resulting in highly fractured underground structures through which water flows freely. Eight distinct types of underground geology can be found in this county, and many of them make excellent aquifers. (An "aquifer" is an underground rock structure that captures and holds water in useful quantities.)
"What is a Spring?" A spring is a water resource formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of ground water at or below the local water table, below which the subsurface material is saturated with water. A spring is the result of an aquifer being filled to the point that the water overflows onto the land surface. They range in size from intermittent seeps, which flow only after much rain, to huge pools flowing hundreds of millions of gallons daily. Many types of springs exist:
- Seepage or filtration spring: The term seep refers to springs with small flow rates in which the source water has filtered through permeable earth.
- Fracture springs: discharge from faults, joints, or fissures in the earth, in which springs have followed a natural course of voids or weaknesses in the bedrock.
- Tubular springs, in which the water flows from underground caverns.
- Thermal Springs, with water temperature above human body temperature.
The waters of Crawfish Springs – and of numerous other equally-large springs in the immediate vicinity – originate from the Knox Group, a formation of thin and thick-bedded dolomite with limestone and dolomite at the top. This formation weathers deeply and has a thick chert and clay mantle. It is easily the thickest formation, about 3,500 feet thick.
Groundwater in this area comes from precipitation, some of which evaporates or is used by surface plants while the rest of it descends to the zone of saturation, this being that part of the earth in which all the pore space and other openings are filled with water under pressure equal to or greater than atmospheric. This water is called ground water, and the upper surface of it is called the water table.
The quantity of water stored in the zone of saturation depends on the amount of open space in the rocks. These openings consist mainly of joints and fractures. Fractures in shale and sandstone are narrow and have small storage capacity, but those in limestone are enlarged by solution and have large capacity.
In this context, the term "solution" refers to the same process that produces so many caves in the area: the dissolving of limestone in the presence of carbonic acid, which is naturally produced as water percolates through the soil.
Joints in limestone and dolomite are highly interconnected, so any well or spring may have access to very large amounts of water. For this reason, limestone such as the Knox Formation is the most important groundwater reservoir in the county.
Water-level records show that the water table level rises very rapidly after a heavy rain, from a few inches to several feet. The water level then begins to subside slowly based on gravity. The heaviest rains occur in January, February and March. During the driest months of July, August and September, surface streams may go dry, although water may continue to flow underground. The thick permeable layer of chert and clay overlaying the Knox Formation acts as a huge sponge to absorb water that otherwise would run off. The water filters slowly down through thick layers of so-called residuum and fills joints and cracks in the water table below. The slow release of ground water from the residuum into the rock openings enables springs such as Crawfish Springs to continue discharging large volumes of water during extended drought. But the amount of water can vary considerably – documented flows in 1954 were 23 million gallons per day, but only 8.9 million gallons per day six years later.
Reference: Geology and Ground-Water Resources of Walker County, Georgia
(US Geological Survey Information Circular #29) Charles W. Cressler, 1964.
Wetlands occur where water from a continuously-reliable source are able to spread out across a surface layer of underground geology which is resistant to the penetration of that water into the soil. The waters emitted by Crawfish Springs (and by several other springs in the immediate area) drain into South Chickamauga Creek, part of an expansive river system which drains over 250,000 acres of land via an estimated 463 miles of streams before emptying into the Tennessee River in Chattanooga. Along the way, they nourish this wetlands, although they do not flow directly through it.
The types of aquatic fauna that might be seen in any particular area are often strongly indicative of the typical water flow patterns that are present within it: strong current, languid current, or stagnant. Strong currents, which refresh the water continuously, are often accompanied by long-leaf aquatic grasses, anchored in the underlying terrain, while more languid currents are typified by islands of vegetation floating on the surface. In both cases, consistent circulation patterns cause the waters to remain relatively free of suspended vegetable matter. Stagnant waters, on the other hand, are typified by infestations of algae which feed upon the conditions found in these more turbid waters.
The two stages – Springs, then Wetlands – are within easy walking distance of one another: 0.7 miles, or about a 15-minute walk one way. (But of course there are other geocaches along the route!) Parking coordinates are provided at both locations for your convenience. Please note that both Stages are only available and accessible by daylight! Do not attempt to visit the springs or wetlands before daylight or after dusk.
Stage One brings you to a very pleasant place in the center of the Town of Chickamauga (see Parking Coordinates), from which you can observe the city’s namesake, and the surrounding ecosystem that it has made possible. (The lake that you now see before you is supplied by both this and several other nearby springs with comparable water flows.) Enjoy the stone bench, and note the historical plaque behind the blue Crawfish 'Welcome' sign for more information on the part this springs has played in history.
-
From how many distinct openings is the water discharging today? (This can vary depending on the season.)
-
From the list of springs type above, what type do you think Crawfish Springs is? Is it affected by the influence of carbonic acid in the water?
-
Notice the wide variety of aquatic plants in the basin in front of you. What characteristics of the fauna in the center of the basin, downstream of the spring openings, suggests to you that the current here is continuous?
-
What is the name of the person who wrote about "this magnificent springs" in his diary, and how did he describe the water?
Stage Two will take you to a different consequence of this same inexhaustible source of fresh, clean water.
After you finish your walk through town, or park at the stage-two coordinates provided, your journey will take you to the “wetlands entrance bridge” coordinates and thence to a lovely two-story tower built directly over the marsh.
(Even if it has rained recently, the pathway will be mostly high-and-dry, except possibly right at the end of the bridge where there might be mud and pools of water. If there has been a lot of rain, the end of the ramp leading up to the tower may also be slightly underwater.)
It may interest you to know that, even if the creek-bed underneath the bridge now appears to be "completely dry," a continuous flow of water actually proceeds underground from the nearby "Coke Oven Wells" – the site of another geocache – emerging above ground somewhere along the trail to your right.
“Wetlands” are, generically speaking, “a distinct ecosystem that is inundated by water, either permanently or seasonally.” However, each one is characterized by the particular situation that gives them birth. The wetlands that you see before you are entirely supplied by the waters of Crawfish Springs (and several other comparably-large springs in the immediate area), yet they are a diversion from their flow into their ultimate watershed – South Chickamauga Creek. They are entirely contained, and protected, within the city limits of the Town of Chickamauga.
The environment within these wetlands, therefore, are characterized by an entirely-consistent source of fresh water which varies only with the seasons. While the exact amount of water that is available at any particular time (and thus, the exact geographic boundaries) will change, the source, flow, quality and disposition of the water will not. Crawfish Springs never runs dry, and neither does any other perennial water source for this wetlands (including the "dry" creek under the bridge). The only thing that changes is the amount of seasonal rainfall.
Wetlands and marshes are important for their impact on water quality, including the trapping of sediments and the transfer of nutrients, as well as stormwater and floodwater retention. Wetlands are critical to the ecosystems of their regions. A huge variety of flora and fauna depend on wetlands, as you can very easily see from here.
Look closely from the observation tower at stage 2, and you will see a thriving ecosystem in action. The landscape is constantly changing, season to season and year to year. With abundant water and vegetation, this area is a great spot to look for birds, amphibians, and small mammals.
-
What color is the water here, versus the color of the water at the springs? To what might you attribute this difference?
-
What suggests to you that the water-level in this place might vary considerably throughout the year?
-
Do you think that this wetlands is ever completely dry? Why or why not?
Please note that the two stages are not wheelchair accessible. Sturdy footwear strongly recommended! Please enjoy, and take lots of pictures!