To develop the coal industries of central Alabama, the US government in the 1880s began building a system of dressed rock locks and dams that concluded in 17 impoundments. The first 16 locks and dams were constructed of sandstone quarried from the banks of the river and the river bed. Huge blocks of stone were hand shaped with hammer and chisel to construct the locks and dams, and a few of these dams were in service until the 1960s. Old Lock 8 was one of these historical locks and dams.
This Army Corps of Engineers park is now an active fishing and camping site. Located here at the park is a swiftly-flowing artesian well.
An artesian aquifer is a confined aquifer containing groundwater under positive pressure. This causes the water level in a well to rise to a point where hydrostatic equilibrium has been reached. A well drilled into such an aquifer is called an artesian well. If water reaches the ground surface under the natural pressure of the aquifer, the well is called a flowing artesian well.
An aquifer is a geologic layer of porous and permeable material such as sand and gravel, limestone, or sandstone, through which water flows and is stored. An artesian aquifer is confined between impermeable rocks or clay which causes this positive pressure. Not all the aquifers are artesian, because the water table must reach the surface. The recharging of aquifers happens when the water table at its recharge zone is at a higher elevation than the head of the well.
An Example of an Aquifer System with Artesian Wells
The level to which water will rise in tightly cased wells in artesian aquifers is called the potentiometric surface. Deep wells drilled into rock to intersect the water table and reaching far below it are often called artesian wells in ordinary conversation, but this is not necessarily a correct use of the term. Such deep wells may be just like ordinary, shallower wells; great depth alone does not automatically make them artesian wells. The word artesian, properly used, refers to situations where the water is confined under pressure below layers of relatively impermeable rock.
Artesian wells were named after the former province of Artois (the old Roman city of Artesium) in France, where many artesian wells were drilled by Carthusian monks from 1126.
So, why does this spot have an artesian well?
Flowing artesian wells are common in the Black Warrior River valley south of Tuscaloosa. In fact, in 1971 The Tuscaloosa News reported that an estimated three millions gallons of water per day flowed from artesian wells in this area of the state. The terrace and alluvial deposits along the Black Warrior River have very productive sand and gravel aquifers at shallow depth. These water-bearing beds are highly permeable and in areas where the saturated thickness is sufficient, allows flows of more than 1000 gallons per minute to individual wells. The highest volume wells are in the southern Warror river valley. North and east of the city of Tuscaloosa (i.e., above the fall line), the dense hard sandstone and limestone along the river generally yield less than 25 gallons per minute to individual wells.
A survey of a number of wells along the river was performed by state geologist Eugene Allen Smith and published in 1907. This particular well was among those surveyed by Smith. He found that the well contained "a strong alkaline muriated water with relatively high percentage of iron." In other words, the water was relatively briny, featuring both sodium and chlorine in levels above 1000 parts per million, or .1 percent. He also noted that sulphates were almost entirely absent from the well, which he felt to be significant.
To log this earthcache, you must answer the following questions. The answers can be found by observation and reading this cache page. Send them to me via my email address on my profile or a geocaching.com message. Do not post them to your log or it will be deleted. You must send me the answers either before logging or at time of logging the cache. All other logs will be deleted!
1. On the wooden fence surrounding the well, how many vertical posts are there, in total?
2. What characteristic of this well makes it a true flowing artesian well?
3. How many gallons per minute does the well put out? This can be figured out with a gallon jug (or better yet, a bucket), a stopwatch, and a little bit of math.
4. Do you think that the flow of the well varies at all? Why or why not?
5. (Optional) Take a photo of yourself (or your GPS) at this site!
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