Update: Apparently there are some kinda odd looking folks walking around here from time to time. Personally I've never been bothered by anyone while here, but unless your like me (6'1, 230lbs) you might feel safer taking a friend along just to be on the safe side. If nothing else they can help pull you from the poo water if your not paying attention and somehow fall off the dam lol
--Warning, you will need a special tool for this EC (Straightened wire coat hanger or something similar). Personally I wouldn't touch the water, that IS a waste water treatment plant behind the dam after all. And lastly, do not attempt this EC during periods of flooding.--
(Good day for a smiley)
(Bad day for a Smiley)
Ok, so, why are they temporary?
Because as soon as water begins filling the reservoir behind the structure; silt, pollutants, and general sediments begin to fill in as well. Over time the sediment fills in the reservoir leaving a flat flood plain behind the dam.
How?
Water is like an earth moving highway. Roughly 480 million years ago the Appalachian mountains began forming from the collision of the continents that resulted in the creation of the super-continent Pangaea. At their peak height, most scientists estimate they were as high (perhaps even higher than) the current Himalayan mountains (Everest is roughly 29,000 ft currently)(4). As time wore away at those enormous mountains the debris had to go somewhere. The rivers and streams slowly but surely collected the debris and, with the help of rain and gravity, transported it down to the coast line depositing it into what is now the Atlantic ocean. This process is called "Sediment transport".
What does it matter?
That process is still going on today and our rivers still collect millions of tons of debris every year. Unfortunately, most of the waterways in the Southeast (And elsewhere for that matter) have been altered by man.... We've built Dams.
Ok, so?
Rocks and sand obviously don't float (unless were talking pumice perhaps), so in order for water to keep this debris moving downstream the water needs to be moving. The faster the water moves, the larger the debris a river can move. When a waterway loses kinetic energy (speed) it also loses some of its ability to move debris - "Deposition". As the name implies sediment will be deposited along the waterway resulting in varying layers of silt. In practical terms, when a stream begins to slow down and widen (as it enters a reservoir) the large stuff ends up on the riverbed first IE: larger rocks. As the water slows even more, finer material can no longer be held in suspension and it is deposited to the bottom as well, such as sand. Finally, as the water reaches its lowest kinetic energy state (Slowest speed) even the finest material cannot be held any longer and it too deposits on the reservoir floor. This means that all along the length of a dam's reservoir, sediment is slowly but surely replacing area that once was open water, thereby reducing the capacity of the reservoir itself. From an aerial perspective it appears as if a large, muddy fan is slowly expanding out from the river into the man made lake, growing closer to the dam itself every year. Eventually the fan will meet the structure and the dam will no longer be usable.
(Image Courtesy of Vermont Department of Environmental Conservation)
Earthcache? Not Hydrocache?
Since Dams are man made structures, the area that is now covered by water and sediment was once an open valley. Obviously, this radically alters the landscape from how the river intended. Furthermore, the sheer weight of water in a dam's reservoir permeates the rocks it sits upon and injects water deep into the ground below. Some studies have implied that this ground water can lubricate ancient cracks in the bedrock resulting in the reactivation of dormant faults, giving us earthquakes even in areas that typically do not have them (2). The longer a dam is in place, the deeper the sediment layered across the original landmass becomes. Eventually, if left unchecked, an aging dam filled in by sediment will create another feature, a Waterfall.
Furthermore, the sediment retained by a dam was originally destined to be deposited by its river into the ocean. In our case, this sediment load helped replenish the coastal plain and barrier islands along the Carolina / Georgia coast line. Instead it is impounded behind a large concrete barrier where it blankets the original earth. As the Glen Canyon Institute explains:
"As today’s dams silt up, so they will leave behind a vast muddy wasteland. Compacted by the weight of a reservoir’s waters, the fine particles of silt which have been deposited in the reservoir form a brick-hard pan as they build up. Even when the last waters of the reservoir have drained away, therefore, the land beneath will not be suitable for basin irrigation or rain-fed agriculture. Only a narrow strip close to the dam, where the courser and thereby less compacted particles of silt are likely to have accumulated, will be suitable for cultivation" (1).
Cut to the chase?
Ok, so our dam here on the Enoree river was built between 1880 and 1895. There may have been a smaller dam here before, but the current 55 foot structure is what remains now. This mill was the first in Greenville county and operated from approximately 1820 - 1935. The mill burned repeatedly over the years and each time was subsequently rebuilt, until the final conflagration in 1943 (3). If we assume that the dam operated as intended from at least 1895 to 1935, that means that the flat, tree dotted area you see behind the dam was produced in a mere 40 years... Not so fast... Today we see that the main discharge channel is wide open with no equipment still channeling water into a turbine (Big hole in the dam that most of the water flows through). Sadly, I can find no reference of when this officially occurred. Furthermore, even with the discharge channel AND the 6 sluice gates wide open, the dam does occasionally refill and even over-top during heavy flooding, which adds more sediment in some places and flushes it out from others. This is a dynamic system that even today is still trying to balance itself, not quite natural, not quite human controlled anymore.
--- Logging Requirements ---
Obviously, please E-mail the answers so you don't give them away.
1. Hope you brought your coat hanger, because your going to be pushing it into the dirt to see how hard the soil is. When you first park your car in the lot, press the end of the coat hanger into the ground near a patch of grass/clover. How far could you get the coat hanger into the dirt?
2. Follow the path down towards the dam itself. You will see a set of stairs leading up over the dam (To the left) and another set further away leading up to an observation point on the dam. You will also see a path that follows the river to the right of those steps and a bald patch of red clay next to the fence. This entire area leading way back into the trees is sediment that has been collected over the years by the dam. Take your coat hanger and see how hard that bald, compacted, patch of red clay is. Is it harder or weaker than the dirt near the grass? How far did you manage to get your soil tester in?
3. Walk further back into the trees and take a few more random samples along the way. Did the soil get more or less densely packed? Any thoughts on why its different?
4. Head back to the dam and walk up to the observation platform. On your way up the steps, notice the bank under the fence where you were walking earlier. This entire bank is collected sediment. From the water line, how many feet of accumulated sediment do you estimate remain? (Obviously this will vary a bit depending on water level).
5. (Not required but recommended) Go enjoy the ruins on the other side. Take some pictures and relax. Maybe do the other geocaches nearby. The whole point of this game is to have fun and explore.
--- Final note. Earthcaches are natural and man made wonders for everyone to enjoy. If you have a premium only earth cache please consider making it open to everyone, leave the premie caches for the container types. If an area is too precious for everyone to come see and experience, then its too precious for a cache. Ok, rant over ---
------- Works Cited -------
(1) Glen Canyon Institute. http://www.glencanyon.org/glen_canyon/sediment
(2) International Rivers. https://www.internationalrivers.org/earthquakes-triggered-by-dams
(3) Historical Marker Project. http://www.historicalmarkerproject.com/markers/HMYGG_pelham-mill_Greer-SC.html
(4) Geology of the Appalachians. https://en.wikipedia.org/wiki/Geology_of_the_Appalachians