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Flat Creek is a tributary of the Chatahoochee River that is approximately 19.70 miles (31.70 km) long.The creek flows initially in a southwesterly direction, then turns sharply south at its meeting with two unnamed branches. Flat Creek's official name by the U.S. Geological Survey is the Flat Creek-Chattahoochee River sub-watershed, and drains an area of approximately 47 square miles. Flat Creek Nature Area consists of 513-acres worth of wetland in Peachtree City that extends 3.5 miles along Flat Creek, from the Lake Peachtree spillway at Kelly Drive/McIntosh Trail downstream to Highway 74. It is administered by the Southern Conservation Trust, which kindly provided their permission for these two Earthcaches. Many thanks to Ms. Akeman, Administrative Coordinator for allowing their creation.
For this Earthcache, We're going to use a few simple definitions.
Sediment is a natural material that is broken down by weathering and erosion and is transported by wind, water, or ice, and/or by the force of gravity acting on the particles. Sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and can eventually become Sandstone or other sedimentary rock. Sediments are often transported by water but can also be transported by wind or glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition.
Types of Sediment By Size (Largest to Smallest):
A boulder is a stone that has been worn or shaped by erosion and a size greater than 10.1 inches in diameter. Some boulders may be small enough to move or roll manually and are colloquially known as stones or simply rocks, while others are considerably larger and unmovable without the use of heavy machinery. For the purpose of this Earthcache, a boulder is any rock larger than 10.1 inches in diameter.
A cobble (also called a cobblestone) is a hard rock whose size of 2.5–10.1 inches in diameter, or larger than a pebble and smaller than a boulder. Cobbles are used as a construction material, for decoration, as filler for road construction or a base for a temporary structure. Cobbles in riverine environments are heavily eroded to a smooth surface.
A pebble is a hard rock with a particle size of 0.07-2.51 inches in diameter. Pebbles are also generally rounded to a smooth surface due to sand or water erosion.
Gravel is a loose aggregation of rocks. Gravel is classified by particle size and includes size classes from granule- to boulder-sized fragments. Gravel can be formed by erosion or mechanical action; as fragments of larger stone that has been crushed. Their size and smoothness is usually irregular. Most naturally occurring gravel in riverine environments is smoothed out by water erosion. Gravel can also be the result of crushing a man made material such as concrete.
Sand is a natural granular material composed of finely grained silliceous materials and rock particles. It is defined by size, being finer than gravel and coarser than silt. For the purpose of this Earthcache, we will include silt and clay particles as sandy particles except when noted.
Sediment transport is the movement of sediment due to a combination of gravity acting upon the sediment, and/or the movement of the fluid in which the sediment is caught. Sediment transport due to fluid motion is found in creeks, rivers, oceans, lakes, seas, and other bodies of water, due to currents and/or tides. Transport can also be caused by glaciers as they flow and on terrestrial surfaces by wind.
A stream bed is the bottom of a stream, river, or creek, and is confined to the bottom of the normal water flow. The lateral confines are known as the stream or river banks during all stages except the flood stage. Under certain conditions a river can branch from one stream bed to multiple stream beds. This is known as stream or river bifurcation. The bed is the part of the channel up to the normal water line, and the banks are that part above the normal water line. Stream beds can range in width from a few feet for a creek, to several thousand feet for the largest rivers in the world. The stream bed may or may not contain flowing water at any time as some only carry water occasionally. Stream beds may cut into bedrock or through sand, clay, silt, or other loose materials commonly brought to the area during earlier stream depositions.
Stream beds are usually what is left once a stream no longer has any water flow (such as in dry seasons) and the beds are usually well protected from wind erosion because the walls made by the stream are usually hard walls. Soft sand and debris usually fill the bed both during wet and dry seasons. Dry stream beds are subject to becoming underground water pockets, or buried stream beds. Depending on the time passed since they became buried, they can be know as vestigial, fossilized or ancient stream beds.
In geology erosion is the action of surface abrasion caused by water flow or wind, that removes soil, rock, or other dissolved material from one location on the Earth's crust, and then transports it to another location. This is not to be confused with weathering which involves no movement of material from its original location. This process is caused by the activity of erosive agents like water, ice and glaciers, snow, wind, etc. Depending on the causal agents, erosion is sometimes divided into glacial erosion, water erosion, snow erosion, and aeolic or wind erosion. The breakdown of rock or soil into sediment is referred to as physical or mechanical erosion. This as opposed to chemical erosion, where the soil or rock material is removed from a rock or other surface by its dissolution into a solvent, usually water, followed by the flowing away of the resulting solution. Eroded sediment may be transported just a few millimetres, or thousands of miles, as distance from original location is usually not a factor considered in its study.
Armor is the association drawn between the flow of water on a stream or river and the erosion rate into the soil underneath with the aid of surface pebbles, rocks or boulders with stream beds or beaches. In other words, armor is a form of erosion prevention. Usually armor occurs naturally. Artificial armor such as the one around man made structures is called riprap. An example of riprap is when shorelines or stream banks are artificially fortified for erosion protection with large boulders or sizable manufactured concrete objects to prevent flooding. Geological modeling shows that stream armor usually sits in a flood stage environment of a stream or river; or in close proximity to the stream bed. Bed armor is most often transported through entrainment, and more specifically suspension and saltation. Both of these processes involve moving the sediment near or around the bed of a river or stream. When a sediment is entrained it is being moved downstream through the forces of the water around it, and once it settles it begins to create a layer on the bed of the river or stream. This layer of sediment changes the hydrology of the river around it, and once this layer on the bottom is formed it affects the hydraulics of the river.
How to log this Earthcache:
Any "Found It" logs without the complete requirements being sent in via email or message, will be deleted. Please answer to the best of your ability. I'm very lenient with answers as long as I can tell you actually visited the site. The GZ is in a suburban neighborhood and in a path frequently used by golf carts, so please be careful, mindful and respectful to the neighbors. Whenever possible, try to send the answers first.
1. Include the GC code of this Earthcache along with the names of all visitors. One set of answers is ok for a group, but include everyone in your group with the answers.
2. What types of sediment do you see in the stream? If the water is cloudy, look to the edge of the water and describe the sediment you see there. It is exactly the same as the sediment you will see at the bottom if you could. What is the predominant color of each of the sediments that you can observe?
3. Look at the smaller particles of sediment. Would you call it sand or silt (Remember the farmer's way of identifying these two types of soil: if it feels soft like flour, it's silt; if it feels rough then it's sand)?
4. How deep do you guesstimate the stream to be at the small pool right below you at the time of your visit?
5. Do you think the armor in the stream is natural or artificial? Why?
6. Post a picture of yourself at the GZ. Your face doesn't need to be in the picture. You can alternatively take a picture of something that identifies you or your group (i.e. a piece of paper listing all your geo nicknames with the GZ in the background). Per the latest Earthcache guideline revision, this is no longer optional, it is now required to be able to claim your find.
Information courtesy of The Encyclopedia Brittanica; Wikipedia, and personal knowledge of geological sciences.
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