Logging Requirements:
Send the answers to #1-#4 to me through my geocaching profile. DO NOT post the answers to any logging requirements on this site.
1. List the name “GC2FWPH Belle Fourche River Sinuosity Index Earthcache” in the first line of your email. Also, list the number of people in your group.
2. Decide whether the Sinuousity Index would classify this river as straight, sinuous, or meander. Do this by: A. Step 1: KNOW: The river "channel length" between points "A" and "B" is 3.4 miles. B. Step 2: Determine the Valley Length. Valley Length = Straight line distance measured from the Starting point (where you are at) to Waypoint 2 (4CHE2 -- N 44 37.808 W 104 40.783) C. Step 3: Calculate the Channel Sinuosity Index. Channel Length divided by Valley Length = the Sinuosity Index (ratio). Then determine if the river is considered straight, sinuous, or meandering
3. From your viewpoint overlooking the river, determine whether (according to the descriptions below) the river is a young, mature or old age river.
4. Do ONE of the following: 1) Drive down to the National Park entrance and tell me what COLOR the "toll booth" is 2) Tell me how many picnic tables are at the overlook?
5. Post a picture of yourself and/or your GPS with your log that shows You with the RIVER in the background behind you.
This channel's course (straight, sinuous, or meander) and the affects of mine tailings on the sedimentation of the area are evident in various places from this location east to Vale, South Dakota.
The Area: The Campground for Devils' Tower is in the most prominent meander neck of Belle Fourche River (at least in this area). If you are staying in the campground feel free to meander (pardon the pun) from one edge of the neck to the other and imagine potential river changes over time.
Sinuousity Index: The meander ratio or sinuosity index is a means of quantifying how much a river or stream meanders (how much its course deviates from the shortest possible path). It is calculated as the length of the stream divided by the length of the valley. A perfectly straight river would have a meander ratio of 1 (it would be the same length as its valley), while the higher this ratio is above 1, the more the river meanders.
The sinuosity index has been used to separate single channel rivers into three general classes: straight (SI=1), sinuous (SI=1 to 1.4) and Meander (SI >1.4) The channel sinuosity index is the channel length (the actual distance traveled/paddled down the river from the Starting point to the Ending point, divided by the valley length (straight line distance from the Starting point to Ending point,) and are calculated from a map or from an aerial as shown in the satellite view or topo map of this area of the Belle Fourche River.
Age or Rivers Diagnosis:
Youthful rivers have the following characteristics: 1. The channel is deeper than it is wide and V-shaped due to downcutting rather than lateral (side to side) erosion. 2. Its velocity is fast and strong and capable of moving all sediment sizes from ions to silts, clay and even boulders. 3. Steep sided cliffs flank the river. 4. A floodplain does not exist, and there are no grassy areas near the river. 5. Because of the fast moving water, rapids may be present. 6. Erosion is more prevalent than deposition.
Mature rivers have the following characteristics: 1. The river flows down a moderate slope. 2. The channel is U-shaped and wider than a youthful river, but deeper than an old age river. In general, the channel is broader with gentler slopes. 3. The velocity is greater than an old age river but less than a youthful one, and can carry all sediment sizes with the exception of boulders. 4. A floodplain exists with grassy areas alongside the river where a person can walk. 5. Meanders may be present but may not be as curvy as those found in old age rivers. 6. Erosion is present although deposition of sediment also occurs.
Old age rivers have these characteristics: 1. The river flows down a very gentle slope. 2. The channel is wider than it is deep with a very broad and U-shape, due to extensive side to side erosion. 3. The velocity of an old age river is generally very slow, and may carry silts and clay. Small sediments suspended in the slow-moving water may give the river a muddy appearance. 4. The general landscape around the river is flatter and less steeply sloped. If hilly areas exist, they are further away from the river channel and kept at a distance by a wide floodplain which flanks the river. 5. The old age river has a wide floodplain with grassy areas beside the river. The floodplain is often marshy and swampy due to flooding of the river valley. 6. Curvy S-shaped meanders are abundant and prominent features of an old age river.
Other definitions:
Meander: A meander in general is a bend in a sinuous watercourse. A meander is formed when the moving water in a river erodes the outer banks and widens its valley. A stream of any volume may assume a meandering course, alternatively eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis. Most meanders occur in the region of a river channel with shallow gradients, a well-developed floodplain, and cohesive floodplain material. Erosion is greater on the outside of the bend where velocity is greatest. Deposition of sediment occurs on the inner edge because the river, moving slowly, cannot carry its sediment load, creating a slip-off slope called a point bar. The faster moving current on the outside bend has more erosive ability and the meander tends to grow in the direction of the outside bend, forming a small cliff called a cut bank. This can be seen in areas where willows grow on the banks of rivers; on the inside of meanders, willows are often far from the bank, whilst on the outside of the bend, the roots of the willows are often exposed and undercut, eventually leading the trees to fall into the river. This demonstrates the river's movement. Slumping usually occurs on the concave sides of the banks resulting in mass movements such as slides.
Sedimentation: Throughout the Rocky Mountain region, floodplains are predominately formed by lateral accretion to the point bar at the inside of the meander bend. Overbank (vertical accretion) deposits are relatively thin. In many of the areas around Devils tower National Monument this accretion is between 5 and 15 cm where the bank is up to 2 meters tall. However, in floodplains that are heavily affected by mine tailing dumps, these overbank deposits can more than double the normative height of the bank with 1 to 2 meters of tailings deposits. Since the mining deposits contain significant waste (lead, cadmium, arsenic, copper and zinc are the most common in this reagion) this leads to a potentially toxic situation for the floodplains. Even though it has in many cases been nearly 100 years since these types of mining practices ended, the affects are still present in the floodplain. Why? Because the amount of vertical drop in a meandering stream is negligible, which means that not very much sediment is carried with it downstream. You will notice, if you drive the roads that border Belle Fourche River that there are absolutely NO rapids or waterfalls on this section of river. There is an elevation change of only a few feet within a twenty mile span of river!
Resources:
Averett, Chemical Quality of Water and the Hydrologic Cycle