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Some features that you may encounter at the New River include: |
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| Rapids | |
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Tower
Creek in Yellowstone National Park
V-shaped
valley characterstic of a youthful stage stream |
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Transition
from youthful to mature stage of development.
Deposition
on the inside of the meander andearly floodplain formation. |
As
a stream starts to develop bends and curves known as meanders, it is
entering the mature stage of development. While still downcutting
its channel, more of the stream's energy goes into lateral erosion.
Mature streams form meanders and early floodplains. Once a stream develops large sweeping meanders, it may also form an extensive floodplain, often two to three times wider than its meander belt. This is characteristic of the old age stage of stream development. The stream has such a low gradient, that lateral erosion clearly dominates any downcutting. Meanders sweep back and forth until the stream may actually loop back on itself. When two meanders are adjacent, during times of high water they may actually rejoin, leaving part of the meander cut off from the main channel of the stream, forming "cut off meanders" or ox-bow lakes.
Tennessee
River from Lookout Mountain, near Chattanooga An old age stream has such a low gradient that large meanders form as the stream moves sediment slowly. On the outer edge of the meander curve, the water moves more quickly and erodes the stream bank, extending the meander further. On the inner edge of the meander, the water moves slowly and sediments are deposited, seen here as sand. As this process continues, the meanders grow more and more extreme and eventually two portions of the stream may be flowing alongside each other. During a period of heavy rainfall, the stream may overflow its banks. When it subsides, the stream follows the shorter path leaving the meander cut off from the stream channel. These "cut-off meanders" may exist with still water for many years before gradually filling with sediments. Note the green loops that were once part of a meander.
Photo from: http://www.geosurv.gov.nf.ca/images/minjpg/73_2.jpg Links to learn more: |
| Floodplains | |
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Floodplain
of creek near Millersville, NC
Creek
with floodplain near Millersville, NC
Creek
at flood stage, occupting part of its floodplain near Millersville,
NC
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A stream gradually progresses from a youthful stage, with a steep gradient, no floodplain, and a fairly straight course through the mature stage, with meanders and floodplains forming. Eventually a stream may reach the old age stage, with well established meanders and a wide floodplain. An old age stream often just reworks the unconsolidated sediment by moving it from side to side with little progression forward. Occasionally after a stream has well established meanders characteristic of the old age stage, some sort of uplift occurs in the area. This uplift results in a much steeper gradient, which causes the stream to resume downcutting. When this occurs, the stream erodes its bed and causes the meanders to be cut so deeply, they become entrenched. So a stream that has meanders (characteristic of an old age stream) that are cut deep into the stream bed due to a steep gradient (characteristic of a young stream) is said to be rejuvenated. A good example of this is shown in the Goosenecks of the San Juan River, in Utah, at this URL: http://www.mines.utah.edu/~wmgg/Geology/UtahGIFS/Goosenecks.html
If uplift raises the elevation of a region, old age streams with established meanders have an increased gradient. This increased gradient causes downcutting to occur, resulting in a stream with meanders that become incised into the rock below. Since the change in gradient from low to high has occurred, this period is known as the rejuvenated stage.
Steams, especially at the mature and old age stage continue to change course and so do not make good political boundaries. The floodplains are flat, usually fertile, and so attractive for farming and development. Since the floodplains are actually a part of the stream, they should never be used for permanent development. Houses will be flooded. Crops will be lost. Floodplains are best left alone and used as recreation areas. The cost of replacing picnic tables is far less than replacing homes and businesses.
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| Potholes | |
| As water flows in a stream channel, small rocks and gravel may bounce and slide along the bottom of the streambed. Occasionally, these rocks may swirl around and start to form a small depression. Over time, other rocks carve these holes deeper and deeper. Potholes formed by a stream may be any size. Some are quite small, others may be the size and shape of a barrel, and others may be more the size of a large hot tub. Since potholes form on the bottom of a flowing stream, they are not easy to find or photograph. If a stream changes course, the potholes may be exposed. | |
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Links to learn more: |
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