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Water flow Old Age

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Water flow Old Age

Meanders

When the stream approaches its old age, the width of its valley is many times that of its meanders. In the mature stage the valley width is equal to that of its meanders. Hence, when the width of valley becomes pester than its meanders, it is understood that the stream has entered old age. The plains change into Peneplains. Some low hills composed of resistant rocks are seen at some places. The main work of river is deposition. Erosion is little. If the valley is not uplifted in to youthful stage, the valley becomes a peneplain.



Flood Plain. It is that part of the valley which is submerged under water at the time of flood. It has slush and slit, which are sometimes very deep. No bore could be made as yet which could lead one to the base-rock. The slope of flood plain is gentle The river flowing in it is loaded with sediment Oxbow Lakes, marshy areas, the decaying gulf like areas, etc., are found in it.

Levees. A stream deposits sediments on both of its banks, which rise like ridges with gentle slopes on the outside. When the stream is flooded. The water rises up against the high embankment ridges. The speed of the water decreases and sediment deposits over the embankments. The natural and high embankments on the sides of the river are known as natural levees.



Peneplain. A river, in order to attain graded condition, levels the plain by deposition. Only a few areas appear rising above the plains. Soft rocks are eroded but hard rocks are not entirely eroded down and look like islands surrounded by level areas. Such raised up areas composed of resistant rocks, which have eroded to a greater extent, are known as monadnocks.

Cuesta. In the old age, the valley has already been eroded to a plain but there are a few landforms which act as interruptions to the uniformity of the place. They have a gentle dip-slope on one side and a steep escarpment slope on the other side. The gentle dip slopes is towards the mouth of the river while the steep escarpment slope faces the direction of the origin of the river. Such features are known as Cuesta. Penk thinks that a cuesta is formed by an upliftment in the course of the river. Others have a different opinion. They think that the cuestas are the remnants of the resistant part of the land, which could not be eroded by the river.

The Long Profile. In our earlier discussion of river hydraulics, we say that there was a tendency for channel gradients to become flatter downstream. However, in detail the long profile or of a river commonly shows many irregularities. These are known knickpoints. Many knickpoints have a structural or lithological origin: bands of resistant rock will create waterfalls or rapids. Other, more subtle steepenings in river long profile might be the result of variations in the load characteristics in the stream. For example, where a river receives a tributary stream loaded with coarse debris, this can lead to the steepening of the gradient of the main river. Knickpoints have also been regarded as a result of changes in sea-level, steepening the thalweg in the lower part of the stream.

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