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Rapids and waterfalls
Waterfalls have a high place in the economy of the country. Hydroelectric planning is dependent upon these waterfalls. Some waterfalls are artificially constructed but here only natural rapids and the waterfalls are described.
Every river tries to attain graded stage by erosion and deposition. If this process is obstructed rapids and waterfalls are formed. The obstruction is due to the presence of rock of different resistance or due to some endogenetic activity.
The formation of rapids or waterfalls depends upon the nature of the junction of the two types of rocks. If the hard rock is slightly tilted at the junction towards the direction of flow, the water falls at many places from small heights. Such falls are known as Rapids. For example, there are many rapids on the Nile (Egypt). A series of rapids are called a Cascade.
If the overlying strata of hard rocks are horizontal or inclined at a very small angle, the upper rock layer is called Cap Rock. The under lying rocks being soft are rapidly eroded. As a result, the water falls vertically from the edge of hard rocks. It is called a Waterfall.
When the waterfalls recede, they do so by forming a gorge. The formation of gorge is an important activity in the youthful stage. Colorado in Arizona.(U.S.A.) has the biggest gorge of the world. It is known as Grand Canyon. It is about 482.8 km. long and 1905 meter deep.
The place where the tributaries of consequent streams meet the main stream, the junction is at the level as that of the mainstream. Such junctions are called accordant junction. Even if the slope of the tributary stream is equal to that of the main stream, the tributary stream cannot cut with the speed of the main stream because of the shortage of water and rock fragments, which are its cutting tools. As a consequence, the bed of the tributary is much higher than that of the main stream and, therefore, the tributary stream appears hanging over the main stream. These tributary valleys are known as hanging valleys and their junctions are called discordant Junctions.
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