The speed and volume of a river varies from place to place along a river's course because of many reasons. In the upper course, the volume of water is low as there are few tributaries. In comparison, the volume of water in the middle course is higher as there are more tributaries supplying water to the main river channel. The volume of water in the lower course is the highest as the lower course has the most tributaries.
However, many other factors will also affect the volume of water in the river. More permeable rocks will result in less surface runoff, thus a lower volume of water. Less permeable rocks will then have more surface runoff, thus a higher volume of water.
Vegetation on land such as trees and plants also affects the volume of water, as vegetation intercepts rain. The upper course usually has more vegetation, while the lower courses have less vegetation intercepting precipitation. Sparse vegetation results in less water infiltrating the ground, thus there will be more surface runoff, resulting in a larger volume of water.
The climate of the particular area will affect the volume of water in a river too. The volume of water varies for wet and dry seasons as the amount of rainfall changes. Generally, in hot and wet equatorial or tropical area, there is a higher volume of water as compared to dry areas such as deserts.
Lastly, the size of the drainage basin will affect the volume of a river. The bigger the size of land area drained by the main river and its tributaries, the higher the volume of water as there is more collection of rainwater compared to a smaller drainage basin which has less surface area for rain to fall on.
The speed of the river, is affected by the gradient of the river. In the upper course, the gradient of the river is steep, thus the water is fast-flowing. In the middle and lower courses, the gradient is gentler, thus the water flows more slowly.
The roughness of the river channel also...
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