The speed and volume of a river varies from place to place along a rivers 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 affects the speed of the water in a river. Generally, the upper course has a rougher river channel while the middle and lower courses have a smoother river channel. When the river bed is uneven and has a large number of obstacles such as rocks, boulders and plants, there is more friction, causing the water to flow more slowly.
The wetted perimeter of the river affects the speed of the water too. The wetted perimeter of the water is the size of the river channel in contact with the water. The upper course has usually a smaller wetted perimeter while the middle course has a larger wetted perimeter. The lower course has the largest wetted perimeter. A larger wetted perimeter decreases the speed of the water due to the friction generated as with more of the river channel being in contact with the rivers water.
Transport process A is suspension. Suspension occurs when small particles such as silt or clay-sized particles are carried within the water by turbulent flow. Transport process B is traction, and occurs when large boulders or rocks rolled along the river bed. Transport process C is saltation, where small pebbles and stones are bounced or hopped along the river bed.
Solution is not shown in the figure. Solution is a river transport process in which minerals are dissolved in the water and carried in solution. As the minerals are dissolved in the water and thus invisible to the naked eye, it then cannot be shown in the figure.
There are 4 main processes of river erosion, including hydraulic action, corrasion, attrition and solution. Hydraulic action is the removing and dislodging of rocks from the bed and banks of the river by the sheer force of the running water. Corrasion, or abrasion, is the grinding of rock fragments carried by the river against the bed and banks of the river. This action both widens and deepens the river channel.
Attrition is the knocking of rock fragments in the water against one another. In the process, the rocks become smaller and rounder as the sharp edges are grounded. Through time, rocks become grain sized silt, clay and other sediments. Solution is the process by which river water reacts chemically with soluble minerals in the rocks and dissolves them. For example, when a river stream flows over an area of limestone, it erodes the limestone by reacting chemically with it and dissolves it.