The long profile of a river illustrates the changes in altitude of the course of the river from its source, along the entire length of its channel, to the river mouth. In general, the long profile is smoothly concave, with the gradient being steeper in the upper course and becoming progressively gentler towards the mouth. Irregularities in the gradient fequenetly occur and may be represented by rapids, waterfalls or lakes.There may also be marked breaks or changes in slope, known as knick points, which are generally the product of rejuvenation. Rejuvenation occurs either when the sea level (in relation to the land) falls or when the land surface rises. Either situation allow the river to revive its erosion activity in a vertical direction. The river adjusts to the new base level, at first in its lowest reaches, and then progressively inland. The processes of erosion, transportation and deposition along the long profile of a typical river are summarised below:
The valley cross profile is the view of the valley from one sie to another. For example, the valley cross profile of a river in an upland area typcially has a v-shape, with steep sides and a narrow bottom. Variations is the cross progile are desicrbed and explained below:
Summary of above:
Upper course: a narrow steep-sided valley where the river occupies all of the valley floor, This is the result of dominant vertical erosion by the river
Middle course: a wider valley with distinct valley bluffs, and a flat floodplain. This is the result of lateral erosion, which widens the valley floor
Lower course: a very wide flat floodplain in which the valley sides are difficult to locate. Here there is a lack of erosion, and reduced competence of the river, which results in large-scale deposition
A graded profile
A graded stream has a long profile that is in equilibrium with the general slope of the landscape. A graded profile is concave and smooth. Stream’s maintain their grade through a balance between erosion, transportation, and deposition. Erosion removes material from bumps in the profile and deposition fills in dips.
Potential and kinetic energy
‘Water, when rain deposits it on an upland, possesses energy. It possesses potential energy, or the energy of position. As the water begins to flow down hill, this potential energy is converted into kinetic energy, or the energy of motion. This kinetic energy can be used up in various ways. For example, turbulence and friction within the moving water uses up kinetic energy. In addition, kinetic energy is used when the water erodes away the surface of the stream channel it is passing through or moves sediments along the stream bed. By the time the river ends in a standing body of water, for example when it enters a lake, all of this kinetic energy has been converted into thermal energy, or heat energy. This heat energy, uniformly spread through the environment, is the most degraded form of energy and cannot accomplish anything.
Potential Energy → Kinetic Energy → Heat Energy
As this kinetic energy of the moving water is transformed into heat energy it performs work, i.e. the application of force over distance. It is this physical work that moves the water and forms the river into what we see.’