ZIMSEC O Level Geography Notes: River Profile
- Rivers can be studied from two aspects viz:
- The long profile-this is the cross section along the river’s entire length from its source to its mouth.
- The short profile-this is the cross section across a river’s valley from the crest line( on one bank) to the channel to the other crest line. This is known as the river’s valley.
- There is only one cross profile but an innumerable short profiles that can be taken at any point in a river’s length.
- The short profile however tends to widen the further one moves downstream.
- The diagram above shows the three main sections of a river/stream’s long profile and the diagram below shows the corresponding typical short profiles at each stage.
- A river’s long profile can be divided into three sections viz:
- the upper course or headwater reaches, the middle course or middle reaches, the lower course or the lower reaches.
- The base level of a river is the lowest point a river can erode its channel, this is equal to the sea level of the ocean into which the river empties.
- it has a steep gradient, less volume of water, there is eddying and splashing as the water flows turbulently.
- Common features include:V-shaped narrow valleys, potholes, interlocking spurs, water falls and rapids, gorges, strewn boulders.
- The most dominant form of erosion is vertical erosion and headward erosion also takes place.
- Its less steep, has more water volume, a wider channel and more velocity due to reduced channel roughness.
- Common features include: Open V-shaped valleys, truncated spurs, meanders, ox-bow lakes and braids.
- Erosion is mostly in the form of lateral erosion.
- Is flat and has a very wide channel with less energy.
- Common features include: bluffs and other flood plain features such as swamps, braiding, deltas, alluvial fans, deferred junctions and natural levees.
- These features are mostly due to deposition which is more dominant than erosion due to the reduced river energy due to the lower gradient and increased wetted perimeter.
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