River capture is the process whereby a strong river diverts a parallel weak river and forms a strong stream through a pirate stream. It is a pirate stream that advances towards the weaker stream and captures it.
In other words, river capture occurs where a river cuts through the watershed and intercepts a river flowing on a higher level. An example of this is the Kunene river in Namibia.
the Kunene used to flow to Etosha pan but was intercepted in its middle course by an eastward eroding river from the coastal plain to the sea.
In order for river capture to develop the following conditions should be in operation:
1. There must be a strong river flowing adjacent to the weak river so that the powerful stream may capture its weak neighbor.
This is the most important condition for river capture. The strong river must have a steeper gradient and more water than the weak river. This means that the strong river has more energy to erode its bed and banks. The weak river, on the other hand, has less energy and is therefore more susceptible to being captured.
2. The powerful river must have greater energy to undertake both vertical and headward erosion.
Vertical erosion is the process of wearing down the bed of a river. Headward erosion is the process of a river eroding its channel upstream. The powerful river must have enough energy to do both of these things in order to capture the weak river.
3. There must be a break in the weaker river’s course.
This break can be caused by a natural event, such as a landslide or a fault, or it can be caused by human activity, such as the construction of a dam. The break in the weaker river’s course allows the strong river to divert some of its flow into the weaker river’s channel.
4. The weaker river must be able to accommodate the diverted flow.
If the weaker river is not able to accommodate the diverted flow, it will overflow its banks and cause flooding. This can damage property and infrastructure and can also pollute the environment.
5. The capture must be stable over time.
Once the strong river has captured the weak river, it must be able to maintain its capture. This means that the strong river must continue to have more energy than the weak river and that the break in the weaker river’s course must not be repaired.
River capture is a complex process that can take thousands of years to occur. However, it is an important process in the evolution of river systems. River capture can change the course of rivers, create new lakes and wetlands, and alter the landscape.
Here are some additional factors that can contribute to river capture:
- The climate: Rivers are more likely to be captured during periods of high rainfall, when there is more water available to erode the weaker river’s channel.
- The geology: Rivers are more likely to be captured in areas with soft rocks, which are easier to erode.
- The topography: Rivers are more likely to be captured in areas with steep gradients, which provide more energy for erosion.
- Human activity: Human activity, such as the construction of dams or the clearing of forests, can also increase the risk of river capture.
- The powerful river must be flowing at a lower and steeper gradient than the weak river.
This means that the powerful river must be flowing at a slower speed and have a steeper slope than the weak river. This is because the slower speed of the powerful river allows it to deposit more sediment, which can build up and create a dam. The steeper slope of the powerful river also means that it has more energy, which can help to erode the weak river’s channel.
- The capturing river must be flowing over rocks that are more easily eroded than the weak river.
This means that the rocks that the capturing river is flowing over must be softer and more easily dissolved than the rocks that the weak river is flowing over. This is because the capturing river will be able to erode the weak river’s channel more easily if the rocks are softer.
the following features are associated with river capture
- the capture stream which is the river that captured the waters of other river
- the river whose water were captured is called the captured stream
- the river that has lost its water now flows in the valley that is too big for the stream this stream is called the misfit stream
- the elbow of the capture is the place where the stream piracy has taken place
- the wind gap is the dry river valley with the river gravel between the elbow of the capture and the misfit stream
What are the steps of river capture?
There are four main steps in river capture:
- Headward erosion: The capturing river erodes its headwaters upstream. This can be caused by a number of factors, including the presence of bends in the river, the presence of tributaries, or natural disasters such as floods and earthquakes.
- Drainage diversion: As the capturing river erodes its headwaters, it diverts the water from the weak river. This can cause the weak river to dry up or to become a tributary of the capturing river.
- River avulsion: The capturing river may also cause avulsion, which is the sudden change in the course of a river. This can happen when the capturing river erodes a new channel that is more direct or when the weak river’s channel is blocked by a dam.
- Antecedent drainage: The capturing river may also inherit the drainage basin of the weak river. This means that the tributaries of the weak river will now flow into the capturing river.
The steps of river capture can take place over a long period of time, or they can happen relatively quickly. The rate of river capture is influenced by a number of factors, including the size and strength of the two rivers, the type of rocks that they are flowing over, and the presence of natural disasters.
What are the benefits of river capture?
River capture is a natural process that can have both benefits and drawbacks. Some of the benefits of river capture include:
- Increased water supply: River capture can increase the water supply to an area by diverting water from a smaller river to a larger river. This can be beneficial for agriculture, drinking water, and other water needs.
- Improved drainage: River capture can improve drainage in an area by creating a more direct course for the water to flow. This can help to reduce flooding and improve water quality.
- Creation of new habitats: River capture can create new habitats for plants and animals. This can be beneficial for biodiversity.
- Rejuvenation of rivers: River capture can rejuvenate rivers by increasing their flow and sediment load. This can help to improve the health of the river ecosystem.
However, river capture can also have some drawbacks, including:
- Loss of water supply: River capture can reduce the water supply to an area by diverting water from a river to another river. This can be a problem for agriculture, drinking water, and other water needs.
- Damage to infrastructure: River capture can damage infrastructure, such as bridges and roads, that are built over the river.
- Disruption of ecosystems: River capture can disrupt ecosystems by changing the course of rivers and creating new lakes and wetlands. This can impact plants and animals that rely on the river for their survival.
- Displacing people: River capture can displace people who live in the area that is affected by the change in the river’s course.