O Level Notes : Geography - landforms and landscape processes - River capture

River capture is the process whereby a stronger river flowing parallel to the smaller river captures the headwaters of the minor stream thereby drawing the water into its own channel. For river capture to occur the following conditions are ideal:

• Two consequent streams flowing side by side
• The stronger consequent river flowing at a lower gradient than the smaller consequent river
• The stronger river has a subsequent tributary growing through head ward erosion towards the minor river

The stronger river having a tributary growing through head ward erosion will end up managing to reach out to the smaller stream. Once the major river's tributary meets the small stream, it will draw the smaller stream's headwater into the major river. Because the major river is flowing at a lower gradient, most of the headwaters of the small stream are diverted into the major river. The smaller stream is therefore effectively beheaded or captured. The small beheaded stream is called a misfit. The tributary drawing the headwaters from the small stream into the bigger one is called pirate stream and the bend where the waters of the small stream are diverted into the major river is called the elbow of capture. With time because the small stream's supply of water has been cut off, there is a waterless point between the elbow of capture and the small captured stream. This waterless point is called the wind gap. The small stream because it was weak upto the extend of being captured is called the misfit.

River Capture

Effects of capture on the captured stream

There are both negative and positive impacts of river capture to the people living near the captured stream. These include:

• Less water for irrigation
• Decreased quantities of aquatic species such as fish and crocodiles
• Low risks of flooding
• Low stream discharge
• The river may completely dry off leading to shortage of water
• Increased rate of deposition due to falling discharge

Effects of capture on the major stream include:

• Increased amounts of water for irrigation
• More aquatic species
• Permanent supply of water
• Increased rate of river erosion
• High risk of flooding
• hydroelectric power generation