River capture.

River capture.

ZIMSEC O Level Geography Notes: River capture

  • This is a process where one River captures the headwaters on a nearby stream.
  • This can occur due to several reasons viz:
  • Tectonic earth movements, where the slope of the land changes, and the stream is tipped out of its former course.
  • Natural damming, such as by a landslide or ice sheet.
  • Erosion, either:
  • Headward erosion of one stream valley upwards into another,
  • Lateral erosion of a meander through the higher ground dividing the adjacent streams.
  • In an area of karst topography, where streams may sink, or flow underground (a sinking or losing stream) and then reappear in a nearby stream valley.

The process.

  • The diagram above shows how river capture can occur.
  • There are two consequent rivers: Stream A and B and Stream B has a tributary (subsequent A)
  • Stream B has higher discharge and thus higher erosional activity than stream A.
  • Stream B might also have a lower base level and thus increasing its ability to erode.
  • Subsequent A migrates upstream (headward erosion) until it reaches Stream A’s channel.
  • Through a process known as watershed migration Subsequent A enlarges its own drainage basin at the expense of Stream A.
  • In time because Subsequent A and Stream B have a lower base level the headwaters of Stream A will be captured and diverted into Subsequent A.
  • The point at which the headwaters of the minor river change direction is known as the elbow of capture.
  • Below this point a wind gap marks the former course of the now beheaded stream or misfit stream.
  • misfit stream is a river whose headwaters were captured resulting in the stream flowing in a valley that is too large to be accounted for by the low discharge.
  • knickpoint and waterfall might form at the elbow of capture especially if the base level of the capturing river is far lower than that of the beheaded stream.

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