GEOGRAPHY TEACHER AGNES River capture Stream capture Stream

River capture Stream capture • Stream capture, river piracy or stream piracy is a

Cont. • River Capture/Beheading/Piracy/Abstraction • Diversion of head waters of one river into the

CONT. • When a river is extending its channel upstream by headward erosion (

CONT. • The headwaters from the minor river may be diverted into the more

How it occurs • At first there a powerful river and a weaker river

Cont. • The powerful river erodes vertically and laterally than the weak river making

cont, • The headwaters of the weaker river start flowing into the valley of

Factors leading to river capture • Tectonic earth movements, where the slope of the

CONT. • Erosion: either Headward erosion of one stream valley upwards into another, •

CONT. • The additional water flowing down the capturing stream may accelerate erosion and

Cont. • The pirate river will now have: (i) increased river discharge (ii) Increased

The beheaded river will have • (i) Reduced river discharge • (ii) Dry river

Slides: 18

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GEOGRAPHY TEACHER AGNES

River capture Stream capture • Stream capture, river piracy or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream.

Cont. • River Capture/Beheading/Piracy/Abstraction • Diversion of head waters of one river into the system of an adjacent powerful river due to erosion. • The river that captures is called pirate. • The captured one is called victim/Misfit/beheaded river.

CONT. • When a river is extending its channel upstream by headward erosion ( the lengthening of a river's course by erosion backwards from its source ), it may come into contact with the headwaters of a river which is less vigorous.

CONT. • The headwaters from the minor river may be diverted into the more rapidly eroding channel. There is often a sudden change of stream direction at the point of capture; this is the elbow of capture. The stream which is cut off is called Misfit stream.

RIVER CAPTURE

How it occurs • At first there a powerful river and a weaker river flowing adjacent to each other.

Cont. • The powerful river erodes vertically and laterally than the weak river making it to flow at a lower level. • At the same time, it extends its valley backwards by headward erosion. • The stronger river eventually joins the valley of the weak river.

cont, • The headwaters of the weaker river start flowing into the valley of the stronger river e. g. R. Tano in Ghana was captured by the Black Volta River and R. Eyong was captured by Imo in S. Nigeria. • The remaining section of the beheaded river is called a misfit/beheaded river. • The dry valley between the elbow of capture and the new course of the misfit stream is called a

Cont,

Factors leading to river capture • 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

CONT. • Erosion: either Headward erosion of one stream valley upwards into another, • or Lateral erosion of a meander through the higher ground dividing the adjacent streams. Within 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

CONT. • The additional water flowing down the capturing stream may accelerate erosion and encourage the development of a canyon/ Gorge. • The natural diversion of the headwaters of one stream into the channel of another, typically resulting from rapid headward erosion by the latter stream.

Cont. • The pirate river will now have: (i) increased river discharge (ii) Increased erosive power (iii) A more steeper gradient (iv) increased velocity

The beheaded river will have • (i) Reduced river discharge • (ii) Dry river valley at downstream • (iii) Small river channel.

END • QUESTIONS