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Stream Piracy / River Capture
The process by which a MORE energetic river (captor stream) erodes through a watershed and captures/diverts the headwaters of a LESS energetic river.

Captor Stream
The MORE energetic river that erodes through the watershed and captures another river. Gains extra water and becomes rejuvenated and overgraded.

Captured Stream
The LESS energetic river that is captured/stolen by the captor stream. It loses its headwaters.

Elbow of Capture
The point/bend where the capture occurred. The captured river CHANGES DIRECTION and begins to flow into the captor stream. Forms a sharp bend (elbow shape).

Wind Gap
The part of the original (captured) river's valley, between the elbow of capture and the misfit stream, that is now DRY and filled with gravel. The valley is now above the water level.

Misfit Stream
The part of the captured river that has LOST its headwaters through piracy. It becomes a small, weak stream flowing in a valley that is now too large for it. Eventually dries up.

Abstraction
The process whereby the WATERSHED becomes LOWER and its position SHIFTS. Occurs because the gradient is different on each side of the watershed → more erosion on the steeper side → watershed lowers and migrates. Example: Drakensberg Mountains.

Effect on Captor Stream after stream piracy
Gains extra water → excess energy → OVERGRADED → rejuvenated → erodes a deep valley upstream by headward erosion.
Effect on Misfit Stream after stream piracy
Loses water → insufficient energy → UNDERGRADED → deposits its load → flows in a valley that is too large for it.
Watershed
The ridge or high ground that separates two adjacent drainage basins. Water on each side flows in different directions.
What is the sequence of events in stream piracy?
Captor stream has steeper gradient → more energy.
Erodes headward through watershed.
Captures the headwaters of the weaker river.
Elbow of capture forms.
Wind gap is left dry.
Misfit stream loses water and dries up.
Captor is rejuvenated.