Stream capture

Stream capture, river 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 down to the bed of a neighbouring stream. This can happen for several reasons, including:

• 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, 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
• Glacier retreat

The cause is not always clear.

The additional water flowing down the capturing stream may accelerate erosion and encourage the development of a canyon (gorge).

The now-dry valley of the original stream is known as a wind gap.