encañonamiento
(encañonar) to channel, form a channel. The River Project - Know Your Watershed Never a deep-channeled river, the River flooded and meandered, ...
www.proz.com/kudoz/spanish_to.../2847137-encañonamiento.htm... - Cached

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Note added at 38 mins (2010-01-29 11:19:50 GMT)
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sorry
in your context it could =

forms a channel/channels its way

Obviously.

...narrow gorge'.

This fits with the clause that follows.

While "encañonar" comes from "cañon," it has also taken on a more metaphorical sense. It could mean 'passes through a canyon', but it is actually creating the canyon.

Examples of "river tunnels through" in the sense of a verb:

disappear as the river tunnels through a canopy of hardwoods between low, wooded bluffs. White-tailed deer and wild turkeys roam the banks, and songbirds ...
www.hawriver.org/library/publications/Guardians_Haw_WNC.pdf -

James Sullivan - 2006 - Travel - 271 pages
The distant karst mountains come into high relief, and soon the river tunnels through 417-foot (127 m) Hang Ca, the first of the caves, followed by Hang ...
books.google.com/books?isbn=0792262034... -

Portrait of the Mississippi - Google Books Result
Howard Jones - 2005 - Nature - 117 pages
... in places by giant snags and fallen trees Dense forests create an eerie all-green environment where the River tunnels through It winds back and forth, ...
books.google.com/books?isbn=1886028745...