Answer:
In the upper reaches (also known as the source) the gradient is at its steepest because of vertical erosion. This changes further downstream as lateral erosion (side to side) from the river and deposition start to replace vertical erosion as the dominant process. Finally, the river really flattens out as it approaches the mouth as deposition become dominant.
The force of abrasion, or what occurs when two factors in a particular environment cause friction and start to disintegrate. The walls get hit by hard winds that slowly file down the composition of the canyon, resulting in the walls becoming deeper.
D. Windmills is the answer
hope it helps you.. :)
<span>Guðni Th. Jóhannesson
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