These canyons were carved by at a time when the stream discharge suddenly .

These canyons were carved by water at a time when the stream discharge suddenly increased.

Explanation:

When the flow of the river suddenly increases, a stronger pressure is established, making the water of that river have a greater impact and reaching the solid part with enough force and creating faults of different depths. These flaws are canyons that have literally been dug out of the water. However, this excavation is the result of the flow of the river.