How does James Dickey use imagery in Deliverance?

Example of Imagery:

I took the knife and turned it so the curved part of the blade was in the wound, and drove it down with both hands. I felt it grate on the shaft. This will have to be it, I said. I’m not going to cut myself any more even if I have to grab the shaft and tear it loose, and tear myself in half with it.

I had never lived sheerly on nerves before, and a gigantic steadiness took me over, a constant trembling of awareness in a hundred places that added up to a kind of equilibrium, that made my arms move in long steady motions and showed me where the rocks were by the differences of the swirling water.