I took my jet boat to the Gulkana for the first time this weekend. The water was quite low. I did well for the most part. I had to jump a small gravel bar comeing down stream as there was people standing all the way across the channel fishing.
Others did not fare soo well. In the one day I was there I saw one guy run into the old bridge pileings right after launching. He had borrowed his friends new boat and seemed to have limited experience. He put a 2 foot hole in the side of the boat and threw himself and two passengers overboard. They were shaken but not hurt.
Up river I saw a newer sport john bouncing off rocks all the way down river. When it was back on the trailer the bottom was ruined. He had run a total of 1/2 mile up river from the bridge.
Long story short, if you are new to jetboating the Gulkana is not a good place to learn.