Let me make this very simple and basic.
I almost died with a buddy two years ago doing this very thing. I am going to tell you want happened so you understand why you do dont want to do it. I am going to leave out certain details because we cannot account for the idiot factor that might read this.
It was a night dive, myself and my buddy had planned the dive. We entered the water by ourselves. We checked in at the stairs saying we were going for a night dive. We were both following the rules for overhead diving. We used the smallest lights to get over to the dam and swim out to the columns. We had done a deep dive early down the faces- no problem and we knew how we would enter the dam.
Once we entered the column we turned on our HID lights. The space was restrictive shaped like a half circle flat on one side and curved around the front. There were no rooms and the columns were not attached inside. We werent in very deep when it started, that little voice in your head that says- you dont want to be here. I sank down a little further (leading the dive) and I heard it again- you really dont want to be here. A second after that I felt something touch my shoulder, I turned around flat 180 degrees- still no one but my buddy above me. We are checking out the grates a little deeper and I felt this strong punch to the back of my head, I was starting to get pissed. Again turning around, my buddy asked if I was ok? I called the dive and we ascend slowly up. We had no risen 10ft when the alarm for the turbines went off. A very loud noise could be felt through the water- BEEP, BEEP. Emotions flooded through my body and I gave the emergency exit hand sign. Followed by the finger- for Fubardd dive. This was probably one of the worst moments in my diving history, we were not keeping to the 30ft per minute ascent rate and my computer was complaining up a storm- too bad. In the back ground you could hear the turbines starting up a slow whirr and it was starting to get louder and stronger. We popped out of out little entrance and I grabbed my buddy and slammed him on top of the column so we were on our knees. We dumped the air in our wings and made sure we were planted. I was not sure of the water movement and you cant always see swirling water. I grabbed some silt and sprinkled it in front of us. The water did not move. Finally, my heart slowed down, my computer calculated that we were still alive at 20ft- Duhhhh. After a minute of sitting on the tops we swam back to the stairs. My buddy was praying the way back I could her him giving thanks. I thanked various religious groups myself and that little voice. We sat at the exit in the water for a minute and said nothing. As we exited the water, a friend and Divemaster asked how was your dive?- we both looked at each other and said nothing and walked up the stairs.
It has taken me sometime to talk about this dive, I figure that my life was spared it is a good think to share it with other people so they might not do the same. So please do not dive inside of the columns. The view is much better from the outside of the column and a lot safer.
