Nobody was awake when the incident actually happened, but the boat was noticed missing at 6:00 am. The Club has a fair size creek that enters the river in the upper left of attachment. Its known that a lot of potentially large debris trees, etc. often flow and enter river from this source. Anyway whatever done the damage flowed down between the inner and docks and caught / hit a pontoon boat on the inner dock represented by the upper arrow. The dock lines on the pontoon boat were thereby broken and it drifted free and luckily undamaged and lodged against walkway on lower dock. The debris then flowed down and hit the lower dock on front by the houseboat.
The Houseboat is represented by the lower arrow on the lower dock. The Houseboat was always secured "tied" well as far as I've ever observed anyway. But the debris evidently was large enough the it crushed up the dock structure itself, thereby freeing up the Houseboat to float downriver and go over the dam.
Excuse the sloppy art, but thought it may give some reference to the chain of events. Pontoon Boat owner was actually lucky in both his boat didn't flow off down river, or get crushed in second hit with the lower dock that took the Houseboat.