"If you're etymological"...tump comes from the British word tumpoke which means to fall head over heels. We prefer to think it's a combination of "tip" and "dump." In fifteen trips, we have not had a whole lot of tumps, and so far nothing really hairy or in dangerously cold weather. It doesn't even seem like the water has ever been dangerously cold, but that could be a matter of perspective.
Kirk had the first ever RRCC tump. On the Duck River in the Spring of 2005, partially excused because of an immminent thunderstorm.
Tim tumped on the lower Buffalo.
We don't have any specific examples to cite to, but it seems like Phil tumped all the time. Until he started stowing away in the bow of other people's canoes.
Big Swan Creek was one big tump-fest
Stuart and Jack were the last to tump. Within sight of the take-out on the Duck last fall.
Tumping is why we don't put all our beers in one basket.