Wow, that's amazing.
But unfortunately, river cruises are always impacted by water flow. When we were suppose to do our river cruise in December 2011, they were having the opposite situation. Instead of problems with high water, they were really lacking in rain and snowfall in the mountains, so the runoff was considerably less than usual. This resulted in very low water and boats not being able to stop in some towns or they would dock at other towns and have to bus passengers into the towns where they were suppose to dock. I didn't hear of any cancellations, as in this case, but they did have several itinerary changes.