Long time, no post..
I was recently in a conference about heat and mass transfer and this river issue came up. Professor Voller (http://www.ce.umn.edu/~voller/) from University of Minnesota and his group are modeling the generation of river deltas and they've shown that significant delta formation can be observed in scale of decades. They use this information in attempt to protect cities from hurricanes there.
This makes me think that we really should sort of use blur on the deltas instead of high-detailed islets and such.