Fill levees with that diaper stuff. Absorbent gelling material is actually fairly cheap, and it seems like several pockets of it would have the actual ability to stop a leak. Pretty much anybody who does such things knows that all it takes is a trickle of water and it's over. A trickle leads to a spray, to a good seeping, to a big hole and finally to a massive breach. All in a very short period of time. If you could have some kind of built-in method to stop the trickle, you'd be set.
If it's good enough at stopping the poop of babies, it should be quite apt at fixing much smaller problems like massive floods. If dams(parents) can use it, dams (walls to stop water) can use it!
Secondly, perhaps the stuff could be made to independently assemble a make-shift levee.
You could get a large container of the stuff hook it unto a chopper and dump in on some quick flooding area. Turn most of the water going a certain direction into gel and divert the river.
It would kill fish, not sure how the hell you'd clean it up.