I found the Stormtec Stormbags at my local hardware store last fall. Basically, they're burlap sacks with water absorbing polymer crystals inside. You soak them in fresh water and the polymer crystals expand to create an alternative to a sandbag. They're lightweight (a pound when dry), easy to transport to the disaster site, and simple to soak and set in place. I've never used them for flood control, but they look like they'd work quite well. When exposed to water they increase 33 pounds in weight in about 5 minutes.
I have used them to soak up an intermittent leak in my husband's garage. We laid it down where the puddle usually forms, and it slurped up all the water, keeping it in one place. They will eventually dry out if set aside in a dry, well-ventilated area, so they can be reused. I put ours up on our plant shelf outside, where it got air on all sides. I expect there's a limit to their reuseability; mostly because they'd get really disgusting after a while.
The Stormbags cost $7.00 each at the Stormtec website, or $340 for a box of 50 bags. They also sell door protection kits that will fit various sizes of doors. They're expensive, compared to regular sandbags, until you consider how easy they are to store and transport and their alternative uses. If you have a small leak having a couple of these on hand is a real time and money saver.
-- Amy Thomson