2013 Young Scientist $25,000 prize winner...

2013 Young Scientist $25,000 prize winner...  Very clever indeed.  If this was all done on his own, it's especially impressive for someone his age.  I particularly like the use of salt to increase the water density.

I suspect his invention will only be useful when small barriers need to be erected (mind you, there's a lot of need for those) – even with the salt, the overall density of his bags will be far less than conventional sandbags, and that will limit the depth of seawater that can be held back.  Also, over time his bags will lose salt (when they're wet), as normal diffusion evens out the salinity of the surrounding water and that inside his bags.  So not a perfect replacement for conventional sandbags, but still a useful and clever way to make a better bag for certain uses...