What Happens to All Those Sandbags Once the Water Goes Down?

We have all been reading and hearing about the terrible situations all up and down the Missouri and Mississippi river valleys. I can not imagine the difficulties that people in those areas are experiencing.

Trying to clean up after a flood is a daunting task. We see on TV and in other media videos and pictures of lots of people filling sandbags and piling them up everywhere.

We have seen many such situations in years past, but after the floods subside we see those same areas as they looked before the flood -- and there are no sandbags in sight.

What happens to all those sandbags once the water goes down? Do the filled bags get stashed away somewhere to be used again later, or is the sand dumped out of the bags and back to where it came from?