Another one of those puzzles in life: When a hurricane approaches, we see on the news people stacking sandbags. But, once the danger passes, where do all the sandbags go? Does someone come around and collect them? Does the sand get dumped back where it came from? The news never covers this aspect! 
Good question. And related, where can I get sandbags if I feel the need to have some?
I looked them up,
Home Depot. Both cloth and plastic. As for getting rid of them - that’s usually up to the landowner. I’ve seen banks of bags that were just moved off to the side to rot months after any chance of flooding. Depends on your tolerance level for trash, I guess.
We bought sandbags in bulk from a building supply place along with sand, when we lived in the Texas Gulf Coast region and flooding threatened. I think the sand was repurposed as a soil amendment after the danger passed.
Filling and lugging sandbags is not one of my more cherished memories.
Pro tip: try not to live too close to a bayou.
♪♪…long time passing…♪♪
Considering that there’s a global sand shortage, shouldn’t we be re-using the sand? Can we re-use the wet sand from sandbags?
If you Google, you can find alternatives to sandbags. Some are things like plastic bladders that you fill with water.
Fight fire with fire, and water with water.
In places that flood every year, or more often, why don’t they just mix cement with the sand, so when the flood’s gone, there’s a permanent flood wall?
I moved to Salt Lake City the summer that they had massive flooding down City Creek Canyon. The SLC people, using entirely volunteer labor, built two sandbag walls parallel to each other to create an artificial river going down one of the city streets to a large storm drain. They built raised walkways across the river, so you didn’t have to go all the way around if you were on foot. At the end of the summer, the sandbag dikes disappeared completely. The next summer they did it all again.
I could see this happening in a place like SLC, with its large LDS population already organized into stakes and wards, and with a tradition of community service. It’s harder for me to imagine it in a place like, say, Boston. Possible, but less likely.
The sandbags used consisted of woven plastic bags that don’t really have a long lifetime. I’ve seen enough of them split open to realize how fragile they were. What they could have done (and probably did ) was to save the sand, reuse the sandbags they could and fill new ones, possibly simply throwing older bags into new bags to save effort.
The bags are usually cheap and not made to last more than a few months; the sunlight degrades them and they fall apart. This is usually a good thing since sand bags are seldom set up in anything other than emergency situations, meaning not ideally planned out from an engineering perspective. You want those haphazard berms to be removed.
Ideally you do something long-term about the issue, but often it’s simply cheaper to rely on cheap throw-away bags (often bought by the govt), low-quality sand or fill from where-ever, volunteer labor to fill them, and good Samaritans to haul the bulk of the mess away after the water recedes. The sand is often just left and swept up by big machinery along with all the deposited mud and other debris they hold back during the flood.
It’s kinda like how you don’t bother sifting through your kid’s vomit to pull out the undigested diced carrots which could go in your compost bin or filter out the water to make tea with; the resource just isn’t valuable enough to spend the money reclaiming.
Generally speaing, they use sandbags in places where they would rather not have a wall most of the time.
I, for one, wouldn’t want to live in a concrete bowl that I have to climb in and out of each time I leave my home. I speak for Cranky Dog when I assure you he would hate it too. Maybe there are some places where a permanent wall makes some sense but there are probably many others where it’s undesirable.
Dumping microplastics into the waterways, no doubt.
I did major sandbagging back in the mid 1980’s when Lake Michigan was trying to eat my parent’s (now my) house. Backbreaking work, and frankly the lake, when rough, just tore them apart. They were ineffective against storm surges when the lake was high. We abandoned their use and focused on seawalls made from pilings, timbers, large rocks and soil stabilizers. THAT worked, then got buried in the drifting dunes when the lake went down.
The lake has been up and down a number of times since then (high again most recently in 2020) and I have seen absolutely no traces of the old sandbags since the early 90’s. Back then they were seen only in fragments, rapidly decaying further.
or, maybe you have
Not with my presbyopia I haven’t. 
Sure, but isn’t that a shortage of construction/industrial type sands?
I guess it depends on what sort of sand you put in the bags. I’ve seen everything from what was basically sandy soil to stuff that was almost small gravel put in bags, but I couldn’t tell the difference between sand for mixing concrete and crap from the beach at the swimming hole.
Your homer beats my lowes. Last time I went for bags I was told they didn’t carry them anymore. They carried them four years ago. I went to a local cement supply joint, no prob.
Dan
After the flooding we’ve had here over the last few years, many householders in potential flood areas are doing what they can to defend their homes:
A barrier across the doors made by having channels on each side with aluminium slats to slot in.
Valves on drains to stop sewage from being backwashed into the house.
Moving all electric outlets and distributor boards higher up the walls so they don’t get drowned if water does get in.
Some more rural houses have barriers all around the property with removable gates etc.
A shopkeeper I know whose premises are right on a river bank has tiled the entire ground floor with swimming pool tiles and adhesive. When they get a flood warning, they move all the stock upstairs or onto staging.
Sandbags are good for the unexpected. The predictable is worthwhile planning for.
You just gave me an idea for a post apocalyptic short story