You regularly see news stories and videos about beach houses that fall into the ocean due to storm surges and/or beach erosion. The ocean basically encroaches on the property and there your investment goes.
What happens if you’ve built a very sturdy house so that the pilings and house survive the surf? (It’s obviously possible to do this if you have the money, the time, and the desire.) If your house is 200’ below the tide line, do your existing property boundaries (legally) survive? Do you own part of the ocean? Is your house considered salvage and can be claimed be someone? Mind you, I’m talking about a house on pilings that is above water level and in reasonably good shape even after the beach has been eroded away.
If the Army Corps of Engineers doesn’t already have a federally funded shore renewal program for the area, it is up to the homeowner to maintain a connection to dry land, unless they are content to live on a man made island. Both options are likely prohibitively expensive and all but the financially incompetent would abandon the property and allow it to be demolished by unencumbered surf and storms. The pilings might survive a while but most houses won’t.
I have heard stories of homeowners who wrote off their property only to receive a property tax bill years later after the local shoreline was replenished.
It will depend on the land law in different jurisdictions. More commonly the law provides for the shifting course of rivers that form lot boundaries - which might add to or subtract from the land you bought in the future. Its all in the fine print.
If you now find yourself the proud owner of a piece of inter-tidal zone, a wetland margin or a shipping channel, you suddenly become obligated to observe and comply with all of the navigation, building, environmental, health and safety laws that now apply, and I expect there would be many. Toilet now discharges into the sea? $100,000 to engineer a robust line taking your waste back to land, or fine for every day it is not fixed. Your house on stilts does not meet tidal surge standards like a commercial wharf? $2M to fix that. Crap blown off your deck during a storm - fines for creating navigation hazards. And so on.
I recall several examples of beach renewal, adding a lot more sand, that simply vanished with the next serious storm surge or two. I suppose it’s a losing battle.
Based on my experience standing on a beach as each wave goes out, I suspect the pilings will simply channel the surges to dig themselves out faster than the beach around them. Blocking water flow produces faster flows around the edges.