By building those islands, China has created a lot of environmental devastation on many levels. Dubai has done the same thing. Here in the US the Army Corps of Engineers used to direct dredging projects on our coastlines. It's a losing battle, so they don't do it anymore. On the East coast in particular you still have a barrier/intracoastal waterway, but it's disappearing.
So that's why we don't do it. Aside from environmental cost, the monetary costs are very high. I'd rather see tax money go to schools and healthcare than to trying to save coastlines which can't be saved. Quixotic is the word that comes to mind.
I live in Norfolk, Virginia very close to a number of beaches. Back in the 1980s or early 1990s, I remember going to one of the beaches on a nature preserve with my grandmother. They had all these big grey bags (possibly giant sand bags, I don't really know what was in them) out maybe 15-20 feet from the shoreline. I guess the distance really depended on the tide. The purpose of the sandbags was to build a barrier to supposedly help catch the sand as the waves pushed it in and keep the sand from being washed back out to sea. I don't know for sure, but they likely were filling the sand in from dredging as well. I was an older teenager at the time so I didn't pay too much attention to the details. I remember wading out to one of these giant grey bags and sitting on it.
With sea level rise going on, I think the big issue now would not be keeping the sand from washing away at beaches so much as it would be building up populated areas to match that rise. To do so, you're looking at not just the surface area to build up but total volume of length, width, and depth. You want to do this with dirt and not sand that can support housing and roads among other things. Imagine how much dirt you'd need to build just one city block up by let's say a very conservative 6 feet to account for the most immediate sea level rise. That's a lot of dirt for just one block. Then add all the other low lying blocks in a city or town, then all the areas that will be low lying after the seas rise. That's a lot of dirt, and you'd still likely need something structural (whether natural like rocks or human made like sandbags, concrete, or even steel beams) to keep it from washing away. Where do you get the dirt? Do you basically strip mine from somewhere else and transport it in? Do you transport in trains, big trucks, or something else and what further toll does the mode of transport leave on the environment?
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The city of Norfolk where I live has constant problems with flooding. All it takes is a good rain or an extra high tide to cover the roads in many places. I've often wondered why they can't just raise the roads a little bit, but also figure this would be a huge undertaking. The other problem is that we are so close to sea level that drainage is a problem. When we get high tides with heavy rains, the water has nowhere lower to drain.
I suspect there are lower cost alternatives with lower environmental impact than trying to build up areas to match sea level rise. A number of these are probably temporary solutions that would help in the short term. Some places have levees to keep water out of low lying areas, some houses near beaches are built on stilts, and of course there are cities like Venice which rely on boats for transportation and travel, rather than cars and other means. Perhaps floating cities would be another option, but probably a high risk during hurricanes.
@melmystery Ok, in my town, we have a dike road. Built in the 50's (I think) when they built the dam, about six miles away, at Ft. Gibson. I have used it a few times to get around a train stuck on the track. We also have an elevated road going out to the lake for overflow.  Â
@laura-f, apologies, I missed your links. Just wanted to help with a tip, but glad you've already got it covered ?Â