In posts we've run about managing Montauk beach reconstruction, two commenters have mentioned the Sand Engine project in the Netherlands. In South Holland, a 1 km² hook-shaped peninsula has been built of sand. (1 km is .62 of a mile.) It extends 1 km into the sea and is 2 km wide at the shoreline. The expectation is that the sand will then nourish the shoreline via littoral drift. This does look interesting, but we haven't the faintest idea whether it would be feasible for Montauk. The geography could be wildly different underwater, it could be environmentally unwise in Montauk, and so on. Of course, the Dutch have been engineering dykes and canals and managing floods since medieval times, because much of the country is under sea level. Perhaps we can learn from them.
· Sand Motor [Official site]
· Sand Engine [Wikipedia]