I think, unqualified speculation, transportation cost scales linearly because most economical exploitation past shores is along river/waterway sand, hence explo

I think, unqualified speculation, transportation cost scales linearly because most economical exploitation past shores is along river/waterway sand, hence exploitation will be not be squared. Squaring coverage territory, as in getting sand from land introduces land shipping, which is even less efficient because cost per distance is subject to geography. Unless, engineered sand comes from coastal infra that takes regional inputs and pipes it strait onto barges, which also makes sense. But wild speculation on my part.