These are visionary proposals for coastal defense, storm-surge protection, and water management on a civilizational scale — barrier islands, tidal gates, subterranean surge vaults, and continental water grids. The cost figures and agency names come from the proposals themselves; our job is to pair each big idea with an honest engineering verdict grounded in what's actually been built before.
Every project below is scored against real precedents: the Dutch Delta Works ($13B in today's dollars), the Thames Barrier, Tokyo's underground flood tunnels, and the limits of modern tunnel-boring machines. Some of these are engineering moonshots. Some are closer than you'd think. All of them ask the same question: what would it cost to stop retreating from the sea — and start engineering for it?
Cost figures are the proposals' own estimates, not ours — treat them as opening bids, not appraisals. Feasibility judgments reference real built precedents wherever they exist. Read what's slowing real projects down →