Coastal cities move flood defences from blueprint to concrete

Construction crews began lowering the first caissons into place this week, marking the moment a long-debated flood plan stopped being a document and started being infrastructure.

The barrier is designed around a simple, uncomfortable assumption: the water is coming up, and the schedule is not negotiable. Engineers sized the gates for a one-metre rise by the end of the century, with foundations deep enough to be raised again if the estimate proves optimistic.

"You build the thing you can afford now in a way that your grandchildren can extend," said the project's chief engineer during a tour of the site. "That is the whole philosophy."

Costs have roughly doubled since the original estimate, a pattern familiar to anyone who follows large civil works. Port officials argue the comparison that matters is not the budget but a single bad storm, which independent assessors put at several times the construction cost in direct damage alone.

Residents in the low-lying districts behind the barrier have watched the debate for years with a mix of relief and suspicion. Relief that something is finally being built. Suspicion that the protection stops exactly where the property values do.