Walking along the Battery in the first soup of summer heat, John Boulé, engineer, points to Castle Clinton, in the park, built to defend New York Harbor against a British invasion in 1812. “That used to be out in the water,” he said.

He nods at the ground. “Where we are standing was water,” he said.

Mr. Boulé is now one of the people with the job of figuring out how to keep it, and the rest of what is now dry New York City, from returning to water.

A former commander of the Army Corps of Engineers for the New York district, Mr. Boulé went to work for the engineering firm of Parsons Brinckerhoff last fall.

His first day of work was Oct. 29, the day Hurricane Sandy hit.

The last time anyone tried to figure out what such a storm would mean for the whole city was never.