We were standing on the levee of the Mississippi River, about an hour west of Boston. Of course, the actual Mississippi River is a half-continent away. We were in fact in a vast, warehouse-size laboratory above a scale model of a bend in the river in Louisiana, painstakingly recreated at 1/65th scale, right down to the simulated sand. The model is one of the most striking parts of an ambitious project to rebuild Louisiana’s vanishing coast , which is rapidly being lost to rising seas and sinking land. Engineers want to be sure their design for a river “diversion” — an enormous mechanism for restoring eroded wetlands — will work. A diversion is a set of gates in a river levee that can be opened and closed. The escaping river water is supposed to sweep sand, sediment and clay into nearby wetlands being annihilated by climate […]