Centuries ago, estuaries around the world were teeming with birds and turbulent with schools of fish, their marshlands and endless tracts of channels melting into the gray-blue horizon.
Fast-forward to today, and in estuaries such as New York Harbor, San Francisco Bay and Miami’s Biscayne Bay – areas where rivers meet the sea – 80% to 90% of this habitat has been built over.
The result has been the environmental collapse of estuary habitats and the loss of buffer zones that helped protect cities from storm surge and sea-level rise. But the damage isn’t just what’s visible on land.
Below the surface of many of the remaining waterways, another form of urbanization has been slowly increasing the vulnerability of coastlines to extreme storms and sea-level rise: Vast dredging and engineering projects have more than doubled the depths of shipping channels since the 19th century.
Some of these oceanic highways enable huge container ships, with drafts of 50 feet below the waterline and lengths of nearly a quarter mile, to glide into forme