Our Very Strange Search for “Sea Level”

Old River Control Auxiliary Structure

The boiling point of water is straightforward, but the boiling point of societies is mysterious.

For one of the essential characteristics of land is that it is higher than water. Gravity causes water to flow down to the lowest point, which should cause the continents to dry out.

Much of Plaquemines lies below sea level—six feet under, people sometimes say. This arrangement is made possible by levees—four sets of them. Two run along the river, one on each bank. Another two—known as “back levees”—run between the parish and the Gulf, to prevent the sea from rolling in. The levees, which keep water out, also keep water in. Whe