In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.
Failing levees, sinking ground, rising sea level, development on drained marsh areas, saltwater intrusion—must be New Orleans, right? Unfortunately, New Orleans is not the only part of the United States that fits this bill. The Sacramento-San Joaquin Delta is a source of drinking water for about two out of every three Californians, and has been an agricultural hub ever since settlers moving West following the Gold Rush drained the wetlands and threw up dikes. More than a thousand miles (1,600 kilometers) of levees protect 700,000 acres (280,000 hectares) of land, and some areas have dropped as much as 15 to 20 feet (five to six meters) below sea level due to the natural oxidation of marsh soils after they are drained. The levees have failed 162 times in their history, and there was a major break in 2004. To compound this serious situation, the population behind the levees is rising as developers build more and more homes in the low-lying floodplains. Where New Orleans' flood defenses are at the mercy of hurricanes, the doomsday scenario for the Sacramento-San Joaquin Delta is an earthquake that could cause serious breaches in the levee system, allowing seawater to flood homes and farmland and foul freshwater supplies.