Forensic Engineering - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 184

CHAPTER 20
Forensic Engineering
The Deepwater Horizon was trying to tell us something was wrong in the Gulf of
Mexico. And the levees are trying to tell us something is wrong in the Sacramento
Delta—if they go, we're all going to be drinking saltwater coffee.
—Professor Robert Bea,
University of California, Berkeley, 2010
THE TWO KINDS OF LEVEES
In places that flood—Holland, central China, the states along the Mississippi River—man
has developed various ingenious methods to control water. Dams and reservoirs and
canals are built in part, or in some cases primarily, to capture excess runoff. But the most
effective and common flood defense are levees, also called dikes: man-made barriers that
stand between a watercourse and human development.
Levees come in all shapes, widths, heights, and angles of incline. Some are made of
nothing more than sandbags, boards, and sheets of plastic and run just a few yards long.
Others are more elaborate, such as the Sny, a reinforced wall of pilings and concrete
that runs for fifty miles along the banks of the Mississippi. But most levees are berms
made up of dirt, sand, or clay—and all that gets scooped up with that material—that are
dredged and piled up along river edges (such as on the Mississippi) or the coastline (as
in New Orleans), to control and restrain water. In some cases (as in the Sacramento-San
Joaquin Delta of Northern California), levees are used to push water out of estuaries or
wetlands to “reclaim” fertile land for farming or for new building lots. Levees are often
partnered with a network of floodwalls, pumps and pipes, drains, gates, canals, and is-
lands—complex systems of hydraulic control that require diligent maintenance to ensure
their integrity.
Carefully engineered, solidly built levees have protected millions of people from
floods and saved billions of dollars in potential damages. But levees are problematic.
They tend to push water away from one area, which intensifies its impact on other, un-
protected areas. They are often poorly built and are expensive and time-consuming to
maintain. And they are only as strong as their weakest point.