Regulated Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 58

FIGURE 3.15 Levee on the Mississippi River. (From U.S. Army Corps of Engineers photograph by Lisa
Coghlan, USACE HQ Photostream.)

TABLE 3.1
Classiication of Levees According to Use

Type Deinition

Mainline and tributary levees Levees that lie along a mainstream and its tributaries, respectively.

Ring levees Levees that completely encircle or “ring” an area subject to inundation from all directions.

Setback levees Levees that are built landward of existing levees, usually because the existing levees have

suffered distress or are in some way being endangered, as by river migration.

Sublevees Levees built for the purpose of underseepage control. Sublevees encircle areas behind the

main levee, which are subject, during high-water stages, to high uplift pressures and
possibly the development of sand boils. They normally tie into the main levee, thus
providing a basin that can be looded during high-water stages, thereby counterbalancing
excess head beneath the top stratum within the basin. Sublevees are rarely employed as
the use of relief wells or seepage berms makes them unnecessary except in emergencies.

Spur levees Levees that project from the main levee and serve to protect the main levee from the

erosive action of stream currents. Spur levees are not true levees but training dikes.

Source: USACE, Design and construction of levees, U.S. Army Corps of Engineers, Waterways Experiment Station,
Vicksburg, MS, 2000.

3.2.4.1 So, How Many Are There?
Who knows? Historically, large numbers of levees have been created and maintained by individu-
als and private and governmental organizations and the total number of levees is largely unknown.
However, following and, in part, motivated by the levee failures resulting from Hurricane Katrina in
2005, a levee safety program was established by the National Levee Safety Program Act of 2007 to:

• Inspect each levee in the United States constructed or maintained by the secretary of the

army or identiied by a state governor, excluding levees whose failure would not pose a
signiicant threat to human life or property

• Notify the governor of the state in which a levee is located of inspection results, hazardous

conditions found, and necessary remedial measures