Knowra Levee Levee A levee is a raised embankment built along a river or coast to contain water and reduce flooding. It may be natural or engineered, and can fail when water overtops or breaches it.
River levee : An embankment built beside a river to keep floodwater within its channel or a designated floodway. This is the standard levee form, shaped by river floods and channel conditions.
Flood control : Measures intended to reduce the frequency or severity of flooding and its damage. Levees are one structural method of reducing flood exposure.
New Orleans levee system : A network of levees, floodwalls, gates, and pumps protecting New Orleans from surrounding waters. Hurricane Katrina exposed failures across this complex urban protection system.
Levee effect : The tendency for flood defenses to encourage development behind them, increasing losses when protection fails or is exceeded. Confidence in levees can concentrate people and property in areas that remain exposed to floods.
Overtopping : Water flowing over the crest of a dam, levee, or other barrier. Floodwater can exceed a levee’s crest and erode its landward slope.
Floodplain : Relatively flat land beside a river that is periodically inundated by floods. Levees separate developed land from the floodplain while often restricting its natural inundation.
Hurricane Katrina : A powerful Atlantic hurricane that struck the Gulf Coast of the United States in August 2005. Its storm surge and levee failures caused catastrophic flooding in New Orleans.
Residual risk : The risk that remains after protective measures have reduced, but not eliminated, a hazard. Even well-maintained levees can be overtopped, breached, or overwhelmed by exceptional floods.
Internal erosion : The movement of soil particles through or beneath an embankment under seepage forces. Seepage can carry levee soil away and develop into a breach.
Levee setback : The relocation of a levee farther from a river to create more space for floodwater. Setbacks give rivers room while retaining protection for land behind the new alignment.
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