A levee is a human-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water to provide protection from temporary flooding (Interagency Levee Policy Review Committee, 2006). Levee failures or breaches occur when a levee fails to contain the floodwaters for which it is designed to control, or floodwaters exceed the height of the constructed levee.
FEMA completed an inventory of all known levees across Pennsylvania in 2009 with an update in 2012, known as the Mid-Term Levee Inventory (MLI) containing levee data gathered for structures designed to protect from the 1%-annual-chance flood event. A total of 317 levee segments and 63 floodwall segments levees have been identified throughout Pennsylvania via the MLI, with at least one levee in 51 of 67 counties (FEMA Region III, 2013). Particularly extensive levee systems have been built in the Scranton Wilkes-Barre area in Luzerne and Lackawanna Counties; Lycoming County also has a significant amount of levee systems.
In the event of a levee failure, flood waters will ultimately inundate the protected area landward of the levee. There is no comprehensive list of levee failures in Pennsylvania, and historically few, if any, have been reported. However, in 2011, Tropical Storm Lee exceeded the design storm level for many levees in Pennsylvania. The probability of future occurrence can be reduced through proper design, construction, and maintenance measures. The age of the levee can increase the potential for failures if it is not maintained. In Pennsylvania, the average age of the federally-authorized levee systems is nearing 50 years, the typical life-span of a levee. Levee failure is also influenced by the frequency and severity of flood events. Therefore, potential future changes in climate and weather conditions, such as predicted increases in heavy precipitation events, may impact the future occurrences of levee failure.
To view a printable pdf file of the Human-made Hazards Risk Assessment, click here.
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HIRA Ranking: 1.7
THIRA Ranking: 3.1
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Vulnerable State Facilities: 250
Vulnerable Critical Facilities: 402
Vulnerable Population: 269,330
Exposed Building Value: $33,483,028,000