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its portfolio and anticipates completing
risk assessments for them all within
several years.
Millions of people live or work
behind levees of the USACE portfolio,
and over $1.5 trillion in property values
exist in what are called leveed areas
(which represent the portion of the
floodplain where floodwaters are
excluded by a levee). Managing this
por t fol io of levees requi res an
understanding of flood risks. USACE
utilizes a risk-management approach to
understand and manage these risks as
well to communicate levee-related
flood risks to stakeholders and the
general population living behind levees.
To further these goals, the agency has
been working since 2006 to establish a
comprehensive inventory, inspection
and risk assessment of all levees within
its portfolio. The inventory and initial
inspections are complete, and initial
risk assessments on the entire portfolio
are expected to be completed over the
next several years. These efforts will
provide a more complete picture of the
physical condition and the associated
flood risks of the USACE levee portfolio,
representing about 10% of the total
levee miles nationally.
Levees at Work
In addition to property, population and
economic activity, levees reduce
flooding risk to some of our most vital
infrastructure. From roads, schools,
police and fire stations to historical
sites and national treasures, there are
countless structures located behind
levees that provide invaluable services
to our communities and nation. These
structures help sustain our economy
and provide venues for recreation,
among other functions. For example,
there are almost 4,500 schools located
behind levees that collectively enroll
over 2 million students. In addition,
over 25% of the nation's oil-refining
capacity is located behind levees.
Damage to, or failure of, these levees
could significantly impact local,
regional and national resources.
One levee system may include
multiple levee segments operated and
maintained by different entities.
However, because levees operate as a
system, the USACE Levee Safety
Program assesses, manages and
communicates with levee sponsors and
the public based on levee systems
rather than segments. Managing risk
associated with one levee system with
multiple entities or communities that
may have differing responsibilities,
resources and perspectives is a
challenge USACE and communities
face together.
Safety Challenges
No levee is flood proof. Levees reduce the
risk of flooding, but no levee system can
eliminate all flood risk. A levee is
generally designed to exclude floodwater
from the leveed area over a
limited range of flood events. If a larger
flood occurs, floodwaters will flow over
the levee. Overtopping occurs when
floodwaters exceed the height of a levee
and flow over its crown. Floodwaters can
also breach or damage levees. A breach
(levee rupture, break or gap) may occur
gradually or suddenly. The most dangerous
breaches happen quickly during
periods of high water. The resulting torrent
of floodwaters can quickly inundate
a large area behind the breached levee
with little or no warning. When a levee
is overtopped, it sometimes erodes the
levee, worsening the flooding and
potentially causing a breach.
Counties with all the nation's levees (source, ASCE/FEMA)
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May/June 2021

Table of Contents for the Digital Edition of May/June 2021
