May/June 2021 - 92

congressional response and resulted in
the Flood Control Acts of 1928 and 1936.
These act s es tabl i shed federal
responsibility for the design and
construction of flood structures such as
levees and dams that were typically
constructed by USACE. They also
prompted construction of thousands of
miles of levees, many built to withstand
the standard project flood, the largest
reasonable flood that could be expected
(usually considered a 500- to 1,000-year
frequency flood). As the science and
engineering understanding of soil
mechanics, hydraulics and hydrology
began to rapidly evolve in the late 1930s
and early 1940s, USACE developed
l evee des i gn and cons t ruc t i on
standards that were almost always
based on local or regional experiences.
In 1978, the agency published its
first levee design and construction
standards: Design and Construction of
Levees (Engineer Manual (EM) 1110 21913);
they were primarily based on the
established levee standards for the
Mississippi River and its tributaries.
This EM was revised in 2000 to include
updates to the typical levee cross
section, relief well design, emergency
flood protection, the use of soil cement
for levee erosion protection, and to
reflect engineer ing and design
standards for levees beyond the
Mississippi River Valley. Added
revisions are occurring to incorporate
advances in analyses and risk-informed
design procedures. Although many
other entities use USACE's standards,
there is no national standard or
guidance for levee design, construction,
or operation and maintenance.
Levee Reviews
Communities in all 50 states, the
District of Columbia, and the territories
of Guam and Puerto Rico have levee
systems they depend on to manage the
risk of flooding. In support of this, the
National Levee Safety Act was passed in
2007 (and amended by the Water
Resources Reform & Development Act
(WRRDA) 2014 and WRDA 2016). As a
92 * DEEP FOUNDATIONS * MAY/JUNE 2021
Levees in the contiguous United States in USACE portfolio
result, USACE was authorized to
conduct a one-time inspection and risk
assessment of all national levees.
Moreover, the agency published a Levee
Portfolio Report in March 2018 that
provided a comprehensive summary
evaluation of the risks associated with
its levee portfolio.
There are approximately 150,000
miles of levees nationally. The USACE
levee portfolio includes about 2,220
levee systems, totaling approximately
15,000 miles in length. Levee sponsors
operate and maintain over 2,000 of
these levee systems, spanning roughly
70% of the length contained in the
entire USACE levee portfolio. More
information is available in the National
Levee Database (NLD) of USACE, which
is at http://nld.usace.army.mil.
The condition of the remaining
120,000 miles of levees is generally
unknown. However, USACE is working
to create a comprehensive understanding
of flood risks posed by the
nation's levees. To do so, the agency is
working with other federal agencies,
states, tribes, regional districts, and
levee owner and operator entities who
are interested in applying USACE
inspection and screening-level risk
assessment methodologies to their
levees. This effort was piloted in 2017,
with collected information being added
to the NLD. Currently, more than 6,000
levee systems outside the USACE levee
portfolio have been inventoried in the
NLD, but have not yet been inspected or
assessed. These 6,000 systems total
15,000 miles.
USACE Offerings
The depth of NLD content makes it an
important resource for sharing levee
information with states, tribes, regional
levee districts and other federal agencies.
As a publicly available source of
levee information, the NLD also promotes
public awareness of the benefits
and flood risks associated with levees.
USACE also has a Levee Safety
Program that is primarily executed
through USACE's 38 Civil Works
Districts and 8 Divisions. As part of the
program, USACE has developed a
scalable risk-assessment methodology
for levees to facilitate risk-informed
decision making, which is central to the
assessment, management and communication
of levee-related flood risks.
In addition, USACE has conducted a risk
assessment of the majority of levees in
http://nld.usace.army.mil
May/June 2021

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