Levee Safety and Risk: Status and Considerations
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December 7, 2017
Levee Safety and Risk: Status and Considerations
Levees can reduce or exacerbate flood risk. Prior to
nonfederal entities (e.g., municipalities, water utilities,
Hurricane Katrina in 2005, there was little public attention
levee districts) for operation, maintenance, repair, and
to the safety of the nation’s levees. The failure of
rehabilitation. Other federal agencies also have constructed
floodwalls (which were designed and constructed by the
levees for their own missions (e.g., International Boundary
U.S. Army Corps of Engineers, or USACE) and breaching
and Water Commission) or assisted in the construction of
of levees in and around New Orleans contributed to
levees that are now operated by nonfederal entities (e.g.,
significant loss of life and economic damage. The events of
U.S. Department of Agriculture). Since its establishment in
2005 led to the enactment of legislation and ongoing efforts
1968, the National Flood Insurance Program (NFIP) has
to inventory, inspect, and assess U.S. levees. Although
encouraged levee construction, operation, and maintenance;
these efforts have improved understanding of levee safety,
this encouragement results from the elimination of flood
significant data gaps remain for many levees in the United
insurance purchase requirements and reduced premiums for
States, and many measures to correct identified safety
structures that are mapped as removed from the 100-year
concerns remain uncompleted. Recent floods and dam
floodplain due to the levee’s protection. The Federal
safety concerns (e.g., Oroville Dam in California) have
Emergency Management Agency (FEMA) is responsible
increased interest in flood risk among policymakers,
for accrediting levees to appear on NFIP insurance rate
including those concerned about federal disaster response
maps (for more on NFIP, see CRS Report R44593,
and recovery spending. This In Focus covers the evolution
Introduction to the National Flood Insurance Program
of efforts to inventory U.S. levees and assess their risks,
(NFIP), by Diane P. Horn and Jared T. Brown).
and policy considerations for decisionmakers.
There may be as many as 100,000 miles of levees in the
Safety and Risk: Introduction and History United States. Nonfederal or private entities are responsible
Levees (i.e., engineered earthen embankments), engineered
for maintaining most existing levees and often have few if
coastal dunes and berms, and floodwalls (which are
any local or state requirements to satisfy regarding levee
constructed of metal or reinforced concrete) are built to
design and safety. Federal agencies are responsible for
reduce flood losses. Herein these structures are collectively
maintaining their own levees in good condition. USACE
referred to as levees. Risk associated with levees is a
owns and maintains 4,200 miles of levees, and it also
function of the hazard (e.g., level and duration of
regularly inspects 8,200 miles of levees that participate in
floodwaters), the performance of the levee (both prior to
its Rehabilitation and Inspection Program (RIP). If the RIP-
overtopping and after being overtopped), and the potential
participating nonfederal levee owner has maintained the
consequences (i.e., what is exposed to loss, damage, and
levee in good condition, USACE uses RIP to repair levees
disruption). Some risk, referred to as residual risk, remains
damaged from a flood or other natural event at a federal
behind a levee. Larger flood events can overwhelm levees;
cost share of 80% to 100%.
also, levees that are poorly designed, constructed, or
maintained can fail. Figure 1 illustrates the components of
Levee Safety and Risk: 2005 to Present
levee risk and some levee performance concerns.
In 2005, when Hurricane Katrina focused public attention
on levee safety, there was no effort for levees equivalent to
Many of the nation’s early levees were privately
the National Inventory on Dams or the National Dam
constructed to protect agricultural lands and rural
Safety Program. (See CRS In Focus IF10606, Dam Safety:
communities. As early as 1917 and regularly thereafter,
Federal Programs and Authorities, by Charles V. Stern et
Congress authorized and funded USACE to construct
al.) Through P.L. 110-114, in 2007 Congress charged the
numerous flood control projects that included levees; the
USACE with developing a National Levee Database
agency continues to own, operate, and maintain some early
(NLD). The NLD is a partial inventory of U.S. levees; it
USACE-constructed levees. Since the late 1980s, USACE-
currently covers 29,000 miles of levees (see Figure 2).
built levees are cost-shared 65% federal and 35%
Nonfederal levee data are provided voluntarily.
nonfederal during construction, and then transferred to
Figure 1. Illustration of Levee Risk Components and Levee Performance Concerns
Source: CRS, adapted from Zina Deretsky, National Science Foundation, and USACE, Risk Assessment for Flood Risk Management Studies, 2017.
https://crsreports.congress.gov
Levee Safety and Risk: Status and Considerations
subsequent appropriations cycles. USACE is attempting to
Figure 2. Levees in National Levee Database in 2017
complete by 2018, at a minimum, a one-time inspection and
risk screening for all NLD levees; this effort may facilitate
state levee safety efforts. States working with USACE on
the NLD include California, Illinois, Ohio, Pennsylvania,
and Texas.
Federal agencies continue working to advance levee safety
efforts. These activities include clarifying guidelines and
developing manuals (e.g., funding a 2015 Guide to Public
Alerts and Warning for Dam and Levee Emergencies for
emergency managers) and participating in outreach and
technical assistance efforts (e.g., the interagency Silver
Source: National Levee Database.
Jackets program to assist with state flood-risk reduction
Notes: Levees in red are USACE-owned levees and Rehabilitation
priorities). Direction in WRRDA 2014 and other legislation
and Inspection Program levees; other levees are shown in purple.
(e.g., P.L. 112-141, §100226) led to efforts by FEMA and
USACE to better coordinate their data sharing on levees
No federal agency is broadly responsible for levee safety,
and levee inspections to assist with FEMA levee
although various agencies participate in aspects of levee
accreditation. Congressional direction also led to FEMA
safety. Ultimately, levee owners are responsible for
altering how levees appear on NFIP insurance rate maps.
maintaining their levees. There also is no broadly
Levees that provide lower levels of protection (e.g., the
levee’s level of protection
applicable national standard or requirement for levee
does not remove the area behind
construction or maintenance. Federal agencies are working
it from the 100-year floodplain) may now be mapped.
toward consistent federal levee guidelines for their use as
Proposals to require that the insurance maps identify
an intermediary step toward the voluntary national levee
residual risk behind levees have not been enacted.
safety guidelines called for in Section 3016 of the Water
Resources Reform and Development Act of 2014 (WRRDA
WRRDA 2014 called for USACE to report biennially on
the nation’s levees
2014; P.L. 113-121). USACE also has developed the Levee
; USACE is preparing a report focused
Safety Action Classification system to characterize a
on USACE-owned and RIP levees. WRRDA 2014 also
levee’s risk and is working to incorporate “tolerable risk
called for a report on levee liability issues; no information
guidelines” into risk screening. These tools help identify
is available on the report’s status. After Hurricane Katrina,
levees of particular concern, such as those that protect
levee liability concerns contributed to various interests
concentrated populations or those that protect smaller
being wary of involvement in design, construction, and
concentrations of people but are in particularly poor
inspection of levees and other flood-control projects.
condition. Although identifying levee risk has improved, a
Policy Considerations
clear path to act on risk assessments for federal and
nonfederal levees has not emerged, nor has there developed
Numerous postdisaster proposals for the construction of
a consistent policy for the federal role in investments to
new levees and floodwalls are being advanced as part of
improve levee safety for various types of nonfederal levees.
disaster recovery efforts in 2017. In addition to funding
Instead, as described in CRS Report R45017, Flood-Risk
considerations, the responses of the 115th Congress and
Reduction and Resilience: Federal Assistance and
other decisionmakers to recent floods and hurricanes may
Programs, by Nicole T. Carter et al., levee-related
be informed by many factors, as well as interest in
improvements may be eligible to be selected or to compete
rebuilding and long-term flood resilience. For example,
for differing types of assistance under various federal
levee safety efforts since 2005 have improved
programs. Also, some states have flood-control or
understanding of residual risk behind levees and identified
infrastructure-assistance programs that may provide some
safety issues at existing levees. Much of the analysis of
financial support. No authoritative estimate of the total
U.S. levee risk to date has been based on hydrologic data
costs to improve U.S. levee safety exists. USACE is
that have not been updated recently. Research efforts are
developing cost estimates to address safety issues for
under way to not only improve these data but also better
USACE-owned and RIP levees.
understand extreme flood hazards. There also is information
on the impact that levee design and construction have on
Unlike state dam safety programs, which operate at some
riverine and coastal ecology, challenges experienced with
level in every state except Alabama, there is little indication
managing land use behind levees, and efforts to use and
that the majority of states have levee inventories or have
protect natural or distributed flood retention in watersheds.
attempted to advance their levee safety oversight efforts in
A question for policymakers is whether—and if so, how—
recent years. Congress in Section 3016 of WRRDA 2014
to integrate new and existing levees into more
authorized a national levee safety initiative (NLSI); as part
comprehensive water and flood-risk management systems.
of the NLSI, Congress authorized FEMA to support the
establishment or improvement of state and tribal levee
Nicole T. Carter, Specialist in Natural Resources Policy
safety programs. This initiative has remained unfunded in
IF10788
https://crsreports.congress.gov
Levee Safety and Risk: Status and Considerations
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10788 · VERSION 3 · NEW
December 7, 2017
Levee Safety and Risk: Status and Considerations
Levees can reduce or exacerbate flood risk. Prior to
nonfederal entities (e.g., municipalities, water utilities,
Hurricane Katrina in 2005, there was little public attention
levee districts) for operation, maintenance, repair, and
to the safety of the nation’s levees. The failure of
rehabilitation. Other federal agencies also have constructed
floodwalls (which were designed and constructed by the
levees for their own missions (e.g., International Boundary
U.S. Army Corps of Engineers, or USACE) and breaching
and Water Commission) or assisted in the construction of
of levees in and around New Orleans contributed to
levees that are now operated by nonfederal entities (e.g.,
significant loss of life and economic damage. The events of
U.S. Department of Agriculture). Since its establishment in
2005 led to the enactment of legislation and ongoing efforts
1968, the National Flood Insurance Program (NFIP) has
to inventory, inspect, and assess U.S. levees. Although
encouraged levee construction, operation, and maintenance;
these efforts have improved understanding of levee safety,
this encouragement results from the elimination of flood
significant data gaps remain for many levees in the United
insurance purchase requirements and reduced premiums for
States, and many measures to correct identified safety
structures that are mapped as removed from the 100-year
concerns remain uncompleted. Recent floods and dam
floodplain due to the levee’s protection. The Federal
safety concerns (e.g., Oroville Dam in California) have
Emergency Management Agency (FEMA) is responsible
increased interest in flood risk among policymakers,
for accrediting levees to appear on NFIP insurance rate
including those concerned about federal disaster response
maps (for more on NFIP, see CRS Report R44593,
and recovery spending. This In Focus covers the evolution
Introduction to the National Flood Insurance Program
of efforts to inventory U.S. levees and assess their risks,
(NFIP), by Diane P. Horn and Jared T. Brown).
and policy considerations for decisionmakers.
There may be as many as 100,000 miles of levees in the
Safety and Risk: Introduction and History United States. Nonfederal or private entities are responsible
Levees (i.e., engineered earthen embankments), engineered
for maintaining most existing levees and often have few if
coastal dunes and berms, and floodwalls (which are
any local or state requirements to satisfy regarding levee
constructed of metal or reinforced concrete) are built to
design and safety. Federal agencies are responsible for
reduce flood losses. Herein these structures are collectively
maintaining their own levees in good condition. USACE
referred to as levees. Risk associated with levees is a
owns and maintains 4,200 miles of levees, and it also
function of the hazard (e.g., level and duration of
regularly inspects 8,200 miles of levees that participate in
floodwaters), the performance of the levee (both prior to
its Rehabilitation and Inspection Program (RIP). If the RIP-
overtopping and after being overtopped), and the potential
participating nonfederal levee owner has maintained the
consequences (i.e., what is exposed to loss, damage, and
levee in good condition, USACE uses RIP to repair levees
disruption). Some risk, referred to as residual risk, remains
damaged from a flood or other natural event at a federal
behind a levee. Larger flood events can overwhelm levees;
cost share of 80% to 100%.
also, levees that are poorly designed, constructed, or
maintained can fail. Figure 1 illustrates the components of
Levee Safety and Risk: 2005 to Present
levee risk and some levee performance concerns.
In 2005, when Hurricane Katrina focused public attention
on levee safety, there was no effort for levees equivalent to
Many of the nation’s early levees were privately
the National Inventory on Dams or the National Dam
constructed to protect agricultural lands and rural
Safety Program. (See CRS In Focus IF10606, Dam Safety:
communities. As early as 1917 and regularly thereafter,
Federal Programs and Authorities, by Charles V. Stern et
Congress authorized and funded USACE to construct
al.) Through P.L. 110-114, in 2007 Congress charged the
numerous flood control projects that included levees; the
USACE with developing a National Levee Database
agency continues to own, operate, and maintain some early
(NLD). The NLD is a partial inventory of U.S. levees; it
USACE-constructed levees. Since the late 1980s, USACE-
currently covers 29,000 miles of levees (see Figure 2).
built levees are cost-shared 65% federal and 35%
Nonfederal levee data are provided voluntarily.
nonfederal during construction, and then transferred to
Figure 1. Illustration of Levee Risk Components and Levee Performance Concerns
Source: CRS, adapted from Zina Deretsky, National Science Foundation, and USACE, Risk Assessment for Flood Risk Management Studies, 2017.
https://crsreports.congress.gov
Levee Safety and Risk: Status and Considerations
subsequent appropriations cycles. USACE is attempting to
Figure 2. Levees in National Levee Database in 2017
complete by 2018, at a minimum, a one-time inspection and
risk screening for all NLD levees; this effort may facilitate
state levee safety efforts. States working with USACE on
the NLD include California, Illinois, Ohio, Pennsylvania,
and Texas.
Federal agencies continue working to advance levee safety
efforts. These activities include clarifying guidelines and
developing manuals (e.g., funding a 2015 Guide to Public
Alerts and Warning for Dam and Levee Emergencies for
emergency managers) and participating in outreach and
technical assistance efforts (e.g., the interagency Silver
Source: National Levee Database.
Jackets program to assist with state flood-risk reduction
Notes: Levees in red are USACE-owned levees and Rehabilitation
priorities). Direction in WRRDA 2014 and other legislation
and Inspection Program levees; other levees are shown in purple.
(e.g., P.L. 112-141, §100226) led to efforts by FEMA and
USACE to better coordinate their data sharing on levees
No federal agency is broadly responsible for levee safety,
and levee inspections to assist with FEMA levee
although various agencies participate in aspects of levee
accreditation. Congressional direction also led to FEMA
safety. Ultimately, levee owners are responsible for
altering how levees appear on NFIP insurance rate maps.
maintaining their levees. There also is no broadly
Levees that provide lower levels of protection (e.g., the
levee’s level of protection
applicable national standard or requirement for levee
does not remove the area behind
construction or maintenance. Federal agencies are working
it from the 100-year floodplain) may now be mapped.
toward consistent federal levee guidelines for their use as
Proposals to require that the insurance maps identify
an intermediary step toward the voluntary national levee
residual risk behind levees have not been enacted.
safety guidelines called for in Section 3016 of the Water
Resources Reform and Development Act of 2014 (WRRDA
WRRDA 2014 called for USACE to report biennially on
the nation’s levees
2014; P.L. 113-121). USACE also has developed the Levee
; USACE is preparing a report focused
Safety Action Classification system to characterize a
on USACE-owned and RIP levees. WRRDA 2014 also
levee’s risk and is working to incorporate “tolerable risk
called for a report on levee liability issues; no information
guidelines” into risk screening. These tools help identify
is available on the report’s status. After Hurricane Katrina,
levees of particular concern, such as those that protect
levee liability concerns contributed to various interests
concentrated populations or those that protect smaller
being wary of involvement in design, construction, and
concentrations of people but are in particularly poor
inspection of levees and other flood-control projects.
condition. Although identifying levee risk has improved, a
Policy Considerations
clear path to act on risk assessments for federal and
nonfederal levees has not emerged, nor has there developed
Numerous postdisaster proposals for the construction of
a consistent policy for the federal role in investments to
new levees and floodwalls are being advanced as part of
improve levee safety for various types of nonfederal levees.
disaster recovery efforts in 2017. In addition to funding
Instead, as described in CRS Report R45017, Flood-Risk
considerations, the responses of the 115th Congress and
Reduction and Resilience: Federal Assistance and
other decisionmakers to recent floods and hurricanes may
Programs, by Nicole T. Carter et al., levee-related
be informed by many factors, as well as interest in
improvements may be eligible to be selected or to compete
rebuilding and long-term flood resilience. For example,
for differing types of assistance under various federal
levee safety efforts since 2005 have improved
programs. Also, some states have flood-control or
understanding of residual risk behind levees and identified
infrastructure-assistance programs that may provide some
safety issues at existing levees. Much of the analysis of
financial support. No authoritative estimate of the total
U.S. levee risk to date has been based on hydrologic data
costs to improve U.S. levee safety exists. USACE is
that have not been updated recently. Research efforts are
developing cost estimates to address safety issues for
under way to not only improve these data but also better
USACE-owned and RIP levees.
understand extreme flood hazards. There also is information
on the impact that levee design and construction have on
Unlike state dam safety programs, which operate at some
riverine and coastal ecology, challenges experienced with
level in every state except Alabama, there is little indication
managing land use behind levees, and efforts to use and
that the majority of states have levee inventories or have
protect natural or distributed flood retention in watersheds.
attempted to advance their levee safety oversight efforts in
A question for policymakers is whether—and if so, how—
recent years. Congress in Section 3016 of WRRDA 2014
to integrate new and existing levees into more
authorized a national levee safety initiative (NLSI); as part
comprehensive water and flood-risk management systems.
of the NLSI, Congress authorized FEMA to support the
establishment or improvement of state and tribal levee
Nicole T. Carter, Specialist in Natural Resources Policy
safety programs. This initiative has remained unfunded in
IF10788
https://crsreports.congress.gov
Levee Safety and Risk: Status and Considerations
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10788 · VERSION 3 · NEW