Order Code RL33129
Flood Risk Management:
Federal Role in Infrastructure
Updated January 18, 2007
Nicole T. Carter
Analyst in Environmental Policy
Resources, Science, and Industry Division

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Flood Risk Management: Federal Role in Infrastructure
Summary
Hurricane Katrina enlivened a national debate on managing flood hazards and
raised concerns about flood vulnerability among communities across the nation. In
the United States, local governments are responsible for land use and zoning
decisions that direct floodplain and coastal development; however, state and federal
governments influences community and individual decisions on managing flood risk.
The federal government constructs some of the nation’s flood control infrastructure,
offers flood insurance, and provides disaster aid.
The 110th Congress, like many earlier Congresses, is faced with numerous flood
control issues, including interest in changing federal policies. Current federal
programs and flood control projects generally target reducing property damage and
vulnerability to a 100-year flood. Discussions include whether current flood
protection is sufficient, whether loss of life and economic and social disruption
should be more prominent considerations in federal policy, and what are the
advantages and disadvantages of a more risk-based approach to federal policy,
spending, and infrastructure design.
This report discusses federal flood-related infrastructure investments, such as
levees, floodwalls, and dams. The report also analyzes flood risk as a composite of
flood threat, consequence, and vulnerability. The report illustrates that federal policy
focuses attention on only some aspects of flood risk and summarizes the options
being discussed for addressing other aspects of flood risk in the aftermath of
Hurricane Katrina.

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Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Federal Flood Control Policy and Infrastructure . . . . . . . . . . . . . . . . . . . . . . 2
Federal Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Flood Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Flood Damage Reduction Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . 4
Reducing Vulnerability to the 100-Year Flood:
Minimum Standard Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Reducing Property Damage Vulnerability: Benefit-Cost Analyses . . . . . . . . 5
Reducing Flood Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Flood Management Issues in the 110th Congress . . . . . . . . . . . . . . . . . . . . . . 8

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Flood Risk Management:
Federal Role in Infrastructure
Introduction
In the United States, local governments are responsible for land use and zoning
decisions that direct floodplain and coastal development; however, numerous federal
and state flood policies and programs influence local, and individual decision-
making. The federal government funds construction of some flood control structures,
manages a flood insurance program, and provides disaster assistance;1 and it
generates essential data through mapping and other efforts. This report discusses
investment decisions for flood control infrastructure (such as levees, floodwalls, and
dams), and how federal policies, programs, and practices that focus on reducing
property damage and vulnerability to a 100-year flood influence these decisions.2
The report also describes how Hurricane Katrina enlivened a national debate on
whether the current flood protection is sufficient and whether a more comprehensive
approach to managing flood risk and federal investments is desirable.
Hurricane Katrina demonstrated that not only property damage, but also other
flooding impacts (e.g., loss of life and economic disruption), may be national
concerns. This report analyzes flood risk as a composite of three factors:
! threat of an event (e.g., probability of a Category 5 hurricane storm
surge or a 200-year flood affecting a particular location);
! consequence of an event (e.g., loss of life, economic loss,
environmental damage, reduced health and safety); and
! vulnerability that allows a threat to cause consequences (e.g., level
of protection provided by levees and dams, and their reliability).3
The remainder of this report is divided into five sections. The first is a primer
on federal flood control policy and infrastructure. The next two sections describe
1 For information on the evolution of federal disaster aid, see U.S. Senate Task Force on
Funding Disaster Relief, Federal Disaster Assistance, S.Doc. 104-4 (1995).
2 The term 100-year flood is the flood elevation that has a 1% chance of being equaled or
exceeded annually. It is not the flood that will occur once every 100 years; 100-year floods
can occur more than once in a relatively short period of time.
3 For more information on this three-part hazard risk framework, see CRS Report RL32561,
Risk Management and Critical Infrastructure Protection: Assessing, Integrating, and
Managing Threats, Vulnerabilities, and Consequence, by John Moteff.

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two aspects of federal policies and practices — the 100-year flood standard, and
benefit-cost analyses — that guide infrastructure investment decisions and how these
federal policies and practices focus attention on only some aspects of flood risk. The
fourth section summarizes how addressing other elements of flood risk are being
discussed in the aftermath of Hurricane Katrina. The fifth section concludes the
report by presenting a primer on the range of flood control issues before the 110th
Congress. This report is not a comprehensive treatment of the topics of flood risk
and flood control; rather, it is an introduction to the current debate on flood policy
and focuses primarily on the U.S. Army Corps of Engineers as the principal federal
agency for flood control infrastructure.
Federal Flood Control Policy and Infrastructure
Federal Interest. The federal role in flood control began in the late 19th
century. Prompted by devastating floods in the Mississippi River basin, Congress
created a commission to oversee the development of a levee system to control the
river’s flow. The Mississippi River Flood of 19274 and floods in the mid-1930s,
ushered in a modern era of federal flood control investment. The Flood Control Act
of 1936 (19 Stat. 1570) declared flood control a “proper” federal activity in the
national interest.5 Section 1 of the act established the following policy:
It is hereby recognized that destructive floods upon the rivers of the United
States, upsetting orderly processes and causing loss of life and property,
including the erosion of lands and impairing and obstructing navigation,
highways, railroads, and other channels of commerce between the States,
constitute a menace to national welfare; that it is the sense of Congress that flood
control on navigational waters or their tributaries is a proper activity of the
Federal Government in cooperation with States, their political sub-divisions and
localities thereof; that investigations and improvements of rivers and other
waterways, including watersheds thereof, for flood-control purposes are in the
interest of the general welfare; that the Federal Government should improve or
participate in the improvement of navigable waters or their tributaries including
watersheds thereof, for flood-control purposes if the benefits to whomsoever they
may accrue are in excess of the estimated costs, and if the lives and social
security of people are otherwise adversely affected.
Since the mid 1980s, local project sponsors (often local governments or special
levee and drainage districts) share construction cost of federal flood control projects
and are fully responsible for operation and maintenance. Local entities (and
sometimes state entities) may construct flood control infrastructure independently
4 For more information on the response to the Mississippi River Flood of 1927, see CRS
Report RL33126, Disaster Recovery and Appointment of Recovery Czar: The Executive
Branch’s Response to the Flood of 1927, by Kevin R. Kosar.
5 The Beach Nourishment Act of 1956 (P.L. 84-826) expanded the federal role in
constructing projects for hurricane, storm and shoreline protection, such as seawalls and the
periodic placement of sand on beaches to control erosion. The Flood Control Act of 1950
(64 Stat. 170) began the Corps’ emergency operations by authorizing flood preparedness and
emergency operations.

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from the federal government, and are responsible for land use and zoning decisions
guiding development in floodplains and coastal areas.
Flood Insurance. By the 1950s, it had become clear to Congress that the
federal response to flood risk through structural flood controls and post-disaster
assistance for flood victims left much to be desired. Public works could not protect
all areas, control all floods, and be completely reliable; meanwhile, private
construction continued in flood-prone areas. Furthermore, relief payments were
problematic because they were unpredictable and necessitated bargaining after each
major flood. Pre-disaster funding via insurance began to look like an attractive
alternative to flood control structures or disaster assistance. Flood insurance
coverage was virtually unavailable from the private insurance markets because
insurers could not profitably sell coverage at an affordable price; attempts at private
flood insurance had been hampered by the catastrophic nature of flooding and
insurers’ inability to develop actuarial rates that reflected the flood hazard risk.
Attempts to create a federal flood insurance program eventually came to fruition
with the National Flood Insurance Act of 1968 (NFIP, P.L. 90-448; 42 U.S.C.
§4012), which authorized the creation of the National Flood Insurance Program
(NFIP). Coverage is available to all owners and occupants of insurable property in
a participating community. Managing flood risk through insurance was expected to
greatly reduce the reliance on federal disaster relief assistance because participating
communities were expected to adopt and enforce building and other standards that
could greatly reduce losses from a 100-year flood.
An on-going issue with flood insurance are the accuracy of the maps used
defining “special flood hazard areas” which are the triggers for NFIP’s flood
insurance requirements; for information on this topics, see CRS Report RL33264,
FEMA’s Flood Hazard Map Modernization Initiative, by Wayne A. Morrissey. Over
75% of the Federal Emergency Management Agency’s (FEMA) flood maps are over
10 years old, raising concerns that the hydrologic data behind the maps is obsolete.
Hydrology can change due to land use changes, channel modifications, erosion, and
climate variability. For example, a 2004 analysis by the Corps found that the 100-
year flood elevation at some locations along the Lower Missouri River is 4 feet
higher than shown on previous flood map. As FEMA’s maps are updated to reflect
current conditions, many communities previously thought protected from the 100-
year flood will not find themselves subject to flood insurance requirements.
A related concern is the certification of levees to FEMA for its administration
of the NFIP. FEMA’s policy requires that levees be structurally sound, properly
maintained, and provide 100-year flood protection (including a 3-foot factor of
safety) before FEMA will recognize that the levees provide protection. The Corps
generally performs the inspections for certifying the levees; the Corps’ inspection
program is neither designed or funded to assess the geotechnical conditions of the
levees nor the hydrological conditions they would be subject to; therefore, levee
certification generally does not represent an evaluation of the structural integrity of
existing levees. Performing such analysis requires could represent a significant cost
for most communities and levee districts. The Corps estimate the cost of performing
geotechnical and hydrologic analyses for 1,600 miles of levees in the Central Valley
of California at $100 million, that is, around $60,000 per mile.

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Flood Damage Reduction Infrastructure. The Corps is responsible for
much of the federal investment in flood control and storm protection infrastructure.6
It has constructed nearly 9,000 miles of the nation’s estimated 15,000 miles of levees.
Corps involvement in flood control construction is predicated on the project being
in the national interest, which is determined by the likelihood of widespread and
general benefits, a shortfall in the local ability to solve the water resources problem,
the national savings achieved, and precedent and law.7
Over the last century, many of the communities most prone to flooding have
been protected by significant investments in structural measures to reduce flood
damages. Many of the current questions and concerns revolve around the following
topics:
! whether the level of protection is sufficient if all consequences are
considered (e.g., intensity and spread of urbanization, concentration
of oil processing and distribution infrastructure);
! whether flood threat and vulnerability have changed (e.g., as the
result of increases in ocean temperature, coastal wetlands losses; and
the reliability of aging levees and dams); and
! how sufficient is the hurricane and storm protection for the nation’s
coastal communities.
Reducing Vulnerability to the 100-Year Flood:
Minimum Standard Approach
In the United States, the 1% annual chance flood, more commonly known as the
100-year flood, is a standard often used as a basis for identifying, mapping, and
managing flood hazards. For example, the NFIP and most state and local
governments use location in the 100-year floodplain or similar coastal zone
inundation areas as triggers for various requirements. The 100-year flood standard
was established at the recommendation of a group of experts in the late 1960s. “It
was selected because it was already being used by some agencies, and it was thought
that a flood of that magnitude and frequency represented a reasonable probability of
occurrence and loss worth protecting against and an intermediate level that would
alert planners and property owners to the effects of even greater floods.”8 The
adoption of the 100-year flood standard in many respects guides perceptions of what
is an acceptable level of vulnerability. The 100-year flood standard is a vulnerability
standard, and not a risk standard. Thus, the question of whether the 100-year flood
6 Other federal agencies are involved with flood control projects, including the U.S.
Department of Agriculture’s Natural Resources Conservation Service, the Department of
the Interior’s Bureau of Reclamation, and the Tennessee Valley Authority.
7 This is described in the Corps’ Digest of Water Resources Policies and Authorities
Engineering Pamphlet EP 1165-21-1 (1999).
8 Association of State Flood Plain Managers, Reducing Flood Losses: Is the 1% Chance
(100-year) Flood Standard Sufficient?(Washington, DC: 2004).

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standard combined with current threat and consequence information results in an
acceptable level of risk remains largely unaddressed; this question is especially
relevant for low probability, high consequence events such as a Category 4 hurricane
hitting a major urban center.
The attempt to provide at least 100-year flood protection often drives local
floodplain management and infrastructure investments, resulting in a measure of
equity within and across communities. That equity in vulnerability, however, results
in uneven levels of risk because flooding of different communities has different
consequences, such as differences in the potential loss of life, social disruption,
structures damaged, and economic impact because of variations in land use and
development patterns.

The National Flood Insurance Program does not differentiate between 100-year
flood protection provided by a flood control structure and flood protection resulting
from natural topography and hydrology. As a result, development behind levees and
downstream of dams providing 100-year flood protection is not designated as located
in a “special flood hazard area,” thus freeing occupants from flood insurance
requirements. While the NFIP largely presumes that levees, dams, and other flood
control structures will not fail, their presence does not entirely eliminate an area’s
vulnerability to flooding.
The residual flood risk behind levees or downstream of dams remains largely
unaccounted for in the NFIP and often is not incorporated into individual, local, and
state decision-making. Residual risk is the portion of risk that remains after flood
control structures have been built and other damage-reducing measures have been
taken. Risk remains because of the likelihood of the measures’ design being
surpassed by floods’ intensity and of structural failure of the measures. Often when
the designs of flood control structures are surpassed or when structures fail for other
reasons, the resulting flood is catastrophic, as shown by the floodwall breaches in
New Orleans (LA) with Hurricane Katrina in 2005. The consequences of floods
increase as development occurs behind levees and below dams; ironically, this
development may occur because of the flood protection provided. The nation’s risk
of low-probability events (e.g., 400-year flood, or Category 4 hurricane) having high-
consequences in terms of lives lost, economic disruption, and property damage is
increased by overconfidence in the level and reliability of structural flood protection
for events that are less probable than the 100-year flood.
Reducing Property Damage Vulnerability:
Benefit-Cost Analyses
The risk posed by low-probability events may be underestimated by current
methods for analyzing flood control investments. The benefit-cost analyses
compiled to support federal decision-making for water resources projects focus on
the “national economic development benefits” of investments; regional, social, and
environmental benefits may be analyzed but often are largely excluded from federal

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decision-making.9 Moreover, the Corps generally limits its benefit-cost analyses of
the consequences of flooding to property damages.10 That is, estimated benefits from
flood control infrastructure investments are primarily the avoided losses to existing
structures and land uses.
The evaluation and recommendation of a flood control project by the Corps
involves multiple steps. After an initial reconnaissance study that is funded by the
federal government, current policy is for the cost of the follow-on feasibility study
to be split 50% federal - 50% nonfederal; flood control and storm protection
construction generally is split 65% federal - 35% nonfederal.11 When Congress
authorizes the Corps to construct a project, the authorization generally is based on a
Chief’s Report. In that report the Corps’ Chief of Engineers typically recommends
the building of one of the alternative plans studied in the agency’s feasibility report,
consisting of an evaluation of alternative plans, benefit-cost analysis, engineering
analyses, and environmental impact assessments.
The Corps’ benefit-cost analysis of a project may result in a recommended plan
for flood control infrastructure providing for protection greater than or less than the
100-year flood. Local project sponsors can request that a “locally preferred
alternative” be built, instead of the plan identified by the benefit-cost analysis. The
NFIP creates incentives for communities to support flood control alternatives
providing at least the 100-year level of protection, but the program provides few
incentives for local flood control entities and cities to provide more than the 100-year
level of protection. For some local leaders and communities, the capital required to
cost-share a Corps flood control project may be a financial barrier to pursuing greater
protection.
The Corps’ benefit-cost analysis does not constitute a comprehensive risk
analysis, because the consequences considered are largely limited to property
damage, leaving out other potential consequences, such as loss of life, public health
problems, and economic and social disruption. The Water Resources Development
Act of 1986 (WRDA; P.L. 99-662) required the Corps to address the prevention of
loss of life in the formulation and evaluation of flood control projects. Section 904
(emphasis added) of the act stated:
Enhancing national economic development (including benefits to particular
regions of the Nation not involving the transfer of economic activity to such
regions from other regions), the quality of the total environment, the well-being
of the people of the United States, the prevention of loss of life, and the
9 This approach to benefit-cost analysis was developed following the Principles and
Guidelines for Water and Related Resources Implementation Studies (P&G), prepared by
the Water Resources Council in 1983 to guide federal water resources development projects.
10 Some consideration is given to business income losses and emergency response costs.
More information on the agency’s benefit-cost analysis is addressed in the its Planning
Guidance Notebook, Engineering Regulation ER1105-2-100 (2000), at [http://www.usace.
army.mil/inet/usace-docs/eng-regs/er1105-2-100/entire.pdf].
11 The construction cost share for periodic beach replenishment as part of a storm protection
project is 50% federal - 50 % nonfederal.

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preservation of cultural and historical values shall be addressed in the
formulation and evaluation of water resources projects to be carried out by the
Secretary, and associated benefits and costs, both quantifiable and
unquantifiable, shall be displayed in the benefits and costs of such projects.
Although potential loss of life is noted in Corps feasibility reports, there are no Corps
regulations or guidelines for how to incorporate loss of life into the agency’s benefit-
cost analyses. Part of the reason for that reluctance to quantifying the value of human
life is that its use in Corps project evaluation is unclear. Many projects have benefits
that exceed costs without including the benefit from lives saved. Therefore, although
preventing loss of life is a goal of federal flood control policy, current practice results
in property damage being the primary consequence metric used for making Corps
flood control investment decisions. A related benefit-cost analysis issue commonly
debated is whether there is a bias toward lower levels of flood protection for low-
income communities due to their lower property values. Another commonly debated
issue is whether there is a bias toward structural flood control measures over
nonstructural options (e.g., buyouts of structures in flood-prone areas).
Reducing Flood Risk
A fundamental question being raised is: do current federal policy, programs,
practices result in an acceptable level of aggregate risk for the nation? Risk
management is being increasingly viewed as a method for setting priorities for
managing some hazards in the United States. Because floodplain and coastal
development are largely managed by local governments, some aspects of national
flood risk management likely would be unwelcome and infeasible, and could be
perceived as resulting in an inequitable distribution of flood protection. For example,
if floods in large urban concentrations are perceived as representing a greater risk for
the nation, federal resources may be directed away from protecting smaller
communities and less-populated states. Two of the concerns raised in discussions
of greater emphasis on risk analysis in the development and design of specific
projects are that risk analysis may result in lower levels of protection being
implemented in some areas, and that information and knowledge are insufficient to
perform an adequate analysis. However, an argument can be made that the federal
government has an interest in reducing risks resulting in national consequences, and
in prioritizing federal involvement and appropriations accordingly.
Factors complicating the determination of the nation’s flood risk include
changing conditions and incomplete information. For example, many flood control
projects were built decades ago using the available data, technologies, and scientific
knowledge of the period that may have underestimated flood hazards for particular
areas. Similarly, there are issues with changes in risk over time due to processes such
as land loss, subsidence, sea-level rise, reduced natural buffers, urban development,
and infrastructure aging. For existing dams, there is some information on
consequences of failure as measured by loss of life, economic loss, environmental
loss, and disruption of lifeline infrastructure (such as bridges and power grids);

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however, the database with this information only tracks the amount and type of
losses, not the likelihood of failure.12
A risk-reduction approach for organizing federal flood-related investments
likely would incorporate many structural and nonstructural flood management
measures already being considered and implemented, but change their priority and
mix. Options considered in a risk-centered approach may include shifting federal
policy toward wise use of flood-prone areas (e.g., rules or incentives to limit some
types of development in floodplains), incorporating residual risk and differences in
riverine and coastal flood risk into federal programs (e.g., residual risk premiums as
part of the National Flood Insurance Program), creating a national inventory and
inspection program for levees, promoting greater flood mitigation and damage
mitigation investments, re-evaluating operations of flood control reservoirs for
climate variability and uncertainty, and investing in technology and science for
improved understanding of flooding threats.
Flood Management Issues in the 110th Congress
The 2005 hurricane season focused the nation’s attention once again on issues
that flood experts have debated for decades. The devastation in the Gulf states
renewed public concerns about reliability of the nation’s aging flood control levees
and dams. The debate over what is an acceptable level of risk — especially for low-
probability, high-consequence events — and who should bear that risk is taking place
not only in Gulf states, but nationally. The concerns being raised range widely,
including interest in providing more protection for concentrated urban populations,
risk to the nation’s public and private economic infrastructure, support for reducing
vulnerability by investing in natural buffers, equity in protection for low-income and
minority populations, and consistency in and the form of flood insurance and
disaster aid.
Response to the 2005 hurricane season included discussions of expanding
mitigation activities (such as floodproofing structures and buyouts of structures on
the most flood-prone lands), investing in efforts to restore natural flood and storm
surge attenuation, and assuring vigilant maintenance of existing flood control
structures, as well as interest in new and augmented structural flood protection
measures. Although major flood events, such as the Midwest Flood of 1993,
generally spur these discussions, the policy changes implemented often are
incremental.13 The 110th Congress, like previous Congresses, faces a challenge in
reaching consensus on how to proceed on anything other than incremental change
because of the wealth of constituencies and communities affected by federal flood
12 For information on dam safety, see CRS Report RL33108, Aging Infrastructure: Dam
Safety, by Nic Lane.
13 After the Midwest Flood of 1993, the Interagency Floodplain Management Review
Committee was directed to evaluate the performance of floodplain management and make
recommendations in current policies and programs of the federal government. The resulting
1994 report, titled Sharing the Challenge: Floodplain Management in the 21st Century, often
called the “Galloway Report” for the Committee’s chair, includes the Committee’s
recommendations; the report is available at [http://eros.usgs.gov/sast/2P-00526.PDF].

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policy. Another practical challenge is the division of congressional committee
jurisdictions over the federal agencies and programs involved in flood mitigation,
protection, and response.14
There are many questions that remain about how events unfolded in the
aftermath of Hurricane Katrina, and much information that is still needed to
understand how to apply and communicate nationally the lessons in the Gulf states
learned about flood risk and disaster preparedness and response. Although there is
no way to protect against all flood risk, it is clear that more information is needed to
evaluate flood risk, to understand the reliability and residual risk of structural flood
protection, and to incorporate the full range of flood consequences into local, state,
and federal decision-making and programs.
14 For example, Senate Committees that would likely have jurisdiction over elements of any
comprehensive change in federal flood policy would include Banking, Housing, and Urban
Affairs; Environment and Public Works; and Homeland Security and Government Affairs.
For a discussion of the jurisdictional issues, see CRS Report RS21643, House Committee
System: Jurisdiction and Referral Reform Options, by Judy Schneider and Paul Rundquist
and CRS Report RL32112, Reorganization of the Senate: Modern Reform Efforts, by Judy
Schneider et al.

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