Midwest Flood: Information on the Performance, Effects, and Control of
Levees (Chapter Report, 08/07/95, GAO/RCED-95-125).
Pursuant to a congressional request, GAO examined the operations of
levees involved in the 1993 Midwest flood, focusing on: (1) whether the
Army Corps of Engineers' flood control levees prevented flooding and
reduced damage or increased the flooding and added to the damage; and
(2) the governments exercise control over the design, construction,
placement, and maintenance of nonfederal levees.
GAO found that: (1) 157 of the 193 Army Corps of Engineers levees found
in the areas affected by the 1993 flood prevented rivers from flooding
and $7.4 billion in damages; (2) 32 of the Corps levees withstood
floodwaters until the water rose above the levees and overtopped them;
(3) 4 of the Corps levees allowed water into protected areas before
their design capacity was exceeded; (4) the Corps estimated that the
breaching of these levees caused about $450 million in damages; (5)
although levees allow floodwater to rise higher than it normally would
because they confine a flood to a portion of a floodplain, the Corps
believe that its levees have the net effect of reducing flooding; (6) no
federal programs specifically regulate the design, placement,
construction, or maintenance of nonfederal levees, however, flood
insurance and disaster assistance programs may exercise control over
certain levees; and (7) 17 states and various local governments have
programs to regulate levees, many of which are in response to the
requirements of the National Flood Insurance Program.
--------------------------- Indexing Terms -----------------------------
REPORTNUM: RCED-95-125
TITLE: Midwest Flood: Information on the Performance, Effects, and
Control of Levees
DATE: 08/07/95
SUBJECT: Flood insurance
Disaster relief aid
Flood control management
Property damages
Safety regulation
Environmental law
Precipitation (weather)
Weather forecasting
IDENTIFIER: Missouri River Basin
St. Louis (MO)
Nebraska
Illinois
Iowa
Kansas
Minnesota
North Dakota
Wisconsin
FEMA National Flood Insurance Program
SCS Emergency Watershed Protection Program
USDA Small Watershed Program
Army Corps of Engineers Levee Rehabilitation Program
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Cover
================================================================ COVER
Report to Congressional Requesters
August 1995
MIDWEST FLOOD - INFORMATION ON THE
PERFORMANCE, EFFECTS, AND CONTROL
OF LEVEES
GAO/RCED-95-125
Midwest Flood
Abbreviations
=============================================================== ABBREV
cfs - cubic feet per second
EDA - Economic Development Administration
FEMA - Federal Emergency Management Agency
GAO - General Accounting Office
NRCS - Natural Resources Conservation Service
NWS - National Weather Service
USGS - U.S. Geological Survey
Letter
=============================================================== LETTER
B-261016
August 7, 1995
The Honorable Robert A. Borski
Ranking Minority Member
Subcommittee on Water Resources
and Environment
Committee on Transportation
and Infrastructure
House of Representatives
The Honorable William L. Clay
House of Representatives
This report responds to your request that we examine the performance,
effects, and control of levees involved in the 1993 Midwest flood.
As agreed with your offices, unless you publicly announce its
contents earlier, we plan no further distribution of this report
until 30 days from the date of this letter. At that time, we will
send copies to the Secretaries of Defense, Agriculture, and the
Interior; the Director, Office of Management and Budget; and other
interested parties. We will make copies available to others on
request.
Please contact me at (202) 512-7756 if you or your staff have any
questions. Major contributors to this report are listed in appendix
VII.
James Duffus III
Director, Natural Resources
Management Issues
EXECUTIVE SUMMARY
============================================================ Chapter 0
PURPOSE
---------------------------------------------------------- Chapter 0:1
The intense rainfall that deluged the upper Mississippi River basin
in the spring and summer of 1993 caused the largest flood ever
measured at St. Louis. This unprecedented event in nine midwestern
states generated the highest flood crests ever recorded at 95
measuring stations on the region's rivers. The catastrophic flooding
caused 38 deaths, as well as extensive damage to property and
agriculture; required the evacuation of tens of thousands of people;
and created large-scale disruptions in transportation, business, and
water and sewer services. The President declared 505 counties to be
federal disaster areas, and estimates of the damage have reached as
high as $16 billion.
The Ranking Minority Member of the Subcommittee on Water Resources
and Environment, House Committee on Transportation and
Infrastructure, and Representative William L. Clay asked GAO to
examine the operation of levees, which are earthen or masonry
structures, including floodwalls, that are typically built along
rivers to keep floodwaters from overflowing adjacent floodplains.
Specifically, GAO was asked to review the extent to which (1) the
U.S. Army Corps of Engineers' (the Corps) flood control levees
prevented flooding and reduced damage during the event; (2) the
federal levees increased the height of the flooding and added to the
damage; and (3) federal, state, and local governments exercise
control over the design, construction, placement, and maintenance of
nonfederal levees.
BACKGROUND
---------------------------------------------------------- Chapter 0:2
The Corps has invested over $23 billion nationwide in flood control
projects, such as reservoirs, levees, floodwalls, and channel
improvements. Today, 251 Corps levees are found in the five Corps
districts covering the upper Mississippi River basin, which includes
the Missouri River basin; 193 of these levees are found in the area
affected by the 1993 flood.
Nearly half of these 193 levees are located on major rivers--the
Mississippi River between Rock Island and Cairo, Illinois, and the
Missouri River between Omaha, Nebraska, and Kansas City, Missouri.
Over one-third of the levees on major rivers protect urban areas,
such as Omaha, Nebraska, and Kansas City and St. Louis, Missouri.
The remaining Corps levees protect agricultural areas. Other Corps
levees lie on tributary streams, and most of them protect small
communities.
A levee's design capacity is based on the particular level of
protection that is justified by an analysis of the risks, costs, and
benefits of constructing the levee. Corps levees generally provide
more protection than do nonfederal levees. A typical Corps levee in
an urban area protects against a large flood that is relatively
unlikely to occur in a given year, such as a flood with an annual
probability of 1 percent--commonly called a 100-year flood. A
typical nonfederal agricultural levee protects against a smaller
flood that is more likely to occur in a given year, such as a flood
with an annual probability of 20 percent--commonly called a 5-year
flood.
RESULTS IN BRIEF
---------------------------------------------------------- Chapter 0:3
According to Corps records, 157 of the 193 Corps levees found in
areas affected by the 1993 flood prevented rivers from flooding about
1 million acres and causing $7.4 billion in damage. Another 32
levees withstood floodwaters until the water rose above the levees
and overtopped them. Four other levees were breached or otherwise
allowed water into protected areas before the levees' design capacity
was exceeded. The Corps estimated the damage caused by the
overtoppings and breachings of these 36 levees at about $450 million.
Because a levee confines a flood to a portion of a floodplain, it
pressures the floodwater to rise higher than it otherwise would.
Whether a levee significantly increases the level of a flood varies
by location. Many other natural and man-made factors, however, also
affect the peak level of a flood, but their exact impact is difficult
to identify. While Corps levees increase the levels of floodwaters
that could cause damage elsewhere, Corps officials emphasized that
the net effect of the Corps levees and reservoirs in the upper
Mississippi River basin is to reduce flooding.
No federal program specifically regulates the design, placement,
construction, or maintenance of nonfederal levees built by private
individuals or by public entities such as levee districts. However,
federal programs for regulating navigable waters and wetlands and for
providing flood insurance and disaster and emergency assistance may
exercise control over certain levees, depending on whether the levees
are built in navigable waters or in wetlands, help qualify a
community for flood insurance, or are damaged in a flood. Seventeen
states have programs to regulate levees, including five of the nine
states involved in the 1993 flood. Local programs to control levees
have generally been created in response to the requirements of the
federal National Flood Insurance Program and state regulatory
programs that require localities to control land use or implement
other floodplain management measures.
PRINCIPAL FINDINGS
---------------------------------------------------------- Chapter 0:4
MOST CORPS LEVEES PREVENTED
FLOODING AND REDUCED DAMAGE
-------------------------------------------------------- Chapter 0:4.1
Of the 181 levees for which the Corps had information on design
capacity and flood flows or levels, 145 performed up to their design
capacity and prevented flooding, 32 met their design capacity until
the floodwaters exceeded their height and overtopped them, and 4
allowed water to enter their protected areas before they were
overtopped. The information showed that many levees withstood flood
flows that were greater than the levees were designed to withstand.
In addition, the levees were able to withstand saturation far longer
than the 1 to 2 weeks contemplated in their design.
For example, the Keach levee in Greene County, Illinois, which was
designed to protect against floods of up to 438.5 feet, withstood
water that rose to 442.8 feet. The levee held because sandbagging
efforts raised its height and prevented the flood from entering the
protected areas.
The Corps has qualified the accuracy and completeness of its and the
National Weather Service's (NWS) estimates of the damage prevented
and incurred because of the broad scope of the flood damage and the
rapid compilation of preliminary estimates. Because of the
methodologies they use to estimate damage, the Corps and NWS report
that their estimates of the damage prevented and incurred are
probably understated.
LEVEES INCREASE FLOOD LEVELS
BUT ARE ONE OF MANY FACTORS
AFFECTING THE EXTENT OF
FLOODING
-------------------------------------------------------- Chapter 0:4.2
Levees in the upper Mississippi River basin increased the height of
water in the 1993 flood, according to three modeling simulations.
The simulations indicated that agricultural levees on the Mississippi
River added up to 2.7 feet to the flood peak at St. Louis. Corps
officials told GAO, however, that the floodwater storage capacity of
reservoirs compensates for the increases in flood levels caused by
levees. Experts agree that natural and man-made factors also
directly affect the height of the water levels and the amount of the
damage that occur during a flood. Natural factors include the
flood's duration, the seasonal level of vegetation, the deposition of
sediment carried by the water, and the water's temperature. Man-made
activities include urban development, agriculture, navigation, and
other development in wetlands.
Studies have indicated that, cumulatively, natural and man-made
changes within the basins have raised the levels of the Mississippi
and Missouri rivers. In addition, precipitation in the upper
Mississippi basin appears to be increasing over the long term. These
trends concern experts because increases in the frequency and extent
of flooding increase the damage it causes.
FEDERAL, STATE, AND LOCAL
GOVERNMENTS EXERCISE SOME
CONTROL OVER NONFEDERAL
LEVEES
-------------------------------------------------------- Chapter 0:4.3
Nonfederal levees are regulated to some extent under two federal
regulatory programs that require permits for constructing levees in
wetlands (the Clean Water Act) or in navigable waters (the Rivers and
Harbors Appropriation Act of 1899). Also, under the National Flood
Insurance Program, the Federal Emergency Management Agency (FEMA)
exempts communities from certain requirements of the flood insurance
program if the communities can show that the levees protecting them
are designed, constructed, located, and maintained according to
specified criteria. Under the levee rehabilitation program, the
Corps will make cost-shared repairs of nonfederal levees that are
threatened or damaged by floods if the levees meet the program's
qualifying standards and have been properly maintained.
Of the nine states involved in the 1993 flood, five--Iowa, Kansas,
Minnesota, North Dakota, and Wisconsin--have programs to regulate
levees. Iowa, for example, generally requires permits for
constructing, operating, and maintaining levees in rural areas and in
urban areas that exceed a minimum size. For each levee, Iowa
specifies requirements for the level of protection, location,
drainage, and other design factors.
Local governments generally exercise more control over local
floodplains and levees than the states or the federal government
because FEMA requires that communities adopt floodplain regulations
to join its flood insurance program. Local ordinances can require
building codes for development in floodplains, and zoning regulations
can restrict land uses--including the construction, operation, and
maintenance of levees--in floodplains.
RECOMMENDATIONS
---------------------------------------------------------- Chapter 0:5
GAO is not making any recommendations.
AGENCY COMMENTS
---------------------------------------------------------- Chapter 0:6
GAO discussed the facts in its report with responsible officials of
the five agencies primarily involved. These included the Chiefs of
the Corps' Readiness, Hydraulics and Hydrology, Central Planning
Management, and Policy Development branches; the Director of FEMA's
Program Implementation Division; the Deputy Chief for Programs of the
Natural Resources Conservation Service; the Chief of the U.S.
Geological Survey's Science and Applications Branch; and the Chief of
NWS' Hydrological Service Branch. Generally, these officials agreed
with the information provided but offered comments, corrections, and
suggestions to improve the accuracy and clarity of the report. GAO
made changes to the report where appropriate.
INTRODUCTION
============================================================ Chapter 1
The 1993 Midwest flood, termed "the Great Flood of 1993," was
unprecedented in the United States in terms of the amount of
precipitation, the recorded river levels, the duration and extent of
the flood, the damage to crops and property, and the economic impact.
The intense rainfall that deluged the upper Mississippi River basin
in the spring and summer of 1993 caused the largest flow\1 ever
measured at St. Louis. Affecting nine midwestern states, the
rainfall generated record-high flood levels\2 at 95 measuring
stations on the region's rivers. Because of the catastrophic
flooding, 38 people died, millions of acres were inundated, property
and agriculture sustained heavy damage, tens of thousands of people
were evacuated from their homes, and transportation, business, and
water and sewer services were disrupted. President Clinton declared
505 counties to be federal disaster areas, and estimates of the
damage have ranged from $12 to $16 billion.
--------------------
\1 Flow is also called discharge and refers to a given volume of
water passing a measurement point in a stream within a specified
period. Flow is commonly expressed in cubic feet per second (cfs).
\2 In this report, we will use the terms "water level" or "flood
level" instead of the term "flood stage" to refer to the height of
the water's surface in a river above a predetermined point that is
usually on or near the channel's bottom.
THE GREAT FLOOD OF 1993
---------------------------------------------------------- Chapter 1:1
The 1993 flood affected most of the upper Mississippi River basin.
The basin drains all or part of 13 states and encompasses about
714,000 square miles, or 24 percent of the contiguous United States.
The upper basin includes the Mississippi River from its source in
Minnesota to its confluence with the Ohio River at Cairo, Illinois.
Its principal tributary is the Missouri River, which joins the
Mississippi at St. Louis, Missouri. Other major tributaries include
the Minnesota, Wisconsin, Iowa, Des Moines, and Illinois rivers.
Figure 1.1 shows the Mississippi River basin and the area of the 1993
flooding, and figure 1.2 compares two satellite images of the St.
Louis, Missouri, area at the confluence of the Illinois, Mississippi
and Missouri rivers during a severe drought and during the 1993
flood.
Figure 1.1: The Mississippi
River Basin and the 1993 Flood
Area
(See figure in printed
edition.)
Source: Flood Discharges in
the Upper Mississippi River
Basin, 1993, U.S. Geological
Survey (USGS) Circular 1120-A,
Department of the Interior
(Washington, D.C.: 1993), p.
1.
(See figure in printed
edition.)
Figure 1.2: Landsat Images of
the St. Louis, Missouri, Area,
Including the Confluence of the
Illinois, Mississippi, and
Missouri Rivers During the 1988
Drought and the 1993 Flood
(See figure in printed
edition.)
Source: Earth Observation
Satellite Company, Lanham,
Maryland.
(See figure in printed
edition.)
SATURATED SOIL, HEAVY
RAINFALL LED TO FLOODING
-------------------------------------------------------- Chapter 1:1.1
The conditions that produced the flood began in the summer of 1992.
According to the Department of Commerce's National Weather Service
(NWS), July, September, and November 1992 were much wetter than
normal in the upper Mississippi River basin. Winter precipitation
was near normal, but a wet spring followed. The period from April to
June 1993 was the wettest observed in the upper basin in the last 99
years. As a result, soils were saturated, and many streams were
flowing well above normal levels when summer rains began.
A persistent atmospheric pattern during the summer of 1993 caused
excessive rainfall across much of the upper Mississippi River basin.
Major flooding resulted primarily from a series of heavy rainfalls
from mid-June through late July. A change in the upper air's
circulation pattern created drier conditions in late July and early
August, but heavy rainstorms brought more flooding to parts of the
upper basin in mid-August.
The rainfall over the upper Mississippi River basin from May to
August 1993 is unmatched in the historical records of the central
United States. Generally, rainfall from the Dakotas to Missouri and
Illinois was well above normal. Figure 1.3 locates the heaviest
concentrations of rainfall from January through July 1993 in the
flood region.
Figure 1.3: Concentration of
Rainfall, January through July
1993
(See figure in printed
edition.)
Source: Precipitation in the
Upper Mississippi River Basin,
January through July 31, 1993,
USGS Circular 1120-B,
Department of the Interior
(Washington, D.C.: 1993), p.
5. The figure is based on data
from NWS.
(See figure in printed
edition.)
Rivers rose above flood levels at about 500 measurement points in the
nine-state region, NWS reported. Record flooding occurred at 95
measurement points in the Upper Midwest--44 on the upper Mississippi
River system, 49 on the Missouri River system, and 2 on the Red River
of the North system. Water flow rates along major parts of the upper
Mississippi and lower Missouri rivers equalled or exceeded floods
with an annual probability of 1 percent--commonly called a 100-year
flood. Figure 1.4 shows where the heaviest flooding occurred.
Figure 1.4: Location of Record
and Major Flooding Along Large
Midwestern Rivers in 1993
(See figure in printed
edition.)
Source: Natural Disaster
Survey Report: The Great Flood
of 1993, NWS, National Oceanic
and Atmospheric Administration,
Department of Commerce
(Washington, D.C.: 1994) p.
1-2.
(See figure in printed
edition.)
Extreme flooding of major river systems like the Mississippi and
Missouri rivers seldom occurs in the summer. During a typical
midwestern summer, a few localized heavy rains are scattered
throughout the region. In 1993, the rare combination of closely
timed and record-level rainfall occurred on both the lower Missouri
and upper Mississippi basins, causing a record flood at St. Louis.
NWS reported that the extended duration of the flood was also
extremely rare. Typically, periods of above-average rainfall during
a midwestern summer last from 2 to 5 weeks, sometimes persisting up
to 8 weeks. In 1993, major flooding continued throughout the summer
along the Missouri and Mississippi rivers. For example, as of
September 1, 1993, Hannibal, Missouri, had experienced 153
consecutive days, or about 22 weeks, of water above flood level.
Flooding continued through the middle of September in many regions
along the Mississippi River.
FLOODING CAUSED WIDESPREAD
DAMAGE
-------------------------------------------------------- Chapter 1:1.2
The administration established the Interagency Floodplain Management
Review Committee to evaluate the performance of existing floodplain
management programs in light of the 1993 flood. Their review of
existing damage estimates for the flood found that these estimates
ranged from $12 billion to $16 billion. The available estimates are
from such federal agencies as NWS and the Federal Emergency
Management Agency (FEMA), which develop estimates for specific
program purposes, such as disaster response and assistance. The
Committee estimated that $4 billion to $5 billion in damage was to
crops in upland areas outside the floodplain, which were destroyed by
the heavy precipitation there. The Committee attributed about $2.5
billion in agricultural damage directly to the flooding.
Other significant damage occurred to about 100,000 residences, more
than 5,000 businesses, many bridges, hundreds of miles of roads and
railroads, and 33 airports. The flood also closed the major rivers
to navigation and affected about 200 municipal water systems, 388
wastewater facilities, and other public facilities, such as public
buildings and parks.
FEMA reported that about 6.6 million acres in the floodplain were
flooded in 1993, of which 63.4 percent were agricultural lands and
2.5 percent were urban areas. The remaining acres in the floodplain
were normally covered by water, were wetlands, and/or were used for
other purposes.
FEDERAL INVOLVEMENT IN FLOOD
CONTROL
---------------------------------------------------------- Chapter 1:2
The primary federal agency involved in flood control is the U.S.
Army Corps of Engineers (the Corps). The Department of Agriculture's
Natural Resources Conservation Service (NRCS)\3 is indirectly
involved in flood control when it addresses the effects of flooding
in agricultural watersheds.\4
--------------------
\3 Under the authority of the Federal Crop Insurance Reform and
Department of Agriculture Reorganization Act of 1994 (P.L. 103-354,
Oct. 13, 1994), the former Soil Conservation Service was abolished
and NRCS was established.
\4 A watershed is a region or area contributing to the water supply
of a particular stream, river, or body of water.
U.S. ARMY CORPS OF
ENGINEERS
-------------------------------------------------------- Chapter 1:2.1
After a series of disastrous floods affected wide areas, the Congress
enacted the Flood Control Act of 1936. This act established a
nationwide policy that (1) flood control was in the interest of the
general public and (2) the federal government would cooperate with
the states and local entities to carry out flood control activities.
The Corps' flood control programs are designed to reduce the
susceptibility of property to flood damage and to relieve human and
financial losses.
The Corps has invested over $23 billion in flood control projects
nationwide. It has constructed more than 600 projects, including
reservoirs and about 10,500 miles of levees and floodwalls. Flood
control reservoirs often provide the capacity to store water for
multiple uses, including municipal and industrial water supplies,
navigation, irrigation, production of hydroelectric power,
conservation of fish and wildlife, maintenance of water quality, and
recreation. Levees and floodwalls are usually turned over to local
sponsors for operations and maintenance.
The Corps is also authorized to perform emergency activities, such as
fighting floods, repairing and restoring flood control works, and
supplying emergency clean water to communities. It also performs
emergency assistance work requested and funded by FEMA. Permanent
repairs to levees and other flood control facilities are provided
under a levee rehabilitation program. Five of the 37 Corps districts
performing civil works activities were involved in the 1993 flood:
St. Paul, Minnesota; Rock Island, Illinois; St. Louis and Kansas
City, Missouri; and Omaha, Nebraska. Of the 251 Corps levees located
in these districts, 193 were in the flooded area.
The Corps operates 98 reservoirs in the upper Mississippi River basin
to reduce flood damage. Of these, 22 were constructed by the Bureau
of Reclamation. While not all of the reservoirs were in the flooded
area, most had some impact on the flood because they stored water.
For example, Corps headquarters officials said the reservoirs stored
more than 20 million acre-feet\5 of floodwater on August 1, 1993,
reducing flood levels throughout much of the flood area--for example,
lowering the crest of the Mississippi River at St. Louis on that day
by 5 feet. In addition to the reservoirs, the Corps has built or
improved more than 2,200 miles of levees for the protection of
communities and agriculture in the basin.
--------------------
\5 An acre-foot is a unit measure of volume equal to 1 acre covered
to a depth of 1 foot. One acre-foot is equal to 326,700 gallons.
CORPS' FLOODPLAIN
MANAGEMENT ASSESSMENT
------------------------------------------------------ Chapter 1:2.1.1
After the 1993 flood, the Congress funded a broad 18-month effort by
the Corps to assess floodplain management in the upper Mississippi
River and lower Missouri River basins. This effort, which was
separate from the work of the interagency committee, describes the
existing resources in the floodplain, identifies alternatives for the
future use of the floodplain, and suggests policy changes and areas
for further study. The assessment was conducted in collaboration
with numerous federal, state, and local governments and interested
parties. The Corps presented its findings and conclusions in a
report published on June 30, 1995.\6
--------------------
\6 Floodplain Management Assessment of the Upper Mississippi and
Lower Missouri Rivers and Their Tributaries (St. Paul, Minn.: June
1995).
NATURAL RESOURCES
CONSERVATION SERVICE
-------------------------------------------------------- Chapter 1:2.2
NRCS' programs are designed to protect and prevent flooding in small
watersheds, repair or relocate agricultural levees that are damaged
in flooding, and convert cropland to wetland reserves. The Small
Watershed Program authorized by the Watershed Protection and Flood
Prevention Act of 1954 (P.L. 83-566) provides for NRCS to install
land conservation measures and flood damage reduction works
nationally. NRCS traditionally works on smaller projects affecting
watersheds of fewer than 400 square miles; the Corps addresses needs
in larger watersheds. In addition, NRCS has authority under the
Flood Control Act of 1944 (P.L. 78-534) for a flood prevention
program for 11 watersheds.
In the nine midwestern states affected by the 1993 flood, NRCS has
performed soil and water conservation work on 3 million acres,
installed 2,964 reservoirs, and worked on 818 miles of channel. NRCS
estimated that its watershed projects prevented $400 million in
damage from the 1993 flood.
When a disaster strikes, NRCS implements the Emergency Watershed
Protection Program under section 403 of the Agricultural Credit Act
of 1978 (P.L. 95-334). This program provides assistance--including
repairs to damaged levees--to reduce hazards to life and property.
FLOOD CONTROL LEVEES IN THE
UPPER MISSISSIPPI RIVER BASIN
---------------------------------------------------------- Chapter 1:3
Levees are linear earthen embankments whose primary purpose is to
prevent high water from reaching the floodplain. They normally
extend from high ground along one side of a floodplain and around it
to another area of high ground. Levees protect the area between the
levee and the high ground.
For stability, an earthen levee is normally constructed so that its
bottom width is several times its height; hence, a levee requires
considerable land area. In urban areas where space is limited, the
Corps builds masonry floodwalls. A long levee system may include a
combination of several segments of earthen levees and floodwalls.
Figure 1.5 represents a cross-sectional view of a typical earthen
levee.
Figure 1.5: Cross-Sectional
View of an Earthen Levee
(See figure in printed
edition.)
Source: GAO's drawing based on
a St. Louis Post-Dispatch
graphic and data from the
Corps.
(See figure in printed
edition.)
Levees reduce but do not eliminate flooding in the floodplain because
levees may be overtopped by floods larger than those for which they
are designed. Generally, the Corps analyzes the risks, costs, and
benefits of constructing a levee to various heights; determines, with
the participation of a local cost-sharing sponsor, how much
protection the levee should provide; and proposes a plan to the
Congress. After reviewing the Corps' analyses, the Congress can
authorize and fund the plan.
The height of a levee is based on the maximum flow (discharge) of
floodwater, measured in cubic feet per second (cfs),\7 associated
with flooding of a particular frequency, or average recurrence level,
at the levee's location. For example, the Kaskaskia Island levee in
the Mississippi River in Illinois, which is designed to withstand a
flood with an average frequency (or recurrence interval) of 50 years,
was built to withstand a water level of 45.7 feet\8 and a flow of
1,010,000 cfs. At other locations, floods of the same frequency will
be associated with different heights and flows. For example, the Des
Moines-Mississippi River levee in Missouri, which also protects
against a flood with an average recurrence interval of 50 years, was
built to withstand a water level of 24 feet and a flow of 371,000
cfs. Both levees provide the same degree, or level, of protection
but have different performance criteria because the river's channel
and flows differ greatly at these levees.
Engineers have accounted for uncertainties in the water level and for
unknown factors--such as wave action, bridge openings, and the
effects of urbanization--by adding 1 to 3 feet to the overall
elevation of a levee's design; this addition is known as freeboard.
A levee should withstand floods up to and including the flood for
which it was designed. Floods larger than the design flood may
overtop or breach the levee--that is, cut a hole through it. The
ways that floods can damage levees--by overtopping, piping,
saturation, and underseepage--are depicted in figure 1.6.
Figure 1.6: Potential Levee
Failure Scenarios
(See figure in printed
edition.)
Note: Overtopping refers to
water flowing over the top of
the levee. This action quickly
erodes the landward slope,
causing a breach in the levee.
Internal erosion, called
piping, occurs when water finds
its way through animal burrows
or channels formed by plant and
tree roots to erode the levee
internally. Through
saturation, water permeates the
levee's material, weakening the
levee's ability to hold
together. Underseepage occurs
when the river pushes through a
loose layer of sand beneath the
levee and weakens the levee's
foundation.
(See figure in printed
edition.)
Source: GAO's drawing based on
a St. Louis Post-Dispatch
graphic and data from the
Corps.
(See figure in printed
edition.)
Hydrologists have several ways of describing the size of a flood at a
specific location. They may refer to the water's level and flow, or
they may refer to the average interval between occurrences of that
particular water level and flow. They also refer to the annual
probability that the same water level and flow may occur. Because
floods occur randomly, the interval between extreme water levels of
the same height are far from uniform--a large flood in one year does
not preclude the occurrence of an even larger flood the next year.
For example, a flood with an average recurrence interval of 100 years
has a 1-percent chance of being equaled or exceeded every year. This
means that a "100-year" flood may occur several times within a
100-year period, or it may not occur at all.
As communities and farms have grown on the floodplains of the upper
Mississippi and Missouri rivers since the early to mid-1800s, levees
have been constructed by various nonfederal entities, ranging from
cities to individuals, to protect floodplains from seasonal flooding.
Owners have wanted to protect the floodplain from flooding because it
has often contained the most fertile land for farming. While no
inventory of nonfederal levees exists, the Interagency Floodplain
Management Review Committee estimated that such levees extend over
5,800 miles in the upper Mississippi River basin.
The Corps estimated that about 1,100 of the 1,358 nonfederal levees
in the area covered by the five Corps districts involved in the 1993
flood failed to keep the flood out of the areas they were designed to
protect or were otherwise damaged. Corps officials told us, however,
that this estimate was approximate and incomplete.
Corps and nonfederal levees protect nearly all of the floodplain in
the upper Mississippi River basin. Above Rock Island, Illinois, the
Mississippi River floodplain is narrow and is filled largely with
navigation pools. The remaining floodplain contains wildlife
refuges, some farmland, and a few levees; scattered towns are
protected by urban levees. Below Rock Island, the floodplain widens
to as much as 6 miles, and because the extensive floodplain is used
for crops, the river is almost continuously lined with Corps
agricultural levees to Fort Madison, Iowa, and from Keokuk, Iowa, to
Cairo, Illinois. In addition, many cities and towns, including St.
Louis, are protected by levees and floodwalls in this section of the
river.
Missouri River floodplains, used predominantly for agriculture, are
protected to varying degrees by levees. Between Omaha and Kansas
City, Missouri, the river is heavily lined with Corps agricultural
levees. Between Kansas City and St. Louis, the Missouri River has
four Corps levees, but the river is heavily lined with nonfederal
levees.
Developed floodplains with larger urban areas--such as Omaha/Council
Bluffs, Kansas City, and St. Louis--are largely protected by Corps
urban levees. Near Kansas City and St. Louis, several residential,
industrial, and commercial areas are built on floodplains behind
levees.
--------------------
\7 A unit of measurement for a river's flow or discharge: 1 cfs is
equal to the discharge of a stream at a rectangular cross section, 1
foot wide by 1 foot deep, flowing at an average velocity of 1 foot
per second. One cfs is equivalent to 7.5 gallons.
\8 This number represents the number of feet above a site-specific
river level, also known as the flood stage, at which damage may start
to occur; it is usually at or above the top of the riverbank.
OBJECTIVES, SCOPE AND
METHODOLOGY
---------------------------------------------------------- Chapter 1:4
The Ranking Minority Member of the Subcommittee on Water Resources
and Environment, House Committee on Transportation and
Infrastructure, and Representative William L. Clay of Missouri asked
GAO to review the extent to which (1) the Corps' flood control levees
prevented flooding and reduced damage during the event; (2) these
federal levees increased the height of the flooding and added to the
damage; and (3) federal, state, and local governments exercise
control over the design, construction, placement, and maintenance of
nonfederal levees.
To address these objectives, we obtained information from the Corps
and other federal agencies, state agencies, and other public and
private organizations. We also interviewed officials and obtained
documents from these agencies and organizations, as well as from
individuals. Appendix I provides further details on our scope and
methodology.
We conducted our review between November 1993 and July 1995 in
accordance with generally accepted government auditing standards. We
discussed the facts in our report with responsible officials of the
five agencies primarily involved: the Chiefs of the Readiness,
Hydraulics and Hydrology, Central Planning Management, and Policy
Development branches in the Corps' Civil Works Directorate; the
Director of FEMA's Program Implementation Division; the Deputy Chief
for Natural Resources Conservation Programs and the Acting Director
of the Watershed Projects Division at NRCS headquarters; the Chief of
the Science and Applications Branch and staff from the Office of
Surface Water at USGS headquarters; and the Chief of NWS'
Hydrological Service Branch. Generally, these officials agreed with
the basic information provided but offered comments, corrections and
suggestions to improve the accuracy and clarity of the report. We
made changes to the report where appropriate.
MOST CORPS LEVEES PERFORMED AS
DESIGNED AND PREVENTED SIGNIFICANT
DAMAGE
============================================================ Chapter 2
According to the Corps, 157 (81 percent) of the 193 Corps levees
located in the area affected by the 1993 flood prevented rivers from
severely flooding about 1 million acres. However, some of these
acres were flooded by smaller streams behind the levees and by
seepage under the levees. Nevertheless, the Corps estimated that the
157 levees prevented about $7.4 billion in damage during the flood.
Another 32 Corps levees withstood flood flows until the water
exceeded their design capacity and overtopped the levees. Three
other levees were breached without being overtopped by floodwaters,
and an opening in an urban floodwall for railroad tracks was not
closed in time to prevent flooding. The Corps estimated that
flooding at the 36 levees caused about $450 million in damage.
To assess the levees' performance, we compared information on the
levees' design values for either flows or water levels (design
capacity) with the flows and water levels recorded during the 1993
event. Data were not available on either the levees' design capacity
and/or the 1993 flows or water levels for 12 of the 193 levees. Data
on the other 181 levees show that 177 withstood the flows and water
levels at least as well as designed and 4 did not. The flood
eventually overtopped some of the levees. Nevertheless, local
flood-fighting efforts at some locations permitted levees to
withstand flows and water levels that exceeded the levees' design
capacity. Most levees also withstood saturation far longer than they
were designed to do.
LEVEES' PERFORMANCE IS MEASURED
AGAINST DESIGN CRITERIA
---------------------------------------------------------- Chapter 2:1
Corps officials told us that generally three basic design criteria
apply to each levee. Two of these are flood level, expressed in
feet, and flow, expressed in cfs. The five Corps districts involved
in the 1993 flood used data on either flood level or flow or on both
criteria to judge the performance of levees. The third design
criterion is the extent to which a levee can be saturated and still
withstand its design flood.
The Corps designs levees to withstand saturation. However, according
to Corps district officials, the time required to reach a levee's
maximum saturation point varies by flood. A Corps manual (No.
1110-2-1913, Mar. 31, 1978) provides that levees are expected to be
exposed to flood flows for only a few days or weeks per year.
Embankments that will be exposed to flows for longer periods must
meet more stringent criteria for earthen dams.
Water standing against a levee for an extended period may move
through or under the levee, leading to problems such as sinkholes\9
or sandboils\10 on the landward side. The higher pressure of the
floodwater will eventually overcome the materials within the levee
and its foundation, and a breach may occur.
To determine whether a levee performed to its design capacity, we
attempted to compare its design flow capacity with actual or
estimated flows during the flood. If the levee's flow capacity was
not available, we used the levee's flood level capacity. Corps
district officials agreed that these measures were acceptable bases
for assessing a levee's performance. As an additional criterion, we
considered the length of time the levee withstood saturation from
flooding.
We asked the Corps to give us the design capacity of, and the flow
rates or water levels at, the 193 levees involved in the flood.
District personnel told us that all or some of the data were not
readily available for 12 levees. They said that Corps field staff or
local officials advised them that the land behind the 12 levees was
not flooded. Therefore, they said they can reasonably assume that
these 12 levees performed within their design capacity. None of the
12 levees were designated as overtopped on Corps levee repair
schedules. Appendix II lists the levees for which insufficient data
were available for our comparison.
--------------------
\9 Sinkholes occur when water pressure creates a void underground and
progressively collapses the soil until the void reaches the surface
and the surface collapses downward.
\10 Sandboils occur when underground water forces its way to the
surface to create a bubbling, or boiling, fountain of water and sand.
MOST CORPS LEVEES PERFORMED TO
THEIR DESIGN CAPACITY
---------------------------------------------------------- Chapter 2:2
Of the 181 levees for which comparative data were available, 177
clearly performed up to their design capacity and sometimes exceeded
it during the 1993 flood. Many levees withstood flows that, in some
cases, were greater than those for which the levees had been designed
because flood-fighting efforts extended their performance by raising
their height. In addition, many levees experienced saturation far
longer than they were designed to do.
Of the 177 levees that clearly met performance criteria, 145
prevented the river from entering the protected floodplain. The
flood eventually exceeded the design capacity of the remaining 32
levees and overtopped them. Only four levees allowed floodwater to
enter the protected floodplain before the levees were overtopped.
Appendix III lists the 145 Corps levees in the flood area that the
Corps said prevented flooding.
Figure 2.1 displays the location of the 193 levees in the flooded
area and identifies the levees that met design criteria but were
overtopped, as well as the levees that were breached or otherwise
failed without first being overtopped.
Figure 2.1: Location and
Performance of Corps Levees in
the 1993 Midwest Flood
(See figure in printed
edition.)
Source: GAO's analysis of data
from the Corps.
(See figure in printed
edition.)
FLOOD-FIGHTING EFFORTS
EXTENDED THE PERFORMANCE OF
SOME LEVEES
-------------------------------------------------------- Chapter 2:2.1
Corps officials said that, in some instances, flood-fighting at
levees prevented water from entering protected areas when the water
reached flow rates or elevations beyond the levees' design capacity.
They said that workers prevented overtopping by piling sandbags and
building other makeshift barriers on the top and landward sides of
the levees. In these cases, a levee exceeded its design capacity in
three ways. First, the added height permitted the levee to continue
holding back the flood even when the water rose above the top of the
levee. Second, the base of the levee withstood the additional water
pressure created by extending the height. Third, because
flood-fighting prevented or delayed overtopping, the levee withstood
saturation far longer than anticipated.
Flood-fighting techniques effectively increased the design capacity
of many levees. For other levees, such as those at St. Louis or
North Kansas City, the success or failure of flood-fighting
determined whether the levees were able to meet their original design
capacity. Examples of flood-fighting efforts during the 1993 flood
are described in appendix IV.
FLOODWATERS EXCEEDED THE
DESIGN CAPACITY OF SOME
LEVEES
-------------------------------------------------------- Chapter 2:2.2
According to the Corps, flooding caused 32 Corps levees to be
overtopped. These levees were designed to protect against floods
whose average recurrence intervals ranged from 20 to 500 years. Of
the 32 levees, 26 were on the Mississippi and Missouri rivers where
the flood was greatest. Five of the other six levees were located on
the Illinois River, and one was located near the Missouri River.
Table 2.1 lists, by Corps district and by river, the 32 levees that
the flood overtopped, the design capacity of each levee, and the
flood's estimated flow or water level at each levee.
Table 2.1
Comparison of Levee Design Capacity With
Flood Flow or Level for 32 Levees That
Were Overtopped
Desi Floo
gn d
wate wate
r r
Design leve leve
recurren Design Flood l l
District/river/levee ce flow flow (fee (fee
project interval (cfs) (cfs) t) t)
---------------------- -------- ------ ------ ---- ----
Rock Island District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Des Moines-
Mississippi 50 371,00 446,00
0 0
Fabius River 50 374,00 404,00
0 0
Green Bay 50 376,00 422,00
0 0
Gregory 50 371,00 393,00
0 0
Hunt/Lima Lake 50 371,00 418,00
0 0
Indian Grave - 50 349,00 419,00
Upstream 0 0
Indian Grave - 50 349,00 419,00
Downstream 0 0
Marion County 50 374,00 418,00
0 0
Sny Island 50 349,00 400,00
0 0
South River 50 349,00 524,00
0 0\a
St. Louis District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Columbia 50 925,00 1,080, 45.0 49.5
0 000
Harrisonville 50 980,00 1,080, 45.0 49.5
0 000
Illinois River
------------------------------------------------------------
Eldred 20 74,200 438. 440.
0 8
Hartwell 20 79,300 440. 440.
5 9
Hillview 20 79,300 440. 443.
5 6
Nutwood 20 56,000 437. 440.
0 2
Spankey 20 76,200 437. 440.
5 8
Omaha District
------------------------------------------------------------
Missouri River
------------------------------------------------------------
MRLU\b L-561 50 13,000 37,700
MRLU L-575 50 35,000 38,000
MRLU R-520\c 200 310,00 307,00
0 0
MRLU R-548 50 304,00 307,00
0 0
MRLU R-562\c 70 300,00 196,00
0 0
Kansas City District
------------------------------------------------------------
Missouri River
------------------------------------------------------------
Chariton 50 476,00 487,00
0 0
MRLU L-246 25 400,00 487,00
0 0
MRLU L-400 100 348,00 503,00
0 0
MRLU L-408\c 100 270,00 335,00
0 0
MRLU L-448-443\c 100 325,00 335,00
0 0
MRLU L-488\c 100 322,00 335,00
0 0
MRLU R-471-460\c 100 325,00 335,00
0 0
MRLU R-482\c 100 325,00 335,00
0 0
MRLU R-500\c 100 309,00 307,00
0 0
Tributary\d
------------------------------------------------------------
Kimsey-Holly Creek 100 308,00 319,00
0 0
------------------------------------------------------------
Note: No Corps levees in the St. Paul District were overtopped.
\a Peak event figure; flow for day of overtopping was not available.
\b Missouri River Levee Unit. This system of levees was authorized
by the Flood Control Acts of 1941 and 1944 as part of the Pick-Sloan
plan for the Missouri River.
\c The next section of this chapter explains why this levee was
overtopped even though some or all of the data do not suggest that it
was overtopped.
\d Because USGS does not have a measurement gauge on Kimsey Creek,
the figures appearing in the table are for the unbuilt portion of the
levee along the Missouri River.
Source: GAO's analysis of data from the Corps and USGS.
LEVEES WERE OVERTOPPED FOR
VARIOUS REASONS
-------------------------------------------------------- Chapter 2:2.3
We compared either the design flow capacity of the levee with the
flood flow recorded at the gauge nearest the levee, or the design
height of the levee with the flood level recorded at the gauge
nearest the levee.
For 29 of the 32 levees, either the flood flow exceeded the design
flow capacity of the levee or the flood level exceeded the design
height of the levee. For example, the peak flood flow for the South
River levee along the Mississippi River just south of Hannibal,
Missouri, was 524,000 cfs, far above the levee's design flow capacity
of 349,000 cfs.
The flood overtopped three levees, identified in table 2.1, even when
the data indicated that the flood flow did not exceed the design flow
capacity of the levees. Corps officials said that these cases may be
generally explained by (1) a decline from the levee's design flow
capacity, which they attribute to a change in the relationship
between the flood level and the flow rate at the levee that resulted
in higher flood levels for the same flow rate; (2) the distance
between the levee and the gauge used to measure the flood flow, which
resulted in an inaccurate flood flow estimate for the levee location;
and (3) the location of the overtopping. For example, the main
portion of Missouri River Levee Unit R-520 was not overtopped, just
as the data indicate. However, the levee was overtopped at a point
along a creek where the levee's design flow capacity was much lower.
The 32 levees whose design capacity was exceeded by the flood were
concentrated in six general areas: above St. Louis, below St.
Louis, the lower Illinois River, southeast Nebraska/northwest
Missouri, north of Kansas City, and central Missouri. With one
exception, the levees in these areas were built by the Corps to
protect agricultural lands from floods. One levee was built to
protect Elwood, Kansas, a community of about 1,000 residents, which
lies across the river from St. Joseph, Missouri.
FOUR CORPS LEVEES WERE
BREACHED OR FAILED
-------------------------------------------------------- Chapter 2:2.4
Three Corps levees, two on the Mississippi River and one on the
Missouri River, were breached without first being overtopped by
floodwaters. In addition, a railroad opening in a floodwall along
the Raccoon River was not closed to prevent flooding in the city of
Des Moines. Table 2.2 lists the design criteria and flood flows for
these four levees.
Table 2.2
Comparison of Levee Design Capacity With
Flood Flow or Level for Four Levees That
Were Breached or Failed
Desi Floo
gn d
wate wate
r r
Design leve leve
recurren Design Flood l l
District/river/ ce flow flow (fee (fee
levee project interval (cfs) (cfs) t) t)
-------------------- -------- -------- ------ ---- ----
St. Louis District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Bois Brule 50 1,010,00 905,00 45.7 46.0
0 0 0 1
Kaskaskia Island
50 1,010,00 898,00 45.7 47.3
0 0 0 8
Rock Island District
------------------------------------------------------------
Tributary
------------------------------------------------------------
Des Moines 100 100,000 116,00
0
Omaha District
------------------------------------------------------------
Missouri River
------------------------------------------------------------
MRLU L-550 50 305,000 196,00
0
------------------------------------------------------------
Source: GAO's analysis of data from the Corps and USGS.
Corps officials said that they would not classify the breaches of the
Bois Brule and Kaskaskia Island levees as performance failures for
two reasons. First, these breaches occurred when the water reached
the freeboard area of the levee, which is the safety zone above the
levee's design height. They said that when water rises above a
levee's design height, the levee cannot be expected to continue
holding against a flood. Second, because the duration of the 1993
flood far exceeded the design standard for levees, some Corps
officials believe that the breaches should not be characterized as
performance failures.
According to Corps district staff, the breach in the third levee,
Missouri River Levee Unit L-550, was caused by the use in the
construction of the levee of a material that allowed underseepage.
Corps staff told us that the fourth levee failed to prevent flooding
because a railroad opening in the floodwall protecting the city of
Des Moines was not closed in time. Each of these situations is
described in appendix V.
CORPS' ESTIMATES OF FLOOD
DAMAGE ARE IMPRECISE
---------------------------------------------------------- Chapter 2:3
In its April 1994 report to the Congress on flood damage for fiscal
year 1993, the Corps qualified the accuracy and completeness of
estimates of the damage prevented and incurred because of the broad
scope of the damage and the rapid compilation of preliminary
estimates. Given their methodologies for estimating flood damage,
the Corps and NWS said that their estimates of both the damage
prevented and the damage incurred, presented in this report, are
probably understated.
The Corps estimated that its levees prevented the flooding of about 1
million of about 1.4 million acres protected. The overtopping and
breaching of levees caused about 400,000 acres to be flooded.
However, in areas behind levees that held, some flooding still
occurred because of heavy seepage through and under the levees and
heavy flows from streams draining areas behind the levees. Corps
officials said that they have not estimated the number of acres
flooded from these sources.
According to the Corps, the levees prevented about $7.4 billion in
flood damage during the 1993 flood. To calculate the damage
prevented, the Corps uses damage curves that employ the principles of
hydrology and economics to graphically depict the estimated costs of
the damage that would occur if a Corps levee were not protecting the
area. Economists compare curves depicting the estimated damage with
and without a levee. The difference is the estimated value of the
damage prevented by the project.
Corps staff said that the severity and duration of the 1993 flood in
the St. Louis district were so great that the existing damage curves
could not be used to estimate the damage accurately. As a result,
Corps personnel extrapolated damage estimates for the 1993 flood from
damage estimates for the large 1973 flood and used their professional
judgment.
Corps staff pointed out that because the dollar values on the damage
curves tend to be outdated, the estimates of flood damage derived
from these curves are probably understated. They said that some of
the dollar values they developed when they constructed the levee have
not been updated to reflect the value of development that has since
occurred behind the levee. They also mentioned that obtaining
information about urban land values requires extensive fieldwork and
research, which are labor-intensive, expensive, and time-consuming.
Corps officials said that because their resources are limited, they
give priority to updating information on the largest urban centers
where the greatest threat of damage exists.
The four Corps districts where levees were overtopped and breached
estimated that about $450 million in damage was incurred behind the
levees. According to the Corps, it did not have sufficient funding
to complete on-site field surveys to estimate the damage incurred
from the 1993 flood and, as an alternative, used a variety of
techniques to estimate the damage.
In the Rock Island District, for example, estimates were based on
data from county-level sources that, according to Corps district
officials, were rough estimates and were specific to only a few
sites. The Omaha and St. Louis districts used computer programs and
actual river elevations to compute the damage incurred, supplementing
these sources with information from surveys of businesses, local and
state government officials, and field personnel from the Department
of Agriculture. The Kansas City District used water levels and
damage curves to estimate the damage incurred.
NWS makes the overall estimates of flood damage suffered each year
that the Corps reports to the Congress. For fiscal year 1993, NWS
estimated that all floods caused more than $16 billion in damage.
According to staff from NWS' Office of Hydrology, loss estimates can
be considered only approximate because they are developed as an
ancillary function to NWS' primary mission of forecasting weather and
floods. They said the quality of resulting estimates is uneven
because of insufficient resources, inconsistent methods and sources,
incomplete data collection by field offices, and early reporting
deadlines.
CONCLUSIONS
---------------------------------------------------------- Chapter 2:4
While data on the design flow capacity of the Corps levees and the
actual flows during the 1993 flood are incomplete, the Corps levees
in the area affected by the 1993 flood generally performed as
designed. In fact, some levees withstood significantly greater flood
flows and elevations than they were designed to withstand, especially
when the duration of the flood is considered. Where the levees did
not prevent water from entering protected areas, the Corps levees
were overwhelmed by the size of the Great Flood of 1993.
LEVEES INCREASE FLOOD LEVELS, BUT
OTHER FACTORS ALSO AFFECT EXTENT
OF FLOODING
============================================================ Chapter 3
By confining floodwaters within a smaller portion of a floodplain
than they would otherwise occupy, levees pressure the waters to rise
higher and flow faster than they would do without restraint. Whether
levees significantly increase flood levels varies by location.
Computer simulations of the 1993 flood estimated that the nearby
Corps levees added up to 2.7 feet to the flood crest at St. Louis
and up to 7.3 feet to the flood crest at other locations.
Corps officials acknowledge that levees increase flood levels and
induce some flooding. However, they emphasized that the net effect
of levees, reservoirs, and navigation structures in the upper
Mississippi River basin is to reduce flood levels and damage. There
is no consensus among researchers, however, about the long-term
effects of these structures on flood levels.
Many factors besides levees help determine the peak level of a flood.
These include the amount of water entering a river from
precipitation, the size and shape of the river's channel and
floodplain, and other natural factors. Human activities, such as
clearing the floodplain for cultivation, have also affected flood
levels.
Studies show that cumulative changes within the basins have caused
higher flood levels for Mississippi and Missouri river flows. In
addition, available evidence suggests that precipitation in the upper
Mississippi basin may be increasing. If these trends continue
upward, rather than cycling downward, more frequent and more
extensive flooding will occur and future damage from flooding may
increase.
EXPERTS AGREE THAT LEVEES
CONTRIBUTE TO HIGHER FLOOD
LEVELS
---------------------------------------------------------- Chapter 3:1
Available studies and the experts we spoke with agreed that levees
generally contribute to higher flood levels above and within the
levied part of a river. They said that the construction of a levee
in a floodplain forces the water into an artificial floodway,\11
causing the water to back up, just as the loss of a traffic lane on a
busy highway causes heavy traffic to become congested. This
restriction raises the level of the water both upstream of the levee
and at the levee itself. It also forces the water to flow faster
than it would if it were permitted to spread out across the whole
floodplain. Figure 3.1 depicts a cross-sectional view of a
floodplain and the floodway created by the construction of a levee.
Figure 3.1: Cross Section of a
Typical Floodplain and Floodway
(See figure in printed
edition.)
--------------------
\11 The floodway consists of the river channel and the adjacent
floodplain areas that remain available to convey a flood after a
levee or other structures are built.
IMPACT OF LEVEES ON FLOOD
LEVELS VARIES
-------------------------------------------------------- Chapter 3:1.1
According to the results of a 1994 study conducted by a federal
interagency team, a levee can increase flood levels from a few inches
to several feet. Factors such as the size of the flood, the height
of the levee, and the dimensions of the floodway compared with those
of the natural floodplain account for much of the variation.
The U. S. Army Engineer Waterways Experiment Station, a Corps
research facility, identified the impact of some of these factors in
a 1991 study requested by FEMA.\12 Using a model developed by NWS,
the Corps simulated a range of hypothetical floods and levees for 150
miles along the Missouri River from Jefferson City to Waverly,
Missouri. This portion of the river is lined by mostly small private
and other nonfederal agricultural levees that do not allow for the
floodway recommended by FEMA.\13 These levees are built to varying
heights and, as a result, do not provide a consistent level of
protection. Overall, these levees prevent only small floods--those
with average frequency intervals below 10 years--from entering the
protected floodplain.
The 1991 study found that the impact of levees on flood levels
increases with the size of the flood until the flood is large enough
to overtop the levees. It also estimated that raising the height of
the existing levees to contain the 100-year flood would further
increase flood levels by about 5 inches. Moving the existing levees
back to FEMA's recommended floodway boundary would reduce peak flood
levels for the 100-year flood by an average of about 1.2 to 1.5 feet.
The study concluded that flood levels are more sensitive to the size
of the available floodway than to the height of the levees.
--------------------
\12 Brad R. Hall, "Impact of Agricultural Levees on Flood Hazards,"
U. S. Army Engineer Waterways Experiment Station, Corps of
Engineers, Technical Report HL-91-21 (Vicksburg: Oct. 1991).
\13 FEMA recommends that a floodway be that portion of the floodplain
that, without encroachment from levees and other structures, would
allow a 100-year flood to pass without increasing the water level by
more than 1 foot.
MISSISSIPPI RIVER BASIN
LEVEES CAUSED SOME INCREASES
IN FLOOD LEVELS BUT
GENERALLY PREVENTED DAMAGE
IN 1993
-------------------------------------------------------- Chapter 3:1.2
The results of three studies show that Corps levees and nonfederal
levees contributed to the flood levels experienced during the 1993
flood. These studies used computer modeling to simulate flows and
water levels in part of a river during the 1993 flood, with and
without levees. Observed differences, therefore, can be attributed
directly to the presence of levees. However, the accuracy of a
model's results depends on the accuracy of the information describing
the flood and the floodplain. It also depends on how well
mathematical equations in the model represent actual hydrologic
processes. These studies are the only modeling efforts on the 1993
flood to date and use models created by or accepted by the Corps.
Because of the extremely complex nature of hydrologic computer
models, we did not review the accuracy of the models or their
results.
In 1993, the St. Louis Post-Dispatch commissioned an associate
professor of civil engineering at the University of Illinois to
simulate the 1993 flood. According to the researcher, the simulation
included the Mississippi River beginning just north of St. Louis and
extending 50 miles downstream to Prairie Du Rocher, Illinois. He
used a Corps model that, for simplicity, assumes that floodwaters
flow at a steady rate rather than at varying actual rates.\14 The
simulation estimated that Corps agricultural levees added about 1.0
to 1.5 feet to the flood crest at St. Louis.\15
The flood's crest passed St. Louis just as two large downstream
agricultural levees were being overtopped and the land behind them
flooded. The Post-Dispatch simulation indicates that if these levees
had not been overtopped or if they had been overtopped at another
time, they would have added from 1.4 to 1.8 feet to the crest. This
would have brought the crest to within a foot of the design capacity
of the St. Louis floodwall.
After the 1993 flood, the administration established an interagency
Scientific Assessment and Strategy Team to provide data and an
analysis of the 1993 flood. At the request of the Interagency
Floodplain Management Review Committee, the team simulated the flood.
The simulation included the Mississippi River and major tributaries
from near Hannibal, Missouri, to Cairo, Illinois, and the Missouri
River from Hermann, Missouri, to the mouth at St. Louis, Missouri.
This area contains Corps urban and agricultural levees and smaller
private and other nonfederal levees. The team used a recently
developed model capable of simulating the varying rates of flow that
occur during a flood. The simulation estimated that Corps
agricultural levees added a few inches to 7.3 feet to the flood
crests at 14 locations. For St. Louis, it estimated that the levees
added a maximum of about 1.5 feet to the flood crest.\16 These
results were consistent with the results simulated for the
Post-Dispatch.
The Corps, as part of its 1995 Floodplain Management Assessment,\17
also ran computer simulations of the 1993 flood. Its analysis, which
included the lower Missouri River and the middle and upper
Mississippi River basins, was performed on a systemwide basis using
the model employed by the Scientific Assessment and Strategy Team.
One simulation estimated that agricultural levees added up to 7.2
feet to the flood levels recorded at 11 locations in the Corps' St.
Louis District, including about 2.7 feet at St. Louis. Similarly,
it estimated that agricultural levees added from a few inches to 4.7
feet to the flood levels along the Missouri River with one exception:
Agricultural levees reduced the 1993 flood levels at Hermann,
Missouri, by about 1 foot.
No evidence is available to show the extent of the damage brought
about by the addition to the flood's height attributable to the
levees, but Corps officials acknowledge that damage was caused by the
levees. The Corps also points out that its levees provided
substantial benefits in 1993 by preventing flooding on about 1
million acres in the developed floodplain. The Corps estimates that
its levees in the Kansas City, Omaha, Rock Island, St. Louis, and
St. Paul districts prevented about $7.4 billion in flood damage.
Although unprotected areas within reach of levee backflows are
subject to greater flooding than would occur if no levees existed,
Corps officials believe that the damage prevented by levees greatly
outweighs that induced by levees. In addition, they said that the
capacity of reservoirs to store floodwater compensates for the
increases in flood levels caused by levees. For example, the
Scientific Assessment and Strategy Team found that storing water in
flood control reservoirs reduced the peak flood level at St. Louis
by 5 feet in 1993. Thus, levees and reservoirs at St. Louis
achieved a net reduction in flood levels.
--------------------
\14 The simulation used the Water Surface Profile Program, called
HEC-2, which was developed by the Corps' Hydrologic Engineering
Center, Davis, California. It is primarily used to compute profiles
of water surface levels for complex rivers and streams.
\15 Robert L. Koenig, "The Flood That Wasn't," St. Louis
Post-Dispatch (Dec. 26, 1993).
\16 Science for Floodplain Management into the 21st Century:
Preliminary Report, Scientific Assessment and Strategy Team,
Interagency Floodplain Management Review Committee (Washington, D.C.:
June 1994), pp. 179-86.
\17 Floodplain Management Assessment of the Upper Mississippi River
and Lower Missouri Rivers and Their Tributaries, U.S. Army Corps of
Engineers, (St. Paul, Minnesota: June 1995)
DEBATE CONTINUES OVER LONG-TERM
EFFECTS OF NAVIGATION AND FLOOD
CONTROL STRUCTURES ON FLOOD
LEVELS
---------------------------------------------------------- Chapter 3:2
Levees are one type of navigation or flood control structure that can
affect flood levels. While the impact of levees on a particular
event, such as the 1993 flood, has been estimated with sophisticated
models, the long-term effects of such structures on flood levels in
the Mississippi River basin is less certain. Over the years,
researchers have used trend analysis to assert a relationship between
long-term increases in flood levels and these structures. However,
the value of this analysis is limited by a lack of accurate
information about historic flood flow rates, as well as by the
conflicting results these studies have yielded.
HISTORICAL RECORDS OF FLOODS
ARE NOT ACCURATE
-------------------------------------------------------- Chapter 3:2.1
Much of the research is based on flow rates estimated for extreme
floods at St. Louis. Some of the flow rates for extreme floods in
the historical record are estimates based on observations of water
levels recorded at the time of the floods. Other flow rates in the
historic record are based on methods or equipment now shown to be
inaccurate. In any case, measuring flow rates during extreme floods
is very difficult and sometimes impossible. Not only can a flood
destroy recording equipment, but it can also prevent access to the
best measurement sites. As a result, 7 of the 10 highest flow rates
recorded for St. Louis before 1993 are estimates rather than actual
measurements.
A more accurate and now generally used device for measuring flow, the
Price current meter, was not used exclusively at St. Louis until
1931.\18 Before that time, various methods of measuring flow rates
were used. Some researchers question the accuracy of these methods
for very high flows because of the findings of two studies conducted
at the University of Missouri at Rolla.
The first study, conducted in 1976, found that estimates of very high
flow rates are subject to large errors and that flows above the banks
of the river could not be estimated satisfactorily.\19 The second
study, conducted in 1979, tested the accuracy of measurement devices
used at St. Louis before 1931.\20 Although the author concluded that
most of the pre-1931 measurements were valid for use in analyses, he
found that 57 percent of the test measurements taken for flows above
the banks of the river using double floats\21 exceeded the
measurements taken with a Price current meter by more than 10
percent. Double floats were used at St. Louis from October 1881
through December 1930. On the basis of his findings, the author
recommended that historical estimates of high flow rates be used only
for the relative ranking of floods.
In 1985-86, researchers at the Corps' Waterways Experiment Station
found a further indication of errors in pre-1933 flow rate
information. Using a physical model of the Mississippi River, the
researchers found that they could reproduce the high water marks at
St. Louis for the 1844 and 1903 floods using flow rates 33 percent
and 23 percent lower than historic flow estimates published by USGS.
--------------------
\18 A Price current meter uses a set of rotating cups, which the
river's current turns to indicate the flow's velocity.
\19 Paul Munger, et al., "Lower Mississippi Valley Division
Potamology Study (T-1)," Institute of River Studies, University of
Missouri (Rolla: 1976).
\20 Glendon T. Stevens, Jr., "SLD Potamology Study (S-3),"
University of Missouri (Rolla: 1979).
\21 Double floats were fabricated by joining a surface float to a
subsurface float with twine.
RESEARCHERS' FINDINGS VARY
-------------------------------------------------------- Chapter 3:2.2
Three studies performed during the 1970s analyzed the trends in water
levels for similar flows at specific locations and produced
dissimilar results. In addition, two of the studies used pre-1939
historical data that are of questionable accuracy. Given the data
and/or methodological problems associated with these studies, no
conclusions can be drawn from them about the long-term impact of
navigation structures (such as dikes) or flood control structures
(such as levees) on flood levels. The following paragraphs outline
the results of each study.
In a 1974 study, researchers at Colorado State University addressed
the impact of constructing levees and channelizing the river for
navigation on water levels and flow rates at St. Louis before and
after 1900.\22 Their comparison found that water levels were higher
for all flows above 300,000 cfs, but maximum annual water levels and
average and maximum annual flow rates remained unchanged. They also
found that lower water levels existed after 1900 for all flows below
300,000 cfs. The researchers asserted that the construction of
navigation dikes and levees between 1900 and 1940 caused both
decreases and increases in the water level's relationship to the flow
rates at St. Louis.
Another study, which was published in 1975 by an associate professor
of geology at St. Louis University and was widely cited during the
1993 flood, compared the relationship between maximum annual water
levels and flow rates at St. Louis in 1973 with the same
relationship during a base period from 1861 through 1927. This study
found that the 1973 flow rate of about 851,100 cfs produced a flood
elevation about 7.9 feet higher than it did during the base period.
The researcher attributed the rise in water level per flow rate to a
combination of navigation works, levees, and riverbed sedimentation.
He has since refined his results and attributes about 4 to 5 feet of
the total increase to levees, about 2 to 3 feet to navigation works,
and about 1 foot to riverbed sedimentation.\23
The Corps has questioned the results of both studies because the
studies used the suspect historical data. In addition, a USGS
headquarters hydrologist who specializes in the statistical analysis
of hydrologic information told us that modeling is better than trend
analysis\24 for identifying the effects of navigation dikes and
levees. The USGS hydrologist said that trend analysis can never
prove what caused the changes identified. Thus, changes in water
levels and flow rates that occur after the construction of navigation
dikes and levees may suggest but do not prove that these structures
are the source of the changes.
In 1975-76, researchers from the University of Missouri at Rolla
attempted to study the effects of levees on flood levels.\25 Unlike
the authors of the 1974 and 1975 studies, they used only post-1930
data to avoid questions about the accuracy of historical data. As a
result, they concluded that the Mississippi River had not experienced
enough floods of sufficient size from 1930 through 1976 to evaluate
the effect of levees on floods.
Their study also examined the effect of navigation dikes on water
levels in the middle Mississippi River. They found that changes in
water level per flow rate between 1934 and 1974 at three major
gauging stations were dissimilar. The University of Missouri
researchers concluded that changes in water level per flow rate at
the study gauges showed no association with dike construction. The
study stated that although the constriction of the channel caused by
building an individual dike must have at least a temporary effect on
the relationship between the water level and the flow rate, the
dissimilar findings at the three gauging stations suggest that the
effect may be restricted to the area immediately around the dike.
Therefore, they said data on water levels and flow rates cannot be
extrapolated from a single point of record to an entire reach of the
river.
--------------------
\22 Daryl B. Simons, Stanley A. Schumm, and Michael A. Stevens,
"Geomorphology of the Middle Mississippi River," Engineering Research
Center, Colorado State University (Fort Collins: July 1974).
\23 Charles B. Belt, Jr., "The 1973 Flood and Man's Constriction of
the Mississippi River," Science, Vol. 189, No. 4204 (1975), p.
681.
\24 Trend analysis arranges data along a time line and then measures
changes or movement in the data.
\25 Jerome A. Westphal, Paul R. Munger, and Clifford D. Muir,
"Mississippi River Dikes and Stage-Discharge Relations," Rivers '76,
Vol. II, p. 138.
OTHER FACTORS AFFECT RIVER
FLOOD LEVELS
---------------------------------------------------------- Chapter 3:3
Although floods result from heavy rainfall during a short time or
above-normal rainfall over a long time--sometimes in combination with
snowmelt--this precipitation interacts with the atmosphere, land
topography, vegetation, soils, channel geometry, and human activities
to determine the amount of runoff. The chief determinants of a
flood's peak level at a particular location in a river are the amount
of water reaching the river as runoff, the size and shape of the
river channel, and the size of the floodway. Assessing the impact of
a single factor, such as levees, on water level is very difficult
because hydrologic models can only approximate the complex processes
that move and store water.
Variations in flood levels under like conditions are not uncommon.
According to the Corps, records of the relationship between high
flows and water levels at St. Louis show about a 5-foot variation in
water levels for like flows. For example, two floods passed St.
Louis within a month in the spring of 1983 with similar flows but
with crests whose height differed by 2.7 feet. According to the
Corps, no accurate accounting for this variation exists.
Over time, some of the factors that help determine a flood's peak
level also shift the range of water levels produced by like flows.
Several studies have addressed the factors, both natural and
man-made, that affect flood levels.
MANY NATURAL FACTORS AFFECT
FLOOD LEVELS
-------------------------------------------------------- Chapter 3:3.1
Natural variables that help determine a flood's peak level include
(1) the flood's duration and whether it is rising or receding, (2)
the seasonal level of vegetation in the floodway, (3) the way the
flood carries sediment, and (4) the water's temperature. Long-term
changes in the river's channel from erosion, past floods, and
earthquakes, as well as the growth of vegetation in the floodplain,
particularly in the floodway, also affect peak flood levels.
A 1994 study on the relationship between flow rate and flood level
simulated hypothetical floods of 4.5 days, 9 days, and 13.5 days with
the same peak flow rate through a channel approximating the
Mississippi River at St. Louis.\26 The study found that the speed
with which a flood reaches its peak flow and the duration of that
peak flow help determine the flood's peak water level. For instance,
in 1993, flow rates of 1,030,000 cfs at St. Louis on 2 consecutive
days increased the water level by half a foot on the second day.
According to the Scientific Assessment and Strategy Team's study, the
vegetation in the floodway affects flood levels because it obstructs
and slows the flow of water, causing the water to rise.
Consequently, the water level in an area covered with shrubs and
trees would be higher than in an area covered with grass. Similarly,
the same flood can be higher during the summer than during the late
fall, winter, or early spring because of the summer foliage.
Researchers have found that swiftly moving floodwater can cause
intense erosion and sedimentation. The transport and deposition of
sediment during a flood can increase or decrease water levels at
various locations. In addition, changes in water temperature affect
the amount and shape of sediment in the river. Cold water carries
more sediment and enlarges the size of the sediment particles,
increasing the friction that, over time, can scour the channel and
increase its flood-carrying capacity, reducing all water levels.
--------------------
\26 J.A. Westphal, University of Missouri at Rolla; C.N. Strauser,
U.S. Army Corps of Engineers; and D.B. Thompson, Texas Tech
University, "Single-Valued Rating Curves," unpublished manuscript
(Rolla: 1994).
HUMAN ACTIVITIES AFFECT
FLOOD LEVELS
-------------------------------------------------------- Chapter 3:3.2
Floodplains reduce flood levels by providing space for the temporary
storage of floodwaters until natural drainage can carry them away.
They also reduce flood velocities. In addition to flood control,
human activities in the last 175 years in agriculture, navigation,
and urban development have altered the floodplains in the upper
Mississippi River basin. These activities have altered water flow
rates, the width and depth of the river channel, the size of the
floodway, the pattern of erosion and sedimentation, the level of
vegetation, and the speed with which precipitation flows into
streams.
CHANGES FOR AGRICULTURE
------------------------------------------------------ Chapter 3:3.2.1
Early development in the upper Mississippi River valley was closely
tied to the rivers. By the late 1800s, settlers had cleared millions
of acres in the floodplain for cultivation. Vegetation in the
unaltered floodplain, especially in wetlands, created resistance to
flow. Researchers have shown with modeling that removing resistance
reduces flood levels and increases flow velocities and erosion. They
speculate that clearing the floodplain for agriculture had the same
effects.
Between 1780 and 1980, an estimated 57 percent of the original
wetlands in the nine midwestern states affected by the 1993 flood
were converted to other uses, mainly agriculture. Wetlands
temporarily store and hold some floodwater for later drainage.
According to the 1994 report from the Interagency Floodplain
Management Review Committee, the loss of wetlands contributes to
higher flood levels for smaller, more frequent floods, like 25-year
or smaller floods.\27
Agricultural land management practices affect the processes of
erosion, sedimentation, and runoff. For example, the Illinois
Natural History Survey found that planting crops in rows and plowing
with moldboards (which lift and turn the soil) increased the rate at
which Illinois lakes were filling with sediment. Although
researchers have observed the influence of agricultural land
management practices on small watersheds, the influence of these
practices on major rivers is still largely speculative.
--------------------
\27 Sharing the Challenge: Floodplain Management into the 21st
Century, Interagency Floodplain Management Review Committee
(Washington, D.C.: June 30, 1994).
CHANGES FOR NAVIGATION
------------------------------------------------------ Chapter 3:3.2.2
Travel to and commerce with early settlements along the rivers
created a demand for improved navigation on the rivers. The Congress
first approved a plan for improving the Mississippi River's channel
in 1881. However, most channel improvements for navigation on the
Mississippi and Missouri rivers were made between 1927 and 1944. The
improvements generally narrowed the natural channels and shortened
the rivers.
The Corps has constructed about 3,100 wing dikes to create and
maintain navigation channels on the Mississippi and Missouri rivers.
Wing dikes are embankments built in the river perpendicular to the
shoreline to increase channel depths by reducing channel widths and
increasing flow rates. The dikes help keep sediment from
accumulating in the main channel and trap it along the shoreline.
The previously cited 1974 Colorado State University study found that,
between 1888 and 1968, wing dikes decreased the average width of the
middle Mississippi River by 2,100 feet, or by about 40 percent. The
report also stated that degradation of the riverbed has occurred
along the middle Mississippi River whenever the channel has been
narrowed.\28
The Corps also stabilizes and dredges hundreds of miles of river bank
and channel, respectively, to maintain open water navigation on the
Missouri and Mississippi rivers. Stabilizing the banks reduces
shoreline erosion, and dredging deepens the channel. In addition,
the Corps has built and operated a system of locks and dams on the
upper Mississippi River since the 1930s. This system converted the
upper river into a series of pools to maintain channel depths at low
and normal flows. A 1988 study of the long-term effects of the
oldest lock and dam on the upper Mississippi River found that
initially the river's width and volume had increased behind the dam.
However, the long-term impact has been to trap sediment. As a result
the river has steadily lost both width and volume and returned to
near pre-dam water levels and flow.\29
--------------------
\28 Simons, Schumm, and Stevens, "Geomorphology of the Middle
Mississippi River".
\29 J.W. Grubaugh and R.V. Anderson, "Long-Term Effects of
Navigation Dams on a Segment of the Upper Mississippi River,"
Research and Management, Vol. 4 (1989), p. 97.
CHANGES DUE TO URBAN
DEVELOPMENT
------------------------------------------------------ Chapter 3:3.2.3
Studies have shown that the growth of urban areas increases the speed
of water running off the land into streams. Rain that falls on
paved, tiled, or other impervious surfaces and runs into storm
drainage systems is delivered to streams more quickly than it could
run off porous surfaces. Hence, urban runoff produces higher,
sharper flood peaks on small rivers and streams than rural runoff.
However, as the water from each small stream joins the water in
larger streams, the effects of urbanization on flood levels are
diluted. One expert told us that researchers have not been able to
measure the impact of urban development on the flooding of the
Mississippi or Missouri rivers because the effects of urbanization
are too small to isolate.
THE UPPER MISSISSIPPI RIVER
BASIN MAY HAVE TO CONTEND WITH
INCREASING FLOOD DAMAGE
---------------------------------------------------------- Chapter 3:4
Recent analyses show that water levels for high flows may be
increasing for some locations in the upper Mississippi River basin.
A continuing Corps study of Missouri River water levels shows that
flow rates that once nearly filled the channel have been producing
higher flood levels since the late 1920s. Similarly, a 1994 study of
flow rates on the Mississippi and Missouri rivers found that flood
levels for like flow rates have increased over time. Evidence also
suggests that precipitation in the upper Mississippi basin may be
increasing. These trends concern the Corps because they increase the
frequency and extent of flooding, thereby increasing the damage from
flooding.
WATER LEVELS AT HIGH FLOW
RATES ARE INCREASING
-------------------------------------------------------- Chapter 3:4.1
According to the Corps' Missouri River Division, seven of nine gauges
on the Missouri River have slowly and consistently produced higher
water levels for the same high flow rates since about 1927. The
rising trends are most noticeable at Nebraska City and Omaha,
Nebraska, and at St. Joseph, Missouri. Table 3.1 shows the
approximate increases in water levels for selected high flow rates.
Table 3.1
Approximate Increases in Missouri River
Water Levels at High Flow Rates
Period Increase
of Flow in water
analysis rate level
Location of gauge (years) (cfs) (feet)
---------------------------- -------- -------- ----------
Bismarck 53 40,000 2
Omaha 62 100,000 6
Nebraska City 63 100,000 7
St. Joseph 66 100,000 6
Waverly 59 200,000 4
Boonville 64 200,000 3
Hermann 52 400,000 4
------------------------------------------------------------
Source: GAO's presentation of data from the Corps.
Statistical studies performed in 1994 at the Environmental Management
Technical Center at Onalaska, Wisconsin, also examined water levels
and flow rates for the period of record at six gauges: St. Louis,
Chester, and Thebes on the Mississippi River; and St. Joseph,
Waverly, and Hermann on the Missouri River.
The studies found that water levels for like flood-level flow rates
have been increasing at all six gauges at an average of about 1.2
inches annually. Over the periods of record, which range from 51
years at Chester to 132 years at St. Louis, increases in water
levels at the six gauges ranged from about 3 to 9 feet.\30 Table 3.2
shows the approximate increase at each gauge.
Table 3.2
Approximate Increases in Water Levels at
High Flow Rates for Six Gauges on the
Mississippi and Missouri Rivers
Period Increase
of Flow in water
record rate level
Location of gauge (years) (cfs) (feet)
---------------------------- -------- -------- ----------
St. Joseph 62 140,000 7.5
Waverly 62 220,000 5.5
Hermann 62 385,000 4.0
St. Louis 132 780,000 9.0
Chester 51 780,000 5.0
Thebes 59 780,000 3.0
------------------------------------------------------------
Source: GAO's presentation of data from the National Biological
Service (Onalaska, Wis.).
The studies also found that, except at Thebes, the trend for maximum
annual water levels is increasing. The studies found no changes in
trends for flow rates.
--------------------
\30 Joseph H. Wlosinski, "Discharges and Water Levels During Floods
on the Upper Mississippi and Lower Missouri Rivers," unpublished
manuscript, Environmental Management Technical Center (Onalaska,
Wis.: Nov. 1994).
THE CLIMATE OF THE UPPER
MISSISSIPPI RIVER BASIN MAY
BE CHANGING
-------------------------------------------------------- Chapter 3:4.2
According to the 1994 Natural Disaster Survey Report issued by NWS,
the duration and size of the 1993 Midwest flood and the wet
conditions leading up to it suggest a significant variation in
climate. An air circulation feature, called El Ni�o/Southern
Oscillation, driven by abnormal sea surface temperatures occurred in
both 1992 and 1993. Preliminary NWS modeling using the temperatures
associated with the El Ni�o episode produced large-scale atmospheric
results resembling the abnormal precipitation and temperature pattern
experienced in 1993. However, NWS stated that it requires more
in-depth and thorough analyses to understand the role played by El
Ni�o in the extreme precipitation.
According to a 1993 report on the Midwest flood by the Illinois State
Water Survey, increases in the volume of water flowing down the
Mississippi River are most closely related to the overall climate and
precipitation. The report states that climate and resulting
precipitation exert such a strong impact on streamflow that it masks
changes from other sources, such as physical changes to the basin.\31
The Illinois State Water Survey reports that, for most locations
along the Mississippi River, average streamflows for the 28-year
period since 1965 have been the highest on record. On the basis of
an 11-year moving average, the Survey calculated that average flow
rates at Clinton and Keokuk, Iowa, and St. Louis, Missouri, have
increased by about 25 to 33 percent over the long-term average since
the mid-1960s. An 11-year moving average is used to describe the
trend because it smooths out natural fluctuations in the data. Also,
average streamflows at Keokuk and St. Louis between 1965 and 1992
are about 17 and 13 percent, respectively, above the long-term
average streamflows based on over 100 years of record. Average
streamflows for the same period for the tributaries between Clinton
and Keokuk, Iowa, for the Des Moines River, and for the Illinois
River are even further above their long-term average streamflows.
According to officials of the Survey, these deviations are
significant because, historically, average streamflow has remained
remarkably consistent with long-term average streamflow.
USGS headquarters officials cautioned that because weather is
cyclical and variable, any trends in climate are difficult to
distinguish from normal weather cycles of higher precipitation and
drought.
--------------------
\31 Nani G. Bhowmik, et al., "The 1993 Flood on the Mississippi
River in Illinois," Illinois State Water Survey, Misc. Pub. 151
(Champaign, Ill.: 1994)
RISING WATER LEVELS ARE
CAUSING CONCERN
-------------------------------------------------------- Chapter 3:4.3
For the 10-year period from 1983 through 1992, NWS estimates that
damage to the United States from flooding totaled about $20.5
billion, or an average of about $2.1 billion annually, unadjusted for
inflation. With the inclusion of data for 1993, the total estimated
flood damage became $36.9 billion, or about $3.4 billion annually
over the 11-year period.
According to the Corps, upward trends in water levels are of concern,
whether they are caused by increased streamflow or by higher water
levels for the same flow rates, because they increase the frequency
of flooding and the area subjected to flooding. For instance,
between 1928 and 1959, flows of 100,000 cfs at St. Joseph, Missouri,
never exceeded water levels of 17 feet, the official level at which
flooding begins. Since 1959, flows of 100,000 cfs have exceeded
flood level 16 times. If changes in the climate of the upper
Mississippi River basin increase precipitation in the future and if
water levels for like flow rates continue to rise, then the damage
from flooding will rise unless the ability of flooding to cause
damage is mitigated.
THE INTERAGENCY FLOODPLAIN
MANAGEMENT REVIEW COMMITTEE
ADDRESSES LEVEES
-------------------------------------------------------- Chapter 3:4.4
The administration's Interagency Floodplain Management Review
Committee was formed to identify the major causes and consequences of
the 1993 Midwest flood, evaluate the performance of existing
floodplain management programs, and recommend changes that make the
programs more effective. Among the Committee's findings and
recommendations are many related to flood control activities,
particularly levees. See appendix VI for a summary.
CONCLUSIONS
---------------------------------------------------------- Chapter 3:5
That levees increase flood levels is subject to little disagreement.
Whether this increase is significant varies from location to
location, but whether unprotected lands are more likely to be flooded
than protected lands depends on the increase in flood levels after
the construction of a levee. Proponents of levees point out that the
impact of a levee should not be isolated because the net effect of
all flood control projects has been to reduce flood levels and
prevent billions of dollars in flood damage.
Levees are only one of many natural and man-made factors that help
determine the peak level of a flood. Cumulative changes within the
upper Mississippi River basin have caused higher water levels for
similar flows. These trends could mean that the damage from flooding
may increase in the future because higher water levels are associated
with more frequent and more extensive flooding.
FEDERAL, STATE, AND LOCAL
GOVERNMENTS EXERCISE SOME CONTROL
OVER NONFEDERAL LEVEES
============================================================ Chapter 4
No federal program regulates the design, placement, construction, or
maintenance of nonfederal levees.\32 However, the federal government
can exercise some control over nonfederal levees through programs
that regulate navigable waters and wetlands and that provide flood
insurance and disaster and emergency assistance.
Overall, 17 of the 50 states have specific programs for regulating
levees. Five of the nine states involved in the 1993 flood have
regulatory programs that, to varying degrees, affect nonfederal
levees. Most often, states are responsible for the overall
coordination of floodplain management activities within the state and
across state lines. In some cases, states may regulate local land
use when localities are unable or unwilling to take the actions
needed to reduce the risk of flooding.
Local governments usually exercise control over nonfederal levees in
response to requirements of the National Flood Insurance Program\33
and state regulatory programs. However, in states without a
regulatory program, local land use regulations generally affect the
placement and construction of levees.
--------------------
\32 Nonfederal levees are those that are not built, maintained, or
operated by the federal government. Some nonfederal levees may
qualify for repairs under federal programs if they have been damaged
by flooding.
\33 The National Flood Insurance Program, administered by FEMA, is a
major component of the federal government's effort to provide
flood-related disaster assistance. The National Flood Insurance Act
of 1968, as amended (P.L. 90-448), established the program to
identify flood-prone areas, make insurance available to property
owners in communities that join the program, and encourage floodplain
management efforts to mitigate flood hazards.
SOME FEDERAL CONTROL OF
NONFEDERAL LEVEES EXISTS UNDER
FEDERAL PROGRAMS
---------------------------------------------------------- Chapter 4:1
Nonfederal levees are regulated to some extent under two federal
programs that require permits to construct or modify levees affecting
navigable waters and wetlands.\34 In addition, the programs of three
federal agencies that provide flood insurance and emergency and
disaster assistance to repair flood-damaged levees affect nonfederal
levees.
Under the National Flood Insurance Program, FEMA exempts communities
from certain requirements of the flood insurance program if they can
show that the levees protecting them are designed, constructed,
located, and maintained according to specified criteria.
As part of its mission to provide disaster assistance, the Corps is
authorized to repair levees through its levee rehabilitation
program.\35 The Department of Agriculture's Natural Resources
Conservation Service (NRCS) provides funds and technical assistance
for the emergency repair of nonfederal levees that are damaged during
a flood.
In all of these programs, the federal government exercises some
direct or indirect control over the nonfederal levees' design,
placement, construction, or maintenance. However, all of these
elements are not always affected by each program. Table 4.1 lists
the federal programs affecting levees, and table 4.2 shows whether
these programs affect a nonfederal levee's design, placement,
construction, or maintenance.
Table 4.1
Federal Programs and Types of Levees
Affected
Federal program Types of levees affected
----------------------------- -----------------------------
Section 10, Rivers and All proposed levees that may
Harbors Appropriation Act of obstruct or alter navigable
1899 U.S. waters.
Section 404, Clean Water Act All proposed levees in U.S.
waters, including wetlands.
FEMA's National Flood Levees certified as providing
Insurance Program protection from a 100-year
flood.
Corps' Levee Rehabilitation Damaged nonfederal levees
Program that have met the Corps'
standards for the program and
have drainage areas that
exceed 400 square miles.
NRCS' Emergency Watershed Damaged levees designed to
Protection Program protect agricultural drainage
areas of less than 400 square
miles or critical
infrastructure in
agricultural areas.
------------------------------------------------------------
Table 4.2
Federal Programs and Levee Elements
Affected
Desi Placemen Constructi Maintenanc
Program gn t on e
-------------------- ---- -------- ---------- ----------
Section 10, Rivers Yes Yes Yes No
and Harbors
Appropriation Act of
1899
Section 404, Clean Yes Yes Yes No
Water Act
FEMA's National Yes Yes Yes Yes
Flood Insurance
Program
Corps' Levee No\a No No\a Yes
Rehabilitation
Program
NRCS' Emergency No No No Yes
Watershed Protection
Program
------------------------------------------------------------
\a Design and construction are involved if the levee must be modified
to meet conditions of the rehabilitation program.
--------------------
\34 The regulatory programs are administered by the Corps under
section 10 of the Rivers and Harbors Appropriation Act of 1899 (33
U.S.C. 403) and section 404 of the Clean Water Act (33 U.S.C.
1344).
\35 This Corps program is authorized under section 5 of the Flood
Control Act of 1941, as amended (P.L. 84-99).
LEGISLATION REQUIRES PERMITS
FOR CERTAIN LEVEES
-------------------------------------------------------- Chapter 4:1.1
Section 10 of the Rivers and Harbors Appropriation Act of 1899
prohibits the obstruction or alteration of navigable U.S. waters
without a permit from the Corps. Section 404 of the Clean Water Act
requires a permit from the Corps when wetlands are to be altered.
Under both of these authorities, the Corps may control the design,
placement, and construction of a nonfederal levee when the levee
affects areas regulated by these programs. However, the owner,
sponsor, or builder is responsible for informing the Corps of the
intent to construct a levee and for obtaining a permit. The Corps'
data do not indicate how many of the 15,000 permits requested for
activities in wetlands or navigable waters in fiscal year 1994 were
for constructing or modifying levees.
For the 1993 flood, the Corps issued a nationwide permit for the
construction of temporary levees and emergency repairs to levees.
This permit encompassed U.S. waters--including rivers, streams,
lakes, and wetland areas--in the counties that had been declared
flood disaster areas. The permit was specific and identified
conditions where it applied. For example, the permit required any
levee that was reconstructed or repaired to be maintained after the
flood. Since some levees were being constructed in new locations,
the Corps could also require that the former location of the levee be
restored to its previous condition. The permit also required that
any temporary levees built must minimize damage to U.S. waters and
that measures must be taken to maintain near-normal downstream flows.
Furthermore, all levees were to be designed and constructed so as to
prevent the channel from being constricted or redirected and erosion
from occurring upstream or downstream.
CORPS' REGULATORY
AUTHORITY MAY EXTEND TO
ADDITIONAL NONFEDERAL
LEVEES
------------------------------------------------------ Chapter 4:1.1.1
Section 10 prohibits the obstruction of the navigable capacity of
waters of the United States without a permit from the Corps. To
clarify the extent of the Corps' authority to regulate levees under
this section, we asked the Corps to provide its interpretation of
this authority. Specifically, we asked whether the Corps has the
authority to regulate upland\36 nonfederal levees. Currently, these
levees are not regulated by the Corps.
In a November 1994 response, the Chief Counsel of the Corps indicated
that the Corps might be able to assert jurisdiction over upland
nonfederal levees on the basis of section 10. While this provision
prohibits the obstruction of the navigable capacity of waters of the
United States, it also prohibits the alteration or modification of
the course, location, condition, or capacity of "any navigable water
of the United States unless recommended by the Chief of Engineers and
authorized by the Secretary of War" before work begins.
From his review of court cases dealing with section 10, the Chief
Counsel opined that a prerequisite to the Corps' exercising
jurisdiction would be circumstances demonstrating an alteration or
modification of the course, location, condition, or capacity of
navigable U.S. waters. However, he noted that a court might require
that jurisdiction be founded on a negative effect and that, arguably,
nonfederal levees have an essentially beneficial effect on navigable
capacity.
The Chief Counsel concluded that if the Corps exercised jurisdiction
over upland federal levees under section 10 without clear authority
and direction from the Congress, this action would likely be
overturned upon appeal to the federal courts.
--------------------
\36 Upland refers to areas on land above the mean high tide line for
tidal waters or the ordinary high water mark of other navigable
waters that do not include U.S. waters such as wetlands.
THE NATIONAL FLOOD INSURANCE
PROGRAM IMPOSES REQUIREMENTS
FOR LEVEES
-------------------------------------------------------- Chapter 4:1.2
FEMA administers a levee certification program under the auspices of
the National Flood Insurance Program. To be certified and to enable
communities to enact less stringent building codes, levees must meet
FEMA regulations specifying design, placement, construction, and
maintenance standards. In all cases, the levee must, at a minimum,
protect against a 100-year flood and, in most cases, have at least 3
feet of height (or freeboard) above the 100-year level of protection.
When FEMA maps a community, it designates the 100-year floodplain and
floodway. When a community joins the insurance program, it must
require that all buildings constructed or substantially improved be
protected to the base flood elevation.\37 This is usually
accomplished by elevating the structure above the base flood
elevation or, in some instances, by floodproofing. While increasing
construction costs, these requirements make buildings more resistant
to flood damage. FEMA officials said that experience confirms that
elevated buildings are less susceptible to flood damage and,
therefore, cost less to repair when a flood occurs. When FEMA
certifies a levee as protecting against a 100-year flood, it exempts
new construction and substantial improvements from the requirement to
build above the base flood elevation. The effect of this exemption
is to increase the costs of repairing buildings that are more
susceptible to flood damage because they are not elevated.
--------------------
\37 The base flood elevation is the height that a 100-year flood
would reach. A 100-year flood is the flood that has a 1-percent
probability of being equaled or exceeded in any given year.
CORPS' PROGRAM REPAIRS
FLOOD-DAMAGED LEVEES
-------------------------------------------------------- Chapter 4:1.3
The Corps will repair, on a cost-shared basis, nonfederal levees that
are damaged by floods if the levees meet the qualifying standards of
the program and are in good standing with the program at the time of
flooding. In order to be accepted into the Corps' rehabilitation
program for damaged nonfederal flood control levees, a sponsor's
levee must meet or be improved to meet the Corps' minimum design
standards before flood damage occurs. The owner may need to modify
the levee in order for the levee to be admitted to the program. Once
in the program, the levee must be maintained in accordance with the
Corps' criteria.
For levees that have qualified, the Corps provides 80 percent of the
repair costs and the levee's sponsor pays the rest. To qualify, the
levee must (1) be publicly sponsored to ensure that the 20-percent
share can be paid, (2) be a primary levee providing a 10-year level
of protection for urban areas and a 5-year level of protection for
agricultural areas, (3) be properly maintained and regularly
inspected, and (4) provide benefits that equal or exceed the cost of
the levee's repair. The rehabilitation program includes levees
maintained by local sponsors, such as levee districts, individual
municipalities, or Indian tribes.
The Corps received 546 requests for assistance under the levee
rehabilitation program after the 1993 flood. Of these requests, as
many as 345 either were declared ineligible for assistance because
the levees did not meet the basic requirements identified above or
had been repaired under other disaster assistance programs, such as
NRCS' program. As of October 1994, the Corps estimated that the
costs of repairing the 201 levees that met its established criteria
would be $250 million.
Also, during 1993, the Corps worked with the Department of Commerce's
Economic Development Administration (EDA) to identify and repair
levees that were deemed to affect the economic development of the
community where the levee was located. The Corps assisted EDA in
assessing the levees that had not qualified for the Corps' program in
advance primarily because they lacked public sponsorship. Because
one of EDA's missions is to provide economic assistance to areas
experiencing sudden and severe economic distress, the agency provided
funding on a cost-shared basis to repair levees that protect critical
public infrastructure.
Working with the Corps, EDA reviewed all applications and funded
those that identified local sponsors to share costs and maintain the
levees. EDA has funded the repair of 13 levees at a cost of about
$4.2 million.
NRCS' PROGRAM AFFECTS SOME
NONFEDERAL LEVEES
-------------------------------------------------------- Chapter 4:1.4
NRCS' Emergency Watershed Protection Program, authorized by the
Agricultural Credit Act of 1978 (P.L. 95-334), funds repairs to
levees. To be eligible for these funds, the levee project must
protect property threatened by a watershed emergency and the owner
must either have exhausted, or lack, the funds needed to remedy the
problem. To be eligible for assistance after the 1993 Midwest flood,
potential applicants were also required by NRCS to show that the
levee restoration project protected property or life, that benefits
exceeded the costs of repair, and that regular maintenance would be
performed. Since the program supports the repair of nonfederal
levees to their preflood condition, it does not control the original
design, placement, or construction of nonfederal levees. However,
because regular maintenance is required for future assistance, the
program does set maintenance standards.
NRCS also received funding in a 1994 supplemental appropriation\38 to
make repairs to levees otherwise ineligible for assistance on
condition that a sponsor share the cost and that the levee qualify
for the Corps' levee rehabilitation program. The levee also had to
be environmentally sound and provide a 5-year level of protection.
While NRCS' Emergency Watershed Protection Program provides for a
smaller proportion of the funding for repairs than the Corps' levee
rehabilitation program (75 percent versus 80 percent), NRCS would
provide 100 percent of the funding in the case of extreme need or
hardship on the part of the levee sponsor. As of February 1, 1995,
NRCS had approved repairs for 375 levees at a cost of $10.2 million
under the Emergency Watershed Protection Program. NRCS had also
determined that 16 levees were eligible for repairs, costing a total
of $650,000, under the supplemental appropriation for fiscal year
1994. NRCS officials reported the agency is evaluating repairs for
26 more levees under the supplemental appropriation. Some of these
repairs were for levees whose drainage area exceeded NRCS' threshold
of 400 square miles and would, therefore, normally have fallen under
the Corps' levee rehabilitation program. However, NRCS was given the
responsibility for repairing these levees under the supplemental
appropriation.
--------------------
\38 Emergency Supplemental Appropriations Act of 1994 (P.L.
103-211).
SOME STATES REGULATE NONFEDERAL
LEVEES
---------------------------------------------------------- Chapter 4:2
In 1992, the Association of State Floodplain Managers issued a
report\39 documenting the scope of floodplain management programs in
the states and found that 17 states regulate levees as part of their
floodplain management programs. Of the nine states involved in the
1993 flood, five states (Iowa, Kansas, Minnesota, North Dakota, and
Wisconsin) have programs to regulate levees. These programs have
standards regulating the design, construction, placement, and
maintenance of levees. We judgmentally selected Iowa as an example
of a state that regulates its levees.
--------------------
\39 Floodplain Management 1992: State and Local Programs,
Association of State Floodplain Managers, Inc. (Madison, Wis.:
1992). The data in this report are from 1991 and were being updated
at the time of our review.
IOWA HAS A REGULATORY
PROGRAM FOR LEVEES
-------------------------------------------------------- Chapter 4:2.1
Iowa's program for regulating levees addresses the design, placement,
construction, and maintenance of nonfederal levees. The program,
which is described in Iowa's statute on floodplain management, is
administered by the state's Environmental Protection Division within
the Department of Natural Resources and has been in existence since
at least 1967.
In general, Iowa requires permits to construct, operate, and maintain
levees in rural areas where the watershed drainage area exceeds 10
square miles and in urban areas where the watershed drainage area
exceeds 2 square miles. Specific requirements must be met to comply
with the statute's criteria for level of protection, placement,
interior drainage, freeboard, or design. For example, Iowa requires
agricultural levees, at a minimum, to protect against a 10- to
25-year flood and urban levees to protect against a 100-year flood.
Urban levees must provide at least 3 feet of freeboard above the
design flood profile. Furthermore, any agricultural levee whose
protection level is increased must comply with the state's equal and
opposite conveyance rule: An increase in the levee on one side of a
river's floodplain cannot cause a disproportionate increase in the
flooding of the river's opposite floodplain.
Iowa officials told us that only one FEMA regulation more strictly
controls levees. Under this rule, development within FEMA's
identified 100-year floodway cannot increase the area designated as
the 100-year floodway. The effect of this rule is that agricultural
levees may be placed farther away from the river than the equal and
opposite conveyance rule may initially require.
SOME STATES HAVE NOT YET
ESTABLISHED REGULATORY
PROGRAMS FOR NONFEDERAL
LEVEES
-------------------------------------------------------- Chapter 4:2.2
Of the nine states involved in the 1993 flood, four (Illinois,
Missouri, Nebraska, and South Dakota) have yet to develop specific
regulatory programs for levees. All of these states have a
floodplain management program that may (1) provide technical
expertise to localities and individuals on complying with FEMA's or
other federal agencies' requirements, (2) regulate local land use
when localities are unable or unwilling to take needed actions to
reduce the risk of flooding, or (3) coordinate local and regional
floodplain management programs. We judgmentally selected Missouri as
an example of a state that does not regulate levees.
Missouri does not currently regulate its levees but has identified
areas of its floodplain management program that need to be improved.
A task force established by Missouri's governor to review and
evaluate the state's floodplain management program recommended the
development of a levee oversight program to help decrease the risk to
life and property from flooding.
The task force recommended in a July 1994 report that Missouri (1)
adopt a permit program for constructing and modifying levees; (2)
identify all existing levees for the purpose of developing design
criteria and policy guidelines; (3) determine the need for setbacks,
relocations, and construction standards; and (4) enact legislation
that would make it easier for levee districts to form and obtain
public sponsorship for participation in the Corps' levee
rehabilitation program. As of June 1995, the Missouri General
Assembly had not yet enacted these recommendations into law.
LOCAL GOVERNMENTS OFTEN
EXERCISE CONTROL OVER
NONFEDERAL LEVEES THROUGH
FLOODPLAIN REGULATIONS
---------------------------------------------------------- Chapter 4:3
Local governments generally exercise more control over local
floodplains and levees than do the states or the federal government.
This is often because FEMA requires the adoption of community
floodplain regulations as a condition for joining its flood insurance
program. The 1992 report by the Association of State Floodplain
Managers noted that every state has granted its localities enough
authority to meet the regulatory requirements of FEMA's flood
insurance program. As a result, localities may enact ordinances that
allow them to (1) require certain building codes for development in
the floodplain, (2) issue zoning regulations describing the types of
land uses permitted in the floodplain, or (3) require that
development incorporate improvements to alleviate potential flood
hazards.
Two exceptions to this local authority exist, however: First, most
localities cannot regulate federal or state property or development
by other localities, and, second, some states have exempted from
local control certain activities that are important to the state's
economy (i.e., transportation, agriculture, mining). Under these
exceptions, a local government could be prevented from exercising
control over a nonfederal levee if, for example, the state determined
that such control would negatively affect the economy of the river's
transportation industry.
In a state that regulates levees, the locality is generally required
to enforce and comply with the state's standards for the design,
placement, construction, and maintenance of levees. For example, in
Iowa, local regulations must meet state requirements. In Minnesota,
the state government may directly regulate levees and enforce
compliance if the local government does not.
In states that do not regulate levees, such as Missouri, local
governments are bound by the standards of FEMA's flood insurance
program if the community participates in the program. According to
the city engineer in St. Louis, the city complies with FEMA's
standards for floodplain management but has not established local
levee regulations.
INTERAGENCY COMMITTEE CALLS FOR
BETTER STATE REGULATION OF
NONFEDERAL LEVEES
---------------------------------------------------------- Chapter 4:4
As part of its review of floodplain management in the aftermath of
the 1993 flood, the Interagency Floodplain Management Review
Committee reported that few states control the design, placement,
construction, and maintenance of nonfederal levees. As explained in
detail in appendix VI, the Committee found that the states'
involvement in many floodplain management activities--including
issuing permits for levees, flood-fighting, and repairing levees--was
highly variable and in need of enhancement. The Committee
recommended that the states assume responsibility for regulating the
location, alignment, design, construction, upgrading, maintenance,
and repair of levees and flood-fighting at levees.
CONCLUSIONS
---------------------------------------------------------- Chapter 4:5
While no comprehensive federal program regulates the design,
placement, construction, or maintenance of nonfederal levees, control
over nonfederal levees is exercised through various federal programs
for regulating navigable waters and wetlands and for providing flood
insurance and disaster and emergency assistance. Not all aspects of
levees are regulated in every program, and not all nonfederal levees
are affected.
Five of the nine states involved in the 1993 flood have regulatory
programs that, to varying degrees, affect the design, placement,
construction, or maintenance of nonfederal levees. Most often,
states are responsible for the overall coordination of floodplain
management activities within the state and across state lines, and
local governments exercise direct control over levees through
land-use regulations. Local governments often impose regulations to
comply with the requirements of the National Flood Insurance Program
and state regulatory programs.
SCOPE AND METHODOLOGY
=========================================================== Appendix I
We conducted our work at the Corps' headquarters in Washington, D.C.,
and district offices in Rock Island, Illinois; St. Louis and Kansas
City, Missouri; and Omaha, Nebraska. We also performed work at USGS'
headquarters in Reston, Virginia, and field offices in Independence
and Rolla, Missouri and Urbana, Illinois; NWS' headquarters in Silver
Spring, Maryland, and field office in Pleasant Hill, Missouri; FEMA's
headquarters; NRCS' headquarters and field office in Champaign,
Illinois; and the Interagency Floodplain Management Review Committee
in Washington, D.C. We visited various groups, such as the
Association of State Floodplain Managers in Richmond, Virginia, and
the National Wildlife Federation in Washington, D.C., and state
government offices, such as the Missouri Department of Natural
Resources and the Illinois State Water Survey. At these locations
and others, we interviewed federal officials, state government
representatives, university researchers, and others knowledgeable
about the 1993 flood. We also contacted a variety of local and state
government officials, associations, businesses, and individuals in
the flooded area.
To determine to what extent federal levees prevented flooding and
related flood damage, we collected data from the Corps and USGS on
the design capacity of the levees and the flows and water levels of
the 1993 flood to analyze how well the levees were able to withstand
the flood. The numbers for the actual flood flows and levels, which
we compared with the levees' design capacity, are based on our
analysis of the best and/or nearest gauge data available from USGS or
the Corps. We compared the number of acres protected by each federal
levee with the number of acres flooded when the levees were
overtopped or breached to estimate the extent to which federal levees
prevented flooding. We collected and analyzed Corps data on the
damage incurred after levees failed, as well as on the damage
prevented by federal levees that withstood the flood. We interviewed
Corps officials about instances when the flood exceeded the levees'
design capacity and discussed the reasons why some levees were
overtopped or breached.
To determine whether levees contributed to the record flood heights
and increased flood damage, we solicited the opinions of 26 experts
representing the Corps, NWS, USGS, FEMA, the State of Illinois, and
the Universities of Illinois and Missouri at Rolla. We also spoke
with other individuals concerned with the effects of levees on
flooding. In addition, we reviewed books and studies containing
information relevant to the effect of levees on flooding.
To describe federal, state, and local control over the design,
construction, placement, and maintenance of nonfederal levees, we
gathered information from sources at each level of government. To
obtain information on federal control over nonfederal levees, we
interviewed officials from the Corps, FEMA, NRCS, and EDA on the
federal programs that may control the design, placement,
construction, and maintenance of nonfederal levees. We interviewed
Corps officials about the applicability of section 10 of the Rivers
and Harbors Appropriation Act of 1899 and section 404 of the Clean
Water Act to the levees and requested a legal opinion from the Corps
on the applicability of these sections to nonfederal levees. From
the Corps, FEMA, NRCS, and EDA, we collected information on the
repair of nonfederal levees. We analyzed a FEMA data base that
identified the levees certified by FEMA in the area affected by the
flood.
To learn what state controls exist over nonfederal levees, we
interviewed representatives of the Association of State Floodplain
Managers, floodplain managers for the states of Iowa and Missouri,
and the Interagency Floodplain Management Review Committee and
reviewed information on the states' regulation of levees. We also
reviewed information on the programs that regulate levees in the five
states involved in the flood that have programs.
To obtain information on local controls over nonfederal levees, we
interviewed state officials in Iowa and Missouri; local officials in
St. Louis and Chesterfield, Missouri; and the Chairman of the
Association of State Floodplain Managers. We also interviewed
officials of FEMA and reviewed documents on the role of the National
Flood Insurance Program in establishing controls over nonfederal
levees.
LIST OF 12 CORPS LEVEES FOR WHICH
DATA WERE NOT SUFFICIENT TO
COMPARE LEVEE DESIGN CAPACITY WITH
FLOOD FLOW
========================================================== Appendix II
District/levee project River or stream
------------------------------ ----------------------------
Rock Island District
------------------------------------------------------------
Worthington Illinois
Lost Creek Illinois
Valley Illinois
Galena Galena
Volga Volga
Omaha District
------------------------------------------------------------
Broken Bow Mud Creek
Hawarden Dry Creek
Macy Blackbird Creek
Kansas City District
------------------------------------------------------------
MRLU R-351, Sec. 2 Little Blue
Abilene Mud Creek
Gypsum Gypsum
Stonehouse Creek Stonehouse Creek
------------------------------------------------------------
Source: GAO's presentation of data from the Corps.
COMPARISON OF LEVEE DESIGN
CAPACITY WITH FLOOD FLOW FOR 145
LEVEES THAT PREVENTED FLOODING
========================================================= Appendix III
Design Flood
Design Flood water water
District/river/levee flow flow level level
project (cfs) (cfs) (feet) (feet)
------------------------ -------- -------- ------ ------
Rock Island District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Bay Island 308,000 400,000 557.0
Bettendorf 385,000 260,000 557.0
Burlington NB 435,000 400,000 536.5
Canton 400,000 446,000 499.0
Clinton 385,000 239,000 585.7
Drury 308,000 340,000 556.3
Dubuque 362,000 239,000 609.3
East Moline 385,000 260,000 572.5
Fulton 385,000 239,000 585.7
Hannibal 444,000 524,000 481.2
Henderson, No. 1 314,000 400,000 536.5
Henderson, No. 2 314,000 400,000 535.0 536.5
Iowa River-Flint Creek 370,000 400,000 547.4
Lock and Dam 17 308,000 400,000 557.0
Lock and Dam 18 314,000 400,000 539.0 541.5
Lock and Dam 20 345,000 446,000 496.5 499.0
Meredosia 239,000 588.0 585.7
Milan 385,000 260,000 557.0
Muscatine (Mad Creek) 364,000 340,000 557.0
Muscatine Island 364,000 340,000 557.0
Rock Island 385,000 260,000 565.0
Sabula 239,000 599.0 585.7
South Quincy 441,000 524,000 489.0
Illinois River
------------------------------------------------------------
Banner Special 82,000 56,600 455.6 449.5
Beardstown 135,000 84,900\a 454.0 446.6
Big Lake 78,000 56,600 451.0 447.0
Coal Creek 135,000 56,600 454.7 446.6
Crane Creek 100,000 56,600 450.0 446.6
East Liverpool 82,000 56,600 455.0 448.0
East Peoria 92,000 56,600 462.4 451.0
Lacey Langellier 110,000 70,800\a 456.0 447.7
Liverpool 82,000 56,600 455.0 448.0
Hennepin 136,000 62,000 462.4 456.0
Pekin and LaMarsh 76,000 56,600 458.0 450.0
Seahorn 87,000 70,800\a 452.0 447.4
Spring Lake 77,000 56,600 455.0 449.5
South Beardstown 135,000 84,900\b 453.8 446.6
Tributary
------------------------------------------------------------
Avon 116,000 785.5 796.8
Carlisle 116,000 785.5 796.8
Dekalb 2,000 1,310 845.0 841.0
Elkport 669.0 659.7\
b
Evansdale 126,300 68,100 844.7
Farmers 29,300 468.0 472.1
Herget 29,300 479.0 477.1
Marengo 52,000 39,000 746.0 740.8
Marshalltown 44,000 19,200 877.0 873.8
Mason and Menard 29,300 489.0 472.1
Oakford 29,300 482.0 472.1
Penny Slough 46,500 587.0 582.4
Southeast Des Moines 116,000 786.0 796.8
Tama 40,500 19,200 873.8
Van Meter 1,900 1,900\c 867.5
Waterloo 126,300 68,100 864.5 844.7
St. Louis District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Big Five 1,025,00 996,000 50.0 47.9
0
Degognia/Grand Tower 1,010,00 1,000,00 45.7 49.7
0 0
MetroEast 1,250,00 1,080,00 52.0 49.6
0 0
N. Main/Main Streets 1,200,00 996,000 49.2 47.9
0
Prairie du Pont 1,250,00 1,080,00 52.0 49.6
0 0
Prairie du Rocher 980,000 1,080,00 45.7 49.6
0
St. Louis 1,250,00 1,080,00 52.0 49.6
0 0
Wood River 1,250,00 1,080,00 52.0 49.6
0 0
Illinois River
------------------------------------------------------------
Big Swan 441.5 443.6
Keach 438.5 442.8
Little Creek 443.3 445.0
Mauvaise Terre 444.5 444.0
McGee Creek 452.0 445.0
Meredosia Lake 445.5 445.0
Scott County 444.0 444.0
Willow Creek 442.5 445.0
Valley City 444.0 444.0
Tributary
------------------------------------------------------------
Coon Run 449.0 444.0
Dively 483.3 477.4
New Athens 422.1 402.0
New Pankey's Pond 448.5 445.0
Omaha District
------------------------------------------------------------
Missouri River
------------------------------------------------------------
Council Bluffs 250,000 115,000 30.3
MRLU L-536 306,000 307,000 25.4
MRLU L-594 295,000 196,000 27.2
MRLU L-601 295,000 115,000 30.3
MRLU L-611-614 250,000 115,000 30.3
MRLU L-624 250,000 115,000 30.3
MRLU L-627 250,000 115,000 30.3
MRLU R-573 295,000 196,000 27.2
MRLU R-613 250,000 115,000 30.3
MRLU R-616 250,000 115,000 30.3
Omaha 250,000 115,000 30.3
Tributary
------------------------------------------------------------
Big Sioux 98,000 66,700 23.1
Clarkson 23,500 6,270 14.3
Emerson 16,300 18,600
Floyd River 71,500 9,680 22.3
Herreid 9,000 1,480
Hooper 47,750 29,900 14.2
Ida Grove 33,500 7,130 9.7
Lincoln 34,400 28,400 26.5
Little Papillion Creek 20,000 1,520
Little Sioux River 35,000 26,300 24.0
Loup River 150,000 27,500 11.0
Mandan 66,000 11,800 15.5
Norfolk 59,000 14,000 10.2
Pierce 24,000 1,570 13.6
Red Oak 93,000 21,600 22.0
Schuyler 68,000 123,000 11.0
Sioux Falls 7,300 18,000 23.8
Waterloo 100,000 42,100 17.3
West Point 130,000 29,900 14.2
Kansas City District
------------------------------------------------------------
Missouri River
------------------------------------------------------------
Birmingham Unit 540,000 541,000 48.9 48.9
East Bottoms Unit 540,000 541,000 48.9 48.9
Fairfax-Jersey Creek 540,000 541,000 48.9 48.9
Missouri/Kansas CID 540,000 541,000 48.9 48.9
MRLU L-455 325,000 335,000 32.7 32.1
MRLU L-476 325,000 335,000 32.7 32.1
MRLU L-497 319,000 307,000 25.7 25.4
MRLU R-351, Section 1 436,000 371,000\ 46.2 48.9
a
MRLU R-440 329,000 335,000 32.1
MRLU R-512/513 309,000 307,000 25.2 25.4
New Haven 529,000 750,000 37.0
North Kansas City 540,000 541,000 46.2 48.9
Tributary
------------------------------------------------------------
Argentine Unit 390,000 170,000 26.9
Armourdale Unit 390,000 170,000 26.9
Auburndale 364,000 170,000 34.9
Barnard 39,000 21,300 26.5
Blue River 35,000 17,900 33.9
Clyde/Elk Creek 36,000 31,100
Fairbury 72,000 24,100 21.2
Frankfort 43,000 18,700 19.8
Lawrence Unit 295,000 190,000 24.7
Little Blue River 18,000 6,600 18.0
Manhattan 220,000 199,000 27.3
Oakland 364,000 170,000 34.9
Osawatomie 130,000 17,100 33.9
Ottawa 80,000 17,100 33.9
Salina 50,000 13,100
Seward 31,000 25,700 28.8
North Topeka 364,000 170,000 34.9
Soldier Creek 314,000 170,000 34.9
South Topeka WW 314,000 170,000 34.9
South Topeka 364,000 170,000 34.9
St. Paul District
------------------------------------------------------------
Mississippi River
------------------------------------------------------------
Guttenberg 350,000 238,700
St. Paul 210,000 104,000
South St. Paul 168,000 105,000
Winona 290,000 168,900
Tributary
------------------------------------------------------------
Dry Run, Decorah 25,000 4,620
Henderson 113,000 86,000
Mankato 150,000 75,600
Marshall 6,500 6,380
Rushford 45,000 8,500
------------------------------------------------------------
Note: For some levees in this table, the numbers for the flood flow
and/or level were higher than for the flow/design level. According
to the Corps, this may be explained by flood-fighting efforts that
enhanced the levees' performance. Also, data from the nearest gauge
may not reflect the actual flood flow or level at a levee because of
the distance separating the levee and the gauge.
\a Estimated by GAO.
\b The 1993 value was not available but was below the value for a
prior flood indicated here.
\c No gauge data were available. However, Corps staff reported flow
was 1,900 cfs or below.
Source: GAO's presentation of data from the Corps and USGS.
FLOOD-FIGHTING EFFORTS THAT
EXTENDED SOME LEVEES' PERFORMANCE
========================================================== Appendix IV
Examples of the flood-fighting efforts that occurred during the 1993
flood follow.
THE KEACH LEVEE, GREENE COUNTY,
ILLINOIS
-------------------------------------------------------- Appendix IV:1
Located along the Illinois River, the Keach levee protects an
agricultural area from 25-year floods. Although the Illinois River
drainage basin received large amounts of rainfall, flooding on the
Illinois River was caused primarily by backwater from the Mississippi
River. At the Keach levee, the local sponsor installed flashboarding
and sandbags to raise the levee's height.\40 The flashboarding gave
way, and water came over the top of the levee for 2 to 3 hours.
According to Corps district personnel, National Guard personnel
locked arms and stood across the top of the levee to prevent sandbags
from washing away. Meanwhile, workers deposited additional sandbags
on the levee to stop the flow of water over it.
--------------------
\40 Flashboarding is a board fence covered with plastic and
reinforced with sandbags to give the levee extra height.
THE NORTH KANSAS CITY LEVEE,
MISSOURI
-------------------------------------------------------- Appendix IV:2
According to the Corps, flood-fighting activities at the North Kansas
City levee prevented flooding of the Kansas City downtown airport.
This levee, which lies along the left bank of the Missouri River, is
part of a system of levees and floodwalls that protects against a
500-year flood. During the flood, the levee developed sinkholes on
its landward side. A stability berm made of gravel was constructed
on the landward side of the levee, and temporary pumps returned water
to the river. Although water reached the levee's freeboard, it did
not overtop the levee. Corps officials said that without these
flood-fighting efforts, the levee would have been breached and the
airport would have been inundated. They estimate that more than $820
million in damage would have resulted.
THE ST. LOUIS FLOODWALL
-------------------------------------------------------- Appendix IV:3
Early in the morning of July 23, 1993, a geyser of water appeared on
the landward side of the St. Louis floodwall. Approximately 100
tons of rock were placed behind the wall, closing off the sinkhole
and slowing the flow of water. Piping and underseepage continued, so
the Corps constructed a ring levee around the hole and placed rock on
the river side of the floodwall. These methods did not reduce the
underseepage, and the sinkhole reappeared at its original location.
Rock was immediately placed in the hole to reduce the underseepage.
The Corps then repaired the hole beneath the wall's foundation,
thereby preventing the collapse of the St. Louis floodwall. The
floodwall protects 7 miles of riverfront in an industrial area with
an appraised property value of $300 million. Figure IV.1 depicts a
section of the St. Louis floodwall.
Figure IV.1: A Section of the
St. Louis Floodwall Along the
Mississippi River
(See figure in printed
edition.)
Source: The Corps.
(See figure in printed
edition.)
FOUR CORPS LEVEES THAT WERE
BREACHED OR FAILED
=========================================================== Appendix V
The following describes (1) three Corps levees, two on the
Mississippi River and one on the Missouri River, that were breached
without first being overtopped by floodwaters and (2) a Corps
floodwall along the Raccoon River in which an opening for a railroad
was not closed to prevent flooding.
KASKASKIA ISLAND, ILLINOIS
--------------------------------------------------------- Appendix V:1
According to Corps district staff, the Kaskaskia Island levee was
breached by excessive underseepage and internal erosion caused by
saturation. The levee encircles Kaskaskia Island, which lies about
70 river miles south of St. Louis in the Mississippi River. This
agricultural levee protects 9,400 acres and the villages of Kaskaskia
and Pujol, which together have about 200 residents, from floods with
average recurrence intervals of up to 50 years.
Water rose above the design height of the levee but was still in the
freeboard area 1 to 2 feet below the top of the levee. Water
pressure from the Mississippi River produced a large sandboil next to
the levee. Attempts to contain the sandboil were overwhelmed by the
great volumes of water and sand erupting from it. A 600-foot-long
breach opened in the levee and water inundated the protected area.
Figures V.1 and V.2 show the Kaskaskia Island levee before and after
it was breached.
Figure V.1: Kaskaskia Island,
Illinois, Levee Before the 1993
Breach
(See figure in printed
edition.)
Figure V.2: Kaskaskia Island,
Illinois, Levee After the 1993
Breach
(See figure in printed
edition.)
Source: The Corps for both
photos.
(See figure in printed
edition.)
BOIS BRULE, PERRY COUNTY,
MISSOURI
--------------------------------------------------------- Appendix V:2
The Bois Brule levee in Perry County, Missouri, an agricultural levee
protecting 26,000 acres and about 200 residents, was also breached by
excessive underseepage and internal erosion. Bois Brule is
immediately downstream from Kaskaskia Island. The levee protects
against floods with an average recurrence interval of up to 50 years.
Water rose above the design height of the levee but was still in the
2-foot freeboard area when it began seeping through the foundation of
the levee. Eventually, a 1,500-foot section of the levee collapsed,
and the protected area was flooded.
MISSOURI RIVER LEVEE UNIT
L-550, ATCHISON COUNTY,
MISSOURI
--------------------------------------------------------- Appendix V:3
Floodwater first overtopped Levee Unit L-550 on the Missouri River on
July 23, 1993. The next morning a 330-foot section of the levee was
breached about 1/2 mile upstream of where the overtopping occurred.
The water at this location was still about 4 feet below the top of
the levee when the levee was breached. As in the other cases, water
seeping under the levee caused the breach, Corps officials reported.
However, the use of sand for previous levee repairs contributed to
the seepage problem.
The Corps repaired a breach in the levee in 1952 with sand dredged
from the river. In 1984, it again repaired the levee with sand
dredged from the river side of the levee. The Corps used the river
sand because, although it was not the best material for repairing
levees, it was available at little cost to the government. Corps
officials said the levee had failed in the same location in 1993
because the sand used in the previous repair became too saturated to
withstand the water. This time, the Corps used commercial sand that
is more impervious to water to repair the levee.
CITY OF DES MOINES, IOWA
--------------------------------------------------------- Appendix V:4
According to the Corps, the flood control plan for the City of Des
Moines, Iowa, Local Flood Protection Project along the Raccoon River
calls for city workers to build a sandbag closure across a 100-foot
opening for a railroad right-of-way that passes through the
floodwall. (See fig. V.3.) Previous floods had never made the
closure necessary. The Corps reported that city workers did not
build the closure before the river rose to record levels on July 11,
1993; flowed through the opening in the floodwall; and flooded 58
blocks of downtown Des Moines occupied by offices, retail businesses,
residences, and industry.
According to the NWS, the forecast of a record flood crest for the
Raccoon River in the area of the railroad opening was given to the
city two days before an even higher crest occurred. The Corps
estimates that the flooding caused about $117 million in damage. The
Corps installed a gate at the railroad track opening after the 1993
flood to permit the more efficient closure of the levee.
Figure V.3: Railroad Opening
at the City of Des Moines,
Iowa, Local Flood Protection
Project Along the Raccoon River
(See figure in printed
edition.)
FINDINGS AND RECOMMENDATIONS OF
THE INTERAGENCY FLOODPLAIN
MANAGEMENT REVIEW COMMITTEE
========================================================== Appendix VI
The administration's Interagency Floodplain Management Review
Committee was formed to identify the major causes and consequences of
the 1993 Midwest flood, evaluate the performance of existing
floodplain management programs, and recommend changes to make the
programs more effective. As stated in its final report, issued in
June 1994, the Committee found that projects for reducing flood
damage and programs for managing floodplains, where implemented,
essentially worked as designed.\41 Flood control reservoirs and
levees prevented billions of dollars in damage. Nevertheless, the
flood overtopped many smaller, locally constructed levees and caused
considerable damage. According to the Committee, the 1993 flood
would have covered much of the floodplains of the lower Missouri and
upper Mississippi rivers whether or not the levees had been there.
The Committee found that the loss of wetlands and vegetation and the
modification of the landscape in the upper basin over the last
century and a half significantly increased runoff. Although efforts
to conserve land and restore wetlands can reduce flood levels in
smaller, more frequent floods, such activities would probably not
have had a significant impact on the 1993 flood.
In the area affected by the 1993 flood, flood control structures were
not completed as part of a plan for an overall system. Rather, they
were developed for specific purposes by private landowners, levee and
drainage districts, and the federal government. The Committee found
that the result is a mixture of federal and nonfederal structures
that provide differing levels of flood protection for similar land
uses.
Because the levees in the area affected by the 1993 flood were built
without benefit of an overall plan, the Committee found that levees
cause problems in some areas by raising flood levels and backing up
flows onto lowlands. It found that many nonfederal levees were
located and designed in a manner that contributes to erosion and
deposition in the floodplain and are built without regard for their
impact on the river and neighboring communities. During large
floods, such as the 1993 flood, levees have minor effects on overall
flood levels but may significantly increase local levels, the
Committee said. It also found that the height and location of levees
are key factors in determining these local effects, as well as in
indicating whether levees will be prone to failure. The Committee
concluded that, in certain locations, levees should not be
constructed and greater setbacks from the rivers would allow the
rivers to behave more naturally during flooding. The Committee also
concluded that locks and dams and other navigation structures did not
raise flood heights in 1993. The Committee estimated that nonfederal
levees extend up to 5,800 miles along rivers in the upper Mississippi
basin.
The Committee found that floods like the one in 1993 are natural
events that will continue to occur at random intervals. Flood
recurrence intervals are difficult to predict, especially given the
nation's short history of hydrologic recordkeeping and limited
knowledge of long-term weather patterns, the Committee noted.
Activities in the floodplain, even when protected by levees, remain
at risk.
On the basis of these conclusions and others, the Committee outlined
the following findings and recommendations on levees for the
administration.
To reduce the nation's vulnerability to flood damage in the
floodplain, full and equal consideration should be given to all
options for reducing damage, including building levees,
evacuating high-risk areas, improving flood warning systems,
floodproofing structures remaining in the floodplain, and
creating additional capacity for storing floodwaters.
To provide for efficiency in operations and consistency in
standards, assign principal responsibility for building and
repairing levees under federal programs to the Corps.
To ensure the integrity of levees and the environmental and
hydraulic efficiencies of the floodplain, increase the role of
states and tribes in ensuring the proper siting, construction,
and maintenance of nonfederal levees. Specifically, the
Committee recommended that states assume responsibility for
regulating the location, alignment, design, construction,
upgrading, maintenance, and repair of levees and for
flood-fighting.
To integrate the management of hydrologic, hydraulic, and ecological
systems in the upper Mississippi River basin, the Committee also
recommended a number of actions to improve the coordination of
federal and state efforts, including (1) the establishment of river
basin commissions and (2) the assignment of responsibility to an
expanded Mississippi River Commission under the Corps for managing
efforts to reduce flood damage, ecosystems, and navigation in the
basin.
The Committee also recommended that the Corps' current floodplain
management assessment of the upper Mississippi River basin be
redirected to develop a plan for reducing flood damage in the basin
that would include both structural and nonstructural measures. They
recommended placing the assessment under the expanded Mississippi
River Commission within the Corps, which would determine how best to
integrate existing facilities in the upper basin into an efficiently
functioning system for reducing flood damage.
--------------------
\41 Sharing the Challenge: Floodplain Management into the 21st
Century, Interagency Floodplain Management Review Committee
(Washington, D.C.: June 30, 1994), pp. 50-51.
MAJOR CONTRIBUTORS TO THIS REPORT
========================================================= Appendix VII
RESOURCES, COMMUNITY AND ECONOMIC
DEVELOPMENT DIVISION, WASHINGTON,
D.C.
John H. Anderson, Jr.
Leo E. Ganster
John P. Scott
KANSAS CITY REGIONAL OFFICE
Julie A. Cahalan
Patricia M. Crown
Frederick T. Lyles, Jr.
Darryl S. Meador
Denice M. Millett
OFFICE OF THE GENERAL COUNSEL
Stanley G. Feinstein