Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 203
7
Findings and Recommendations
The Committee on Flood Control Alternatives in the American River Basin
was charged to review technical and policy issues that arose from the Sacramento
District's 1991 American River Watershed Investigation (ARWI) and, where
possible, subsequent planning activities. The committee's task was to evaluate
the scientific and engineering knowledge on which the selection of a flood hazard
reduction strategy for the area will ultimately be based. The committee also
endeavored to provide insights on public policies concerning flood hazard man-
agement that are of concern to the nation.
In line with that dual charge, the committee offers some thoughts specific to
the USACE planning process as it was applied to the American River basin. The
committee also comments more broadly on the nature of flood risk assessment
and its application nationwide. The findings relate to (1) the identification and
evaluation of alternatives in Sacramento District planning documents, (2) envi-
ronmental issues in the upper American River basin, (3) risk methodology, (4)
flood risk management behind levees, and (5) the implications of the American
River example to resources planning and decisionmaking.
The key issue in the planning process, and in this report, is how to reduce
flood risk in the lower American River basin given a decisionmaking arena that
includes significant scientific uncertainty and organized opposition to some of
the possible risk reduction alternatives. This report discusses the uncertainties
that confront floodplain managers and offers suggestions in many areas, includ-
ing the need for additional research. But decisionmakers, agency officials, and
interest groups reading this report should not use calls for additional research as
an excuse for not taking action.
203
OCR for page 204
204
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
It is time to select and implement flood risk reduction strategies for the
American River basin. There are still areas where data and information are
incomplete, particularly in our understanding of environmental impacts, but that
should not forestall the decisionmaking process. Data collection and interpreta-
tion can continue as the decisionmaking process proceeds. Adaptive manage-
ment techniques can be used to select approaches that can be monitored, evalu-
ated, and revised as implementation proceeds and additional information becomes
available.
It is important to understand that even if Sacramento achieves its stated goal
of a "200-year level of protection," the city will still face a significant residual
flood risk. The risk would be equal to a probability of flooding of 1 in 200 per
year or about 22 percent over a 50-year period, essentially a 1 in 5 chance over 50
years. If flood risk in the city of Sacramento or Natomas is 1 in 100 per year, then
the residual risk over 50 years is about 40 percent, or about the probability of
getting "heads" with a single flip of coin.
Moreover, estimation of the residual risk of flooding alone does not provide
owners and occupants of facilities in the floodplain with a complete picture of the
consequences and damages that are likely to result from flooding. Estimates of
flood risk should be augmented by estimates of likely loss of life and property
damages, which are affected by evacuation opportunities, warning times, and the
likely depth and character of flooding. Such vulnerabilities can be communi-
cated by realistic scenarios that illustrate how a flood event would look and what
losses are likely to occur.
Perhaps the worst thing that might be done is to create a false sense of
security or to encourage people to think that any proposed project provides com-
plete protection from flooding. Therefore, flood risk management needs to be an
ongoing part of urban planning in the city of Sacramento, including in particular
the Natomas area, to reduce residual vulnerability to disastrous flood losses. One
element of such management is improved flood risk communication, which would
give investors and residents in the area a better understanding of the risks and
vulnerabilities they face.
It is increasingly evident that the nation has entered an era when construction
of new water projects will be rare. Budget constraints, environmental consider-
ations, and organized interest groups all contribute to this situation. Because
society is less willing to build new facilities, we must find ways to obtain more
from existing facilities. We need to operate existing facilities more efficiently
and to upgrade planning methods, system instrumentation, modeling capabilities,
and other tools used to support operation. With better knowledge, we can make
existing systems more efficient and more responsive to public needs without
necessarily accepting greater risks. Such improvements would not preclude all
new construction, but rather would reduce the need for new facilities.
Despite this general admonition to strive for greater efficiency from existing
systems, the committee cautions that reoperation of Folsom Dam and Reservoir
OCR for page 205
FINDINGS AND RECOMMENDATIONS
205
cannot solve all the water problems faced in the American River basin. In the
struggle to solve the myriad problems caused by too much or too little water in
the Sacramento area, more may be asked of Folsom than it is able to deliver.
The issue decisionmakers face is how best to determine and then implement
an acceptable flood risk management program for the American River basin.
Beyond all the complexities and subtleties, the ultimate question is whether the
flood damage reduction offered through a combination of measures not including
a new dam is acceptable, or whether a new upstream dam is necessary to reduce
risk to a more acceptable level. The committee cannot answer that question, in
part because detailed technical analyses comparing the current range of alterna-
tives are still being developed (these analyses are expected in the Sacramento
District's forthcoming supplemental information report, scheduled to be avail-
able in the summer of 1995) and, importantly, because that judgment is beyond
the committee's authority or appropriate role.
The public should be forewarned that even when the technical analyses are
available, there will be no simple technical answer. Scientists and engineers can
and should provide careful analyses and interpret the information so it is avail-
able to support decisionmakers, and they should be frank about uncertainties and
risks. But the decision to be made should ultimately reflect more than technical
factors; it should reflect economic considerations and value judgments pertaining
to the appropriate use of natural resources, public monies, acceptable levels of
risk, and willingness to accept constraints on land use. The final decision on
these issues rests with the public and the political officials who represent them.
IDENTIFICATION AND EVALUATION OF ALTERNATIVES
Committee's Reaction to the 1991 and 1994 Reports
The structural flood protection measures and alternatives described in the
1991 American River Watershed Investigation (USAGE, Sacramento District,
1991), as supplemented by the 1994 Alternatives Report (USAGE, Sacramento
District, 1994a) are reasonably complete, although supporting analysis for the
1994 document remains to be seen. Alternative assumptions could have been
selected, as discussed in Chapter 2, but the committee found no omissions or
errors of a degree that should call the overall results into question.
Planning Reoperation of Folsom Dam
One concern identified soon after publication of the 1991 ARWI involved
the operating policies assumed for analysis of flood control effectiveness of
Folsom Dam. Since then, ongoing investigations of interim Folsom reoperation
have been exploring a more dynamic allocation of Folsom storage capacity based
on the level of storage in upstream reservoirs. The 1994 Alternatives Report
OCR for page 206
206
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
assumed that the reoperation plan will be adopted as part of the without-project
alternative. For alternatives that involve new low-level Folsom outlet works, the
analysis should include modification of the Folsom operating policies to take full
advantage of the new release capacity. Likewise, planning studies of a proposed
dam at Auburn should investigate how to operate the dam to achieve the desired
flood protection at Sacramento while minimizing environmental impacts. The
committee was concerned by the fact that it was unable to evaluate how Folsom
reoperation and other alternative reservoir operating policies were considered in
the 1994 Alternatives Report. In particular, the committee could not identify or
assess the assumptions made about the initial conditions in Folsom Reservoir and
about the operation of Folsom Dam under the various alternatives considered.
These concerns are expected to be addressed in upcoming documents, but resolu-
tion of these questions should not slow the planning process.
Recommendation
· In the American River planning studies, significant effort should continue
to be devoted to development of effective but practical flood control operating
policies that make full use of the storage and release capacities of Folsom and
other reservoirs in the American River watershed so that the evaluation of alter-
natives will reflect the level of flood control that the system realistically can
achieve and actually should achieve.
Levee Capacity and Long-term Channel Stability
in the Lower American River
Currently, there is disagreement among experts about the capabilities of the
levees along the lower American River. The committee is concerned about
uncertainties related to the proposed alternatives for repairing and enlarging the
levees to permit conveyance of "objective releases" from Folsom Reservoir
greater than 115,000 cfs. Development of channel and levee stability data should
include an understanding of the basic alluvial stratigraphy of the lower American
River because the stability of the underlying sediments is critical. Some model
and data uncertainty is inevitable, and if that uncertainty about levee adequacy is
unacceptable either to the public or decisionmakers, then flood risk reduction
alternatives beyond levees such as building a dam at the Auburn site- may
prove unavoidable.
Recommendations
· Before the option of raising and enlarging the levees to permit convey-
ance of 130,000, 145,000, or 180,000 cfs is included in the flood damage reduc-
tion project, the Sacramento District, in concert with SAFCA and other local
interests, should ensure that sufficient data and professional consensus concern
OCR for page 207
FINDINGS AND RECOMMENDATIONS
207
ing the structural stability of specific levees during flow conditions exceeding
115,000 cfs is developed to provide assurance that the levees can contain these
higher flows.
· Although it should not slow the decisionmaking process, the Sacramento
District, in concert with SAFCA and other local interests, should consider con-
ducting additional work to better understand the long-term geomorphic response
of the American River to mining impacts and Folsom Dam because these factors
may influence long-term channel stability.
Severity of the American River Flood Risk
Flood risk for the American River is probably greater and more uncertain
than indicated by the current estimates. High floods in the latter half of the
American River flood series appear to be related to changes in the seasonal
distribution of precipitation in the region.
Recommendation
· USACE should assess the magnitude of uncertainty in the American River
flood risk and damage estimates by performing a sensitivity analysis involving
re-computation of the estimates using just the second half of the American River
flood record, from 1950 to the present.
Hydraulic Modeling of the Sacramento-American River System
A better understanding of the complex flow behavior in the neighborhood of
Fremont weir and Sacramento weir, Yolo Bypass, and the river junctions be-
tween the Feather and Sacramento rivers and the Sacramento and American
rivers is needed over the long-term to support water management decision-mak
1ng in the system.
Recommendations
.
The Sacramento District should develop a two-dimensional unsteady flow
model of the lower basin to support decisionmaking.
· The Sacramento District should investigate sediment movement and ac-
cumulation at weirs, especially during high flows in key areas of the Sacramento
and American river system.
Design Considerations for a Dry Dam at Auburn
If constructed without gates, a 425-foot-high dam at the Auburn site would
be twice as high as any ungated dam that has been constructed by USACE.
OCR for page 208
208
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
Operational gates are important for dam safety and for providing flexibility in the
dam's operation, allowing operators to coordinate with Folsom and other flood
control facilities and to minimize environmental impacts in the upper American
River canyon by regulating drawdown.
Recommendations
· If a dry dam is built at the Auburn site, it should incorporate operational
gates to provide flexibility in the operation of the dam for dam safety consider-
ations, to allow coordination with other facilities, and to minimize environmental
impacts.
· Because of the size and possible impacts of a dam at the Auburn site, dam
safety studies focused on possible seismic risk should be conducted, reviewed,
revised, and acted on as necessary.
· Additional research is needed to better understand the potential impacts of
inundation on canyon soils and slope stability, and how those impacts might be
mitigated through design or operational considerations.
Hydrologic Monitoring in the Watershed
Soil moisture and snowpack water content affect flood risk in the basin, as
does the storage level in reservoirs in the upper American River basin. Measure-
ments of snowpack and streamflow levels are routinely made and used as input to
a hydrologic forecasting system operated by the National Weather Service and
the California Department of Water Resources that describes the hydrologic sta-
tus of the basin and provides streamflow forecasts using current hydrologic con
. .
Tons.
Telemetering of existing streamflow gages and provision of additional tele-
metered streamflow gages for measuring inflows to Folsom Reservoir are needed
to provide reasonable levels of real-time data for reservoir operations and Ameri-
can River basin flood control management. There is also a need for a streamflow
gage or improved definition of spillway outflow rating between Folsom and
Nimbus dams to ensure accurate control of releases from Folsom.
Recommendations
· Plans to expand the stream-gaging network in place in 1994 should con-
sider installing telemetry in existing gages and providing additional telemetered
streamflow gages at the Folsom Lake inlets to provide timely information on the
movement of water toward Folsom and downstream toward Sacramento. Plans
should also consider providing telemetered capability for accurate, real-time gag-
ing of outflows from Folsom Reservoir. Gages should be strategically located at
OCR for page 209
FINDINGS AND RECOMMENDATIONS
. , .. ... . ~.
209
various elevations within the American River watershed and should be equipped
with telemetering equipment to facilitate real-time operations.
· As part of watershed monitoring, the Bureau of Reclamation and USACE
should coordinate with the National Weather Service, California Department of
Water Resources, U.S. Geological Survey, and others as appropriate in efforts to
consider how to use existing data and forecast products and how best to accom-
plish installation of additional monitoring capacity.
Folsom Operating Guidelines and Training
Lapses or delays in Folsom flood operations can have adverse impacts on
system performance, as was the case in the 1986 flood. Operators may be
reluctant to rapidly increase or decrease American River discharges as will be
required to ensure that high levels of flood risk reduction are achieved by Folsom
Reservoir. Steps need to be taken to ensure that lapses in operation do not occur.
Recommendation
· Stricter operating guidelines and operator training, using continuous in-
teractive simulation of different storms, should be implemented to help system
operators prepare for and deal with flood events.
Maintaining Efficiency of Flood Control System Operation
Population growth, increasing development, and other changes in the Ameri-
can River watershed create a dynamic flood risk, and it is critical that system
operating plans be revisited and revised periodically. For example, as discussed
in Chapter 2, it was evident that during the 1986 flood existing operating rules did
not adequately consider the existence of 100,000 acre-feet of storage behind the
cofferdam upstream of Folsom, even though the dam was designed to breach in a
30-year flood event.
Folsom Reservoir, despite its limitations, is the critical component in the
flood control system for Sacramento. Consequently, it is essential that it be
operated as efficiently as possible. Potential improvements are being considered
in the ongoing development of the Folsom Flood Management Plan. But it is not
clear how this ongoing effort considers Folsom reoperation, nor how it considers
potential changes in the outlet capacity or storage capacity of the dam, or in the
potential construction of upstream storage. It is essential that the operation plan
for Folsom evolve in response to changes in the American River flood control
system, technological improvements that facilitate reservoir operation, changes
in political and economic demands on reservoir storage space, and potential
changes in flood regime due to changes in climate and long-term watershed
conditions. True efficiency of operations must include all steps from planning
OCR for page 210
210
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
through execution, and some long-term mechanism for reviewing operating plans
and their implementation is essential.
Recommendations
· The operating plan for Folsom Reservoir should be periodically evaluated
and revised as necessary, especially as added experience is gained from extreme
events.
· The evaluation and improvement of flood control operating rules for res-
ervoirs such as Folsom should consider contemporary technological capabilities
in precipitation and runoff forecasting, remote sensing of rainfall, rainfall-runoff
simulation, and real-time monitoring of precipitation, upstream reservoir storage,
soil moisture, snowpack, and streamflows. In the future, such capabilities may
help operators increase readiness, including temporary encroachment on the con-
servation and power pool when a major rainfall event is almost certain to occur.
ENVIRONMENTAL ISSUES
Knowledge of Ecosystem Tolerance and Slope Stability
Knowledge of flood tolerances of upland California native plants is limited,
and the extent of impacts on Auburn canyon plant communities from a dry dam
cannot yet be projected reliably. It can be stated with certainty, however, that
even temporary inundation will yield a variety of impacts from submersion,
landslides, erosion, and other physical changes that will affect the canyon envi-
ronment. The nature and extent of impacts cannot be quantified reliably because
of the absence of field data on the impacts of periodic inundation on evergreen,
physiologically active upland plant communities.
Recommendation
· As long as a dam at the Auburn site remains a proposed or selected
alternative, field and laboratory research should continue to better understand the
variables affecting the area's plant communities, especially slope stability given
fluctuating water levels.
Improving Resource Management
Traditional environmental impact assessments fail to evaluate flood risk
management alternatives in an ecosystem context because they use a species-
oriented framework. This approach has limited usefulness.
OCR for page 211
FINDINGS AND RECOMMENDATIONS
Recommendations
.
211
Environmental impacts should be characterized within the context of the
regional significance of the resources involved. Potential scenarios for shifts to
different ecosystems or ecotypes and the positive or negative consequences asso-
ciated with these shifts should be described in environmental impact documents.
· Adaptive management, an approach that includes careful monitoring and
opportunities to alter management strategies based on that monitoring, should be
incorporated into the American River planning process to allow decisionmakers
to proceed with planning while retaining management flexibility. This approach
will enhance the mitigation of environmental impacts, even as research to gather
new information continues.
Reservoir Operations to Minimize Environmental Impacts
The operating policy for Folsom Dam and a dry Auburn dam, if it were built,
would affect the frequency and depth of inundation in the canyon and the rates of
drawdown and related impacts. Given the uncertainty of effects in the canyon, a
dry dam should be operated jointly with other measures to minimize the fre-
quency of impoundment. A dry dam should not be a first defense against large
floods, but rather it should be used to contain peak flows from extreme events.
Recommendation
· Should any alternative that includes a dam at the Auburn site be consid-
ered or pursued as a flood risk reduction measure, then the gate design and
operating policies should provide options to control the depth and frequency of
inundation, allowing operators to reduce plant mortality while keeping draw-
down rates low to reduce environmental impacts from landslides.
RISK METHODOLOGY
Risk and Uncertainty Planning Methodologies
The new USACE flood risk and uncertainty analysis procedures are an inno-
vative and timely development that should improve national flood protection
planning. The committee sees significant merit in the USACE efforts to better
recognize uncertainty in its planning efforts. As time passes, the USACE risk and
uncertainty procedures will undoubtedly improve. However, the committee is
concerned about the formulation of key steps in the current guidelines and the
particular approaches taken to apply the guidelines in the American River plan-
n~ng process.
In particular, the treatment of hydrologic uncertainties, and other potential
OCR for page 212
212
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
sources of uncertainty, in the new USACE risk methodology inflates the esti-
mated risk of flooding and the estimates of flood damages that might be avoided
by a project. This upward bias is a concern if the methodology is adopted
nationwide because it could distort the economic evaluation of projects. (The
committee did not have the resources to determine or evaluate the actual distor-
tion for the American River study.)
Recommendations
· USACE needs to develop a consistent scientific methodology and an
effective vocabulary for description of residual flood risks and uncertainties to
technical and public audiences.
· To avoid the problem of bias described above, and to simplify the analysis
so that it can be more easily understood, the primary descriptions of the expected
economic damages and the probability of flooding should be based on traditional
estimates of the flood-flow frequency relations and other factors that contribute
to flood risk and damage, such as those given in Bulletin FIB, without the
expected probability or other uncertainty adjustments.
· Best estimates of expected annual damages and the risk of flooding should
be supplemented by descriptions of the uncertainty or the possible errors in such
performance criteria due to hydrologic, hydraulic, and economic uncertainties.
Uncertainty and its impact can be described by a standard error or percentiles of
the distribution of system performance criteria due to uncertainty, or the prob-
ability that the net economic benefits might turn out to be less than zero. This
would be consistent with the requirement in the USACE risk and uncertainty
procedures that "the estimate of NED (National Economic Development) ben-
efits will be reported both as a single expected value and on a probabilistic basis
. . . for each planning alternative." It is the committee's understanding the
American River study will not address economic uncertainties.
Estimates of expected damages and economic benefits associated with dif-
ferent projects, and the probability of flooding at different locations, are likely to
be the primary criteria describing flood risk and economic impacts. It will often
be useful to calculate other indices of system performance and the reliability of
different components of the river channel and levee system. The committee
questions in general the value of the system "reliability" index adopted by the
USACE and employed in the American River study. It seems to be an awkward
combination of traditional and new concepts that would easily be misunderstood.
Ecological Risk Assessment
Ecological risk assessment is not yet sufficiently developed to provide much
useful guidance for evaluation of flood control alternatives in the American River
OCR for page 213
FINDINGS AND RECOMMENDATIONS
213
planning effort at this time. However, it does provide a new approach to help us
think about environmental impacts and select questions for investigation; it will
be increasingly important in helping planners broaden the context examined in
future planning activities.
Recommendation
· USACE should follow the rapidly evolving potential of ecological risk
assessment and adopt this approach as it develops to improve the decisionmaking
process.
FLOOD RISK MANAGEMENT BEHIND LEVEES
Federal Participation in Flood Damage Reduction Projects
for the American River
Development within the levees of the Natomas Basin faces chronic flood
risk. Improvements in the existing flood protection system including the reop-
eration of Folsom Dam and levee expansion are in progress or foreseeable. Other
measures that might contribute to flood hazard reduction, such as construction of
a dry flood storage dam at Auburn, are hypothetical and speculative at this writ-
ing. Environmental, fiscal, and political factors are likely to continue to delay or
even eliminate that option from consideration. The future level of reliable flood
protection therefore is difficult if not impossible to assess in light of both hydro-
logic and sociopolitical uncertainty.
Those who propose to permit new development in the Natomas basin should
not assume that federal flood control projects on the American River will elimi-
nate flood risk or that the only flood risk is from the American River. Additional
hazards are presented by the Sacramento River and by limited internal drainage
capabilities. In addition, flood risk will continue for the already developed parts
of the city. The committee does not sanction the development of Natomas, but in
acknowledgment of the development pressures and in recognition of extensive
existing development, the committee recommends that future federal participa-
tion in flood damage reduction projects for the American River be conditioned
upon the following:
Recommendations
· Congress should explicitly determine whether flood control projects on
the American River warrant federal involvement based on the presence of wide-
spread national benefits from flood protection or on a limited ability of the
community to provide its own flood protection.
· If a federal interest in flood protection works in the American River basin
OCR for page 214
214
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
is established, project construction should be delayed until SAFCA, working
with FEMA and private insurers, has a program to require new development at
Natomas and in the city to purchase flood insurance at actuarially sound rates for
the residual flood risk appropriate to the alternative selected.
· SAFCA should implement a flood hazard mitigation plan that includes
flood risk communication, flood warning systems, evacuation plans to reduce
loss of life, highway and other infrastructure designs to facilitate evacuation, and
floodproofing and elevation requirements wherever cost effective. The public
should be informed of the inherent flood risks pertaining to the Natomas Basin
despite the levee system.
Reforming National Flood Risk Management Policy
A recent report, Sharing the Challenge (IFMRC, 1994), suggested that the
standard project flood (defined as the "most significant flood event" expected to
occur) be adopted as the basis for planning a comprehensive flood risk manage-
ment program. To obtain maximum benefits, a comprehensive flood risk man-
agement strategy should consider nonstructural flood damage reduction measures
together with structural measures, especially as applicable in currently undevel-
oped areas such as the Natomas Basin. These measures should include appropri-
ate floodplain zoning, floodproofing, education, and, when feasible, relocation.
A comprehensive program would ensure that people who locate in hazardous
areas bear, to the extent practicable, the costs of that location decision by paying
a substantial share for flood water control works, by accepting restrictions on
development in flood prone areas (foregone development value), and by paying
adequate insurance premiums against the residual flood risk after structural and
nonstructural measures have been implemented.
Recommendations
.
USACE, FEMA, and other relevant federal agencies should adopt an
agreement governing federal participation in structural and nonstructural flood
risk management efforts to require that benefiting local communities have a
program requiring new development to purchase flood insurance at actuarially
sound rates for residual flood risk. Existing development should also purchase
residual risk insurance. The federal government, possibly working with private
insurers, should develop provisions for sharing the cost of flood insurance premi-
ums and flood damage reduction measures with communities and individuals
who implement structural and nonstructural flood damage reduction measures.
· Congress should reform the cost-sharing requirements in the 1986 Water
Resources Development Act to increase the nonfederal cost share above currently
authorized levels. Exemptions to the cost share requirement could be made if it is
OCR for page 215
FINDINGS AND RECOMMENDATIONS
215
demonstrated that flood control benefits are widespread, or that the benefiting
communities have limited ability to pay for otherwise justified flood protection,
or that communities have committed to flood mitigation programs assigned a
high rating in the National Flood Insurance Program's community rating system,
thereby exceeding minimum federal criteria for floodplain management.
· Congress should define all cost-sharing requirements as a percentage of
total project costs. Under special conditions when the local sponsor can demon-
strate both that noncash contributions (e.g., lands, easements, and rights of way)
are necessary for the project and that they will be undertaken, such contributions
should be allowed to offset nonfederal cost responsibilities.
WATER RESOURCES PLANNING AND DECISIONMAKING
Risk Communication for the American River
The Sacramento District continues to use the term "level of protection" in its
presentations and publications and has not developed good explanations of its
new risk and uncertainty procedures and of the results from their application in
the American River. However, sound risk communication is of central impor-
tance to effective risk management.
Recommendations
· The Sacramento District should cease using "level of protection" and act
with SAFCA and other local leaders to build and publicize realistic scenarios to
describe the consequences of a levee being overtopped or breached, with the goal
of educating the public about the risk and increasing preparedness. Description
of the vulnerability of the Sacramento and Natomas areas to storm events that
overtop or breach the levee system should clearly address the extreme depth of
flooding possible, the transportation difficulties that will be faced, and the prob-
lems recovering from flooding in a closed basin.
· As the change-over in terminology occurs, and "level of protection" con-
tinues to be used, the Sacramento District and SAFCA should interpret the con-
cept of 100-year "level of protection" in ways that more clearly articulate the
risks in terms with meaning to the public. For example, using the old terminol-
ogy, a 100-year "level of protection" includes a 40 percent chance of at least one
catastrophic flood event in the next 50 years. Thus the probability of at least one
catastrophic flood within the lifetime of most residents is roughly equal to the
probability of flipping a coin and getting heads. Similarly, the Sacramento Dis-
trict and SAFCA should interpret the flood risk on the American River with a
200-year "level of protection" as a 22 percent chance over the next 50 years that
flood waters will overtop the levees and inundate the Sacramento area.
OCR for page 216
216
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
Risk Communication in Federal Programs
USACE, as an agency, has great national influence in flood management
planning. Its new risk and uncertainty assessment procedures should contribute
to understanding the likelihood and consequences of flood events under different
risk management alternatives. The traditional term "level of protection" may
mislead the public and is not consistent with the analytical outcomes expected
from the new USACE procedures.
Recommendations
· USACE should select a technically sound risk communication vocabulary
and approach to communicating flood risk likelihood and consequences and use
it consistently in all reports and presentations.
· USACE should work with FEMA, as well as other agencies, the states,
and private insurers, to develop a standardized vocabulary that adequately con-
veys risk and vulnerability from flooding.
Improving USACE Risk and Uncertainty Assessment
and Risk Communication
Several of the findings and recommendations listed above address the com-
mittee's concerns with the USACE approach to risk and uncertainty analysis and
risk communication, as these were described to the committee. The risk and
uncertainty procedures are clearly new and still under development. In fact, the
American River is one of the first applications, and almost surely the most com-
plex yet attempted. Some committee members questioned whether the methodol-
ogy was sufficiently well developed to be adopted as the basis of the evaluation
of such an important and controversial project. On the other hand, there is a
tradition in USACE and among engineers to work out the details of analysis
methodologies as they are being implemented.
Recommendation
· USACE should convene an intra-agency workshop that would include
invited outside experts familiar with risk communication issues and risk and
uncertainty procedures related to water resources projects. The purpose of the
workshop would be to review the concerns expressed by this committee and
others pertaining to the new USACE approach to risk and uncertainty analysis, as
well as the USACE approach to the communication of those results to technical
and general audiences. The workshop should develop guidelines that have broad
support among risk analysis experts within and outside USACE.
OCR for page 217
FINDINGS AND RECOMMENDATIONS
217
Planning for the American River
Failure by SAFCA and the Sacramento District to incorporate a wide range
of purposes and institutional adjustments into plan formulation and to open the
American River planning process to multiple interests was a barrier to reaching
agreement on a flood risk management alternative.
Recommendations
· Flood risk management decisions for the American River are influenced
by the larger context of California water management, including several recent
environmental rulings, and can be addressed properly only within that context.
As a result, the state of California should not expect the flood control controversy
on the American River to be resolved solely under the Sacramento District's
leadership. The state needs to increase its participation in, and resources dedi-
cated to, basin-wide water resources planning. State leadership is critical to build
a consensus on technical and institutional strategies to manage competing water
demands.
· If no agreement is reached on an acceptable approach to flood risk man-
agement in the near future, the Sacramento District and SAFCA should expand
the consensus-building efforts of the Lower American River Task Force. This
expanded effort should address the full array of purposes that were originally part
of the study authorization, including water supply and allied purposes. It should
also work to identify institutional agreements that can be employed to address
these purposes. In this effort, the Sacramento District and SAFCA might request
the leadership and assistance of the state of California's Resources Agency.
The American River as Part of a Larger California Water System
The proposed shift in release patterns from Folsom Reservoir related to
reoperation to reflect upstream storage levels may affect seasonal releases into
the Sacramento River and the delta system. Changes in releases have implica-
tions that go beyond the American River basin. Likewise, the Central Valley
Project Improvement Act (P.L. 102-575, Title 34) and the federal-state water
quality standards announced in December 1994 for the San Francisco/Sacra-
mento-San Joaquin delta estuary may affect Folsom operations and water release
requirements.
Recommendation
· Development of flood control operating guidelines for the American River
needs to recognize the wider impacts of reoperation of storage facilities in the
OCR for page 218
218
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
American River basin, including revised downstream water quality and habitat
requirements.
Reforms in Federal Planning
Plan formulation demands the creation of the widest possible range of engi-
neering and institutional alternatives so that agreements can be reached among
multiple decisionmakers.
Recommendation
· USACE should issue guidance to its districts stressing the requirement to
maintain a broad view of water resource planning purposes and address those
multiple purposes throughout the planning process, including both the develop-
ment and evaluation of institutional as well as engineering measures. Especially
when contentious disagreements are involved, USACE should advise its districts
to facilitate but not dominate local decisionmaking.
CONCLUSION
This committee was charged to evaluate the scientific and engineering knowl-
edge on which the selection of a flood hazard reduction strategy for the lower
American River will ultimately be based, and to provide insights where possible
on public policies concerning flood hazard management in the Unites States. To
these ends, the committee has presented more than 20 findings and associated
recommendations. These are offered in a spirit of constructive criticism and to
encourage the continued progress in reducing the American River basin's flood
risk and in the evolution of the nation's understanding of flood risk management.
The committee reiterates its concern that nothing stated in this report should be
used as an excuse for delaying action in the American River basin. It is time to
select and implement appropriate flood risk reduction strategies.
Representative terms from entire chapter:
flood risk
