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OCR for page 85
Environmental Issues
The American River basin possesses significant environmental values. The
upper American River, known for its steep gradient, free-flowing white water,
and relatively natural plant communities, was listed under the state's Wild and
Scenic River classification system in 1978. In 1981, a 23-mile stretch of the
lower American River was designated under the National Wild and Scenic River
System as a sport fishery and a critical recreational resource. Sacramento owes
its nickname, "River City," its identity, its sense of history, and its regional
character to the American River, which flows through the city's center, and to the
Sacramento River, which joins near the city's historic district.
The 1991 American River Watershed Investigation (ARWI) raised a number
of contentious environmental issues. A key concern was whether the description
of the environmental impacts of the various proposed project alternatives was
adequate. This chapter reviews how the 1991 ARWI and the associated environ-
mental impact statement/environmental impact report (EIS/EIR', referred to here
as the 1991 ARWI report (USAGE, Sacramento District, 1991), considered envi-
ronmental impacts. It pays particular attention to the assessment of environmen-
tal impacts associated with the proposed Auburn dry dam alternative and associ-
ated inundation impacts in the American River canyon, but also addresses a range
of other environmental considerations. In addition, the chapter discusses whether
the planning process is adequate to produce plans that consider a full array of
feasible alternatives that integrate social, environmental, and flood risk reduction
factors. (Chapter 6 addresses planning issues in more detail.)
85
OCR for page 86
86
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
TREATMENT OF ENVIRONMENTAL ISSUES
IN THE ARWI REPORT
Overview of NEPA and CEQA
The 1991 ARWI was prepared to meet the requirements of both the National
Environmental Policy Act (NEPA) of 1969 and the California Environmental
Quality Act (CEQA). NEPA Section 102 requires an environmental impact
statement for "major federal actions significantly affecting the quality of the
human environment." The Council on Environmental Quality (CEQ) oversees
the implementation of the NEPA act. Guidelines prepared by CEQ and federal
agencies and a large number of legal cases have established that the major legal
issues associated with the EIS process are determining when one must be done
(i.e., determining what is a major federal action) and determining the adequacy of
a prepared statement with regard to the accuracy of description, the identification
and quantification of probable environmental impacts, and the exploration of
reasonable alternatives. CEQA passed a year later and, although based on NEPA,
had some different provisions. It is implemented through a state agency, the
Office of Planning and Research, and has its own guidelines for preparation of
environmental impact reports. Both CEQA and NEPA guidelines urge the issu-
ance of joint reports that satisfy both state and federal law (Heyman, 1974; Remy
et al., 1994~.
Like the federal act, CEQA was conceived primarily as a means to document
and consider the environmental implications of actions. Unlike NEPA, CEQA is
not merely a "procedural" statute but contains substantive provisions that agen-
cies are to comply with. Under NEPA the federal government is required only to
give "appropriate consideration" to environmental values and presumably can
take actions causing environmental damage even if feasible and effective mitiga-
tion measures could easily be implemented. In contrast, CEQA requires agencies
to implement feasible mitigation measures and alternatives identified in the envi-
ronmental impact reports. In addition to this important distinction, CEQA places
an emphasis on any growth-inducing impacts associated with proposed actions
and the potential of population growth to stress existing community service fa-
cilities (Secretary for Resources, California, 1973; Remy, 1994~.
Both NEPA and CEQA provide guidance on the development of alternatives
in the EIS and EIR. CEQ guidelines state (Council on Environmental Quality,
1973~:
A rigorous exploration and objective evaluation of the environmental impacts
of all reasonable alternative actions, particularly those that might avoid some or
all of the adverse environmental effects, is essential. Sufficient analysis of such
alternatives and their environmental costs and impact on the environment should
accompany the proposed action through the agency review process in order not
to foreclose prematurely options which might have less detrimental effects.
OCR for page 87
ENVIRONMENTAL ISSUES
87
The American River is a significant recreational resource. The lower river is an important
sport fishery, while the upper river is a steep, free-flowing river valued by boaters. (Ruth-
erford H. Platt, University of Massachusetts, Amherst.)
Examples of such alternatives include the alternative of taking no action, or of
postponing action pending further study; alternatives requiring actions of a sig-
nificantly different nature which would provide similar benefits with different
environmental impacts (e.g., nonstructural alternatives to flood control pro-
grams, or mass transit alternatives to highway construction).
CEQA's guidance states, "Attention should be paid to alternatives capable of
substantially reducing or eliminating any environmentally adverse impacts, even
if these alternatives substantially impede the attainment of the project objectives,
and are more costly" (Secretary for Resources, California, 19731.
Environmental Information Deficiencies in the 1991 ARWI
There were several areas where the lack of scientifically based descriptions
of environmental impacts prevented the 1991 ARWI from serving as an adequate
planning document to assess the impacts of proposed projects. The most signifi-
cant information deficiencies were in the assessment of (1) potential impacts of
periodic inundations from a dry dam on the plant communities located in the
upper American River canyon, (2) potential impacts of inundation on canyon
soils and geologic stability, and (3) potential impacts on ecosystems and regions.
Information gathered since the issuance of the 1991 ARWI is still incomplete, so
it is not possible to determine or quantify impacts from inundation by a dry dam
in the American River canyon. An adequate EIS/EIR would have described the
situation in these terms and made recommendations for a research plan.
OCR for page 88
88
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
NEPA and CEQA guidelines call for impact assessments to consider re-
gional and ecological contexts, but readers of the 1991 ARWI report cannot
discern the regional significance of the fisheries, plant communities, wildlife, or
the landscape of the upper American River canyon. It is also unclear whether
potential ecosystem shifts might result from the cumulative effects of inundation,
unstable geology, and plant regeneration problems. The regional significance of
such an ecosystem shift was not explored. For example, if the wild trout fishery
were affected in the Middle Fork, how would this affect the status of other
fisheries in the region or state? Environmental impact assessments must not only
identify the probable effects of an action, but also estimate the magnitude and
evaluate the importance of these effects. Numerous reports from the early 1970s
observed that the assessment process suffered from lack of a systematic means of
reporting impact significance and provided procedures to remedy the problem
(Leopold et al., 1971; Warner et al., 1974; Dickert and Domeny, 1974~. Because
of the scale of the controversy associated with building a dam on a scenic river,
uncertainties about the significance of impacts will only hinder decisionmaking
and efforts to gain public consensus. The measures that have been taken to
improve the 1991 ARWI should provide significant benefit. The 1994 Alterna-
tives Report (USAGE, Sacramento District, 1994a) contains a more thorough
consideration of options to reduce flood damage, but this preliminary document
does not provide analysis of the environmental impacts or gains associated with
the different alternatives. A supplemental EIS/EIR was not available in time for
this committee's review, so it cannot comment on the final planning document.
Project Alternatives Assessment in the 1991 ARWI
To meet the requirements of NEPA, and CEQA in particular, the 1991 ARWI
reports should have provided substantial environmental analysis of the different
alternatives that could be used to increase conveyance in the lower American
River. Environmental restoration project components and geomorphological con-
siderations involving sediment transport and deposition in the lower American
and Sacramento rivers, weirs, and bypasses should have been integrated into
project alternative scenarios. If geomorphological factors were judged to have no
influence on managing or increasing conveyance capabilities in the lower river
systems or bypass, then these conclusions should have been substantiated.
Following the release of the 1991 ARWI, a number of significant changes
occurred that enabled the 1994 Alternatives Report to present a fuller array of
project alternatives. The 1991 ARWI focused strongly on reservoir related op-
tions, while the 1994 report was oriented more toward river flood conveyance.
Coordination with upstream hydroelectric reservoirs has been arranged to im-
prove Folsom flood operations. The local project sponsor has hired consultants
in geomorphology to integrate the rebuilding of lower American River levees
with riparian habitat restoration. Before and during the preparation of the 1994
OCR for page 89
ENVIRONMENTAL ISSUES
89
Alternatives Report, the Lower American River Task Force, assembled by the
local sponsor, met with the goal of actively soliciting the input of any public and
agency stakeholders in the lower American River on environmental and public
safety needs (SAFCA, 1994b). A more extensive risk and uncertainty analysis
was conducted, which should help Sacramento officials better select risk reduc-
tion alternatives that balance public safety, financial, and environmental costs.
During the period between issuance of the two reports, local initiatives were
begun in cooperation with the Sacramento District to restore wetlands in the Yolo
Bypass. (The first Yolo Bypass wetland restoration projects date back to 1990.)
The interagency Yolo Basin Working Group and the District began an assess-
ment of how to integrate both flood protection and environmental restoration
objectives in the Yolo Bypass. By 1994, interagency agreements had been ap-
proved for the multi-objective management of the Bypass for endangered species
protection, wetland and wildlife habitat restoration, and flood control. In 1994
the California Reclamation Board passed Resolution 94-3, requesting that USACE
initiate a new reconnaissance study of the Sacramento River Flood Control Project
for the purpose of cooperating with other federal and state agencies and public
interests leading to a "comprehensive multi-objective river corridor management
plan." The local sponsor has realized that the public interest in the environmental
values of the upper American River canyons must be an integral component in
any flood damage reduction plan and toward this end has reordered its project
. . .
priorities.
The USACE goal is to design projects and conduct analyses of these designs.
Land use planning traditionally has been a local responsibility and this division
between the two levels of government often results in the omission of consider-
ation of how the two elements project design and land use are interrelated.
USACE environmental assessments do not generally deal with the secondary
impacts of flood damage reduction alternatives, even though such impacts are
possible and indeed probable. For example, in the American River case, if an
Auburn dam were built as multi-purpose facility, it might open up significant
suburban development in Sierra foothill counties such as Placer and E1 Dorado
Counties. On the other hand, if a single-purpose flood control dam were built at
the Auburn site, it might facilitate development in the Natomas Basin. The state
of California's CEQA guidelines do require explicit attention to the relationships
between land use and facilities development.
A truly comprehensive EIR/EIS, might explore how development options
could increase or reduce the need for an Auburn flood control facility, levee
improvements, or other measures. It would identify the land use development
options near Sacramento with the highest to lowest flood risks. In other words,
the description of flood risk reduction alternatives would include land use alter-
natives and how they can be used to lessen the risk exposure of population growth
centers.
A report with an adequate representation of alternatives would also describe
OCR for page 90
9o
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
how nonstructural measures could be integrated with other measures to form
flood risk reduction alternatives. Nonstructural alternatives alone will not pro-
vide adequate flood risk reduction for most areas in the American River flood-
plain, but they can provide important supplements to levee or dam construction
scenarios. Easily placed and removed temporary dams for doorways and win-
dows for central Sacramento structures could have been used during flood events
such as 1986, when great uncertainties about levee stability and channel capacity
on the American River threatened the area. New construction could require
elevation of structures both in older developed areas and newly developing areas.
A combined flood warning and flood proofing system could be used regionwide.
Current efforts under way by the city of Sacramento to produce a compre-
hensive floodplain management plan present an opportunity to integrate federal
flood control facilities planning along with the National Flood Insurance Pro-
gram and local plans. The city plan places new emphasis on floodplain zoning,
land use planning, floodproofing, flood warning, and evacuation plans. Presum-
ably, the supplemental EIS/EIR preparation is well timed with these local efforts
for producing integrated plans. Chapter 5 addresses these floodplain manage-
ment issues in greater detail.
Limitations of the Environmental Impact Assessment
Approach to Project Planning
Good project planning should be more than just an exercise in disclosure of
the potential consequences of a project. The EIS/EIR process can serve as a
dynamic planning tool to facilitate development of project alternatives and com-
munity consensus. Public and private stakeholders should be involved as co-
participants in the identification of reasonable alternatives, rather than merely
reviewing draft reports. The Sacramento Area Flood Control Agency's Lower
American River Task Force, organized subsequent to release of the 1991 ARWI
to plan levee improvement projects, seems to offer a successful model for im-
proved project planning, although this effort is still in progress and thus it is
premature to comment on its ultimate usefulness.
The 1991 ARWI identified a preferred alternative plan and described its
impacts. It then identified the manner and extent of mitigation that might take
place. The concept of environmental mitigation provides an unsatisfactory frame-
work for this water planning process. Environmental mitigation assumes that
environmental factors are considered separately, after hydraulic, hydrologic, and
engineering factors. One of the conceptual weaknesses of this planning frame-
work is that the objectives of civil works projects and the objectives of restoration
projects are viewed as mutually exclusive, competitive objectives or as trade-
offs, rather than as mutually supportive objectives. This lack of integration
contributed to the reason the 1991 ARWI report did not adequately address ways
for managers concerned with reducing flood damage to find incremental gains in
OCR for page 91
ENVIRONMENTAL ISSUES
91
reducing flood risk using different management schemes for levees, weirs, and
bypasses as well as reservoir reoperations. The pressures placed on the Fish and
Wildlife Service (FWS) to provide quantification for plant mortality for a dry
Auburn dam, when FWS staff felt quantification based on existing information
was not scientifically defensible, is symptomatic of the mitigation-based empha-
sis. The quantification was forced too early in the planning process for FWS to
be able to develop a mitigation plan to make specific projects possible.
In situations where trade-offs between hydraulic or other engineering con-
cerns and natural resources need to occur, mitigation is an appropriate remedy.
Mitigation is only as good as its implementation, however, which creates signifi-
cant uncertainties. In comments on the 1991 ARWI, the public expressed disap-
pointment in past mitigation performances (e.g., of USACE on its Warm Springs
Dam and New Melones DamJ. In response to this sentiment, project mitigation
strategies that address public distrust should be developed.
If environmental features are not determined to be required for mitigation,
they are treated as add-one, or "enhancements," to a project. The current practice
of USACE is not to engage in enhancement projects and to relegate these as
"separable" projects to the responsibility of local sponsors (Kiesck, 1994~. While
federal participation in environmental restoration and enhancement projects is
fully authorized, planning practice in 1991 and even in 1995 has not yet reflected
these legislative policies.
ASSESSING THE IMPACTS OF A DRY DAM
The probable environmental impacts of an Auburn dry dam to the American
River canyon are of central importance in determining the desirability of flood
risk reduction alternatives. Two critical areas in which information has been
deficient are the impacts of periodic inundation on canyon soils and geologic
stability and impacts on plant mortality. The significance of these two issues is
that the degree to which canyon hillslope failures or vegetation mortality do or do
not damage scenic or ecological values has an important bearing on the public
perception of the desirability of a dry dam. Landsliding can degrade scenic val-
ues, alter the physical and ecological base for plant and wildlife communities,
and degrade fisheries through sedimentation of stream channels. A combination
of geological instability and inundation stress on plant communities could alter
canyon scenery and ecology.
Many Sacramento area residents assign high value to the aesthetic, environ-
mental, and recreational attributes of the scenic canyons of the North and Middle
Forks of the American River. To accommodate this public sensitivity, the Sacra-
mento District and local flood control planners, with public input, proposed a
"dry dam" an innovation at this scale. The dry dam at Auburn was conceived as
an environmentally sensitive alternative to a previously planned multipurpose
dam. As described in the 1991 ARWI, the dam would have impounded peak
OCR for page 92
92
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
flows during periods when upstream runoff exceeded the dam outlet capacity.
The ungated outlet would have been sized to allow unrestricted passage of nor-
mal streamflow volumes, and flow volumes exceeding outlet design would have
been detained only for the length of time required to drain through the outlet.
This alternative would presumably decrease impacts to vegetation, wildlife, aes-
thetics and recreation that normally accompany permanent pool multipurpose
dams (USAGE, Sacramento District, 1991~.
The range of technical issues raised concerning the potential dry dam im-
pacts includes how to predict impacts from unstable geology and soils in inun-
dated zones; how to predict impacts from inundation of nonriparian chaparral,
oak woodland, and digger pine communities, which are not covered by inunda-
tion literature; how to determine the impacts of indirect, longer-term influences
stemming from inundation; how to determine the overall ecosystem response to
inundation; and how to collect valid data from existing sites with some similarity
in plant communities that have undergone inundation events.
Canyon Slope Stability
There is a legitimate concern over hillslope stability in the upper American
River canyon, given the frequency of hillslope failures in the region, the condi-
tion of the slopes, and the importance of saturation to slope failures. The extent
of impacts cannot be quantified because of a lack of empirical data on depths of
anticipated drawdowns and long-term effects of vegetation changes on slope
stability. This section evaluates what is known about potential effects on slope
stability of deep inundation and rapid drawdowns as might occur behind a dry
Auburn dam. Further study on the stability of slopes under current conditions
and over extended time scales will be necessary if the dry dam option is pursued.
Physical Mechanisms of Slope Failure
Slope failures are common in the Sierra Nevada and west central California,
where single storm events have generated numerous failures (Campbell, 1975;
Ellen and Fleming, 1987; DeGraff, 1994~. Many conditions commonly associ-
ated with landslide susceptibility (Cooke and Doornkamp, 1990) pertain to the
Middle Fork canyon. Most landslides in California occur during the winter and
spring rainy season, which is also the Deriod likely to coincide with deen inunda
tion.
~-r
Inundation and rapid dewatering affect slope stability. Rising-stage failures
are not a dominant concern in cohesive materials because high pore pressures are
offset by hydrostatic forces of the submerging water (Taylor, 1937; Chandler,
1986~. They can, however, be a concern in granular, noncohesive materials
(Chandler, 1986), such as steep riverwash materials or unconsolidated roadbeds.
Rapid dewatering, on the other hand, may pose a substantial problem in the
OCR for page 93
ENVIRONMENTAL ISSUES
93
canyon. Rapid drawdowns can generate slope failures due to increased effective
shear stresses while pore pressures remain high (Chandler, 1986), especially in
fine-grained materials (Brunsden, 19791. Excess pore pressure is not supported
by grains and can be resisted only by soil cohesion (Taylor, 1937~. Experimental
results indicate that grain-contact stresses may fall to zero, causing pore-water
pressures to locally support the entire stress field (Iverson and LaHusen, 19891.
Some failures occur progressively through the cumulative deterioration of
friction elements in the matrix until resisting strength is seriously compromised
(Brunsden, 1979; Chowdhury, 1992~. For example, clay mineral grains may
become locally aligned along a failure plane, which facilitates subsequent fail-
ures (Chandler, 1986~. Laboratory results indicate that pore-water fluctuations
can propagate outward from existing shear zones, leading to expansion of shear
zones (Iverson and LaHusen, 1989~. These factors imply that deep inundation
and rapid drawdowns could decrease shear strengths and increase mass wasting
hazards long after the inundation period.
Past Hillslope Failures
Landslides generated by rapid drawdown are common. For example, draw-
downs during the failure of the Teton Dam in Idaho in 1976 resulted in the failure
of about 3.6 million cubic yards of material from the canyon walls (Schuster and
Embree, 1980; Cedergren, 1989~. In addition, major landslides can cause dam-
ming of valleys (Evans, 1986) and dam failures downstream. The Vaiont slide in
Italy, which was triggered in part by buoyant forces due to elevated ground water
levels in response to reservoir filling, was catastrophic both in volumetric propor-
tions and loss of life, because it led to failure of the dam below (Cedergren, 1989;
James and Kiersch, 1991~.
There is little empirical information on drawdowns approaching the rates or
magnitudes that might occur behind an ungated Auburn dry dam (USAGE, Sac-
ramento District, 1991), although rates could be controlled and damage lessened
if controllable gates were employed. Drawdowns in the canyon following the
cofferdam breach in 1986 generated numerous landslides and provide the most
direct indicator of landslide potential at this location, although no slopes were
monitored. The 1986 conditions are regarded as a worst-case scenario for a
single, isolated geomorphic event, as drawdown was extremely rapid and was
completed within a few hours. An inventory and analysis of landslides in the
canyon identified and mapped at least 35 small new slides caused by the 1986
inundation and about 5 slides interpreted as reactivated older slides (USAGE,
Sacramento District, 1991, Appendix M). In addition, two large ancient failures
were recognized as having potential to fail, and it was recommended they be
monitored. These slides are the River Mile 22.4 Slide, which had part of its toe
removed by the 1986 flood, and the Cherokee Flat Slide. The Sacramento Dis-
trict concluded that there have been several episodes of prehistoric slides and that
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94
FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
they make up only a small percentage of the total canyon area, but that it is
impossible to determine the magnitude and frequency of sliding in the canyon.
The nature of expected canyon inundation was provided explicitly in the
form of depth-duration-frequency curves for the original dry dam (USAGE, Sac-
ramento District, 1991), although frequencies should have been increased for
events with recurrence intervals of less than 10 years due to derivation from an
annual maximum rather than a partial duration flood series (Stedinger et al.,
19931. A similar set of curves should be generated for any new planned structure.
In the initial dry dam plan, the Sacramento District mapped inundation areas
using the depth-frequency-duration curves and concluded that inundation im-
pacts would be insignificant, with an estimated 1,927 acres of vegetation lost to
combined inundation and mass wasting (USAGE, Sacramento District, 1991~. It
concluded that following a period of inundation-induced slides, stability would
soon be reached: "Most likely, each episode of filling and emptying should cause
fewer failures as the unstable portions of the slopes are gradually removed and
eventually the canyon walls should stabilize" (USAGE, Sacramento District,
1991, Appendix M). An alternative model, however, could be that failures will
propagate upslope beyond the inundation upper limit (WRC-Environmental and
Swanson, 1992) and that slope stability would not be reestablished as long as
there is a substantial amount of colluvium at high gradients.
FWS was critical of the proposed dry dam alternative. On the basis of
analysis of aerial photographs in the lower canyon, it concluded that slope fail-
ures would be substantial and would have adverse effects on vegetation and
habitats in the canyon (FWS, 1991~. The California Department of Water Re-
sources (CDWR) expanded on the FWS study by analyzing soil maps and aerial
photographs further up the canyon, where soils are coarser "rained and more
permeable (CDWR, 1991~. It found that permeable soils tended to remain stable
through the 1986 inundation, while prominent scarps developed in impermeable
soils. The study concluded that 35 percent of the inundation area is coarse
riverwash not susceptible to failure. Of the remaining area, 50 percent (all
permeable soils) would be stable under drawdown rates for the 400-year flood
control dams but possibly unstable under rates for the 200-year dam (which were
proposed at nearly twice those for the 400-year dam), and 15 percent (all imper-
meable soils) could be unstable under either drawdown rate. These values have
been criticized for underestimating potential failures because (1) the soil perme-
ability model did not account for throughflow or rainfall excess contributions
from upslope unsaturated zones, (2) the threshold head differential was overesti-
mated, and (3) pool drawdown rates were underestimated (WRC-Environmental
and Swanson, 1992~.
The CDWR study modeled slope stability by comparing soil drainage rates
to drawdown rates. The soil-water approximations, based on a ground water
model, appear valid, but the criterion for interpreting those values has been
criticized (WRC-Environmental and Swanson, 19921. A critical head differential
OCR for page 95
ENVIRONMENTAL ISSUES
95
was estimated between reservoir stage and soil piezometric head above which
slope failures were presumed to occur. This threshold was set at 35 feet based on
debris-flow scar lengths (including toeslope sediment accumulation areas' mea-
sured from the landslide maps. This 35-foot critical head differential has been
criticized as too large for several reasons (WRC-Environmental and Swanson,
1992):
· Failures often begin on upper slopes and propagate down across lower
slopes, so slide lengths exceed initial failure planes (WRC-Environmental and
Swanson, 1992; DeGraff, 1994~.
· Failure plane lengths do not necessarily equal head differences at the
onset of sliding because failure planes can extend both above the saturated zone
and below the reservoir water surface.
· Subsequent analysis located numerous small slides not recognized by the
CDWR study and concluded most slides were less than 30 feet in length (WRC-
Environmental and Swanson, 19929.
· Critical head differentials derived from the difference between reservoir
stage and soil piezometric head were compared by CDWR (1991) to much slower
drawdown rates than those anticipated (WRC-Environmental and Swanson,
19921.
Fugro-McClelland and Leiser (1991) suggested that the CDWR estimates of
areas susceptible to mass wasting were excessive because they neglected the
stabilizing effects of vegetation roots. These authors subtracted the entire area of
fine-grained soils (400 acres) on the premise that those slopes would ultimately
fail whether inundated or not, and lowered the remaining area of susceptible
coarse-grained soils by 50 percent, from 2,200 to 1,100 acres, on the premise of
root stabilization. This assessment was arbitrary and inappropriate because the
model did not analyze slope shear strengths, it evaluated slope stability using an
empirical relation between head differentials and landslide scar lengths. There is
no physical basis for decreasing the CDWR (1991) estimated areas of slope
stability to account for vegetation roots.
Landslide scar length distributions, a slope-elevation-frequency graph, draw-
down analyses, and a slope failure frequency by elevation curve were presented
by WRC-Environmental and Swanson (1992~. They concluded that stresses on
slopes will be much greater than CDWR (1991) estimates, that drawdown rates
greater than 3 ft/hr (3 times the CDWR threshold) will occur on more than 50
percent of the slopes, and that about 80 percent of the inundated slopes (2,300
acres) are "extremely likely to fail" (WRC-Environmental and Swanson, 19921.
They called for analyses to establish critical drawdown rates, stable slope angles
for this rate, and mapping of stable and rock rubble areas based on inundation
depths, topography, and soils. The WRC-Environmental and Swanson (1992)
report also estimated slope failure cumulative frequencies, but the frequency
OCR for page 103
ENVIRONMENTAL ISSUES
103
but nonetheless are important to highlight. They include impacts on riparian
vegetation in the lower American River, the value of a geomorphic perspective,
recreational conflicts, impacts on fish and wildlife resources, and the need for an
ecosystem approach to environmental assessment.
Impacts on the Lower American River Plant Community
In addition to the environmental considerations assessed in the upper Ameri-
can River, the flood control planners also had to take a cautious approach to flood
damage reduction alternatives that could affect the popular and heavily used
American River Parkway on the lower American River, which flows through
urban Sacramento. The alternative involving the increase in releases from a
reoperated Folsom Reservoir through the American River Parkway levees was
considered a contentious environmental issue because of projected impacts on
parkway vegetation. Levee reconstruction and/or clearing for channel capacity
or levee safety could have impacts on the riparian resources and quality of the
river environment. The historically concerned and well-organized constituency
associated with the parkway put the planners in the position of balancing public
opinion of potential impacts to the upper American River against public opinion
of potential impacts to the lower American River a seemingly intractable posi-
tion.
The Detailed Report on Fish and Wildlife Resources prepared for the 1991
ARWI by the FWS shows a net loss of 679 acres of riparian forest, marsh, and
shrub vegetation along the lower American River for the without-dam 150-year
protection alternative. This alternative would have changed the operations of
Folsom Reservoir to release flows up to 180,000 cfs through the American River
Parkway and levee system located in Sacramento. These estimates were arrived
at assuming the need to rebuild American River levees, remove vegetation, riprap
them, and remove vegetation to increase channel capacities in the floodplains.
These impact estimates also assumed short- to long-term loss of riparian vegeta-
tion due to removal of the vegetation from the construction necessary to rebuild
portions of the Sacramento Weir and Bypass and Yolo Bypass (Monty Knudsen,
personal communication, FWS, August 1994~.
New studies and institutional developments since the release of the 1991
ARWI reports change the impact assessments of this alternative on riparian and
wetland species. The new institutional developments have served to relieve what
was initially perceived as an untenable deadlock between upper American River
public concerns and lower American River public concerns. As a result of
innovative efforts by SAFCA to integrate the concerned public into its planning
and design teams and of its openness to environmentally positive levee enhance-
ment projects, the levee improvement projects can now be reclassified as envi-
ronmentally beneficial projects. Levee improvement plans call for the integra-
tion of native riparian plantings into the projects, thereby providing net benefits
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FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
for riparian plant communities compared to the existing situation (SAFCA,
1994b).
Other institutional changes include the previously mentioned program initi-
ated by the California Resources Agency to view the Yolo Bypass as an opportu
nity for restoring and increasing riparian environments.
In 1994 the agency
announced new cooperative agreements to begin these restoration projects. The
local and state agencies therefore are now viewing flood control improvement
projects as opportunities to improve environmental values.
Geomorphological Influences on Flood Control
Water resources planning traditionally uses hydrologic data and hydraulic
models as the focus of engineering studies. The realization that geomorphologi-
cal influences, including stream dynamics, need to be routinely integrated into
project designs and models has been advocated by fluvial geomorphologists for
some time (Leopold, 1974), but only recently have hydraulic engineers and geo-
morphologists made progress in integrating consideration of natural river
dynamics into project design and hydraulic models (Shields, 1982; Cook and
Doornkamp, 1990; Neill et al., 1990; USACE, 1992~.
The 1991 ARWI, for the most part, considered geomorphology in terms of
its potential influence on upper American River environmental impacts associ-
ated with periodic flooding from a dry dam. But geomorphological issues should
have received more consideration in the 1991 ARWI in analyzing the levee
management options on the lower American River. Channel adjustment, which
has the potential to increase the conveyance of floodwaters in the lower Ameri-
can, and the sediment transport and deposition in weirs and bypasses, are both
important considerations not examined in the 1991 ARWI.
If geomorphological factors are not considered, options for increasing flood
conveyance while limiting environmental impacts or increasing opportunities for
environmental restoration can be overlooked. An increase in conveyance of
floodwaters due to increased channel capacities (a result of channel degradation)
may make it easier, for example, to allow more riparian restoration on the levees
along the lower American River. An increase or decrease in storage capacities of
bypasses also has implications for restoration opportunities. There may be
systemwide benefits from reduction in flood damage if routine sediment removal
at the Fremont and Sacramento weirs can improve the hydraulics of the Yolo
Bypass and can lower water surface elevations upstream in the lower American.
Sediment removal may represent a cost-effective and environmentally sensitive
method of increasing lower river channel capacities.
An understanding of stream dynamics is critical to the design of levee im-
provements, particularly if there is a commitment to design the improvements
with soil-bioengineering revegetation systems instead of traditional riprap. The
anticipation of future channel adjustments becomes an integral part of multiple
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ENVIRONMENTAL ISSUES
105
objective levee improvement programs that must balance conveyance capacities
and structural reliability of levees with riparian restoration opportunities. Fi-
nally, a better awareness of geomorphological processes provides a potential for
incremental gains or losses of conveyance or storage capacities in the whole
flood system.
Given the recent emphasis on considering more management options for the
lower American, the local sponsor has commissioned consultants to evaluate the
geomorphology in the lower American River as it relates to bank and levee
stability. Given the geomorphological processes acting on the lower American
River, the possibility of future channel degradation in the lower river deserves
more consideration. The lower river may not have yet attained an equilibrium
state from past historical influences. These two factors deserve attention in the
formulation of current and ongoing alternatives.
Recreation Conflicts
Although the 1991 ARWI included nominal consideration and analysis of
recreation resources and interests, it became clear in subsequent complaints that
planners had not sufficiently involved this segment of the population in real
negotiation during the formulation and evaluation of alternatives. Opposition to
the dry dam proposal was to a significant extent organized by these interests. The
SAFCA Lower American River Task Force is a step in the direction of resolving
the impasse, but only a partial solution. Recreational issues will continue to be
unresolved without substantial effort by all parties.
There are numerous recreational areas in the American River watershed that,
by western standards, support heavy public use. For example, the American
River is the most popular of all the white water rafting rivers in California
(CSLC, 1994~. The development and heavy use of these areas are due largely to
the proximity of the basin to the dense population centers of Sacramento and the
San Francisco Bay area. Recreation areas are located throughout the basin, from
Discovery Park in Sacramento, up the lower American River along the American
River Parkway, to the Folsom Recreation Area, and beyond to the Auburn State
Recreation Area above the proposed Auburn dam site.
In the upper American River basin, the rivers act as natural corridors through
the mountains and attracted human travel and activity long before contact with
western civilization. The area is characterized by deep canyons with steep walls
covered by chaparral, and narrow rugged valley bottoms and occasional rapids.
White water rafting is a popular use of all three forks of the American River. The
North and Middle Forks are particularly challenging, with many Class IV and V
rapids, resulting in white water boating activities of state and national signifi-
cance. The major rapids on the North and Middle Forks provide unique scenic
features with minimal human intrusion. A dry dam in the upper canyon would
significantly disrupt these activities and affect scenic and natural values.
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FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
The North Fork above the project area, from the Colfax Iowa-Hill bridge
upstream to near Heath Springs, was designated a National Wild and Scenic
River in 1978. In January 1993, the Bureau of Reclamation determined that the
Middle Fork and the North Fork within the project area are eligible for Wild and
Scenic designation, and a suitability study is under way.
The Auburn State Recreation Area lies mainly within the projected inunda-
tion zone of the originally proposed Bureau of Reclamation Auburn dam. The
area is less than an hour from Sacramento and is visited by about half a million
people each year. Because of its location and the diversity of opportunity, recre-
ational use of this area will undoubtedly grow rapidly in the future.
In 1972 the lower American River was included in the State Wild and Scenic
River System. In 1981 the exceptional anadromous salmonid fishery and other
important recreational values of this reach of the river led to its designation as a
unit of the National Wild and Scenic River System. The recreational units of the
lower basin are linked together by an award-winning trail system. The Jedediah
Smith Trail includes bicycle, pedestrian, and equestrian trails from Discovery
Park to Folsom Reservoir.
Recreational facilities along the American River begin in Sacramento at
Discovery Park, at the confluence of the American and Sacramento rivers. Above
Discovery Park, the American River Parkway extends 23 miles upstream to the
Folsom State Recreation Area at Nimbus Dam. The parkway is largely on the
floodplain bordered by high levees that isolate it from the surrounding urban
development. The parkway functions not only as a recreational area, but increas-
ingly as an urban transportation artery for pedestrians and bicycles. The parkway
was used by an estimated 5.5 million people in 1988, and annual use is expected
to grow to 7.5 million by year 2000 and 9.6 million by 2020. A 1983 survey
found that more than half of these visits were associated with water-enhanced
activities such as jogging, nature study, hiking, and picnicking, and that about a
third of the visits were associated with water-related activities such as swimming,
boating, and fishing. About 12 percent of the recreational use on the lower
American River is by boating primarily rafting, canoeing, and kayaking. These
activities are highly seasonal in nature, with about 90 percent occurring between
Memorial and Labor Days (USAGE, Sacramento District, l991J.
Fishing continues to be the biggest recreational use of California rivers, and
angling use of the lower American River is particularly important. About 55
percent of the total catch of chinook salmon in the freshwater of the entire
Sacramento River basin for the year 1991 came from the American River.
Catches of steelhead and American shad from the American River in the same
year were also comparatively large, making up 48 and 44 percent, respectively, of
the total Sacramento River basin harvest (CSLC, 19941.
Because of the size of Folsom Reservoir and its proximity to the Sacramento
metropolitan area, Folsom State Recreation Area is one of the most heavily used
areas in the state park system. The recreation area begins at the upper end of the
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ENVIRONMENTAL ISSUES
107
parkway at Lake Natomas, an afterbay formed by Nimbus Dam. Recreational
activities include fishing, power boating, sail boating, and windsurfing; there are
conflicts between power boating and windsurfing. About 2.1 million people visit
Folsom Reservoir each year, mostly Central Valley residents during the summer
(USAGE, Sacramento District, 1991J. Reoperation of Folsom Reservoir will
result in a lower pool during part of the year, adversely affecting recreational
opportunities there. Mitigation is included in the reoperation plan.
Prior to urbanization and development, there was little public recreation
development in Natomas, but bird hunting and watching on privately owned
farmlands were common and continue today through the lease of hunting rights
to hunting clubs. Much of the land along the Sacramento River in the Natomas
area is privately owned, but the river channel is heavily utilized for recreational
fishing and water sports including power boating, jet skiing, and kayaking. De-
velopment in the Natomas Basin would limit these recreational opportunities.
Impacts on Fish and Wildlife Resources
Given the importance placed on fish and wildlife by Sacramento area resi-
dents and visitors, potential impacts to these resources warrant careful review.
Fish habitat in the project area of the North Fork has been degraded by a number
of past actions, extending as far back as placer mining in the mid- 1 800s. Years of
habitat degradation have combined with high summer water temperatures to limit
the value of North Fork as a fishery resource in the reach that would be affected
by a dam of any kind. Though the Middle Fork has also experienced some habitat
degradation, the cool water outflow from Oxbow Dam supports a substantial
population of large wild trout, both brown and rainbow. This population quali-
fied as an "outstandingly remarkable" resource during the Wild and Scenic River
Eligibility Assessment conducted by the Bureau of Reclamation in 1992.
The fish resources of Folsom Reservoir consist of both warmwater and
Goldwater species. The warmwater species, primarily bass, catfish, and sunfish,
are adversely affected by fluctuations in surface elevation during the spawning
season. These fluctuations, along with low nutrient levels in the reservoir, result
in relatively low annual production for the warmwater fishes. The Goldwater
species, trout and salmon, are maintained by stocking, though limited natural
reproduction occurs in tributary streams.
The once abundant chinook salmon resource of the Sacramento River basin
has been reduced to a fraction of its original importance. Of the four distinct
seasonal runs of this species, only the fall run now occurs in any numbers, and the
winter-run fish is classified as endangered under the Federal Endangered Species
Act (Fisher, 1994~. Historic runs of salmon in the American River were esti-
mated above 130,000 and included both spring- and fall-run fish. Both races of
chinook were nearly decimated by hydraulic mining and dam construction in the
late 1800s and early 1900s (Gerstung, 1971~. The principal anadromous fish still
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FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
surviving in the American River is the fall-run chinook salmon, now limited to
the reach below Nimbus Dam. This population supports the extensive sport
fishery mentioned above and also a significant sport and commercial harvest in
the ocean. Over the period 1967 to 1991 (the baseline for the Central Valley
Project Improvement Act), the river supported an average run of 32,000 naturally
spawning fall chinook adults, about 22 percent of the total Sacramento River run
of 143,000. Returns to Nimbus Hatchery below Nimbus Dam for the same period
averaged 7,300 fish, 35 percent of the average Sacramento River total of 21,000
hatchery returns. The "naturally spawning" portion of the chinook run is actually
heavily influenced by hatchery fish. Some of the fish spawning in the river are
progeny of hatchery parents that fail to return to the hatchery, and some of the
naturally produced fish interbreed with hatchery stock. The natural run in the
American River has declined in recent years (the average run in the past 5 years
was about 50 percent of the 25-year average). Steelhead in the American River
are substantially less abundant and nearly entirely supported by hatchery produc-
tion (1967 to 1991 average returns to Nimbus Hatchery were about 1,700 fish).
Fishery values in the Natomas Basin are much lower than those upriver.
However, the Natomas area is highly significant for its wildlife values. Thou-
sands of migratory waterfowl use the basin for feeding and resting. The Natomas
basin reach of the Sacramento River supports one of the highest concentrations in
California of nesting territories for the Swainson's hawk, a state-listed threatened
species. And the southern portion of the American River basin in Sacramento
and Sutter counties, including the Natomas basin, provides one of the most im-
portant habitats remaining in California for the threatened giant garter snake (EIP
Associates, 19921.
Significant fish species in the zone of influence of the lower American River
(principally in the San Francisco Bay and Delta, affected by flow releases from
Folsom Reservoir' include the striped bass, which provides one of the most
important sport fisheries of the state, and the endangered winter-run chinook
salmon (reclassified from threatened status in January 1994), which passes the
mouth of the American River on its way to spawning grounds in the upper
Sacramento River basin. Other sensitive species affected by American River
flows include the federally listed as threatened delta smelt, primarily resident in
the bay and delta, and the Sacramento splittail (proposed for threatened status by
the FWS in January 1994), which occurs both in the delta and in the lower
reaches of the American River.
Two other federally listed species occur in the project area, the bald eagle
(federally listed as threatened) and the valley elderberry longhorn beetle (feder-
ally listed as threatened). The eagle occurs in significant numbers only on Folsom
Reservoir. The beetle occurs in association with elderberry shrubs primarily in
riparian areas of the upper canyon and the lower American River.
Owing to the extent of historical habitat degradation in the upper basin,
impacts of a detention dam in the canyon are much more likely to be significant
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ENVIRONMENTAL ISSUES
109
to recreational and rafting interests than to fisheries or fish habitat, particularly in
the North Fork. However, the important wild trout fishery in the Middle Fork
could be substantially affected if canyon wall sloughing following inundation is
extensive.
Under current operations the major limitation to success of the fishery re-
source of the lower American River is the flow and temperature regime below
Nimbus Dam. The period of major concern is during the spawning migration of
the fall-run chinook salmon. Owing to low flows during that time and to inad-
equate control of temperature of the releases from Folsom Dam, temperatures in
the river often exceed those suitable for survival of incubating salmon embryos.
Also of concern are temperatures and flows for rearing of juvenile salmon and
steelhead during spring or summer. The salmon are less at risk because the
juveniles leave the river by the early summer of their first year, before tempera-
tures reach maximum levels. Steelhead, however, must rear one or two full years
in the river before moving to the ocean. As a consequence of high summer
temperatures and limited flows, natural rearing of steelhead has been virtually
eliminated; more than 95 percent of returning fish are the result of hatchery
rearing (Snider and Gerstung, 1986J. A number of State Water Resources Control
Board rulings regulate releases from Folsom Reservoir but they are inadequate to
protect fish habitat. High temperatures and substantial and rapid fluctuation in
flows are a major limitation to significant natural production of salmonids in the
lower river (Snider and Gerstung, 1986; Williams, 1995~.
Some relief is potentially available as a result of a recent court decision,
resolution of which is still evolving. The case involved the Environmental De-
fense Fund et al. v. East Bay Municipal Utilities District et al. At issue was
where EB MUD would be allowed to divert an annual 150,000 acre feet, for
which it had contracted with the Bureau of Reclamation. The utility district
wished to divert the water through the Folsom-South Canal, above Nimbus Dam.
Environmental groups and others held that the diversion should occur lower
down in the river system to protect the public trust resources of the river. In a
decision handed down in January 1990, Judge Hodge of the Alameda County
Superior Court allowed diversion through the Folsom-South Canal, provided that
sufficient flow was available in the lower American River to support the anadro-
mous fishery and other trust resources. The judge approved minimum flows for
each season and mandated an ongoing research program. He also appointed a
Special Master to oversee the research, which was to be directed toward reducing
the overwhelming uncertainty that surfaced throughout the trial and also toward
more accurately defining the required minimum flows (Williams, 19951. The
decision was based in part on the Public Trust Doctrine (Sax, 1993) and has the
potential to influence water management in the state for some time. Owing to
provisions in the state constitution, members of the public in California have a
special right to use navigable waters for all purposes. The Public Trust Doctrine
gives the state particular responsibilities for protecting all beneficial uses of such
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FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
waters (CSLC, 1994), and it was this authority, in part, invoked in the Hodge
. .
c .eclslon.
Given that reservoir operation already has a substantial detrimental impact
on the fish populations, there seem to be no significant additional impacts on
fisheries of the reservoir or the lower river from any of the alternatives in the
original 1991 ARWI proposal. It also appears that no major additional effects
would be associated with interim reoperation of Folsom Reservoir. In fact, the
reoperation EIR/EA (SAFCA, 1994a) made several significant concessions to the
anadromous fishery and to protection of endangered species. It ensures that if
reoperation would require flow levels lower than the "Hodge flows," then Hodge
flows would be met, provided that water were available. This obligation would
be met by converting, to the extent possible, all potential environmental impacts
to reductions in CVP water delivery. In a contract with the Bureau of Reclama-
tion, signed in March 1995, SAFCA agreed to compensate the federal govern-
ment for this water debt by acquiring sufficient water or water rights from other
sources. SAFCA also agreed to finance modifications to the temperature control
louvers in Folsom Dam to ameliorate high temperatures in the river, and to fund
an evaluation of the impacts of reservoir reoperation on habitat of the Sacramento
splittail in the lower river (SAFCA, 1994a).
Direct impacts of flood reduction measures in the Natomas Basin appear to
be insignificant, but the indirect impacts of the additional development that would
be allowed by flood protection could be important to habitat of the threatened
giant garter snake and Swainson's hawk. The giant garter snake, listed as threat-
ened by the state and federally listed as threatened in October 1993, has recently
been given a high profile by the National Biological Service. Development of a
giant garter snake Habitat Conservation Plan has been named one of 12 new
national priority ecosystem initiatives of the agency. Though contractors for
SAFCA had already produced a draft Habitat Conservation Plan for both the
Swainson's hawk and the giant garter snake (EIP Associates, 1992), the plan to
be developed under this newer proposal will be critical to land development plans
in the Natomas Basin.
Another major source of uncertainty in the realm of aquatic resource issues is
the question of how the additional water required to reduce salinity and improve
habitat for endangered fish species in the bay and delta will be allocated. The
complicated and interwoven set of circumstances surrounding this issue is dis-
cussed in Chapter 6.
Projecting Ecosystem Responses in Impact Assessments
Since the preparation of the 1991 ARWI reports, federal resource manage-
ment agencies have adopted new strategies to consider and evaluate potential
impacts within the framework of whole ecological systems. This shift is an effort
to correct for past practices. Too often in the past, the focus of environmental
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ENVIRONMENTAL ISSUES
111
assessment has been on dominant plant or animal species at the expense of
understanding the important role that interactions among species and their envi-
ronment may have on the species and community survival and the role of corri-
dors and linkages of natural environments. The 1991 ARWI report was, for the
most part, no exception to this narrow focus, although the FWS did raise the
possibility of significant shifts in ecological systems due to disturbances that a
dry dam could trigger. It noted the absence of information on impacts to the plant
communities (emphasis added).
Ecosystem responses to a dry dam could include wildlife community shifts
associated with plant community shifts because of habitat changes. Positive
ecosystem changes could occur to the Lower American Parkway, in which levee
rebuilding and associated revegetation projects could help reintroduce greater
riparian species diversity.
Because of the significance of potential impacts of inundation on the plant
communities in the American River canyon, an ecosystem framework for de-
scription of these probable impacts is particularly important. An adequate envi-
ronmental assessment should attempt to provide descriptions on how ecosystem
dynamics, function, and structure could react to changes made to the system. In
the 1991 ARWI report the focus on potential inundation tolerances of individual
species loses sight of this critical larger picture. The potential for ecosystem
shifts in the American River canyon could be related to the direct impacts of
periodic inundation on plants or to the indirect impacts previously discussed,
such as changes to the composition of soils, soil microbiota, or community tree or
shrub densities.
The significance of such potential ecosystem losses and shifts needs to be
discussed in a regional context. An example of a regional ecosystem approach to
characterizing environmental impacts would be a discussion of the regional or
statewide value of riparian and oak woodlands. The 1991 ARWI noted that of the
state's original riparian habitat, less than 5 percent remains today. Moreover, less
than 2 to 3 percent of the woody riparian habitat remains along the Sacramento
River. What is the value of the riparian environment in the upper American River
in this context? What is the value of the upland woodlands that could be lost
through a combination of inundation and hillslope failure?
An effort to frame impacts in a regional context could, for example, recog-
nize that oak woodlands are an ecosystem of increasing concern to plant commu-
nity ecologists. Studies of foothill oak populations indicate that they do not have
the age distribution of healthy vigorous populations. Communities of valley,
blue, and Engelmann oaks show a narrow cluster of middle-aged trees, with few
young or old ones. The fear is that middle-aged oaks could reach the natural limit
of their life span and disappear, to be replaced by other less productive and less
diverse communities. Lack of reproductive success is attributed to a combination
of factors including deforestation, overgrazing by gophers, deer, and cattle, intro-
duction of exotic grasses, and alteration of fire cycles. It is estimated that the
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FLOOD RISK MANAGEMENT AND THE AMERICAN RIVER BASIN
state has lost over a million acres of oak woodland since the 1940s (Barbour et
al., 1993~. The potential area of impact in the upper canyon support two of the
state's three "oaks of special concern," the valley oak, Quercus lobata, and the
blue oak, Quercus douglasii.
Although sensitive species of oaks could be of concern, inventories of the
Cosumnes River watershed suggest that rare landscape forms could be of even
greater regional significance in the upper American River watershed. Inventories
of rare landforms and vegetative patterns indicate that montane oak woodland
and shrub communities are more widespread, for example, than the remnants of
Central Valley riparian systems and associated oak woodlands. Nonetheless, a
central issue to explore is, how many miles of canyons with free-flowing rivers,
scour zones, steep canyon walls, and a diversity of ecosystems do we have (Hart,
personal communication, 19951? Future impact evaluations should draw on the
methods for inventorying and evaluating landscape uniqueness (Leopold, 1969;
Riley, 1974~.
Scenarios should be developed for the potential ecosystem shifts of each
vegetative community that could be affected. Information so far suggests the loss
of old and young individuals and shifts to deciduous species. Chaparral commu-
nities disturbed by periodic inundation or landslides could shift to grasslands or
even "communities" of invasive exotics. Inundation would likely result in the
replacement of any native perennial grasses, ranked very rare by the state, by
more weedy, nonnative annual grasses. Disturbances in lower canyon elevations
could increase the extent of riparian zones, which typically occupy disturbed
environments (Knudsen, 1991; Keeley, 1992; Hart et al., 1994; Meredith et al.,
19941. While the forecasting of ecosystem shifts still remains in the realm of
speculation, the potential for both positive and negative ecological and aesthetic
changes should become part of the evaluation of impacts in future assessments.
CONCLUSION
The 1991 ARWI raised a number of contentious environmental issues, in-
cluding debate over whether the descriptions of the environmental impacts of the
various proposed alternatives was adequate. Based on its review, the committee
determined that there were several areas of the 1991 ARWI where the lack of
scientifically-based descriptions of environmental impacts prevented the report
from serving as an adequate planning document. The most significant deficien-
cies were in the assessment of impacts that might be caused by periodic inunda-
tions from a dry dam on the plant communities in the upper American River
canyon, the impacts of inundation on canyon soils and geologic stability, and an
ecosystem and regionally-based assessment of impacts. Whether subsequent
activities are filling some or perhaps all of these gaps is unclear at this time, but
these questions should be resolved with the expected publication of the Sacra
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ENVIRONMENTAL ISSUES
113
mento District's Draft Supplemental Information Report, expected in the summer
of 1995.
Public officials ultimately face a difficult decision: given the significant
flood hazard to Sacramento, landslide hazards in the American River canyon may
be deemed a necessary cost of flood protection. If this option is pursued, great
sensitivity to environmental values should be incorporated. If a dry dam contin-
ues to be included among the alternatives under consideration, the committee
suggests that the following research needs and issues be given consideration:
· The Sacramento District should form a team of experts in plant physiol-
ogy, plant ecology, and geomorphology to design a research plan that combines
field experiments, observations, vegetation mapping, landscape uniqueness data,
and modeling of landslide risks to develop a canyon inundation impact assess-
ment that can secure acceptance and credibility from the scientific community.
.
The two large old slides should be thoroughly mapped, analyzed, and
monitored to assess the potential hazards of catastrophic failure.
.
If dry dam outlets and storage are to be used they should be designed to
accommodate high sediment loads in anticipation of a worst-case scenario of
numerous hillslope failures.
.
Rates of drawdown should be minimized but should be sufficient to pre-
vent substantial vegetation mortality until more is known about long-term veg-
etation responses to inundation and slope responses to subtle vegetation changes.
· Gate design and operating policies should consider the depth and fre-
quency of inundation while keeping drawdown rates low. These conflicting
constraints prevent a dry dam from being used as a first line of defense and
instead restrict it to use as a last resort to contain peak discharges from extreme
rare events. This philosophy could be made explicit in the Folsom Dam operat-
ing policy.
Representative terms from entire chapter:
lower american
