Flood Risk Management and the American River Basin An Evaluation (1995) / Chapter Skim
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3 ENVIRONMENTAL ISSUES
3 ENVIRONMENTAL ISSUES
Pages 85-113
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From page 85... ...
, considered environmental impacts. It pays particular attention to the assessment of environmental impacts associated with the proposed Auburn dry dam alternative and associated inundation impacts in the American River canyon, but also addresses a range of other environmental considerations.
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From page 86... ...
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 mitigation measures could easily be implemented. In contrast, CEQA requires agencies to implement feasible mitigation measures and alternatives identified in the environmental impact reports.
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From page 87... ...
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)
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From page 88... ...
Environmental restoration project components and geomorphological considerations 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.
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From page 89... ...
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 .
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From page 90... ...
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 improved 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.
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From page 91... ...
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.
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From page 92... ...
This alternative would presumably decrease impacts to vegetation, wildlife, aesthetics and recreation that normally accompany permanent pool multipurpose dams (USAGE, Sacramento District, 1991~. The range of technical issues raised concerning the potential dry dam impacts includes how to predict impacts from unstable geology and soils in inundated zones; how to predict impacts from inundation of nonriparian chaparral, oak woodland, and digger pine communities, which are not covered by inundation 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.
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From page 93... ...
There is little empirical information on drawdowns approaching the rates or magnitudes that might occur behind an ungated Auburn dry dam (USAGE, Sacramento District, 1991) , although rates could be controlled and damage lessened if controllable gates were employed.
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From page 94... ...
In the initial dry dam plan, the Sacramento District mapped inundation areas using the depth-frequency-duration curves and concluded that inundation impacts 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)
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From page 95... ...
· 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.
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From page 96... ...
There has been no subsequent frequency analysis, and landslide magnitude-frequency relationships remain undetermined. Long-term Hillslope Stability The minimal impacts of slope failures estimated by the Sacramento District and the CDWR studies were also questioned on the basis that the time frame considered, 100 years, was too short (WRC-Environmental and Swanson, 1992~.
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From page 97... ...
Reports completed in 1994 under contract to SAFCA and the Sacramento District concluded that existing inundation research and field observations at Auburn canyon and the Keswick Dam area of the Sacramento River do not adequately support defensible estimates of inundation effects on vegetation in the American River canyon (Chasse and Platenkamp, 1994; Hart et al., 1994~. These reports concluded that the initial information developed for the 1991 ARWI and its environmental impact report and statement and habitat evaluation procedures was inadequate to support the quantified estimates of inundation losses used in the 1991 analysis.
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From page 98... ...
In addition, SAFCA contracted for some of the experimental field data proposed by Keeley. It hired consultants to conduct inundation studies involving the submergence of plants in Folsom Reservoir (Hart et al., 1994J and to collect field data from the Sacramento River below Keswick Dam that could be applied to the Auburn Canyon case (Meredith et al., 1994~.
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From page 99... ...
No new citations were found that contained information on flood tolerances of upland species that would occur in the American River canyon" (Chasse and Platenkamp, 1994~. Experimental Research and Data Collection from Sites with Similar Plant Communities Experimental field research involving the actual submersion of some Auburn Canyon plants in Folsom Reservoir and collection of observational data on plants affected by inundation on the Sacramento River were begun in 1994 in line with Keeley's (1992)
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From page 100... ...
It has rocky soils, which are hard to saturate and drain quickly, and the site is more drought prone than the Auburn canyon. These conditions can either contribute to greater survival because good drainage or dryer conditions might be critical factors, or the conditions might represent stresses that produce higher mortality levels than would be the case in the upper American River canyon.
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From page 101... ...
The report summarized the findings of the different research documents prepared for the ongoing American River investigations, identified the areas of conflicts among the reports, and helped identify the points on which experts agree. The report stated unequivocally that the available information on plant inundation does not support precise estimates of inundation effects on vegetation in the American River canyon and called for a research strategy that openly acknowledges this uncertainty.
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From page 102... ...
OTHER ISSUES OF CONCERN Beyond consideration of the dry dam alternative, there are a number of other environmental issues related to flood control planning in the American River basin. These are generally less contentious than those surrounding the dry dam,
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From page 103... ...
Impacts on the Lower American River Plant Community In addition to the environmental considerations assessed in the upper American 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.
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From page 104... ...
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.
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From page 105... ...
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.
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From page 106... ...
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.
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From page 107... ...
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.
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From page 108... ...
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.
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From page 109... ...
Under current operations the major limitation to success of the fishery resource 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.
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From page 110... ...
Projecting Ecosystem Responses in Impact Assessments Since the preparation of the 1991 ARWI reports, federal resource management 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.
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From page 111... ...
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 description of these probable impacts is particularly important.
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From page 112... ...
The most significant deficiencies were in the assessment of impacts that might be caused by periodic inundations 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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From page 113... ...
If this option is pursued, great sensitivity to environmental values should be incorporated. If a dry dam continues 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 physiology, 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 assessment that can secure acceptance and credibility from the scientific community.
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