Chapter V: Environmental Consequences

Introduction

The National Environmental Policy Act (NEPA) requires that environmental documents disclose the environmental impacts of a proposed federal action, reasonable alternatives to that action, and any adverse environmental effects that cannot be avoided should the proposed action be implemented. This chapter analyzes the environmental impacts of the four Merced Wild and Scenic River Revised Comprehensive Management Plan and Supplemental Environmental Impact Statement (Revised Merced River Plan/SEIS) alternatives on natural resources, cultural resources, the visitor experience, and social resources. This analysis provides the basis for comparing the beneficial and adverse effects of the alternatives.

In compliance with NEPA, the environmental analysis evaluates the potential effects of the alternatives on all of the park's natural, cultural, visitor experience, and social resources, including those not encompassed within the Outstandingly Remarkable Values (ORVs). However, since this document must comply with the requirements of the Wild and Scenic Rivers Act, the potential effects of the alternatives on the ORVs for each segment are addressed in the resource analysis. In addition, how each alternative protects and enhances the ORVs under the Wild and Scenic Rivers Act is summarized in the tables at the end of the analysis section for each alternative.

This analysis only addresses environmental consequences associated with the development and implementation of a user capacity program for the Merced River corridor and the reassessment of the river corridor boundary based on the location of ORVs and related management zoning prescriptions in the El Portal segment. The remaining management elements as previously described and analyzed in the Merced River Plan/FEIS are not being revisited or reanalyzed in this Plan.

Due to the conceptual nature of the alternatives, their potential consequences can be addressed only in qualitative terms. The conclusions presented herein are based on review of existing information provided by the National Park Service. If and when specific National Park Service management actions are proposed as a result of this plan, National Park Service staff will determine whether more detailed environmental documentation is required, consistent with the provisions of NEPA.

Following this introduction, Chapter V presents the methodologies used in the environmental impact analysis. The impact analyses sections are organized by alternative. The first section analyzes Alternative 1 (the No Action Alternative), including impacts on natural resources, cultural resources, the visitor experience, and social resources and presents mitigation measures, cumulative impacts, and impact conclusions. The same framework of analyses is applied to Alternatives 2, 3, and 4 in subsequent sections. Environmental impacts are summarized in table III-12 at the end of Chapter III.

Cumulative Impacts

A cumulative impact is described in regulations developed by the Council on Environmental Quality (CEQ), regulation 1508.7, as follows:

". . . a "Cumulative impact" is the impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (Federal or non-Federal) or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time."

Appendix E contains the list of past, present, and reasonably foreseeable actions included in the cumulative impacts analysis. These cumulative actions are evaluated in the impact analysis in conjunction with the impacts of an alternative to determine whether they would have any additive effects on a particular natural, cultural, or social resource. Because many of these cumulative actions are in the early planning stages, the evaluation of cumulative impacts was based on a general description of each project.

The Revised Merced River Plan/SEIS is a programmatic document and does not recommend implementation of specific large-scale construction or development related actions. As a result, the cumulative impacts analysis is presented in qualitative terms, rather than in specific measured or quantitative terms. General guidance and methodologies for the cumulative impacts analysis in this document follow those published by the CEQ (CEQ 1997). Cumulative impacts have been analyzed for each alternative, and can be found following the environmental consequences analysis for each resource topic. The methodology for defining the context, intensity, duration and type of cumulative impact for a specific resource topic is the same as that described for the environmental consequences analysis of each resource topic.

Impairment

Impairment is an impact that, in the professional judgment of the responsible National Park Service manager, would harm the integrity of park resources or values, including the opportunities that otherwise would be present for the enjoyment of those resources or values. The need to analyze and disclose impairment impacts originates from the 1916 Organic Act, which mandated the National Park Service "to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."

An impact would be less likely to constitute impairment if it is an unavoidable result (which cannot reasonably be further mitigated) of an action necessary to preserve or restore the integrity of park resources or values (NPS 2000c). An impact would be more likely to constitute impairment to the extent that it affects a resource or value whose conservation is:

·       Necessary to fulfill specific purposes identified in the establishing legislation or proclamation of the park

·       Key to the natural or cultural integrity of the park or to opportunities for enjoyment of the park

·       Identified as a goal in the park's General Management Plan (NPS 1980a) or other relevant National Park Service planning documents

Impairment of park resources was evaluated on the basis of the type and intensity of impacts, and in terms of the types of resources affected. Impairment is generally considered for natural, cultural, and scenic resources. Overall, beneficial impacts would not constitute impairment. With respect to the intensity of impacts, negligible and minor adverse impacts are not of sufficient magnitude to constitute impairment. Moderate and major adverse impacts may constitute impairment, but not automatically. Rather, these impacts must be analyzed with respect to the three criteria presented above. Impairment is generally considered for geological, hydrological, biological, cultural, and scenic resources. Impairment determinations are not required for resource topics that are not considered to be park resources or values. Thus, impairment is addressed in the conclusion section of the appropriate resource topics under each alternative.

Methodologies

This section presents the methodologies used to conduct the environmental impact analyses. The section begins by describing methodologies and assumptions common to all resource topic areas, and then presents methodologies specific to individual resource topic areas in the following order:

Natural Resources: Geology, Geohazards, and Soils; Hydrology, Water Quality, and Floodplains; Wetlands; Vegetation; Wildlife; Rare, Threatened, and Endangered Species; Air Quality; and Noise

Cultural Resources: Archeological Resources; Traditional Cultural Resources; and Historic Sites, Structures, and Landscapes

Visitor Experience: Recreation; Interpretation and Orientation; Visitor Services; and Wilderness Experience

Social Resources: Land Use; Transportation; Scenic Resources; Socioeconomics; and Park Operations and Facilities

Each resource topic area includes a discussion of the impacts of each alternative, including the identification of the impacts or affects of the actions comprising the alternative, and a characterization of the impacts in terms of context, intensity, duration, and type of impact. The context of the impact considers whether the impact would be local or regional. The intensity of the impact refers to the severity or magnitude of the impact, and considers whether the impact would be negligible, minor, moderate, or major. The duration of the impact considers whether the impact would occur in the short term (temporary) or the long term (permanent). The type of impact considers whether the impact would be beneficial or adverse to the natural, cultural, or social environment.

Annual park visitation peaked at just over 4.19 million visitors in 1996. Park visitation decreased from 1996 through 2004 to approximately 3.39 million visitors annually. However, for the purposes of this analysis, it is expected that overall park visitation will increase slowly over the next 15 years under existing park management policies (the No Action Alternative). Although it is not known how much annual visitation would increase by 2020, it is expected that increased visitation during peak periods would require implementation of restricted access to Yosemite Valley during some peak visitation periods. Increased visitation demand by 2020 would be expected to trigger the need to implement restricted access on an increasing number of days during the peak season, and it is expected that there would be more restricted access days in 2020 than is currently experienced. Increases in 2020 visitation levels would be expected to occur primarily during the current non-peak periods (e.g., before and after peak summer months, and on weekdays during peak summer months).

With the implementation of a VERP program and possibly limits, some of the alternatives could result in decreased visitation to segments of the Merced River corridor. As a result, it is assumed that by 2020 some visitors could be displaced to other areas of the park or displaced from the park itself.

This document is a programmatic plan that looks at broad user capacity program frameworks. The plan does not recommend implementation of specific developments or actions. To provide decision makers and the public with an accurate idea of the environmental consequences of the Revised Merced River Plan/SEIS alternatives, the analysis team identified potential actions that management could implement under the frameworks provided under each of the action alternatives and analyzed their effects as compared to conditions under the No Action Alternative. The environmental consequences analyses are qualitative rather than quantitative, because the action alternatives are conceptual and specific actions are not prescribed under this plan.

The environmental consequences analysis in this chapter evaluates the potential effects of implementation of various types of management actions. Because implementation of VERP would allow for park management to use a variety of management tools to address user-related impacts, the analysis evaluates the potential effects of a broad range of actions - from public education to construction of improvements to visitor access restrictions. In reality, implementation of the VERP program would likely result in the implementation of a number of these measures, as determined to be appropriate based on site-specific circumstances. VERP is an adaptive management process, and management actions would change and evolve based on the continued monitoring of actual conditions versus desired conditions. Thus, if VERP monitoring indicated there was a yellow light condition (see figure II-6 in Chapter II), park management could begin implementing measures such as public education, installation of temporary barriers, or other easily management actions to bring conditions back within standards. If conditions were to continue to decline, park management would most likely implement additional, more restrictive or intensive measures to address the impacts. Because the VERP program requires park management to take actions to keep conditions within adopted standards, or to improve conditions that do not meet the standards, park management would continue to implement a variety of measures as needed to meet the adopted standard. Therefore, although the effects of individual management actions taken in the short term are identified in each section, the overall effect of the VERP component of the action alternatives would be to protect and enhance the condition of park resources and ORVs in the long term.

Finally, the No Action Alternative for the Revised Merced River Plan/SEIS includes the implementation of all of the elements of the Merced River Plan (with the exception of VERP), as well as implementation of other existing user capacity measures described in Chapter II, such as the trailhead quota system and facility limits. Although each of the action alternatives also includes implementation of the Merced River Plan elements and the user capacity program as described under the No Action Alternative, the analysis in this chapter focuses on the effects of implementing the additional user capacity elements of each action alternative (VERP, limits) compared to the No Action Alternative.

Natural Resources

Geology, Geohazards, and Soils

This impact assessment focused on effects that geologic processes in the Yosemite National Park would have on visitors, employees, and facilities under each alternative of the Revised Merced River Plan/SEIS. Geologic processes can negatively affect visitors, employees, and facilities when events such as rockfalls, earthquakes, and severe soil instability result in injury, death, or damage to facilities.[1] The assessment also focused on the effect the Revised Merced River Plan/SEIS alternatives would have on the geologic processes, namely, the formation and conservation of soil resources. Impacts associated with management actions discussed in this Revised Merced River Plan/SEIS could affect current soil resources through accelerated erosion, soil loss, or soil removal.

Several assumptions regarding facility placement, geologic design parameters, and public safety were integrated into this assessment, as summarized below.

·       It is not possible to avoid risks due to geologic processes such as earthquakes and rockfalls. Considering this, some facilities located within the park, especially in Yosemite Valley, the Merced River gorge, and El Portal would be exposed to risks of damage from rockfalls.

·       Geotechnical studies to determine soil stability conditions would be performed prior to placing, designing, or relocating a facility within the park, and facility design within Yosemite National Park would conform to accepted building codes regarding seismic design parameters.

·       In emergency situations, the National Park Service may mechanically trigger a rockfall, but in most cases the National Park Service allows natural processes to occur unimpeded.

·       The National Park Service has developed geologic hazard guidelines for development within Yosemite Valley (Appendix C in NPS 2000e). The focus of these guidelines is to protect visitors, employees, and infrastructure from geologic hazards and to locate facilities out of geologically hazardous areas.

·       In the event of a rockfall, the National Park Service would close the affected area to protect visitor and employee safety. Rocks on roads would be removed, but rockfall talus in rivers would not be removed, unless the river is dammed and flooding threatens utilities or facilities.

Geologic risks that affect public safety are rarely predictable, and the extent to which they can affect people and property cannot be quantified. Quantitative analysis of other potential effects, such as soil erosion, removal, and loss was not feasible for this impact assessment due to the programmatic nature of the plan. Rather, analysis of effects was qualitative, and professional judgment has been applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts. When possible, mitigation measure(s) were incorporated into this Revised Merced River Plan/SEIS to reduce the intensity of adverse effects.

Impact Assessment

The impact assessment addressed geologic hazards (earthquakes and rockfalls) and impacts to soil resources. Geologic hazards that would expose people to injury and infrastructure to damage were considered in terms of impacts to public safety. Geologic impacts related to facility development or natural resource protection were considered in terms of depletion of or adverse effects on soil resources. Potential management actions under each alternative were evaluated in terms of the context, intensity, and duration of the geologic impacts, and whether the impacts were considered to be beneficial or adverse to visitors, infrastructure, or soil resources.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or impacts specific to the river corridor, including the El Portal Administrative Site. In considering geologic hazards, it was assumed that the impacts would be consistently local.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on public safety or soil resources. Minor impacts were those that would be present but would not be expected to have an overall effect on those conditions. Moderate impacts would be clearly detectable, and could have an appreciable effect on public safety and soil resources. Major impacts would have a substantial, highly noticeable influence on public safety and soil resources.

There will always be a potential for adverse impacts to life and property due to geologic hazards in Yosemite National Park. Therefore, management actions to avoid placement of facilities (or reduce numbers of people) in areas susceptible to geologic hazards may decrease the risks but would not necessarily reduce the intensity of the impact.

Duration. The duration of an impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of impacts. A long-term impact would have a permanent effect on public safety and geologic conditions.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to public safety and soil resources. Beneficial impacts would improve soil resources by restoring areas and limiting development. Adverse impacts would expose people and property to effects of earthquakes and rockfall events. Adverse impacts also would deplete or negatively alter soil resources.

Hydrology, Floodplains, and Water Quality

This section analyzed potential changes to hydrologic processes of the Merced River, including the river's interaction with its floodplain as well as water quality. This qualitative assessment focused on the physical and chemical processes of the Merced River that might be altered under the management practices called for as part of the proposed alternatives. Quantitative analyses of any potential changes to the Merced River were not feasible due to the programmatic nature of the plan. Analysis of the alternatives was qualitative and based on identified hydrologic processes, as described in the Hydrology, Floodplains, and Water Quality section in Chapter IV, Affected Environment.

Streamflow

The analysis examined potential changes to the free-flowing nature of the river as a result of the potential management actions listed under each of the action alternatives. This section addressed existing and potential future restrictions on streamflow and the possibility of removing current streamflow restrictions, such as dams or levees.

Floodplain

This section qualitatively analyzed the impacts or benefits to the river's floodplain due to potential changes in intensity and location of visitor use along the river. Due to the qualitative nature of this assessment, a reduction or modification of visitor use and facility development in the floodplain was perceived to be beneficial to the floodplain and protection of the river channel.

Water Quality

The analysis identified potential effects on water quality associated with visitor use and the generation of nonpoint-source pollution, such as refuse and automobile-related pollutants. Additionally, the analysis examined potential impacts on water quality from construction or removal of facilities within the river's floodplain.

Impact Assessment

Proposed management actions for each alternative were evaluated in terms of the context, intensity, and duration of the hydrologic impacts, and whether the impacts were considered to be beneficial or adverse to the hydrologic environment.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur at localized areas due potential management actions within the corridor. Regional impacts would be impacts on the entire river corridor within Yosemite National Park.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on the hydrology or quality of the river. Minor impacts were effects on hydrologic processes that were slightly detectable but not expected to have an overall effect on the character of the river or its floodplain. Moderate impacts would be clearly detectable and could have an appreciable effect on hydrologic processes, the adjacent floodplain, or water quality. Major impacts would have a substantial, highly noticeable influence on the hydrologic environment and could permanently alter river processes, floodplain formation and evolution, and water quality.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional activities, such as facility construction or road removal. A long-term impact would have a permanent effect on the hydrologic environment, such as altering the dynamic processes that govern the free-flowing nature of the river, floodplain formation and evolution, or the condition of water quality.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to the hydrologic environment. Beneficial impacts would sustain streamflow dynamics, allow natural processes to prevail, and protect or improve water quality. Adverse impacts would negatively alter hydrologic processes, thereby hindering natural processes and reducing protection of the river, its floodplain, and water quality.

Wetlands; Vegetation; Wildlife; and Rare, Threatened, and Endangered Species

National Park Service policy is to protect the natural abundance and diversity of all of the park's naturally occurring communities. To provide a consistent basis for analyzing impacts, and to ensure that alternatives are compared using the same frame of reference, the methodology described below was developed.

Some aspects of impact assessment methodology relate simply to whether an action breaches federal laws, regulations, and executive orders; similar state laws (for example, the California Endangered Species Act); or National Park Service Management Policies 2001 (NPS 2000f). A second level of impact assessment must address issues and concerns expressed during public scoping. The third, and probably the most important, level compares a projected impact with the natural history of a species or the known sensitivities of a habitat.

This assessment was based on the assumptions listed below.

·       The greater the size of a biotic community and the stronger its links to neighboring communities, the more valuable it is to the integrity and maintenance of biotic processes. Development limits the size of a community and fragments and disassociates communities from each other.

·       The more developed areas become, the less valuable they are as wildlife habitat. New development would increase human presence and increase the potential for soil, wildlife, and vegetation disturbance. The potential for negative wildlife interactions (such as human injury from wildlife and the introduction of unnatural food sources) also would increase. The removal of development from an area would increase the value of the habitat. However, in some cases, dispersal of the same number of visitors may well have a greater impact than an existing "containment" of disturbance within a designated area.

·       The effects of human food on the behavior, distribution, and abundance of wildlife species would continue in existing developments and would begin in new developments unless adequate facilities, education, and enforcement were provided.

·       The juxtaposition of natural communities to roads and other developments hinders the use of prescribed fire for restoring historic fire intensity, frequency, and severity.

·       Development and activities near sensitive habitats may adversely affect adjacent natural communities. Modifications of a river channel may cause channel instability and shifting, increased bank erosion, and changes in flood-flow elevations. The presence of well-vegetated banks and a sufficient width of riverbank protects the integrity of the river channel and shore.

·       Disturbance in or near a river and its tributaries may reduce the productive capabilities of associated natural communities. Modifications to river form, soil compaction, loss of riparian vegetation, removal of woody debris, and accelerated erosion and sediment transport influence important habitat characteristics such as riffle/pool complexes, substrate type, location, and cover. These physical aspects often determine the composition of vegetative and aquatic communities.

·       Roads change water inflow and outflow patterns and may dewater sections of meadow. The lack of a sufficiently high water table in meadows allows invasive plants to outcompete native vegetation and encourages conifer establishment, which threatens meadow communities.

·       Roads generally form barriers for wildlife and fragment habitat.

·       Development and impacts in riparian zones may influence critical water quality elements such as water temperature, suspended sediments, and nutrients. These elements interact in complex ways in aquatic systems and directly and indirectly influence patterns of growth, reproduction, and migration of aquatic organisms.

·       Ecological restoration of native communities would involve some short-term adverse impacts (e.g., smoke from prescribed burning) but over time can successfully replicate natural processes.

Quantitative analysis--that is, determining a measure of impact such as decibels of sound reaching the nest of a spotted owl--was not feasible for this methodology because this plan is programmatic and does not look at the implementation of specific actions. Qualitative analysis relies substantially on professional judgment, supported by extrapolation of relevant research, where appropriate, to reach reasonable conclusions as to the context, intensity, duration, and type of potential effect. When possible, mitigation measure(s) were incorporated into the document to reduce the adverse effects of impacts to natural resources.

Impact Assessment

The starting point for impact assessment is the natural processes of the Merced River corridor, including size, physical foundation, and components of the natural communities and ecosystems.

Proposed management actions under each alternative were evaluated in terms of the context, intensity, and duration of the impacts, as defined below, and whether the impacts were considered to be beneficial or adverse to the natural environment. Generally, the methodology for natural resource impact assessment follows direction provided in the Council of Environmental Quality Regulations for Implementing the National Environmental Policy Act, section 1508.27.

Context. Context suggests that certain impacts depend upon the setting of the proposed action. For instance, impacts that reduce the value of the Merced River in providing connectivity between habitat types could be minor if such connections are abundant in a given region, moderate or major if they are not. The context of the impact considers whether the impact would be local or regional.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. These designations are used to describe both beneficial and adverse impacts. Negligible impacts were effects considered detectable but having no principal effect on biological resources. Minor impacts were effects that were detectable but not expected to have an overall effect on natural community structure. Moderate impacts would be clearly detectable and could have an appreciable effect on individual species, community ecology (e.g., the numbers of different kinds of amphibians present), or natural processes (e.g., fire). Major impacts would have a substantial, highly noticeable influence on natural resources. This would include impacts that have a substantial effect on individual species, community ecology, or natural processes.

Duration. Under this heading, both short- and long-term effects are relevant. A short-term impact would be temporary in duration and associated with transitional types of impacts, such as facility construction or bridge removal. Long-term impacts are somewhat more conjectural. For example, long-term declines in bird species diversity at heavily used sites may take decades to become evident.

Type of Impact. The type of impact considers whether the impact would be beneficial or adverse to biological resources. Effects to biological resources are considered beneficial if an action causes no detrimental effect and results in an increase in rare species or habitat components, native ecosystem processes, native species richness/diversity, or native habitat quantity and quality.

Air Quality

The air quality impact assessment involved the identification and qualitative description of the types of actions under the various alternatives that could affect air quality, corresponding emissions sources and pollutants, and relative source strengths. Based on the relative source strengths, a qualitative assessment was performed to determine the potential for higher pollutant emissions or concentrations, taking into account the frequency, magnitude, duration, location, and reversibility of the potential impact. In addition, regional pollutant transport issues were evaluated in the context of regional cumulative impacts.

Several assumptions were integrated into this assessment:

·       This plan would not affect the smoke management policies in the Fire Management Plan (NPS 2004b).

·       This plan would not affect the campfire regulations in the Valley.

·       The National Park Service would continue to ensure that all stationary emissions sources under its control or under the control of its concessioners comply with applicable air district rules and regulations.

·       The National Park Service would continue to participate in the regional air quality planning processes for ozone, PM-10/PM-2.5, and visibility impairment and would continue to review applications for new or modified major stationary sources upwind of the park, pursuant to Prevention of Significant Deterioration regulations.

·       The National Park Service would comply with U.S. Environmental Protection Agency's (U.S. EPA's) general conformity rule for any future actions that would occur within Madera County, which is part of San Joaquin Valley Air Basin, a nonattainment area for the national 1-hour ozone, 8-hour ozone, and PM-10 standards, and within Mariposa County, which is a nonattainment area for the national 8-hour ozone standard.

Quantitative analysis of potential air quality impacts was not feasible due to the programmatic nature of this plan. Rather, analysis of effects was qualitative, and professional judgment was applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts. When possible, mitigation measure(s) were incorporated into the plan to reduce the intensity of adverse effects.

Impact Assessment

The air quality impact assessment of the plan evaluated how types of changes would affect air pollutant emissions and concentrations. Air quality impacts were evaluated in terms of their context, intensity, and duration, and whether the impacts were considered to be beneficial or adverse.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or impacts specific to the river corridor, including the El Portal Administrative Site. Regional impacts would be those related to the applicable air basins: Mountain Counties Air Basin and San Joaquin Valley Air Basin. With respect to air quality issues, both local and regional perspectives were relevant.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on air quality. Minor impacts were those that would be present but not expected to have an overall effect on those conditions. Moderate impacts would be clearly detectable and could have an appreciable effect. Major impacts would have a substantial, highly noticeable influence on local or regional air quality.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of impacts. A long-term impact would have a permanent effect on air quality.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to air quality. Beneficial air quality impacts would reduce emissions or lower concentrations, and adverse impacts would have the opposite effect.

Noise

The noise impact assessment involved the identification and qualitative description of the types of actions proposed under each alternative that could affect the ambient noise environment, corresponding noise sources, relative source strengths, and other characteristics. Based on the relative source strengths, a qualitative assessment was performed to determine the potential for a substantial increase in ambient noise levels in areas where natural quiet is an important resource. Assessments were also performed where noise-sensitive uses are located or would expose persons to excessive noise levels taking into account the frequency, magnitude, duration, location, and reversibility of the potential impact. In addition, regional noise issues such as aircraft overflights were discussed in the context of long-term trends in wilderness noise exposure.

Quantitative analysis of potential noise impacts was not feasible due to the programmatic nature of this plan. Rather, analysis of effects was qualitative, with professional judgment applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts. When possible, mitigation measure(s) were incorporated into the plan to reduce the intensity of adverse effects.

Impact Assessment

The noise impact assessment evaluated how these three basic types of changes of the plan would affect the ambient noise environment in the corridor. Noise impacts were evaluated in terms of their context, intensity, and duration, and whether the impacts were considered to be beneficial or adverse.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or impacts specific to the river corridor, including El Portal. In considering noise impacts, it was assumed that the impacts would be consistently local.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on the ambient noise environment. Minor impacts were those that would be slightly detectable but not expected to have an overall effect on those conditions. Moderate impacts would be clearly detectable and could have an appreciable effect. Major impacts would have a substantial, highly noticeable influence on the ambient noise environment.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of impacts, such as construction noise impacts. A long-term impact would have a permanent effect on the ambient noise environment related to park operations.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to the ambient noise environment. Beneficial noise impacts would reduce associated levels and/or exposure, while adverse impacts would have the opposite effect.

Cultural Resources

Section 106 of the National Historic Preservation Act requires a federal agency to take into account the effects of its undertaking on properties included in, or eligible for inclusion in, the National Register of Historic Places (National Register) and provide the Advisory Council on Historic Preservation the reasonable opportunity to comment. This also applies to properties not formally determined eligible, but which are considered to meet eligibility requirements.

The methodology for assessing impacts to historic resources is based on the 1999 Programmatic Agreement (see Appendix H in the Merced River Plan/FEIS) (NPS 1999w). This includes: (1) identifying area of potential impact; (2) assessing the level of resource information available, and conducting appropriate research and evaluations necessary to obtain information about resources potentially eligible for listing in the National Register; (3) comparing the area of potential effect with that of resources listed, eligible, or potentially eligible for listing in the National Register; (4) identifying the extent and type of effect; (5) assessing these effects according to procedures established by the Advisory Council's regulations; and (6) considering ways to avoid, minimize, or mitigate adverse effects (36 CFR 800).

Cultural resource impact analysis in this environmental impact statement is described in terminology consistent with the regulations of the CEQ. CEQ regulations require that the impacts of alternatives and their component actions be disclosed. It is intended that the impact assessment will comply with the requirements of both NEPA and Section 106 of the National Historic Preservation Act. The determination of effect for the undertaking (implementation of the alternative) required by the 1999 Programmatic Agreement is included in the Conclusions section for each alternative. Consistent with CEQ regulations, the analysis of individual actions includes identification and characterization of potential impacts, including an evaluation of impact intensity. This is a fundamental difference between NEPA and the National Historic Preservation Act; the National Historic Preservation Act requires determinations of no effect or effect, and furthermore, where there is a determination of effect, requires a determination of whether that effect is adverse or not adverse. Effect is evaluated on the basis of whether an undertaking alters the characteristics of a property qualifying it for eligibility to the National Register. Intensity of impacts in the cultural resource analysis then, for purposes of NEPA, is defined as:

Negligible - Impact is barely perceptible and not measurable; confined to small areas or a single contributing element of a larger national register district or archeological site(s) with low data potential

Minor - Impact is perceptible and measurable; remains localized and confined to a single contributing element of a larger national register district or archeological site(s) with low to moderate data potential

Moderate - Impact is sufficient to cause a change in character-defining feature; generally involves a single or small group of contributing elements or archeological sites(s) with moderate to high data potential

Major - Impact results in substantial and highly noticeable change in character-defining features; involves a large group of contributing elements and/or individually significant property or archeological site(s) with high to exceptional data potential

Archeological resources are typically considered eligible for inclusion in the National Register because of the information they have or may be likely to yield. Intensity of impacts to archeological resources relates, additionally, to the importance of the information they contain and the extent of disturbance or degradation.

Traditional cultural resources are considered eligible for inclusion in the National Register as Traditional Cultural Properties when they are rooted in a community's history and are important in maintaining the continuing cultural identity of the community and meet National Register criteria for evaluation and integrity. Intensity of impacts to traditional cultural resources may relate to access and use of, as well as changes to, traditionally important places.

Historic sites, structures, and landscapes are considered eligible for inclusion in the National Register when they are associated with events that have made a significant contribution to the broad patterns of our history; when they are associated with the lives of persons significant in our past; or when they embody the distinctive characteristics of a type, period, or method of construction. Intensity of impacts to historic sites, structures and landscapes may relate to the extent of degradation of site and structural integrity, including the loss of landscape characteristics.

Council of Environmental Quality regulations, moreover, call for a discussion of the "appropriateness" of mitigation and NPS-12, the National Environmental Policy Act Guideline of the National Park Service, requires an analysis of the "effect" of mitigation. The "resultant" reduction in intensity from mitigation is an estimate of the effectiveness of mitigation under NEPA. It does not suggest that the level of effect as comprehended by Section 106 is similarly reduced.

Mitigation for NEPA purposes in this environmental impact statement is based on the park's 1999 Programmatic Agreement and includes avoidance of adverse effects or application of one or more Standard Mitigation Measures described in Stipulation VIII(A) of this Agreement. Avoidance strategies may include application of the Secretary of the Interior's Standards, design methods such as vegetation screening when placing new facilities in a historic district, and development of design standards to ensure compatibility.

In the case of archeological resources, mitigation includes avoidance of sites through design by minimizing effects through recovery of information that makes sites eligible for inclusion in the National Register. Generally, this data recovery will be based on the 1999 Archeological Synthesis and Research Design. In accordance with Stipulation VIII of the 1999 Programmatic Agreement, Standard Mitigation Measures may be implemented when avoidance is not feasible or prudent and the undertaking may result in an adverse effect on historic properties. Standard Mitigation Measures include documentation according to standards of the Historic American Buildings Survey/Historic American Engineering Record as defined in the October 1, 1997, Re-Engineering Proposal. The level of this documentation, which includes photography and a narrative history, would depend on significance (national, state, local) and individual attributes (individual elements of a cultural landscape, individually significant structures, etc.). When demolition of a historic structure is proposed, a select few architectural elements and objects may be salvaged for reuse in rehabilitating similar structures or added to the park's museum collection. However, only a limited number of elements and objects can be added to the museum. In addition, the story of history of alteration of the human environment, and reasons for that alteration, will be interpreted to park visitors.

According to Stipulation VII(C) of the 1999 Programmatic Agreement, effects on archeological resources are considered "not adverse" for purposes of Section 106 if data recovery is carried out in accordance with the 1999 research design. Under the revised regulations of the Advisory Council on Historic Preservation of May 18, 1999 (36 CFR 800, Protection of Historic Properties, Final Rule and Notice), data recovery is considered to be an "adverse effect." However, according to Part 800.3(A)(2) of those revised regulations, provisions of programmatic agreements in existence at the effective date of the new regulations are governed by the regulations in place when the Agreement was developed.

The National Park Service would continue to consult with culturally associated American Indian tribes according to stipulations of the Programmatic Agreement and specific agreements, such as the October 17, 1999, Agreement Between the National Park Service, Yosemite National Park, and the American Indian Council of Mariposa County, Inc. for Conducting Traditional Activities, to develop appropriate mitigating strategies for effects to traditional cultural resources. Such strategies could include identification of and assistance in providing access to alternative resource gathering areas, continuing to provide access to traditional use or spiritual areas, and screening new development from traditional use areas.

Visitor Experience

This impacts analysis evaluated four separate aspects of visitor experience: recreation, orientation and interpretation, visitor services, and wilderness experience. Separate methodologies have been developed for each of these impact areas. This analysis evaluated the quality characteristics of the visitor experience in terms of how they might be altered as a result of the various user capacity measures and management zone actions described in the alternatives.

Visitor experience in Yosemite National Park encompasses a broad spectrum of elements, including access to and availability of recreational opportunities, orientation and interpretation programs, various visitor services, and access to the Yosemite Wilderness. In addition, every individual visitor to Yosemite brings unique expectations and thus each has a unique experience. This Revised Merced River Plan/SEIS identifies, where possible, how the quality of the experience would change given application of potential management actions discussed in each of the action alternatives.

Developing a quantitative analysis of potential effects on visitor experience is not feasible because of the programmatic nature of this plan. Analysis of effects is therefore qualitative, and professional judgment was applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts.

Recreation

Assumptions for the recreation analysis are based on visitor studies conducted over the last several years (Manning et al. 1999a, b; ORCA 2000). The assumptions that framed the analysis included the following:

·       Under all alternatives, visitor demand would increase in all areas between 1999 and 2020.

·       The visitor preference for use of private vehicles to access the park would not change.

·       Lodging and camping facilities damaged and removed as a result of the January 1997 flood would not be replaced in the same place they were previously located.

·       Under the No Action Alternative, there would be no change in access to the Yosemite wilderness areas and no change to the wilderness permit system.

·       Under the No Action Alternative, stock use would continue as currently managed.

·       A diverse range of recreational activities is desirable.

·       Most visitors to the Valley feel that traffic congestion and crowding reduce the quality of visitor experience.

The analysis was based on whether there was a complete loss of a recreational opportunity, a change in access to or availability of a recreational opportunity, or a change in the aggregate of recreational opportunities for the visitor. This analysis evaluated how potential management activities under the various alternatives would affect recreation opportunities available in all segments of the Merced Wild and Scenic River within Yosemite National Park. The range of recreational opportunities includes floating, swimming and wading, hiking, backpacking, camping, rock climbing, fishing, sightseeing, photography, nature study, bicycling, and stock use.

Orientation and Interpretation

The impact analysis was based on whether there would be a change in the availability of the existing range of interpretation programs and orientation/information sources and services throughout the park resulting from potential management actions for each alternative.

Visitor Services

The analysis identified how potential management actions under the various alternatives would affect visitor services provided by the National Park Service, and the park partners, including the primary park concessioner. The services analyzed include all campgrounds (i.e., Merced Lake Backpackers Campground, Moraine Dome Backpackers Campground, Little Yosemite Valley Backpackers Campground, Camp 4, North Pines Campground, and Upper and Lower Pines Campgrounds), lodging (i.e., Yosemite Lodge, the Merced Lake High Sierra Camp, Housekeeping Camp, The Ahwahnee, Curry Village, and the Wawona Hotel), and food service and retail outlets in the Valley and in Wawona.

Wilderness Experience

Impact analysis associated with wilderness experience was based on whether there would be a change in opportunities for solitude and primitive recreation for visitors in the wilderness, and/or a change in the ability of the visitor to access the Yosemite Wilderness.

Impact Assessment

The assessment of potential impacts focused on the context, intensity, and duration of impacts that would result from the proposed management actions described for each alternative, relative to the four aspects of visitor experience, and whether those impacts were considered to be beneficial or adverse to visitor experience. The assessment looked specifically at whether access to or availability of some aspect of visitor experience would be altered.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or impacts specific to the river corridor, including the El Portal Administrative Site. Regional impacts would be impacts on the affected region, which is defined in Chapter IV, Affected Environment.

Intensity. The intensity of the impact considers whether the impact to visitor experience would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable to the visitor and therefore expected to have no discernible effect. Minor impacts were effects that would be slightly detectable, though not expected to have an overall effect on the visitor experience. Moderate impacts would be clearly detectable to the visitor and could have an appreciable effect on the visitor experience. Major impacts would have a substantial, highly noticeable influence on the visitor experience and could permanently alter access to and availability of various aspects of the visitor experience.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration or association with transition types of activities. It is not likely that there would be temporary visitor experience impacts associated with this plan. A long-term impact would have a permanent effect on the visitor experience, such as the permanent closure of a campground.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to visitor experience. Beneficial impacts would allow greater access to or availability of a recreational opportunity, interpretation or orientation program, other visitor services, or to a wilderness experience. Adverse impacts would reduce access to or availability of these four aspects of visitor experience.

Social Resources

Land Use

For the purposes of an environmental analysis under NEPA and National Park Service guidelines on NEPA policies, land use within Yosemite National Park has the sole designation of public parklands. From the NEPA perspective, the public parklands land use designation includes the myriad of uses that may occur in a public park, including camping, hiking, parking, etc. Although the National Park Service is re-evaluating the management zoning in the El Portal segment of the Merced River corridor in the action alternatives, the management zones only designate management direction for particular areas within the park and do not change the basic land use of the park. This Revised Merced River Plan/SEIS addresses only the management of lands under National Park Service control within Yosemite National Park and the El Portal Administrative Site. The basic designation of land use for the park, as defined by NEPA, would not change as a result of implementing any alternative of this Revised Merced River Plan/SEIS.

The land use analysis assumes that National Park Service policy concerning the acquisition of private lands within or adjacent to the park would not change. Thus, there would be no difference in land use policies between the No Action Alternative and the action alternatives.

Impact Assessment

Proposed management actions under each alternative were evaluated in terms of the context, intensity, and duration of land use impacts, and whether the impacts were considered to be beneficial or adverse to existing land use patterns.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur at specific locations within the park. Regional impacts would be related to regional land use patterns. For the purposes of this document, it was assumed that land use impacts would be consistently local.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on land use patterns or land use compatibility. Minor impacts were effects on land use patterns that would be slightly detectable but would not be expected to have an overall effect on those conditions. Moderate impacts would be clearly detectable and could have an appreciable effect on land use patterns or result in land use incompatibility. Major impacts would have a substantial, highly noticeable land use incompatibility or would result in substantial changes to land use patterns.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of activities. A long-term impact would have a permanent effect on land use patterns or land use compatibility.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to land use patterns. Beneficial impacts would improve compatibility among land uses. Adverse impacts would negatively alter land use patterns or result in new land uses that would not be compatible.

Transportation

The focus of this impact assessment was on the effect of potential management actions on traffic volumes and associated traffic flow and safety conditions. It was assumed that current alternative transportation services (regional public transit, shuttle buses, or Valley floor tours, etc.) would remain essentially unchanged under this plan. Given the programmatic nature of this plan, it was assumed that the plan would not result in any substantial, quantifiable construction activity. It was also assumed that the park would continue to implement restricted access to Yosemite Valley during peak season periods when criteria for implementation were met.

Quantitative analysis of potential effects was not feasible for this impact assessment due to the programmatic nature of the plan. Rather, analysis of effects was qualitative, and professional transportation engineering judgment was applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts. When possible, mitigation measure(s) were incorporated into the plan to reduce the intensity of adverse effects.

Traffic Flow Conditions

This section assessed potential changes in traffic volumes associated with changes to in-park visitor accommodations and/or parking facilities that could result from implementation of management action described for each alternative. Changes in traffic volumes were then judged as to whether they would substantially change the levels of congestion on the roadway system serving Yosemite National Park.

Traffic Safety/Conflicts

This section assessed potential changes in parking facilities (location and number of parking spaces) that could result from implementation of management actions for each alternative. Possible changes in parking availability (e.g., parking supply could be reduced, with resulting unmet parking demand being accommodated by visitors parking their vehicles at roadside locations) were then judged, in the context of prevailing traffic volumes, as to whether increased roadside parking would substantially affect the potential for traffic conflicts.

Impact Assessment

Proposed management actions for each alternative were evaluated in terms of the context, intensity, and duration of the transportation impacts, and whether the impacts were considered to be beneficial or adverse to traffic flow or traffic safety conditions.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or specific to the river corridor, including the El Portal Administrative Site. Regional impacts would be impacts on regional highways providing access to the park.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on traffic flow or traffic safety conditions. Minor impacts were effects on traffic flow or traffic safety conditions that would be slightly detectable but would not be expected to have an overall effect on those conditions. Moderate impacts would be clearly detectable and could have an appreciable effect on traffic flow or traffic safety conditions. Major impacts would have a substantial, highly noticeable influence on traffic flow or traffic safety conditions and could permanently alter those conditions.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of activities. A long-term impact would have a permanent effect on traffic flow and/or traffic safety conditions.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to traffic flow or traffic safety conditions. Beneficial impacts would improve traffic flow and traffic safety by reducing levels of congestion and occurrences of vehicle/vehicle, vehicle/bicycle, and vehicle/pedestrian conflicts. Adverse impacts would negatively alter traffic flow and traffic safety by increasing levels of congestion and occurrences of such conflicts.

Scenic Resources

The scenic resources analysis assumes that any management action taken under each alternative would conform with the National Park Service 1916 Organic Act. For the purposes of this analysis, management actions for each alternative would be assumed to have an impact (negative or beneficial) on scenic resources if they:

·       Introduce into or remove from the visual landscape any human-built structure or infrastructure, as it is viewed from within the Merced River corridor

·       Substantially change the quality of the visual landscape, whether foreground, intermediate ground, or background

·       Affect perceived viewer sensitivity, which is a function of the extent to which viewer activity is dependent on visual quality. This would include the viewer's experience in seeing any single viewpoint and in moving through a sequence of viewpoints, such as would be experienced in hiking along the river

The scenic resources analysis is confined to an examination of the physical effects on viewsheds and on physical attributes of landscape features that define important views. The ability of a visitor to enjoy a particular visual landscape or sequence of landscapes also is affected by the quality of the air between the viewer and the landscape. The effect of air quality on visual resources, specifically visibility, is examined in the air quality section.

Impact Assessment

The overriding management purpose of any national park, as defined by the National Park Service 1916 Organic Act, is to conserve the scenery and natural and historic objects. Following this direction, the National Park Service determines impacts on scenic resources by examining the potential effects of each alternative on both the physical component (any change to the landscape character and/or features) and with respect to how that change is experienced (any change in visibility, viewpoints, etc.).

Impacts of the various alternatives and the associated management actions on visual resources are examined and determined by:

·       Comparing the existing visual character of the landscape, characterized in terms of the color, textural scale, and formal attributes of landscape components and features, and the degree to which potential management actions under each alternative would affect (i.e., contrast or conform with) that character

·       Analyzing changes in experiential factors, such as whether a given action would result in a visible change, the duration of any change in the visual character, the distance and viewing conditions under which the change would be visible, and the number of viewers that would be affected

Scenic resources impacts consist of a substantial change that would: (a) change existing landscape character, whether foreground, intermediate ground, or background, and be visible from viewpoints the National Park Service has established as important; (b) change access to historically important viewpoints, or a sequence of viewpoints; or (c) change the visibility of a viewpoint or a sequence of viewpoints.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts are site-specific to the scenic resource. Therefore, it was assumed that all scenic resource impacts would be local.

Intensity. Impacts are classified as negligible, minor, moderate, or major. The intensity of the impact depends both on the extent of the physical effect and the duration of that effect. A negligible impact would be barely perceptible and confined to a limited viewpoint. A minor impact would result in little change in existing landscape character and minor and temporary effects on viewers. A moderate impact would be noticeable to the viewer from one or more scenic viewpoints. A major impact would cause a substantial change in landscape character, a permanent change in access to viewpoints or sequence of viewpoints, or a permanent and substantial effect on visibility of a viewpoint or sequence of viewpoints.

Duration. The duration of the impact considers whether the impact would occur in the short term (e.g., temporary) or the long term (e.g., permanent).

Type of Impact. Impacts were evaluated in terms of whether the impact would be beneficial or adverse to the scenic resource. Beneficial impacts would improve the scenic resource. Adverse impacts would degrade the scenic resource.

Socioeconomics

The impacts analysis evaluated four separate socioeconomic areas: the social environment, visitor populations, the regional economy, and the primary park concessioner. Separate methodologies have been developed for each of these impact areas.

It is assumed that park overnighters who are potentially displaced from lodging in the park under the action alternatives would instead stay in the gateway communities as local overnighters. It is further assumed that in the short-term, some displaced park overnighters who may wish to lodge overnight in the region (as local overnighters) may not be able to due to a lack of lodging capacity in the gateway region, particularly during the peak season. In the long term, however, it is assumed that the regional lodging market would respond to visitor demand, and those displaced park overnighters would become local overnighters.

Quantitative analysis of potential effects on socioeconomic conditions was not feasible due to the programmatic nature of the plan. Rather, analysis of effects was qualitative, and professional judgment was applied to reach reasonable conclusions as to the context, intensity, and duration of potential impacts. When possible, mitigation measures were incorporated into the plan to reduce the adverse effects of socioeconomic impacts.

Social Environment

This section analyzed potential changes to the social environments of the communities of Yosemite Valley, El Portal, and Wawona, including housing, employee commute, community amenities, and recreational opportunities associated with the potential management actions under each of the action alternatives.

Visitor Populations

The analysis identified potential changes in park visitor accommodations that could result from implementation of management actions under each alternative. This section described changes in the composition of Yosemite visitors (e.g., park overnighters, local overnighters, and day visitors) and qualitatively addressed potential changes in visitor spending.

Regional Economy

This section qualitatively analyzed the impacts of changes in visitor spending and shifts in employment associated with the potential limits on park accommodations and other facilities. Due to the qualitative nature of the analysis, these impacts were addressed in terms of the affected region as a whole, and not at the individual county level.

Concessioner

The analysis identified how potential management actions under each alternative would affect facilities operated by the primary park concessioner. The analysis assumed that these facilities could be removed or reduced, and analyzed the impact on concession revenues.

Impact Assessment

Proposed management actions under each alternative were evaluated in terms of the context, intensity, and duration of the socioeconomic impacts, and whether the impacts were considered to be beneficial or adverse to the socioeconomic environment.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or specific to the river corridor, including El Portal. Regional impacts would be impacts on the affected region, which is defined in Chapter IV, Affected Environment.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on the socioeconomic environment. Minor impacts were effects on the socioeconomic environment that would be slightly detectable but would not be expected to have an overall effect. Moderate impacts would be clearly detectable and could have an appreciable effect. Major impacts would have a substantial, highly noticeable influence on the socioeconomic environment and could permanently alter the socioeconomic environment.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of activities. A long-term impact would have a permanent effect on the socioeconomic environment.

Type of Impact. Impacts were evaluated in terms of whether the impact would be beneficial or adverse to the socioeconomic environment. Beneficial socioeconomic impacts would improve the social or economic conditions in the park or in the affected region. Adverse socioeconomic impacts would negatively alter social or economic conditions in the park or in the affected region, or would affect low-income populations.

Park Operations and Facilities

Impacts associated with potential management actions taken under each alternative were determined by examining:

·       Direct changes to staffing requirements, and policies associated with park operations

·       Indirect effects of park operations staffing, such as effects on utility and roadway infrastructure, flooding, and provision of utilities, especially potable water and sewer services

·       Direct increases in energy use and conservation policies caused by changes in park operations staffing, or policies

Impact Assessment

Potential management actions for each alternative were evaluated in terms of the context, intensity, and duration of impacts to park operations and facilities, and whether the impacts were considered to be beneficial or adverse to park operations and facilities.

Context. The context of the impact considers whether the impact would be local or regional. For the purposes of this analysis, local impacts would be those that occur within Yosemite National Park or specific to the river corridor, including El Portal. Regional impacts would be impacts that occur throughout the Sierra Nevada region. For the purposes of this analysis, it was assumed that all impacts would be local.

Intensity. The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. Negligible impacts were effects considered not detectable and that would have no discernible effect on park operations and facilities. Minor impacts were effects on park operations and facilities that would be slightly detectable but would not be expected to have an overall effect on the ability of the park to provide services and facilities. Moderate impacts would be clearly detectable and could have an appreciable effect on park operations and facilities. Major impacts would have a substantial, highly noticeable influence on park operations and facilities and include those impacts that would reduce the park's ability to provide adequate services and facilities to visitors and staff.

Duration. The duration of the impact considers whether the impact would occur in the short term or the long term. A short-term impact would be temporary in duration and would be associated with transitional types of activities. A long-term impact would have a permanent effect on park operations and facilities.

Type of Impact. Impacts were evaluated in terms of whether they would be beneficial or adverse to park operations and facilities. Beneficial impacts would improve park operations and/or park facilities. Adverse impacts would negatively affect park operations and/or facilities and could impede the park's ability to provide adequate services and facilities to visitors and staff.

Alternative 1: No Action

Natural Resources

Geology, Geohazards, and Soils

Analysis

Under Alternative 1, park would implement existing user capacity program, including the elements of the Merced River Plan (boundaries, classifications, Outstandingly Remarkable Values [ORVs], management zoning prescriptions, and River Protection Overlay), legal mandates, the General Management Plan, and other park policy documents. Geologic processes/conditions ORVs include the mature, meandering nature of the Merced River through Yosemite Valley, a classic V-shaped river through the gorge, evidence of ice-age glaciation (U-shaped and hanging valleys), extraordinary granite features (e.g., exfoliation domes), and the transition from igneous to metasedimentary rocks in the El Portal area. The following discussion provides an overview of the types of geologic impacts that could occur within the Merced River corridor under Alternative 1 in 2020 compared with existing conditions.

Rockfall Hazards. Rockfalls can be expected throughout Yosemite National Park in any area that has steep rock cliffs. Under Alternative 1, mass movement from unstable rock slopes would continue to result in rockfalls, debris flow, and rock avalanches, exposing visitors to potential injury and facilities to damage. Along the Merced River, rockfalls can occur in the upper wilderness reaches, along the edges of Yosemite Valley, within the gorge, and along the South Fork where the river is contained within canyons. Most rockfalls are associated with triggering events such as earthquakes, climatic changes such as rainfall events, or gradual stress release and exfoliation of the granite. Incidents of injury to visitors and damage to facilities from rockfall hazards are most likely to occur in the developed valley and canyon areas of the Merced River and South Fork corridor, such as in Yosemite Valley, the Merced River gorge along the El Portal Road, El Portal Administrative Site, and possibly in Wawona. The risk of rockfalls to visitors and facilities is considered low in the less-traveled and undeveloped wilderness areas, although rockfalls do occur throughout the park. Facilities located within proximity of the talus zone or within the rockfall shadow zone are most susceptible to damage from rockfalls. Rockfall frequency in the talus zone can be yearly to every several decades; risks posed by rockfalls include casualties and structural damage. Avoiding all rockfall-related risk is not possible, especially in narrow, steep valleys or canyons. The configuration of the Yosemite Valley walls and relatively narrow canyons suggest there are no "safe" areas within areas susceptible to rockfall risks (USGS 1998).

In the short term, management of user capacity in the river corridor under Alternative 1 would have no impact related to rockfall hazards. Current park management policies and the Yosemite Valley Geologic Hazard Guidelines (Appendix C in NPS 2000e), which require most new facilities and uses to be placed outside the talus zone and the rockfall shadow zone, would continue to be implemented, and levels of visitation would be similar to existing levels. Therefore, there would be no discernible increase in exposure of visitors or facilities to rockfall hazard. In the long term, however, visitation levels under Alternative 1 could reasonably be expected to increase until facility or utility capacities were reached. Such an increase would result in an increase in the number of park users exposed to rockfall hazards. Long-term impacts associated with an increase in the number of visitors exposed to rockfall hazards would be local, negligible to minor depending on future visitation levels), and adverse.

Seismic Hazards. Yosemite National Park is susceptible to earthquake ground shaking generated in seismically active zones on the east and west margins of the Sierra Nevada. Historically, seismic events in the Sierra Nevada and Yosemite National Park have been relatively infrequent; however, when they do occur, the resultant ground shaking is capable of triggering rockfalls and producing ground accelerations that are higher than some older, less structurally stable buildings can tolerate. Typically, risks of injury to visitors and damage to facilities from seismic events would be relatively greater in the developed portions of Yosemite National Park, such as Yosemite Valley, El Portal, and Wawona, compared with less developed and more remote areas. Buildings and other facilities placed within saturated alluvial soil could also be susceptible to secondary hazards from seismic ground shaking, including liquefaction and seismically induced settlement. Earthquakes are unavoidable, and those in the Sierra Nevada region would continue to expose visitors to potential hazards from ground shaking.

In the short term, management of user capacity in the river corridor under Alternative 1 would have no impact related to seismic hazards. Current park management policies and the Yosemite Valley Geologic Hazard Guidelines would continue to be implemented, and levels of visitation would be similar to existing levels. Therefore, there would be no discernible increase in exposure of visitors or facilities to seismic hazards. In the long term, however, visitation levels under Alternative 1 could reasonably be expected to increase until facility or utility capacities were reached. Such an increase would result in an increase in the number of park visitors who would be exposed to the effects of seismic ground shaking in the event of an earthquake. Long-term impacts associated with an increase in the number of visitors exposed to seismic hazards would be negligible to minor (depending on future visitation levels), and adverse.

Impacts to Soils. Management zoning prescriptions, implementation of the River Protection Overlay, protection of certain biological ORVs, implementation of the trailhead quota system, and other management tools implemented or available under Alternative 1 would continue to protect soils from excessive disturbance, erosion, or compaction along most of the 81-mile river corridor. However, visitor use in certain areas of Yosemite National Park can adversely affect soils by contributing to erosion, soil compaction, and removal of surface soils. Compaction of native soils can result from concentrated visitor use in localized areas or excessive vehicular traffic in unpaved areas. Excessive surface water runoff or loss of protective vegetation cover can cause erosion. Under management zoning for Alternative 1, specific segments of the Merced River, especially those zoned Developed (3A-3C), would continue to be subjected to such concentrated visitor use, resulting in continued erosion and compaction in these areas. Visitor use in the upper wilderness reaches and undeveloped areas adjacent to the main stem and South Fork of the Merced River would continue to be less concentrated and limited by the existing trailhead quota system, management zoning, and other applicable park management plans and guidelines; therefore, concentrated visitor use would not intensify impacts to soil resources in these areas. In addition, under Alternative 1, areas within and adjacent to the river corridor that have been restored and rehabilitated could be closed under the authority of the Superintendent's Compendium. Park management could also take certain actions under the user capacity program in response to data showing the need to protect resources (for example, closing a beach to commercial raft removal to protect the riverbank). Protection of certain biological ORVs within the River Protection Overlay, such as riverine and wetland habitat, also serve to protect soils in these areas. However, current use of well-developed and well-traveled areas within the park would continue to cause erosion and compaction. Continued river access would result in increased erosion, removal of vegetation, and decreased soil stability.

Under Alternative 1, existing management policies would continue to be implemented, and, in the short term, levels of visitation would be similar to existing levels. In the short term, current management of user capacity in the river corridor outside El Portal would have a negligible adverse impact due to the incremental effects of ongoing concentrated use with respect to soil erosion and compaction. In the long term, visitation levels under Alternative 1 would be expected to increase until facility or utility capacities were reached. However, no increases would occur within wilderness areas because the trailhead quota system would remain in effect. Such an increase would exacerbate the adverse effects of concentrated visitor use on park soils in certain areas zoned for relatively high use. Existing policies and programs to protect park resources and values under Alternative 1 would moderate the effects of future increases in park visitation in these areas and thus would reduce the extent of the adverse impact on park soils. Long-term impacts on park soils associated with an increase in the number of visitors by 2020 would be negligible to minor (depending on actual future visitation levels), and adverse.

The boundary for the El Portal segment of the river in Alternative 1 is defined by the 100-year floodplain or the River Protection Overlay, whichever is greater. Land within the boundary is zoned for Park Operations and Administration (3C) within developed areas and Day Use (2C). Under this alternative, future development could occur outside the river boundary within the El Portal Administrative Site, consistent with the legislative intent for the site. Temporary construction-related erosion could occur during periods of rain, while soil is exposed, and prior to the site restoration and cleanup phases of future projects. Erosion and soil loss typically occur immediately after initial site grading or following construction or a fill slope with exposed soil. Mitigation measures common to all alternatives (listed in Appendix B) include preparation, prior to commencement of any construction activities, of a stormwater pollution prevention plan to control erosion and sedimentation, and implementation of and compliance with all operational requirements in the plan during construction. With implementation of a stormwater pollution prevention plan during construction, erosion and soil loss associated with grading and construction activities would result in a local, short-term, minor, adverse impact. Long-term soil degradation would be minimal due to erosion controls and the intermittent nature of the grading activities. Implementation of the mitigation measures would reduce adverse effects on soils at the El Portal Administrative Site to negligible to minor.

Summary of Alternative 1 Impacts. Considering the unpredictable and unavoidable nature of rockfalls and earthquakes in conjunction with an expected, albeit limited, increase in park visitation over the long term, there would be a local, long-term, negligible to minor, adverse impact on public safety from geohazards, including rockfall and seismic ground shaking. Considering the ongoing effects of more concentrated visitor use that would occur in some areas of the river corridor, there would be a local, short-term and long-term, negligible to minor, adverse impact on soil resources due to erosion, compaction, and soil removal. However, current park management policies would continue to enhance and protect the geologic processes/conditions ORVs within the individual river segments.

Cumulative Impacts

Cumulative impacts related to geohazards and soil resources are based on analysis of past, present, and reasonably foreseeable future actions, in combination with potential effects of this alternative. The projects identified below include only those projects that could affect geologic resources within the Merced River corridor or in the park vicinity.

Rockfalls would remain an unavoidable and unpredictable hazard within Yosemite Valley, the gorge, and other areas along the river corridor. Actions proposed in the Yosemite Valley Plan would remove and relocate facilities from the base of the talus zone, consistent with the Yosemite Valley Geologic Hazard Guidelines. For example, plans proposed under the Curry Village and East Yosemite Valley Campgrounds Improvements and Curry Village Employee Housing projects incorporate the placement of essential, special, and standard facilities outside the base of talus and rockfall shadow zones, as appropriate. Although rockfall hazards cannot be eliminated, the Yosemite Valley Plan would remove the most hazard-vulnerable facilities, thereby resulting in a regional, long-term, minor, beneficial impact.

Earthquakes are unavoidable and unpredictable and represent a potentially long-term, adverse impact to public health and safety. However, past, present, and reasonably foreseeable future actions would result in a local, long-term, minor, beneficial cumulative impact to public health and safety with respect to seismic hazards, due to the efforts of the National Park Service to apply current building codes and consider geologic and seismic hazards in planning and management activities. These efforts protect site facilities in areas that could be directly affected by ground failure.

Although certain past, present, and reasonably foreseeable future projects proposed within the park and vicinity would increase soil degradation during construction activities or due to increased development, many park projects, especially those included in the Yosemite Valley Plan, contain restoration elements to protect valuable soil resources. Full implementation of the Yosemite Valley Plan would restore approximately 177 acres of soils, of which approximately 136 acres would be high-value resource soils. Future ecological restoration projects include the Visitor Use and Floodplain Restoration Program, which involves the ecological restoration of six campgrounds, Housekeeping Camp, and The Ahwahnee tennis court. The current ecological restoration project at Cook's Meadow involved the removal of an abandoned roadway and will be complete upon the construction of a boardwalk to provide meadow access while allowing the free flow of water in the meadow and protecting vegetation and soils. Past restoration projects included the Merced River Ecological Restoration at Eagle Creek, which involved restoration of the eroded creek channel, revegetating the creek banks, and redirecting visitor traffic to minimize bank erosion. The Lower Yosemite Fall Project removes a parking lot and restores it to natural conditions. The Happy Isles Gauging Station Bridge Removal and Cascades Diversion Dam Removal projects restored to a substantial degree the free-flowing condition in these areas, thus helping to reduce riverbank erosion. However, some cumulative actions could result in short-term or long-term degradation of soil resources; such projects include construction of campgrounds, lodging, employee housing, roadway rehabilitation projects, and other facilities. Although these types of projects could have site-specific, short-term, adverse effects (e.g., potential short-term construction erosion and soil loss), a key objective of each of these projects is to reduce soil degradation and better manage natural resources.

Although rockfalls are unpredictable and unavoidable by nature, rockfall and earthquake hazards under Alternative 1 and the cumulative projects would result in a local, long-term, minor, beneficial impact to public safety in Yosemite National Park and the El Portal Administrative Site. These beneficial effects would be the result of efforts by park management to relocate critical facilities outside the talus slope and rockfall shadow zones, to avoid construction of new facilities in these hazard areas, and to conduct appropriate geotechnical studies prior to construction of facilities on soils susceptible to seismic ground shaking. Ongoing management programs would limit the increase in future visitation, thereby limiting the increase in the numbers of users exposed to geohazards under Alternative 1 and the cumulative projects. The overall cumulative actions in combination with Alternative 1 would result in a net regional, long-term, minor, beneficial impact on soil resources.

Impairment

Alternative 1 would have a local, short-term and long-term, negligible to minor, adverse impact on geologic resources and soils. Although soil resources are a key natural resource component within Yosemite National Park, the effect of this alternative on soils would occur in very localized areas and would not be considered severe. The extent and quality of soil resources throughout most of the Merced River corridor would remain high. Therefore, Alternative 1 would not impair geologic resources for future generations.

Hydrology, Floodplains, and Water Quality

Analysis

The following discussion provides an overview of the types of impacts to hydrology, floodplains, and water quality that could occur within each segment of the Merced River corridor under Alternative 1, the No Action Alternative. Under Alternative 1, user capacity within the river corridor would be managed as it has been in the past, as identified and described in the park's General Management Plan and other current park policy and guideline documents (see table III-1). When visitor demand exceeds infrastructure capacities or when resources are being adversely affected, the park implements proactive measures and, in certain circumstances, specific restrictions to provide adequate protection for visitors and affected resources.

Impacts in Wilderness. The hydrologic processes ORV in the Wilderness segment includes the river's free-flowing character and excellent water quality. The ORV description also notes the river gradient, natural conditions (e.g., glacial remnants, a logjam in Little Yosemite Valley), and numerous cascades. Of the qualities described for the ORV, most are relatively insensitive to user-related impacts, with the exception of water quality. Water quality in the Wilderness segments is considered to be excellent.

User capacity within Wilderness segments of the Merced River would be addressed through the continued implementation of the trailhead quota system and periodic monitoring of wilderness resource conditions. If it is determined through monitoring that some areas are experiencing degradation due to overuse, park management would take proactive measures to restore resources and help prevent further damage.

In wilderness areas zoned Untrailed (1A) and Trailed Travel (1B), no new structures such as utilities, bridges (other than minor footbridges), and commercial overnight facilities are to be constructed. As such, Alternative 1 would not affect the floodplain or its ability to accommodate flood flow. Furthermore, visitation to the Wilderness segments of the river corridor is seasonal in nature and is controlled thr