IV. Environmental Consequences

Introduction

The National Environmental Policy Act 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 two Happy Isles Gauging Station Bridge Removal Project Environmental Assessment alternatives on natural, cultural, and social resources. The analysis provides the basis for comparing the beneficial and adverse effects of the alternatives.

Following this introduction, the chapter 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, and social resources and presents cumulative impacts and impact conclusions. The same framework is then applied to Alternative 2 in the subsequent section. Environmental impacts are summarized in table II-1: Summary of Environmental Consequences, located at the end of Chapter II of this document.

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.

To determine potential cumulative impacts, projects within Yosemite Valley were identified. The cumulative projects identified included past actions, as well as any planning or development activity currently being implemented or planned for implementation in the reasonably foreseeable future. Appendix A contains the list of cumulative projects 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 if they have any additive effects on a particular natural, cultural, or social resource. Because most of the cumulative projects are in the early planning stages, the evaluation of cumulative impacts was based on a general description of the project.

Context, Duration, Intensity, and Type of Impact

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 the immediate vicinity of Happy Isles Gauging Station Bridge or within Yosemite Valley.

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 or demolition-related impacts. Long-term impacts are those effects that would last ten years or more or would be permanent.

Intensity

The intensity of the impact considers whether the effect would be negligible, minor, moderate, or major. Negligible impacts would not be detectable and would have no discernible effect. Minor impacts would be slightly detectable, but would not be expected to have an overall effect on the character of the resource. Moderate impacts would be clearly detectable and could have an appreciable effect. Major impacts would have a substantial, highly noticeable influence.

Type of Impact

Impacts were evaluated in terms of whether they would be beneficial or adverse. Beneficial impacts would improve resource conditions. Adverse impacts would deplete or negatively alter resources.

Impairment

Pursuant to the 1916 Organic Act, the National Park Service has a management responsibility “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.” As a result, the National Park Service cannot take an action that would “impair” park resources. National Park Service Management Policies 2001 provide guidance on addressing 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. An impact would be less likely to constitute an impairment to the extent that 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 2000e). 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; or

· Identified as a goal in the park’s General Management Plan or other relevant National Park Service planning documents.

For the Happy Isles Gauging Station Bridge Removal Project, the Merced River is the key resource for which impairment must be addressed. As identified in the Merced Wild and Scenic River Comprehensive Management Plan and the Yosemite Valley Plan, the Merced River is central to the Valley’s scenery and ecological processes. 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. 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 do not automatically do so. Rather, these impacts must be analyzed with respect to the three bulleted criteria above. In addition, when considering potential impairment of the Merced River, not all resource topics have been analyzed. Impairment is considered for geologic, hydrological, biological, cultural, and scenic resources and recreation. However, analyses for air quality, noise, and park operations do not discuss impairment of the Merced River because these resource topics are peripheral to the protection of the Merced River, the intent of the 1916 Organic Act, and the Management Policies 2001 impairment mandate.

Director’s Order #12 requires that impairment be addressed in all environmental assessments and draft and final environmental impact statements, as well as in the decision documents (Finding of No Significant Impact, Record of Decision). Within this environmental assessment, impairment is addressed in the conclusion section of each impact topic 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, Geologic Hazards, and Soils; Hydrology, Floodplains, and Water Quality; Wetlands; Vegetation; Wildlife; Special-Status Species; Air Quality; and Noise

Cultural Resources: Archeological Resources; Ethnographic Resources; and Cultural Landscape Resources, including Historic Sites and Structures

Social Resources: Scenic Resources, Recreation, and Park Operations and Facilities

Each resource topic area includes a discussion of the impact assessment and the context, duration, intensity, and type of impact. The context of the impact considers whether the impact would be local or regional. The duration of the impact considers whether the impact would occur in the short term (temporary) or the long term (permanent). The intensity of the impact considers whether the impact would be negligible, minor, moderate, or major. The type of impact considers whether the impact would be beneficial or adverse to the natural, cultural, or social environment.

Pursuant to National Environmental Policy Act requirements, the impact analyses for Alternative 1 (the No Action Alternative) compare resource conditions under Alternative 1 in the year 2010 to existing conditions in the year 2001. The impact analyses for the action alternative (Alternative 2) compare the action alternative in the year 2010 to the No Action Alternative in the year 2010.

It is assumed that annual park visitation would increase over 2001 levels by the year 2010. In 2010, annual visitation demand is assumed to be the same for both alternatives.

Natural Resources

Geology, Geologic Hazards, and Soils

This impact assessment focused on effects that geologic processes in the Yosemite National Park would have on visitors, personnel, and facilities under each alternative of the Happy Isles Gauging Station Bridge Removal Project. Geologic processes can negatively affect visitors, personnel, 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 what effect the project alternatives would have on geologic processes, namely the formation and conservation of soil resources. Actions prescribed in the Happy Isles Gauging Station Bridge Removal Project could affect 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 those in Yosemite Valley, the Merced River gorge, and El Portal, would be exposed to the risk 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 will allow natural processes to occur unimpeded.

· The National Park Service is currently revising its management policies pertaining to geologic resources and hazards. The focus of these guidelines will be 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 may affect people and property cannot be quantified. Analysis of effects was qualitative, and professional judgment has been applied to reach reasonable conclusions as to the context, duration, and intensity of potential impacts.

Hydrology, Floodplains, and Water Quality

This assessment focused on the fluvial processes of the Merced River, and how (relative to the No Action Alternative) the action alternative (Alternative 2) would affect hydrologic processes, both during project demolition and following project completion. The hydrology impact assessment evaluates how demolition activities to remove the bridge would affect channel morphology, flooding, and water quality. Hydrology impacts were evaluated in terms of their context, duration, and intensity, and whether the impacts were considered to be beneficial or adverse.

The analysis examined potential changes to channel morphology (channel depth, position, and streamflow) as a result of the alternatives. The analysis addressed existing and potential future restrictions to streamflow, potential repositioning of the channel bed, potential channel bed scour and bank erosion or instability, flow rates, and sediment transport mechanics. The analysis qualitatively analyzed the impacts to the river’s floodplain due to removal of the Happy Isles Gauging Station Bridge. Due to the qualitative nature of this assessment, the removal of a streamflow constriction is considered to be beneficial to the floodplain and river channel. The analysis identified potential effects on water quality associated with demolition operations, such as the location of construction staging areas near the Merced River and use of heavy equipment during bridge removal.

Wetlands

The National Park Service is committed to minimizing wetland loss. The wetland protection mechanisms used by the National Park Service include Executive Order 11990, Protection of Wetlands; Director’s Order #77-1, Wetland Protection, and its accompanying Procedural Manual #77-1; Clean Water Act Section 404; and the “no net loss” goal outlined by the White House Office on Environmental Policy in 1993. Executive Order 11990 requires that leadership be provided by involved agencies to minimize the destruction, loss, or degradation of wetlands. The National Park Service’s Director’s Order #77-1 and Procedural Manual #77-1 provide specific procedures for carrying out the Executive Order. Section 404 of the Clean Water Act authorizes the U.S. Army Corps of Engineers to grant permits for construction and disposal of dredged material in waters of the United States. Wetland impacts were estimated using wetland-specific data collected in the field during the spring of 2001. Wetland data were compared to each alternative to determine area of potential effect.

Vegetation

Impacts on vegetation communities have been assessed in terms of duration, intensity, and type in site-specific, parkwide, and regional contexts. Two primary parameters were used to evaluate the intensity of impacts on vegetation: (1) the size and continuity of the plant community, and (2) the natural structure, productivity, diversity (integrity), and rarity of the plant community.

Other not-so-visible impacts (such as encroachment of wetland habitats by non-native species) would continue to be managed by vegetation management staff in conjunction with National Park Service programs involved in the protection and long-term management of the park’s vegetative resources.

Wildlife

This section addresses the effects of alternatives on wildlife and their habitat. Nearly all wildlife concerns can be addressed by considering the effects of alternatives on wildlife habitat as represented by general vegetation types. A description of how vegetation impacts would affect wildlife is described within this section.

Impacts on wildlife have been assessed in terms of changes in the amount and distribution of wildlife habitat, the size and connectivity of habitat, the integrity of the site (including past disturbance), the potential for habituation of wildlife to humans, and the relative importance of habitats.

Special-Status Species

Wildlife

The impact evaluation for special-status wildlife species for each alternative was based on the following: (1) the possibility of a species or its preferred habitat types occurring in areas expected to be affected; (2) the direct loss of habitat or individuals; (3) the partial loss of habitat from its modification; and (4) the species’ sensitivity to disturbance from human activities that may cause it to abandon currently occupied habitat or deter it from occupying suitable habitat.

Vegetation

The assessment of potential impacts to special-status plant species was based on comparisons between the No Action Alternative and the action alternative. Impacts have been evaluated considering species’ sensitivity to impacts (based on rarity, resilience, size of population, and extent of species throughout the park); location of species in proximity to new disturbance, and mitigation measures applied as appropriate for the species and the site.

Air Quality

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

The air quality impact assessment involved the identification and qualitative description of the types of activities associated with the Happy Isles Gauging Station Bridge Removal Project 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.

Many localities have emissions-based regulations in place, however, neither the National Park Service nor the Mariposa County Air Pollution Control District has established emissions-based criteria for evaluating the significance of demolition-phase impacts. In the absence of such recommendations, the typical approach is to qualitatively evaluate the significance of temporary demolition-related impacts. The analysis of effects was qualitative, and professional judgment was applied to reach reasonable conclusions as to the context, duration, and intensity of potential impacts. When possible, mitigation measure(s) were incorporated into the project to reduce the intensity of adverse effects.

Noise

The noise impact assessment involved the identification and description of the types of actions 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. 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.

Cultural Resources

Section 106 of the National Historic Preservation Act requires a federal agency to take into account the effects of its undertakings on properties included in, or eligible for inclusion in, the National Register of Historic Places and to provide the Advisory Council on Historic Preservation the reasonable opportunity to comment. This requirement 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 (Advisory Council on Historic Preservation 1999). This methodology includes: (1) identifying areas that could be affected; (2) assessing the level of resource information available and conducting appropriate inventories 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, reduce, or mitigate adverse effects.

The cultural resource analysis in this environmental assessment is provided in terminology consistent with regulations of the Council on Environmental Quality. Council on Environmental Quality regulations require that the impacts of alternatives and their component actions be disclosed. These regulations are intended to comply with the requirements of both the National Environmental Policy Act and Section 106 of the National Historic Preservation Act. Consistent with the Council on Environmental Quality regulations, the analysis of individual actions identifies and characterizes potential impacts and includes an evaluation of impact intensity. This is a fundamental difference between the National Environmental Policy Act and the National Historic Preservation Act; the National Historic Preservation Act requires determinations of no effect or effect, and where there is an effect, a determination as to whether that effect is adverse or not adverse.

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

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

Council on Environmental Quality regulations call for a discussion of the “appropriateness” of mitigation and Director’s Order 12, Conservation Planning, Environmental Impact Analysis and Decision-Making, requires an analysis of the “effect” of mitigation. The reduction in intensity due to mitigation is an estimate of the effectiveness of mitigation under the National Environmental Policy Act. It does not suggest that the level of effect as determined by Section 106 is similarly reduced. Although adverse effects under Section 106 may be mitigated, for example, the effect remains adverse.

Mitigation for National Environmental Policy Act purposes in this environmental assessment 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. According to stipulation VII(C) of the 1999 Programmatic Agreement, impacts to 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 Code of Federal Regulations [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 remain in effect.

The National Park Service would continue to consult with culturally associated 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 ethnographic 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.

Relative to the No Action Alternative, the action alternative would result in the controlled demolition of the Happy Isles Gauging Station Bridge. The Cultural Resources impact assessment evaluated how the action alternative would affect the cultural resources environment—or the cultural landscape—at the project site. Cultural resource impacts were evaluated in terms of the their context, duration, and intensity, and whether the impacts were considered to be beneficial or adverse.

Social Resources

Scenic Resources

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 determined impacts on scenic resources by examining the potential effects of the Happy Isles Gauging Station Bridge Removal Project on the landscape character and/or features and how any changes may be experienced (visibility, viewpoints, etc.).

Impacts of the Happy Isles Gauging Station Bridge Removal Project on visual resources were examined and determined by:

· Comparing the existing visual character of the landscape in terms of the color, contextual scale, and formal attributes of landscape components and features, and the degree to which actions that may result from the Happy Isles Gauging Station Bridge Removal Project 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 substantial changes that would alter (1) existing landscape character, whether foreground, intermediate ground, or background, and would be visible from viewpoints the National Park Service has established as important; (2) access to historically important viewpoints or sequence of viewpoints; or (3) the visibility of a viewpoint or sequence of viewpoints.

Recreation

Yosemite National Park offers a broad spectrum of recreational opportunities, including access to and availability of such activities as hiking, swimming and wading, backpacking, camping, horseback riding, rock climbing, fishing, sightseeing, photography, nature study, and bicycling. In addition, every visitor to Yosemite brings unique expectations, and thus each has a unique experience. The environmental assessment identifies, where possible, how the quality of the experience would change as a result of demolition of the Happy Isles Gauging Station Bridge.

Developing a quantitative analysis of potential effects on recreation is not feasible. Analysis of effects is therefore qualitative, and professional judgment was applied to reach reasonable conclusions as to the context, duration, and intensity of potential impacts.

One assumption that framed the analysis was visitor demand will increase over 2001 levels and will be the same among all of the alternatives.

Analysis was based on whether there would be 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.

Park Operations and Facilities

For purposes of this analysis, an alternative is assumed to have an impact (adverse or beneficial) on park operations and facilities if it:

· Results in direct changes to park operations, facilities, or staffing requirements or policies associated with park operations.

· Causes indirect effects on park operations, facilities, or staffing, such as effects on utility and roadway infrastructure, flooding, and impacts on provision of utilities, especially potable water and sewer services.

Alternative 1: No Action

Alternative 1, the No Action Alternative, maintains the status quo at the Happy Isles Gauging Station Bridge. It provides a baseline from which to compare the action alternative, to evaluate the magnitude of proposed changes, and to measure the environmental effects of those changes.

Under the No Action Alternative, no management action would be taken to repair or remove the bridge. This condition of benign neglect would be expected to eventually result in the uncontrolled and sudden failure of the Happy Isles Gauging Station Bridge. Bridge collapse would likely occur during a period of high flow and it is assumed that this collapse would occur within the next ten years. The National Park Service would remove the bridge debris from the Merced River as soon as it would be feasible, however, removal activities would not be able to commence until low flow conditions, which could be several months subsequent to bridge collapse. Debris removal activities would likely span a river segment of at least 500 linear feet, between Happy Isles Gauging Station Bridge and Happy Isles Vehicle Bridge.

Natural Resources

Geology, Geologic Hazards, and Soils

Analysis

Geologic hazards could cause further structural damage to the Happy Isles Gauging Station Bridge and contribute to greater structural degradation that could accelerate the eventual collapse of the bridge structure. The bridge is already severely damaged and likely to collapse within the next 10 years during a high-flow event. This collapse could occur in either a single event during high springtime river flows or gradually, as the abutment foundations degrade from continued scour. Uncontrolled collapse of the bridge could also cause unpredictable riverflows, potentially eroding banks, undermining trails, endangering the water supply lines to Yosemite Valley, and damaging the Happy Isles Gauging Station located immediately downstream of the river-right abutment. Under Alternative 1, Happy Isles Gauging Station Bridge would continue to be subjected to possible structural damage from earthquakes. Earthquake-induced ground shaking could accelerate structural degradation reducing the period of time before the bridge collapses. The bridge is located in an area of moderate seismicity, and earthquakes from several remote sources could trigger ground shaking sufficient to cause observable ground movement at the bridge site. The bridge has withstood numerous small and some relatively large earthquakes over the past 80 years without significant damage or collapse. However, the damage sustained in the 1996 rockfall and the 1997 flood has substantially compromised the bridge’s structural integrity. Earthquake-induced damage could accelerate degradation of the river-left abutment and contribute to the bridge’s eventual failure. Ground shaking from an earthquake could also be strong enough to cause sudden bridge collapse, given the instability of the structure.

As in the past, Happy Isles Gauging Station Bridge would be subject to damage from debris generated during rockfalls. A rockfall event, although relatively infrequent, could deposit boulders on Happy Isles Gauging Station Bridge, as it is located within the rockfall shadow zone (USGS 1999b). Granitic material colliding with the bridge structure could cause further damage to the concrete abutments and bridge span or cause sudden bridge failure. Damage to the bridge from a rockfall could therefore accelerate degradation and eventual failure, or result in immediate bridge collapse.

Retrieval of bridge materials scattered downstream during an uncontrolled collapse would require multiple ingress and egress points for construction equipment and personnel, potentially destabilizing the riverbank in locations between Happy Isles Gauging Station Bridge and Happy Isles Vehicle Bridge. Debris retrieval activities would result in short-term impacts to soil resources and could include excessive erosion, soil compaction, and loss of topsoil. Long-term soil impacts would include residual damage to soil resources such as bank erosion and loss of topsoil caused by diverted flood waters following the bridge collapse. Short-term bridge debris retrieval activities and the long-term results of erosion caused by diverted flood waters would therefore result in local, short- and long-term, moderate, adverse impacts to soil resources. Soil resources, throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected by this alternative.

Summary of Alternative 1 Impacts. Uncontrolled collapse and the retrieval of bridge debris material would cause bank destabilization, erosion, and soil loss resulting in local, short- and long-term, moderate, adverse impacts to soil resources.

Cumulative Impacts

Cumulative impacts to geological resources are based on analysis of past, present, and reasonably foreseeable future actions in the Yosemite region in combination with potential effects of this alternative. The projects identified below include only those projects that could affect geological resources within the Yosemite Valley.

Past development projects intended to serve park visitors in Yosemite National Park have included hotels, visitor centers, campgrounds, and bridges, with associated roads and parking lots. In addition, facilities required to support park infrastructure, including employee housing, utility facilities, maintenance yards, and supply storage areas, have been developed throughout the Valley. As popularity of Yosemite attracted a greater number of visitors, the number and magnitude of these projects increased to meet visitor demand. Past facility development has occurred in areas that are susceptible to damage from geohazards (rockfalls and seismic events) and has contributed to the overall degradation of soil resources in the park.

Rockfall hazards would be reduced through projects that relocate people and facilities away from rockfall hazard zones, such as removal of units at Housekeeping Camp and Curry Village located within the talus slope zone, as identified in the Yosemite Valley Plan. However, other projects could expose additional visitors to the risk of rockfalls, such as the Trail Reconstruction from Happy Isles to Vernal Fall and Happy Isles Site Improvements. Additionally, rockfall hazards constitute a long-term adverse impact to park visitors, as multiple facilities are located in the talus slope and rockfall shadow zones. Happy Isles Gauging Station Bridge is located in the rockfall shadow zone although it is not located in the talus slope zone. Earthquakes are unavoidable and unpredictable and represent a potentially long-term, adverse impact to public health and safety. Past, present, and reasonably foreseeable future actions would result in local, long-term, minor, beneficial cumulative impacts to public health and safety from geologic hazards due to an overall reduction in the density of people and facilities in the talus slope zone.

Certain development projects could result in increased degradation of soil resources, such as expansion of campgrounds and construction of lodging and employee housing in Yosemite Valley, as identified in the Yosemite Valley Plan. However, other projects related to habitat restoration, such as removal of roads through Stoneman and Ahwahnee Meadows, and the Merced River at Eagle Creek Ecological Restoration (Yosemite Valley), would have long-term, beneficial effects on soils. Although these types of projects may have slight site-specific, short-term, adverse effects (e.g., potential construction erosion and soil loss), an objective of these projects is to restore and manage natural resources and reduce soil degradation. For example, full implementation of the Yosemite Valley Plan would restore approximately 177 acres of soil, of which approximately 136 acres would be high value resource soils in Yosemite Valley. The cumulative projects would result in local, long-term, minor, beneficial cumulative impacts to soil resources.

Alternative 1 and the cumulative projects would result in a local, long-term, minor, beneficial impact to public safety in Yosemite Valley due to the overall reduction in the density of facilities in the talus slope and rockfall shadow zones. The local, long-term, minor, beneficial impacts to soil resources under the cumulative projects would be somewhat diminished by the potential soil erosion and bank destabilization under Alternative 1, resulting in a net local, long-term, negligible, beneficial impact to soil resources.

Conclusions

Under Alternative 1, uncontrolled collapse and the retrieval of bridge debris material would cause bank destabilization, erosion, and soil loss resulting in local, short- and long-term, moderate, adverse impacts to soil resources.

Impairment

The No Action Alternative would result in local, short- and long-term, moderate, adverse impacts to soil resources in the immediate vicinity of the Happy Isles Gauging Station Bridge due to bank destabilization, erosion, and soil loss. Although the Merced River system and its geologic resources are key natural resource components within Yosemite Valley, the effect of this alternative on the riverbanks and soils would be localized to the immediate project area, and the effect would not be considered severe. The extent and quality of soil resources throughout the remainder of the Yosemite Valley segment of the river would remain unaffected by this alternative. Therefore, Alternative 1 would not impair soil resources.

Hydrology, Floodplains, and Water Quality

Analysis

Under Alternative 1, the existing condition and placement of Happy Isles Gauging Station Bridge would continue to adversely influence river hydrology and present a potential flood hazard. A bridge, like any fixed structure in a river, can alter flow dynamics and result in localized morphologic changes to the bed and banks of the river. The Happy Isles Gauging Station Bridge locally constricts river flow and increases flow velocity, which leads to erosion of the banks, down-cutting of the riverbed, and scouring at the bridge abutments and nearby riverbanks. These processes are ongoing and can be observed as bank erosion, both downstream and upstream of the abutments, and excessive scour beneath the river-left bridge abutment. During the January 1997 flood, debris accumulated upstream of the bridge and caused water to flood beyond the river channel on both sides of the abutment, causing excessive erosion and threatening the integrity of the bridge structure. Considering that the Happy Isles Gauging Station Bridge, if left in place, would continue to constrict river flow and negatively affect the natural hydrologic regime, Alternative 1 would have a local, long-term, adverse impact on hydrologic processes that influence river morphology. However, when the bridge collapses on its own accord under Alternative 1, natural river hydrology would be restored, resulting in a local, long-term, minor, beneficial impact on hydrologic processes.

The Happy Isles Gauging Station Bridge is damaged and is anticipated to fail in the next 10 years under the current practice of benign neglect. The rockfall and associated windblast in July 1996 and the floods of January 1997 caused structural damage and excessive scouring, especially to the river-left abutment. Continued scouring and undermining of the river-left abutment would eventually lead to either partial or full collapse of the abutments and the bridge deck. Failure could be gradual, lasting over several years as the abutment foundation degrades, or one flood event could be sufficient to dislodge the structure and initiate a complete failure.

When failure does occur, either large bridge sections or smaller abutment segments would collapse into the Merced River. Depending on the flows at the time of collapse, large pieces of fallen bridge structure could act as a dam, diverting flows to either side of the riverbanks. Smaller segments could also restrict and divert flows, leading to bank erosion or riverbank scour. Until the pieces could be removed from the river after collapse, when flow reduces sufficiently, bank erosion would continue and possibly threaten to expose and undermine the water supply lines located in the river-left bank. Flows diverted by debris could cause the river to leave the channel and result in localized flooding on either side of the river. Uncontrolled collapse of the bridge could also result in damage to the Happy Isles Gauging Station and streamflow gauge (a water stage recorder). In addition, bridge collapse (and possible damming) could disrupt recordation of stream flow data (flow rate, water level, and temperature) due to altered gauging station pool levels, river flow velocities, and channel geometry resulting in anomalous readings in an 86-year-long continuous historic record. Damage to the gauging station would be short-term, assuming that the instrumentation could be repaired. Disruption in the 86-year record would be short-term assuming that after the collapse, the measurements would again equilibrate and although there would be anomalous readings in the record at the time of bridge collapse, subsequent measurements would be consistent. Due to the potential for bridge collapse and subsequent erosion and flooding, in addition to the potential disruption of the gauging station and gauging station pool levels, Alternative 1 would have a local, short-term, moderate, adverse impact on hydrologic processes. However, these adverse impacts would be outweighed by the long-term benefits associated with eliminating a constriction to stream flows, allowing for eventual restoration of the natural hydrologic regime after the bridge collapses. Should the gauging station be damaged beyond repair, the adverse effects would be long term.

The current water quality problem caused by Happy Isles Gauging Station Bridge is attributed to the increased sediment load, which is introduced into the river from continued scouring of the river-left abutment. This sedimentation is not substantial and would continue under Alternative 1. When the bridge collapsed, either gradually or suddenly, water quality impacts would be temporarily substantial. Water quality would be affected primarily by sediment released into the river from behind and beneath the bridge abutments and by concrete, steel, and asphalt from the bridge structure. Fine-grained sediments would flow farthest downstream and cause the greatest impact to the river by increasing turbidity, while solid structural materials from the bridge (concrete, steel, and asphalt) would constitute less of a water quality impact. In addition, retrieval of the collapsed bridge materials scattered downstream would require use of construction equipment along the river between Happy Isle Gauging Station Bridge and Happy Isles Vehicle Bridge. Debris retrieval activities could dislodge sediment from the riverbed and banks. Sediment and debris delivery to the river would continue if the bridge remained and eventually failed; therefore, Alternative 1 would represent a local, long-term, moderate, adverse impact to water quality.

Summary of Alternative 1 Impacts. Alternative 1 would have local, short-term, moderate, adverse impacts on hydrologic processes and water quality due to the catastrophic collapse of the Happy Isles Gauging Station Bridge, subsequent debris retrieval activities, and potential damage to the Happy Isles Gauging Station. Over the long term, the collapsed bridge would be removed and natural river hydrology would be largely restored in this area, which would have a local, long-term, minor, beneficial impact on hydrologic processes.

Cumulative Impacts

Cumulative effects to hydrologic processes are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of Alternative 1.

The Merced River has been historically affected by a variety of projects that have introduced obstructions into the river channel, modified the floodplain, and adversely affected water quality. Alterations to hydrology have occurred through development and use within the Merced River corridor since Euro-American settlement. Examples of actions that have had adverse effects on the hydrologic processes of the Merced River include placement of riprap, removal of large woody debris, and construction of bridges, dikes, flood walls, impoundments, dams, and buildings. Conversely, actions such as riverbank restoration projects, removal of impoundments and bridges, and limiting visitor use to particular areas help restore the natural river flow and reduce bank erosion.

Reasonably foreseeable future projects that would have beneficial impacts on hydrologic processes and water quality include such restoration actions as those presented in the Yosemite Valley Plan. Elements of the Yosemite Valley Plan include removal of Sugar Pine Bridge, which constrains flows of the Merced River, rehabilitation of the Yosemite Falls corridor, restoration to natural conditions of campgrounds located within the floodplain, and removal of facilities from the 100-year floodplain. Alternatively, adverse impacts could occur by implementing the Yosemite Valley Plan projects including construction of additional lodging, campsites, and a visitor transit center in the Valley. Overall, the Yosemite Valley Plan would have a beneficial effect on river hydrologic processes and water quality.

The Merced Wild and Scenic River Comprehensive Management Plan protects river-related natural resources through the application of management elements, including the River Protection Overlay, management zoning, protection and enhancement of Outstandingly Remarkable Values, Section 7 determination process, and implementation of a Visitor Experience Resource Protection framework.

Other future projects include the Happy Isles Gauging Station Replacement Project, Repair of Flood Damaged Trails at Happy Isles, Merced River at Eagle Creek Ecological Restoration (Yosemite Valley), and the Replacement/Rehabilitation of the Yosemite Valley Main Sewer Line. Cumulatively, these projects are anticipated to have beneficial impacts on hydrologic processes and water quality of the Merced River.

While some of the past, present, and reasonably foreseeable future projects along the Merced River in Yosemite Valley would ultimately remove constrictions to streamflows, enhance water quality, rehabilitate eroded streambanks, and reduce degradation of stream characteristics in the Merced River, others would result in adverse water quality impacts and bank erosion. Thus, the cumulative projects would result in a local, long-term, minor, beneficial impact to hydrologic processes and water quality.

The past, present, and future projects in Yosemite Valley, considered cumulatively with Alternative 1, would have a local, long-term, minor beneficial effect on hydrologic processes and water quality in Yosemite Valley. The long-term beneficial effects associated with removal of the collapsed bridge under Alternative 1 would contribute to the beneficial cumulative effects, and largely offset the short-term adverse effects associated with the catastrophic collapse of the bridge.

Conclusions

Alternative 1 would have local, short-term, moderate, adverse impacts on hydrologic processes and water quality due to the catastrophic collapse of the Happy Isles Gauging Station Bridge, subsequent debris retrieval activities, and potential damage to the Happy Isles Gauging Station. Over the long term, the collapsed bridge would be removed and natural river hydrology would be somewhat restored in this area, which would have a local, long-term, minor, beneficial impact on hydrologic processes.

The past, present, and future projects in Yosemite Valley, considered cumulatively with Alternative 1, would have a local, long-term, minor, beneficial effect on hydrologic processes and water quality in Yosemite Valley. The long-term beneficial effects associated with removal of the collapsed bridge under Alternative 1 would contribute to the beneficial cumulative effects, and largely offset the short-term adverse effects associated with the catastrophic collapse of the bridge.

Impairment

Alternative 1 would result in local, short-term, moderate, adverse effects to hydrologic processes and water quality associated with catastrophic collapse of the bridge, but local, long-term, minor, beneficial effects associated with the ultimate removal of the bridge. Although the Merced River system and its associated hydrologic processes are a key resource within Yosemite Valley, the adverse effects of this alternative on river hydrology are primarily localized, temporary in duration, and largely offset by the long-term beneficial effects of ultimate bridge removal. The short-term adverse effects of this alternative would not be considered severe. Therefore, Alternative 1 would not impair hydrologic resources within the Merced River corridor.

Wetlands

Analysis

In the near term, Happy Isles Gauging Station Bridge would remain and the river-left abutment would continue to restrict the free flow of the Merced River and cause site-specific erosion. Over the long term, Happy Isles Gauging Station Bridge would continue to degrade and eventually fail. Bridge collapse would likely occur during a period of high flow and it is assumed that this collapse would occur within the next ten years. Collapse of the bridge could result in extensive erosion, as well as uncontrolled release of bridge debris into the Merced River. Bridge materials could affect downstream riparian and aquatic resources, either during transport (e.g., large bridge debris could remove trees) or upon deposition. Large chunks of concrete, rebar, and other bridge materials could dam the river, divert the river from its channel, or substantially erode the otherwise stable riverbanks in this area. Sudden erosion would threaten the river-left bank of the river. Diverted river flows and erosion could result in loss of vegetation along the riverbanks. Bridge debris could be deposited along the river channel and banks downstream to Happy Isles Vehicle Bridge and beyond and would alter local hydrologic patterns and the aquatic environment.

Activities associated with removal of bridge debris likely would not commence until low flow conditions, which could be several months subsequent to bridge collapse. Adverse effects would result from heavy equipment and debris removal activities and could include soil compaction, dust, vegetation removal, root damage, erosion, and potential introduction and spread of non-native species. The addition of silt, the resuspension of sediment, or the introduction of construction-related pollutants (fuels, lubricants, etc.) could degrade the quality of aquatic habitats. Debris removal would have local, short-term, minor to moderate, adverse effects to approximately 0.7 acre of aquatic habitat.

Failure and subsequent removal of the river-left abutment would help restore the free-flowing condition of the Merced River and return this portion of the river to a more natural state, thereby enhancing its biological integrity. Although the channel of the Merced River would stabilize and natural recolonization would occur over time, this effect likely would not be realized for 10 or more years. In the interim, erosion and erosion-related effects (e.g., bank instability, sediment deposition into the aquatic environment) would continue. Therefore, these effects would have a local, long-term, negligible to moderate, adverse impact on the aquatic environment. Overall, Alternative 1 would result in a local, negligible to moderate, adverse impact on aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species in the immediate vicinity of the Happy Isles Gauging Station Bridge. The extent and quality of riparian, wetland, and other riverine wildlife habitats throughout the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. Alternative 1 would result in local, short- and long-term, negligible to moderate, adverse impacts to aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species in the immediate vicinity of the Happy Isles Gauging Station Bridge.

Cumulative Impacts

Cumulative effects to wetland and aquatic resources are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects that have the potential to affect local wetland patterns.

Wetland and riparian systems of the Merced River corridor have been substantially altered by development and visitor activities. These changes have negatively influenced the size, form, and function of wetlands and the plants, wildlife, and aquatic species that inhabit them. Cumulative effects would be mixed, combining both adverse and beneficial effects. Cumulative beneficial effects on wetlands include wetland restoration, rehabilitation projects, and ecosystem management. Cumulative adverse effects would be related to increased facilities, regional growth, and visitor demand.

Reasonably foreseeable future actions within Yosemite Valley are considered to have an overall beneficial effect on wetlands. For example, the Merced Wild and Scenic River Comprehensive Management Plan protects river-related natural resources through the application of management elements, including the River Protection Overlay, management zoning, protection and enhancement of Outstandingly Remarkable Values, and implementation of a Visitor Experience Resource Protection framework. Full implementation of the Yosemite Valley Plan would result in a net gain of 118 acres of wetlands in Yosemite Valley through actions such as restoration of Upper River and a portion of Lower Pines Campgrounds to natural conditions; removal of roads through Stoneman and Ahwahnee Meadows; and removal of other bridges (e.g., Sugar Pine and possibly Stoneman) affecting the natural flow of the Merced River. Farther downstream, removal of the Cascades Diversion Dam would also remove an unnatural constriction to the free flow of the Merced River, thereby enhancing natural river dynamics including wetlands and aquatic systems below Yosemite Valley. Some Yosemite Valley Plan projects, such as construction of a replacement footbridge at the Happy Isles area, construction of a vehicle bridge across Yosemite Creek near Yosemite Lodge, and expansion of some campgrounds in Yosemite Valley, have the potential to adversely affect local wetlands. These projects would be designed to ensure the long-term protection of wetlands consistent with the Merced River Plan, the Clean Water Act, and Executive Order 11990: Protection of Wetlands.

Cumulative actions would have a long-term, major, beneficial cumulative effect on wetlands within Yosemite Valley due to wetland restoration efforts. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net local, long-term, major, beneficial effect on wetland patterns.

Conclusions

Alternative 1 would result in local, short- and long-term, negligible to moderate, adverse impacts to aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species in the immediate vicinity of the Happy Isles Gauging Station Bridge. Cumulative actions would have a local, long-term, major, beneficial cumulative effect on wetlands within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net local, long-term, major, beneficial effect on wetland patterns.

Impairment

The No Action Alternative would result in a local, negligible to moderate, adverse impact to aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species within the vicinity of the Happy Isles Gauging Station Bridge. Although the Merced River system and its related wetlands are key resources within Yosemite Valley, the effect of this alternative on wetland resources would be primarily localized, and the effect would not be considered severe. The extent and quality of riparian, wetland, and other riverine habitats throughout the remainder of the Yosemite Valley segment of the river would remain unaffected. Therefore, Alternative 1 would not impair wetland resources.

Vegetation

Analysis

In the near term, Happy Isles Gauging Station Bridge would remain and the river-left abutment would continue to restrict the free flow of the Merced River and cause site-specific erosion. Over the long term, Happy Isles Gauging Station Bridge would continue to be undermined and eventually fail. Bridge collapse would likely occur during a period of high flow and it is assumed that this collapse would occur within the next ten years. Collapse of the bridge could result in extensive erosion, as well as an uncontrolled release of bridge debris into the Merced River. Bridge materials could affect downstream vegetation, either during transport (e.g., large bridge debris could remove trees) or upon deposition. Large chunks of concrete, rebar, and other bridge materials could dam the river, divert the river from its channel, or substantially erode the otherwise stable riverbanks in this area. Sudden erosion would threaten the river-left bank of the river. Several mature black oaks, live oaks, and incense-cedars would likely be lost by erosional undermining or by the direct impact of bridge debris.

Activities associated with removal of bridge debris likely would not commence until low flow conditions, which could be several months subsequent to bridge collapse. Adverse effects to vegetation may include removal or trimming of trees or shrubs to gain access to the river for heavy equipment, soil compaction, root damage, and potential introduction and spread of non-native species. Debris removal would have local, short-term, negligible to minor, adverse effects to native vegetation.

Failure and subsequent removal of the river-left abutment would help restore the free-flowing condition of the Merced River and return this portion of the river to a more natural state, thereby enhancing its biological integrity. Although the channel of the Merced River would stabilize and natural recolonization would occur over time, this effect likely would not be realized for 10 or more years. In the interim, erosion and erosion-related effects (e.g., bank instability, undermining of streamside vegetation) would continue. Therefore, these effects would have a local, long-term, negligible, adverse impact on vegetation. Overall, Alternative 1 would result in a local, negligible, adverse impact to vegetation in the immediate vicinity of the Happy Isles Gauging Station Bridge. The extent and quality of vegetation, including riparian, wetland and other riverine habitats, throughout the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. Alternative 1 would result in local, short- and long-term, negligible, adverse impacts to vegetation in the immediate vicinity of the Happy Isles Gauging Station Bridge.

Cumulative Impacts

Cumulative effects to vegetation are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects that have the potential to affect local vegetation patterns.

Vegetation in Yosemite Valley has been substantially altered by development and visitor activities. These changes have negatively influenced the size, form, and function of vegetation communities and the plants and wildlife that inhabit them. Cumulative effects would be mixed, combining both adverse and beneficial effects. Cumulative beneficial effects on vegetation include restoration, rehabilitation projects, and ecosystem management. Cumulative adverse effects would be related to increased facilities and visitor demand.

Reasonably foreseeable future actions within Yosemite Valley are considered to have an overall net benefit to vegetation. For example, the Merced Wild and Scenic River Comprehensive Management Plan protects river-related natural resources through the application of management elements, including the River Protection Overlay, management zoning, protection and enhancement of Outstandingly Remarkable Values, and implementation of a Visitor Experience Resource Protection framework. Full implementation of the Yosemite Valley Plan would restore approximately 175 acres, of which approximately 160 acres would be high value resource vegetation in Yosemite Valley. Such proposed actions include removal and restoration of several campgrounds; removal of roads through Stoneman and Ahwahnee Meadows; and natural vegetation restoration actions in several areas. Although certain Yosemite Valley Plan projects, such as construction of new parking and lodging facilities, and expansion of campgrounds in Yosemite Valley, have potential to adversely affect local vegetation, these projects would be designed to ensure the long-term protection of sensitive vegetation communities consistent with the Merced River Plan and the Vegetation Management Plan.

Cumulative actions could have a long-term, major, beneficial cumulative effect on vegetation within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, could have a net long-term, moderate, beneficial effect on vegetation patterns.

Conclusions

Alternative 1 would result in local, short- and long-term, negligible, adverse impacts to vegetation in the immediate vicinity of the Happy Isles Gauging Station Bridge. Cumulative actions would have a long-term, major, beneficial cumulative effect on vegetation within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net long-term, moderate, beneficial effect on vegetation patterns.

Impairment

The No Action Alternative would result in a local, negligible, adverse impact to vegetation in the immediate vicinity of the Happy Isles Gauging Station Bridge. Although the Merced River system and its related vegetation are key resources within Yosemite Valley, the effect of this alternative on vegetation would be localized, and the effect would not be considered severe. The extent and quality of vegetation, including riparian, wetland, and other riverine habitats, throughout the remainder of the Yosemite Valley segment of the river would remain unaffected. Therefore, Alternative 1 would not impair vegetation resources.

Wildlife

Analysis

Under Alternative 1, the Happy Isles Gauging Station Bridge would continue to be undermined and eventually fail. Bridge collapse would likely occur during a period of high flow and it is assumed that this collapse would occur within the next ten years. Collapse of the bridge could result in extensive erosion, as well as an uncontrolled release of bridge debris into the Merced River that could temporarily affect aquatic resources, fish, and wildlife. Bridge debris could adversely affect mature trees and the banks and channel of the Merced River, which provide habitat for species such as raptors, small mammals, and non-native fish. Large chunks of concrete, rebar, and other bridge materials could dam the river, divert the river from its channel, or substantially erode the otherwise stable riverbanks in this area. Sudden erosion would threaten the river-left bank of the river and would likely remove several mature black oaks, live oaks, and incense-cedars—potential nest and perch locations for raptors and songbirds. Suspended sediments would temporarily reduce dissolved oxygen levels, which could affect respiration of aquatic invertebrates. Large debris would temporarily modify the channel and substrate of the Merced River at this location, which could have a negligible, adverse impact on fish passage.

Activities associated with removal of bridge debris likely would not commence until low flow conditions, which could be several months subsequent to bridge collapse. Adverse effects would result from heavy equipment and debris removal activities and could include dust (e.g., potential adverse impacts to invertebrate respiration), vegetation removal (e.g., potential adverse impacts to nest and perch sites), and introduction of construction-related pollutants (e.g., temporary degradation of fisheries habitat). The amount of sediment potentially released during the retrieval is expected to be minor and would not cause turbidity or sedimentation sufficient to adversely affect fisheries resources downstream of the project. Debris removal would have local, short-term, negligible to minor, adverse effects to wildlife.

Failure and subsequent removal of the river-left abutment would help restore the free-flowing condition of the Merced River and return this portion of the river to a more natural state, thereby enhancing its biological integrity and fish habitat. Over time, the channel of the Merced River would stabilize, natural recolonization would occur, and wildlife habitats would normalize. Although this effect likely would not be realized for 10 or more years, local wildlife would adjust. Overall, Alternative 1 would result in a local, short-term, negligible to minor, adverse impact to wildlife in the immediate vicinity of the Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on wildlife would be local, negligible to minor, and beneficial. The extent and quality of rich habitat for a diversity of river-related species throughout the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. Alternative 1 would result in a local, short-term, negligible to minor, adverse impact to wildlife in the immediate vicinity of Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on wildlife would be local, negligible to minor, and beneficial.

Cumulative Impacts

Cumulative effects to wildlife are based on analysis of past, present, and reasonably foreseeable future actions within Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects that have the potential to affect local wildlife patterns.

Wildlife communities have been manipulated almost since the inception of the park. Regional wildlife has been historically affected by logging, fire suppression, rangeland clearing, grazing, mining, draining, damming, diversions, and the introduction of non-native species . Park rangers trapped fur-bearing mammals until 1925; mountain lions were considered dangerous predators and controlled through the 1920s; and black bears were artificially fed as a tourist attraction until 1940. Natural wildland fires, with their generally beneficial effects on wildlife habitat, were routinely suppressed until 1972 (Wuerthner 1994). Past and ongoing activities include recreational use and construction of bridges, diversion walls, roads, pipelines, riprap, buildings, campgrounds, and other recreational features.

Reasonably foreseeable future actions within Yosemite Valley are considered to have an overall net benefit to wildlife. For example, the Merced Wild and Scenic River Comprehensive Management Plan protects river-related natural resources through the application of management elements, including the River Protection Overlay, management zoning, protection and enhancement of Outstandingly Remarkable Values, and implementation of a Visitor Experience Resource Protection framework. Full implementation of the Yosemite Valley Plan would increase the size, continuity, and integrity of wildlife habitats in Yosemite Valley. Although certain Yosemite Valley Plan projects, such as improving El Portal Road from the El Portal/Big Oak Flat Road intersection to Pohono Bridge and expansion of campgrounds in Yosemite Valley, have potential to adversely affect local wildlife, these projects must be designed to ensure the long-term protection of sensitive vegetation communities consistent with the Merced River Plan and the Vegetation Management Plan. In addition, implementation of the Visitor Experience and Resource Protection framework (included in both the Merced River Plan and Yosemite Valley Plan) will help reduce adverse effects of visitor use on wildlife habitat and patterns.

Cumulative actions would have a local, long-term, minor to moderate, beneficial cumulative effect on wildlife within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net local, long-term, minor to moderate, beneficial effect on wildlife patterns.

Conclusions

Alternative 1 would result in a local, short-term, negligible to minor adverse impact to wildlife in the immediate vicinity of Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on wildlife would be local, negligible to minor, and beneficial. Cumulative actions would have a local, long-term, minor to moderate, beneficial cumulative effect on wildlife within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net long-term, minor to moderate, beneficial effect on wildlife patterns.

Impairment

The No Action Alternative would result in a local, short-term, negligible to minor, adverse impact to wildlife and rich habitat for a diversity of river-related species in the immediate vicinity of Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on wildlife would be local, negligible to minor, and beneficial. Although the Merced River system and its related wildlife are key resources within Yosemite Valley, the adverse effect of this alternative on wildlife would be localized, short-term, and would not be considered severe. The extent and quality of wildlife and rich habitat for a diversity of river-related species throughout the remainder of the Yosemite Valley segment of the river would remain unaffected. Therefore, Alternative 1 would not impair wildlife resources.

Special-Status Species

Analysis

Activities associated with removal of bridge debris likely would not commence until low flow conditions, which could be several months subsequent to bridge collapse. Adverse effects would result from heavy equipment and debris removal activities and could include vegetation removal (e.g., potential adverse impacts to nest and perch sites for special-status raptors), and introduction of construction-related pollutants (e.g., temporary degradation of Wawona riffle beetle habitat). The amount of sediment potentially released during the retrieval is expected to be minor and would not cause turbidity or sedimentation sufficient to adversely affect aquatic resources for special-status species downstream of the retrieval area. Debris removal would have local, short-term, negligible to minor, adverse effects to special-status species.

Failure and subsequent removal of the river-left abutment would help restore the free-flowing condition of the Merced River and return this portion of the river to a more natural state, thereby enhancing its biological integrity and habitat for aquatic special-status species such as Wawona riffle beetle. Over time, the channel of the Merced River would stabilize, natural recolonization would occur, and habitats would normalize. Although this effect likely would not be realized for 10 or more years, local special-status species, such as raptors, would adjust. Potential effects to Wawona riffle beetle would be more pronounced due to this species’ restricted habitat and short life span. Overall, Alternative 1 would result in a local, short-term, negligible to minor, adverse impact to special-status species in the immediate vicinity of the Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on special-status species would be local, negligible to minor, and beneficial. The extent and quality river-related species throughout the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. Alternative 1 would result in a local, short-term, negligible to minor, adverse impact to special-status species in the immediate vicinity of the Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on special-status species would be local, negligible to minor, and beneficial.

Cumulative Impacts

Cumulative effects to special-status species are based on analysis of past, present, and reasonably foreseeable future actions within Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects that have the potential to affect local special-status species.

Natural habitats have been manipulated almost since the inception of the park. Regional wildlife and vegetation patterns have been historically affected by logging, fire suppression, rangeland clearing, grazing, mining, draining, damming, diversions, and the introduction of non-native species. Past and ongoing activities that affect special-status species include recreational use and construction of bridges, diversion walls, roads, pipelines, riprap, buildings, campgrounds, and other recreational features.

Reasonably foreseeable future actions within Yosemite Valley are considered to have an overall net benefit to special-status species. For example, the Merced Wild and Scenic River Comprehensive Management Plan protects river-related natural resources through the application of management elements, including the River Protection Overlay, management zoning, protection and enhancement of Outstandingly Remarkable Values, and implementation of a Visitor Experience Resource Protection framework. Full implementation of the Yosemite Valley Plan would increase the size, continuity, and integrity of habitats, especially meadow, riparian, black oak, and upland habitats, for special-status species in Yosemite Valley. Although certain Yosemite Valley Plan projects, such as construction of new lodging and parking facilities, and expansion of campgrounds in Yosemite Valley, have potential to adversely affect local special-status species, these projects must be designed to ensure the long-term protection of special-status species consistent with the Merced River Plan and the Endangered Species Act. In addition, implementation of the Visitor Experience and Resource Protection framework (included in both the Merced River Plan and Yosemite Valley Plan) will help reduce adverse effects of visitor use on special-status species.

Cumulative actions would have a local, long-term, moderate, beneficial cumulative effect on special-status species within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net local, long-term, moderate, beneficial effect on special-status species.

Conclusions

Alternative 1 would result in a local, short-term, negligible to minor, adverse impact to special-status species in the immediate vicinity of the Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on special-status species would be local, negligible to minor, and beneficial. Cumulative actions would have a local, long-term, moderate, beneficial cumulative effect on special-status species within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would have a net local, long-term, moderate, beneficial effect on special-status species.

Impairment

The No Action Alternative would result in a local, short-term, negligible to minor, adverse impact to special-status species in the immediate vicinity of the Happy Isles Gauging Station Bridge. Long-term effects of Alternative 1 on special-status species would be local, negligible to minor, and beneficial. Although the Merced River system and its related special-status species are key resources within Yosemite, the adverse effect of this alternative on special-status species would be localized, short-term and would not be considered severe. The extent and quality of rich habitat for a diversity of river-related species throughout the remainder of the Yosemite Valley segment of the river would remain unaffected. Therefore, Alternative 1 would not impair special-status species resources.

Air Quality

Analysis

Alternative 1 would result in local, short-term, minor, adverse impacts on air quality due to bridge debris removal activities. Bridge debris could be deposited along the river channel and banks downstream to Happy Isles Vehicle Bridge and beyond. Effects would be primarily related to use of equipment, dust, and vehicle trips to and from the area. The Happy Isles Gauging Station Bridge is located in a region that experiences exceedances of ozone and PM-10 standards. Debris removal activities would temporarily affect pollutant concentrations in the vicinity of the project (primarily fugitive dust from removal activities and vehicle travel over paved surfaces heavily laden with earthen materials). These activities would generate substantial amounts of dust, including particles with diameters of 10 microns or less (PM-10) and particles with diameters of 2.5 microns or less (PM-2.5), primarily from “fugitive” sources (i.e., emissions released by means other than through a stack or tailpipe). Dust emissions would vary from day to day, depending on the level and type of activity, silt content of the soil, and the weather.

Alternative 1 would also result in tailpipe emissions associated with use of mobile debris removal equipment, construction-worker commute trips, and truck trips to haul bridge materials from the site to appropriate recycling facilities. These emissions could affect regional air quality, but impacts would be short-term, negligible, and adverse.

Debris removal activities would generate emissions of ozone precursors and carbon monoxide (criteria air pollutant emissions) as well as toxic air contaminants from use of diesel-powered equipment. Toxic air contaminants are less pervasive in the atmosphere than criteria air pollutants, but they are linked to short-term (acute) or long-term (chronic or carcinogenic) adverse human health effects. Toxic air contaminants do not have corresponding ambient air quality standards. However, the limited duration of debris removal activities would limit the potential for diesel particulates to adversely affect local air quality, resulting in local, short-term, minor, adverse effects. There would be no long-term effect on air quality under this alternative.

Summary of Alternative 1 Impacts. Bridge debris removal activities under Alternative 1 would result in regional and local, short-term, negligible to minor, adverse impacts to air quality. There would be no long-term effect on air quality under this alternative.

Cumulative Impacts

Cumulative effects to air quality are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects within Yosemite Valley that could affect air quality or that could be affected by air pollutant sources within the Merced River corridor nearest the project site.

Since 1950, the population of California has tripled, and the rate of increase in vehicle-miles-traveled has increased six-fold. Air quality conditions within the park have been influenced by this surge in population growth and associated emissions from industrial, commercial, and vehicular sources in upwind areas. Since the 1970s, emissions sources operating within the park, as well as California as a whole, have been subject to local stationary-source controls and state and federal mobile-source controls. With the passage of time, such controls have been applied to an increasing number of sources, and the associated requirements have become dramatically more stringent and complex. In the 1980s, a Restricted Access Plan was developed for use when traffic and parking conditions in Yosemite Valley are overcongested. The plan has the effect of reducing the number of incoming vehicles and their related emissions until the traffic volume and parking demand in Yosemite Valley decrease sufficiently (as visitors leave the Valley) to stabilize traffic conditions.

The Yosemite Valley Plan proposes to enhance the quality of the visitor experience in Yosemite Valley by reducing automobile congestion and limiting crowding. It also proposes traffic management systems and options for the size and placement of parking lots, both within and outside of Yosemite Valley. Parking lot(s) outside the Valley could be used to intercept day visitors and shift those visitors to Valley-bound shuttle buses. The Yosemite Valley Plan would have a long-term, moderate, adverse impact on nitrogen oxide emissions from using diesel buses through 2015, but long-term, minor to major, beneficial impacts to volatile organic compounds, carbon monoxide, and particulate matter emissions.

The purpose of the Merced Wild and Scenic River Comprehensive Management Plan is to protect and enhance the Outstandingly Remarkable Values and free-flowing condition of the river for the benefit and enjoyment of present and future generations. The protection of natural resources under this plan would benefit air quality.

Reasonably foreseeable future actions proposed for Yosemite Valley could have beneficial or adverse impacts on air quality. For example the National Park Service’s Shuttle Bus Replacement Project could have a net beneficial effect on air quality by improving the attractiveness of alternative modes of transportation and thereby reducing private automobile trips. Although the Shuttle Bus Replacement Project would have localized, short-term, adverse air quality effects, the general goal of the project is to relieve congestion and to provide for alternative means of transportation. As such, this project would encourage travel to the park by alternative (nonprivate vehicle) modes and would have a long-term, beneficial effect on air quality.

Other reasonably foreseeable future National Park Service projects not anticipated to have a net adverse or beneficial effect on air quality (except for short-term, localized impacts during construction) include: Replacement/Rehabilitation of Yosemite Valley Main Sewer Line, Merced River at Eagle Creek Ecological Restoration Project (Yosemite Valley), Trail Reconstruction from Happy Isles to Vernal Fall, Repair Flood-Damaged Trail Bridges at Happy Isles, and Happy Isles Site Improvements.

Although cumulative growth in the region will tend to adversely affect air quality, implementation of ongoing state and federal mobile-source control programs would ameliorate this effect to a degree. With respect to particulate matter, conditions in the Valley would be determined by both regional sources and local sources, and could be beneficial or adverse. Considered with the adverse impacts associated with regional air quality influences, the cumulative projects would have a local, long-term, moderate, beneficial effect on air quality in Yosemite Valley.

Alternative 1 and the cumulative projects would result in local, long-term, moderate, beneficial impacts on air quality. The short-term, adverse effects associated with bridge debris removal activities would not offset the long-term, beneficial effects of the cumulative projects.

Conclusions

Bridge debris removal activities under Alternative 1 would result in regional and local, short-term, negligible to minor, adverse impacts to air quality. There would be no long-term effect on air quality under this alternative.

Impairment

Impairment of the Merced River is not addressed under air quality because this resource topic is peripheral to the protection of the river for future generations.

Noise

Analysis

Alternative 1 would result in local, short-term, moderate, adverse impacts on noise due to bridge debris removal activities. Bridge debris could be deposited along the river channel and banks downstream to Happy Isles Vehicle Bridge and beyond. Effects would be primarily related to bridge debris removal activities (such as crane operation) and debris haul trips, which would also raise ambient noise levels along haul routes. Operation of heavy-duty equipment at the site during retrieval activities could generate substantial amounts of noise and would occur within close proximity to river recreation uses. Other sensitive land uses (e.g., campgrounds) located downstream from the area would be affected in the short-term as well. Table IV-1 provides typical noise levels generated by construction equipment. Noise in the area between Happy Isles Gauging Station Bridge and Happy Isles Vehicle Bridge would vary depending upon a number of factors, such as the number and types of equipment in operation on a given day, usage rates, the level of background noise in the area, and the distance between sensitive uses and the construction site.

TABLE IV-1: Typical Noise Levels from Construction Equipment

*Equipment*	*Typical Noise Level (dBA) 50 feet from the Source***
Air Compressor	81
Backhoe	80
Compactor	82
Concrete Mixer	85
Concrete Pump	82
Crane, Derrick	88
Crane, Mobile	83
Dozer	85
Generator	81
Grader	85
Impact Wrench	85
Jack Hammer	88
Loader	85
Paver	89
Pneumatic Tool	85
Pump	76
Rock Drill	98
Roller	74
Saw	76
Scraper	89
Truck	88

dBA = A-weighted decibels

Source: FTA 1995

The specific mix of equipment to be used in bridge cutting and removal is unknown, but could include the use of cranes, excavators, backhoes, skid steer loaders, trucks, graders, jack hammers, concrete saws, etc. Noise levels would decrease by about 6 dBA with each doubling of distance from the site (e.g., noise levels from crane use would be in the range of 83 to 88 dBA at 100 feet from the site, and about 77 to 82 dBA at 200 feet from the site).

Over the long term, the acoustical environment in the vicinity of Happy Isles Gauging Station Bridge would be shaped largely by natural sources of sound (i.e., rushing water and wind) punctuated by human-caused sources of noise, such as motor vehicles and aircraft.

Summary of Alternative 1 Impacts. Eventual uncontrolled bridge failure would result in a local, short-term, moderate, adverse impact to the ambient noise environment due to bridge debris removal activities. Over the long term, the ambient noise environment in the vicinity of Happy Isles Gauging Station Bridge would be shaped largely by natural sources of sound (i.e., rushing water and wind) punctuated by human-caused sources of noise.

Cumulative Impacts

Cumulative effects to the ambient noise environment are based on the analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The projects identified below include those projects within Yosemite Valley that could affect noise within the river corridor near the project site or could be affected by noise sources within the corridor.

The Yosemite Valley Plan proposes to enhance the quality of the visitor experience in Yosemite Valley by reducing automobile congestion, limiting crowding, and expanding orientation and interpretation services. It also proposes traffic management systems and options for the size and placement of parking lots, both within and outside of Yosemite Valley. Parking lots outside the Valley could be used to intercept day visitors and shift those visitors to Valley-bound shuttle buses. Overall, general sound levels associated with traffic along most roadways in the Valley would be reduced, representing a long-term beneficial impact.

Reasonably foreseeable future actions proposed for Yosemite Valley could have beneficial or adverse impacts on noise. For example, the National Park Service’s Shuttle Bus Replacement Project could have a net beneficial effect on the ambient noise environment by improving the attractiveness of alternative modes of transportation and thereby reducing private automobile trips. Although the Shuttle Bus Replacement Project would have localized, short-term, adverse noise effects, the general goal of the project is to relieve congestion and to provide for alternative means of transportation. As such, this project would encourage travel to the park by alternative (nonprivate vehicle) modes and would have a long-term beneficial effect on noise. To the extent that transportation-related projects would replace automobile trips in the Valley with bus trips, the anticipated beneficial effect would depend upon ridership levels (and the corresponding number of automobile trips that would be avoided) and the technology selected for the buses.

Other reasonably foreseeable future National Park Service projects not anticipated to have a net adverse or beneficial effect on the ambient noise environment (except for short-term, localized impacts during construction) include: Replacement/Rehabilitation of Yosemite Valley Main Sewer Line, Merced River at Eagle Creek Ecological Restoration (Yosemite Valley), Trail Reconstruction from Happy Isles to Vernal Fall, Repair Flood Damaged Trail Bridges at Happy Isles, and Happy Isles Site Improvements.

The gradual increase in annual visitation to the park would likely offset the beneficial effects of cumulative actions that would tend to reduce vehicle trips and their associated noise, resulting in a local, long-term, minor, adverse effect on the noise environment. Alternative 1 would contribute to this impact in the short term.

Conclusions

Eventual uncontrolled bridge failure would result in a local, short-term, moderate, adverse impact to the ambient noise environment due to bridge debris removal activities. Over the long-term, the ambient noise environment in the vicinity of Happy Isles Gauging Station Bridge would be shaped largely by natural sources of sound (i.e., rushing water and wind) punctuated by human-caused sources of noise.

Impairment

Impairment of the Merced River is not addressed under noise because this resource topic is peripheral to the protection of the river for future generations.

Cultural Resources

Archeological Resources

Analysis

Under Alternative 1, there would be no change in management and treatment of archeological sites in the Happy Isles area. Bridge collapse would likely occur during a period of high flow and it is assumed that this collapse would occur within the next ten years. Bridge debris could dam the river, divert the river from its channel, or substantially erode the otherwise stable riverbanks in this area, especially the river-left bank, which could unearth sensitive prehistoric or historic archeological resources in the vicinity of Happy Isles Gauging Station Bridge downstream to Happy Isles Vehicle Bridge. Although the banks of the Merced River would stabilize over time, this effect likely would not be realized for 10 or more years. In the interim, erosion and erosion-related effects (e.g., bank instability and erosion that could potentially affect archeological resources) would continue. Since the intensity of impacts would depend upon the nature, location, and extent of disturbance as well as the quantity and data potential of the archeological site(s) affected, it is not possible to determine the intensities of those impacts. Activities associated with removal of bridge debris are not anticipated to involve earth moving and grading that could affect archeological resources. Any actions undertaken by the National Park Service would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement. The evidence of thousands of years of human occupation, reflected in the large number of archeological sites, throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. There would be no change in the treatment and management of archeological resources in the Happy Isles area as a result of Alternative 1. Bridge collapse and subsequent bank erosion has potential to have a long-term adverse effect on archeological resources in the vicinity of Happy Isles Gauging Station Bridge. Since the intensity of impacts would depend upon the nature, location, and extent of disturbance as well as the quantity and data potential of the archeological site(s) affected, it is not possible to determine the intensities of those impacts. Any site-specific planning and compliance actions would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement.

Cumulative Impacts

Cumulative impacts to archeological resources are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative.

In general, any archeological resources within Yosemite Valley are the result of thousands of years of human occupation. Development of facilities within Yosemite Valley has disturbed or destroyed numerous archeological resources and compromised the integrity of numerous other such resources, which has had an adverse cumulative effect on archeological resources.

Reasonably foreseeable future actions proposed in the region that could have an adverse cumulative effect on archeological resources in Yosemite include development-related projects, such as implementing the Yosemite Valley Plan, the Replacement/Rehabilitation of Yosemite Valley Main Sewer Line, and the Merced River at Eagle Creek Ecological Restoration (Yosemite Valley). The extensive grading and ground disturbance likely required for these cumulative projects could disturb individual archeological resources. Each of these cumulative projects is near the main stem of the Merced River, which is an archeologically sensitive area. The Yosemite Valley Plan would have a local, long-term, adverse cumulative effect on cultural resources in Yosemite Valley due to possible disturbance associated with earth-moving, construction, and demolition projects. The National Park Service would follow guidelines of the 1999 Programmatic Agreement and would avoid adverse effects to archeological resources to the greatest extent feasible.

The Merced Wild and Scenic River Comprehensive Management Plan provides a framework for decision-making on future management actions within the Merced River corridor through the application of a consistent set of decision-making criteria and considerations composed of seven management elements: boundaries, classifications, Outstandingly Remarkable Values, the Section 7 determination process, management zoning, the River Protection Overlay, and the Visitor Experience and Resource Protection framework. The Merced River Plan would have a local, long-term, adverse cumulative effect on archeological resources.

The cumulative projects within and in the vicinity of the main stem of the Merced River in Yosemite Valley would result in a local, long-term, negligible to minor, adverse impact on archeological resources due to the potential disturbance of such resources.

Alternative 1 and the cumulative projects within and in the vicinity of the main stem of the Merced River and in Yosemite Valley would result in a local, long-term, negligible to minor, adverse impact on archeological resources.

Conclusions

There would be no change in the treatment and management of archeological resources in the Happy Isles area as a result of Alternative 1. Bridge collapse and subsequent bank erosion has potential to have a long-term, adverse effect on archeological resources in the vicinity of Happy Isles Gauging Station Bridge. Since the intensity of impacts would depend upon the nature, location, and extent of disturbance as well as the quantity and data potential of the archeological site(s) affected, it is not possible to determine the intensities of those impacts. Any site-specific planning and compliance actions would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement.

Impairment

Although archeological sites along the river are key cultural resources within Yosemite Valley, the effect of this alternative on archeological resources would be primarily localized, and the effect would not be considered severe. In addition, the No Action Alternative would not change the treatment and management of archeological resources. Archeological sites throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected. Therefore, Alternative 1 would not impair archeological resources.

Ethnographic Resources

Analysis

Under Alternative 1, there would be no change in the management and treatment of ethnographic resources in the Happy Isles area. Therefore, no measurable impacts to ethnographic resources would occur as a result of this alternative.

Summary of Alternative 1 Impacts. There would be no change in the treatment and management of ethnographic resources as a result of Alternative 1. Any site-specific planning and compliance actions would be accomplished in accordance with stipulations in the park’s 1999 Programmatic Agreement, and the park would continue to consult with culturally associated American Indian tribes under this Programmatic Agreement and the cooperative agreement for traditional uses. Therefore, no measurable impacts to ethnographic resources would occur as a result of this alternative.

Cumulative Impacts

Cumulative impacts to ethnographic resources discussed herein are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative.

Ethnographic resources and their traditional cultural associations have been lost or damaged in Yosemite Valley through past development, visitor use, natural events, and widespread disruption of cultural traditions. Nevertheless, Yosemite National Park retains many sites and resources of significance to local and culturally associated American Indians.

In general, the ethnographic resources within the main stem of the Merced River are the result of thousands of years of human occupation. Development of facilities within Yosemite Valley has disturbed or destroyed numerous ethnographic resources and compromised the integrity of numerous other such resources, which has had an adverse cumulative effect on ethnographic resources.

Reasonably foreseeable future actions proposed in the region that could have an adverse cumulative effect on ethnographic resources in Yosemite Valley include development-related projects, such as implementing the Yosemite Valley Plan. Under the Yosemite Valley Plan, traditional gathering areas would be disturbed and modern development would be expanded at historic village areas. Overall, implementation of the Yosemite Valley Plan would have a local, long-term, adverse effect on ethnographic resources.

The Merced Wild and Scenic River Comprehensive Management Plan provides a framework for decision-making on future management actions within the Merced River corridor through the application of a consistent set of decision-making criteria and considerations composed of seven management elements: boundaries, classifications, Outstandingly Remarkable Values, the Section 7 determination process, management zoning, the River Protection Overlay, and the Visitor Experience and Resource Protection framework. Potential future actions that could occur under the management zones of the Merced River Plan, however, could have adverse effects on ethnographic resources. As a result, the Merced River Plan could have a local, long-term, adverse cumulative effect on ethnographic resources.

An example of a reasonably foreseeable project that could beneficially affect ethnographic resources in Yosemite Valley is the Merced River at Eagle Creek Ecological Restoration project (Yosemite Valley). This cumulative project could restore native plant habitat, which would be a long-term, beneficial impact on ethnographic resources. The intensity of this impact would depend on the extent to which gathering sites were restored and access to traditional use areas were continued.

The cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on ethnographic resources due to the disturbance of such resources. Alternative 1 would not contribute to this impact.

Conclusions

There would be no change in the treatment and management of ethnographic resources as a result of Alternative 1. Any site-specific planning and compliance actions would be accomplished in accordance with stipulations in the park’s 1999 Programmatic Agreement, and the park would continue to consult with culturally associated American Indian tribes under this Programmatic Agreement and the cooperative agreement for traditional uses. Therefore, no measurable impacts to ethnographic resources would occur as a result of this alternative.

Impairment

The No Action Alternative would not have a direct, indirect, or cumulative impact on ethnographic resources or their treatment and management. Ethnographic resources throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected. Therefore, Alternative 1 would not impair ethnographic resources.

Cultural Landscape Resources, including Historic Sites and Structures

Analysis

All cultural landscape resources, historic sites, and structures would continue to be managed as they are today.

The Happy Isles Gauging Station Bridge is expected to eventually collapse, resulting in the loss of this contributing feature of the Yosemite Valley Cultural Landscape, eligible for listing in the National Register of Historic Places. Uncontrolled collapse of the bridge could also damage the historic Happy Isles Gauging Station and streamflow gauge and historic Happy Isles Vehicle Bridge. This could result in a local, long-term, minor, adverse impact to the cultural landscape. Because follow-on actions undertaken by the National Park Service would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement, the adverse impact would be somewhat reduced. Nationally significant historic resources, such as designed landscapes and developed areas, historic buildings, and circulation systems (trails, roads, and bridges), throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 1 Impacts. There would be no change in the treatment and management of cultural landscape resources as a result of Alternative 1. The uncontrolled collapse of the Happy Isles Gauging Station Bridge would result in the loss of this cultural resource and could cause damage to the Happy Isles Gauging Station and streamflow gauge and historic Happy Isles Vehicle Bridge. This would result in a local, long-term, minor, adverse impact to the cultural landscape. Because follow-on actions would be accomplished in accordance with stipulations in the park’s 1999 Programmatic Agreement, the adverse impact would be somewhat reduced.

Cumulative Impacts

Cumulative impacts to cultural landscape resources are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative.

Cultural landscape resources have been lost or damaged in Yosemite Valley through past development, visitor use, and natural events resulting in adverse cumulative impacts to the cultural landscape. In the Happy Isles area, cultural resources include the Happy Isles Gauging Station Bridge, the Happy Isles Gauging Station, the Happy Isles Vehicle Bridge, and the 1927 Yosemite Fish Hatchery, converted to a nature center in 1957. Disappearing structures and sites in other areas include homestead cabins, barns, road and trail segments, bridges, mining complexes, railroad and logging facilities, historic tourist facilities, blazes, and campsites. These resources are reminders of the area’s ranching, grazing, lumbering, mining history, and early tourism.

Reasonably foreseeable future actions proposed in the region that could affect cultural landscape resources include Yosemite campground rehabilitation projects, such as those identified in the Yosemite Valley Plan. The Yosemite Valley Plan would result in the removal, relocation, or modification of historic buildings and structures, and the introduction of modern facilities and development within historic districts and contributing portions of the cultural landscape. The Yosemite Valley Plan would also restore native vegetation communities to patterns more in keeping with the cultural landscape and historic setting of the Valley. Overall, implementation of the Yosemite Valley Plan would adversely affect the cultural landscape.

Protection of cultural resources is an integral component of the Merced Wild and Scenic River Comprehensive Management Plan. The plan provides a framework for decision-making on future management actions within the Merced River corridor through the application of a consistent set of decision-making criteria and considerations composed of seven management elements: boundaries, classifications, updated Outstandingly Remarkable Values, the Section 7 determination process, management zoning, the River Protection Overlay, and the Visitor Experience and Resource Protection framework. The Merced River Plan would have a beneficial cumulative effect on cultural resources, including cultural landscapes, historic sites, and historic structures.

The cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on the cultural landscape due to the disturbance of such resources. Alternative 1 and the cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on cultural landscape resources.

Conclusions

There would be no change in the treatment and management of cultural landscape resources as a result of Alternative 1. The uncontrolled collapse of the Happy Isles Gauging Station Bridge would result in the loss of this cultural resource and could cause damage to the Happy Isles Gauging Station and streamflow gauge and historic Happy Isles Vehicle Bridge. This would result in a local, long-term, minor, adverse impact to the cultural landscape. Because follow-on actions would be accomplished in accordance with stipulations in the park’s 1999 Programmatic Agreement, the adverse impact would be somewhat reduced.

Alternative 1 and the cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on cultural landscape resources.

Impairment

Although cultural landscape resources along the Merced River are key to the cultural integrity of Yosemite Valley, the effect of this alternative on the cultural landscape would be primarily localized, and the effect would not be considered severe. In addition, the No Action Alternative would not change the treatment and management of cultural landscape resources. Cultural landscape resources throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected. Therefore, Alternative 1 would not impair cultural landscape resources.

Social Resources

Scenic Resources

Analysis

Under Alternative 1, the Happy Isles Gauging Station Bridge would remain in its existing condition without maintenance or repair. Because it is considered hazardous and is expected to eventually fail, the bridge would continue to be fenced off to prevent public access. The existing cyclone fencing at both ends of the bridge would continue to intrude visually upon the scenic character of Happy Isles. In addition, the condition of the bridge itself would continue to deteriorate until the bridge collapsed, adding to the now visible signs of disuse and disrepair to the intrusive effects of the fencing. In its current state, the river-left abutment has separated from the river-left wingwall, dropping the bridge beam and thus breaking the continuity of the horizontal line of the bridge deck. Cracks have opened at the junction of the river-right abutment and the supporting boulder, disrupting the visual connection between the bridge and the riverbank. The concrete surfaces of the bridge, abutments, and wingwalls are pitted and cracked and the bridge deck surfaces are in disrepair. Under Alternative 1, it is assumed that the bridge’s continuing deterioration would eventually result in its sudden and uncontrolled failure. Bridge debris would litter the channel of the Merced River, diminishing the scenic quality of the river channel where it was deposited.

The failure of the bridge is also likely to result in sections of the structure gouging the banks and scouring the river bottom downstream from Happy Isles, leaving substantial and highly visible evidence of damage to the banks and to stands of vegetation. Under Alternative 1, it is assumed that debris deposited in the channel by the bridge’s collapse would be removed by the National Park Service as soon as feasible. However, depending on the time of year and river conditions when the bridge failed, completion of clean up could be delayed for a period of months. Construction and transport equipment needed to remove the concrete debris from the river would temporarily increase the visual intrusion effects of the bridge’s failure. Once debris was removed from the river, damage to the riverbanks and vegetation could continue to be visible for a period of years. The continuing deterioration of the existing bridge, deposition of debris in the river following failure of the bridge, and operation of equipment to remove and transport the debris would result in a local, short-term, minor, adverse effect on scenic resources at Happy Isles.

The long-term effect of the bridge’s failure under Alternative 1 would be to remove a structure that in its present condition is a source of visual intrusion upon the scenic character of Happy Isles. As noted above, the ongoing deterioration of the bridge deck and supporting members is plainly visible and detracts from views of the natural landscape in which the bridge is an element. Removal of the existing bridge would result in a local, long-term, minor, beneficial effect on scenic resources at Happy Isles.

Summary of Alternative 1 Impacts. The No Action Alternative would result in a local, short-term, minor, adverse impact to scenic resources the vicinity of Happy Isles Gauging Station Bridge, due to the visual intrusion effects of the bridge debris that would litter the Merced River when the bridge collapsed and of the equipment operating to remove the debris, as well as potentially longer-lasting damage to the riverbanks and vegetation. Prior to collapse of the bridge, the existing cyclone fencing and the deteriorating condition of the bridge would continue to intrude upon the scenic character of Happy Isles. Due to its dilapidated and deteriorating condition, the existing bridge is a visually intrusive element in views of the natural landscape at Happy Isles. The ultimate removal of the bridge under Alternative 1 due to its failure would eliminate a landscape feature that currently contrasts with and detracts from the scenic resource values of Happy Isles. The existing bridge’s removal under Alternative 1 would result in a local, long-term, minor, beneficial impact to scenic resources at Happy Isles.

Cumulative Impacts

Cumulative impacts to scenic resources are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley, in combination with potential effects of this alternative. The projects identified below include only those projects that could affect scenic resources within the river corridor or in the immediate project vicinity.

Scenic resources have been affected by numerous past actions since the inception of the park. Primary among these is the alteration of natural communities caused by Euro-American settlers who lived in the park. For example, agricultural activities and the development of tourism resulted in the drying out of the Valley by breaching the moraine and controlling naturally occurring fires, which affected vegetation patterns along the Merced River. Broad-leaved trees along the riverbanks were replaced by the comparatively dense stands of conifers that exist today. These events have resulted in a local, long-term, adverse effect on scenic resources, as the conifers now block views of visually important landscape features that were visible throughout the Valley before the vegetation patterns were changed.

Reasonably foreseeable future actions that would have a net beneficial cumulative effect on scenic resources include those that improve the general health of ecosystems viewable from or within the Merced River corridor (e.g., the Merced River at Eagle Creek Ecological Restoration Project, Merced River Plan, and implementation of the Yosemite Valley Plan). The Merced River Plan prescribes the restoration of degraded areas of the Merced River corridor, resulting in beneficial impacts on scenic resources, and implementation of the Yosemite Valley Plan would restore 140 acres and result in a net decrease in development within Yosemite Valley.

Reasonably foreseeable projects that would have an adverse effect on scenic resources include development-related projects (e.g., construction of lodging at Yosemite Lodge and Curry Village pursuant to the Yosemite Valley Plan). The local, long-term, adverse effects of these reasonably foreseeable projects would be related to the potential introduction of new structures and/or infrastructure that would intrude into views of important scenic resources within, or viewable from the Merced River corridor. For example, new development at Curry Village could increase the development density in the vicinity of the river and reduce the vegetative screening of the existing Curry Village complex.

The cumulative projects within and in the vicinity of the Merced River corridor would result in a local, long-term, major, beneficial cumulative impact on scenic resources in Yosemite Valley because of the overall emphasis on restoring disturbed or developed land to natural conditions and improving the health of ecosystems within Yosemite Valley.

Alternative 1 and the cumulative projects within and in the Merced River corridor would result in a local, long-term, major, beneficial impact on scenic resources in Yosemite Valley. This is due to the overall emphasis on restoring disturbed or developed land to natural conditions and improving the health of ecosystems within Yosemite Valley and the removal of the existing, Happy Isles Gauging Station Bridge, which in its dilapidated and deteriorating condition is visually intrusive in views of the natural landscape from Happy Isles. The beneficial effects on scenic resources associated with restoring disturbed land and improving ecosystem health and removal of the existing bridge would outweigh the short-term, adverse effects associated with Alternative 1 and the cumulative development-related projects.

Conclusions

The No Action Alternative would result in a local, short-term, minor, adverse impact to scenic resources in the vicinity of Happy Isles Gauging Station Bridge, due to the visual intrusion effects of the bridge debris that would litter the Merced River, as well as damage to the riverbanks and vegetation when the bridge collapsed. In addition, prior to collapse of the bridge, the existing cyclone fencing and the deteriorating condition of the bridge would continue to intrude upon the scenic character of Happy Isles. However, the No Action Alternative would result in a local, long-term, minor, beneficial impact on scenic resources at Happy Isles, due to the removal of the existing bridge, which in its dilapidated and deteriorating condition is visually intrusive in views of the natural landscape from Happy Isles.

Alternative 1 and the cumulative projects within and in the Merced River corridor would result in a local, long-term, major, beneficial impact on scenic resources in Yosemite Valley because of the overall emphasis on restoring disturbed or developed land to natural conditions and improving the health of ecosystems within Yosemite Valley and the removal of the existing bridge. The beneficial effects on scenic resources associated with restoring disturbed land and improving ecosystem health and the removal of the existing bridge would outweigh the short-term, adverse effects associated with Alternative 1 and the cumulative development-related projects.

Impairment

The No Action Alternative would result in short-term, adverse, but long-term, beneficial impacts to scenic resources within the vicinity of the Happy Isles Gauging Station Bridge. Although the Merced River is central to the Valley’s scenery, the short-term, adverse effect of this alternative on scenic resources in Yosemite Valley would be primarily localized and of temporary duration, and would not be considered severe. Scenic resources throughout the remainder of the Yosemite Valley segment of the river would remain unaffected. Therefore, Alternative 1 would not impair scenic resources.

Recreation

Analysis

Access to the bridge is currently prohibited due to its unsafe condition, which resulted from damage sustained during the January 1997 flood. Cyclone fencing has been installed to prevent use of the bridge, although park visitors occasionally disregard the posted notices prohibiting access and climb over the fence. The lack of a river crossing at Happy Isles restricts river-related recreational activities that made use of the bridge prior to its closure, including hiking and sightseeing. Lack of access to the bridge also prevents its use as a platform for viewing and photographing the river and its banks in the vicinity of Happy Isles.

Failure of the bridge under Alternative 1 would affect river-dependent active recreational uses, including swimming, wading, and fishing, that occur both in the immediate vicinity of the Happy Isles Gauging Station Bridge and downstream from the bridge in Yosemite Valley. Depending on the manner in which the bridge failed, people recreating in the river could be exposed without warning to falling and/or tumbling bridge debris, potentially resulting in serious injuries or fatalities. The potential for injury and/or fatalities in the event of a catastrophic bridge failure would be a local, short-term, major, adverse effect of Alternative 1.

In addition, debris deposited in the river channel and increased sedimentation following failure of the bridge could temporarily degrade water quality and alter water flows, adversely affecting river conditions that currently support active recreational pursuits (e.g., swimming and fishing) in the vicinity of Happy Isles. The effects of bridge failure on water quality and flows would result in a local, short-term, moderate, adverse impact to active recreational activities in the immediate vicinity of the bridge as well as downstream.

Failure of the bridge under Alternative 1 would deposit debris and sediment in the Merced River. Gouging of the downstream riverbanks and scouring of the river channel are also likely to result from collapse of the bridge as pieces of the structure tumble downstream; damage to the riverbanks and channel could be substantial if the bridge were to fail into the river during high flows. The visually intrusive effects of bridge failure on scenic resources (e.g., damage to the riverbanks and vegetation and the presence of debris in the river channel and of construction equipment needed to remove the debris) would result in a local, short-term, minor, adverse impact on passive recreational activities such as sightseeing and photography.

Under Alternative 1, temporary obstruction and/or closure of existing trails and associated delays and restrictions on trail use for pedestrians and stock users would be likely to occur following failure of the bridge. The bridge would fail at a time and in a manner that cannot be accurately predicted but that could be catastrophic, requiring an immediate response carried out under emergency conditions. Clean-up tasks under Alternative 1 likely would extend for some distance downstream due to the uncontrolled break-up and transport of bridge materials in the river, and could halt or curtail pedestrian and stock user activities in the vicinity of the bridge for an extended period of time. Accordingly, Alternative 1 would result in a local, short-term, minor to moderate, adverse effect on pedestrian activities in the bridge vicinity.

Summary of Alternative 1 Impacts. The potential for injury and/or fatalities in the event of a catastrophic bridge failure would be a local, short-term, major, adverse effect of Alternative 1. The effects of bridge failure on water quality and flows would result in a local, short-term, moderate, adverse impact to active recreational activities (e.g., swimming and fishing) in the immediate vicinity of the bridge as well as downstream. The visually intrusive effects of bridge failure on scenic resources (e.g., damage to the riverbanks and vegetation as well as the presence of debris in the river channel and of construction equipment needed to remove the debris) would result in a local, short-term, minor, adverse impact on passive recreational activities such as sightseeing and photography. Temporary obstruction and/or closure of existing trails and associated delays during clean-up operations after the bridge failed would result in a local, short-term, minor to moderate adverse effect on pedestrian activities in the bridge vicinity. Over the long term, no impacts on recreational resources would be expected.

Cumulative Impacts

Cumulative impacts on recreation are determined based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The projects identified include only those that could affect recreation in Yosemite Valley.

Examples of reasonably foreseeable future actions that could have a beneficial cumulative effect on recreational opportunities include projects proposed under the Yosemite Valley Plan, such as development of a new visitor center in Yosemite Village, expanded transit service distributing visitors to more park destinations, and expansion of campgrounds in Yosemite Valley. Other reasonably foreseeable projects that could have a beneficial cumulative effect on recreation include the following: Repair of Flood Damaged Trail Bridges at Happy Isles, Happy Isles Site Improvements, Trail Reconstruction from Happy Isles to Vernal Fall, the Merced River at Eagle Creek Ecological Restoration (Yosemite Valley), and the Shuttle Bus Replacement Project. These projects could result in short-term disruptions of recreational activities due to construction, but in the long-term, they would provide expanded recreational opportunities in Yosemite Valley and improved transit service distributing visitors to more park destinations (although spontaneity would be reduced due to fewer private cars in the Valley).

The Merced Wild and Scenic River Comprehensive Management Plan would have a beneficial cumulative effect on recreation in Yosemite Valley by protecting and enhancing a spectrum of recreational opportunities available in the Valley. In addition, the management zoning prescribed under the Merced River Plan would provide for various types of recreation, from opportunities for solitude to interactive and group-based recreational activities.

The cumulative projects would have a local, long-term, moderate, beneficial effect on recreation due to expanded recreational opportunities in Yosemite Valley and improved transit service distributing visitors to more park destinations.

Alternative 1 and the cumulative projects in Yosemite Valley would result in a local, long-term, moderate, beneficial impact on recreation due to expanded recreational opportunities in Yosemite Valley and improved transit service distributing visitors to more park destinations. The site-specific, short-term, minor to major, adverse impacts on river-related recreation activities resulting from bridge failure would be offset by the beneficial impacts of the cumulative projects.

Conclusions

The potential for injury and/or fatalities in the event of a catastrophic bridge failure would be a local, short-term, major, adverse effect of Alternative 1. The effects of bridge failure on water quality and flows would result in a local, short-term, moderate, adverse impact to active recreational activities (e.g., swimming and fishing) in the immediate vicinity of the bridge as well as downstream. The visually intrusive effects of bridge failure on scenic resources (e.g., damage to the riverbanks and vegetation as well as the presence of debris in the river channel and of construction equipment needed to remove the debris) would result in a local, short-term, minor, adverse impact on passive recreational activities such as sightseeing and photography. Temporary obstruction and/or closure of existing trails and associated delays during clean-up operations after the bridge failed would result in a local, short-term, minor to moderate, adverse effect on pedestrian activities in the bridge vicinity. Over the long term, no impacts on recreational resources would be expected.

Impairment

The No Action Alternative would result in local, short-term, minor and moderate, adverse impacts on river-related recreation activities resulting from bridge failure. Although the Merced River system and river-related recreation are important components of providing opportunities for enjoyment of the park, the effect of this alternative on recreation would be primarily localized to the Happy Isles Gauging Station Bridge area and limited in duration, and the effect would not be considered severe. The diversity and quality of river-related recreational opportunities throughout the remainder of the Yosemite Valley would remain unaffected. Therefore, Alternative 1 would not impair river-related recreational opportunities.

Park Operations

Analysis

Under Alternative 1, the Happy Isles Gauging Station Bridge would remain in place without maintenance or repair. Although the bridge is fenced off and access to it is prohibited, people occasionally climb the fence to cross the river or look at the bridge. For safety purposes, park operations staff is required to discourage such encroachments and prevent public access to the extent feasible. Over the long term, the bridge would continue to deteriorate and eventually fail, likely during high flow conditions. The collapsed bridge could block the flow of the river, which would be forced to flow around bridge, causing substantial erosion on both banks as well as other adverse impacts to the river. Park operations staff would be required to remove the bridge debris as soon as feasible under emergency conditions and repair damaged facilities around the bridge site.

Excess erosion on the river-left bank would threaten the water supply lines that are components of the principal water supply for Yosemite Valley. As shown in figure II-1, three water supply lines would be threatened by erosion on the river-left bank. One is an 18-inch main that extends from a water tank, which holds Yosemite Valley’s principal supply of water (located south of the Nature Center at Happy Isles), to a juncture directly opposite the Happy Isles Gauging Station Bridge. From this point, the other two mains, one 18 inches and the other 12 inches in diameter, extend to the northwest to supply water to different parts of Yosemite Valley. The juncture of the three water supply lines is approximately 25 feet from the top of the river-left bank.

In the event of an uncontrolled failure, the entire bridge and abutments could come down in large concrete blocks. Extensive damage could occur to the Happy Isles Gauging Station adjacent to the river-right abutment if the collapsing bridge tore away part of the wall and embankment that supports the gauging station, or if the bridge were to slam against the gauging station or the wall and embankment that support it. The bridge segments could also be carried downstream, potentially causing damage to the Happy Isles Vehicle Bridge approximately 500 feet downstream. Debris from the failed structure would be deposited downstream to Happy Isles Vehicle Bridge and possibly beyond.

Bridge collapse could result in a short-term (immediate) and dramatic increase in demand for the full range of park operations and emergency response staff to remove bridge debris and repair damaged facilities around the bridge site, a local, short-term, moderate to major, adverse impact. In addition, uncontrolled failure of the bridge could result in damage to the principle water supply lines for Yosemite Valley, the Happy Isles Gauging Station, and Happy Isles Vehicle Bridge. This would have local, long-term, moderate to major, adverse effects on park facilities, depending on the nature and extent of damages.

Summary of Alternative 1 Impacts. Bridge collapse could result in a short-term (immediate) and dramatic increase in demand for the full range of park operations and emergency response staff to remove bridge debris and repair damaged facilities around the bridge site, a local, short-term, moderate to major, adverse impact. In addition, uncontrolled failure of the bridge could result in damage to the principle water supply lines for Yosemite Valley, the Happy Isles Gauging Station, and Happy Isles Vehicle Bridge. This would have local, long-term, moderate to major, adverse effects on park facilities, depending on the nature and extent of damage.

Cumulative Impacts

Cumulative effects on park operations and facilities are based on analysis of past, present, and reasonably foreseeable future actions in Yosemite Valley in combination with potential effects of this alternative. The extent to which past, present, or reasonably foreseeable future projects could have a cumulative effect, when combined with this alternative, is determined largely by whether such projects would affect park facilities or the demand for park operations services and facilities. Projects that affect park facilities themselves or the demand for facilities management, resource management, and maintenance of utility systems services in particular would have the potential for cumulative effects with the proposed project.

Park operations and facilities have been affected by numerous past National Park Service management decisions and projects since the inception of the park. Recent past projects include Repair of Flood Damaged Trail Bridges at Happy Isles, Happy Isles Site Improvements, Merced River Plan, and implementation of the Yosemite Valley Plan. Overall, there is no net adverse or beneficial effect of these past actions on park operations and facilities.

Reasonably foreseeable future actions that would have a beneficial cumulative effect on park operations and facilities are those that could reduce the number of visitors entering the park, reduce the number or amount of facilities within the park, or reduce long-term maintenance activities. An example is the Replacement/Rehabilitation of the Yosemite Valley Main Sewer Line. Although this project would have short-term, adverse effects associated with planning, construction, replacement, and rehabilitation, its overall effect would be to reduce long-term maintenance. Therefore, this project would have a long-term, beneficial cumulative impact on park operations and facilities.

Examples of reasonably foreseeable projects that would have an adverse effect on park operations and facilities are the Merced Wild and Scenic River Comprehensive Management Plan and the Yosemite Valley Plan. Implementation of these plans would substantially increase demand on park operations and facilities in the short term during planning, repair, rehabilitation, construction/demolition, development of the VERP framework, and replacement of facilities (e.g., removal of the road through Stoneman Meadow, construction of new campsites, and restoration of large areas of Yosemite Valley to natural conditions). Implementation of these plans is expected to have local, short- and long-term, moderate to major, adverse impacts on park operations and facilities.

Overall, the past, present, and reasonably foreseeable future actions would have local, moderate, adverse cumulative impacts because of the increased demand on park operations, services, and facilities, over both the short and long term. These cumulative effects, in combination with Alternative 1, would result in local, short- and long-term, moderate to major, adverse impacts on park operations and facilities, depending upon the nature and extent of damage to facilities.

Conclusions

Past, present, and reasonably foreseeable future actions, in combination with Alternative 1, would result in local, short- and long-term, moderate to major, adverse impacts on park operations and facilities, depending upon the nature and extent of damage to facilities.

Impairment

Impairment of the Merced River is not addressed under park operations because this topic is peripheral to the protection of the river for future generations.

Alternative 2: Controlled Demolition

Alternative 2, Controlled Demolition, would partially remove the Happy Isles Gauging Station Bridge. The river-right abutment, which is located on a large boulder on the riverbank, would be retained to protect the historic Happy Isles Gauging Station. Alternative 2 would involve separating the bridge into liftable segments and removing the segments using equipment located on the riverbank. A temporary containment system (e.g., a reinforced tarp, netting, cage, or floating barge) would be installed beneath the Happy Isles Gauging Station Bridge to catch small amounts of debris during partial bridge removal. This containment system would prevent slurry from concrete saws, as well as some small solid debris, from falling into the Merced River. However, not all demolition debris would be prevented from falling into the river. Masonry debris greater than 2 inches in any dimension and all metal debris that inadvertently fall into the river would be removed. A temporary structural support system (e.g., scaffolding, jacks, or mechanical lifts) may be installed, if necessary, to prevent uncontrolled collapse of the bridge structure during demolition or to anchor the containment system.

Natural Resources

Geology, Geologic Hazards, and Soils

Analysis

Bridge removal would have short-term, adverse, demolition-related effects on soils (e.g., excavation, compaction). However, demolition of the bridge would occur in a controlled manner (e.g., working within a delineated area and applying Best Management Practices such as providing erosion and sediment control measures). Since Alternative 2 would avoid the more extensive adverse effects of bank erosion and bank tramping due to bridge debris retrieval activities described under Alternative 1, Alternative 2 would have a local, short- and long-term, negligible, beneficial effect on soil resources. In addition, site restoration and stabilization would repair eroded areas and increase the protection of riverbanks, adjacent trails, and Yosemite Valley’s water supply line, resulting in a local, long-term, minor, beneficial impact on soils.

Potential damage to the river-right abutment from rockfalls would be a long-term public safety risk, as Alternative 2 would use this abutment as a viewing platform following bridge demolition. Future destabilization of the river-right abutment from a rockfall could cause damage to or destruction of the viewing platform, which would result in a public safety risk for those in the immediate Happy Isles area and for those downstream of the released debris. The right-river viewing platform would also be subject to future seismic events, and some level of damage could occur, although collapse from ground shaking is unlikely. Overall, Alternative 2 would have a long-term, negligible, adverse impact to public health and safety due to potential damage to the viewing platform from geologic hazards. The impact would be negligible because the risk of potential adverse effects to public health and safety is slight.

Summary of Alternative 2 Impacts. Since Alternative 2 would avoid the more extensive adverse effects of bank destabilization, erosion, and soil compaction and loss due to uncontrolled bridge collapse and debris retrieval activities described under Alternative 1, Alternative 2 would have a local, short- and long-term, negligible, beneficial effect on soil resources. Site restoration and stabilization would repair eroded areas and increase the protection of riverbanks, adjacent trails, and the water supply line, resulting in a local, long-term, minor, beneficial impact on soils. Retention of the river-right abutment as a viewing-platform would result in a long-term, negligible, adverse impact to public health and safety due to potential damage to the viewing platform from geologic hazards.

Cumulative Impacts

The cumulative impact analysis for geology in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Past, present, and reasonably foreseeable future actions would result in long-term, minor, beneficial cumulative impacts to soil resources and to public health and safety from geologic hazards.

Alternative 2 and the cumulative projects would result in a local, long-term, minor, beneficial impact to soil resources and public safety from geologic hazards. Alternative 2 would avoid the more extensive adverse effects of soil erosion and bank destabilization compared to Alternative 1. Overall, the cumulative projects would restore soils in the Valley, reduce soil degradation, and decrease the density of people and facilities in the talus slope zone.

Conclusions

Since Alternative 2 would avoid the more extensive adverse effects of erosion and bank destabilization due to uncontrolled bridge collapse and debris retrieval activities described under Alternative 1, Alternative 2 would have a local, short- and long-term, negligible, beneficial effect on soil resources. Site restoration and stabilization would repair eroded areas and increase the protection of riverbanks, adjacent trails, and the water supply line, resulting in a local, long-term, minor, beneficial impact on soils. Retention of the river-right abutment as a viewing-platform would result in a long-term, negligible, adverse impact to public health and safety due to potential damage to the viewing platform from geologic hazards.

Alternative 2 and the cumulative projects would result in a local, long-term, minor, beneficial impact to soil resources and public safety from geologic hazards. Alternative 2 would avoid the more extensive adverse effects of bank erosion compared to Alternative 1. Overall, the cumulative projects would restore soils in the Valley, reduce soil degradation, and decrease the density of people and facilities in the talus slope zone.

Impairment

Alternative 2 would result in beneficial effects on soil resources, but a negligible, adverse impact to public health and safety due to potential damage to the viewing platform from geologic hazards. Although the Merced River system and its geologic resources are key natural resource components within Yosemite Valley, the effect of this alternative on public health and safety from geologic hazards would be localized to the immediate project area and the risk to public health and safety would be slight. Therefore, the effect would not be considered severe, and Alternative 2 would not impair geologic resources.

Hydrology, Floodplains, and Water Quality

Analysis

Under Alternative 2, the Happy Isles Gauging Station Bridge would not adversely influence river flow dynamics and hydrologic processes or present a potential flood hazard because the majority of the bridge would be removed, thus eliminating the constriction that restricts natural flow of the river. Retaining the river-right abutment and establishing it as a viewing platform would continue to protect the adjacent Happy Isles Gauging Station from damage and excessive scouring in high flow conditions, which would have a beneficial effect on hydrologic processes. The overall flow conditions during flood stage would not be noticeably altered by the presence of the viewing platform although it could be inundated during extremely high flows. Entire removal of the river-left abutment would remove a flow constriction and return flows to near-natural conditions along the river-left bank. Removing the constriction of the bridge would arrest or eliminate ongoing erosion along the riverbank, especially in areas where the bridge abutments cause downstream eddies that are currently eroding the river-left bank. Filling and shaping the void to match adjacent bank composition once the river-left abutment is removed would stabilize the riverbank. The presence of the river-right abutment as a viewing platform would not initiate or increase streambank scour caused by upstream eddies because the abutment is anchored on the large boulder that controls the majority of flow around the abutment.

Similar to Alternative 1, removing the Happy Isles Gauging Station Bridge would help restore the active flood regime and hydrologic processes. The removal of the Happy Isles Gauging Station Bridge would eliminate constriction of river flow and improve the local, natural hydrologic regime. Alternative 2 would have a local, long-term, minor, beneficial impact on the hydrologic processes that influence river morphology compared to Alternative 1 due to the avoidance of bank erosion and localized flooding associated with catastrophic bridge collapse, protection of the Happy Isles Gauging Station from damage, and stabilization of the riverbank once the river-left abutment is removed.

Removal of the Happy Isles Gauging Station Bridge under Alternative 2 would cause minor amounts of sediment to be release into the river. The sediment would originate from the finer-grained material behind and beneath the river-left abutment. As the abutment is removed, these materials could be dislodged and released into the river. However, the amount of sediment released is expected to be minor and would not cause excessive turbidity downstream. Measures to control sediment sources using the proposed containment system (e.g., a tarp, net, barge, or cage suspended beneath the bridge) would serve to capture the majority of sediment released during demolition. Sediment sources include concrete dust generated during bridge cutting, friable concrete dislodged while the concrete sections are removed, and steel fragments.

Sediment loads would increase temporarily should the structural support system be constructed to brace the bridge during demolition operations. If utilized, the system necessary to support the bridge and prevent uncontrolled collapse would need to be securely anchored to buttress the bridge and tolerate its weight upon collapse. Such a support system would require a substantial foundation possibly consisting of vertical supports, mechanical lifts, and temporary foundation blocks. Construction and placement of a structure capable of supporting the weight of the bridge could disturb a considerable amount of fine-grained material and cause higher than normal turbidity. Constructing the support system with wheeled or tracked equipment in the river would place additional sediment in suspension. Temporary ramps built to place equipment in the river could also dislodge sediment from the riverbed and banks. Use of a barge to capture sediments could disturb the underlying riverbed, causing increased turbidity downstream. However, the sediment dislodged during construction of the structural support system would only temporarily impact water quality within a localized area and the sediment would settle out downstream, particularly considering that demolition will take place during periods of low flow. The sediment dislodged by construction associated with Alternative 2 is anticipated to be less than would occur under the No Action Alternative since demolition would occur in a controlled manner (e.g., within a delineated work area, during low flow conditions, with the application of Best Management Practices). Alternative 2 would avoid the more pronounced sedimentation effects described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on water quality compared to Alternative 1.

Water quality could be compromised if petroleum compounds were discharged from heavy equipment. The proposed Best Management Practices implemented under this alternative would ensure that petroleum releases from heavy equipment are minimized within the demolition area. Although there are potential sources of pollutants (i.e., sediment, petroleum products) associated with the demolition phase of this project, removal of the bridge would eliminate a long-term source of pollutants, including sediment from continued scouring and undermining of the river-left abutment, and concrete and steel from long-term degradation of the bridge or sudden collapse. As a result, Alternative 2 would have a local, short-term, negligible, beneficial effect on water quality compared to Alternative 1.

Summary of Alternative 2 Impacts. Alternative 2 would have local, short- and long-term, negligible to minor, beneficial impacts on hydrologic processes and water quality due to the avoidance of bank erosion and localized flooding associated with catastrophic bridge collapse, reduced sedimentation, protection of the Happy Isles Gauging Station, and controlled removal of the bridge compared to Alternative 1.

Cumulative Impacts

The cumulative impacts analysis for Alternative 2 is the same as described under Alternative 1. The beneficial and adverse cumulative effects would result in an overall local, long-term, minor, beneficial impact to hydrologic processes and water quality.

The past, present, and reasonably foreseeable future actions considered cumulatively with Alternative 2, would have a local, long-term, minor, beneficial impact on hydrologic processes. The beneficial impacts associated with Alternative 2 would nominally contribute to overall beneficial cumulative impacts on hydrologic processes and water quality.

Conclusions

Alternative 2 would have local, short- and long-term, negligible to minor, beneficial impacts on hydrologic processes and water quality due to the avoidance of bank erosion and localized flooding associated with catastrophic bridge collapse, reduced sedimentation, protection of the Happy Isles Gauging Station, and controlled removal of the bridge compared to Alternative 1.

The past, present, and reasonably foreseeable future actions Yosemite Valley, considered cumulatively with Alternative 2, could have a local, long-term, minor, beneficial impact on hydrologic processes. The beneficial impacts associated with Alternative 2 would nominally contribute to overall beneficial cumulative impacts on hydrologic processes and water quality.

Impairment

Alternative 2 would have local, short- and long-term, negligible to minor, beneficial impacts on hydrologic processes and water quality. Alternative 2 would not impair hydrologic resources within Yosemite Valley.

Wetlands

Analysis

Partial removal of the Happy Isles Gauging Station Bridge would have local, short-term, adverse, demolition-related effects to approximately 0.6 acre of aquatic habitat. Effects would result from heavy equipment and demolition activities and could include soil compaction, dust, vegetation removal, root damage, erosion, and potential introduction and spread of non-native species. The addition of silt, the resuspension of sediment, or the introduction of construction-related pollutants (fuels, lubricants, etc.) could degrade the quality of aquatic habitats. Because demolition would occur in a controlled manner (e.g., within a delineated work area, during low-flow conditions, with the application of Best Management Practices), Alternative 2 would avoid the more pronounced adverse effects of debris retrieval activities described under Alternative 1. The application of mitigation measures described in Chapter II (Best Management Practices) would further reduce the potential adverse impacts to aquatic habitats. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on the aquatic environment compared to Alternative 1.

Minor regrading and revegetation would increase bank integrity. Alternative 2 would result in no net loss of wetland functions or values. Implementation of Alternative 2 would result in a site-specific, long-term, negligible to minor, beneficial effect on aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species. The extent and quality of riparian, wetland, and other riverine habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected.

Summary of Alternative 2 Impacts. Alternative 2 would result in a site-specific, long-term, negligible to minor, beneficial effect on aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species. The extent and quality of riparian, wetland, and other riverine habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for wetland resources in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Conclusions

Alternative 2 would result in a site-specific, long-term, negligible to minor, beneficial effect on aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species. The extent and quality of riparian, wetland, and other riverine habitats throughout the remainder of this segment of the river would be unaffected. Cumulative actions would have a local, long-term, major, beneficial cumulative effect on wetlands within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net local, long-term, major, beneficial effect on wetland patterns.

Impairment

Given the incorporation of mitigation into the design of this alternative, Alternative 2 would result in a local, long-term, negligible to minor, beneficial impact to aquatic resources and riverine areas that provide rich habitat for a diversity of river-related species. Alternative 2 would not impair wetland resources within Yosemite Valley.

Vegetation

Analysis

Partial removal of the Happy Isles Gauging Station Bridge would have local, short-term, adverse, demolition-related effects to native vegetation in the immediate vicinity of Happy Isles Gauging Station Bridge. Effects would result from heavy equipment and demolition activities and could include soil compaction, dust, vegetation removal, root damage, erosion, and potential introduction and spread of non-native species. Mature trees would be retained to the extent practicable. A mature canyon live oak immediately adjacent to the river-left abutment could be adversely affected during demolition, although the National Park Service would take all reasonable precautions to avoid damaging the tree and its root structure. Because demolition would occur in a controlled manner (e.g., within a delineated work area, with the application of Best Management Practices, etc.), Alternative 2 would avoid the more pronounced adverse effects of debris retrieval activities described under Alternative 1. The application of mitigation measures described in Chapter II (Best Management Practices) would further reduce the potential adverse impacts to native vegetation to a negligible intensity.

Minor regrading and revegetation would increase bank and vegetation integrity. Implementation of Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on vegetation, including riparian, wetland, and other riverine areas that provide rich habitat for a diversity of river-related species. The extent and quality of vegetation, including riparian, wetland, and other riverine habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected.

Summary of Alternative 2 Impacts. Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on vegetation, including riparian, wetland, and other riverine areas that provide rich habitat for a diversity of river-related species.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for vegetation in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Cumulative actions would have a long-term, major, beneficial cumulative effect on vegetation within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net long-term, major, beneficial effect on vegetation patterns.

Conclusions

Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on vegetation, including riparian, wetland, and other riverine areas that provide rich habitat for a diversity of river-related species. The extent and quality of vegetation, including riparian, wetland, and other riverine habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected. Cumulative actions would have a long-term, major, beneficial cumulative effect on vegetation within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net long-term, major, beneficial effect on vegetation patterns.

Impairment

This alternative would restore this portion of the river to a more natural state, thereby enhancing its biologic integrity. Implementation of Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on vegetation, including riparian, wetland, and other riverine areas that provide rich habitat for a diversity of river-related species. Alternative 2 would not impair vegetation resources within Yosemite Valley.

Wildlife

Analysis

Localized, short-term, minor effects on wildlife could occur during demolition of the Happy Isles Gauging Station Bridge. Effects would be related to heavy equipment and human intrusion and could include increased dust, vegetation removal, noise, sedimentation, elevated turbidity, and decreased oxygen levels. Because demolition would occur in a controlled manner (e.g., within a delineated work area, during low-flow conditions, with the application of Best Management Practices), Alternative 2 would avoid the more pronounced adverse effects of debris retrieval activities described under Alternative 1. The application of containment system and other mitigation measures (e.g., Best Management Practices) would further reduce the potential adverse impacts to native fish and wildlife. Minor regrading and revegetation would increase bank integrity, somewhat improving wildlife habitat and reducing the potential for long-term periodic aquatic habitat disturbances. Implementation of Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on wildlife and rich habitat for a diversity of river-related species. The extent and quality of wildlife habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected.

Summary of Alternative 2 Impacts. Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on wildlife and rich habitat for a diversity of river-related species. The extent and quality of wildlife habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for wildlife in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Cumulative actions would have a local, long-term, minor to moderate, beneficial cumulative effect on wildlife within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net local, long-term, minor to moderate, beneficial effect on wildlife patterns.

Conclusions

Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on wildlife and rich habitat for a diversity of river-related species. The extent and quality of wildlife habitats throughout the remainder of the Yosemite Valley segment of the river would be unaffected. Cumulative actions would have a local, long-term, minor to moderate, beneficial cumulative effect on wildlife within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net local, long-term, minor to moderate, beneficial effect on wildlife patterns.

Impairment

Given the incorporation of mitigation into the design of this alternative, Alternative 2 would result in a local, long-term, negligible, beneficial impact to native wildlife and rich habitat for a diversity of river-related species. Alternative 2 would not impair wildlife resources or values.

Special-Status Species

Analysis

Localized, short-term, minor effects on special-status species could occur during demolition of the Happy Isles Gauging Station Bridge. Effects would be related to heavy equipment and human intrusion and could include increased dust, vegetation removal, noise, or decreased oxygen levels. These actions could result in direct losses of nests or burrows, reproductive habitat for Wawona riffle beetle (mossy rocks within the channel of the Merced River), and indirect effects through the disturbance of nesting birds. The addition of silt, the resuspension of sediment, or the introduction of construction-related pollutants (fuels, lubricants) could degrade the quality of habitat for special-status species, particularly Wawona riffle beetle. Because demolition would occur in a controlled manner (e.g., within a delineated work area, during low-flow conditions, with the application of Best Management Practices), Alternative 2 would avoid the more pronounced adverse effects of debris retrieval activities described under Alternative 1. The application of mitigation measures described in Chapter II (e.g., Best Management Practices) would further reduce the potential adverse impacts to special-status species.

Minor regrading and revegetation would increase bank integrity and river habitat, somewhat improving habitat for birds, raptors, and Wawona riffle beetle at the site of the bridge. Implementation of Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on the extent and quality of river-related species. The extent and quality of river-related species throughout the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 2 Impacts. Alternative 2 would result in a site-specific, local, long-term, negligible, beneficial effect on the extent and quality of river-related species. The extent and quality of river-related species throughout the Yosemite Valley segment of the Merced River would be unaffected.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for special-status species in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Cumulative actions would have a local, long-term, moderate, beneficial cumulative effect on special-status species within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net local, long-term, moderate, beneficial effect on special-status species.

Conclusions

Alternative 2 would result in a site-specific, long-term, negligible, beneficial effect on the extent and quality of river-related species. The extent and quality of river-related species throughout the Yosemite Valley segment of the Merced River would be unaffected. Cumulative actions would have a local, long-term, moderate, beneficial cumulative effect on special-status species within Yosemite Valley. Thus, past, present, and reasonably foreseeable future actions, in combination with Alternative 2, would have a net local, long-term, moderate, beneficial effect on special-status species.

Impairment

Given the incorporation of mitigation measures into the design of this alternative, Alternative 2 would result in a local, long-term, negligible, beneficial impact on the extent and quality of river-related species. Alternative 2 would not impair special-status species resources or values.

Air Quality

Analysis

Partial removal of the Happy Isles Gauging Station Bridge would have local, short-term, adverse impacts on air quality. Effects would be primarily related to use of equipment, dust, and vehicle trips to and from the demolition site. Demolition activities would temporarily affect pollutant concentrations in the vicinity of the project primarily due to fugitive dust from demolition activities and vehicle travel over paved surfaces heavily laden with earthen materials, as well as tailpipe emissions associated with demolition equipment and emissions of ozone precursors and carbon monoxide from the use of diesel-powered equipment. Because demolition would occur in a controlled manner, working within a delineated area, Alternative 2 would avoid the more extensive adverse effects of bridge debris retrieval activities described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on air quality compared to Alternative 1.

Summary of Alternative 2 Impacts. Because demolition would occur in a controlled manner, Alternative 2 would avoid the more extensive adverse effects of bridge debris retrieval activities on air quality described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on air quality compared to Alternative 1.

Cumulative Impacts

The cumulative impact analysis for air quality in Alternative 2 is the same as described under the No Action Alternative. Please see the discussion of cumulative impacts under Alternative 1.

Considered with the adverse impacts associated with regional air quality influences, the cumulative projects would have a local, long-term, moderate, beneficial effect on air quality in Yosemite Valley. Alternative 2 and the cumulative projects would result in local, long-term, moderate, beneficial impacts on air quality.

Conclusions

Because demolition would occur in a controlled manner, Alternative 2 would avoid the more extensive adverse effects of bridge debris retrieval activities on air quality described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on air quality compared to Alternative 1.

Alternative 2 and the cumulative projects would result in local, long-term, moderate, beneficial impacts on air quality.

Impairment

Impairment of the Merced River is not addressed under air quality because this resource topic is peripheral to the protection of the river for future generations.

Noise

Analysis

Partial removal of the Happy Isles Gauging Station Bridge would have local, short-term, adverse impacts on noise. Bridge cutting and removal activities would generate the highest noise levels. Demolition-related material haul trips would also raise ambient noise levels along haul routes. Operation of heavy-duty equipment at the site during demolition could generate substantial amounts of noise and would occur within close proximity to river recreation uses. Other sensitive land uses (e.g., campgrounds) located farther from the site would be affected to a lesser extent. Noise at the site would vary depending upon a number of factors, such as the number and types of equipment in operation on a given day, usage rates, the level of background noise in the area, and the distance between sensitive uses and the construction site. Alternative 2, however, would avoid the more extensive adverse effects of bridge debris retrieval activities on the ambient noise environment described under Alternative 1 by working within a delineated area. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on the ambient noise environment compared to Alternative 1.

After bridge removal, the acoustical environment in the vicinity of Happy Isles Gauging Station Bridge would be shaped largely by natural sources of sound punctuated by human-caused sources of noise.

Summary of Alternative 2 Impacts. Since demolition would occur in a controlled manner, Alternative 2 would avoid the more extensive adverse effects of bridge debris retrieval activities on the ambient noise environment described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on the ambient noise environment compared to Alternative 1.

Cumulative Impacts

The cumulative impact analysis for noise in Alternative 2 is the same as described under the No Action Alternative. Please see the discussion of cumulative impacts under Alternative 1.

The gradual increase in annual visitation to the park would likely offset the beneficial effects of cumulative actions that would tend to reduce vehicle trips and their associated noise, resulting in a local, long-term, minor, adverse effect on noise. The local, short-term, negligible, beneficial impact to the ambient noise environment associated with Alternative 2 would not offset the cumulative adverse effects.

Conclusions

Since demolition would occur in a controlled manner, Alternative 2 would avoid the more extensive adverse effects of bridge debris retrieval activities on the ambient noise environment described under Alternative 1. Therefore, Alternative 2 would have a local, short-term, negligible, beneficial effect on the ambient noise environment compared to Alternative 1.

The gradual increase in annual visitation to the park would likely offset the beneficial effects of cumulative actions that would tend to reduce vehicle trips and their associated noise, resulting in a local, long-term, minor, adverse effect on noise. The local, short-term, negligible, beneficial impact to the ambient noise environment associated with Alternative 2 would not offset the cumulative adverse effects.

Impairment

Impairment of the Merced River is not addressed under noise because this resource topic is peripheral to the protection of the river for future generations.

Cultural Resources

Archeological Resources

Analysis

Archeological resources in the Happy Isles area include historic and prehistoric sites. Since no prehistoric archeological resources have been identified within the immediate project area, analysis of archeological resources for this alternative is limited to a discussion of historic archeological sites.

Partial removal of the Happy Isles Gauging Station Bridge would require demolition operations along the banks of the Merced River, which could unearth sensitive historic archeological resources. Ground-disturbing activities could result in a local, long-term, minor, adverse impact to historic archeological resources. Minor regrading and revegetation would increase bank integrity and decrease potential erosion, therefore avoiding adverse erosion-related effects described under Alternative 1. Any actions would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement. Archeological resources throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 2 Impacts. Alternative 2 could have a local, long-term, minor, adverse impact to historic archeological resources due to ground-disturbing activities. Any actions would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for archeological resources in Alternative 2 is the same as described under the No Action Alternative. Please see the discussion of cumulative impacts under Alternative 1. Alternative 2 and the cumulative projects within and in the vicinity of the main stem of the Merced River and in Yosemite Valley would result in a local, long-term, negligible to minor, adverse impact on archeological resources.

Conclusions

Alternative 2 could have a local, long-term, minor, adverse impact to historic archeological resources due to ground-disturbing activities. Any actions would be performed in accordance with stipulations in the park’s 1999 Programmatic Agreement.

Alternative 2 and the cumulative projects within and in the vicinity of the main stem of the Merced River and in Yosemite Valley would result in a local, long-term, negligible to minor, adverse impact on archeological resources.

Impairment

Disturbance of historic archeological resources could take place during bridge demolition under Alternative 2. This action would be subject to site-specific planning and compliance and would be undertaken in accordance with stipulations in the park’s 1999 Programmatic Agreement (Advisory Council on Historic Preservation 1999). Although archeological sites along the river are key cultural resources within Yosemite Valley, the effect of this alternative on historic archeological resources would be primarily localized to the Happy Isles Gauging Station Bridge area, and the effect would not be considered severe. Archeological sites throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected. Therefore, this alternative would not impair archeological resources or values.

Ethnographic Resources

Analysis

There are known ethnographic resources in the Happy Isles area, however, there are no known ethnographic resources within the area of potential effect. As a result, Alternative 2 would have no effect on ethnographic resources. The National Park Service would continue to consult with culturally associated groups throughout the environmental compliance process.

Summary of Alternative 2 Impacts. Alternative 2 would have no effect on ethnographic resources.

Cumulative Impacts

The cumulative impact analysis for ethnographic resources in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1. The cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on ethnographic resources due to the disturbance of such resources. Alternative 2 would not contribute to this impact.

Conclusions

Ethnographic resources exist in the Happy Isles area exist, however, there are no known ethnographic resources in the Happy Isles Gauging Station Bridge demolition area. As a result, ethnographic resources would not be affected under this alternative.

Impairment

Alternative 2 would not have a direct, indirect, or cumulative impact on ethnographic resources or their treatment and management. Ethnographic resources throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected. This alternative would not impair ethnographic resources or values.

Cultural Landscape Resources, including Historic Sites and Structures

Analysis

Under Alternative 2, the potential for degradation of cultural landscape resources in the main stem of the Merced River would be similar to the impacts described under Alternative 1, since the Happy Isles Gauging Station Bridge would no longer exist under either alternative. The primary difference is that the bridge would be removed in a controlled manner under Alternative 2, compared to uncontrolled collapse of the bridge under Alternative 1. The controlled removal of the bridge under Alternative 2 would allow for the continued use of the Happy Isles Gauging Station and Happy Isles Vehicle Bridge, since any damage to the streamflow gauge and vehicle bridge that could result from uncontrolled collapse of the bridge would not occur.

The Happy Isles Gauging Station Bridge is a historic resource that contributes to the cultural landscape as a feature of the circulation system of Yosemite Valley. Removal of the bridge would constitute an adverse effect on a historic property. However, at the present time, the bridge is in a significantly deteriorated condition and presents a public health and safety hazard due to possible uncontrolled collapse. The extensive flooding in 1997 greatly contributed to the structural damage of the Happy Isles Gauging Station Bridge. In 1999, the National Park Service at Yosemite, the California State Historic Preservation Officer, and the Advisory Council on Historic Preservation entered into a Programmatic Agreement (Advisory Council on Historic Preservation 1999). As avoidance of the historic property is not feasible or prudent, the standard mitigation measures described in the Programmatic Agreement will be implemented. These measures include Historic American Engineering Record documentation, which was completed in 1991; salvage of any architectural elements of the bridge determined to be of cultural value; and interpretation of the bridge and its associated gauging station and streamflow gauge.

The controlled removal of the Happy Isles Gauging Station Bridge, which would ensure the continued use of the historic Happy Isles Gauging Station and Happy Isles Vehicle Bridge, would result in a local, long-term, minor, beneficial impact to historic resources compared to the No Action Alternative. Nationally significant historic resources, such as designed landscapes and developed areas, historic buildings, and circulation systems (trails, roads, and bridges), throughout the remainder of the Yosemite Valley segment of the Merced River would be unaffected.

Summary of Alternative 2 Impacts. The controlled removal of the Happy Isles Gauging Station Bridge, which would ensure the continued use of the historic Happy Isles Gauging Station and Happy Isles Vehicle Bridge, would result in a local, long-term, minor, beneficial impact to historic resources.

Cumulative Impacts

Because the direct effects of this alternative are minimal, the cumulative impact analysis for cultural landscape resources in Alternative 2 is the same as described under the No Action Alternative. Please see the discussion of cumulative impacts under Alternative 1. The cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on the cultural landscape due to the disturbance of such resources. Alternative 2 would somewhat offset the adverse cumulative impact due to the protection of the historic Happy Isles Gauging Station and Happy Isles Vehicle Bridge compared to the No Action Alternative.

Conclusions

The cumulative projects in Yosemite Valley would result in a local, long-term, minor, adverse impact on the cultural landscape due to the disturbance of such resources. Alternative 2 would somewhat offset the adverse cumulative impact due to the protection of the historic Happy Isles Gauging Station and Happy Isles Vehicle Bridge compared to the No Action Alternative.

Impairment

Alternative 2 would result in a local, minor, long-term, beneficial impact to historic resources. As a result, Alternative 2 would not impair the cultural landscape.

Social Resources

Scenic Resources

Analysis

Under Alternative 2, the existing Happy Isles Gauging Station Bridge would be removed as soon as feasible. Removal of the bridge would avoid the adverse scenic resource impacts associated with the structure remaining in place under Alternative 1. Specifically, the evidence of ongoing deterioration of the bridge structure and deck is a source of visual intrusion. Demolition of the bridge, along with removal of the existing chain-link fence, would remove the visually incompatible feature. In addition, planned removal of the bridge under Alternative 2 would prevent the effects of uncontrolled bridge collapse discussed under Alternative 1. Alternative 2 would avoid the deposition of bridge debris in the river of channel and the associated gouging of the riverbanks and channel. Accordingly, Alternative 2 would have a local, short-term, minor, beneficial impact as compared to Alternative 1.

Like Alternative 1, Alternative 2 would require the use of equipment to remove and transport bridge materials from the existing site. The presence and operation of the equipment would detract from the scenic resource values of the natural landscape at Happy Isles. However, it is likely that under Alternative 2, because demolition and removal activities would be planned and controlled, bridge removal and transport equipment would operate for a shorter period of time and within a more limited area of the river than would be the case if the bridge collapsed. Accordingly, in avoiding the effects associated with uncontrolled bridge failure under Alternative 1, Alternative 2 would have a local, short-term, minor, beneficial impact.

In the long term, as under Alternative 1, removal of the bridge would have a beneficial effect on the scenic resource values of the natural landscape at Happy Isles. As noted in the discussion of Alternative 1, due to its dilapidated and deteriorating condition, the existing bridge is visually incompatible with, and thus intrudes upon, its natural surroundings. However, Alternative 2, unlike Alternative 1, includes contouring and revegetation of the river-left bank. While the effects of bridge collapse under Alternative 1 on the existing abutments are unknown, the river-right abutment would remain in place under Alternative 2, providing a platform that would afford visitors views of the Merced River upstream and downstream.

In addition, efforts would be made to preserve the visually distinctive canyon live oak tree immediately adjacent to the river-left abutment and other mature trees in the work area. (If, however, it is determined that a tree must be removed, this would eliminate an element from the natural scenic landscape.) As stated in the discussion of mitigation measures in Chapter II, damage to trees would be avoided, in contrast to the damage likely to occur along the riverbanks under Alternative 1 from uncontrolled collapse of the bridge. Any trees damaged during demolition under Alternative 2 would be repaired or replaced. Therefore, the impact associated with tree removal under Alternative 2, if it occurred, likely would be local, short-term, minor, and beneficial as compared to Alternative 1. Site revegetation would ameliorate this effect and would increase riparian vegetation and natural landscape patterns in the area.

The long-term effects of bridge removal would be beneficial under both Alternative 1 and Alternative 2. However, due to the restoration efforts and the provision of a viewing platform on the river-right abutment, Alternative 2 would result in a local, long-term, minor, beneficial impact to scenic resources compared to Alternative 1.

Summary of Alternative 2 Impacts. In avoiding the effects associated with uncontrolled bridge failure under Alternative 1, which include debris deposited in the river channel and visually prominent damage to the riverbanks and vegetation, Alternative 2 would have a local, short-term, minor, beneficial impact on scenic resources. The long-term effects of bridge removal would be beneficial under both Alternative 1 and Alternative 2. However, due to the restoration efforts and the provision of a viewing platform on the river-right abutment, Alternative 2 would result in a local, long-term, minor, beneficial impact to scenic resources compared to Alternative 1.

Cumulative Impacts

The cumulative impact analysis for scenic resources in Alternative 2 is the same as described under the No Action Alternative. Please see the discussion of cumulative impacts under Alternative 1.

The cumulative projects within and in the vicinity of the Merced River corridor would result in local, long-term, major, beneficial impacts on scenic resources in Yosemite Valley because of the overall emphasis on restoring disturbed or developed land to natural conditions and improving the health of ecosystems in Yosemite Valley.

Alternative 2 and the cumulative projects within and in the vicinity of the Merced River corridor would result in local, long-term, major, beneficial impacts on scenic resources in Yosemite Valley. This is due to the avoidance of extensive and visually prominent damage to the river channel and banks that would follow uncontrolled bridge failure, the removal of the existing dilapidated bridge, and the overall emphasis on restoring disturbed or developed land to natural conditions and improving the health of ecosystems in Yosemite Valley.

Conclusions

In avoiding the effects associated with uncontrolled bridge failure under Alternative 1, which include debris deposited in the river channel and visually prominent damage to the riverbanks and vegetation, Alternative 2 would have a local, short-term, minor, beneficial impact on scenic resources. The long-term effects of bridge removal would be beneficial under both Alternative 1 and Alternative 2. However, due to the restoration efforts and the provision of a viewing platform on the river-right abutment, Alternative 2 would result in a local, long-term, minor, beneficial impact to scenic resources compared to Alternative 1.

Impairment

Alternative 2 would have an overall beneficial impact on the visual landscape. Therefore, Alternative 2 would not impair scenic resources or values.

Recreation

Analysis

The controlled removal of the Happy Isles Gauging Station Bridge under Alternative 2 would avoid the potential for serious injuries and/or fatalities to recreational users of the river associated with sudden, massive failure of the bridge. Avoidance of hazards to recreational users of the river would be a local, short-term, major, beneficial impact of Alternative 2.

Alternative 2 would avoid effects resulting from bridge failure on river-dependent active recreational uses in the vicinity of the bridge and downstream. Under Alternative 1, debris and increased sedimentation in the river following bridge failure would temporarily prevent or disrupt swimming, wading, and fishing. Under Alternative 2, bridge removal would be controlled to prevent deposition of debris in the river and increased sedimentation. Accordingly, compared to Alternative 1, Alternative 2 would result in a local, short-term, minor, beneficial impact on river-dependent active recreational uses.

Alternative 2 would avoid the impacts on passive recreation activities identified for Alternative 1 other than the temporary effects on scenic resources of operating heavy equipment to remove the bridge. Specifically, Alternative 2 would avoid the visually intrusive effects of damage to the riverbanks and vegetation, as well as deposition of debris in the river channel, that would result from failure of the bridge under Alternative 1. Moreover, under Alternative 2 a river-viewing platform would be constructed on the river-right abutment that would provide park visitors with an additional location for sightseeing, photography, and nature study. Accordingly, compared to Alternative 1, Alternative 2 would result in a local, short-term, minor, beneficial impact on sightseeing, photography, and other recreational pursuits to which the enjoyment of scenic resources is essential.

Removal of the bridge under Alternative 2 would temporarily interfere with recreational opportunities in the area of the bridge. Construction workers would use the John Muir Trail along the river-right bank to access the demolition work site. Hikers would experience temporary delays of up to 30 minutes so that workers could safely move trucks and heavy equipment into and out of the demolition area. The pedestrian walkway that extends from Happy Isles Loop Road to the Nature Center at Happy Isles would also be temporarily closed to pedestrians for up to 30 minutes at a time to allow the contractor to move trucks and heavy equipment to the site. Trail barricades would be installed at three locations along the trails on the river-left bank to protect public health and safety during demolition activities (as shown in figure II-4). However, similar temporary obstruction of existing trails and associated delays for pedestrians and stock users would be likely to occur in the event of bridge failure, as anticipated under Alternative 1. Failure of the bridge would occur at a time and in a manner that cannot be accurately predicted but that could be catastrophic, requiring an immediate response carried out under emergency conditions. Clean-up tasks under Alternative 1 likely would extend over a larger area than removal activities under Alternative 2, due to the uncontrolled break-up and downstream transport of bridge materials in the river, and could halt or curtail pedestrian and stock user activities in the vicinity of the bridge for an extended period of time. Accordingly, compared to Alternative 1, Alternative 2 would result in a local, short-term, negligible to minor, beneficial effect on pedestrian activities in the bridge vicinity.

Summary of Alternative 2 Impacts. Avoidance of the potential for injury and/or fatalities in the event of a catastrophic bridge failure would be a local, short-term, major, beneficial effect of Alternative 2. Alternative 2 would also result in a local, short-term, minor, beneficial impact on river-dependent active recreational uses (e.g., swimming, wading, fishing); a local, short-term, minor beneficial impact on photography, sightseeing and other recreational pursuits to which the enjoyment of scenic resources is essential; and a local, short-term, negligible to minor, beneficial impact on pedestrian activities in the bridge vicinity.

Cumulative Impacts

The cumulative impact analysis for recreation in Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Alternative 2 and the cumulative projects in Yosemite Valley would result in a local, long-term, moderate, beneficial impact on recreation due to beneficial effects on recreational activities in the bridge vicinity, expanded recreational opportunities in Yosemite Valley, and improved transit service distributing visitors to more park destinations. Alternative 2 and the cumulative projects in Yosemite Valley would result in a local, long-term, moderate, beneficial impact on recreation due to increased access for visitors and expanded recreational opportunities in Yosemite Valley. The short-term, adverse impact due to temporary trail delays in the vicinity of the bridge during demolition activities would be offset by the beneficial impacts of the cumulative projects.

Conclusions

Avoidance of the potential for injury and/or fatalities in the event of a catastrophic bridge failure would be a local, short-term, major, beneficial effect of Alternative 2. Alternative 2 would also result in a local, short-term, minor, beneficial impact on river-dependent active recreational uses (e.g., swimming, wading, fishing); a local, short-term, minor beneficial impact on photography, sightseeing, and other recreational pursuits to which the enjoyment of scenic resources is essential; and a local, short-term, negligible to minor, beneficial impact on pedestrian activities in the bridge vicinity.

Impairment

Alternative 2 would result in a local, short-term, negligible to minor, beneficial effects on river-related recreation in the vicinity of Happy Isles Gauging Station Bridge. Alternative 2 would not impair river-related recreational opportunities within Yosemite Valley.

Park Operations and Facilities

Analysis

Because implementation of Alternative 2 would entail the use of heavy equipment to cut and remove the bridge and to contour and regrade the river-left bank, there is a risk of accidental damage to existing park facilities, particularly the water supply lines on the river-left bank and the Happy Isles Gauging Station on the river-right bank. On the river-left bank, the water supply lines are only 18 to 20 feet west of the proposed cut line at the edge of the river-left apron. While this provides a margin for error, it should be noted that the adverse impact of accidental damage to any of these water lines would be substantial—especially to the single 18-inch line leading from the water tank—because it would interrupt the delivery of water to the rest of Yosemite Valley. Damage to the water supply lines’ valves, which are located closer to the surface than the pipelines, could also interrupt water service in Yosemite Valley and entail costly repairs. The process of contouring and grading the river-left bank could damage the drainage pipe that leads from the eastern water supply line to an outfall site just north of the river-left apron. Damage to the drainage pipe itself would not result in a substantial impact, as the pipe is not critical to the everyday functioning of the water supply system. However, vibrations traveling up the pipe could damage the valve or the nearby water supply lines, resulting in the need for more difficult and costly repairs. The risk of accidental damage to the water supply lines or the drainage pipe would be reduced due to the notification program that would be implemented as a mitigation measure (see Chapter II).

After the bridge is removed, the river-left bank would be contoured, graded, and shaped to match adjacent bank composition (boulders, cobbles, and gravels). The large size of substrate materials along this stretch of the river provides for bank stability, which would protect the water supply lines located approximately 25 feet from the top of the river-left bank.

On the river-right side, the Happy Isles Gauging Station could accidentally be damaged by heavy equipment brought in for bridge removal. Demolition plans require fencing off the gauging station to protect it from demolition activities, which would substantially reduce the risk of this potential impact. Because Alternative 2 leaves the river-right abutment in place to protect the gauging station from erosion, potential adverse impacts to the station as a result of bank erosion are considered minor.

Because demolition would occur in a controlled manner under this alternative (e.g., working within a delineated area and applying Best Management Practices such as a utility notification program), Alternative 2 would avoid the more extensive adverse effects to park facilities associated with catastrophic bridge collapse described under Alternative 1. Therefore, Alternative 2 would have a local, long-term, negligible, beneficial effect on park facilities compared to Alternative 1.

Implementation of Alternative 2 would entail oversight of all aspects of the project by park staff, including design and engineering, demolition activities, utilities protection, and site restoration. Controlled removal of the bridge under this alternative, however, would place fewer demands on park operations staff than Alternative 1, which could require emergency response to catastrophic bridge collapse and repair of damaged facilities. As a result, Alternative 2 would have a local, short-term negligible, beneficial effect on park operations compared to Alternative 1.

Summary of Alternative 2 Impacts. Alternative 2 would result in local, long-term, negligible, beneficial impacts on park facilities because of the avoidance of potential catastrophic damage to park facilities compared to Alternative 1. This alternative would have a local, short-term, negligible, beneficial impact on park operations due to reduced demands on park operations staff under the controlled bridge demolition compared to greater demands required for emergency response to bridge collapse and repair of potentially damaged facilities under Alternative 1.

Cumulative Impacts

The cumulative impact analysis for park operations and facilities under Alternative 2 is the same as described under the No Action Alternative. Please see discussion of cumulative impacts under Alternative 1.

Overall, the past, present, and reasonably foreseeable future actions would have local, moderate, adverse cumulative impacts because of the increased demand on park operations, services, and facilities, over both the short and long term. These cumulative effects, in combination with Alternative 2, would result in local, short- and long-term, moderate, adverse impacts on park operations and facilities due to the increased demand these projects would place on park operations, services, and facilities. The negligible, beneficial effects under Alternative 2 would not offset the adverse effects associated with the cumulative projects.

Conclusions

Alternative 2 would result in local, long-term, negligible, beneficial impacts on park facilities because of the avoidance of potential catastrophic damage to park facilities compared to Alternative 1. This alternative would have a local, short-term, negligible, beneficial impact on park operations due to reduced demands on park operations staff under the controlled bridge demolition compared to greater demands required for emergency response to bridge collapse and repair of potentially damaged facilities under Alternative 1.

The cumulative projects, in combination with Alternative 2, would result in local, short- and long-term, moderate, adverse impacts on park operations and facilities due to the increased demand these projects would place on park operations, services, and facilities. The negligible, beneficial effects under Alternative 2 would not offset the adverse effects associated with the cumulative projects.

Impairment

Similar to Alternative 1, Alternative 2 would not impair park resources or values.

[1] Throughout Chapter IV, unless otherwise noted, “rockfalls” is used as a generic term to refer to rockfalls in the stricter sense but also to rockslides, debris avalanches, debris flow, and rock avalanches.