Chapter III: Affected Environment
This section presents the analysis topics included in this
Cascades Diversion Dam Removal Project Environmental Assessment and a rationale
for their inclusion. These topics were selected based on federal law, regulations,
and executive orders; National Park Service management policies; and concerns
expressed by the public, park staff, or other agencies during scoping and
comment periods. This section also provides a discussion of topics that were
dismissed from further analysis.
A short rationale for each impact topic considered in this
chapter is given below. A description of the existing conditions for each
selected topic is provided later in this chapter. The affected environment
described in this chapter encompasses the geographical area affected by all of
the alternatives. The potential impacts of each alternative within each topic
area are presented in Chapter IV, Environmental Consequences.
Impact Topics Considered in this Plan
Natural Resources
The federal and state Endangered Species
Acts (and associated legislation), Clean Water Act,
Clean Air Act, and National Environmental Policy Act require that the effects of any federal
undertaking examine natural resources. In addition, National Park Service
management policies and natural resource management guidelines call for the
consideration of natural resources in planning proposals. Cascades Diversion Dam
is located on the Merced Wild and Scenic River
within Yosemite National
Park – an area of abundant natural resources. It
is therefore necessary to characterize both these natural resources and the
environmental consequences to these resources that could result from
implementation of Cascades Diversion Dam Removal Project alternatives.
Analysis was performed for the following natural resource
topics: geology, geologic hazards, and soils; hydrology, floodplains, and water
quality; wetlands; vegetation; wildlife; special-status species; air quality;
and noise.
Cultural Resources
The National Historic Preservation Act, the Archeological
Resources Protection Act, Native American Graves Protection and Repatriation
Act, and the National Environmental Policy Act require that the effects of any federal
undertaking on cultural resources be examined. In addition, National Park
Service management policies and cultural resource management guidelines call
for the consideration of cultural resources in planning proposals. Significant cultural
resources exist within the project area and adjacent areas and could be
affected by the alternatives. Therefore, analysis was performed for
archeological resources, ethnographic resources, and cultural landscape
resources, including historic sites and structures.
Social Resources
The analysis of social resources
examines the effects of the Cascades Diversion Dam Removal Project on the social
environment within the park. Analysis of transportation examines the effects of
the Cascades Diversion Dam Removal Project on visitor access to the park.
Conserving the park’s scenery is a crucial component of the National Park
Service 1916 Organic Act and the park’s enabling legislation. Stewardship of Yosemite
National Park requires
consideration of two integrated purposes: to preserve Yosemite’s
unique natural and cultural resources and scenic beauty, and to make these
resources available to visitors for study, enjoyment, and recreation. The
National Environmental Policy Act requires that socioeconomic impacts of the
Cascades Diversion Dam Removal Project be addressed.
Analysis was performed for the following social resource
topics: transportation, scenic resources, recreation, orientation and
interpretation, socioeconomics, and park operations and facilities.
Impact Topics Dismissed from Further Analysis
Environmental Justice
No aspect of the action alternatives of the Cascades
Diversion Dam Removal Project would result in disproportionately high and
adverse human health or environmental effects on minority or low-income
populations. Any restriction on travel or access to any area of the park that
might result from the Cascades Diversion Dam Removal Project would be equally
applied to all visitors, regardless of race or socioeconomic standing. As well,
none of the action alternatives would change current management direction
concerning housing policy in Yosemite
National Park, El Portal, or
other areas adjacent to the park. Policies concerning the future availability
of housing in these areas are already in place and would not change as a result
of the project. Therefore, the action alternatives would not result in
destruction or disruption of community cohesion and economic vitality;
displacement of public and private facilities and services; increased traffic
congestion; and/or exclusion or separation of minority or low-income
populations from the broader community.
Natural Resources
Prime and Unique Agricultural Lands
There are no known agricultural lands in the project area,
and the project would not have any indirect effects to downstream agricultural
lands.
Social Resources
Land Use
Land uses within Yosemite
National Park are classified as “Parklands,”
regardless of the individual types of land uses within the park. Implementation
of the project would not affect Parklands land uses within the park.
Public Health and Safety
Public health and safety is not presented as a separate
topic in this analysis, since many sections (water quality, recreation, park
operations, and others) evaluate park-related public health and safety issues.
Museum Collection
Implementation of elements of the Cascades Diversion Dam
Removal Project action alternatives could indirectly affect the museum
collections by generating minimal additions to the collections due to
archeological data recovery performed as mitigation for direct site impacts.
Such additions would require museum storage space and ongoing collections
maintenance and management.
Visitor Services
There are no visitor services (overnight accommodations,
food service, retail service, or other services) within the area of potential
effect of the action alternatives. Implementation of the project would not have
any direct or indirect effects on visitor services in adjacent areas.
Night Sky and Wilderness Experience
There is no designated Wilderness within the area of
potential effect of the action alternatives. Implementation of the project
would not have any direct or indirect effects to designated Wilderness in
adjacent areas. No element of the Cascades Diversion Dam Removal Project would
affect the night sky within the park.
Yosemite
National Park lies on the western
slope of the Sierra Nevada, a massive mountain range
dividing central and northern California
from more arid lands to the east. The Sierra Nevada
ecoregion (which extends through the foothill zone on the west side and the
base of the escarpment on the east side) is about 450 miles long and 100
miles wide. Elevations in the park range from approximately 2,000 feet to
13,114 feet. Most of the 747,969 acres of the park is designated Wilderness
(94%, or 704,624 acres).
The Merced River flows from the
headwaters in the high elevations of the Sierra Nevada,
through Yosemite Valley, and down to the San
Joaquin Valley,
where it contributes to the San Joaquin
River. The Merced River
contains separate and unique watersheds, sustains separate hydrologic and
aquatic resources, and supports differing levels of development. The main stem
of the Merced River drains approximately 250,000 acres from
the headwaters within the park to the Foresta
Bridge in the El Portal area. The
main stem of the Merced River flows a total of 140 miles
from its headwaters to the confluence with the San
Joaquin River. The
South Fork drains the southern portion of the park, an area of approximately
76,000 acres. The Tuolumne River
drains the northern portion of the park, an area of approximately
435,000 acres.
The major vegetation zones of the Sierra Nevada
ecosystem form readily apparent, large-scale, north-south elevational bands
along the axis of the mountain range. Major east-west watersheds that dissect
the Sierra Nevada with steep canyons form a secondary
pattern of vegetation. On the west side, forest types change with increasing
elevation, from ponderosa pine to mixed conifer to firs. Straddling the crest
of the Sierra Nevada is a zone of subalpine and alpine
vegetation. Fire suppression, in concert with changing land-use practices, has dramatically
changed natural fire regimes of the Sierra Nevada,
altering ecological structures and functions in the Sierra Nevada
plant communities (UC Davis 1996a,b,c,d).
Aquatic and riparian systems are the most altered and
impaired habitats of the Sierra Nevada. Dams and
diversions throughout most of the Sierra Nevada have
altered stream-flow patterns and water temperatures. Foothill areas below about
3,300 feet appear to have the greatest loss of riparian vegetation of any
region in the Sierra Nevada (UC Davis 1996a,b,c,d).
Recreational opportunities abound in Yosemite
National Park in developed and
wilderness areas alike; however, the types and quality of activities vary
considerably between these two areas. Recreational opportunities are made more
memorable because of the natural beauty of Yosemite Valley,
El Portal, and wilderness environments. These areas offer a wide range of
recreational experiences for the visitor, including hiking, picnicking, camping, climbing, skiing, fishing,
photography, swimming, nature study, stock use, bicycling, sightseeing, and rafting. The availability of one or
more of these opportunities varies by location.
The four basic categories of park operations are resources
management, facility management, visitor protection, and interpretive services.
Park infrastructure and facilities include wilderness trails, roads, bridges
and tunnels, campgrounds and lodging, and utilities. National Park Service
management policies require that all facilities be managed, operated, and
maintained to minimize energy consumption of nonrenewable fuels. The policies
also require that new energy-efficient technologies be used where appropriate
and cost effective.
Local Setting – Cascades Diversion Dam Project Area
Cascades Diversion Dam is located on the main stem of the Merced
River in Yosemite National
Park, adjacent to the intersection of El
Portal Road and Big Oak
Flat Road. Other elements of the former hydroelectric
generating facility include the river-right and river-left abutments that flank
the dam, the intake structure, the screenhouse (located atop the intake), the penstock
(which historically conveyed water from the dam to the powerhouse), the powerhouse,
and the transmission lines. The Cascades Diversion Dam project area, which is
defined as the impoundment segment of the Merced River corridor (the dam, the
area from the upstream impoundment to 200 feet below the dam, and surrounding
areas) (see figure II-1), consists of approximately 660 feet of stream
channel and bank areas that support mixed conifer forest with pockets of
riparian and oak woodland plant communities. The Cascades Diversion Dam project
area also includes El Portal Road
adjacent to the dam area (and wastewater, electrical, and telephone lines under
the road), the El Portal Road
and Big Oak Flat Road
intersection, a parking area on the north side of El Portal
Road, and a vehicle turnout west of the
screenhouse. The project area also includes Pohono Quarry, located
approximately one mile upstream of the dam, to the north of Pohono
Bridge and El
Portal Road.
Throughout this environmental assessment, the analysis
will focus of the impacts of actions within the Cascades Diversion Dam project
area for the resource topics presented in this section. However for some
resource topics discussed in this environmental assessment (such as noise, air
quality, scenic, and wildlife), the local setting may extend beyond the
boundaries shown on figure II-1.
Geology, Geologic Hazards, and Soils
Geology and Geologic History
Cascades Diversion Dam is located immediately upstream of
the Merced River gorge, which begins where the gradient
of the Merced River abruptly increases and the river
enters the gorge. The gorge has remained an incised, V-shaped feature because
most recent glacial events did not extend down the Merced River
beyond Yosemite Valley.
The granitic rocks within the Merced River
gorge consist primarily of tonalite; the Bass
Lake tonalite is the dominant
bedrock feature. Geologic materials underlying Cascades Diversion Dam and
supporting the abutments and the intake structure are believed to be
heterogeneous sand and gravel deposits that are underlain by thick
(approximately 200 feet), coarse-grained deposits of glacially deposited rock
and glacial lake deposits.
Geologic Hazards
The Merced River flows through
geologically active areas, where geologic and hydrologic forces continue to
shape the landform. Geologic hazards associated with these forces, such as
earthquakes and rockfalls, present potentially harmful conditions to visitors,
personnel, and facilities in Yosemite
National Park.
The Sierra Nevada
range of Yosemite
National Park is not considered an
area of particularly high seismic activity. The project area lies in seismic
zone 3, as defined by the Uniform Building Code Seismic Zone Map (International
Conference of Building Officials 1997). Throughout recorded history, most
earthquakes of Richter magnitude 5 or above have been centered in the eastern Sierra
Nevada or in the western portion of California
near the San Andreas Fault Zone. A relatively small number of earthquakes
over magnitude 5, but many earthquakes under magnitude 5, have been generated in
the Sierra Nevada batholith underlying the project area
(USBR 1983). No active or potentially active earthquake faults have been
identified in the mountain region of Yosemite
National Park (CDMG 1990);
therefore, the risk of fault rupture or surface displacement beneath the dam is
negligible. Yosemite can undergo seismic shaking associated with earthquakes on
fault zones to the east and west margins of the Sierra Nevada
range, as has occurred in the past. These fault zones include the Foothills
Fault Zone, the volcanically active area in the Mono Craters–Long Valley
Caldera area, and along the various faults within the Owens
Valley Fault Zone (CDMG 1996).
Rockfalls
Rockfall is a generic term that refers to all slope
movement processes, including rockfall, rockslide, debris slide, debris flow,
debris slump, and earth slump. Rocks have become dislodged and fallen off the
sheer granite cliffs throughout the geologic history of Yosemite.
Rockfalls can displace large volumes of rock and can occur due to such
processes as the climate-related expansion and contraction of rock, seismic
shaking, or exfoliation. Most rockfalls are triggered by events such as
earthquakes, rainstorms, or periods of warming that produce a rapid melting of
snow. The magnitude and proximity of the earthquake, intensity and duration of
the rainfall, the thickness of the snow-pack, and the pattern of warming all
influence the triggering of rockfalls. However, some rockfalls occur without a
direct correlation to an obvious event and are probably associated with gradual
stress release and exfoliation of the granitic rocks (USGS 1998).
Significant incision of the river has created the
present-day relief of the gorge and a change in gradient of over 2,000 feet in
roughly seven miles between Pohono Bridge
(upstream of the dam) and the park boundary (downstream of the dam). The gorge
area has experienced more rockfall incidences than any place in the park.
Several of these have occurred along El Portal Road.
The high incidence of rockfalls is partly due to the steep, narrow configuration
of the gorge, riverbank undercutting, and historic human activity such as the
construction of El Portal Road.
These events have been well documented (USGS 1992b) and provide information
regarding historic rockslide hazards along the Merced River gorge and in areas
where unstable rock slopes are known to pose a risk of future rockfall events.
The frequency and magnitude of rockfall events vary considerably. Many small
rockfalls may occur every year and go unnoticed, while larger rockfalls occur
much less frequently (USGS 1998). The National Park Service is revising its
management policies regarding geologic hazards, with the intent to better
protect park visitors and staff by avoiding placement of structures in areas
with a high potential for rockfall impact.
Soils
The soils in relatively flat topographic positions near
the Cascades Diversion Dam form from glacial and alluvial sediment deposition
processes originating in Yosemite Valley, or by alluvial and colluvial
deposition occurring locally within the gorge or near El Portal. Soils that
formed in old river channels consist of alluvial boulders, cobbles, river wash,
and loamy sands. These soils have, for the most part, moderate to severe
development limitations and thus require the implementation of engineering and
mitigation measures.
Hydrology, Floodplains, and Water Quality
Merced River Gorge and El Portal Watershed
Cascades Diversion Dam is located on the Merced
River at the point of transition from the flat-bottomed Yosemite
Valley to the glaciated V-shaped
river to the gorge. The Merced River gorge begins below
the dam and continues downstream to the western park boundary at El Portal.
Within this area, the Merced River has a much steeper
gradient than in Yosemite Valley and consists mostly of
continuous rapids. As the river exits Yosemite Valley,
it cascades at an average gradient of approximately 70 feet per mile through
the narrow, steep-sided Merced River gorge. The riverbed
and banks are largely composed of boulders and cobbles, ranging in size from a
few inches to several yards in diameter.
The steeper river gradient in this area prevents the river
from meandering as extensively as in Yosemite Valley.
Additionally, riverbank areas in many locations have been developed and
hardened for road and facility protection. Because of the steep gradient and
development, the shifting of the river channel in El Portal usually occurs only
during periods of large floods.
The Pohono Bridge
gauging station is approximately one mile upstream of Cascades Diversion Dam,
and therefore flows at the gauge are generally considered representative of
flows at the dam. Historic flow measurements at the Pohono
Bridge gauging station have ranged
from a high of about 25,000 cubic feet per second to a low of less than
10 cubic feet per second. The mean average daily flows are highest in May
and June (approximately 2,000 cubic feet per second) and lowest during the
months of September and October (less than 100 cubic feet per second) (USBR
2001). Data on flow through the gorge between Cascades Diversion Dam and El
Portal are not available because there are no stream measurement stations
downstream of the Pohono Bridge gauging station.
The reach of the Merced River
between the Cascades Diversion Dam and Powerhouse, about 6,000 feet downstream,
descends at a gradient of approximately 0.06 feet per foot and then levels
to a gradient of about 0.009 feet per foot at the Cascades Picnic Area.
The depositional regime of the river changes significantly as the river
gradient is reduced. In the steeper reaches just downstream of the dam, the
river bed is composed of large boulders; in the flatter reaches, where the
reduced flow gives finer material an opportunity to settle out, the streambed
is composed of cobbles, sand, and silts. The majority of the fine-grained
material the river carries past Cascades Diversion Dam is deposited in the
flatter, lower-energy river conditions that currently exist near the Cascades
Picnic Area.
Upstream of the dam, the river gradient is approximately
0.01 feet per foot. Suspended sediments and bedload discharging from Yosemite
Valley have accumulated behind the dam since it was constructed.
Sediment buildup has limited the volume of impounded water to approximately
40 acre-feet, with backwater extending approximately 550 feet upstream
from the dam (USBR 1983). The backwater pool ranges in width from 80 to 240
feet (USGS 1988).
To facilitate the generation of hydroelectric power,
Cascades Diversion Dam was designed to channel riverflows primarily through the
penstock. The intake for the former penstock is located in the river-right
abutment and has a maximum capacity of 115 cubic feet per second. The
majority of riverflows in excess of the penstock intake capacity flow over the
crest of the dam, although the dam is designed to allow for underflow. A very
small portion of riverflow therefore travels beneath the dam, and seepage is
estimated to be between 5 to 15 cubic feet per second (USBR 1983).
Precipitation
The overall climate is temperate, with hot, dry summers
and cold, wet winters. Approximately 85% of the precipitation falls between
November and April. December, January, and February have the highest average
precipitation, with a monthly average of 6 inches in Yosemite Valley
at 4,000 feet. Average precipitation in Yosemite Valley
is 36.5 inches, while annual rainfall decreases to 25 inches in El Portal at
2,000 feet. Snowmelt drives the peak streamflows that occur in May and June,
and minimum riverflow is observed in September and October.
Alluvial Processes
Yosemite National
Park is composed of and underlain by various
granite rock types, and weathering, erosion, and transport of sediment can be a
very slow process. In areas of Yosemite
National Park, clays, silts, and
organic debris have accumulated with the gravels and sands of the decomposed
bedrock. These soils are subject to erosion and alluvial processes. The
construction of Cascades Diversion Dam in 1917 caused a change in sediment
transport dynamics along the Merced River. The dam
created a condition in which sediment that normally moved through the river
system would settle and become trapped. In addition, historic photographs
indicate that a rock and sediment island was already present immediately
upstream of what is now the Cascades Diversion Dam (Kennedy/Jenks Consultants
2002). The amount of sediment and other materials present prior to dam
construction is not known. It is estimated that 4,450 cubic yards of sediment
were deposited behind Cascades Diversion Dam in the 10 years after its
construction (NPS 1991), and that approximately 1,400 cubic yards of
sediment were deposited between 1931 to 2002 (Kennedy/Jenks Consultants 2002). The
amount of sediment deposited between 1927 and 1931 is not known. Sedimentation
buildup led the National Park Service to dredge the dam in 1938, lowering the
sediment bed to 2.5 feet below the dam crest. The volume of impounded sediments
is currently estimated to be between 15,000 and 20,000 cubic yards (Kennedy/Jenks/Chilton
and ROMA Design Group 1988), including material present before dam construction
and material built up behind the dam following construction.
Floodplains
A floodplain plays a necessary role in the overall adjustment
of a river system. It exerts an influence on the hydrology of the basin and
also serves as a temporary storage for sediment eroded from the watershed.
Periodic flooding provides sediment and nutrients that are essential for the
aquatic and vegetative health of the floodplain. Floodplains are features that
are both the products of the river environment and important functional parts
of the system. However, human-made structures placed within a floodplain, such
as Cascades Diversion Dam, can impede or alter natural flow.
From Cascades Diversion Dam downstream through
El Portal, the Merced River is steep and confined
in a narrow gorge. In this area, the floodplain is quite narrow and the flow
velocities are very high. The river channel in El Portal can shift during large
floods, including movement of large boulders that define the channel. Within
this area, El Portal Road
has altered the floodplain by providing a barrier to channel migration. During
extreme events, the Merced River has shown the capacity
to undermine or spill over and damage the roadway. Discussion of flooding and
floodplains is most relevant in terms of the potential loss of life and the
influence of development in the floodplain.
Water Quality
Water quality throughout Yosemite
National Park is considered to be good and generally above state and federal
standards. The surface water quality of most park waters is considered
beneficial by the State of California
for wildlife habitat, freshwater habitat, contact and noncontact recreation,
canoeing, and rafting, as indicated in the Central Valley Regional Water Quality
Control Board’s Water Quality Control Plan (Basin Plan). An inventory of water
quality data prepared by the National Park Service indicated excellent
conditions in many parts of the park, but some water quality degradation was
noted in areas of high visitor use (NPS 1994b).
Occasional concentrations above drinking water and
freshwater criteria have been noted within the Merced River
for lead, cadmium, and mercury (NPS 1994b). Potential sources of these metals
include leaded gasoline, wastewater discharge, campsites, fuel storage
facilities, and stormwater runoff from developed surfaces such as parking lots.
Water quality has been affected by the extensive and
concentrated visitor use of the Merced River in popular
areas. High use of the streambank induces bank erosion through the loss of
vegetative cover and soil compaction. Bank erosion can result in the widening
of the river channel and loss of riparian and meadow floodplain areas. Water
quality is thus affected through increased suspended sediments, higher water
temperatures from a lack of riparian cover, and lower dissolved oxygen levels
due to these elevated temperatures and to shallower river depths. Turbidity, a
measure fine suspended sediments, was collected from sampling points near
Cascades Diversion Dam in 2002 and 2003, as shown on table III-1.
|
Measurement Location
|
Nephelometric Turbidity
Units
|
|
|
|
|
|
|
|
|
|
|
|
Pohono
Bridge
|
0.50
|
0.53
|
0.97
|
0.29
|
0.26
|
|
Below Cascades Diversion Dam
|
0.31
|
0.43
|
0.55
|
0.31
|
0.24
|
|
Powerhouse
|
0.18
|
0.25
|
0.46
|
0.35
|
0.24
|
|
Foresta Bridge
|
0.14
|
0.19
|
0.42
|
0.17
|
0.30
|
SOURCE: NPS 2002; 2003c
Human activities and the use of vehicles can distribute
water pollutants that may collect on land surfaces and later be transported
into the river or its tributaries by stormwater runoff. These pollutant sources
are referred to as nonpoint sources because they accumulate from various areas
and not from a single point source. Construction activities that disturb soil,
generate dust, and cause occasional petroleum releases from equipment and
vehicles can represent a short-term nonpoint pollution source. Recreational
activities such as horseback riding, swimming, and hiking can lead to the
introduction of organic, physical, and chemical pollutants into aquatic
systems. Nonpoint-source runoff from roads and parking lots may potentially
affect water quality by introducing organic chemicals and heavy metals.
Wetland
data presented in this section are intended to provide general descriptions of
wetland and water-dependent communities in the Cascades Diversion Dam project
area. Refer to the Vegetation section for descriptions of vegetation, the
Wildlife section for data relating to wildlife and aquatic species, and the
Special-Status Species section for information on protected species of plants
and wildlife. Refer to Appendix C, Wetland Statement of Findings for the
Cascades Diversion Dam Removal Project.
Wetland Classification and Definition
Wetlands are transitional areas between terrestrial and
aquatic ecosystems, where water is usually at or near the surface or the land
is covered by shallow water. Wetlands have many distinguishing features, the
most notable of which are unique soils, saturated for at least part of the
year, and vegetation adapted to or tolerant of saturated soils. Wetlands are
considered highly valued resources because they perform a variety of
hydrological and ecological functions vital to ecosystem integrity.
The Cowardin system is used as the basis for wetland
classification and protection by the National Park Service. The Cowardin system
classifies wetlands based on the type of vegetative cover and lifeform,
flooding regime, and substrate material. Jurisdictional wetlands are delineated
and classified to meet regulations of Section 404 of the Clean Water Act.
Cowardin wetlands include jurisdictional wetlands, but may also include certain
nonvegetated sites lacking soil, if they meet specific criteria.
Wetlands in the Cascades Diversion Dam Project Area
Wetlands within the Cascades Diversion Dam project area
are broadly classified as riparian in nature and include aquatic, riparian, and
floodplain communities. The riparian zone is the plant
community adjacent to a river or stream channel and serves as the interface
between the river and the surrounding floodplain and upland communities.
Riparian areas are characterized by the combination of high species diversity,
high species density, and high productivity. Riparian plant communities are
discussed in the Vegetation section, below.
Specific wetland classes identified within the project
area are limited to riverine (rivers, creeks, and streams) and palustrine
(shallow ponds, marshes, swamps, and sloughs). Using the Cowardin
classification, specific wetland and deepwater classes within the project area
include:
§
Riverine
upper perennial – main channel of the Merced River
§
Palustrine
forest – riparian forest habitat along the Merced River
subject to various flooding regimes
§
Palustrine
scrub shrub – riparian scrub (e.g., willow) habitat along the Merced
River subject to various flooding regimes
The following discussion provides general descriptions for
each wetland class identified in the vicinity of the Cascades Diversion Dam.
Riverine Upper Perennial
Riverine upper perennial habitat within the project area
includes the open and flowing water of the Merced River
as well as the permanently flooded rock-, cobble-, or sand-bottom channel with
little to no in-stream vegetation. Upstream of Cascades Diversion Dam,
occasional sandbars form within and at the channel edge and typically support
willows and emergent vegetation (grasses and herbs). Based on the National Park
Service guidelines, the majority of the Merced River
would be classified as wetland. Channel portions that lie at a depth of 2
meters below low water would be considered deepwater. The main channel of the Merced
River would likely be considered nonwetland by the U.S. Army Corps
of Engineers; however, it would be subject to jurisdiction under Section 404 of
the Clean Water Act as nonwetland waters of the United
States.
Palustrine Forest
Palustrine forests are
the riparian forest habitats along the Merced River that are regularly inundated by normal high-water
or flood flows. In the project area, deciduous cottonwoods, willows, and alders
dominate the riparian corridor. Substrate under the palustrine forest community
varies from rock, gravel, and sand to clays, loams, and mud. Palustrine forests
(riparian forests) are classified as wetlands based on the National Park
Service guidelines (USFWS 1995). These areas are classified as either wetland
or nonwetland waters of the United States
by the U.S. Army Corps of Engineers, depending on site-specific vegetation,
soils, and hydrologic conditions.
Palustrine Scrub Shrub
This habitat type occurs sporadically along the banks of
the main stem of the Merced River. It is regularly
inundated by normal high-water or flood flows. This habitat is dominated by
various willows and often intergrades with meadow (palustrine emergent) and
riparian (palustrine forest) communities. These communities are typically
classified as wetlands under both the National Park Service (USFWS 1979) and
U.S. Army Corps of Engineers classification systems.
Cascades Diversion Dam Wetland and Aquatic Habitats
The following narrative describes
wetland and water-associated communities along the Merced River
from
Pohono Bridge
(upstream of the dam) to El Portal (downstream of the dam). Within this
area, the Merced River transitions at the dam from the
flat, U-shaped valley to the steep, V‑shaped gorge. Through the gorge, the
river has a much steeper gradient compared to Yosemite Valley
and consists mostly of continuous rapids to El Portal. The riverbed and banks
are largely composed of boulders and cobbles, ranging in size from a few inches
to several feet in diameter.
The floodplain upstream of the dam is slightly wider and
characterized by varied topography; hummocks and depressions create diverse
habitats, which in turn yield greater plant species diversity. Adjacent to the
water, a mixture of sedges and rushes are found in the wettest sites. Willow
species are all present in the near-bank area of the floodplain. Recently
germinated willow and cottonwood seedlings, herbaceous species, a variety of
grass species, and other vegetation are found in the floodplain upstream of the
dam. See the Vegetation section below for more information.
The floodplain within the dam and impoundment area is
almost entirely located on the river-left side of the Merced River.
The river-right side of the river has a narrow, steep riparian area constricted
by El Portal Road, with
only a narrow band suitable for supporting wetland plant species. The
floodplain on the river-left bank is somewhat restricted due to the impoundment
area and shading from steep, north-facing cliffs. Willow
species, cottonwood, alder, herbaceous species, and other vegetation are found
in the project area. See the Vegetation section, below, for more information.
Approximately 30% of the floodplain within the impoundment area upstream from
the dam is bare soil, likely a result of deposition from the flood of January
1997.
The Merced River gorge downstream
of the dam is steep, with a narrow floodplain band of riparian vegetation along the river course. Riparian
species in this area are generally characterized by isolated pockets of willow,
white alder, and oaks. See the Vegetation section below for more information.
The following narrative provides a general description of
vegetation in the Cascades Diversion Dam project area. Vegetation within the
area can be loosely defined as riparian and upland. Actual descriptions of
vegetative communities, including distributional limits, habitat requirements,
community sensitivities, and a list of plant species characteristically found
within each community, appear in the Vegetation
Management Plan (incorporated by reference) (NPS 1997f).
Riparian Plant Communities
Riparian zones extend outward from bank edges of the Merced
River into adjacent forest communities. Riparian ecosystems play a
critical role in a variety of ecological processes. Situated at the interface
between terrestrial and aquatic ecosystems, the riparian zone acts to buffer
hydrologic and erosional cycles, control and regulate biogeochemical cycles of
nitrogen and other key nutrients, limit fire movements, and create unique
microclimates for animal species (Rundel and Stuner 1998).
Riparian zones upstream of the dam and at the dam and
impoundment are characterized by broadleaf deciduous trees such as white alder,
black cottonwood, and willow species. Riparian vegetation is regularly
disturbed by the deposition and removal of soil and the force of floodwaters.
Plants in this zone readily colonize newly formed river-edge deposits. The
distribution of riparian communities varies with soil saturation and frequency
of disturbance. For example, big-leaf maple riparian forests grow on moist,
gravelly soils in protected spots on alluvial soils bordering streams, whereas
sandbar willow woodlands occur on point and mid-channel bars that are washed
over annually by spring floods (Acree 1994).
The floodplain upstream of the impoundment includes a
mixture of small-fruited bulrush, sedge, beaked sedge, and a variety of rush
species in the wettest sites adjacent to the water. Sandbar willow, red willow,
and arroyo willow are all present in the near-bank area of the floodplain. Low
pockets are densely populated with recently germinated willow and cottonwood
seedlings, probably resulting from the January 1997 flood. Bare soil is being colonized
by horsetail, dogbane, and goldenrod. A variety of grass species, including
hairgrass, reed grass, and brome, occur throughout the floodplain. Inflated
sedge is concentrated between 1 and 5 feet above the water level. White
alder is sparse and corresponds roughly with the bankfull mark.
The dominant willow species in the dam and impoundment
area is red willow, with sandbar willow and arroyo willow intermixed. Black
cottonwood and white alder are minor components. Herbaceous species include
small-fruited bulrush, various species of sedge and rush, horsetail, dogbane,
and goldenrod. As noted above under Cascades Diversion Dam Wetland and Aquatic
Habitats, approximately 30% of the floodplain in the impoundment area is bare
soil.
The Merced River gorge downstream
of the dam is steep, with a narrow floodplain band of riparian vegetation along the river course. The
riparian zone, especially to the river-left, remains largely untouched by human
intrusion (with the exception of the El Portal Road
corridor and development in El Portal). Riparian species in this area are
generally characterized by isolated pockets of willow, white alder, and oaks.
Native ash trees occur in the wetter areas, as do historic orchard components
in some locations. Foothill pines and valley oaks tend to dominate the drier
terraces adjacent to riparian sites, with a lower proportion of mature oaks
than in the oak communities due to higher moisture levels and shallower soils
caused by past flood scouring.
Upland Plant Communities
Five upland forest types are found in the vicinity of the
project area. Mixed coniferous forest is found on the floor of the Valley.
Canyon live oak forest, north-facing mixed conifer/canyon live oak talus
forest, and south-facing mixed conifer/canyon live oak forest occur on the
talus slopes above the Merced River. The chaparral/oak
woodland zone occurs throughout the gorge.
Canyon live oak communities grow on both north- and
south-facing talus slopes and often form pure or almost pure stands. This
community is common on the steep canyon walls along El
Portal Road. A small stand of shrub and tree
variety tanbark oak is located adjacent to the river-left dam abutment. This is the only stand of the tree
variety of tanbark oak and one of two known stands of the shrub variety of
tanbark oak in YosemiteNational
Park. Fires in the canyon live oak community are infrequent
but intense, with a fire return interval of 20 to 50 years on south-facing
slopes. Most trees and shrubs in this community crownsprout after fire.
Mixed conifer communities are normally dominated by
ponderosa pine and generally grow at elevations of 3,000 to 5,000 feet. This
habitat also contains incense-cedar, sugar pine, and occasional California
black oaks. The most common understory shrubs are Mariposa manzanita,
deerbrush, and bear-clover. This species intergrades with the narrow riparian
band on the river-left side of the Merced River above
the dam and impoundment.
The mixed conifer community is naturally adapted to
low-intensity, frequent fires. Nearly 100 years of
fire suppression has resulted in a change from open forest to dense thickets of
shade-tolerant tree species, including incense-cedar, white fir, and
Douglas-fir. Under natural conditions, the return interval for fire is
estimated at eight to 12 years (NPS 1990). Present conditions, however,
often generate fires of much greater intensity than under a natural fire
regime.
The Merced River gorge is in the
mixed conifer and chaparral/oak woodland zone (Sawyer and Keeler-Wolf 1995). It
is lined with a narrow band of riparian vegetation along the river course and
bordered by a dense mosaic of chaparral and foothill woodland communities on
the steep canyon walls. Vegetation communities include blue oak woodland, interior
live oak woodland, foothill pine/oak woodland, interior live oak/chaparral, and
riparian woodland.
Non-native, or introduced,
plant species have become established in the upland forest zones, although not
to the extent they have in meadows and California
black oak communities. These species are the result of either deliberate or
accidental introductions and are not part of the naturally evolved community.
Many of these species are indicators of past agricultural activities that
occurred throughout the area. Approximately 180 non-native species have been
identified in the park, primarily in the chaparral/oak and mid-elevation
forests (Fritzke and Moore 1998). Non-native species are generally herbaceous
and associated with ground disturbance (one-time or reoccurring). Typical
species include European annual grasses and bull thistle.
All of the communities in this area are adapted to
frequent natural fires sparked by
lightning. Fire suppression has led to increased vegetative density, especially
on north-facing slopes where recent fires have been successfully suppressed.
Yosemite National
Park, one of the largest and least-fragmented
habitat blocks in the Sierra Nevada, supports a diverse
and abundant assemblage of wildlife. Its importance in protecting the long-term
survival of certain species and the overall biodiversity of wildlife in the Sierra Nevada
was recognized in the reports prepared as part of the Sierra Nevada Ecosystem
Project (UC Davis 1996a,b,c,d).
The Merced River
corridor also plays an essential ecological role in linking wildlife habitats
across the park’s landscape and elevational gradients; this fact forms an
important part of the framework for this analysis. For wildlife populations to
be viable, resources and environmental conditions must be sufficient for
foraging, resting, cover, and dispersal of animals. Arrangement, types, and
amounts of resources must be sufficient for the needs of reproductive
individuals on daily, seasonal, and yearly scales. Habitat must also be well
distributed over a broad geographic area to allow breeding individuals to
interact spatially within and among populations, and a stable, relatively
undisturbed riparian corridor supplies a mechanism for this kind of ecological
connection.
Wildlife of Cascades Diversion Dam and Merced River
Gorge
Montane hardwood conifer (mixed conifer) is the
predominant upland habitat type adjacent to riparian areas at the elevation of Yosemite
Valley and below. This type is broadly transitional from the
higher, largely coniferous stands and both surrounds and gives way to montane
chaparral at its downhill edge. As such, its wildlife community includes
species common to higher and lower elevations, leading to high species
diversity.
Wildlife Resources
The area encompassing the project area
and Merced River gorge is lined with a narrow band of
riparian vegetation along the river course, bordered by a dense mosaic of
chaparral and foothill woodland communities (chaparral/oak woodland zone) on the
steep canyon walls. Birds commonly found in this zone include stellar’s jay,
Cooper’s hawk, western screech owl, white-headed woodpecker, mountain
chickadee, winter wren, and dark-eyed junco. While the U.S. Fish and Wildlife
Service lists the American dipper as a species of local or regional concern,
this species is common within the park and is considered a general wildlife
species within this environmental assessment. Mammals include deer mouse,
bushy-tailed woodrat, spotted skunk, mule deer, ringtail, and bobcat (NPS
2003b). More significantly, the rock outcrops and associated crevices of the
gorge probably harbor a high density of special-status bat species (e.g.,
spotted bat, California
mastiff bat) (CDFG 1999). Many of these species are also present in Yosemite
Valley. Bat species such as Townsend’s big-eared bat and Yuma
myotis occasionally use human structures and are vulnerable to impact (Pierson
and Rainey 1993).
Fish Resources
The river reach between Cascades Diversion Dam and El
Portal is characterized by steep gradients, large boulders strewn throughout
the channel, and frequent pools and cascading waterfalls. The north side of the
canyon consists of foothill pine and oak woodland vegetation. There is no
floodplain in this reach. The only native fishes known to have passed through
the gorge and established populations in Yosemite Valley are rainbow trout and
Sacramento sucker, though the native rainbow trout strain has likely been
altered by the introduction of non-native strains. The calm waters at Cascades
Picnic Area provide a natural pool habitat for fish and likely support small
numbers of brown and rainbow trout. Sacramento
suckers are likely found throughout the gorge in small numbers. Riffle sculpin
are also found in some parts of the gorge. Fishes native to the Merced
River below the gorge include rainbow trout, Sacramento
sucker, Sacramento pikeminnow,
hardhead, California roach, and
the riffle sculpin. These species are widespread in the Central
Valley waters and are not of special status or recreational value.
This reach of the Merced River also supports introduced
populations of smallmouth bass and brown trout; fly-fishing for these species
is popular in certain areas.
Lake McClure,
located 55 miles below El Portal, is heavily stocked with non-native and native
species to enhance sport fishing. Species with such wide geographical
distributions as Florida
largemouth bass, channel catfish, and chinook salmon are found in Lake
McClure. Sport fishes commonly
found in the lower Merced River above Lake
McClure include smallmouth bass,
rainbow trout, and brown trout. Fly-fishing for these species is popular in
certain areas. It is doubtful, however, that these species (except possibly rainbow
trout) would move above El Portal through the Merced River
gorge.
Special-Status Species
Species Considered
A total
of 55 special-status wildlife species and 28 special-status plant species (83 total)
have been considered in the evaluation of this project (see Appendix D,
Special-Status Species Evaluation). These species were identified based on data
gathered from the National Park Service, the U.S. Fish and Wildlife Service
(USFWS 2002), and the California Natural Diversity Data Base. The National Park Service has determined that 71
species (out of 83 total) are not known or likely to occur in the
vicinity of the project area. In addition,
preferred habitat for 71 species is also not likely to occur in the vicinity of
the project area. The remaining species, the Wawona riffle beetle, harlequin
duck, California spotted owl, and a number of special-status bat
species, are described below.
These species are further evaluated in Chapter IV,
Environmental Consequences, of this environmental assessment. The remaining
special-status species are described in Appendix D, Special-Status Species
Evaluation. Additional data on these species are included in the Biological
Assessments for the Merced River Planand
Yosemite Valley Plan (incorporated by
reference) (NPS 2000a; 2000c; 2001a), which are on file at Yosemite National
Park.
Critical Habitat
Critical habitat has not been designated for any federally
listed species that is known or has potential to occur within the project area.
However, critical habitat for the California
red-legged frog has been designated by the U.S. Fish and Wildlife Service
northwest of the project area within Yosemite
National Park (Federal Register 2001).
Special-Status Wildlife
Federal Special-Status Wildlife
Wawona Rifle Beetle. This
aquatic species is listed as a species of concern due to its limited
distribution in the North and South Forks of the Merced River.
Habitat includes rocks and mossy areas within the river channel.
The Wawona riffle
beetle is rare in rapid streams of California from 2,000 to 5,000 feet in elevation (Usingner
1956). The Wawona riffle beetle was previously known only from a few locations
in California (Chandler 1954; Brown 1972); recently, however,
it was found in several widely scattered locations in northern California as well as southern Oregon and Idaho (Shepard and Barr 1991). Adults and larvae are
found together, usually in cool, small to medium-sized mountain streams and
rivers. They are most abundant in aquatic mosses and are rarely found in
streams that exhibit seasonal variations in flow, heavy sediments, muddy or
sandy bottoms, or low oxygen content (NPS 1997a).
Suitable habitat for
the Wawona riffle beetle occurs in the Merced River through Yosemite Valley and El Portal and the South Fork of the Merced River in Wawona. It was described and named after
specimens collected in the South Fork of the Merced River in Wawona. The California Academy of Sciences
has records for seven specimens collected in the Merced River canyon between 1923 and 1932. These specimens
were collected from 0.5 mile west of El Portal to 5.3 miles west of El
Portal in rockslide areas (Roth 1972). Additional surveys have also found the
beetle in the Merced
River (Arnold 2001; USGS
1999).
Surveys were conducted in the fall of 2002 for the Wawona
riffle beetle along an approximately 3.5-mile stretch of the Merced
River from Pohono Bridge
to the Cascades Picnic Area. Suitable habitat was observed throughout the study
area; however, no life-stage of the beetle was found. Suitable habitat included
areas of aquatic mosses with a prevalence of partially submerged and submerged
boulders, and where the river channel was at least partially shaded by trees
growing along the shoreline. In more open, sunlit stretches of the river
channels, such as at beaches and adjacent to meadows, mosses were occasionally
observed on boulders where some shading was usually evident, but not in the
more exposed areas. Due to the low water level at the time of the survey,
aquatic mosses that would normally be submerged were exposed. While the species
was not observed during the survey, it is anticipated that it would be observed
in this area during periods of higher water levels, based on the presence of
suitable habitat and previous observations of the beetle (ESA 2002).
Harlequin Duck.California is the extreme southern extent of the range of
this species. Harlequin ducks winter in marine waters along rocky coasts from San Luis ObispoCounty north, and breed inland along fast-flowing, shallow rivers and streams.
Both wintering and breeding populations of the harlequin duck have declined all
over California, probably due to human disturbance along
breeding streams and the damming of rivers. It is likely harlequin ducks still
breed in California, but rarely. Nests are established near swift
rivers or streams in recesses sheltered overhead by stream banks, rocks, woody
debris, or low shrubs. Nests are usually within 7 feet of the water, but can be
up to 90 feet away. In breeding areas, harlequin ducks feed primarily on
invertebrates; in marine wintering habitat, mollusks and crustaceans are major
foods.
The last sighting of transients in Yosemite
National Park occurred near Table
Rock just upstream from Cascades Diversion Dam in the spring of 2000. Nest
observation occurred upstream of Cascades Diversion Dam in 2002 (NPS 2003b).
California
Spotted Owl. This species is
found from the southern Cascades south through the entire Sierra Nevada and in the central Coast Ranges. Surveys through
1993 estimated approximately 1,600 spotted owl sites (pairs and territorial
singles) in the Sierra
Nevada. California spotted owl habitat varies from oak and
ponderosa pine forests to lower elevation red fir forests up to 7,600 feet in
elevation. Prime habitat occurs between 3,000 and 7,000 feet.
Breeding occurs from
about mid-February to mid- or late September, at which time the young are
largely independent of their parents. Eggs are laid and incubated by the female
from early April through mid-May. Nests are usually tree cavities, broken-off
trees and snags, abandoned nests of other species, or mistletoe clumps. Trees
used for nesting are usually very large. Nesting and roosting habitat of
spotted owls is typically dense forest, with a canopy closure of greater than
70%. The presence of black oak in the canopy also enhances habitat quality.
Surveys and
inventories to determine the distribution and abundance of spotted owls in the
park were conducted from April through August of 1988 and 1989 by the
California Department of Fish and Game. Surveys covered 142,700 acres of forest
habitat at elevations between 3,000 and 7,000 feet. These elevations form a
narrow band on the west slope of the Sierra Nevada.
Owls were seen or responded to imitated spotted owl calls at 58 sites over the
two seasons. U.S. Forest Service protocol was used to establish pair occupancy.
Reproductive activity was observed serendipitously. Two nest trees and four
sites with young were observed in 1989. Combined crude densities were estimated
to be 0.18 owls/square kilometer. Based on the Gould and Norton study, the known
or “occupied” habitat for the spotted owl in the park totals about 142,000
acres. In Yosemite
Valley, National Park
Service wildlife staff has confirmed spotted owl sightings near Happy Isles, MirrorLake, the Chapel, and the base of Cathedral Rocks. No nesting owls
occur within the project area, though suitable habitat is present (NPS 1999; 2003b).
Spotted Bat. This species is found in
western North America, from British
Columbia into Mexico.
It lives in desert scrub and open forest areas and roosts in cliff faces and
rock crevices. The species forages in a wide variety of habitats, primarily for
moths. There is a significant population of
spotted bats in Yosemite
Valley (Pierson and
Rainey 1995). Auditory bat surveys were conducted in 1993 at 24 stations in Yosemite Valley in four habitats: large open meadows, wetlands,
forest, and open ponderosa pine forest. Acoustic surveys detected the spotted
bat in meadow and wetland habitats only (Pierson and Rainey 1993). The spotted
bat forages on the north side of El Capitan Meadow, just below El Capitan, Bridalveil Meadow, Leidig Meadow, and the
Ahwahnee Meadow (Pierson and Rainey 1993). The species was not found in Cook’s
Meadow or Stoneman Meadow. A study of potential bridge roosting sites
along State Route 120 found no evidence of spotted bats at any of the six sites
within the park (Pierson et al. 2001).
It is likely that the
spotted bat roosts on or near Half Dome and El Capitan (Pierson and Rainey 1993). Yosemite Valley had the highest population of spotted bats of
any localities surveyed in California (Pierson and Rainey 1995). Acoustic data collected in 1994 suggest there
is a significant population of spotted bats in the Wawona area (Pierson and
Rainey 1993; 1995).
Long-Eared Myotis Bat. This species is
found across much of western North America, from British
Columbia south to California
and New Mexico. The species is
found in a wide range, from the coast to the high Sierra Nevada,
and in montane oak woodlands. The species lives in coniferous forests in
mountain areas and roosts in small colonies in caves, buildings, under tree
bark. Mist-net bat surveys were conducted in
Yosemite Valley from 1993 to 1996 at MirrorLake, Cook’s Meadow, El Capitan Meadow, Cathedral and Cascades Picnic Areas,
and at Yosemite Creek below Yosemite Fall. The long-eared myotis bat was
captured at the Cathedral and Cascades Picnic Areas and at the Yosemite Creek
site (Pierson and Rainey 1993; Pierson et al. 2001).
It was also captured in Wawona.
Fringed Myotis Bat.This
species is found in much of California,
up to British Columbia, and is
scattered across several southwestern states and into Mexico.
It is found to at least 6,400 feet in the Sierra Nevada,
in deciduous/mixed conifer forests. This species feeds over water, in open
habitats, and by gleaning from foliage; it roosts in caves, mines, buildings,
and trees, especially large conifer snags. Grinnell
and Storer found the fringed myotis bat in 1924 in a location just outside the
park boundary. Mist-net bat surveys were conducted in Yosemite Valley in 1993 at MirrorLake, Cook’s Meadow, El Capitan Meadow, and at Yosemite Creek below Yosemite
Fall (Pierson and Rainey 1993; 1995). The fringed myotis bat was captured in
Cook’s Meadow and the Yosemite Creek site (Pierson and Rainey 1993). It was
not found in mist-netting surveys in 1994 in Yosemite Valley (Pierson and Rainey 1995). Mist-net surveys
conducted in 1996 did find the fringed myotis bat in El Capitan Meadow and at
the Cascades Picnic Area (Pierson et al. 2001). Suitable habitat also
occurs throughout the Merced River gorge.
Long-Legged Myotis Bat. The
range of this species includes most of western North America,
as far north as Alaska and south
to central Mexico.
The species prefers forested mountainous areas and is sometimes found in desert
lowlands. The species is found up to high elevations in the Sierra
Nevada, in montane coniferous forest habitats. The long-legged
myotis bat forages over water, close to trees and cliffs, and in openings in
forests; it roosts primarily in large-diameter snags. The species forms nursery
colonies numbering hundreds of individuals, usually under bark or in hollow
trees. The long-legged myotis bat was recently
recorded in the park (Pierson et al. 2001), which was the first siting since it was found in the Grinell and
Storer survey (1924). These sightings were recorded at Cascades Creek and
Yosemite Creek. In addition, there have been several sightings
throughout Yosemite Valley. Suitable habitat also occurs
throughout the Merced River gorge, upper Merced
River, and along portions of the South Fork.
Yuma Myotis Bat. This species is found across much of the western
United States
and into western Canada,
usually below 8,000 feet in elevation. The species forages over open, still, or
slow-moving water and above low vegetation in meadows. The Yuma
myotis bat roosts in buildings, caves, or crevices; nursery colonies choose
caves, mines, buildings, or under bridges. The species skims low over water to
snatch up flying insects. Mist-net bat surveys
were conducted in Yosemite
Valley in 1993 at MirrorLake, Cook’s Meadow, El Capitan Meadow, Yosemite Creek below Yosemite Fall,
Cathedral Picnic Area, and Cascades Picnic Area (Pierson and Rainey 1993; 1995;
Pierson et al. 2001). The Yuma myotis bat
was captured at Mirror Lake, El Capitan Meadow, the Yosemite Creek site, and
both the Cathedral and Cascades Picnic Areas. This species was also found in
recent mist-netting surveys in Yosemite Valley
and Wawona (Pierson and Rainey 1993; 1995), and in hand-net or visual surveys
at bridge crossings at Cascades and Wildcat Creeks (Pierson et al. 2001). There have also been several
sightings throughout Yosemite Valley. Suitable habitat
also occurs throughout the Merced River gorge, upper Merced
River, and along portions of the South Fork.
Greater Western Mastiff Bat. The range
of this species includes southern California
and Arizona, extending into Mexico.
The species is found in a variety of habitats to over 8,000 feet in elevation.
The species roosts primarily in crevices in cliff faces and occasionally in
trees and buildings; it is detected most often over meadows and other open
areas, but will also feed above forest canopy, sometimes to high altitudes
(1,000 feet). There is a significant population of greater
western mastiff bats in Yosemite
Valley, as determined
by mist-netting surveys (Pierson and Rainey 1995; Pierson et al. 2001). Auditory bat surveys were conducted in 1993 at
24 stations in Yosemite
Valley in four
habitats: large open meadows, wetlands, forest, and open ponderosa pine forest.
Acoustic surveys detected the greater western mastiff bat in Bridalveil Meadow,
El Capitan Meadow, Leidig Meadow, Cook’s Meadow, Ahwahnee Meadow, Stoneman
Meadow, Wosky Pond, MirrorLake, and wetlands near Happy Isles. It was also
detected in a few upland habitats east of El Capitan Meadow and Sentinel Beach
Picnic Area. Recent mist-netting surveys found the greater western mastiff bat
in the Cascades Picnic Area (Pierson et al. 2001). Yosemite Valley has the highest population of the greater
western mastiff bat of any locality surveyed in California (Pierson and Rainey 1995). It also has been
captured in Wawona (Pierson and Rainey 1995). Suitable habitat also
occurs throughout the Merced River gorge, upper Merced
River, and along portions of the South Fork.
Pale Big-Eared Bat.This
species is found in all habitats up to the alpine zone. It requires caves,
mines, or buildings for roosting and prefers mesic habitats, where it gleans
from brush or trees along habitat edges. The species has been recorded at Wildcat
Creek Bridge
and Mirror Lake
(CDFG 1999), and there have been several sightings throughout Yosemite
Valley.
Townsend’s Big-Eared Bat. In California, the Townsend’s big-eared bat is found from low
desert to mid-elevation montane habitats. The majority of records are from low
to moderate elevations, though the Townsend’s big-eared bat has been found
from sea level to almost 10,000 feet in elevation. Maternity colonies have been
found up to over 5,000 feet in elevation in the Sierra Nevada. The Townsend’s big-eared bat is concentrated
in areas with mines (particularly in the desert regions to the east and
southeast of the Sierra Nevada) or caves (in the northeast portion of California and karstic regions in the Sierra Nevada and Trinity Alps) as roosting habitat (Pierson
and Fellers 1998). In 1994, mist-net bat surveys were conducted in Tuolumne
Meadows, PateValley, and Wawona. The Townsend’s big-eared bat was captured in Wawona
(Pierson and Rainey 1993; 1995). It was also captured in Yosemite Valley in 1993 and 1996 (Pierson and Rainey 1993; 1995;
Pierson et al. 2001).
State-Listed Special-Status Species
Pallid Bat.The pallid bat is found throughout California, primarily in the low to mid-elevations,
although it has been found to elevations over 10,000 feet in the Sierra Nevada. It is found in a variety of habitats, from desert
to coniferous forest and nonconiferous woodlands. It is particularly associated
with ponderosa pine, redwood, and giant sequoia habitats. It selects a variety
of day roosts, including rock outcrops, mines, caves, hollow trees, buildings,
and bridges. Recent research suggests a high reliance on tree roosts. It
commonly uses bridges for night roosts (Pierson et al. 2001). Between 1994 and 1998, mist-net bat surveys were
conducted in Tuolumne Meadows, Cascades Picnic Area, MirrorLake, PateValley, and Wawona. The pallid bat was captured in PateValley at MirrorLake, the Cascades Picnic Area, and Wawona (Pierson and Rainey 1993; 1995; Pierson
et al. 2001). It was also captured in Yosemite Valley in 1993 (Pierson and Rainey 1993; 1995).
Special-Status Vegetation
A total of 28 plant species that have special federal,
state, or park status have been evaluated herein (see Appendix D,
Special-Status Species Evaluation). Six plants are classified as federal
species of concern (or federal species of local concern), one of which is also
listed by the park as rare; three are listed as rare or threatened by the State
of California; and the remaining 19 are listed by the park as rare. None of the
plant species evaluated have been located within the project area.
Air Quality
Yosemite National Park is classified as a mandatory Class
I area under the federal Clean Air Act (42 United States Code 7401 et seq.) (see
Appendix A, Regulations and Policies). This air quality classification is aimed
at protecting parks and wilderness areas from air quality degradation. The act
gives federal land managers the responsibility for protecting air quality and
related values from adverse air pollution impacts, including visibility,
plants, animals, soils, water quality, cultural and historic structures and
objects, and visitor health.
The project area is in Mariposa
County, which is regulated by the
Mariposa County Air Pollution Control District. Mariposa County Air Pollution
Control District is responsible for developing a state implementation plan for
federal and state nonattainment pollutants in its jurisdiction. State
implementation plans define control measures that are designed to bring areas
into attainment. Mariposa County
is currently in attainment or is unclassified for all national ambient air
quality standards. However, Mariposa exceeds two California
ambient standards: ozone throughout the county and particulate matter less than
10 microns in diameter (PM10) in Yosemite Valley. Basic
components of a state implementation plan include legal authority, an emissions
inventory, an air quality monitoring network, control strategy demonstration
modeling, rules and emission limiting regulations, new source review
provisions, enforcement and surveillance, and other programs as necessary to
attain ambient air quality standards.
Sensitive Receptors
Land uses such as recreation areas, campgrounds, schools,
child-care centers, hospitals, and convalescent homes are considered to be more
sensitive than the general public to poor air quality because the population
groups associated with these uses have increased susceptibility to respiratory
distress. Persons engaged in strenuous work or exercise have increased
sensitivity to poor air quality. Residential areas are considered more
sensitive to air quality conditions compared to commercial and industrial areas
because people generally spend longer periods of time at their residences. Recreational
uses are also considered sensitive compared to commercial and industrial areas
due to the greater exposure to ambient air associated with outdoor activities.
Recreational users along the Merced River near the
project area and users of the Cascades Picnic Area would be the closest
sensitive receptors to the project area.
Introduction
By
definition, noise is human-caused sound and is considered to be unpleasant and
unwanted. Whether a sound is considered unpleasant depends on the individual listening
to the sound and what the individual is doing when the sound is heard (i.e.,
working, playing, resting, sleeping). Natural sounds within Yosemite
National Park and adjacent to the Merced
River are not considered to be noise. These sounds result from
natural sources such as waterfalls, flowing water, animals, and rustling tree
leaves. The enjoyment of such river-related natural sounds is considered an important
visitor experience. The existing noise within the park results from mechanical
sources such as motor vehicles, generators, and aircraft, and from human
activities such as talking and yelling.
Existing Noise Sources
Motor Vehicles
The noise environment at Cascades Diversion Dam is
primarily influenced by automobiles, recreational vehicles, buses, and trucks
(motor vehicles) accessing the park via El Portal Road and Big Oak Flat Road.
Noise from motor vehicles is loudest immediately adjacent to El
Portal Road but, due to generally low background
sound levels, can be audible a long distance from the roadway. Atmospheric
effects such as wind, temperature, humidity, topography, rain, fog, and snow
can significantly affect the presence or absence of motor vehicle noise in
various areas of the Merced River corridor. Noise levels
from motor vehicles will be loudest where and when activity levels are the
greatest and nearest to the area.
Aircraft
As part of a report to Congress (NPS 1994a), the National
Park Service conducted a visitor survey in Yosemite
National Park. Of the visitors
surveyed, 55% reported hearing aircraft sometime during their visit. The report
notes that recognition of noise from aircraft was highly variable from location
to location, and that visitor recognition of noise was greater in areas of
lower development. In Yosemite, a majority of the
comments came from wilderness trail users.
Other Sources
Other mechanical sources of noise within the park and near
the Merced River include roadway construction equipment,
generators, radios, and park maintenance equipment (i.e., mowers and chainsaws).
The frequency of use and the location of these sources vary by season.
Background Sound/Noise Levels
Current sound levels adjacent to the main stem of the Merced
River vary by location and season (the volume of water in the
river being lower in the fall and higher in the spring). Current noise levels
are also influenced by the number of visitors to the park and by the proximity
of mechanical noise sources.
Sound and noise levels are measured in
units known as decibels. For the purpose of this analysis, sound and noise
levels are expressed in decibels on the “A”-weighted scale, or dBA. This
scale most closely approximates the response characteristics of the human ear to
low-level sound. Human hearing ranges from the threshold of hearing (0 dBA)
to the threshold of pain (140 dBA). Environmental sound or noise levels
typically fluctuate over time, and different types of noise descriptors are used
to account for this variability. One of these descriptors, Leq, is the
energy-equivalent level, which is the equivalent steady-state level which, in a
stated period, reflects the same acoustic energy as the actual time-varying
level during the same period.
A sound-level measurement was obtained on the Cascades
Diversion Dam intake structure in September 2002 using a Metrosonics dosimeter
(Model 308-b). The dosimeter was calibrated with a Metrosonics sound-level
calibrator. At this location, the average sound-level (Leq) over a 10-minute
period was 62.6 dBA, and the maximum noise level recorded was 78.5 dBA.
Motor vehicle traffic accounted for most of the noise, as the measurement was
taken 30 feet from the center of the intersection of El
Portal Road and Big Oak
Flat Road. The water level and flow of the river
was low at that time, and the sound of water flow in the river was not audible,
even during periods with no traffic.
Sound levels were measured approximately 500 feet east
(upstream) of the Cascades Diversion Dam in September 1999 for development of
the Merced River Plan. This portion of the river is calm due to impoundment
from the dam. At this location, measured sound levels were roughly 48.5 dBA,
with a recorded maximum level of 63.0 dBA when a bus passed on Northside
Drive. Measured sound levels indicate that the
background (minimal) sound level near the project site is roughly 48.5 dBA.
Overview of Human Occupation
American Indians
The area now comprising Yosemite
National Park was first inhabited
by people between 4,000 and 6,000 years ago. The area surrounding the
intersection of El Portal Road
and Big Oak Flat Road has
been used as a site of human occupation and a travel corridor over the past
several thousand years. Some preliminary evidence from the El Portal area
indicates that people may have been living there as long as 9,500 years ago.
The park area contains hundreds of archeological sites, evincing thousands of
years of occupation. There is evidence of technological change through time, a
highly developed trade network, at least one population replacement, and
significant environmental manipulation through the use of fire.
When Euro-Americans first entered Yosemite
Valley in 1851, the Indians living there were most likely Southern
Sierra Miwok; however, parties of the Mono Lake Paiute and adjacent Miwok
groups would periodically enter the Valley for trade (Barett and Gifford 1933).
The upland areas of the Merced River drainage were
frequented by Southern Sierra Miwok, possibly Mono Lake Paiute, and at least
traversed by Western Monos and possibly Chukchansi Yokuts. El Portal was
inhabited by Miwok people as well.
As awareness of Yosemite
Valley
grew, hotels and other travel-related amenities were developed. Management of
the Valley was taken over by Euro-American institutions, and American Indian
interests were subject to decisions made without their influence. Labor
shortages led many Paiute Indians to take up permanent residence in Yosemite
Valley. Traditions changed as Indian people built nontraditional
houses, vacated old village sites, and built new villages. These changes were
due in part to efforts by Euro-Americans to centralize the Indian people as a
tourist “attraction” and control their activities.
At least seven Indian tribes claim traditional
associations with Yosemite National
Park, and the National Park Service has entered
into various agreements with the American Indian Council of Mariposa County,
Inc., the political organization representing the Southern Sierra Miwok tribe.
Individuals from most of these tribes continue to maintain cultural
associations with lands and resources in Yosemite
National Park through traditional
ceremonies, gathering of traditional plants, and other activities.
Euro-Americans
The Euro-American history of the Merced
River
gorge began in the 1870s, when James Hennessey of El Portal built and
maintained a trail between El Portal and Yosemite Valley
through the gorge. The Coulterville and Yosemite Turnpike Company constructed
the Coulterville Road, which
entered the Merced River
canyon just west of the Cascades area and continued east to Yosemite
Valley. In 1907, after two years of construction, the Yosemite
Valley Railroad Company completed the El Portal Road
between the rail terminus at El Portal and Yosemite Valley.
The “All Year” Highway (State Route 140) was completed in 1926 and increased
accessibility into Yosemite Valley.
In the early part of the twentieth
century, National Park Service Director Stephen T. Mather envisioned a “new Yosemite”
where modern comforts of hot water, restaurants, and electricity could be
experienced “to meet the ever-increasing demand for every type of experience.” In
1917, visitation reached a total of 34,510. This
increased visitation meant a greater need for providing those modern visitor
comforts, which ultimately led to the 1918 completion of the Cascades Diversion
Dam and Hydroelectric Powerhouse.
The Yosemite Hydroelectric Power Plant and associated
structures (including the dam) (NPS ID Number 439) were constructed during
1917-1918 to provide electrical power to Yosemite Valley.
Water was diverted from the Merced River into a wooden
penstock that paralleled El Portal Road
and dropped into the power plant, where electricity was generated. The
electricity was then conducted along 11-kilovolt overhead power lines from the
power plant to Yosemite Valley. The hydroelectric
complex is listed in the National Register of Historic Places, significant for
engineering. The hydropower system is no longer in use, and many elements of it
have been removed in consultation with the State Historic Preservation Officer
and Advisory Council on Historic Preservation (NPS 1986). The five adjacent
Cascades residences north of El Portal Road, which are no longer in use, were
constructed to provide housing for individuals responsible for maintaining and
operating this system.
Archeological Resources
To date, approximately 6% of park lands have been
inventoried for archeological resources, and over 1,100 archeological sites
have been documented. Most of the inventories focus on lower-elevation
developed areas and road corridors; however, some wilderness areas have also been
surveyed. In most cases, inventories have been conducted in support of park
development projects as part of the environmental and historic preservation
compliance process. The most recent comprehensive overview of archeological
resources and their informational value is presented in An Archeological Synthesis and Research Design for Yosemite National
Park, California (Hull and Morrato 1999). This document summarizes the
results of past archeological research and presents research questions and
methodologies for furthering understanding of prehistoric and historic lifeways
in the Yosemite region.
Archeological resources in the Merced River
corridor include historic and prehistoric sites. The historic sites are
associated with development and use of this canyon as a travel corridor and
include rock quarries, dumps, the remains of two work camps, a few unidentified
structural foundations, and the Coulterville Road
blacksmith shop. The shop is located in the talus west of the Cascades area where
a forge was built to serve travelers along this road. Four prehistoric
American Indian archeological sites are located in and adjacent to the Cascades
area. These sites are likely seasonal villages and contain features such as
mortar rocks, midden soil, lithic scatters, and rockshelters.
Ethnographic Resources
American Indian people continue their traditional cultural
associations with park lands and resources. Other than the Yosemite
Valley study by Bibby (1994), little formal research has been
conducted to inventory and document traditional resources important to American
Indian people. A parkwide ethnographic overview was prepared during the 1970s,
but needs to be revised based on currently available information. Some
ethnohistory studies, focusing primarily on Yosemite Valley
and El Portal, have also been conducted.
The National Park Service consults with American Indian
people about management of park lands, especially regarding undertakings and
park resources of concern. Some of the primary concerns are access to park
areas; gathering of plant materials for food, medicinal, and utilitarian
purposes; protection of archeological and burial sites; and interpretation of
Indian culture and prehistoric and historic lifeways. The National Park Service
is required to consult on the basis of Government-to-Government Relations with
federally recognized Indian tribes, and on a more informal basis with
nonfederally recognized tribes. There is no ethnographic information or direct
historical data related to American Indian occupations at the Cascades
Diversion Dam Removal Project area. People would most likely have passed
through the area while traveling between Yosemite Valley
and the lower elevations of the Merced River gorge, and ethnographic
resources could occur within the project area and the gorge, such as plant
material traditionally gathered for basketry, food, ceremonies, insect
repellant, etc. Plants and materials that are or could be present within the
project area and downstream include willows, wormwood, bracken fern, manzanita,
bay leaf, clump grass, tulle reeds, and mushrooms (NPS 2003a).
Cultural Landscape, including Historic Sites and Structures
Cultural landscapes are the result of
the long interaction between people and the land, and the influence of human
beliefs and actions over time upon the natural landscape. Shaped through time by
historical land use and management practices, as well as politics and property
laws, technology, and economic conditions, cultural landscapes provide a living
record of an area’s past, a visual chronicle of its history. The dynamic
nature of modern human life contributes to the continual reshaping of cultural
landscapes, making them a good source of information about specific times and
places, but at the same time rendering their long-term preservation a challenge.
Based on a cultural
resources inventory completed in support of the reconstruction of El Portal Road, the National Park Service, in consultation with
the State Historic Preservation Officer, determined that the Merced Canyon
Travel Corridor is a significant historic property, eligible for listing in the
National Register of Historic Places. The primary element of this property is El Portal Road itself, originally constructed as a wagon road in
1905, and substantially reconstructed in 1925. The road includes
hand-laid stone parapet guardwalls and drainage catchment structures. Following
consultation with the State Historic Preservation Officer and the Advisory
Council on Historic Preservation, the majority of these features were
documented and removed as part of the El Portal Road Improvement Project.
Remaining features include rock quarries, historic trash scatters, sections of
pre-1925 roadbed, historic work-camp sites, and the Arch Rock Entrance Station
complex (eligible for the National Register as an individual property), which
consists of a ranger residence/office, entrance kiosk, parking lot, and
restroom building.
The Merced Canyon Travel Corridor
determination of eligibility document (NPS 1997e) describes the important
landscape characteristics of this property: “...the views of the Merced
River Canyon, the use
of natural materials, and purposeful design of situating the travel corridor in
sympathy with the natural landscape.”
Another historic resource in the gorge
includes the structures and features associated with the Yosemite Hydroelectric
Power Plant (also known as the Cascades Powerhouse). Structures included within
the historic property listing are the diversion dam, the intake, screens and
screenhouse, the penstock, the surge tank, the powerhouse and equipment, and the
11-kilovolt distribution line into Yosemite Valley. Some
of these features were removed during the 1980s, but some elements still remain,
including the dam, the abutments that flank the dam, the intake structure, and
the screenhouse. Other remaining elements of the former hydroelectric generating
facility include part of a penstock that historically conveyed water from the
dam to the powerhouse (nearly all of the penstock has been removed), the
powerhouse, and the transmission lines, all of which are more than a mile
downstream from Cascades Diversion Dam. Today the powerhouse is used as a
transfer facility from Pacific Gas and Electric Company transmission lines to
National Park Service transmission lines. The dam, abutments, intake structure,
and screenhouse remain as they were when decommissioned in 1985. Also considered
contributing to this property are the five Cascades residences and garages north
of El Portal Road,
constructed between 1917 and 1924. These structures are not being used and are
schedule for removal under the Yosemite Valley Plan. These structures
are located outside of the Cascades Diversion Dam project area.
A historic site consisting of a linear road feature of
four segments is located immediately south of El
Portal Road and north of the river, downstream of
Cascades Diversion Dam. The resource is a segment of Coulterville Stage Road,
completed to Yosemite Valley in the summer of 1874, and
joined with El Portal Road west
of Cascades Picnic Areain 1907.
Some portions of this site are obliterated or obscured by road fill from El
Portal Road, located immediately north and above
Coulterville Stage Road (NPS 1997d). The Yosemite
section of Coulterville Stage Road is considered an important historical resource
and, as such, is listed in the National Register of Historic Places.
Yosemite Roadway System
Regional
highways leading into Yosemite National
Park (State Routes 41, 120, and 140)
transition into the internal parkwide road system; there are no state highways
within the boundaries of the park, though state route numbers are used on park
signs to help orient visitors. Two of these roadways are within the project
area; Big Oak Flat Road
meets El Portal Road
opposite the dam site. El Portal Road continues east into Yosemite Valley.
El Portal Road is about
eight miles long within the park. Outside the park boundaries, this road
connects to State Route 140. El Portal Road
enters the park at the El Portal Administrative Site, passes through the
Arch Rock Entrance Station, and joins Big Oak Flat
Road one mile west of Pohono
Bridge. It is maintained for
year-round access. The road is characterized by steep, rocky canyon walls with
small river flats and terraces and has a typical pavement width of
27 feet.
Big Oak Flat Road
is about 18 miles long. It leads from the Big Oak Flat Entrance Station through
Hodgdon Meadow and Crane Flat, and joins El Portal
Road one mile downstream from Pohono
Bridge. (Big Oak
Flat Road also provides access to the Valley from
the Tioga Pass
entrance.) Outside the park, this road connects to State Route 120. Big Oak
Flat Road may be used as a through route in
conjunction with other major park roads and is maintained for year-round
access. The topography changes from mountainous on the east end of the road to
rolling at the west end. The paved roadway width ranges from 22 to28 feet.
Traffic Conditions
Daily traffic volumes recorded at fixed counter locations
within the park indicate a trend of steady growth in traffic, but traffic
volumes do not exceed the capacity of El Portal Road
or Big Oak Flat Road. The
only stop sign in the project vicinity is adjacent to the dam and is for
traffic turning in either direction onto El Portal
Road from Big Oak Flat
Road. This intersection occasionally experiences
moderate congestion on busy summer days.
Transit and Tour Bus Services
While bus transportation in Yosemite
National Park includes public
transportation, charter and tour bus operations, concessioner-operated
tours, and shuttle bus services operated by the park concessioner, there are no
bus stops within a mile of Cascades Diversion Dam. Charter and tour buses
frequently travel to and from Yosemite Valley on El
Portal Road and Big Oak
Flat Road.
Parking Facilities
There is a small parking lot located approximately 20 feet
east of the El Portal Road
and Big Oak Flat Road
intersection. This lot has room for roughly 12 automobiles. There is no
pedestrian crosswalk or traffic control for pedestrians to cross the road
towards the dam intake and the river. In addition, there is an informal turnout
on the river-right side of El Portal Road
immediately downstream of Cascades Diversion Dam. This area has room for
approximately five cars. Neither the parking lot nor turnout has marked
parking spaces, and parking in the project area is not in high demand. These
areas are typically used for short-term private automobile parking and are not
typically used by tour buses. The parking area may be used during winter as a
location for putting on or removing tire chains and as a snowplow turnaround.
The parking area may also be used as an equipment staging and traffic control
area for road closure activities or for heavy equipment staging for nearby
maintenance operations, such as clearing landslide debris. The parking area and
turnout may also be used by visitors orienting themselves to park destinations
(i.e., consulting maps) or by visitors with disabled vehicles. The entrance to Pohono
Quarry from El Portal Road
is within an informal turnout that may be used by visitors to access the Merced
River.
Visual resources within the project area and the
V-shaped Merced River
gorge are somewhat limited because of the steep terrain and forest cover.
However, some views of dramatic rock formations are available from the Cascades
Diversion Dam project area. Pulpit Rock can be seen on the south wall of the
gorge approximately 0.25 mile downstream of the dam, and the Rostrum can be
seen approximately 1.25 miles downstream. In the late 1970s, the National Park
Service conducted a visual analysis that identified the 11 most important
features within Yosemite Valley, in terms of the
landscape features most visitors look for and are able to distinguish. Two of
those features, Bridalveil Fall and Cathedral Rocks, are partly visible from
the banks of the Merced River in the vicinity of the dam
and from the dam intake structure, although obscured in part by intervening
vegetation. The slope of the riverbed in the vicinity of the dam is relatively
steep (USBR 2001), producing visually dramatic rapids among the rocks and
boulders downstream of the dam during high water flow. Upstream, the impounded
river is flat and wide behind the dam. As described in the Merced River Plan,
the dam, abutments, and screenhouse constitute human-made historic structures
that intrude into the views from within the Merced River
corridor; these structures do not, however, dominate the natural landscape from
any viewpoint. Pohono Quarry is not visible
from El Portal Road or the Merced
River due to dense forest cover in this area.
Big Oak Flat Road
meets El Portal Road
opposite the dam site. This junction of two major park roads gives this section
of the river corridor added visibility. Although no formal hiking trails follow
the river here, a parking area located on the north side of El Portal Road just
east of the Big Oak Flat Road junction affords access (for visitors in
private vehicles) to this part of the river, for viewing and other recreational
purposes.
The reach of the river that includes the
dam site is identified as Scenic B in the Yosemite Valley Scenic Analysis map
that was prepared for the Merced River Plan (2001a). This classification
indicates that this area is “included in scenic views less commonly chosen by
historic photographers and painters, or compose[s] less significant modern
views, based on park management observations” (NPS 2001a).
There are no formalized recreation opportunities within the
project area. Recreation activities near Cascades Diversion Dam include
sightseeing, picnicking, swimming, fishing, climbing, and non-motorized
watercraft use. Groups occasionally use the parking lot near Cascades Diversion
Dam as a meeting place and then proceed to other areas of the park.
Sightseeing
Sightseers use the Cascades Diversion
Dam intake structure to view the river and rock formations of the Merced
River
gorge. It was not, however, the intention of the park to create a public
viewpoint at this location, and there is no pedestrian crosswalk from the
parking lot north of El Portal Road to the intake structure. While there
are no formal hiking trails near the dam, visitors are known to walk on the dam’s
wooden crest and the exposed riverbanks and rocks when water levels are low.
Visitors also use vehicle turnouts to access the river for sightseeing
activities.
Picnicking
The Cascades Picnic Area is
approximately one mile downstream from the dam. The nearest picnic areas
upstream – Cathedral
Beach and El Capitan
– are more than two miles from the dam. Informal picnicking near Cascades
Diversion Dam takes the form of lunch on riverside boulders, at the parking area
near the dam, or at roadside turnouts.
Swimming
During the summer, visitors and residents swim in the Merced
River gorge, although a sign on the intake structure railing prohibits
swimming near Cascades Diversion Dam. The National Park Service does not
officially designate swimming areas. However, there are numerous known swimming
holes along the Merced River downstream to an area known as Steamboat Bay and
to Arch Rock, some more accessible than others.
Fishing
Though a sign on the intake structure railing prohibits
fishing near Cascades Diversion Dam, visitors enjoy fishing other stretches of
the Merced River near the dam. Only brown trout and
rainbow trout are sufficiently common for routine fishing in the Merced
River. Fishing in Yosemite
National Park is bound by the same
regulations that apply elsewhere in the state and are enforced by the National
Park Service.
Climbing
Rockclimbing regularly occurs within the Merced
River gorge. Most climbing takes place at the Rostrum, Steamboat
Bay, and the Cookie (east of the
Arch Rock Entrance Station) in the spring and fall, when higher elevations are
unavailable due to inclement weather. Climbing groups are known to park near
Cascades Diversion Dam and then hike to a climbing site approximately one-half
mile up Big Oak Flat Road.
Non-Motorized Watercraft
Very little rafting and kayaking occurs near Cascades
Diversion Dam, while a limited amount of white-water rafting and kayaking takes
place downstream along the Merced River in the El Portal
area. Since approximately 1984, commercial rafting operations have launched
rafts just downstream of Red Bud Picnic Area (outside of El Portal) through an
agreement with the Bureau of Land Management. Private rafters also launch near
the gas station in El Portal, although this is not a heavily used area.
There are no formalized orientation opportunities within the
project area; however, information regarding general trip planning and
orientation is available from a variety of sources.
Orientation
Yosemite’s web site provides
information about park lodging and activities, safety, resource protection, and
accessibility. The park’s public information office mails pre-visit materials
to those requesting them by phone, fax, or mail. The Yosemite Association also
offers an interactive
web site and sells Yosemite-related publications and other interpretive
resources. The park provides updated information, publications, and seasonal
staffing to local, multi-agency visitor centers where visitors can stop en
route. Once at park entrance stations, visitors receive free park publications
with trip and activity planning information, including the Yosemite Guide and Yosemite
Today newspapers. During the summer and early fall, contact stations in
Wawona and Big Oak Flat are staffed to provide additional assistance, and a
visitor center is open during the summer in Tuolumne Meadows.
Wayfinding in areas near Yosemite
Valley
can sometimes be challenging, as the main visitor center is located toward the
east end of the Valley. The park’s free publications distributed at entrance
stations contain maps and wayfinding information. Visitors can also gain limited
information from roadside signs throughout the park, such as those at the El
Portal Road and Big Oak
Flat Road intersection adjacent to Cascades
Diversion Dam.
Interpretation
The Division of Interpretation in Yosemite
assists people in making connections to the park through a program of guided
walks and talks, curriculum-based education, informal interactions along
trails, dramatic presentations, cultural demonstrations, off-site talks to
gateway communities, public open houses, media relations, as well as exhibits,
publications, signs, and films. Interpretation facilities are vital components
of the National Park Service mission to foster enjoyment, education, and
inspiration. Interpretation aims to inspire people to gain a greater
understanding of themselves and the world through their national park
experience. There are no formalized interpretation activities at Cascades
Diversion Dam.
The affected socioeconomic region
includes Madera
County, Mariposa
County, and Tuolumne
County, the three counties in which
Yosemite National Park
is located. The Yosemite Valley Plan
provides a socioeconomic profile of the regional economy for 1996 that presents
the size of each county’s principal economic sectors in terms of population,
employment, and output. Output data have been updated based on trends in local
area personal income provided by the U.S. Bureau of Economic Analysis through
the year 2000 (the most recent data available for the area). The resulting
estimates for 2000 provide a reasonable socioeconomic profile of the
three-county region, given that it has not experienced any significant
structural changes to its economy since 1996. Employment data for 2000 is
provided by the California Employment Development Department.
Regional Economy
Population
In 2000, the total population of the three-county affected
region was approximately 194,740 (see table III-2). Madera
County is the most populous county,
with roughly 123,109 residents. Mariposa
County has a total population of
approximately 17,130 residents.
|
Madera
|
123,109
|
|
Mariposa
|
17,130
|
|
Tuolumne
|
54,501
|
|
Total
|
194,740
|
SOURCE: U.S.
Bureau of the Census 2002
Employment
The employment figures include all waged, salaried, and
self-employed jobs in each county, and both full-time and part-time workers. In
2000, total employment was approximately 60,040 in the three-county area.
Approximately 65% of the total employment in the affected region was in Madera
County. Mariposa
County accounted for approximately
8% of total employment in the affected region. Table III-3 provides total
employment estimates for the counties by industry sector.
2000 Employment By Major Industry Sector
|
Industry Sector
|
Madera
|
Mariposa
|
Tuolumne
|
Total
|
|
Agriculture
|
11,900
|
10
|
180
|
12,090
|
|
Construction & Mining
|
1,600
|
140
|
980
|
2,720
|
|
Manufacturing
|
3,400
|
180
|
1,250
|
4,830
|
|
Transportation, Public Utilities
|
1,100
|
90
|
430
|
1,620
|
|
Trade (Wholesale & Retail)
|
5,700
|
690
|
3,800
|
10,190
|
|
Finance, Insurance, Real Estate
|
600
|
90
|
530
|
1,220
|
|
Services
|
7,500
|
1,970
|
4,230
|
13,700
|
|
Government
|
7,600
|
1,730
|
4,540
|
13,870
|
|
Total
|
39,200
|
4,890
|
15,950
|
60,040
|
SOURCE:
California Employment Development Department 2002
Output
Economic output is a measure of productivity. Measures of
economic output vary depending upon the industry sector. For the agricultural,
wholesale trade, and retail trade sectors, output is measured by the value of
products sold. In the manufacturing sector, output is a measure of the value
added by the manufacturer or the value of shipments. In the service sector,
output is measured as receipts in dollars.
The estimated total output of goods and services for the
three-county affected region in 2000 was about $6.9 billion (2000 dollars) (see
table III-4). Madera County
accounted for approximately 66% of total economic output in the affected
region. Mariposa County,
which had the smallest economy in the affected region, accounted for
approximately 7% of output. Based on output, manufacturing was the largest
economic sector in the three counties.
2000 Economic Output By County and Industry Sector (in
Millions of 2000 Dollars)
|
Industry Sector
|
Madera
|
Mariposa
|
Tuolumne
|
Total
|
|
Agriculture
|
$
1,080.6
|
$
28.3
|
$ 44.3
|
$
1,153.2
|
|
Construction & Mining
|
$
322.5
|
$
54.1
|
$
234.2
|
$
610.8
|
|
Manufacturing
|
$
989.1
|
$
53.0
|
$
345.4
|
$
1,387.5
|
|
Transportation & Public Utilities
|
$
434.8
|
$
65.5
|
$
199.6
|
$
699.9
|
|
Trade (Wholesale & Retail)
|
$
280.9
|
$
17.8
|
$
122.4
|
$
421.2
|
|
Finance, Insurance, Real Estate
|
$
494.7
|
$
103.2
|
$
315.9
|
$
913.8
|
|
Services
|
$
579.5
|
$
59.2
|
$
371.4
|
$
1,010.1
|
|
Government
|
$ 363.7
|
$
89.4
|
$
243.5
|
$
696.6
|
|
Total
|
$
4,545.8
|
$
470.5
|
$
1,876.8
|
$
6,893.1
|
SOURCES: Micro IMPLAN Group 1996, adjusted according to
U.S. Bureau of Economic Analysis trends in personal income
Taxable Retail Sales
Taxable retail sales are good indicators
of annual spending in the travel-service sectors, since they represent the taxes
paid for transactions with consumers. The total taxable retail sales figures
include the taxes paid by businesses on raw materials and services. In 2000, the
total taxable retail sales for the affected region was approximately
$1.5 billion (2000 dollars). Madera
County accounted for about 58% of
total taxable retail sales. Mariposa County
accounted for about 8% of total taxable sales. Table III‑5 shows
total taxable retail sales by county.
2000 Total Taxable Retail Sales By County (in Millions of
2000 Dollars)
|
County
|
Total Taxable Sales
|
|
Madera
|
$881.0
|
|
Mariposa
|
$127.3
|
|
Tuolumne
|
$500.8
|
|
Total
|
$1,509.1
|
SOURCE: California
State Board of Equalization 2002
County Profiles
MaderaCounty.
The central economic activity in Madera
County is agriculture, which
constitutes nearly one-third of the county’s total employment and over 24% of
the county’s economic output (see tables III-3 and III-4). The agricultural
sector stimulates production in related sectors of the economy, including jobs
in food processing, transportation, and wholesale trade.
In Madera County,
the construction and mining sector accounts for over 4% of employment and over
7% of total economic output in the county (see tables III-3, and III-4).
MariposaCounty.
Recreation and tourism are major industries in Mariposa
County. The county’s primary
recreation area/tourist attraction is Yosemite
National Park, much of which lies
within the county, including the developed areas of Yosemite Valley.
Major recreation areas in Mariposa County
include Stanislaus National
Forest and Sierra
National Forest, including the U.S.
Forest Service/Bureau of Land Management managed recreation areas along the Merced
River.
The services sector accounts for approximately 40% of
employment and 22% of economic output in Mariposa
County. Government is also a major
economic sector in the county, accounting for 35.4% of employment and 19% of
total output. The finance, insurance, and real estate sector accounted for 22%
of economic output, although only about 2% of total employment. In Madera
County, the construction and mining
sector accounts for only 3% of county employment and 11.5% of total economic
output in the county (see tables III-3 and III-4).
TuolumneCounty.
Yosemite National Park
is in the southeastern portion of Tuolumne
County and Cascades Diversion Dam
is easily accessible from Tuolumne County,
via Big Oak Flat Road. The
government sector was the largest employer in the county in 2000, accounting for
28.5% of employment and 13% of economic output (see tables III-3 and III-4).
The services sector accounts for 26.5% of employment and 19.8% of the total
economic output. Most of the job growth in Tuolumne
County is expected in the services,
retail trade, construction, and manufacturing sectors. The services sector is expected
to create the greatest number of new jobs, reflecting an increased demand for
business, health, personal, and hospitality services.
In Tuolumne County,
the construction and mining sector accounts for nearly 6% of county employment
and 12.5% of total output in the county (see tables III-3, and III-4).
Park Operations
Park facilities and infrastructure in
the vicinity of the dam include El Portal Road,
Big Oak Flat Road, Cascades
Diversion Dam, and Pohono Bridge.
Utilities under El Portal Road include a wastewater line (which extends
between El Portal and Yosemite Valley), electrical conductors (which extend
from a substation at the Cascades Powerhouse to a substation in Yosemite
Valley), and a telephone line. There is one public telephone and trash cans at
the public parking area on the north side of El Portal
Road from the dam. The telephone provides access to
the park’s emergency response system through 911. The parking lot provides a
location for snowplow turnaround, equipment staging and traffic control for road
closure activities, and heavy equipment staging. Pohono Quarry is used for
staging and materials storage for past and ongoing park projects. Although the
dam itself is deteriorated and outdated and was decommissioned as a
hydroelectric facility in 1986, the park performs minor repairs on attendant
structures such as the safety railing. Minor miscellaneous park operations and
facilities equipment, such as traffic cones and signs, are currently stored in
the screenhouse.
Park operations and facility staff,
particularly the Facilities Management and Resources Management divisions, would
be responsible for overseeing contract work undertaken for the project.
Facilities Management responsibilities include buildings and grounds, roads and
trails, utilities, and design and engineering. Resources Management
responsibilities include natural and cultural resource monitoring and
evaluation, impact mitigation, restoration, and wildlife management.
Biodiversity, or biological diversity, is generally
accepted to include genetic diversity within species, species diversity,
and a full range of biological community types. The concept is that a
landscape is healthy when it includes stable populations of native
species that are well distributed across the landscape
|
