Introduction
The National Park Service has prepared the Final Yosemite Valley Plan/Supplemental Environmental Impact Statement (SEIS) to provide direction and propose specific actions to preserve Yosemite Valley’s natural, cultural, and scenic resources, and to provide opportunities for high-quality, resource-based experiences for visitors. It is based on the broad goals of the 1980 General Management Plan for Yosemite National Park and complies with the management elements of the Merced River Plan. The Final Yosemite Valley Plan/SEIS identifies the Merced River ecosystem as a highly valued resource, affording it a high priority for protection and restoration. The purpose of this Floodplain Statement of Findings is to review the Final Yosemite Valley Plan/SEIS in sufficient detail to:
· Provide an accurate and complete description of the flood hazard assumed by implementation of the proposed action (without mitigation)
· Provide an analysis of the comparative flood risk among the alternatives presented in the Final Yosemite Valley Plan/SEIS
· Describe the effects on floodplain values associated with the proposed action
· Provide a thorough description and evaluation of mitigation measures developed to achieve compliance with Executive Order 11988 (Floodplain Management) and the NPS Floodplain Management Guideline (1993)
Floodplain Extent
The best available data were used to determine the extent of existing floodplain boundaries and water surface characteristics of the Merced River. The Stantec (2000) and Cella Barr Associates (1998) model was used to analyze the extent of the 2-, 10-, 25-, and 100-year floodplains in the east end of Yosemite Valley between Happy Isles and the west end of Yosemite Lodge. The line that delineates the January 1997 flood extent was used to determine the 100-year floodplain in the west end of Yosemite Valley from the west end of Yosemite Lodge to Pohono Bridge. The U.S. Army Corps of Engineers Merced River study (1998) was used to determine the 100-year and 500-year floodplain in El Portal. The U.S. Army Corps of Engineers floodplain map (1981) was used to determine the 100-year and 500-year floodplains in Wawona.
The Proposed Action
The Final Yosemite Valley Plan/SEIS aims to restore degraded areas and reduce development within the Merced River ecosystem and other highly valued natural and cultural resource environments. It strives to reduce traffic congestion and supports the use of alternative fuels to reduce mobile sources of air pollution. It would expand orientation and interpretation services. It proposes to move housing, administrative headquarters, offices, and other functions out of Yosemite Valley. Many of these functions would move to the El Portal Administrative Site on the western boundary of the park. The plan establishes locations for the placement of parking areas, both within and outside of Yosemite Valley. Attachment A of this Statement of Findings lists the nonexempted actions in the floodplain that are proposed in the Final Yosemite Valley Plan/SEIS.
Existing Structures in the Floodplain
The NPS Floodplain Management Guideline (1993) divides actions into the following three groups:
· Class I actions – include administrative, residential, warehouse and maintenance buildings, and nonexempted (overnight) parking lots
· Class II actions – those that would create “an added disastrous dimension to the flood event.” Class II actions include schools, clinics, emergency services, fuel storage facilities, large sewage treatment plants, and structures such as museums that store irreplaceable records and artifacts.
· Class III actions – Class I or Class II actions that are located in high hazard areas such as those subject to flash flooding.
The regulatory floodplain for Class I actions is the 100-year floodplain. The regulatory floodplain for Class II Actions is the 500-year floodplain. There are no Class III actions in the project area.
Most existing structures in the regulatory floodplain in Yosemite Valley are Class I actions. Structures in the regulatory floodplain include five motel units at Yosemite Lodge, the human-built rock-rubble pile at the base of Yosemite Falls, the Concessioner Headquarters building at Yosemite Village, Indian Creek employee housing, three Ahwahnee Row houses, 248 units at Housekeeping Camp, the historic Superintendent’s House (Residence 1), and the concessioner stable (see Attachment A).
Under the proposed action in the Final Yosemite Valley Plan/SEIS, the following structures would be removed from the regulatory floodplain: five motel units at Yosemite Lodge, the human-built rock-rubble pile at the base of Yosemite Falls, the historic Superintendent’s House (Residence 1), and the concessioner stable. The Concession Headquarters building and the Indian Creek employee housing area would be redeveloped as parking and visitor services. The three Ahwahnee Row houses in the regulatory floodplain would remain and be mitigated by actions such as raising the finished flood elevation of the houses above the floodplain. The precise mitigation for the Ahwahnee Row houses would be developed as part of subsequent site design for the Yosemite Village area.
Housekeeping Camp has 264 total lodging units; 248 units are in the regulatory floodplain and 16 units are outside the floodplain. Under the proposed action in the Final Yosemite Valley Plan/SEIS, 164 Housekeeping units would be removed from the regulatory floodplain and 84 units would remain in the floodplain. There would be 100 total lodging units retained at Housekeeping Camp, though 16 of these units would not be in the floodplain.
The regulatory floodplain for the museum collection, a Class II action, is the 500-year floodplain. Under the proposed action in the Final Yosemite Valley Plan/SEIS, the museum collection would be housed in Yosemite Village in a facility adjacent to the existing visitor center’s West Auditorium. This location is outside of the 100-year floodplain.
The 500-year floodplain has not been delineated in the Yosemite Village area. The 500-year floodplain would be determined before specific site design is initiated. If the proposed location falls within the 500-year floodplain, the museum collection would be protected through design of the new facility. Specimens and artifacts would be stored off the floor in museum cabinets and on shelving and/or on the second floor of the facility, above the predicted 500-year flood level.
The Cascades Diversion Dam is located west of Pohono Bridge in Yosemite Valley. This dam was constructed in 1917 and 1918 as part of a small hydroelectric generating plant. Though the plant is no longer functional, the dam remains in place. Safety engineers have classified the dam as a “high hazard potential structure” which requires immediate corrective action. Under the proposed action in the Final Yosemite Valley Plan/SEIS, Cascades Diversion Dam would be removed.
Most existing structures that are found in the regulatory floodplain in El Portal are Class I actions. These structures include 86 beds at Hennessey’s Ranch (Trailer Village and Abbieville), the El Portal Hotel (used for employee housing and Yosemite Institute administrative headquarters), the El Portal Market, the Motor Inn (12 employee housing cabins), the National Park Service warehouse complex, and the ranger station. There are two existing Class II actions in the regulatory floodplain in El Portal: the gas station and the bulk fuel storage facility.
Under the proposed action in the Final Yosemite Valley Plan/SEIS, the bulk fuel storage facility would be removed from the regulatory floodplain in El Portal. Housing at Hennessey’s Ranch (Trailer Village and Abbieville) would be removed and replaced with permanent housing that would be protected by an expanded flood-protection levee and/or mitigated by appropriate housing design. The area that includes the El Portal Market, El Portal Hotel, Motor Inn, and ranger station would be redesigned to support community services and parking. The gas station would remain and its location would be re-evaluated as part of the site planning process for El Portal. The National Park Service warehouse complex would remain.
In Wawona, four Class I structures at the Pioneer Yosemite History Center are in the regulatory floodplain. These structures are the Jorgensen Studio, the Hodgdon Homestead Cabin, the acting superintendent’s headquarters, and the Yosemite Transportation Company Office. These structures would remain in place.
Proposed Actions
Under the Preferred Alternative in the Final Yosemite Valley Plan/SEIS, the following facilities would remain or could be placed in the regulatory floodplain in Yosemite Valley:
· Yosemite Lodge – A small portion of the development area designated for Yosemite Lodge, near the Wellness Center, is in the regulatory floodplain. If no practicable alternative site for overnight parking is identified within the Yosemite Lodge development area during subsequent site design, a small portion of new overnight parking would be constructed in the regulatory floodplain.
· Three Ahwahnee Row houses - All of the Ahwahnee Row houses would remain, three of which would exist within the regulatory floodplain. Potential flood-related impacts on the Ahwahnee Row houses would be mitigated through design adjustments such as raising the finished floor elevation out of the floodplain.
· Yosemite Village – The Concessioner Headquarters building and Indian Creek employee housing area would be redeveloped to accommodate a transit center with day-use parking and associated new visitor services.
· Housekeeping Camp - 84 units at would remain in the floodplain and 164 units would be removed from the floodplain (16 additional units would remain outside of the floodplain).
Under the Preferred Alternative in the Final Yosemite Valley Plan/SEIS, the following facilities would remain or could be placed in the regulatory floodplain in El Portal:
· Hennessey’s Ranch – Mobile homes and trailers would be removed from the site and replaced with permanent housing. This site would be protected with by an expanded flood-protection levee and/or mitigated by appropriate housing design.
· Village Center – This area has been designated for necessary support facilities, commercial services, and parking. Parts of this area are in the regulatory floodplain. The exact placement of new and replacement facilities would be determined in subsequent site design. New development could include a community center, post office, enlarged grocery store/deli, laundry, recreation facilities, hair salon, medical clinic, and office spaces.
· The National Park Service warehouse complex at Railroad Flat would remain. A new two-story building (approximately 8,500 square feet) would be constructed adjacent to the existing warehouse complex to house National Park Service Resource Management staff.
· The gas station would remain in El Portal. The location of the gas station would be reevaluated as part of future site planning in El Portal.
In Wawona, parts of the Pioneer Yosemite History Center would remain in the regulatory floodplain.
General Characteristics of Flooding in the Area
Flooding on the Merced River consists of two general types: those that occur during the late fall and winter (November through March) primarily as the result of intense warm rainfall on an existing snowpack, and those that occur during the spring and early summer resulting from unusually rapid annual snowmelt. At the beginning of the wet season the ground is extremely dry, and about 3 to 5 inches of precipitation is required to satisfy the retention storage capacity of the soil before any significant runoff occurs. Later in the season, when the ground may be very wet and there may be a moderate snow cover at the higher elevations, heavy rainfall over the basin causes large flood runoff. An intense warm storm with a high freezing level may result in flood runoff from almost the entire basin, with as much as 2 inches of snowmelt augmenting the rainfall. Most of the runoff from the Merced River basin occurs from November through July.
The Merced River in Yosemite Valley has a well-developed, relatively wide floodplain that is confined by steep valley walls. In the middle reach of the Merced River in Yosemite Valley, between Clark’s Bridge and the El Capitan moraine, the river flows through a shallow channel approximately 100 to 300 feet wide. Typically, the main channel in this reach has the capacity to convey 2- and 5-year flow events within the existing channel banks (Stantec 2000). Historic discharge in the river, measured at the Pohono Bridge gauging station, has ranged from a high of about 25,000 cubic feet per second to a low of less than 10 cubic feet per second. At Pohono Bridge, the mean daily discharge rate is about 600 cubic feet per second.
In the middle reach of Yosemite Valley (between Clark’s Bridge and the El Capitan moraine), the Merced River meanders across a broad floodplain and through a series of bends and divides. During 25- and 100-year floods, waters substantially overflow the meandering channel path and flow straight down the Valley (Stantec 2000). Near Yosemite Lodge and downstream to the El Capitan moraine, flood waters back up against the moraine and tend to be deep and slow. This backwater influence, which reduces flow velocities and increases flow depths, can extend up to 4.5 miles upstream of the El Capitan moraine past Sentinel Bridge (Stantec 2000). Flow velocities in this backwater area for 2- and 10-year events are actually higher than for 25- and 100-year events in both channel and overbank areas due to the backwater influence (Stantec 2000).
The river channel in El Portal is steeper. Consequently, flow velocities are high. With increased velocity, lateral shifting of the channel can occur during large floods. The levees at the east edge of Hennessey’s Ranch (Trailer Village and Abbieville) and near Village Center prevented water from entering the site during the 1997 flood, though there is the potential for overtopping during larger events.
In Wawona, the floodplain is situated in an elongated alluvial valley. The gradient of the South Fork Merced River in Wawona is steeper than the Merced River in Yosemite Valley, and the velocity of runoff is greater during flood events. Therefore, the South Fork Merced River in Wawona is more likely to shift laterally during large floods, than the Merced River in Yosemite Valley.
In Wawona, upstream of the Big Creek confluence, the average annual flow was 174 cubic feet per second between 1958 and 1968, as measured at the Wawona gauging station, with an estimated maximum flow of 15,000 cubic feet per second in December 1955.
Justification for Use of the Floodplain
New Development
Yosemite Lodge. The Yosemite Lodge area is constrained by natural boundaries as well as by development boundaries such as Camp Four (Sunnyside Campground) and the Merced River. These boundaries limit the possibility of non-floodplain sites for Lodge facilities. A small portion of the Yosemite Lodge development area identified in the Final Yosemite Valley Plan/SEIS, near the Wellness Center, is in the regulatory floodplain. If no practicable alternative site for overnight parking is identified within the Yosemite Lodge development area during subsequent site design, a small portion of new overnight parking would be constructed in the regulatory floodplain.
Floods of consequence in Yosemite Valley have occurred with advance warning, in that it takes a prolonged period of intense rain for at least 24 hours to create flood conditions. In high flood conditions similar to those of the January 1997 flood, there would be slow water movement in the potential parking area. Early warning and evacuation can mitigate risks to humans and property in the Yosemite Lodge area.
The small parking lot within the regulatory floodplain would have a minimal effect on flood characteristics during high water levels. The new parking area would prevent the re-establishment of floodplain-related natural communities that would likely be riparian areas. If the natural communities were in place, flood velocities would be slightly slower. The National Park Service would, to the greatest extent possible, locate the parking lot outside of the regulatory floodplain.
The Yosemite Museum Collection. Under the proposed action in the Final Yosemite Valley Plan/SEIS, the museum collection would remain in Yosemite Village in proximity to museum exhibit space. This would allow staff to easily move collection objects to and from exhibit space, allow users of the research library to easily access the collection, and protect the collection from risks involved with transfer to another location.
Some parts of the Native American collection are strongly associated with Yosemite Valley. These articles have a higher intrinsic value to American Indian and other groups when stored in the Valley.
The museum collection would be housed in Yosemite Village in a facility adjacent to the existing visitor center’s West Auditorium. The 500-year floodplain would be delineated in this area. If the proposed location falls within the 500-year floodplain, the museum collection would be protected through design of the new facility. Specimens and artifacts would be stored off the floor in museum cabinets and on shelving and/or on the second floor of the facility, above the predicted 500-year flood level.
El Portal. In 1958, Congress designated El Portal as an Administrative Site for Yosemite National Park in order that “utilities, facilities, and services required in the operation and administration of Yosemite National Park may be located on such site outside the park.” Under the Final Yosemite Valley Plan/SEIS, many administrative and operational facilities would be removed from the floodplain in Yosemite Valley and relocated to El Portal. The El Portal Administrative Site would become the principal location for National Park Service and concessioner employee housing, National Park Service and concession headquarters, other administrative facilities that are needed for the operation of Yosemite National Park, and community support facilities. Community support facilities could include a community center, post office, enlarged grocery store/deli, laundry, recreation facilities, hair salon, and a gas station.
The El Portal Administrative Site lies at the bottom of a steep river canyon. Therefore, the amount of suitable building space is limited due to limits imposed by the steep terrain, natural resources, and cultural resources. The National Park Service evaluated all potential building sites in El Portal and identified eight sites that could accommodate new development: Hennessey’s Ranch, Hillside West, Hillside East, Village Center, Rancheria Flat, Old El Portal, undeveloped areas at Railroad Flat, and Riverside. In order to accommodate the actions proposed in the Final Yosemite Valley Plan/SEIS, each of these sites (except Riverside) would be needed for various levels of development to achieve the goals of the Final Yosemite Valley Plan/SEIS. The Final Yosemite Valley Plan/SEIS also determined that retaining all housing in Yosemite Valley or moving housing to Foresta were not practicable alternatives because these options did not meet National Park Service goals and/or were not feasible.
The Riverside site was removed from consideration for development for the following reasons: the site contains significant cultural resources; a bridge would need to be constructed across the Merced River to access the site; evacuation would be limited to a single access road (the bridge) during a flood; the site is subject to river erosion; potential impacts to special-status species could occur; and the site contains high-quality wildlife habitat.
A new two-story building (approximately 8,500 square feet) would be constructed adjacent to the existing warehouse complex at Railroad Flat to house National Park Service Resource Management staff. Resource Management staff have been divided among temporary office spaces in Yosemite Valley and El Portal since the flood of 1997 when their previous office, the Superintendent’s House (Residence 1) was flooded. The new site was selected to consolidate Resource Management staff outside Yosemite Valley in a permanent location with easy access to other National Park Service staff. The site is level, previously disturbed, adequately sized, has utility access, and adjacent land uses are similar. The new Resources Management building would be sited to minimize encroachment into the regulatory floodplain. The building would be elevated with a finished floor above the 100-year floodplain.
Existing Development
Ahwahnee Row Houses (three houses in floodplain). These houses would not be removed because there is a considerable need for single-family housing in Yosemite Valley and the houses are important contributing elements to the Yosemite Valley cultural landscape. Potential flood-related impacts on the Ahwahnee Row houses would be mitigated through design adjustments such as raising the finished floor elevation out of the floodplain.
Housekeeping Camp. Currently, 248 units at Housekeeping Camp are within the 100-year floodplain. These units are available seasonally, and the area is closed for overnight use in the winter. In the Final Yosemite Valley Plan/SEIS, 84 units at Housekeeping Camp would remain in the floodplain along with six miscellaneous structures (such as restrooms and the store). The 164 units that are closest to the Merced River would be removed from the floodplain.
For many years, Housekeeping Camp has provided visitors with a rustic lodging experience in Yosemite Valley. Unique camping shelters equipped with bedding eliminate the need for visitors to purchase large amounts of camping equipment. Also, Housekeeping Camp is the only lodging available in the Valley where overnight visitors can cook their own food.
Housekeeping Camp is closed during the winter when most high-flow events have occurred. There would be sufficient time to evacuate visitors in the unlikely event that evacuation would be necessary. To preserve the floodplain values in areas near to the river while still preserving the unique visitor experience, the 164 units that are closest to the Merced River would be removed and 84 units would remain within the floodplain.
National Park Service Warehouse Complex at Railroad Flat in El Portal. When the first phases of this extensive warehouse/office complex were planned and constructed in 1994 and 1995, U.S. Army Corps of Engineers map data determined that most of the complex would be out of the floodplain. Though the warehouse complex was not affected by the 1997 flood, new information based on data from the January 1997 flood (USCOE 1998) has revised the 100-year floodplain boundary to indicate that most of the complex is in the 100-year floodplain. It is not practicable to relocate this large facility.
Floods of consequence in El Portal have occurred with advance warning, in that it takes a prolonged period of intense rain for at least 24 hours to create flood conditions. Risks to humans can typically be mitigated by warning and evacuation. Most offices in the warehouse complex are on the second floor, outside of the regulatory floodplain. Most of the vehicles and heavy equipment stored at the warehouse complex could be moved to higher ground in the event of a flood. In addition, the roadway and embankment have been reinforced since the flood of 1997 and a retaining wall was constructed around the south end of the facility. These features could keep floodwaters from entering the site.
Gas Station in El Portal. A strong need exists for a gas station in El Portal to serve local residents (numbering about 1,000 which include National Park Service, concessioner, and park partner employees) and park visitors. There are no gas stations in Yosemite Valley. The closest gas stations to El Portal are located in the community of Midpines (along Highway 140) and at Crane Flat (along the Big Oak Flat Road), both of which are a 30-minute drive from El Portal under good driving conditions.
The gas station in El Portal would remain, and its location would be re-evaluated during the site design process for El Portal. The gas station would comply with all state and federal standards.
Pioneer Yosemite History Center in Wawona. Parts of this interpretive site are located in the regulatory floodplain. Four buildings in the Pioneer Yosemite History Center are listed on the National Register of Historic Places (the Jorgensen Studio, the Hodgdon Homestead Cabin, the acting superintendent’s headquarters, and the Yosemite Transportation Company Office. Though these buildings are in the regulatory floodplain (100-year floodplain), past floods have had only minor impacts on these buildings. These buildings would be left in place and cleaned and repaired as necessary in the event of a flood. In addition, the structures are small and would have only a slight impact on flood flow characteristics during periods of high water.
Redevelopment
Visitor Services and Transit Center at Yosemite Village. Several areas in Yosemite Valley have been zoned to concentrate intensive visitor use in order to protect the renowned qualities of Yosemite Valley, while still providing services for the public. In the Preferred Alternative of the Final Yosemite Valley Plan/SEIS, Yosemite Village would serve as a parking area and transportation hub, as well as the site for a new visitor center. Placement of the visitor center near the transportation hub would allow visitors to easily access park orientation materials and information, as well as make transportation connections to other areas.
Parts of the Yosemite Village area fall within floodplain boundaries, particularly in the vicinity of the existing Concessioner Headquarters building. Visitor services and a transit center are proposed for redevelopment in this area. Site-specific design has not been completed, and the specific nonexempted actions that would fall within floodplain boundaries are not known. The National Park Service would, to greatest extent possible, locate as many non-exempt facilities outside the regulatory floodplain as possible. Should structures to support visitor services be proposed within the floodplain at this location, a subsequent Floodplain Statement of Findings would be developed as a part of future site planning.
Description of Flood Risk
Yosemite Valley
Floods of consequence in Yosemite Valley typically have occurred with advance warning, in that it takes a prolonged period of intense rain for at least 24 hours to create flood conditions. Risks to humans can typically be mitigated by warning and evacuation.
In Yosemite Valley, the character of flooding varies in different locations in response to site-specific hydrology. From Clark’s Bridge to Housekeeping Camp in the east Valley, the Merced River inundates areas outside the main river channel with shallow, swift flows that cut across meandering river bends. Near Yosemite Lodge and downstream to the El Capitan moraine, flood waters back up against the moraine and dense vegetation, resulting in lower velocity and significant depths. At Housekeeping Camp, velocities are relatively higher with lower depths.
The historic discharge in the river, measured at the Pohono Bridge gauging station, has 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 daily discharge rate is about 600 cubic feet per second.
El Portal
The El Portal area is located in an extremely high energy, narrow river canyon with little area that is outside the floodplain and suitable for development. Due to high flood velocities that occur at high flows, infrastructure and development must be located above flood levels or be massively armored.
Floods of consequence in El Portal typically have occurred with advance warning, in that it takes a prolonged period of intense rain for at least 24 hours to create flood conditions. Warning and evacuation can typically mitigate risks to humans. Evacuation of flood-prone areas should be mandatory during flood events of any appreciable size.
Wawona
Floods of consequence in Wawona typically have occurred with advance warning, in that it takes a prolonged period of intense rain for at least 24 hours to create flood conditions. Risks to humans can typically be mitigated by warning and evacuation.
Comparative Risks Among Alternatives Presented in the Final Yosemite Valley Plan/SEIS
The major differences in terms of the regulatory floodplain between the Preferred Alternative and the other action alternatives are as follows (See Attachment A):
· In Alternatives 3 and 4, Yosemite Village in the vicinity of Concession Headquarters and Indian Creek employee housing area would not be redeveloped for a transit center and visitor services.
· In Alternatives 3 and 4, more units (212 as opposed to 164) would be removed from the regulatory floodplain at Housekeeping Camp.
· In Alternatives 3, 4, and 5, the bulk fuel facility in El Portal would remain within the regulatory floodplain.
In the Preferred Alternative, the National Park Service would, to the greatest extent possible, try to locate as many nonexempt facilities outside the regulatory floodplain at Yosemite Village. Existing employee housing would be removed and replaced with nonovernight uses. These facilities are not within areas subject to frequent flooding, and with the early warning system and evacuation plan in place, the risk to human safety would be minimized.
Designs or Modifications to Minimize
Harm to Floodplain Values or Risks to Life and Property
All actions in the Yosemite Valley Plan would adhere to the mitigation measures described below. In addition, certain actions would require additional mitigation measures as detailed design plans are completed. The design of all new structures and facilities would incorporate the following methods for minimizing flood damage:
· Applicable existing and new structures and facilities will meet the terms and conditions of the National Flood Insurance Program “Floodplain Management Criteria for Flood-Prone Areas” (44 CFR, Section 60.3) and meet applicable local, county, or state requirements for flood-prone areas.
· Human health and safety will be protected by an active flood response plan. The flood evacuation plan developed during the January 1997 flood will be revised as necessary to reflect new actions in the Yosemite Valley Plan. The revised plan will detail notification and evacuation procedures, including the responsibilities of individual park employees for advanced preparedness. This plan will also outline procedures for removing or securing park property, records, and utility systems; procedures to facilitate emergency communication; procedures for conducting rescue and salvage operations; procedures for safe operations during the flood event; and procedures for post flood operations and clean-up.
· Impacts on natural and cultural resources would be minimized and mitigated by design of facilities. The design for impermeable areas would provide for appropriate drainage to ensure that natural resources are not further degraded by associated runoff following flood events.
A detailed Floodplain Statement of Findings would be developed as a part of future planning for the following areas as site-specific design is completed for:
· Parking and visitor services at Yosemite Village (if non-exempt structures are proposed within the regulatory floodplain)
· Overnight parking at Yosemite Lodge (if proposed within the regulatory floodplain)
· Village Center in El Portal, Hennessey’s Ranch (Trailer Village and Abbieville), (if nonexempt structures are proposed within the regulatory floodplain), and
· The National Park Service warehouse complex at Railroad Flat, as the location and design of the new Resources Management building and National Park Service functions and offices in the area are finalized.
Conclusion
The 1980 General Management Plan and the 2000 Merced River Plan/Final Environmental Impact Statement (FEIS) provide broad goals for the management of floodplain-related resources in Yosemite National Park. The General Management Plan sets forth goals for management of the park as a whole. The Merced River Plan/FEIS was developed to provide direction and guidance on compliance with the Wild and Scenic Rivers Act, and protection and enhancement of the outstandingly remarkable values identified for the Merced River. These plans guided the development of the alternatives evaluated in the Final Yosemite Valley Plan/SEIS. All of the action alternatives in the Yosemite Valley Plan/SEIS contain provisions to protect and restore the Merced River ecosystem. The Final Yosemite Valley Plan/SEIS directly conforms to the National Park Service Floodplain Management Guideline, particularly with respect to restoration and protection of natural floodplain values, risks to life and property, and design of structures to be consistent with the intent of the “Floodplain Management Criteria for Flood-Prone Areas” (44 CFR, Section 60.3).
The Preferred Alternative in the Final Yosemite Valley Plan/SEIS would have beneficial impacts on floodplain values by linking river-associated wetlands and meadows that have been degraded or fragmented into one large and dynamic, river-governed ecosystem. Facilities that would be removed from the regulatory floodplain in Yosemite Valley include five motel units at Yosemite Lodge, Indian Creek employee housing area, 164 units at Housekeeping Camp, the historic Superintendent’s House (Residence 1), and the concessioner stable. In El Portal, the bulk fuel storage facility would be removed from the regulatory floodplain.
The Preferred Alternative in the Final Yosemite Valley Plan/SEIS would substantially reduce potentially hazardous conditions associated with flooding by relocating many facilities out of the floodplain. However, the National Park Service has determined that in select locations there is no practicable alternative to a limited amount of new development, existing development, and redevelopment within the regulatory floodplain.
In El Portal, permanent employee housing would be developed at Hennessey’s Ranch (Trailer Village and Abbieville) within the regulatory floodplain. The National Park Service evaluated all potential building sites in El Portal and identified seven potential sites that could accommodate development. In order to achieve the goals of the General Management Plan and the Final Yosemite Valley Plan/SEIS, all of these sites (except one that was deemed unacceptable) would be needed for various types of development.
The Hennessey’s Ranch site (Trailer Village and Abbieville) is suitable for housing because it is relatively flat, is currently developed, and has two existing access routes from the adjacent highway. The new permanent housing at Hennessey’s Ranch (Trailer Village and Abbieville) would be protected with by an expanded flood-protection levee and/or mitigated by appropriate housing design. There are no additional sites in El Portal that would be suitable for this development due to the steep terrain of the area and natural and cultural resource constraints such as protected species habitat and American Indian burial sites.
A new two-story building would be constructed adjacent to the existing warehouse complex at Railroad Flat to house National Park Service Resource Management staff. The new site was selected to consolidate the division outside Yosemite Valley in a permanent location with easy access to other National Park Service staff. The site is level, previously disturbed, adequately sized, has utility access, and adjacent land uses are similar.
The museum collection would be housed in Yosemite Village in a facility adjacent to the existing visitor center’s West Auditorium. This location is outside of the 100-year floodplain. The 500-year floodplain has not been delineated in the Yosemite Village area. The 500-year floodplain would be determined before specific site design is initiated. If the proposed location falls within the 500-year floodplain, the museum collection would be protected through design of the new facility. Specimens and artifacts would be stored off the floor in museum cabinets and on shelving and/or on the second floor of the facility, above the predicted 500-year flood level.
It may be necessary to locate a small amount of overnight parking at Yosemite Lodge in the regulatory floodplain. Whether the site would be necessary would be determined as a part of future site-specific design processes.
The National Park Service has determined a need to retain the following existing structures within the regulatory floodplain: 84 units at Housekeeping Camp, three Ahwahnee Row houses, the warehouse complex in El Portal, the gas station in El Portal, and 4 buildings at the Pioneer Yosemite History Center in Wawona. At Housekeeping Camp, 164 units would be removed from the regulatory floodplain and 84 units within the floodplain would be retained to fill the need for the type of services that Housekeeping Camp provides to park visitors. The three Ahwahnee Row houses would be retained to fill the need for single-family housing in Yosemite Valley and because the houses are important contributing elements to the Yosemite Valley cultural landscape. Potential flood-related impacts on the Ahwahnee Row houses would be mitigated through design adjustments such as raising the finished floor elevation out of the floodplain. The warehouse complex in El Portal, the gas station in El Portal, and four buildings at the Pioneer Yosemite History Center in Wawona would remain in place and be repaired and cleaned as necessary in the event of a flood. The gas station would comply with all state and federal standards. Human life and safety would be protected through an active flood evacuation plan.
The National Park Service has determined a need to redevelop portions of Yosemite Village in Yosemite Valley and Village Center in El Portal that are within or have portions within the regulatory floodplain. Parts of the Yosemite Village area would be redeveloped to accommodate a new transit center with visitor services. Parts of the Village Center area would be redeveloped to accommodate support facilities and commercial services. These facilities are not within areas subject to frequent flooding, and with an early warning system and evacuation plan in place, the risk to human safety would be minimized. During site design, the National Park Service would, to the greatest extent possible, locate nonexempt facilities outside the regulatory floodplain.
The National Park Service concludes that the Preferred Alternative would reduce the impacts of potentially hazardous conditions associated with flooding in Yosemite Valley and El Portal, largely due to the removal of facilities in Yosemite Valley from the floodplain and removal of the bulk fuel storage facility in El Portal. Mitigation and compliance with regulations and policies to minimize impacts to water quality, floodplain values, and loss of property or human life would be strictly adhered to during and after construction. Individual permits with other federal and cooperating state and local agencies would be obtained before construction is undertaken. Overall, there would be a long-term, moderate, beneficial impact on floodplains. Therefore, the National Park Service finds the Preferred Alternative in the Final Yosemite Valley Plan/SEIS to be acceptable under Executive Order 11988 for the protection of floodplains.
References
Cella Barr Associates
1998 Hydrologic and Hydraulic Investigation for Proposed Campgrounds in Yosemite National Park, California. Prepared for the National Park Service.
Stantec Consulting, Inc.
2000 Draft Hydrologic and Hydraulic Analysis, Phase II, Yosemite National Park, CA. Prepared for the National Park Service.
1981 Flood Hazard Information, South Fork of the Merced River, Wawona.
1997 US Army Corps of Engineers, Sacramento District.
Merced River near Yosemite, California. Letter report.
1998 Merced River near Yosemite, California; Hydrology and Hydraulics Technical Reports. Sacramento District.
William L. Jackson, Smillie, Gary M., and Martin, Michael W.
1997 Analysis of the Hydrologic, Hydraulic and Geomorphic Attributes of the Yosemite Valley Flood: January 1-3, 1997. Technical Report NPS/NRWRD/NRTR-97/129. National Park Service, Water Resources Division. Fort Collins, Colorado.
U.S. Geological Survey (USGS), U.S. Department of the Interior
1992 Topographic maps: El Capitan. Half Dome.