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Floodplain Statement of Findings for the Curry Village and East Yosemite Valley Campground Improvements Project
The National Park Service recently prepared the Yosemite Valley Plan to provide for managing natural and cultural resources, park facilities, and visitor experiences in the Valley. Implementation of actions presented in the Yosemite Valley Plan will further the park's goals of restoring, protecting, and enhancing the resources of the Yosemite Valley; providing opportunities for high-quality, resource-based visitor experiences; reducing traffic congestion; and providing effective park operations to meet the park's mission. Many of the over 250 actions will result in restoration of developed and disturbed areas to natural conditions, redevelopment of some areas, and development of other areas to accommodate visitor and employee services. During development of the Yosemite Valley Plan, the need to remove utility infrastructure from environmentally sensitive areas and to consolidate utilities into environmentally preferable areas was identified. The National Park Service has designed the Curry Village and East Yosemite Valley Campground Improvements Project to provide detailed location, program, and design criteria for the Yosemite Valley Plan– approved actions in Curry Village and the east Yosemite Valley campground areas facilities within Yosemite Valley . The need for the project, as identified in the Yosemite Valley Plan , developed over time due to increased visitor use and the resulting impacts to Curry Village and the campgrounds as well as to visitor demand for expanded or additional facilities. In addition, the 1997 flood damaged several areas and facilities within the project area, resulting in a need for upgrades to these facilities. A goal of the Yosemite Valley Plan is to increase the overall number and the quality of campsites, while removing sites from the Merced River floodplain and avoiding rockfall zones. The Curry Village and East Yosemite Valley Improvements Project would provide the required design documentation to enable implementation of conceptual improvements identified in the Yosemite Valley Plan. The goals of the project reflect the goals of the Yosemite Valley Plan , which are to: • Restore, protect, and enhance the resources of Yosemite Valley • Provide opportunities for high-quality, resource-based visitor experiences • Reduce traffic congestion • Provide effective park operation, including employee housing, to meet the mission of the National Park Service The purpose of this Floodplain Statement of Findings is to review the Curry Village and East Yosemite Campground Improvements Project 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 alternative sites • 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 . Yosemite Valley has a well-developed floodplain, with major roads and structures along or within both sides of the floodplain. The character of the floodplain varies in different locations because of local hydraulic controls. The 100 -year floodplain is typically used to define the general floodplain boundary. The Merced River watershed has had 11 winter floods since 1916 caused by warm winter rains falling on snow and partially melting the accumulated snowpack. The January 1997 flood was the largest recorded within the park; it was estimated to have a recurrence interval of 90 years (NPS 1997 c). The extent of the area affected by this event is shown on Figure F- 1 , and is used as a proxy for the 100 -year floodplain in this analysis. The flood inundated roads, picnic areas, park offices, and lodging units. The U.S. Geological Survey estimated that the flood had a peak discharge of 10 , 000 cubic feet per second at Happy Isles and 25 , 000 cubic feet per second at Pohono Bridge ( Eagan 1998 ). Curry Village and South Camp were not within the flood extent, while portions of the proposed amphitheater site, 31 drive-in campsites in Upper Pines Campground, and 125 drive-in campsites in Lower Pines Campground were within the flood extent. As currently operated, 29 drive-in campsites in Lower Pines and 31 drive-in campsites in Upper Pines are within the 1997 flood extent. The floodplain of the Merced River is well-developed in some sections, such as in meadow areas in Yosemite Valley . In other areas, the floodplain is lacking due to narrowing canyon/valley walls, which occurs in west Yosemite Valley . From Clark 's Bridge to Housekeeping Camp in the east Valley, the Merced River floods areas outside the main river channel with shallow, swift flows that cut across meander bends. Farther downstream of Housekeeping Camp to the El Capitan moraine (to the west of the project area), the floodplain becomes broader and well developed. In that area, flood water energy is dissipated as it spreads out over the flatter and more expansive plain. Stoneman Meadow, which lies between Lower Pines Campground and Curry Village , is located within the floodplain and is maintained and rejuvenated by periodic flood waters. The Curry Village and East Yosemite Valley Improvements Project would provide the detailed location, program, and design criteria for the Yosemite Valley Plan– approved actions in Curry Village and the east Yosemite Valley campground areas within Yosemite Valley . All new development occurs within the approved zones identified by the Yosemite Valley Plan . The need for the project, as identified in the Yosemite Valley Plan , developed over time due to increased visitor use and the resulting impacts to Curry Village and the campgrounds as well as to visitor demand for expanded or additional facilities. In addition, the 1997 flood damaged several areas and facilities within the project area, resulting in a need for upgrades to these facilities. A goal of the Yosemite Valley Plan is to increase the overall number and the quality of campsites, while removing sites from the Merced River floodplain and avoiding rockfall zones. Proposed 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. All of the actions proposed under the Curry Village and East Yosemite Valley Campground Improvements Project are considered Class I actions. The regulatory floodplain for Class I actions is the 100 -year floodplain. The project would upgrade existing facilities and increase the number of campsites in the area to serve the increased visitor demand. The number of cabins-with-bath in Curry Village would also be increased. The project would implement the River Protection Overlay, as identified in the Yosemite Valley Plan. Both action alternatives would improve visitor safety by removing existing campsites in Lower Pines currently located in the floodplain and the River Protection Overlay, and would allow for the future ecological restoration of the vegetation along the Merced River. None of the proposed project features would be located within the River Protection Overlay. None of the proposed Curry Village cabins-with-baths or building improvements are within the 100 -year floodplain. This project would result in a total of 415 operating campgrounds in the Upper Pines, Lower Pines, and South Camp areas, as compared to 318 campsites currently operated in these areas. Lower Pines campground would be redeveloped to eliminate the 29 currently operated sites within the 1997 flood extent while reducing the total number of operational sites from 78 to 60 , all of which would be outside the 1997 flood extent. In Upper Pines, a new drive-in loop would be added with 30 sites outside the 1997 flood extent. Overall, this project would reduce the number of drive-in campsites within the 1997 flood extent by 29 , while adding a total of 12 more drive in campsites in the Upper Pines and Lower Pines area. The proposed action also includes 45 to 59 walk-in sites to be added within an area designated in the Yosemite Valley Plan that is within the 1997 flood extent. Other proposed project features within the floodplain include an amphitheater and associated restroom at the site of a parking lot associated with existing stable facilities. General Characteristics of Flooding in the Area Floods on the Merced River are of two general types: those that occur during the late fall and winter (November through March) primarily as the result of intense rainfall, and those that occur during the spring and early summer resulting from 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 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. Yosemite Valley has a well-developed, relatively wide floodplain that is confined by steep valley walls. The Merced River in Yosemite Valley has a relatively mild slope, with an average of 0 . 1 %. In the middle reach of the Merced River in Yosemite Valley , downstream of Clark 's Bridge to 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 between 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. The mean daily discharge rate is about 600 cubic feet per second. Justification for Use of the Floodplain Yosemite Valley is the most visited area in Yosemite National Park and the Merced River is a major attraction in the Valley. The Yosemite Valley Plan provides a framework for managing natural and cultural resources, park facilities, and visitor experiences in the Valley. The project proposes improvements within Yosemite Valley that are designed to efficiently serve the areas identified for redevelopment and new development under the Yosemite Valley Plan , while minimizing impacts on highly valued natural and cultural resources. The Curry Village and East Yosemite Valley Improvements Project provides for the development of visitor facilities primarily located in environmentally preferable areas and results in a net increase in the total number of campsites in the project area to offset the removal of campsites in other parts of Yosemite Valley located within the floodplain and other environmentally sensitive areas. Proposed project features located within the floodplain were identified in the Yosemite Valley Plan, and are considered necessary to accommodate planned restoration of environmentally sensitive areas while maintaining an appropriate level of camping and visitor serving facilities within Yosemite Valley . Description of Site-Specific Flood Risk The Merced River watershed has had 11 winter floods since 1916 caused by warm winter rains falling on snow and partially melting the accumulated snowpack. The January 1997 flood was the largest recorded within the park; it was estimated to have a recurrence interval of 90 years (NPS 1997 c). The flood inundated roads, picnic areas, park offices, and lodging units. The U.S. Geological Survey estimated that the flood had a peak discharge of 10 , 000 cubic feet per second at Happy Isles and 25 , 000 cubic feet per second at Pohono Bridge ( Eagan 1998 ). Curry Village and South Camp were not within the flood extent, while portions of the amphitheater, Upper Pines Campground, and Lower Pines Campground were between 23 and 70 % flooded. The extent of this event is shown on Figure F- 1 . This project would result in a total of 415 operating campgrounds in the Upper Pines, Lower Pines, and South Camp areas, as compared to 318 campsites currently operated in these areas. All of the new drive-in campsites would be outside the 1997 flood extent, and 29 currently operating drive-in sites within this area would be eliminated. This proposal also includes the development of 45 to 59 new walk-in sites in Upper Pines that are within the 1997 flood extent, all in an area specifically designated for this use in the Yosemite Valley Plan. It should be noted that walk-in campsites are limited to four persons per site, and drive-in sites allow up to six persons per site. As a result, the proposed action represents only a minor increase in the number of campers potentially exposed to flood hazard while adding a total of 97 additional campsites. Risks to campers associated with floods are also mitigated by the closure of these camping areas during periods of highest flood risk. Design or Modifications to Minimize Harm to Floodplain Values or Risks to Life and Property Actions occurring within the floodplain would be subject to the provisions of the National Park Service Floodplain Management Guideline (NPS 1993 a) and Executive Order 11988 (Protection of Floodplains). The following mitigation measures would be applied to protect facilities within the floodplain: • Incorporate methods for minimizing flood damage into the design of all new structures, as contained in the National Flood Insurance Program Floodplain Management Criteria for Flood-Prone Areas (Code of Federal Regulations 44 : 60 . 3 ) and in accordance with any local, county, or state requirements for flood-prone areas. The area along the river corridor that would receive flood waters during a 100 -year flood event. A 100 -year flood event is one that has a 1 % chance of occurring in any given year. In the year following a 100 -year event, there is the same probability ( 1 %) that a 100 -year flood will occur. • Scenic qualities of the floodplain area would be enhanced by the removal of drive-in campsites currently located in the floodplain area. New walk-in sites in the floodplain are expected to have less visual impact on the floodplain than would a comparable number of drive-in sites. The proposed action would reduce potentially hazardous conditions associated with flooding by reducing the number of campsites within the floodplain in Yosemite Valley . In addition, it would allow for the future ecological restoration of the vegetation along the Merced River . The National Park Service concludes that the proposed action would reduce the impacts of potentially hazardous conditions associated with flooding in Yosemite Valley . Mitigation and compliance with regulations and policies to prevent impacts to water quality, floodplain values, and loss of property or human life would be strictly adhered to during and after the construction. Individual permits with other federal and cooperating state and local agencies would be obtained prior to construction activities. No long-term adverse impacts would occur from the proposed actions. Therefore, the National Park Service finds the proposed action to be acceptable under Executive Order 11988 for the protection of floodplains.
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| Finding of No Significant Impact (main) - Letter from the Superintendent - Finding of No Significant Impact (table of contents) - Finding of No Significant Impact (document) - Wetland Statement of Findings - Floodplain Statement of Findings - Environmental Assessment Errata and Response to Substantive Comments |
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