Wawona, Turtleback Dome and Hetch Hetchy Installation of Global Positioning Systems

Yosemite National Park » Wawona, Turtleback Dome and Hetch Hetchy Installation of Global Positioning Systems » Document List

This project proposes to install three Global Positioning System (GPS) monuments and one co-located satellite-based repeater in Yosemite National Park. The purpose of these installations is to document geologic processes (e.g., plate movements associated with earthquakes and tectonics). The Plate Boundary Observatory (PBO) is a geodetic observatory designed to study crustal deformation between the Pacific and North American Plates. The proposed GPS monuments in Yosemite are part of a large grid of installations incorporating most of the western United States. The GPS monuments would be installed at three sites: 1) a helipad north of Wawona (retained for emergency purposes only), 2) at Turtleback Dome, and 3) off the Hetch Hetchy Road south of "Poopenaut Pass". All three proposed sites are within 200 feet of paved roads, and are therefore not in designated wilderness. Because the intent of this project is to record plate movements, which are relatively small and occur over long timescales, the three GPS monuments and one satellite repeater would need to be in place for at least 10 years, and should be considered permanent or long-term installations.

A typical GPS monument requires approximately 28 square m (300 square ft or .007 ac) for the GPS monument, equipment enclosures, power systems (solar panels), and data communications (see supporting materials). The above ground component would include an enclosure box with the GPS instrument, the GPS monument and antenna, and solar panels. These GPS monuments must be installed in bedrock. Approximately 6 foot-deep holes would be hand-drilled in bedrock using a hand held rotary drill. No drilling fluids would be used, and all rock debris generated by drilling would be stored for eventual site restoration. A center hole and 3 or 4 perimeter holes would be drilled at ~55 degree angles such that stainless steel rods inserted in the holes meet to form a tripod/quadpod monument. The legs of the monument would extend approximately 6 feet
into the earth and be epoxied into place. A leveling adapter, geodetic grade GPS antenna and radome (16" diameter) would be attached to the threaded top of the vertical leg. The entire above ground assembly would be approximately 5-feet high and have a footprint approximately 5-feet in diameter. The GPS station would also consist of a mast-mounted equipment enclosure and solar panels, which would be located within 30-feet of the monument. In the 25" x 20" x 34" enclosure would be the GPS receiver, radio transceiver, solar power regulator, and battery backup. An antenna cable would be placed in
trenched PVC conduit between the monument and the enclosure. All equipment entering the park would be cleaned and sterilized. Installation time is ~1-2 days for each site. The proposed satellite repeater would be co-located with a GPS monument site on Turtleback Dome. The satellite repeater would be mounted on the mast that holds the enclosure box (if no solar panels are used), on its own mast (if solar panels are needed), or it can be mounted on a nearby building or tower. PBO requests the use of AC power at the Turtleback site; if granted, PBO would not install solar panels, thus reducing visual impact at the site. PBO researchers and RMS staff (Park Geologist) have worked closely with Historic Architecture and Landscape personnel, archeologists, and tribe members to select the most appropriate sites for the GPS monument. NPS Wawona Fire personnel were involved in selecting a suitable site at the Wawona helipad. PBO researchers have identified ways to camoflauge the instruments, particularly at the Hetch Hetchy site, to reduce visual impact.