Sierra Pacific Power, Alturas Transmission Line

Northern CA

As part of Sierra Pacific Power Company’s $159M construction project for 265 miles of the 345 KV Alturas transmission line, ANDREGG was tasked with Environmental Staking of approximately 70 miles of the primary centerline route from Madeline, California to Wendel, California through the intertie at Ravendale, California. In addition, secondary alternate routes were staked as the project progressed.

The Alturas line requirements were to stake the line for environmental and archeological study of the proposed primary route and secondary alternate routes. The work required centerline staking with spike, lath and flagging at intervisible stations, not to exceed 500 feet spacing.  The work was completed using Real Time Kinematic GPS surveying technique in order to achieve less than 0.25-foot horizontal and vertical accuracy. Each stake was marked and recorded for the line’s engineering stationing as well as its UTM horizontal coordinate position and the NGVD 29 elevation. This precise survey was utilized to help the engineering analysis of the line’s ground profile and of the proposed tower locations.

One of the challenges of this project was that most of the line was inaccessible by vehicle either due to rough terrain or environmental or archeological sensitivity. This meant that 90% of the line had to be accessed and staked on foot, carrying stakes and equipment along the way.

Another challenge was due to the precise nature of the survey, GPS broadcast reference base stations had to be set up in order to transmit precise corrections to the rover units involved in staking the line. For longest range, every attempt was made to set base stations up on high points, hills and/or mountains. These also had to be accessed by foot most of the time. To further complicate the project, the environmental staking had to be completed in one environmental season, beginning late winter. To alleviate some of the access issues and to expedite the aggressive schedule toward the end of the season, ANDREGG employed the use of a helicopter for a few hours a day. The helicopter was utilized to fly along the route dropping lath and supplies at key locations and to set up GPS base stations on high hills and mountains. This helped with the mobilization of crews and equipment at remote areas along the route.