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Home arrow Archives   The American Surveyor     

Towers of Power - Surveyors Trek the Central Plains to Locate Next Generation Transmission Lines Print E-mail
Written by Vicki Speed   
Tuesday, 29 July 2008

A 3.231Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

As originally planned, the Eastern Plains Transmission Project, one of the country's largest power expansion projects in progress, is expected to ultimately deliver about 1,000 miles of much-needed new high-voltage transmission lines and related facilities in eastern Colorado and western Kansas.

Proposed by Tri-State Generation and Transmission Association (Tri-State) and the Rocky Mountain Region of Western Area Power Administration (Western), two major power suppliers in the region, this expanded network is crucial to meeting increasing demand and enhancing reliability of the existing power delivery system.

Much of the project is in the hands of a group of surveyors that must walk, ride or fly the entire 1,000-plus miles of plains and prairie­multiple times. Using a range of tools for the job­ from ATVs and hiking boots to GPS and LiDAR­an innovative and energetic group of surveyors has pulled out all the stops to move this job forward with safety, quality and speed.

The Path of Power
The proposed transmission expansion project plans call for new transmission lines­14 in all­to ultimately cross 15 counties in eastern Colorado and six counties in western Kansas, thereby connecting eight existing substations and four new substations.

Since project inception, Western and Tri-State have completed conceptual corridor studies and started early engineering design. The studies identified preliminary corridor alignments for each proposed transmission line.

Western is preparing an extensive environmental impact statement for the project. In 2006, the public weighed in on the line locations and other issues, offering comments and concerns. From the comments and engineering and environmental evaluations, new alignments were created and other alignments removed from consideration. The refined individual alignments were combined to create a set of alternative routes for each transmission line.

Ultimately, Western and Tri-State developed as many as four alternative routes for each of the 14 proposed transmission lines during this early study phase. Through the environmental impact statement process, the alternative routes will be refined further, and ultimately, a single route will be determined for each transmission line.

Early on in the process, Western and Tri-State called in Ayres Associates, a nationwide survey/mapping and engineering consulting firm, to lead a team of professionals in the aerial and ground reconnaissance data gathering phase of the project. The overall route survey effort will ultimately help the owners validate and refine the proposed corridors and locate the actual powerline poles­all in just two years.

Prairie Possibilities
At first glance, two years to survey 1,000 miles of network may seem like plenty of time. Photogrammetry and LiDAR held promise to make this job a bit easier by providing the client the additional information necessary to revise proposed routes as needed based on environmental concerns, engineering demands or public requests.

However, photogrammetry and LiDAR require a sound ground-based reference network­a network that is near non-existent on the Colorado and Kansas plains. In preparation for mapping, Ayres Associates' surveyors first looked to establish a reference network tied to existing or newly positioned high accuracy reference network (HARN) monuments.

A team of six Ayres Associates surveyors took to the highways that span the network, marking 33 pre-located points using the Leica System GPS1200 base stations and rovers. The team of surveyors set additional static positions at 6-mile intervals.

Surveyors noted that while there are no reference stations on the plains, there also is little tree cover. GPS works well. Crews completed the initial reference network using static four-hour sessions. The existing control network stayed almost exclusively on the public roadway.

However, as work progressed, crews had to have access to the entire route, and about 80 percent of it fell on private property. Access to some sites was limited to foot traffic because of crops, rough terrain, and environmental and historically-sensitive areas. At those times, the survey team used RTK GPS with the base stations set on the 6-mile control points to establish additional points at 3-mile intervals along the proposed route right-of-way.

Once the control network was complete, Ayres Associates dispatched aerial photography and LiDAR missions. Both missions used airborne GPS tied to the newly formed control network. The aerial photography was flown to produce 1"=250' negative scale imagery, which will provide optimum clarity to the subsequent orthophotography. LiDAR was obtained to provide a 2-foot contour over the entire corridor. The aerial photography and LiDAR will be used to develop detailed 1-foot contours on the transmission tower site to allow the designers to calculate leg extensions.

By March 2007, Western and Tri-State had further defined the 14 transmission line routes and were ready to begin gathering data to support engineering detailed design.

In a project with this level of detail, even the best aerial imaging will not eliminate the need for work in the field. Ayres Associates surveyors set out to gather facility locations and miscellaneous features not discernible on the aerial images or LiDAR data. This required a detailed plan to walk, drive or ride across all 1,000 miles­again.

Regimented Routine
To keep the project on track and moving quickly, Ayres Associates standardized its equipment and trained surveyors in specific data gathering aspects.

At any one time, one crew might be gathering section controls while another is working on facility locations. Crews worked seven days a week for three weeks, followed by one week off. Staff members average about 70 to 75 hours a week.

Ayres Associates sends out seven two-person crews into the field in trucks that are equipped with laptops with a Wi-Fi connection as well as a Leica SmartStation and SmartRover. After setting up the base station, the crew splits. One crew member works his or her way up the route using a 4x4 survey truck. The other crew member works down the route using an ATV as transportation. After the crew members reach the maximum range of their rovers (about 6 miles), they each meet back at the base station and then leap frog the base station ahead 12 miles.

At the end of each day, the crews link up to a file transfer site and send the data to the Limon, Colorado, project office for post-processing, where it is cleaned and uploaded to design software. Currently, the facility survey effort is about 40 percent complete.

Weather Woes
While the survey team members knew at the onset of the project that the geographic makeup of eastern Colorado and western Kansas is predominantly vast and remote prairie lands with few major roadways, they also found it hosts some uniquely challenging weather conditions.

From experiencing the find-cover-fast thunderstorms to the surprisingly common golf ball-size hailstorms, surveyors quickly learned firsthand proper safety measures during storms, particularly tornadoes. During one ice storm, survey crews discovered that it takes about a quarter-inch of ice on the GPS antennae before the equipment shuts down.

Ayres Associates crews from offices across the country were called in for the project and not all were accustomed to the dangers the varying weather posed. A crew from Arizona learned very quickly that standing in front of a window to watch an approaching tornado is extremely dangerous.

In one instance, a tornado went through the town of Holly, Colorado. Two of Ayres Associates' survey crews were in a hotel just 16 miles from Holly that night.

The project served to remind all crew members of the need to respect the power of Mother Nature, the importance of good safety training, and the value of speedy and accurate tools, especially GPS. To date, crews have been over all 1,000 miles of the proposed network at least once. They'll be going back to each route to gather more details, as the client refines the final routes.

Ayres Associates is contracted to finish the preliminary data gathering phase by late 2008 and then begin the construction staking portion of the project to locate the 5,000-plus towers that are spaced approximately 1,100 feet on center.

Vicki Speed is a freelance writer specializing in the architecture, engineering, surveying and construction industry. 

A 3.231Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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