Energizing Work: Corridor Mapping
As technology moves the US towards a smarter grid that relies on more energy sources and pushes their output over longer distances, the physical power infrastructure must keep pace with it. This means modernizing, upgrading, and building power lines and sub-stations that will handle the increased loads necessitated by increasing demand.
Continental Mapping has a long track record of supporting its energy and utility clients with surveying and mapping in corridor selection, design, construction and maintenance. Satellite-based mapping, aerial imagery and lidar, conventional survey, and now unmanned aerial systems (UAS) all play a role in the process depending on location and need. This article focuses on corridor mapping for two different energy clients.
American Transmission Company (ATC)
ATC provides electric transmission service from the Upper Peninsula of Michigan, throughout much of Wisconsin and into portions of Illinois. ATC owns and manages more than 9,500 miles of high-voltage transmission lines and 530 substations within the region. As demand for energy grows, so too must the power capacity of their transmission lines. An important goal of every ATC project is reducing impacts on existing land owners.
Continental Mapping has been providing mapping and GIS consulting services to ATC since 2003.
To meet growing needs and support better reliability in Fond Du Lac County, WI ATC decided to plan for a new 138,000-volt transmission line. ATC identified this growing region as one susceptible to low voltages and power outages. The new line would provide adequate redundancy to shut down other lines for essential maintenance without disrupting service.
The corridor consisted of 18 miles of land within Fond Du Lac County, WI located roughly 50 miles northwest of Milwaukee. Some existing 67KV transmission line infrastructure was in place in parts of the predominantly rural area. Windmills are a commonality in the project area, so energy produced in this corridor is part of a nationwide interest in harnessing renewable sources of power to feed ever increasing energy demand. Critical to the design was a current and accurate understanding of existing infrastructure.
Continental Mapping was asked to perform high accuracy mapping of the entire proposed corridor. New aerial photography was acquired that supported the development of a digital terrain model (DTM) capable of supporting 1’ contours, 1”=50’ scale planimetric mapping. and 3” pixel resolution color orthophotos.
Grant County, WA Public Utility District (Grant County PUD)
The Columbia River is powerful. A host of hydro-electric dams in Grant County, WA slow the mighty Columbia River to provide critical energy to the growing population in the Pacific Northwest. To meet increased local need, the Grant PUD required planning and design of a corridor to support the design and construction of a new, 35.5 mile 230kV line. The line was to be built on both newly acquired and existing right-of-way and intended to carry an increased energy load. The selected corridor included two supply routes into a population center, several river and canyon crossings, and ties to substations on both ends.
Grant County PUD required the width of the corridor to be 2000’ throughout the 35.5 mile stretch. Continental Mapping planned the flight and survey control. Airborne GPS (ABGPS) was utilized during the acquisition to minimize the need for ground control (49 pre-marks). That approach provided the support to achieve the required precision without requiring extensive field survey control. The approach also helped the project remain within budget, also a major public pressure point.
During the flight, Continental Mapping acquired 250 images at a scale of 1”=400’ in order to develop 1”=100’ planimetric mapping with a DTM that could support 2’ contours. That imagery was used to develop topographic mapping that included all visible features including: paved road edges, haul roads, drives, parking areas, buildings, visible utilities, poles, fences, signs, vegetation, hydrology, and miscellaneous features visible in the imagery. The DTM was collected with break lines and mass points necessary to describe the terrain and support the 2’ contour specification. The map accuracy exceeded the project’s goal — ASPRS Class 1 Map Accuracy Standards.
Digital orthorectified photos, geo-referenced to the ground control and supported by the DTM were developed at a ground sample distance (GSD) of 0.25’. The imagery covered the project site and extended beyond the project corridor width by 100’, providing a valuable backdrop for the topographic mapping.
When the mapping was completed and the associated boundary surveys and field verification of the mapping were done, the Grant County PUD had the tools needed to plan for the location and construction of the towers for the transmission line.
