From the breakup of a major fully integrated utility emerged North America's first stand-alone electric transmission utility in 2002. AltaLink, located in the province of Alberta, Canada, owns and operates approximately 11,800 km (7332 miles) of line and equipment at more than 300 substations covering more than 207,000 sq km (79,923 sq miles).

A harsh western Canadian climate, aging facilities and increased demand on the system resulting from load growth all present significant challenges to maintaining safe and reliable transmission service to more than 85% of Alberta's population. As a newly formed electric transmission utility, one of AltaLink's first actions was to review and revise its vegetation management program. In 2002, AltaLink started seeing some indications that perhaps its existing vegetation management program was not as sustainable as it was originally thought to be and that significant changes were needed to meet reliability and safety requirements.

Evaluating the Vegetation Management Program

Like other utilities across North America, AltaLink was faced with growing vegetation management requirements on an increasingly tight budget. Operating on a limited budget, the vegetation management program was largely focused on reacting to vegetation management hot spots. The utility identified hot spots as areas where immediate vegetation management is required to ensure the safe operation of the transmission lines. This hot-spotting approach meant the utility was spending more time traveling between sites and less time completing the necessary vegetation management. Furthermore, because it was only focused on getting the most hazardous trees each time, AltaLink sometimes had to return to the same sites in subsequent years.

In 2002, AltaLink had a few sites that needed to be cut at 4 a.m. because later in the day, as the lines sagged with heavier loading, the trees were within the workers' limits of approach. The utility was spending more money and hitting fewer locations, therefore limiting what it was able to complete in a year. AltaLink attempted to handle all hot spotting with internal resources in order to stretch its budget. Ultimately, the hot-spotting volume became too great to be handled internally, so contractor assistance was arranged to complete the work.

Identifying Priority Sites

Those first few years at AltaLink were challenging. With the support of independent contractors, primarily Rick Johnson, Barry Rothel and Stu Olsen, AltaLink managed to avoid grow-in outages. The contractors helped in identifying and addressing a growing number of hot spots. With AltaLink staff stretched thin, the utility learned to depend on its contractors; in fact, they essentially became part of the team.

The increasing number of hot spots was a real concern, especially in the aftermath of the Northeast blackout in August 2003. This blackout changed the landscape for transmission utilities. A new operating environment emerged based on the recognition that the last three North American cascading outage events had a common cause: lines sagging into trees. The North American Electric Reliability Corporation (NERC) incorporated new standards that imposed severe financial penalties on utilities experiencing grow-in outages on critical and 200-kV or higher-voltage lines.

A Case for Funding

AltaLink's existing vegetation management program was not sustainable as the utility was spending the majority of its resources on hot-spot vegetation management rather than on a comprehensive, long-term program.

The utility was faced with two challenges in developing a new vegetation management program:

  • How would it create a sustainable vegetation management program to ensure safe and reliable service?

  • How would it justify and quantify the costs of the program to obtain approval from its regulator?

AltaLink's management was aware of the need for increased vegetation management funding, but they were unsuccessful in a 2002 general tariff application (GTA), or rate case, and only mildly successful in a 2004 GTA, receiving about one-third of the requested increase.

While success with the regulator had been limited, AltaLink believed the amount of vegetation management funding had been restricted because the only compelling evidence it had presented was the increasing number of priority sites. Thus, AltaLink believed there was an opportunity to try again if it could provide a broader base of evidence. The utility needed a more-comprehensive quantification of the vegetation management program status and a means of showing the progression of risk associated with the status quo funding as compared to the risk with increased funding. It also needed to call on outside expertise to provide an unbiased view of AltaLink's vegetation management conditions and associated risks.

Quantifying Risks

AltaLink brought in Sig Guggenmoos of Ecological Solutions Inc. (ESI; Sherwood Park, Alberta), a recognized vegetation management expert specializing in quantifying vegetation management program risks. AltaLink and ESI were confident that if the need and risks were scientifically derived, the regulator could be convinced to provide the requested funding or, in refusal, accept ownership of the consequences should the defined risks be realized. ESI quantified the ongoing vegetation management work volumes and costs as well as AltaLink's current program status. Also provided were several measures of risk showing the progression of risk associated with maintaining the current funding level.

Given that a rate case is a public and documented process, scientifically derived needs and risks provided the regulator with an understanding of the impact the requested funding would have on the reliability of the system. AltaLink and ESI had only four months to develop the resource needs and quantify risks in preparation for the next GTA. However, this time constraint proved to drive innovations in AltaLink's approach.

First, ESI provided a conceptual approach for understanding vegetation management. In summary, the approach consisted of the following: There is an annual workload volume increment of β€œnew growth (biomass addition) and dead or dying trees (additions to hazard or decadent trees)” that needs to be addressed. Because the biomass addition and increase in decadent trees can both be described by logarithmic or sigmoid curves, the vegetation management workload can be modeled and predicted by the same (Fig. 1).

The annual workload volume increment was developed from a derivation of the total area of tree exposure within rights-of-way, the extent of tree exposure alongside the rights-of-way, average tree mortality and growth rates. Monetizing the various work-type volumes provides the funding necessary for the least-cost sustainable vegetation management program, which was valued at $2.46 million annually.

The inventory of vegetation management work requiring attention over the next 16 months was derived from AltaLink's line patrol data. This permitted a calculation of the current inventory of work to be done (a workload liability of $8.1 million), which was well in excess of the annual workload volume increment ($2.46 million). Due to further growth and hazard tree additions over the year, the unfunded backlog of work was valued at more than $5.64 million at the end of the year. The rate of change in the backlog value was determined and modeled (Fig. 2).

Using the inventory values identified through line patrols, historical vegetation management expenditures, the value of the annual workload volume increment, and total tree and brush exposure, future costs were modeled (Fig. 2). It was shown that at the current funding levels, the amount of work was not decreasing but in fact increasing, and it would continue to do so for 10 to 15 years. This was one measure of the risk associated with underfunding: In the near term, every dollar of shortfall would be compounded by a rate of approximately 19%.

By applying logarithmic modeling to the number of priority sites, ESI identified another measure of risk. The projection illustrated in Fig. 3 shows hot spots were expected to quadruple over the next three years. This projection illustrated that, in the near future, the number of hot spots were very likely to overwhelm AltaLink's vegetation management efforts and grow-in outages would be experienced.

With the rate of expansion of the workload and current unfunded backlog of work known, the funding requirements to achieve the least-cost sustainable vegetation management program were calculated. The recovery period had to be matched to maintenance cycles driven by average growth rates, contractor staff and equipment availability, and the ability of internal staff to handle the resulting workload. A nine-year period was chosen for the catch-up phase. During this time period, AltaLink's vegetation management funding would be approximately 70% greater than it had been.

The regulator responded positively to the risk-assessment evaluation, accepting AltaLink's findings and approving the request for additional funding. Coming from an independent third party, the report appeared balanced and fully explained the need to increase spending, it was not just blaming the current situation on the shortage of funds.

The regulator appreciated AltaLink's responsiveness to the findings and recommendations in ESI's report.

In 2005, AltaLink increased its vegetation management budget prior to receiving the 2007 ruling to ensure it exceeded the annual workload increment value. This commitment was continued β€” in the absence of a ruling, putting the AltaLink owners' money at risk β€” for the following two years. AltaLink's experience over the last few years shows it is possible to work with the system and regulators in order to develop a balanced and sustainable program for the ongoing maintenance of transmission systems.

Tracking System Streamlines

Based on a recommendation from the ESI report, AltaLink added a unit-cost tracking system and has moved data collection and storage from a paper-based system to a computer-based database system. Past patrol data collected on spreadsheets was bulk-loaded into AltaLink's transmission line maintenance electronic database. The database was adapted to address size restrictions and increase functionality. Since 2007, AltaLink has added a feature that enables maintenance items to be entered by field personnel using PDAs.

AltaLink also modified procedures to eliminate duplication of records when feeding data into the system from aerial patrols. AltaLink's independent consultants Olsen and Johnson spent four months cleaning up the data through record checks and site visits. With data conflicts resolved, the database can be queried to show workload. GPS tracking during air patrols, combined with enhanced procedures, ensures field data remains current and correct. The work reporting system database shows work units performed with associated costs given by location, work order, contractor and foreman.

With the funding increase, the level of activity in the field greatly increased. And with an integrated digital tracking system, AltaLink now has the ability to monitor unit costs and provide the data necessary to demonstrate prudence in fund management. Results are showing a reduction in the average per hectare cost of vegetation management, and the utility was able to report to the regulator in a 2008 GTA filing that average per hectare costs had decreased 47% from 2005 costs.

Aerial patrols indicate that at the end of 2010, AltaLink will be nearly halfway through the catch-up phase. This agrees with the projections ESI made going into the 2007 rate case that shows the utility is on track to meet forecasted goals. AltaLink is not yet at the point where it can say it has a sustainable program in place. If the funding is cut before the backlog of work is caught up, AltaLink would soon lose the benefits it has gained and be back at square one.

The ability to track the work required and completed and to determine the unit costs of various activities and the contractor cost increases are all important in portraying the complete picture. Care must be taken to ensure maintenance plans are in place for any new facilities and funds are allocated far enough in advance to manage them in the most-efficient manner possible. With increased investment in vegetation management, AltaLink has not experienced any tree-related outages caused by sag-ins or swing-outs.

AltaLink is continuing to work with ESI in summarizing and reporting its progress to the regulator as part of the rate applications. Furthermore, the utility has been able to provide a balanced and impartial long-term vegetation management plan. It is very important to maintain the trust that has been built up between AltaLink and the regulator by being as open as possible with regard to the vegetation management program. AltaLink is also working with ESI to develop a means of quantifying risk on individual lines.

A Collective Commitment

AltaLink's first few years of operation were challenging, and without the commitment, cooperation and support of its contractors, the utility would not have been able to avoid the grow-in outages. This refers not just to the contractors who helped directly in identifying and remedying hot spots but to all the contractors. With AltaLink staff stretched thin, it became essential to develop relationships based on competence and trust, without which ongoing maintenance of the system had little chance of success.

Resourcefulness and decisiveness on the part of the collective team was, and continues to be, essential to the success of AltaLink's vegetation management program. Everybody has to be on the same page and realize that errors result in safety, reliability and liability issues. To retain the best people, engage them by giving them a broad scope of responsibility, allow them the opportunity for personal and professional growth, encourage prompt communication when they encounter something outside their area of expertise, notice and express appreciation for the job they are doing and support their decisions.

AltaLink is the beneficiary, and this attitude of mutual respect has a big financial payoff. The utility continues to work collaboratively with its external contracting companies to meet its vegetation management requirements, ensuring that it maintains safe and reliable service for the homes, farms and businesses that rely on its transmission system every day.


Alan Lucas (alan.lucas@altalink.ca) is the senior maintenance analyst for lines and rights-of-way for AltaLink. With more than 32 years experience in line maintenance and design, he is a registered engineering technologist and a professional licensee of the Association of Professional Engineers, Geologists and Geophysicists of Alberta.

Kevin Tritten (kevin.tritten@altalink.ca) is AltaLink's vegetation management coordinator, a licensed Alberta pesticide applicator and a certified utility arborist/utility specialist. An Olds College Agronomy graduate, he is a past president of the Industrial Vegetation Management Association of Alberta (IVMAA) and continues to volunteer his time with the IVMAA and International Society of Arboriculture Prairie Chapter committees.

History of Priority Sites Requiring Immediate Mitigation
Year Number of Sites
2000 40
2001 75
2002 281
2003 347
2004 473
2005 631