Sidebar: Outage Risk from Emerald Ash Borer Infestations at LG&E and KU

By J.M. Sparkman, Environmental Consultants Inc.

Emerald ash borer (EAB) is a voracious wood-boring insect from China that, as its name implies, prefers to dine exclusively on ash. Unlike many wood-boring pests that mainly attack diseased or dying trees, the EAB is adept at attacking living, healthy ash trees, threatening to eradicate ash trees, with consequent devastating economic and ecological impacts (“Emerald Ash Borer Invasion of North America: History, Biology, Ecology, Impacts, and Management,“ Annual Review of Entomology, Vol. 59.)

Why Utilities Should Care

Since its discovery in Michigan in 2002, EAB has spread to more than 22 states and two Canadian provinces, killing tens of millions of trees along its path. Many of these trees now pose an immediate risk to overhead electric facilities. Utility vegetation management programs in the affected states and provinces are scrambling to mitigate interruptions resulting from dead ash trees and to understand the potential impacts to system reliability.

In the state where it all began, Consumers Energy has estimated that tree outages due to EAB will increase annual tree-caused outages by 150% in coming years if no corrective action is taken.

AEP, emerald ash borer

Utilities outside of the current known areas of infestation, but within the native range of susceptible ash species (primarily the entire eastern half of the U.S.), must also heed warning and begin to take proactive steps to understand EAB’s potential impact to their electrical systems. EAB illustrates a classic example of the pay-now-or-pay-later philosophy. Pay now to develop a mitigation strategy to proactively remove or treat all ash trees that could impact electrical facilities, thereby retaining cost control over their removals or treatments. Or, wait and pay later, after the trees have died, and risk escalated removal costs from catastrophic equipment damage, outages and lost revenue, as well as costs associated with negative customer impact. Consumers Energy estimated the reactive removal of dead ash trees was roughly threefold higher than the estimated proactive removal costs. The choice is clear.

LG&E and KU Case Study

Louisville Gas and Electric Co. (LG&E) and Kentucky Utilities Co. (KU) began noticing significant ash tree mortality around their system in early 2012. Recognizing the need for a long-term strategic solution to address the outage risks, LG&E and KU engaged the services of Environmental Consultants Inc. (ECI) to assist with quantifying the ash tree population on approximately 18,000 miles (28,968 km) of primary overhead distribution line and to develop an effective mitigation plan and budget specific to their needs.

ECI began by designing a random sample survey to estimate the population of ash trees with significant height and relative position to strike the overhead primary conductor should they fall. Data was collected by trained ECI survey personnel across 13 operations centers. Several height and distance measurements were taken for each tree tallied as well as multiple tree characteristics to ascertain the health, condition, diameter, proximity to conductors and other spatial factors for each tree.

Analysis and Results

The field data collected by ECI was analyzed and used to calculate line-strike probability for each tree tallied within the sample data. Factors such as tree elevation in relation to the primary conductor, total tree height, conductor height and horizontal distance from the conductor were considered in the probability calculation. Probability of line contact was estimated as the percentage of the fall radius that would impact the primary conductor. Line-contact probability coupled with the estimated number of ash trees capable of making line contact was used to approximate the potential impacts to service reliability.

The final mitigation plan provided LG&E and KU with several key results:

  • A workload estimate for the number of ash trees to be removed from the system
  • Ash population characteristics, including demographic breakouts, accessibility and current tree health
  • Line-strike probability percentages
  • Estimated cumulative reliability impacts
  • Budget requirements
  • Reactive versus proactive cost comparisons.

The bottom line: approximately 54,000 ash trees were estimated to have the potential to contact the LG&E and KU overhead distribution system. The cost to remove those risk trees was estimated at US$26.9 million over 10 years. Like Consumers Energy, it was estimated that the cost to proactively remove the trees is significantly cheaper than the alternative approach, although, in comparison, a conservative estimate for the reactive removal cost was only 22% higher at LG&E and KU. However, more importantly, the proactive approach was estimated to save LG&E and KU more than 16,000 tree-caused outages over the 10-year period.

LG&E and KU have supplemented their risk tree program with sufficient dollars to address the removal of healthy, as well as declining, ash trees. Their investment to date has resulted in tree outages remaining relatively flat from previous years.

“The EAB study with ECI provided LG&E and KU with a snapshot of the ash tree population, thus allowing LG&E and KU to effectively budget for a long-term solution,” stated Terry Wright, manager of forestry service at LG&E and KU.


J.M. Sparkman (jmspark@eci-consulting.com) is the manager for consulting services at Environmental Consultants Inc. (ECI).
His experience includes more than 25 years of UVM forestry including regional management responsibilities for a large investor-owned utility. His recent experience with ECI includes emerald ash borer risk assessments, numerous vegetation program assessments, utility benchmarking, and the design and implementation of regrowth studies.