Fueled by dry weather, drought, strong winds and warm temperatures, wildfires erupt quickly and spread rapidly, burning millions of acres of land each year and consuming everything in their path. These wildfires are occurring more frequently and with more intensity than ever before, causing extensive damage and raising concern for utilities nationwide.
Not only can wildfires, storms and ice threaten a utility’s assets, they can pose substantial risks to transmission system reliability.
Although Chelan County Public Utility District (PUD) transmission lines span a relatively small geographic area, the terrain varies dramatically from near-desert to deeply forested mountains, with conditions that regularly include snow and ice storms, gusty winds and wildfires.
For the past five years, multiple wildfires affected several locations in Washington’s Chelan County, including downtown Wenatchee and the city of Chelan. Chelan PUD knew it was time to look at their system differently.
It turns out, Chelan PUD’s customer-owners agreed. During a strategic planning initiative that began in 2014, customers overwhelmingly supported reinvesting in Chelan PUD’s facilities and people to improve the quality of life in the county.
Shortly after, Chelan PUD contacted HDR, a design firm specializing in engineering, architecture, environmental and construction services. Chelan PUD asked the firm to help evaluate wildfire risk to infrastructure, and the potential for a performance failure of the district’s power transmission system.
A utility risk assessment for wildfire was developed by an HDR team of transmission engineers, fire ecologists, meteorologists, risk analysts, GIS specialists and other subject-matter experts. The team worked with Chelan PUD transmission and GIS staff. The HDR team employed a visualization tool that uses GIS mapping, vegetation surveys, terrain models and other risk factors to develop a customized risk assessment for the client. Using this information, HDR analyzed the existing Chelan PUD assets and distributed them into ranges of relative risk. This helped Chelan PUD prioritize its operations and maintenance budgets for immediate upgrades. This process will also help Chelan PUD better manage capital investments and ensure long-term resiliency, contributing to a positive bottom line.
To develop Chelan PUD’s risk assessment, HDR’s fire ecologist used data collected from several sources including Landscape Fire and Resource Management Planning Tools (LANDFIRE). Fire intensity was interpreted from the LANDFIRE data for elevation, slope, aspect, fuel model, canopy cover, canopy height, crown base height and crown bulk density, with considerations for weather and fuel-moisture data. Fire intensity was evaluated using modeling software FLAMMAP 5.0., which was interpreted into the risk score.
The risk assessment framework for this study was based on the level of risk or “risk score” of each pole/structure within the system, relative to the entire system. This assessment evaluated the likelihood of performance failure due to wildfire intensity and infrastructure material (e.g., wood or steel poles), and weighed them against the consequences of system criticality, structure accessibility and replacement cost.
Chelan PUD developed a comprehensive system criticality review of each transmission line section. It was based on factors such as:
• The number of customers served;
• Bulk electric system and local reliability concerns;
• Common corridor lines (likely to lose more than one line in event of a fire);
• Revenue-generation considerations of powerhouse lines (which are directly tied to hydro-generation facilities); and
• Line voltage.
HDR and Chelan PUD next evaluated economic and accessibility considerations. Replacement cost was estimated for each line section, and ranked from most- to least-expensive. Accessibility was included as a risk factor. This considered the ability to monitor during a high alert, and to clear and grub around structures before a fire; the ability for fire responders to prevent a threat to the infrastructure during a wildfire; and the time needed to restore service in the event of an outage.
Finally, the HDR team took the data to finalize the approach and assigned a risk score to each criterion, identifying highest and lowest risks. The final risk scores were integrated into the visualization tool built around Chelan PUD’s GIS database for future use as an asset-management resource.
The primary intent of this study was to provide Chelan PUD with the decision support necessary to develop a strategic, cost-effective plan to avoid service failures as result of wildfire — and ultimately to produce a system with long-term resilience to this threat.
Chelan PUD is using the risk assessment results to determine how to put its long-term fire prevention program in place. This includes evaluating and updating plans for operations and maintenance, and capital projects. With the highest-risk areas identified, Chelan PUD can prioritize its efforts in the areas of concern: line segments with the highest combined risks to wildfire intensity, likelihood of damage, criticality to the system, cost of replacement, and accessibility to monitor and return to service after a failure.
Many of the highest-scoring line segments are in remote areas where fuel conditions are conducive to a destructive fire. Some of these lines provide direct service to customers with little system redundancy and more-flammable building materials, such as wood. This information is being used to evaluate the best way to mitigate and reduce the PUD’s overall risk profile within existing budgets. These measures include operations and maintenance spending for:
• Applying fire retardant paint (hardening) to wood transmission poles;
• Building access roads to reduce risks associated with accessibility;
• Moving forward with capital upgrades and replacements through feasibility studies; and
• Doing preliminary designs for future line rebuilds.
Chelan PUD also is seeking opportunities to investigate other industry programs and processes to reduce its overall risk of service failures due to wildfire.
Chelan PUD staff can use the data they have to continue monitoring the system after upgrades are completed, and reevaluate wildfire conditions on a schedule. They also can add or substitute different hazards, such as a mudslide, flooding, ice and wind storms, or an earthquake, to the evaluation.
The Chelan PUD and HDR teams worked together to review the wildfires that were causing service failures, while also considering other important risk factors to Chelan PUD’s operations. This approach can be used to evaluate the risk of additional hazards or natural events yet to come.
Meet the Authors
Steve Wickel, Chelan County PUD