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Energy Infrastructure and Climate Change: Protecting Erodible Slopes in Fire-Prone Areas

Posted by Katie Bocskor

Energy infrastructure is critical to the functioning of modern societies, and its protection against natural disasters and environmental threats is a top priority. Climate change exacerbates these disaster risks, with extreme weather conditions and wildfires being of particular concern, considering potential damage to the energy infrastructure and disruption of energy supply. Wildfires cause rapid, severe destruction, and, aside from damage to infrastructure, can impact our climate, vegetation, and atmosphere.

To measure the size and impact wildfires have, scientists use observations from several low Earth-orbit satellites, including the Copernicus Sentinel-3. These tracking satellites gather shortwave-infrared data combined with other techniques to differentiate between burned areas and other low reflectance covers such as clouds. The European Space Agency (ESA) compiles that long-term dataset to analyze global fire trends. According to the ESA, fire affects an estimated four million square kilometers (1.5 million square miles) of Earth´s land each year [1]. That is 400,000,000 hectares (990,000,000 acres) yearly—about half the size of the United States of America, an area larger than the country of India. The United Nations Environment Programme (UNEP) Rapid Response Assessment on Wildfires compiles findings from over 50 experts from research institutions, government agencies, and international organizations around the globe, and confirms that “wildfires are growing in intensity and spreading in range” with an “annualized economic burden for the United States to be between $71.1 billion and $347.8 billion USD” [2].

As wildfire seasons become longer and more extreme, the level of response must be increased. The United States and Canada have renewed an arrangement of cooperation to provide mutual aid during wildfire emergencies [3]. This, as Canada expects the 2023 wildfires, their worst on record, to continue into the winter season, with nearly 18 million hectares (44.5 million acres) burned to date through September 2023, as registered by the Canadian Wildland Fire Information System (CWFIS) [4].

In California, about 4.5 million hectares (11 million acres) have burned in wildfires over the past seven years, with an average of 485,623 hectares (1.2 million acres) per year [5]. The University of California´s Agriculture and Natural Resources (UCANR) Fire Network has studied post-incendiary erosion trends and offers a series of videos and other resources for wildfire and post-wildfire management. UCANR confirms the “chance for erosion is significantly greater and can result in mass movements of soil and water if vegetation has been burned off…with steep, hilly areas especially vulnerable” [6].

Project Case Study: Protecting Energy Infrastructure

The project owner had recently completed facility renovations and needed to repair and protect the slopes and hillsides surrounding the facility. However, the project owner had attempted other vegetated and non-vegetated erosion control methods in the past, and due to recent wildfires, drought cycles, and heavy erosion, those previous efforts did not achieve the desired level of long-term protection. The project owner and their contractor sought to meet initiatives from the U.S. Department of Agriculture (USDA) Forest Service for land management practices designed to mitigate erosion before and after severe fire events, and in evaluating possible solutions, the GEOWEB® Geocell Slope Protection System was identified for further evaluation and analysis. GEOWEB Geocells are three-dimensional cellular confinement products made from strips of high-density polyethylene (HDPE) welded together to create an expandable honeycomb-shaped structure. The geocells confine the soil or aggregate fill, minimizing movement and migration of the embankment materials by functioning as anchored containers in the upper soil layer. The geocell system resists sheet flow, preventing severe erosion and controlling rill and gully formation, especially in erosive post-incendiary soils.

Accordingly, the GEOWEB slope protection system was determined to have a high probability of achieving project objectives, and the facility owner ultimately selected the GEOWEB System utilizing tendon-based anchorage and ATRA® Tendon Clips (load transfer devices) in lieu of conventional staking techniques. The repair areas comprised two hillside areas of approximately 6,500 m2 (70,000 sf), with varying slope angles from 40-100°, and varying vertical heights from 6 m to 34 m (20 ft to 110 ft). After analysis of the site parameters, calculations for appropriate anchorage, planning for proximity to and around energy structures, it was determined that the 15 cm (6 in) GEOWEB Geocell with load transfer devices, integral connectors, high strength tendons, and earth anchors provided proper anchorage of the system without interference with existing infrastructure, as shown in Figure 1 below.

Fig. 1. Installation of tendoned GEOWEB Geocell System at energy facility.

The actual rock size chosen for the infill was based on slope angle and site hydraulic conditions, with earth anchor pullout strength determined by the Engineer of Record based on the manufacturer´s recommended factor of safety and site soil conditions. Aggregate infill was placed from crest to toe, using a rock slinger to assist workers and limiting the drop of the infill to prevent geocell wall distortion, as seen in Figure 2 below.

Fig. 2. A rock slinger helps workers place infill on steep slopes.

The tendon-anchored system with aggregate infill satisfied the needs of the project owner´s installation for long-term performance, burn protection, erosion control, and low maintenance while offering flexibility of fit without interference with the newly installed energy infrastructure.

GEOWEB Cellular Confinement System Options and Benefits

The GEOWEB Cellular Confinement Systems (CCS) offers a broad range of surface protection treatments for slopes that are subject to erosive forces. The inherent flexibility of the system, combined with a variety of adaptable anchoring techniques, permits the application of soft or hard armoring techniques to steep slopes. By ensuring the long-term stability and effectiveness of slope cover materials, underlying soils are protected, and customizable aesthetic objectives can be achieved. When slope reclamation and revegetation is desired, the geocell system provides the ability to fully vegetate slope surfaces that could not otherwise support plant life, with appropriate anchorage (based on specific site conditions) to hold the system to slope [7].

The GEOWEB walls, which contain the topsoil infill in a vegetated system, form a series of check-dams extending throughout the protected slope. Normal rill development, produced when concentrated flow cuts into the soil, is prevented since flow is continuously redirected to the surface. This mechanism also disrupts flow velocity and hence the erosive force of runoff. A predetermined depth of topsoil and the developing vegetative root mass is contained and protected within the individual cells. Roots become intertwined with the perforated cell walls, thereby creating an integrated, blanket reinforcement throughout the slope surface. In arid regions, it has been observed that the GEOWEB Geocells can enhance the development of indigenous vegetation by retaining a higher proportion of available moisture in the near-surface soil zone.

When vegetation is not appropriate or desired, aggregates or concrete infill may also be used for GEOWEB slope protection, stabilizing and protecting the surface. Aggregate infill reduces environmental impacts by allowing water infiltration on the slope face, reducing sheet flow runoff, and by precluding the need for irrigation systems, particularly in drought-prone areas, as might otherwise be required to maintain a vegetated slope cover. In this particular energy project installation, it was also chosen as a burn-protection zone around the newly installed energy infrastructure.

Protection of Energy Infrastructure Against Extreme Weather Events & Wildfires

The protection of energy infrastructure against extreme weather events and wildfires becomes increasingly more challenging as climate change exacerbates those threats. The National Park Service and the California Department of Forestry and Fire Protection (CAL FIRE) have started to collaborate with Indigenous communities to return traditional burning to the land as a wildfire prevention method [8]. Local tribes have helped to set prescribed burns in Yosemite National Park, among other wooded areas, as preventative protection against damaging wildfires like the Oak fire that burned over 8,000 hectares (20,000 acres) west of Yosemite National Park as shown in Figure 3 below.

Fig. 3. Oak Fire near Mariposa, California, photo courtesy NPR and David McNew/AFP via Getty Images.

In addition to prescribed burns, erosion control solution sets must perform uniformly with a balance of properties for robust and resilient performance, as highlighted in the Overview of Resilience Concept by Bruneau et. al [9]. Resilience in infrastructure includes qualities that help reduce vulnerability, minimize the consequences of threats, accelerate response and recovery, and facilitate adaptation to disruptive events. All of these are likely to be expressed as essential for the solution sought in pre- and post-incendiary erosion control, especially for energy sector infrastructure.

Within the resilience framework, the concept of robustness presents unique opportunities for innovative solutions such as the high-quality GEOWEB Geocells to be integrated into infrastructure designs and contribute toward achieving infrastructure resilience goals. Redundancy to maintain functional requirements in disruption occurs with the use of aggregate infill, serving as both fire protection and a permeable hard-armoring stabilization of the slope. The resourcefulness of the GEOWEB Geocells with tendons and ATRA Tendon Clips with specific engineering values allows resources to be mobilized in an effective manner, without interference to existing energy structure. The rapidity in response of The GEOWEB Geocell System allows infill to be placed and the slope to be stabilized quickly, achieving project goals in a timely manner with reasonable labor and equipment inputs from contractors.

GEOWEB Geocells should be considered an industry best practice option for slope stabilization and a solution for pre- and post-incendiary erosion control on hilly, dry terrain prone to wildfire, drought, and erosion. The type of system as shown below in Figure 4 is an appropriate option for permanent and resilient erosion control at similar energy infrastructure sites around the world.

Fig. 4. Aggregate infill of geocell system at energy facility.

References