Engineering a Safe Future at Lake Success
If you visit Lake Success near Porterville in Tulare County, you’ll be met with one of the Central Valley’s hidden treasures: a tranquil lake surrounded by rolling foothills covered in mustard seed plants, lush valley crops to the west and the massive Sierra Nevada to the east. If you look closely, you’ll notice that this scenic view is unlike any other in California. And unlike many other Western lakes, there are no drought-related fears of low-water levels. The lake’s capacity is being expanded to offer better protection from floods.
Traversing Lake Success, owned and operated for flood control, recreation and irrigation by the U.S. Army Corps of Engineers, are Southern California Edison’s new H-frame hybrid electrical towers. They suspend two high-voltage, 220-kilovolt power lines that transport electricity from the Big Creek Hydroelectric Project to customers south of the Grapevine.
Previously, SCE’s transmission lines were held above the lake’s two-mile width by lattice steel towers for more than 100 years. But metal, when submerged under water for so long, is susceptible to corrosion, severely damaging the structure’s integrity. When the time came to replace the towers, SCE’s engineers knew they would need a design to withstand rust, decay and corrosion for the next century.
“We were informed by the Corps that they were planning to increase the water level at the lake by 10 feet, and that would have further flooded and damaged the existing structures,” said Hamid Arshadi, SCE major construction project manager. “We had to consider corrective actions because, as you can imagine, if a 220-kilovolt line touches the lake’s water, it would be a disaster.”
In 2015, SCE began developing solutions that would support the increased lake level; meet state and federal wire-to-water clearance requirements; and continue to deliver safe and reliable electricity to customers. To create distance between the water and metal, engineers employed the H-frame hybrid design, using concrete to form the base and stainless steel to support the lines at the top of the structure. More commonly seen on the East Coast, hybrid towers are specifically designed to carry power lines across large bodies of water.
“This is the first time we’re using this type of structure for a 220-kilovolt transmission line,” said Saeed Sadeghi, SCE senior engineering project manager. “With this design, the concrete is five feet higher than the maximum height of the lake, so the water will never contact the metal portion of the structure. We designed these structures to last forever; we don’t expect them to deteriorate.”
Fourteen existing towers were replaced with 13 new H-frame hybrid structures ranging in height from 120 to 190 feet above ground, each extending an additional 25 feet underground for further reinforcement. The hybrid towers are not only less invasive and more cost effective, but they are also designed to mitigate safety hazards for recreational boaters and swimmers.
“Because people boat in the area, there were reports that people would hop on the towers and jump off and dive,” said Cody Brodeur, SCE transmission engineer. “This was very concerning and part of the remediation we had to do.”
Despite delays due to the COVID-19 pandemic, construction was completed two months ahead of schedule earlier this year without any impact on the power grid. This summer, water will cover the fields of mustard seeds that are visible during spring and the new hybrid towers will begin their perpetual task of protecting the transmission lines so they safely coexist with Lake Success below.
“This is very rewarding because we see that these projects will be here for years and years,” said Sadeghi. “Way after we’re all gone, these 220-kilovolt transmission lines will still be here and serving our communities.”