Costs differ for cliffside wire netting
How much does it cost to install and purchase those wire mats used to hold back the rockslides from highways?
Answer: The state Department of Transportation has spent nearly $15 million installing protective netting at three sites on Oahu.
At Waimea Bay, netting was installed in 2000, and Kamehameha Highway moved away from the cliffside at a cost of $7.5 million, said transportation spokesman Scott Ishikawa.
"The whole intent of the 2000 project was to allow the rocks to fall along the grassy area behind the fence" to slow down their momentum or bounce, he said.
Although the fencing was heavily damaged during an April 2006 rockslide, "it did its job of holding back most of the boulders," he said.
In 2003 a metal "hairnet" was draped on the steep upper slopes of Makapuu at a cost of $1.5 million.
Several rainstorms since then have caused rocks to tumble down.
However, Ishikawa said, "The netting didn't allow the rocks to pick up too much momentum or ricochet off the cliff, where it would have landed on the highway itself." Instead, the rocks fell on the side of Kalanianaole Highway, where they were picked up.
The lower slope of Makapuu, closer to Sea Life Park, will be worked on next year.
More recently, two types of "netting" were installed on a hillside along Kailua Road as part of a $5.8 million project.
"Anchored wire mesh" was the brown netting used on the makai side of the project, with regularly spaced "anchors" all over the hillside, Ishikawa said. The cost of this part of the project was about $1.7 million.
A "cable net system" is the black netting seen on the mauka end of the project. The net covers the hillside but is anchored only at the top and the bottom, Ishikawa said. This system cost about $490,000.
The costs don't include a $630,000 "rockfall protection fence" along the upper portion of the project site, which also has "netting" on it, Ishikawa said.
Meanwhile, work to restore Kailua Road to its regular alignment will run until October, he said.
Another high-profile rockfall incident involved the hillside at Castle Junction.
However, the Transportation Department's $7.8 million Castle Junction project did not require protective netting, Ishikawa said. Instead, the steep slope was cut back to a safer angle, and 18,000 truckloads of dirt were hauled away.
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