66 O'ahu rockfall sites identified as high-risk
| • | $6 million more needed for Makapu'u rockfall site |
| • | Map: Top 10 potential rockfall sites |
By Mike Leidemann
Advertiser Transportation Writer
The state has identified 66 highway sites on O'ahu that have a high risk of rockfall and acknowledged that fixing all the problems could take years and cost hundreds of millions of dollars.
O'ahu's top rockfall hazards
Source: State Department of Transportation |
In the meantime, the state plans an aggressive campaign to mitigate the dangers, from posting signs in danger zones to constructing expensive catchment devices, according to state Transportation Director Rod Haraga.
The findings are contained in a $290,000 study that reviewed more than 400 potential landslide areas near O'ahu highways and created a list of the most dangerous.
The report says engineers found 66 slopes above nearby highways where the potential for rockfall is high. Fifty-one other areas were rated moderately high.
The sites are scattered across the Island. Four of the Top 10 areas are on Kamehameha Highway — near Kahuku, Waimea Bay and Wahiawa, while three others are along a 3-mile stretch of Pali Highway passed by thousands of commuters every day.
The correct sites are Kalaniana'ole Highway at Castle Junction, Kalaniana'ole Highway near Kapa'a Quarry Road and Kailua Road just before Kailua town.
In all, 13 of the high and moderate danger sites are on Kalaniana'ole Highway, 12 on the Pali Highway and 10 along H-1 Freeway.
Haraga said the state will work on a plan to ease the danger.
"Once the plan is set, we will work as quickly as possible in constructing catchment devices to deal with the issue."
The report's release yesterday coincided with completion of $1.5 million in emergency landslide prevention work at Makapu'u, site of a rockfall last October. However, the report still lists the area as No. 1 in potential landslide danger and suggests it may cost $17 million more to fix the problem.
No. 2 on the list is an area just north of Waimea Bay, not far from another large rockslide in 2000. The preliminary cost estimate for that site is $8.4 million.
The study, conducted by the Honolulu firm Earth Tech, evaluated each of the potential rockfall sites and gave them a hazard rating based on 12 criteria, including rockfall history, the height and slope of the adjacent hillside, erosion rates, the size of a catchment area along the highway, and the number of cars passing by at any given time.
On that basis, each site was given a final point total and rated either high, moderate or low in rockfall danger.
The report notes that many of O'ahu's highway corridors were created decades ago by blasting methods that created instability in the adjacent rock formations, thus increasing the potential for rockfalls.
"The danger is greatest where a highway winds through a heavily populated area or in a location where a highway serves as the sole thoroughfare of the surrounding communities," the report said.
Haraga said he did not know how much it will cost to fix the problems. "I wouldn't even want to guess at this stage," he said.
However, the report assigns a preliminary cost estimate to each site, with some going as high as $50 million. Cost estimates for the top 10 sites alone add up to $89.5 million.
The Transportation Department has set aside $1 million a year to design solutions to fix some areas, although they might not necessarily be the projects on the top of the list, Haraga said.
Haraga said a variety of factors will be used to decide which sites are addressed first, including costs, availability of money, what kind of rock catchment system is needed and whether a detour road is available.
Because some of the problem sites are on private land, the state must work with each landowner to arrive at a solution before anything can begin, he said.
"Some may take longer than others," Haraga said. "If we can get to one right away, we will do it real quick."
The report released yesterday deals only with O'ahu rockfalls. Haraga said another study will be done to identify potential rockfall hazards on Neighbor Islands.
Advertiser reporter Mike Gordon contributed to this report.
Correction: A Department of Transportation report on potential rockslide areas misidentified three sites. The correct sites are Kalaniana'ole Highway at Castle Junction, Kalaniana'ole Highway near Kapa'a Quarry Road and Kailua Road just before Kailua town. Other information was contained in a previous version of this story.
