KAILUA — A curtain of mesh will be strung along a hillside at the entrance to Kailua to help protect motorists from rocks that tumble from the slopes, especially during heavy rains.

A series of landslides and incidents of falling boulders that occurred during last spring's rains prompted the $5.8 million project above Kailua Road, according to the state Department of Transportation.

The contractor, Prometheus Construction, is building a drainage and rockfall catchment ditch high above the road. A fence will be installed and mesh draped over the lower slopes.

Work on the DOT emergency rockfall project is expected to wrap up in May. Two additional months will be needed, however, to restore the alignment of Kailua Road, which was altered to make way for the construction, and install median landscaping.

"The good news is minimal lane closure, if any at all," said DOT spokesman Scott Ishikawa.

In the aftermath of the rains that drenched the area in March, the state rerouted the road away from the hillside, making it safer for motorists. The sidewalk next to the slope was closed.

The rockfall project involves drilling nearly 1,000 anchors into the hillside, said Cliff Tillotson, vice president of Prometheus. The hillside area will be seeded and covered with an "erosion blanket," Tillotson said. The work also will require demolishing some of the rock and stabilizing boulders with cables, he said.

"One of the challenges for our engineers is how to leave the communication lines in place" while drilling is under way, he said.

Workers have hauled drilling apparatus — roughly the size of a Volkswagen Bug — up the hillside. Held in place with cables, the equipment appears to be precariously perched over the road. After the anchors are secured, a helicopter will be used to put the mesh in place, Tillotson said.

The state has dealt with rockslide problems elsewhere around the island in recent years. Emergency projects began at Waimea Bay in 2000, Makapu'u in 2002, and Castle Junction in 2003. After responding to the Waimea and Makapu'u problems, the state paid for a 2003 study that evaluated 400 sites and called 66 of them problematic.

The study ranked the Kailua project as No. 8 on the list of most hazardous rockfall areas on O'ahu. It moved to the emergency level during a stretch of nearly six weeks of rain that left boulders and rocks littering the street below.

"Once an area starts sliding you have to take your money and use it on the emergency job," Ishikawa said.

The state has plans to next year begin a second phase at Makapu'u, Ishikawa said. The first phase turned into an emergency project when rocks fell on the highway in 2002, Ishikawa said.

"Makapu'u was supposed to be done in one swoop but because of the rockslide they decided to tackle the upper ridge first," he said. The state expects to finish the project next year.

Waimea — No. 2 on the study's list and located above Waimea Beach Park — could be tagged for the next rockfall project. Project work there, however, could be problematic, though, because there is no place to build a bypass road if workers need to completely close a portion of the highway, said outgoing state Transportation Director Rod Haraga.

"This is going to be really tough because eventually it will have to be done," he said. "I can't put a bypass road on the back side. Once you close the road down, you can't get through."

Reach Eloise Aguiar at eaguiar@honoluluadvertiser.com.