KAILUA — Unusual erosion has undermined the lifeguard tower at Kailua Beach Park, forcing the city to move the protective shelter to a new location.

Within a week, 30 feet of sand fronting the tower was swept away by high surf and tides, coupled with strong winds, said lifeguard Capt. Kevin Allen.

Erosion this time of year isn't unusual at the Windward beach park, and a fair amount of sand had already shifted during December. However, last week's weather conditions and 8- to 10-foot surf caused a dramatic change as water ate away at the shoreline and tower foundation.

"Every year the sand moves from this side ... then it comes back," Allen said. "It's the weather pattern. But this was one very unusual occurrence."

The beach from the tower foundation to the boat ramp looks as if a giant knife had sliced down on the sand dunes fronting the shoreline, creating a cliff-like appearance. Some areas, especially near the Ka'elepulu Stream outlet, are about 15 feet high.

"I've seen them exposed only three times in the last 20 years, so this is pretty bad," he said, adding that he's waiting to see if the condition is temporary. "I'm not convinced this is long-term chronic erosion."

BEACHES UNDER STUDY

Fletcher, chairman of the Department of Geology and Geophysics at the UH-Manoa, leads a team of 10 researchers who are looking at the pattern of coastal erosion over the last 100 years for every beach on O'ahu and Kaua'i. His team has completed its study of Maui beaches.

The waves, wind and spring tide, which is a higher than normal high tide, contributes to erosion, he said. The stream mouth gets plugged with sand, and once a month the city opens it to allow the stream to flush. If that sand is removed from the beach, that too could be adding to the erosion, Fletcher said.

The beach and its users are lucky these conditions didn't happen during the summer when the water is warmer.

"When the water is hot, the sea level goes up because things expand when it's warm, but here we are in winter," he said. "If this had happened in the summer, it would be even worse."

The city is planning for worse conditions as far as the lifeguard tower is concerned. It won't install the tower at a permanent site, said Allen, the lifeguard captain.

TOWER BUILT TO MOVE

The tower will be attached to a portable base on skids that can be moved should conditions improve or worsen, he said.

The fiberglass tower, installed in 2001, will be set about 20 feet back and toward Lanikai from its present foundation beginning Tuesday. This will give the lifeguard a clear view to the boat ramp but whoever is on duty will have to look through ironwood trees to see in the other direction.

Allen said he didn't think this would be a problem, but the situation will be evaluated after some time. If the trees need to be removed, he said, the issue would be taken to the Kailua Neighborhood Board for input.

Lifeguards are primarily responsible for people who visit the beach park, but they will patrol the rest of Kailua Bay beaches on an all-terrain vehicle, he said. The coastline in the bay is more than three miles long.

Several hundred people visit the beach park during the week and many more come on weekends, Allen said.

"Public safety is the determining factor," Allen said. "We're here to save lives, and if we can't see, then we're limited."