Millions of gallons of untreated sewage have poured into the Ala Wai Canal since Friday, and the city expects to pump in millions more over the next four to seven days — the time it will take crews to repair a major sewer-main rupture.

While the sewage poses an environmental and health concern, pumping it into the canal is the only way to prevent the waste from backing up into Waikiki homes, hotels and businesses, city officials said yesterday.

"We really have no other alternative," Mayor Mufi Hannemann said. "This is the most challenging main break that the city has faced in a number of years. We don't have an easy fix."

The breaks in the line on Kai'olu Street appear to have been caused by a combination of the very heavy flow of rainwater into the sewage system and the settling problems of an aging sewer line, said Eric Takamura, director of the city Department of Environmental Services.

Complications included rain that kept filling the area around the cracked 42-inch concrete pipe and the need to work around underground utilities, Hannemann said.

The pressurized sewer line was built in 1964 to carry raw sewage from the Beachwalk Wastewater Pumping Station toward the Sand Island Wastewater Treatment Plant. The line carries most of the sewage generated in Waikiki, Manoa and Mo'ili'ili — about 15 million gallons each day, city officials said.

Hannemann said city officials remain in constant communication with the state Health Department, helping monitor water quality and currents. He said no signs were posted to warn people out of the waters off Waikiki beaches because the current was taking the flow out of the canal in the opposite direction.

Surfers are warned to avoid Ala Moana Bowls, Rock Pile and In Betweens because the current clips those surf spots near the mouth of the canal before skirting Magic Island and making its way toward the airport.

Chris Ball, president of the Hawaii Canoe & Kayak Team, said all of his crews are staying out of the Ala Wai until they get the word that it's safe to go back in.

"We have practice every day, but we've suspended practice until the signs are down and it's OK to paddle in there," Ball said. He said the teams instead paddled yesterday and today in Hawai'i Kai, and some worked on their running and conditioning instead of getting in the water.

Ball said he believes most teams are steering clear of the water until officials give the go-ahead.

"There were a few canoes in the Ala Wai on Saturday," he said, adding that he didn't see any yesterday morning.

"We've got a lot of little kids," Ball said. "Sometimes they flip and fall out of the kayaks, and we don't want them in that water."

Takamura, the city's environmental services director, said it's difficult to measure exactly how many millions of gallons continue to flow into the Ala Wai because the sewage is not pumped through a station where it would be measured.

Instead, Takamura said, the untreated effluent is being pumped from the pipes into the Ala Wai in at least six places.

He said repairs will take at least four days, and crews may need closer to seven days to fix the cracked joint.

City Managing Director Wayne Hashiro said the ruptured concrete pipe already was slated for replacement and rehabilitation, with design work expected to begin this year and construction of a permanent replacement expected to begin in two to three years.

Takamura said the city plans to seal the cracked area several ways, including a wrap of lead wool and fiberglass, then steel-reinforced concrete around the area, which is about 10 feet below street level.

Hannemann said city crews and a contractor remained hard at work on the repairs through the holiday weekend. He apologized for the inconvenience to Waikiki residents and visitors caused by the sewage flow, the traffic problems and the noise.

But he said crews are working as quickly as possible to make a repair that will last two to three years until a more permanent fix takes place.

Meanwhile, a demonstration project on the Ala Wai that uses plants to clean parts of the canal is hoping for another year of testing. That's the word from Chad Durkin, project manager for Natural Systems Inc., which partnered with Marine Agritech to place thousands of 'akulikuli plants on floating rafts to help improve the water quality.

Durkin said the permit ends next month, but he'd like to see it extended by a year. He said it has proved effective at improving water quality through the organisms that live on the roots of the plants, helping clean the water.

He said the sewage spill won't harm his project. "If anything, the nutrients from the sewage will benefit the plants," he said.

His rafts of plants can't clean the entire canal of millions of gallons of raw sewage pumped in daily, but his project could help if it was expanded, Durkin said. And he pointed to a project in Fuzhou, China, where the process was used to clean the water in a quarter-mile-long canal fed by 80,000 gallons of sewage each day.

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.