City officials today will provide details of what sewer construction to expect in Waikiki in the coming months and years as they begin work on projects designed to prevent a repeat of the huge sewage spill in March.

City officials have said they were forced to pump 48 million gallons of raw sewage into the canal after the large pipe broke to prevent sewage from backing up into hotels and homes nearby. The spill closed some of Waikiki's most famous beaches and caused health concerns.

Today, Mayor Mufi Hannemann will go to the Beachwalk area near where the March 24 break occurred on Kai'olu Street and describe the initial steps, which include installation of a 42-inch-diameter emergency bypass line.

Officials also are preparing to begin a separate but related project, building a new sewer line in the area.

Hannemann spokesman Bill Brennan said the bypass line will cost an estimated $20 million, including $2 million already spent on fixing the break in the existing 42-inch pipe.

He said the city plans to lay 7,200 feet of temporary 42-inch pipe as a bypass line that will run most of the way along the mauka side of the Ala Wai until it gets to Ala Moana Boulevard.

Brennan said the city expects to use the bypass line in several months when it does some work along Kai'olu near the break, then shift the effluent back to the existing pipe.

But the "temporary bypass" will likely remain in place for five or six years, Brennan said.

"It will be in there until a new permanent line is in place," Brennan said. "It's there in case the current line ruptures again. We may never use it."

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.