LIHU'E, Kaua'i — Crews in search of evidence of a spillway that some residents say was covered up are expected to begin excavation along the rim of the failed Kaloko Reservoir dam during the next week.

The excavation is part of the state attorney general's continuing investigation into what caused the dam breach and flood that killed seven people downstream in March. The catastrophe occurred during a rare, extended period of heavy rain that caused damaging flooding on O'ahu and Kaua'i.

A legal action filed by the families of those killed in the flood maintains that Kaloko was built with a spillway and that the feature was altered under the jurisdiction of dam owner Jimmy Pflueger.

The state attorney general's office yesterday would not comment, but Attorney General Mark Bennett as early as a month after the dam failure said that the state's engineering consultants were considering excavating in the area where the spillway was believed to have been.

There are no known witnesses to the catastrophic failure of the 400 million-gallon reservoir at dawn on March 14, which dispatched a wave of mud, rocks, raging water and debris through the rural community of Wailapa Valley. The flood tore trees out by the roots and buildings off by their foundations, and killed seven people asleep in homes on land owned by Bruce and Cynthia Fehring along Wailapa Stream.

The spillway — whether Kaloko had one, and if so, whether it had been altered — was an early focus of investigation. A spillway is a drainage structure built into dammed reservoirs to divert excess water before it can overtop the reservoir dam.

Area residents who visited the reservoir during the 1970s through the early 1990s said they recall driving across a concrete structure that was part of a spillway, and that it was at the northern end of the reservoir, off the dam wall. No such concrete structure was visible to people who inspected the site after the dam breach. And some investigators said they could find nothing that looked like a spillway.

"We were surprised not to find one. We looked," said engineer Ray Kong, of the U.S. Army Corps of Engineers, in the weeks after the dam failure.

Pflueger attorney Bill McCorriston in the weeks after the dam failure said the spillway was still there. He denied that the spillway had been altered and said there was no evidence of a relationship between the spillway and the dam breach.

Calls to McCorriston's office were not returned yesterday.

"Whether the outflow had any substantive part in the dam's failure is a matter under study," McCorriston told The Advertiser in April.

Kaloko Reservoir, sometimes written Ka Loko, was built in 1890 for the Kilauea Sugar Co. After the sugar firm closed, owner C. Brewer sold former Hono-lulu auto executive Pflueger the majority of the reservoir, including the portion that contains the dam. That sale is recorded in county tax records as having occurred in 1989.

The remainder of the reservoir is owned by the Mary N. Lucas Trust, of which Pflueger is a beneficiary as the grandson of the late Mary Lucas.

Pflueger has filed his own legal action, arguing that state officials and C. Brewer had knowledge of problems with the dam but failed to inform Pflueger of them when he bought the property. Pflueger's representatives also argue that while he owns the reservoir, he has no authority to manage its water levels.