A court-ordered study has concluded that the U.S. Army Corps of Engineers' dredging practices in the Mobile Bay ship channel did not cause erosion on Dauphin Island, according to documents released this week.

But beach erosion experts familiar with the island's sand delivery system called the report's conclusions and methods "arbitrary" and "physically impossible." The report also seems to contradict conclusions reached by the corps as far back as 1978, according to a Press-Register analysis of corps documents.

The study was released this week by lawyers representing Dauphin Island property owners who filed a lawsuit in 2000, claiming that dredging of the channel by the corps has blocked the natural westward flow of sand onto their beaches. The suit claims that corps practices caused massive erosion on the island.

The 316-page impact study was conducted as part of a 2006 settlement agreement between Dauphin Island and the federal government. Mark Byrnes, a Massachusetts-based coastal engineer, was appointed the chief investigator for the study.

The study concludes that scientific and historical data show "no measurable negative impacts associated with historical channel dredging."

As part of the settlement, three experts appointed by the involved parties were assigned to review the conclusions.

Dauphin Island's expert, Florida-based coastal engineer Robert Dean, wrote in his March 7 dissent that he has what he calls "valid questions" about the "arbitrary methodology" used in the study, and the study therefore should be considered inconclusive.

His dissent means the Corps of Engineers has until May to decide between two courses of action: Return to the U.S. Federal Court of Claims to resolve the dispute or declare the study inconclusive and consider beach restoration or other options, according to the terms of the settlement.

Scott Douglass, a coastal engineer with the University of South Alabama, has long maintained that sand moving in from the east falls into the ship channel, where it collects until the corps dredges it up and dumps it offshore -- a conclusion that motivated property owners to file the lawsuit.

"There is no way it cannot have an impact on the down-drift beaches," Douglass said on Friday, after learning about the study's conclusions. "It's physically impossible."

A 1978 report by the Corps of Engineers also attributed the erosion of 11 miles of Dauphin Island's western end to channel dredging, warning that if no action were taken, "erosion would continue to claim valuable property on the island, ultimately causing hardships for island property owners and a lessening of the area's attractiveness for recreational activities."

The report states that 6.8 million cubic yards of material had been removed from the channel and "it is assumed that none of the dredged material returns to shore."

The impact study released this week, though, claims that neither Douglass nor the corps "relied on a detailed evaluation of the historical dredging records" or historical records of the shoreline and water to reach their conclusions.

In a letter to Dauphin Island property owners dated March 20, their lawyer, Richard Davis, wrote that "we will urge the Corps of Engineers to declare the final report inconclusive and initiate the feasibility study."

Lawyers representing the federal government could not be reached for comment on Friday.

The impact study claims that breaches in the island caused by past hurricanes and storms have become refilled with sand, and the current break in the island caused by hurricanes Ivan in 2004 and Katrina in 2005 has also begun to close.

"If sufficient sand quantities were not being supplied to the island throughout the historical record, storm breaches along central Dauphin Island would be difficult to fill and beaches would not recover very rapidly," the impact study states.

The study also points to the far western end of the island, which has grown about three miles since about 1920, a period of active channel dredging, the study states.

Dean's dissent claims that "some of these data were collected many years ago at times when the survey control and technology were of lesser quality than at present."

(Staff Reporter Ben Raines contributed to this report.)