The Virginia Supreme Court on Friday dismissed one of the last major legal challenges to Alexandria’s controversial 2012 Potomac River waterfront redevelopment plan, finding that it had been lawfully adopted by the City Council in March.

The challenge, launched by three Old Town residents known as the “Iron Ladies,” contested city officials’ rejection of a petition that would have forced the council to pass the plan with a “supermajority.”

The original passage of the waterfront redevelopment plan, in January 2012, fell one vote short of a supermajority. But in March of this year, a newly elected City Council reaffirmed that decision by a 6 to 1 supermajority vote.

The high court said that because the plan passed by a supermajority in March, the case is moot, and there’s no relief it can provide.

The plaintiffs’ attorney, Roy Shannon, said Friday that although the case was dismissed, it effectively forced the city to change its methods of doing business.

“The crux of our challenge was the process,” he said. “The [council] had to revote because they did it wrong. I know for a fact they do it differently now. . . . That’s the benefit of the judicial process, to correct the legislative mistakes.”

City Attorney James Banks said the court’s decision was a major ruling for the city’s plan to redevelopment valuable waterfront property along the Potomac. Changes along the Old Town waterfront are underway, and this summer, the city established an office to manage the waterfront plan, as well as other projects.

The city plan allows developers to build two hotels and adds parks and restaurants. It also rezones eight blocks between two properties owned by the Robinson Terminal Warehouse Corp., which bookend the Old Town riverfront. Robinson is a subsidiary of The Washington Post Co.

The “Iron Ladies” — April Burke, Beth Gibney and Marie Kux — had attempted to file a last-minute protest petition opposing the waterfront rezoning as the city’s planning office was closing Jan. 20, 2012.

Unsuccessful there, they tried to file the protest with the city’s planning director, Faroll Hamer, during a City Council meeting the next day, a Saturday, but Hamer refused to accept it on the grounds that her office was not open.

Had the petition been accepted, it would have meant that, as a matter of city law, the waterfront plan could not pass without six votes. It passed by a 5 to 2 vote.

The city's Board of Zoning Appeals ruled three months later that Hamer was wrong to refuse the petition.

The city appealed that decision to Alexandria Circuit Court, which dismissed the case. The plaintiffs then appealed to the Virginia Supreme Court.

The legal challenges to the waterfront plan are not quite over, however. Shannon said he plans to amend a complaint that the Circuit Court dismissed last month, possibly reviving a challenge by his clients to the council’s vote in March.

In another case, arguments will be held Tuesday over the Old Dominion Boat Club’s control of Wales Alley, which leads to the waterfront. Circuit Court a year ago ruled that the private boat club could not prevent the city of Alexandria from making changes to the alley, because the club no longer owns an easement to it.

The boat club, based at the foot of King Street on the waterfront, owns an adjacent parking lot and parking spaces along the Strand.

The city has been negotiating with the club for years to either remove the parking lot or allow public access along the waterfront. Last week, the city announced that it had offered to settle the outstanding issues but that the boat club has not formally responded, Banks said.