The cities of Denham Springs and Walker and others filed a class-action lawsuit against the state Department of Transportation and Development on Thursday, claiming a median barrier built along Interstate 12 caused widespread destruction by preventing the flow of rainwater during the historic August flooding in Livingston and East Baton Rouge parishes.

The 19-mile median wall, built between eastbound and westbound lanes of I-12 as part of the “Geaux Wider” project, acted as a dam that interrupted the natural flow of water, causing damage that would not have occurred otherwise, according to the lawsuit filed in Baton Rouge state court.

City officials hope the lawsuit will spur the state to fix the problems they say were created by the private contractors who designed and built the wall — and to do so before another flood threatens. They also want the state to correct the design for future I-12 expansions.

“Our primary goal is to make sure this never happens again,” Joshua Palmintier, of DeGravelles Palmintier law firm, said during a press conference held at Walker Town Hall. “We are optimistic this process can be started quickly and economically, before the next hurricane season.”

Palmintier, whose firm signed onto the case at the request of former Walker Mayor Rick Ramsey, said many of the 100,000 or more homes and businesses that flooded north of the wall were not covered by flood insurance because they were not in high-risk flood zones.

Denham Springs Mayor Gerard Landry said another flood like the one in August “would mean the death of several cities along the I-12 corridor.”

“We’ve barely survived it once. I don’t think we could sustain a second time,” he said.

Livingston Parish President Layton Ricks said unless Gov. John Bel Edwards steps in, the problems will continue with future floods.

Rodney Mallett, a DOTD spokesman, said in an emailed statement that safety barriers built on Louisiana interstates are designed and constructed according to national standards.

He said Gov. Edwards and DOTD Secretary Shawn Wilson met with Ramsey to discuss his concerns about the I-12 median wall.

“The unprecedented flood event resulting from historic rains caused tremendous damage and destruction,” Mallett said. “We continue to study the ramifications of public infrastructure in natural disasters. DOTD’s focus is on what is best for citizens of Louisiana. In doing so, safety of the traveling public must always be our first priority.”

The lawsuit targets not only the state, but also 20 private contractor firms that worked on the interstate project, and seeks damages for property and economic losses from the flooding.

The naming of one private firm as a defendant presents a potential conflict for Livingston Parish government. Forte & Tablada serves as the parish’s planning review engineering firm.

Ricks said he did not know what role Forte & Tablada may have played in the design and construction of the barrier wall. Nor had he realized the firm would be among the named defendants until the day before the lawsuit was filed, he said.

“Our intent is to support this lawsuit, but I want to make sure the Parish Council is fully informed, as I have now been, of all the potential players in this situation before the parish signs on,” Ricks said.

Also joining the press conference Thursday in support of the lawsuit were Central Mayor Jr. Shelton and newly seated Walker Mayor Jimmy Watson, who said the wall must be fixed and residents whose homes were built a foot above base flood elevation and still received 3 feet or more of water should get some kind of relief.

Follow Heidi Kinchen on Twitter, @HeidiRKinchen.