The state Department of Land and Natural Resources is exploring an idea to create a new lagoon-type beach next to the Waikiki Aquarium.

The lagoon would be between the aquarium and the concession area, said Dolan Eversole, a University of Hawai'i coastal geologist and adviser to the state's Office of Conservation and Coastal Lands. He added that it would be similar in concept, although a third or half the size of, the lagoons at Ko Olina.

Such a project would involve excavating part of Kapi'olani Park to make way for a lagoon-type beach spanning roughly 200 feet horizontally and about 150 feet inland from the existing shoreline, he said. Breakwater structures allowing for water circulation would likely be in line with the existing shoreline, he said. Eversole estimated the project could cost up to $4 million, but said there are many variables that would affect the cost.

"It would provide a new recreational opportunity — quiet water setting, swimming and recreational beach," Eversole said.

Eversole emphasized that creating a lagoon is still a concept. He said department officials are bouncing around the idea of possibly creating two smaller lagoons, but are leaning toward one medium-sized lagoon.

The department doesn't have funding for such a project and has yet to receive feedback from the administration and the community about the idea, he said. If state officials decide to go ahead with the proposal, the department would first need funding from the Legislature for a feasibility study, which could take up to two years and result in different designs for the project, he said.

"We're a long ways off from actually implementing it, but we're kind of bouncing the idea around," Eversole said.

"We're just thinking of another recreational opportunity and a way to enhance the (Kapi'olani) Park use. This hasn't really gone through the channels. We want to talk to the mayor about it and the city officials and kind of get their ideas, too."

The department also is looking at long-term approaches to protect beaches from sand erosion. Officials plan to begin a $500,000, 30-day sand replenishment project this month at Kuhio Beach.

"We're always interested in protecting existing beaches where we can and enhancing those that are experiencing erosion and coastal damage — trying to enhance those opportunities," he said. "And Waikiki is kind of a special case because of its social, recreational and economic value as well."

Reach Lynda Arakawa at larakawa@honoluluadvertiser.com.