The measure, which comes after a decade-long conflict among the central and local governments and residents over how to protect the Bangudae Petroglyphs, is expected to help South Korea's efforts to apply by 2017 to have them added to the UNESCO world heritage list.
Under their agreement, the so-called "kinetic dam" will encircle the national treasure, located on the lower part of a cliff in a tributary of a river, to protect the rock art from being damaged by inundation.
The small dam, set to be made with steel frames and the transparent material of polycarbonate, will be easy to move and dismantle, and its height will be adjusted according to water level, officials said.
"The Cultural Heritage Administration and the Ulsan municipal government reached an agreement for our great cause. I hope the Bangudae Petroglyphs are preserved as a precious asset of the world," Prime Minister Chung Hong-won said during their signing ceremony for a memorandum of understanding to push for the new preservation measures.
The engravings on the rock face of Bangudae Cliff were first discovered in 1971 by a team of experts from Seoul's Dongguk University and were designated as the country's National Treasure No. 285. They were listed on the UNESCO World Heritage Tentative List in 2011.
The engraved images include numerous humans, animals, ships, tools and nets. Experts say they are presumed to have been made some time between the late Neolithic period and the Bronze Age.
The engravings, however, are only visible for about six months of the year because Sayeon Dam, constructed downstream in 1965, submerges them under water for the rest of the year. Such a pattern of repeated submerging has eroded and damaged the engravings, according to experts.
The cultural heritage agency has insisted the level of the dam should be lowered to prevent further damage to the site since 2003 when Ulsan city began exploring ways to protect them, but the city authority has opposed the move, saying the plan would worsen the shortage of drinking water for its citizens.
"The new structure will protect the site from being flooded, and its transparent wall will allow penetration of light so as to prevent the engravings from being moss-covered," a government official said.
"After conducting a technological review, we will make a final decision on how to build the dam. If the dam turns out to be unfit as a long-term solution, it will be used just temporarily before we come up with another way," he added.