Confirmed 'Mullet Upstream Movement' Through Nakdong River Estuary Barrage Opening... Second Opening from Tomorrow

First opening of the sluice gates at the Nakdong River estuary barrage.

[Sejong=Asia Economy Reporter Joo Sang-don] From April 26 to May 21 this year, the first phase of opening the Nakdong River estuary sluice gate for one month confirmed the upstream movement of marine fish such as mullet. The government plans to conduct the second phase of opening for one month starting from the 22nd.

The Ministry of Environment, together with the Ministry of Oceans and Fisheries, Busan City (Mayor Park Hyung-joon), and Korea Water Resources Corporation, disclosed on the 21st the 'Results of the First Phase Opening Operation of the Nakdong River Estuary Sluice Gate' conducted for about one month from April 26 this year to restore the brackish water ecosystem where the sea and river meet at the Nakdong River estuary, along with the 'Second Phase Opening Operation Plan.'

The first opening allowed a total inflow of 1.79 million cubic meters of seawater during the period including the spring tide when the sea tide (sea level height) is higher than the river water level, allowing seawater to enter the river.

During the opening operation period, it was confirmed that seawater flowed in even when the sea tide was lower than the river water level due to the density difference between seawater and river water. Additional seawater inflow was also observed during the ecological communication period (same as the opening operation period). Ecological communication involves keeping one sluice gate open either upstream or downstream throughout the entire period, including the seawater inflow period, to allow marine fish to move upstream.

During the first opening operation period, salinity in the river showed an increasing trend upstream and was detected up to 10 km upstream from the sluice gate, but it did not spread further due to rainfall and increased upstream flow. At the end of the opening operation (May 21), some of the inflowed salinity remained in the deepest part 7.5 km upstream of the sluice gate but was continuously diluted.

Fish surveys conducted at three upstream and two downstream points of the sluice gate before and after ecological communication opening confirmed that eels, which were not detected upstream before the opening, appeared after the opening. This indicates that ecological communication was achieved through the opening. Additionally, mullet observed downstream of the sluice gate just before the opening were confirmed moving upstream during surface opening at the sluice gate. During bottom opening, the movement of juvenile mullet was confirmed through closed-circuit television (CCTV) monitoring underwater fish, proving that both bottom and surface openings enable ecological communication.

The Ministry of Environment will conduct the second phase opening of the Nakdong River estuary sluice gate from the 22nd to June 20. The sluice gate will be operated so that seawater enters only up to about 12 km upstream of the dike, below the Daejeo sluice gate, to avoid affecting agriculture in the western Nakdong River area.

During this second opening period, a restoration project for colonies of the sedge family and the annual herb Saeseommaejagi, which are major food sources for winter migratory swans, will also be promoted.

The Ministry of Environment plans to plant Saeseommaejagi upstream and downstream of the Nakdong River estuary sluice gate and use drones to scatter seeds, following the release of 50,000 juvenile salmon in March and 50,000 juvenile Southeast Asian freshwater crabs in June this year.

Park Jae-hyun, Director of Water Environment Policy at the Ministry of Environment, said, "During the first opening period in the dry season, we stably created a brackish water environment in the Nakdong River estuary, and we plan to conduct three additional openings this year using various methods. We will continue to communicate sufficiently with stakeholders related to the sluice gate opening, including farmers, fishermen, civic groups, and experts, to establish an optimal sluice gate operation plan that everyone can agree on."

This content was produced with the assistance of AI translation services.