Nakdong River weir openings fail to curb algae due to drought

An initiative to open four weirs on South Korea's Nakdong River to combat severe algal blooms has been deemed largely unsuccessful due to persistent drought. The Ministry of Climate, Environment, and Energy had planned to lower the water levels at the Gangjeong-Goryeong, Dalseong, Hapcheon-Changnyeong, and Changnyeong-Haman weirs between July 30 and August 5. However, the water levels were not reduced as significantly as planned, hindering the effectiveness of the operation.

Environmental organizations argue that the ministry's failure to fully open the weirs, citing drought as a reason, prevented the removal of algae. Data shows that while the Gangjeong-Goryeong weir's water level was lowered by the planned 90cm, the Dalseong weir was only lowered by 34cm out of a planned 90cm. Similarly, the Hapcheon-Changnyeong weir saw a reduction of only 19cm from a planned 60cm, and the Changnyeong-Haman weir was lowered by 21cm from a planned 54cm. This partial opening also affected the duration the weirs were kept open, with lower sections experiencing shorter opening periods.

“

Due to the drought and low water volume in the Nakdong River, it would have taken a long time to restore the water level if we had opened the weirs as planned. We changed the plan to lower the water level less to avoid problems with water supply for agriculture.

The consequences of this limited operation were stark: algal cell counts increased across most monitoring points. For instance, the area upstream of the Gangjeong-Goryeong weir saw a 31.2-fold increase in algal cells, from 9,327 to 290,851 between July 27 and August 3. Other areas, including intake facilities and downstream sections, also experienced significant increases, some more than tenfold.

Ministry officials explained that the reduced water flow during the drought meant that fully lowering the weir levels would have taken too long to recover, potentially impacting water supply for agriculture. They expressed intentions to reopen all eight weirs on the Nakdong River when conditions permit and highlighted the need to improve water intake and pumping facilities for unrestricted weir operations. However, environmental groups remain skeptical, questioning the ministry's commitment to addressing the algae problem effectively.

“

A mere 20cm opening was ineffective for removing algae and actually increased it. We requested the opening of the four weirs from June when water levels were sufficient, but the ministry delayed it, claiming the algae was not severe. Now, they say they cannot open them due to insufficient water, making us doubt if the ministry actually intends to open the weirs.