The Mekong River Commission (MRC) on Friday urged China and Lower Mekong countries to share water-release plans to help manage risks caused by sharp falls in water levels.
In a statement, the MRC secretariat in Vientiane said the Mekong had fallen to “worrying levels” between Jinghong hydropower station in China’s Yunnan province and the Mekong Delta in Vietnam.
“Continuing this flow pattern could have an impact on river transport, fish migration, agriculture and river weed collection,” said Dr. Winai Wangpimool, director of the secretariat’s technical support division.
“To help the Lower Mekong countries manage risks more effectively, we call on China and the Lower Mekong countries themselves to share their water release plans with us,” the director said.
The statement said water levels had dropped “considerably” since the beginning of the year due to lower rainfall, flow changes upstream, hydropower operations in Mekong tributaries, and outflow restrictions from the Jinghong dam.
“There have been sudden rises and falls in water levels immediately downstream of Jinghong and further down to Vientiane, which has been challenging for authorities and communities to prepare for and respond to possible impacts,” Dr. Winai said.
The statement said monthly rainfall had been consistently lower than average since November, falling by 25 percent.
On Thursday, it said, data indicated that outflow at the Jinghong station was 775 cubic metres per second — down almost half from its normal level of about 1,400 metres per second in December.
In Cambodia, water levels “have been declining steadily” in Kampong Cham and Neak Luong on the Mekong River, Phnom Penh on the Bassac River and Prek Kdam on the Tonle Sap River, the statement said.
Water levels at these locations “remained lower than their long-term averages since early November,” it said, adding that average daily falls have been 0.2 metres since January.
At Stung Treng and Kratie, however, Mekong water levels remain higher than the long-term average, fluctuating between declines of 0.02 metres and increases of 0.05 metres.
The MRC said the Mekong in Nakhon Phanom in northeast Thailand had recently turned an aquamarine colour due to the low flows, a slow drop in river sediments, and the presence of algae on the river bottom.
The statement said several factors were behind the change in colour — which also occurred in late 2019.
“The fine sediments normally found in the fast flowing and deeper water that give the river its brownish appearance are no longer present, creating clearer water conditions,” it said.
“When sunlight hits the river, the clearer water absorbs what are known as ‘long-wavelength colours’ at the red end of the light spectrum, which gives the river its blue-green hue.
“The clearer water allows microscopic plants or algae to grow on the sand and bedrock river bottom turning the margins of the river green.
“Algae are normally flushed away by the river current, but due to the low water levels it has accumulated in certain sections of the river.”
Dr. So Nam, chief environment management officer at the MRC secretariat, said blue-green water was “likely to spread to other stretches of the Mekong where low flows are experienced” — as happened did in 2019.
He said potential impacts included changes in the productivity of the river with less food available for aquatic insects, invertebrates and small fishes.
This will affect the productivity of aquatic biodiversity — reducing fish catches and threatening the livelihoods of local communities.
Dr. So Nam said the Mekong’s blue-green colour might persist until flows increase with the onset of the next flood season, which usually begins in late May.
Normal conditions may be restored if large volumes of water are released from storage reservoirs in the Upper Mekong dams in China and tributary dams.
That would mobilise sediments and return the Mekong to its typically brown appearance, the statement said.
The MRC noted that China’s Ministry of Water Resources notified the four Lower Mekong countries in January that the outflow from Jinghong would be restricted to 1,000 metres per second from Jan. 5 to 24 due to maintenance of transmission lines.
“The Ministry, however, did not specify the river water level before the outflow restriction nor the volume to be restored on Jan. 25,” it said.
The MRC recalled that China agreed last year to share year-round water level and rainfall data with the commission.
“China pledged to notify the MRC and its Member Countries of any abnormal rise or fall in water levels or discharge, and provide relevant information on factors that might lead to sudden flooding,” it said.
Source: Agency Kampuchea Press