The Mekong River Commission (MRC) has warned that the lack of water in the Tonle Sap Lake is still critical even though the flow of the Tonle Sap River finally started reversing last week.
As Mekong water levels rise at the end of the annual dry season, the Tonle Sap River changes direction with flows heading upstream towards the lake from mid-June.
But in its wet-season situation report released Thursday, the MRC’s Flood and Drought Management Centre in Phnom Penh said it did not observe the reversal until Aug. 4.
“The delay of the reverse flow was due to the low water levels on the Mekong mainstream,” the report said.
“Low inflows from the Mekong River are most likely affected by less rainfall in the upper sub-catchment areas,” it added.
The MRC hydrograph for the Tonle Sap River at Phnom Penh Port showed that water levels had risen to sightly above all-time lows as of 07:00 on Thursday (see chart).
“Although the reverse flows have started, the volume of the Lake up to this point is considered to be in a critical situation,” the report said.
The centre noted that low inflows from the Mekong were accompanied by low inflows from tributaries around the Tone Sap Lake.
With more than half the lake’s inflow coming from the Mekong, “flow alterations in the mainstream could have direct impacts on the Tonle Sap water levels,” it said.
Low water levels along the mainstream “have resulted from less inflows from tributaries and low inflows from upstream part since June,” the report said.
“This could have been partly due to reservoir operations in the mainstream of the Upper Mekong Basin and from tributaries” in the Lower Mekong Basin.
The upper basin’s contribution to Mekong flows from China is about 16 percent by the time the river discharges through the Mekong Delta into the sea.
But the main contribution comes from two major left-bank tributaries between Vientiane in Laos and Stung Treng, which has recently been experiencing an extreme drought.
These tributaries are “another potential reason for the low flows in the mainstream” between January and July.
But the MRC reiterated that it had “no official data” to quantify or verify their contribution to mainstream Mekong flows or the extent of such impacts.
Between Monday and Thursday this week, the MRC forecast Mekong River water levels to increase by 0.06 to 0.95 metres between Stung Treng and Neak Loeung.
Between Monday and Wednesday, Tonle Sap water levels were forecast to climb by 0.05 to 0.45 metres at Prek Kdam and Phnom Penh Port.
Bassac River water levels between Chaktomuk and Koh Kel were forecast to rise 0.55 metres in the same period.
In a separate drought forecast for the seven days to Sunday, the centre said Kratie, Mondulkiri, Stung Treng and Rattanakiri provinces would continue to suffer from moderate, severe and extreme drought.
“Low density rainfall in July is the main factor causing deficit soil moisture,” the forecast said.
Source: Agency Kampuchea Press