CHIANG RAI – Since early May 2025, Thai authorities and military engineers have been working hard along the Sai River in Mae Sai, Chiang Rai. Their main goal is to prepare for the rainy season and prevent another flood like the one at the end of last year.
Their plan includes building new flood barriers and dredging the Ruak River, a tributary south of the Sai. These efforts are part of a joint agreement with Myanmar, set to be finished between 18 April and 20 June.
The Sai River is narrower and shallower than before, due to mud and sediment left by last year’s flood. Even light rain at the end of April caused water to spill over the banks, flooding border markets and nearby areas on both sides.
Thai teams are building a three-metre-high floodwall on the Mae Sai side. The work stretches around three kilometres, from the Cave Pa Chom community through Hua Fai, Sailom Joy, Ko Sai, and Mai Lung Khon, ending at the second Thai-Myanmar Friendship Bridge.
The structure uses a base of sand and soil, reinforced with seven-metre-long concrete piles driven four metres into the ground. The finished wall stands about twenty to thirty centimetres higher than last year’s highest flood level, with both permanent and temporary sections.
Excavators continue to clear out the Ruak River from Ko Chang in Mae Sai down to the Golden Triangle in Chiang Saen.
They dig out sections of fifty to one hundred metres at a time, removing silt and soil to ease water flow and prevent the banks from collapsing. Temporary wooden piles help hold the riverbank until the digging is done.
Meanwhile, Myanmar has yet to begin dredging its share of the Sai River in Mae Sai, despite the earlier agreement. Authorities there are only building concrete flood barriers at certain spots.
Chiang Rai governor Charin Thongsuk says the new Thai floodwall should be enough to handle high water, but real safety depends on Myanmar starting its dredging.
Myanmar, formalised through bilateral discussions, assigns Myanmar responsibility for dredging a 12.8-kilometre section of the Sai River, while Thailand handles a 14-kilometre stretch of the Ruak River and an additional 18 kilometres of the Sai River.
Myanmar’s internal challenges, including political instability and environmental issues, may contribute. Large-scale gold mining in Shan State, particularly in Mong Hsat, has increased sediment in the Sai River, making dredging more urgent but also more complex.
These operations, often linked to the United Wa State Army and junta-aligned militias, have gone largely unregulated since the 2021 coup, complicating coordination for dredging.
Without Myanmar’s dredging, the Sai River, now narrowed to less than 50 meters from its original 200 meters, remains prone to overflow, as seen in the April 2025 flooding in Mae Sai and Tachileik.
Both sides acknowledge the need to address upstream mining and remove encroaching structures, but Myanmar’s delays could undermine these efforts, leaving communities vulnerable
Chiang Rai’s governor has asked the Ministry of Foreign Affairs to push for quick action on the Myanmar side, so the river can better cope with heavy rain.
