CHIANG RAI – The People’s Network for the Protection of Kok-Sai-Ruak-Khong Rivers, together with 19 local groups, issued a formal statement and sent a letter to the Prime Minister, the Minister of Natural Resources and Environment, and the Director General of the Department of Water Resources.
They called for a halt to the proposed sediment curtain project, valued at 173 million baht, planned for the Kok and Sai Rivers. Their main concern was the project’s lack of thorough academic research and proper community consultation.
According to Lanner News, the protest comes at a time when the Kok and Sai river basins face serious risks from arsenic and heavy metal contamination in both the soil and water. These issues impact local livelihoods, farming, and long-term confidence in both environmental health and tourism.
From Multi-Billion Baht Weirs to Reduced Sediment Curtains
Back in June 2025, the Department of Water Resources put forward a large-scale scheme to build 10 sediment-trapping weirs and sluice gates on the Kok River. The proposed budget was more than 8.6 billion baht, with nearly 300 million baht set aside each year for maintenance.
This drew strong criticism from academics and residents, who argued the plan lacked proper research and failed to explain how the weirs would handle heavy metals like arsenic, cadmium, or manganese.
There was also no clear analysis of the impact on nearby communities and conservation zones. Most significantly, the department never held a public consultation with the residents living along the river.
A month later, in July, the department revised its plan; this time proposing four sediment curtain installations with a reduced budget of 173 million baht. Three would be located in Mae Ai District (Chiang Mai), with the fourth at the border between Mae Ai and Mueang Chiang Rai districts. The department intended to bring this proposal to Cabinet in September and start construction by December 2025.
Critics argue this change is mostly a new spin on the old project rather than a new solution. They point out that the revised approach still lacks proper groundwork and local involvement.
Project Details: Sediment Curtains
According to the project documents, each sediment curtain site would include:
- A double-layer weir, 80 metres wide and 200 metres long, is used to slow water flow.
- Three sediment curtain units, designed to trap contaminated sediment.
- Settling ponds and drying fields, about 220 by 100 metres, for storing and drying the sediment before removal.
Each site would cover about 13.75 rai (just over five acres), taking up land used by local farmers and parts of protected forests next to the river.
Big questions remain. There is no clear plan for how the trapped sediment will be disposed of, whether there will be safeguards to stop contaminated dust from spreading to nearby farms, or what the real cost will be to get rid of the sediment.
Public Network’s Key Concerns
In their public statement, the 19 groups highlighted several major concerns:
- Lack of Environmental Study: There is no impact assessment, nor any study of long-term effects. The community’s input, especially from those directly affected, was left out.
- Unclear Budget: The 173 million baht does not cover compensation, land buyouts, transportation or disposal of sediment, or new roads and bridges required by the project.
- Doubtful Effectiveness: It is unclear how much heavy metal pollution the sediment curtains could remove, or which types they can trap effectively.
- Risks to Farms and Villages: The slower river flow could increase toxin build-up in flooded farmland and other areas, potentially raising health risks and harming crops.
The network stressed that without serious research and meaningful input from the community, the project would tackle symptoms rather than root causes. They urged the government to stop the sediment curtain project and called for all environmental measures to involve public consultation and comply with scientific standards and laws, to avoid unintended harm.
Unanswered Issues
Reporting from The Mekong Butterfly raised additional points:
- How will the farmland and forest required for the project be handled?
- What measures will prevent the spread of dust during sediment drying and removal?
- Will the changed river flow increase toxic sediment in farmland?
- How might building the weirs and installing the curtains affect the river ecosystem, especially local fish and biodiversity?
The Mekong Butterfly argues that the fight against arsenic and heavy metals in the river must be holistic and involve the community from the start, rather than being rushed through with top-down solutions.
For many, the sediment curtain project has come to represent more than a response to pollution—it has become a test of the government’s openness and commitment to real public engagement.
If officials move ahead without careful study or real consultation, it will only deepen existing problems, both in how budgets are used and how decisions are made. On the other hand, if the government pauses to study the issue with broad community input, the project could offer a genuine way forward for the Kok-Sai river basin.
