Conservationists have raised concern that the state's 40 billion plan to divert water from the Salween River's tributaries into the Chao Phraya River is not economically viable and will be detrimental to the environment.
Veteran conservationist Hannarong Yaowalers, president of Thai Water Partnership, Sunday urged the authority to drop the project.
"The investment cost is astronomical compared to the benefits gained. In total, water diverted by this project will cost 65 baht per cubic metre for the first year of operation. That figure is vastly higher than the normal cost of 0.50 baht. The authority must carefully weigh the cost against the benefits," said Mr Hannarong, a former member of defuct National Reform Committee (NRC).
The plan is to divert water from the Yuam and Ngao rivers, both tributaries of Salween River that demarcates the Thai and Myanmar border. The project is an initiative of the Royal Irrigation Department (RID) to divert water into the Bhumibol dam in Tak, and then flush the excess into the Chao Phraya River for farmers in the lower mid-region to use during the dry season when shortages are a problem.
Mr Hannarong made his comment after his inspection of the Yuam and Ngao Rivers in Mae Hong Son's Sop Moei district.
The RID hired Panya Consultants Co Ltd, S&T Consultant Co Ltd and Naresuan University to conduct a feasibility study on the project in Sept 2016. The results are set to be announced next week after which the RID will make a decision whether to ask for government approval to proceed.
Under the scheme, a 71-metre high dam would be built across the Yuam River and a power plant will also be built in Mae Sariang district. A water pump will be built to pump water up rivers through an underground tunnel.
The electricity cost of the water pump alone is estimated at 2.4 billion baht annually. In addition, Pongpat Meebenjamat, coordinator of the Salween River resources management network, said residents fear the project could damage the natural waterway and even submerge some communities.
Somkiat Prajamwong, secretary-general of National Office of Water Resource (NOWR), said the authority has yet to make a final decision. He did, however, attempt to allay fears about environmental impact, saying: "We are building the tunnel in order to protect the forest."
Acknowledging the high cost of electricity, Mr Somkiat said the project is vital for dealing with droughts that occur every year and affect the farming industry which is a major income source of the country. "Water shortages affect the lower basin of the Chao Phraya every dry season. This project is essential to bolster water security," Mr Somkiat told the Bangkok Post.