The Rs10.05 billion tunnel project of the Sunkoshi Marin Diversion Multipurpose Project in Sindhuli is doing better than expected as 14 percent of physical progress has been achieved in less than six months.

According to the project officials, out of the proposed 13.3-kilometre-long tunnel, 4.5 kilometres have been dug since the work began in mid-October last year.

The diversion tunnel will redirect part of the flow of the Sunkoshi River to the Bagmati River to irrigate farmlands in the Tarai. The construction site is located in Sindhuli district, about 120 km southeast of Kathmandu, on BP Highway.

The Rs83.51 billion Sunkoshi Marin project located in Sindhuli and Ramechhap districts envisages taking water from the Sunkoshi River and directing it into the Bagmati River to irrigate 122,000 hectares of farmland in Rautahat, Dhanusha, Mahottari, Sarlahi and Bara districts in the southern plains.

According to the project officials, the irrigation scheme is estimated to cost Rs37.3 billion and the hydropower component Rs46.19 billion. The tunnel is part of the irrigation component.

The water from the Sunkoshi will first be diverted to the Marin River in Sindhuli through the 7-metre-wide tunnel before being channelled into the Bagmati River. The water will then be collected at a barrage and distributed to irrigate the fields.

Low water flows in the Bagmati River have caused severe difficulties for farmers in Rautahat and Sarlahi districts in irrigating their fields. In the dry season, irrigation facilities are not available.

The project proposes to construct a 12-metre-high barrage across the Sunkoshi River and divert a discharge of 67 cubic metres per second through the tunnel to Kusumtar located in Ward 6 of Kamalamai Municipality.

A powerhouse will be built on the Marin River to generate 28.62 megawatts of electricity.

Mitra Baral, the project chief, said they planned to dig 500 to 700 metres of the tunnel every month.

A tunnel boring machine has been used to cut through the hills, which makes Sunkoshi Marin the second project after the Bheri Babai Diversion Multipurpose Project in Surkhet to do so.

The other end of the tunnel will be at Kan Dungri, which lies around 700 metres below the Triveni, which is the confluence of the Tamakoshi and Sunkoshi rivers, in Sunkoshi Rural Municipality.

According to the senior divisional engineer Ashok Raj Gautam, the project has not faced any hurdles yet. “The work in some part of Chure has been completed,” said Gautam. “We have begun digging on the Mahabharat range.”

The work would be completed before the set deadline of 22 months, Gautam claimed.

“The work at the Mahabharat range part, however, will be more difficult,” Gautam said.

China Overseas Engineering Co. won the contract for the construction of a tunnel for the Sunkoshi Marin Diversion Multipurpose Project in 2021.

The Sunkoshi Marin Diversion Multipurpose Project intends to provide a round-the-year irrigation facility to five drought-prone districts in the southern plains, decades after it was envisioned.

The project was first mooted in 2016 when the government had planned to begin a scheme titled Prosperous Tarai-Madhesh Irrigation Special Programme to provide water to the parched farmlands in five drought-prone Tarai districts.

At that time, the Ministry of Irrigation had proposed to develop the Sunkoshi Marin Diversion Multipurpose Project to provide irrigation facilities to these districts.

Insufficient rainfall has long been a recurrent problem here. A massive outflow of youths to foreign lands has created a shortage of labourers to carry out agricultural activities, making things more difficult for the local farmers.