The installation of a tunnel boring machine at the Sunkoshi Marin Diversion Multipurpose Project in Sindhuli is expected to begin in May.

The machine will gouge out a 13.3-km-long tunnel to connect the Sunkoshi and Bagmati rivers. It will be the second such tunnel in Nepal after the Bheri Babai tunnel in the southwest.

For the last four months, workers have been flattening the land at the mouth of the proposed tunnel to create a platform where the machine will be installed.

The tunnel will redirect part of the water 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 machine will start digging from the site in Kamalamai Municipality-2, Kusumtaar.

"A 200-metre-long platform needs to be built to install the machine," said Mitra Baral, chief of the project. "The tunnel boring machine has been made in China, and as per the agreement with the project developer, it will arrive in Nepal via Kolkata port in India by May."

Baral said that the tunnel digging work would begin after four months.

In February last year, China Overseas Engineering Co won the contract for the construction of a tunnel for the Sunkoshi Marin Diversion Multipurpose Project by offering to do it for Rs10.05 billion, nearly Rs6 billion less than the price quoted by the government.

The Chinese company will use a tunnel boring machine to cut through the hills, which will make Sunkoshi Marin the second project after the Bheri Babai Diversion Multipurpose Project in Surkhet to perform such an engineering feat.

The 12.2-km Bheri Babai tunnel was also constructed by China Overseas Engineering Co to irrigate 51,000 hectares of land in Banke and Bardia districts in south-western Nepal.

Biswo Nath Poudel, vice-chairman of the National Planning Commission who inspected the project site recently, said the government had arranged financial resources for the project, and that the project should not be delayed at any cost.

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 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 a 7-metre-wide tunnel before being channelled into the Bagmati River. The water will then be collected at a barrage and distributed to irrigate fields.

Low water flows in the Bagmati River have caused severe difficulties for farmers in Rautahat and Sarlahi districts to irrigate 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 also be built on the Marin River to generate 28.62 megawatts of electricity.

The installed capacity of the hydropower project had initially been set at 42.3 megawatts. During the feasibility study, planners decided that a 28.62 megawatt project would be most economical and viable.

The Sunkoshi Marin Diversion Multipurpose Project intends to provide round-the-year irrigation facilities 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 launch a scheme entitled Prosperous Tarai-Madhes Irrigation Special Programme to provide water to 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, creating a shortage of labourers to carry out agricultural activities, has made things more difficult for local farmers.

The proposed multipurpose project will inundate 312 hectares of land, and create a pond in Sunkoshi and Khadadevi rural municipalities and Manthali municipality affecting 3,026 households, as per a draft of the environmental impact assessment.

The scheme will also submerge a 1-km stretch of Banepa-Bardibas Highway (BP Highway) and a 475-metre stretch of the road will have to be realigned to accommodate water intake and other structures.