Challenges faced in diverting Saptakoshi River water to canals

By Hari Prasad Koirala,Urlabari, Dec. 18: The structures of the Sunsari-Morang Irrigation Project, Nepal’s largest irrigation scheme constructed by India in 1975 to deliver Saptakoshi River water to farmers’ fields, have become severely dilapidated. 

Although the structures were built nearly five decades ago and have outlived their lifespan, the government has been carrying out annual maintenance to distribute water through the main canal and 21 branch canals.

The irrigation project provides water to 68,000 hectares of farmland in Sunsari and Morang districts. 

However, with the structures deteriorating, concerns have grown over potential collapse of siphons and bridges atop the canals during the monsoon floods. 

The siphon and bridge over the Lohandra River were destroyed by floods on August 12, 2017, forcing farmers east of the river to depend solely on rainwater for six years. 

The destruction resulted in damage worth Rs. 340 million, leaving 11,000 hectares of farmland without irrigation.

Currently, most of the bridges, siphons, aqueducts, and control cross regulators along the 53 km-long-canal from Koshi to Keroun have fallen into disrepair.

According to Manohar Sah, Chief of the Sunsari-Morang Irrigation Project, the situation has become dire. “Fifty years ago, the population and farmland were smaller, with only 15-20 per cent of the land cultivated for wheat, mustard, and maize.” 

“But today, 80-90 per cent of the land is under cultivation, leading to a water shortage during the winter. The source lacks sufficient water, as water from Koshi must be diverted eastwards to ensure supply,” said Sah.

The project was handed over to the government in 1975 after India constructed an intake at Chatara to release 45.3 cubic metres of water per second (cumecs), along with a 53 km-long main canal, 11 branch canals, and 36 minor canals.

Since 1980, the government has been developing the project with financial support from the World Bank.

With the capacity of the main canal to carry 60 cumecs, its deteriorating structures now pose challenge during the monsoon. 

The Saptakoshi River, known as the second-highest silt-depositing river in Asia, has aggravated the situation. 

One of the two machines used to remove silt from the canal intake has been out of operation for years, leaving a single machine to work for 18 hours a day, yet failing to keep the canal clear. 

As a result, sedimentation in the canal has worsened, necessitating the construction of a “weir” (a structure to control water flow) on the Saptakoshi River.

Khangalal Sah, secretary of the Chatara Main Canal Water Users’ Committee, said, “At least 30 cusecs of water per second are required for winter crops, but only 6-10 cumecs are available at the water source. The newly built bridge over Saptakoshi has shifted the water flow westwards, leaving the eastern intake dry.”

“In areas with spurs, even ants have started crossing the dry stretches. If a weir is not built to block and redirect water, agricultural production in Sunsari and Morang could decline by 60 per cent.” 

He emphasised the need for the government to prioritise the project to maintain food security and agricultural production.

Most structures built five decades ago with bricks are now in a dilapidated condition and are being operated with repairs and makeshift solutions.  Chief Sah explained that replacing all structures would require billions of rupees, an amount beyond the government’s reach. 

Annually, Rs. 500 million is spent on maintenance. Currently, projects worth Rs. 1.07 billion are under construction to address the dwindling water source from Saptakoshi by diverting water from smaller local streams and wetlands into the main canal.

The 53-km-long main canal comprises eight super passages, 36 aqueducts, two siphons, and 16 control cross regulators, all of which are now in disrepair. 

Annual maintenance of these structures incurs Rs. 500 million, according to Chief Sah. 

To address the water diversion issue, the project has constructed eight spurs on the Koshi River’s western bank at a cost of Rs. 600 million. With these measures falling short, the main canal user committee has proposed constructing a weir to direct water into the intake.

Tapan Das, chair of the main canal committee, remarked, “The water flow has shifted towards Udayapur. Once the Sunkoshi-Marin Diversion Project is operational, 67 per cent of Koshi’s water will automatically be diverted, and the remaining flow could also shift westwards.”

“If that happens, the Sunsari-Morang Irrigation Project might as well be shut down.” Das further pointed out that 45 per cent of Nepal’s total grain production relies on Jhapa, Morang, and Sunsari districts.