The ambitious Gohpur–Numaligarh underwater road-cum-rail tunnel project in Assam is moving ahead with plans for four artificial islands in the Brahmaputra. These islands will serve as approach and infrastructure platforms for the tunnel and are designed to withstand the river’s severe floods and erosion.

What is the Project?

The project, spearheaded by the National Highways and Infrastructure Development Corporation Limited, will create a 33.77-kilometre greenfield corridor, including a 15.79-kilometre twin-tube underwater tunnel.

• Two artificial islands will support road infrastructure, while two will support the railway system.
• The road islands will be around 1.4 kilometres and 1.6 kilometres long, while the railway islands will be approximately 2 kilometres each.
• The project has a civil construction cost of about ₹11,982 crore and a construction period of five years.
• One tunnel tube will carry four-lane road traffic, while railway infrastructure will be accommodated in the other tube.
• The tunnel is designed for a 100-kilometre-per-hour speed, around 30,756 passenger car units of traffic and a 100-year structural design life.

Engineering for the Brahmaputra

The most challenging aspect is protecting the tunnel from riverbed scour—the removal of soil and sand from the riverbed by powerful flowing water.

• The artificial islands must have a finished reclamation level at least 2.5 metres above the highest flood level.
• The tunnel must retain at least 25 metres of riverbed cover above its crown even at maximum scour depth.
• Cross passages will be provided every 500 metres, improving emergency safety and evacuation between the twin tubes.

These provisions are particularly important because the Brahmaputra is characterised by high discharge, intense floods, sediment movement and riverbank erosion.

Connectivity and Strategic Importance

• The tunnel will connect NH 15 & NH 715 and integrate two railway networks on the northern and southern sides i.e. Rangia–Murkongselek Railway & Furkating–Mariani loop line.
• It will provide significant benefit to the states of Assam, Arunachal Pradesh, Nagaland and other NE states.
• It can reduce travel barriers created by the Brahmaputra and promote regional economic integration. 
• It will facilitate movement of goods, access to markets and faster movement between Upper Assam and northern Assam.
• It will generate approx. 80 lakh person-days of direct and indirect employment.

About the Project

• The Cabinet Committee on Economic Affairs has approved the construction of India’s first underwater twin-tube road-cum-rail tunnel beneath the Brahmaputra River in Assam.
• The project will connect Biswanath’s Gohpur on NH-15 (North Bank) and Golaghat’s Numaligarh on NH-715 (South Bank)  through a 33.7 km access-controlled corridor.
• Once completed, it will become the first underwater road-rail tunnel in India and the second in the world, after the Fehmarnbelt link between Germany and Denmark.

Key Features of the Project

• The 33.7-km corridor will include a 15.79 km twin-tube tunnel and 17.91 km of approach roads (10.15 km on Gohpur side and 7.76 km on Numaligarh side).
• The twin-tube tunnel will be constructed using Tunnel Boring Machine (TBM) technology beneath the Brahmaputra River.
• The tunnel will be located approximately 57 metres below the riverbed, ensuring safety and structural stability.
• It will provide road connectivity, while one of the tunnel tubes will also accommodate railway infrastructure, enabling multimodal transport.
• The twin-tube structure will consist of two separate tubes, each designed for a two-lane highway. 
• One of the tubes will also have a rail-cum-road facility, with the railway line embedded within the roadway. 
• In normal times, the tunnel will operate as a four-lane road. 
• During exigencies, one tube will facilitate railway operations, converting it into a two-lane road with one railway line. Cross passages will be provided at every 500 metres for safety. 
• The project will be developed under the Engineering, Procurement and Construction (EPC) mode, where the contractor handles design, construction, and delivery.
• The construction cost is estimated at Rs 11,982.36 crore, while the total capital cost stands at Rs 18,662.02 crore. 
  • The cost will be shared between the Ministry of Road Transport & Highways and the Ministry of Defence in an 80:20 ratio. 
  • The Government of Assam will bear 50 % of the SGST on the construction cost, amounting to around Rs 539 crore.
• Major implementing and stakeholder agencies include:
  • National Highways and Infrastructure Development Corporation Limited
  • Indian Railways
  • Government of Assam
  • Indian Army (due to strategic importance)

Exam Hook – Prelims

Consider the following statements about the Gohpur–Numaligarh tunnel project:

1. It will pass beneath the Brahmaputra in Assam.
2. The project includes both road and railway infrastructure.
3. It is designed with protection against riverbed scour.

Which of the statements given above is/are correct?

Answer: 1, 2 and 3.

One-Line Wrap

The Gohpur–Numaligarh underwater tunnel represents a major engineering response to the Brahmaputra’s challenging river environment while opening a new connectivity corridor across Assam.