Tenders are scheduled to be out in May for the construction of the 26km long Melamchi Water Supply Project tunnel through the challenging Himalayan Mountains 14km east of Kathmandu in Nepal.

Tunnel construction will be split into two contracts. Contract No.1, comprising the headworks and the upper 20km of the tunnel, will be open to tender to Swedish and Norwegian contractors and Contract No.2, covering the remaining 6km of tunnel will be put out to international tender.

Designed by the project’s consulting engineer, Norplan of Norway, the tunnel runs through the Precambrian Kathmandu Complex of the Higher Himalayas consisting of migmatites, banded gneisses, schists and quartzites and has a maximum overburden of 1200m. Excavation will utilize drill and blast drives of about 13m2 to 18m2 cross section. With three adits along the alignment (see diagram) the tunnel can be advanced from up to seven faces. It is expected that the drilling of sounding holes and grouting of the face will be necessary during advance to combat water ingress. The tunnel will be mostly unlined, although a spokesman for Norplan told T&TI that some less stable ground sections may require concrete lining as rock support. The tunnel has also been designed with a low gradient to allow rail bound mucking techniques.

The intake is situated at the Melamchi river, at the confluence with the Ribarma river from where the raw water will be transferred to a treatment facility near Sundaijal in the Kathmandu Valley. The project has been designed to alleviate the major potable water shortage in the area whilst improving health and economic development.

Although costs were unavailable as T&TI went to press, Contract No.1 is to be funded by the Norwegian Agency for Development Cooperation, the Swedish International Development Agency and His Majesty’s Government of Nepal (HMGN) with Contract No.2 financed by the Asian Development Bank (ADB) and HMGN. The client is the Melamchi Water Supply Development Board.

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Figure 1: Alignment of the 26km long Melamchi water diversion tunnel east of Kathmandu in Nepal