MELAMCHI TUNNEL TEST Deadline 2021

The testing and commissioning of the Melamchi Drinking Water Project will start on January 2021

Dec. 4, 2020, 8:59 a.m. Published in Magazine Issue: VOL. 14 No. 07, November 27, 2020 ( Mangsir 12, 2077) Publisher: Keshab Prasad Poudel Online Register Number: DOI 584/074-75

After suffering a major set-back in July, Melamchi Drinking Water Project will start testing and commissioning of the project only by completing a thorough inspection from foreign experts.

Although the project was scheduled to start the testing at the beginning of December, completing all the remaining works, including the damaged gate and audit tunnel, the decision now is to bring foreign experts for final inspections of the work and gate before filling the water.

“Following thorough inspections and observations by foreign experts, we will start final testing and commissioning. It will start only in January 2021,” the secretary of the Ministry of Water Supply told New Spotlight. “We have learned a lot of lessons from the past and we will resume testing and commissioning after all technical inspections.”

The tunnel is going to be re-tested correcting the error after an incident occurred in course of a trial run around four months ago.

A spokesperson at the Ministry of Water Supply, Ritesh Kumar Shakya, said that a plan has been set to test the tunnel again sending water in it as activities to correct the previous error are likely to be completed. He shared that the activities to correct the errors in the sluice gate to the tunnel are likely to be completed within December.

Following the completion of the corrective works on the tunnel gate within November, a high-level foreign expert will likely arrive in December to inspect the work and see the corrective step taken in the tunnel.

Drinking water would be distributed in Kathmandu Valley only after the water reaches the water treatment center at Sundarijal. There are two water treatment centers in Sundarijal.

The water diverted from the Melamchi stream in Sindhupalchok district would be distributed soon after the water reaches Sundarijal, Kathmandu as necessary structures have already been constructed in Kathmandu Valley for the same.

An incident occurred on July 14 when the gates of the tunnel at Helambu rural municipality-1 of Sindhupalchowk district collapsed due to a technical error.

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A committee formed under the Joint-Secretary of the Ministry, Ramakanta Dawadi, to study the incident concluded that the incident had taken place as the gates, which should be inside the tunnel, were kept outside the tunnel.

The Melamchi Water Supply Project (MWSP) is considered to be the most viable long-term alternative to ease the chronic water shortage situation within the Kathmandu Valley. The Project is designed to divert about 170 MLD of freshwater to Kathmandu Valley from the Melamchi River in the Sindhupalchowk district. Augmenting this supply by adding about a further 170 MLD each from the Yangri and Larke rivers, which lie in the upstream proximity of Melamchi is also being investigated as future supply sources.

It is said that the main reason for the failure of the gate is that the door opened into the adit, rather than into the main waterway. Had it been installed to open into the waterway, it would have been self-locked by the water pressure. The water pressure instead pushed the adit door open.

According to a report presented by the inquiry committee, there is structural damage to the tunnel and its rock support in filling and the rapid emptying of the tunnel. Similarly, the rock of audit and other infrastructure remains intact.

The tunnel is designed as a lined tunnel with rock bolts and shotcrete for immediate support and with 35cm of shotcrete final lining specified by the design. Reaches in good quality rock classification 1, 2 and 3 are unlined.

With the incident, the Ministry has already directed to change the design of the gates and install them to open into the waterway.

There are a total of 29 control gates for the operation of the water supply tunnel including five 12.5m 2 adit bulkhead gates with a radial gate at the intake and a control gate at the downstream end.

The gates for the project are designed, supplied and imported to Nepal and installed by a company from India. The project contractor, Sinohydro of China, completed the civil works associated with the installation of the gates including the rock support around the doors and the shotcrete support of the adit junction with the main tunnel. All the adit gates were closed ahead of the watering-up test.

The accident was caused due to errors in the knot bolts used to lock the adit bulkhead door. "The door had been tightened with 30-knot bolts. The knot bolts got slipped due to the water pressure, which unbolted the door," a quote said.

Learning from the last accident, a team of project officials led by secretary Belbase of the Ministry of Water Supply will start filling water only after thorough inspections of the tunnel and repair of damage.

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Photo Courtesy: Surya Thapa's facebook wall

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