Upper Tamakoshi Hydropower Halts Production for Critical Reservoir Flushing Amidst Monsoon Challenges

The Upper Tamakoshi Hydropower Project, a cornerstone of Nepal's energy infrastructure, temporarily ceased its 456-megawatt electricity generation on Sunday for a crucial 10-hour period. This strategic shutdown was necessitated by the urgent need to clear a significant accumulation of sediment – comprising stones, sand, and silt – from its reservoir, a direct consequence of recent torrential monsoon rains and subsequent flooding in the upstream areas.

Located in Bigu Rural Municipality, Dolakha, the Upper Tamakoshi project is the largest hydropower facility built with domestic investment, playing a pivotal role in stabilizing the national grid. However, its operation is frequently challenged by the geological vulnerabilities of the Himalayan region, particularly during the monsoon season when heavy rainfall leads to increased sediment load in rivers. The recent floods caused an unprecedented buildup of debris, posing a substantial risk to the plant's operational integrity.

Project officials explained that the emergency measure was critical to prevent potential technical malfunctions and severe damage to the plant's machinery. Sediment accumulation can clog the trash racks, which filter water entering the turbines, and, more critically, lead to abrasive wear and tear on the high-precision turbine blades. Such damage could result in prolonged shutdowns and costly repairs, jeopardizing the nation's power supply.

The "reservoir flushing" operation commenced early Sunday morning, involving the opening of two large gates to completely drain the reservoir. This process allows the high-velocity water to scour and wash away the accumulated sand and silt from the reservoir bed. According to Acting Project Manager Purnagopal Ranjit, the team aimed to complete the flushing by evening, with electricity generation expected to resume after 6 PM. While routine reservoir cleaning is typically scheduled twice a year, the intensity of this year's early monsoon floods necessitated an expedited intervention.

In anticipation of the significant increase in water flow downstream, the project issued a public safety alert, urging residents along the Tamakoshi River in Dolakha, Sindhuli, and Ramechhap districts to exercise extreme caution. The sudden release of a large volume of water from the dam could create flood-like conditions, posing risks to those near the riverbanks. The advisory specifically warned against fishing, bathing, washing clothes, or taking livestock near the river throughout the day.

The Upper Tamakoshi Hydropower Project has a history of grappling with sediment challenges, having undergone similar emergency flushing operations in the past. The primary culprits are the tributary rivers that feed into the Tamakoshi, carrying vast quantities of geological debris from the fragile mountainous terrain. Effective sediment management remains one of the most complex technical aspects of operating hydropower projects in Nepal's unique geography.

Despite the 10-hour production halt, the Nepal Electricity Authority (NEA) assured the public that alternative arrangements were in place to manage the national power supply, minimizing any significant disruption. Technical teams continuously monitored the flushing process, ensuring its efficiency and safety. Upon successful completion, the reservoir will be refilled, and all six generating units are expected to resume full-capacity production, leveraging the high water flow characteristic of the monsoon season. This essential maintenance is vital for the long-term safety, efficiency, and extended lifespan of the project's critical machinery, securing Nepal's energy future.