Nepal Built a 111 MW Power Plant Inside the Himalayas — Then the Flood Came

Deep inside the Himalayas, engineers spent more than a decade building Nepal’s 111 MW Rasuwagadhi Hydroelectric Project. This was not a giant storage dam. Rasuwagadhi is a run-of-river hydropower system designed to divert part of a Himalayan river through more than four kilometers of underground waterway, use roughly 168 meters of gross head to drive three vertical-axis Francis turbine-generator units, and return the water downstream through a tailrace. Its powerhouse was built underground. Its headrace tunnel stretches about 4,185 meters through the mountain. Its hydraulic system was designed around a discharge of 80 cubic meters per second. Commercial operation finally began on December 31, 2024. Then, just over six months later, disaster arrived from upstream. On July 8, 2025, a glacial flood traced by Nepal’s disaster-management authorities to the rapid discharge of a supraglacial lake associated with the Purepu Glacier in Tibet moved into the river system leading toward Nepal. At Rasuwagadhi, the flood damaged headworks and hydromechanical systems, inundated parts of the underground powerhouse, filled the tailrace tunnel with debris and logs, damaged access infrastructure, and forced generation to stop. But this was not a giant dam collapse. The underground powerhouse cavern did not simply cave in. The deeper engineering problem was that even a power station protected by a mountain still has to remain connected to the river outside. In this documentary, we follow the full engineering process: the Himalayan terrain, the run-of-river concept, the 4.185 km headrace tunnel, difficult underground geology, the powerhouse cavern, Francis turbine installation, hydraulic head and pressure, tailrace and transmission systems, more than a decade of construction, and the July 2025 flood that exposed the vulnerability of the plant’s river interfaces. The central question is simple: How can engineers put a power station inside a mountain — and still remain vulnerable to the r