Kathmandu, Aug. 30 -- The road to Rasuwagadhi was less a conventional highway than a narrow shelf cut into the steep walls of the Bhotekoshi gorge. In places, the asphalt clung directly to the mountainside above the river, with the milky-turquoise Bhotekoshi roaring far below. The road edge plunged almost vertically into the churning rapids, leaving barely enough room for two cargo trucks or containers to squeeze past each other.

At the end of this precarious corridor lies the Rasuwagadhi border point in Rasuwa district, Nepal's main overland gateway to China. Across the frontier is Gyirong, known in Nepal as Kerung, a Chinese border town connected to Tibet's road network.

The floods that tore through the Bhotekoshi corridor on August 2...