The upper reaches of the Raidāk River are also known as the Thimphu Chhu or further downstream as the Wang Chhu. It is a tributary of the Brahmaputra, the mighty Himalayan river that flows through India and empties into the Bay of Bengal in Bangladesh. At the Tashichho Dzong in Thimphu, the riverbed is 2,121 m above sea level. en.wikipedia.org/wiki/Raid%C4%81k_River