The Kanda River (神田川, Kandagawa) stretches 24.6 km from Inokashira Park in Mitaka to the Sumida River under the Ryōgoku Bridge at the boundary of Taitō, Chūō, and Sumida. Its entire length lies within Tokyo, Japan. It drains an area of 105.0 km². The government of Japan classifies it as a Class I river.
Tributaries and Branches:
The Zenpukuji, Momozono, and Myōshō-ji rivers are tributaries of the Kanda. The outer moat of the Imperial Palace is also a tributary. The Nihonbashi River is a distributary of the Kanda.
Kanda River Underground Diversion Channel:
Construction began in the 1980s of a diversion tunnel which could temporarily store excess water which historically has been a big problem causing flooding to thousands of homes during powerful typhoons or torrential downpours. The Kanda River Underground Diversion Channel is actually one huge tunnel built under major roads. The plan is to construct a 4.5-km tunnel, 13 m wide tunnel 40 meters below street level.
The first 2 km section was completed in 1997, and it can hold the runoff of 50 mm of rain falling in one hour. The reservoir has drawn water from the river on more than a dozen occasions since it opened, and the Kanda River has not flooded during that time. Plans call for the tunnel to be extended to Tokyo Bay, literally creating a second, underground Kanda River.