Rokugo Floodgate Protecting Area from Floods for 94 Years; Retro Showa Era Facility Continues as Local Symbol

By Morio Kodama / Yomiuri Shimbun Staff Writer

13:32 JST, March 17, 2025

I headed downstream on the causeway from the Rokugo Bridge over the Tama River that connects Tokyo and Kanagawa Prefecture, watching people enjoy running along the river. I soon found Rokugo Floodgate. The floodgate has been in service since before World War II and attracts people’s attention with its Showa era design, including rounded floodgate pillars and brick foundations.

According to the Keihin River Office of the Land, Infrastructure, Transport and Tourism Ministry, which manages the facility, it consists of two concrete pillars 6.3 meters in height from the levee and an iron door 5.9 meters in width. When the river’s water level at the floodgate rises to 2.5 meters, the iron door is lowered to prevent water from flowing into a residential area. The floodgate was used during typhoons in October 2019 and June 2023, according to the office.

In 1931, the floodgate was built near a discharge outlet of an agricultural water channel alongside repair work of the Tama River levee.

Construction of the floodgate was driven by population increase. Many people moved into the area from central Tokyo after it had been devastated by the massive 1923 Great Kanto Earthquake. The population of then Rokugo town, now Tokyo’s Ota Ward, where the floodgate is located, increased by more than three times over 10 years from 1920.

While the amount of domestic wastewater discharge increased, farmland areas that absorb rainwater decreased due to urban development. The river flooded frequently. Construction of the floodgate was decided in order to protect the town from flood damage.

There is a basin for tying up small boats on the residential side of the floodgate, indicating the area once thrived on water transportation. Tsuneo Yanagihara, a resident, said in a nostalgic tone, “Many boats used for loading and unloading coal residue and gravel would pass through the floodgate.”

Suimon-dori (Floodgate street) shopping street, located between the floodgate and Keikyu Line Zoshiki Station, is often buzzing with activity. The floodgate is still a symbol of the town.

Rokugo Floodgate is registered as a civil engineering heritage site selected and endorsed by the Japan Society of Civil Engineers (JSCE).

“The floodgate is essential to the history of the Tama River and the local community,” said Taro Tajima, an official at the Ota Ward folk museum.

This year marks the 94th anniversary of its completion. While the development of drainage facilities and other reasons have decreased the role of the facility, it still receives an annual inspection and other maintenance in order to keep protecting the community as an active water control facility.

Rokugo Floodgate

Address: 2-35 Minami-Rokugo, Ota Ward, Tokyo

Access: About a 15-minute walk from Keikyu Line Zoshiki Station

Memo: The closest route to the floodgate is to go across National Highway Route 15 (Daiichi Keihin) from Zoshiki Station and pass through Suimon-dori shopping street.