The Three-Way Water Flow: The Shimomasuda Irrigation Canal

A Unique Irrigation Canal

The Masuda Main Irrigation Canal draws water from the Natori River to deliver essential water to the fields of Natori City and Iwanuma City.

Among those waterways, the Shimomasuda Irrigation Canal, which runs from the upper sluice gate in the Tegurada district, past the south side of Natori Station, near the Natori Post Office, and south of the Cultural Hall parking lot, all the way to the Sendai Eastern Road, has a rare design where the flow is split into three.

Why was it built this way? We asked the Natori Land Improvement District about it.

Even if the flow is together, the functions are separate

Regarding this waterway, only the central channel is an actual "irrigation canal," while the channels on the left and right are "drainage canals."
Most of the current structure was built in the mid-1970s. Around this time, starting in the late 1960s, water pollution caused by domestic wastewater flowing directly into canals became a problem across Japan. Many people have likely seen photos or footage from that era showing rivers foaming due to laundry detergent.
During that period, when developing a waterway passing through the densely populated Masuda district, this design was adopted to separate the irrigation water coming from upstream from the drainage water flowing in from the surrounding area, a configuration rarely seen elsewhere in the country.

Nowadays, with the development of septic tanks and sewage systems, domestic wastewater rarely flows into the drainage canals. Except when water is being run through to prevent the accumulation of mud and the like, water usually flows only through the central "irrigation canal."

To protect the fields and rice from water pollution caused by domestic wastewater

Amidst the nationwide problem of water pollution, there was a desire to deliver clean water to the fields. I felt the strong determination of our predecessors, embedded in this rare design, from this very waterway.