Do you know about the Okawazu Branch of the Okawazu River, which will celebrate its 100th anniversary this year?

  • Niigata
  • Sightseeing

Okawazu Diversion in Niigata, a prefecture of rivers

The Shinano River is known as the longest river in Japan and one of the three largest rivers in Japan. Did you know that among its many tributaries is a man-made river that is also known as the "New Shinano River"?
The Okawazu Diversion introduced here is a man-made river whose construction began in earnest in the Meiji Era and the water supply was completed in 1922.
The Okawazu Diversion, which celebrates its 100th anniversary this year, is one of the largest flood control projects in Japan and is filled with the history of flood control in the Echigo Plain.
Here are some spots where you can experience the history and grandeur of the project.

What is the Okawazu Diversion?

The Okawazu Branch of the Shinanogawa River flows from the Shinanogawa River on the left side and continues to the back of the image.
The Shinano River flows across Nagano and Niigata Prefectures. Of its 367 km length, the Okawazu Diversion, which branches off at a point about 50 km from the mouth of the river, flows into the Sea of Japan at a length of 9.1 km.
The Shinano River feeds the Echigo Plain, a rice-producing region, and was constructed to prevent flooding during heavy rains.
Two huge weirs at the junction of the Shinano River (Shinano River side: Okawazu wash weir, Okawazu diversion side: Okawazu movable weir) control the volume of the Shinano River to 270 m3 per second, and any water exceeding this level is sent through the diversion to the Japan Sea.
The Okawazu Diversion Canal is lined with 2,600 cherry trees planted on the embankment in honor of the construction of the Okawazu Diversion Canal.

History of the Okawazu Diversion

Echigo Plain plagued by flooding

Courtesy of the Shinanogawa Okawazu Museum
The Shinano River, which has a very large volume of water, has brought many blessings to the Echigo Plain, but at the same time, it has caused a lot of flood damage since ancient times.

The Echigo Plain is a marshy area with poor drainage, and once flooded, it takes a long time for the water to recede.
As a result, the Okawazu Diversion Project (Phase I) began in 1870. However, the construction was halted in 1875 based on the opinion of a foreign engineer that "the construction of the Okawazu Diversion would make the water depth at the mouth of the Shinano River shallower and affect Niigata Port.
After that, many industrialists and residents continued to appeal for the necessity of the Okawazu Diversion.

Then, in July 1896, a major flood event known as "Yokota-giri" occurred. Many levees broke, inundating a very large area (180㎢) from Nagaoka to almost the entire Niigata area, and many people lost food and shelter.

Construction

Large machinery used in the construction work: Shinanogawa Okawazu Museum
Landslide (1915)Courtesy of the Shinanogawa Okawazu Museum

In response to the growing demand for the construction of the Okawazu Diversion, the government officially decided to construct the project in 1907, and the second phase of construction began in 1909. The construction work was of an unprecedented scale at the time, involving as many as 10 million people, and was also referred to as the "Panama Canal of the Orient" due to the lavish use of the latest large machinery and state-of-the-art technology from Japan and abroad.
The canal has been called "the Panama Canal of the Orient." It has been two centuries since the first petition was submitted, and after nearly 15 years of construction, the canal was opened to traffic on August 25, 1922, despite the problems of massive landslides and other problems.

It is deeply moving to know that such large-scale construction work was done 100 years ago.

From the passage of water to the present day

Movable weir constructed by repair work (1931) Courtesy of: Shinanogawa Okawazu Museum
In 1927, the Jizai-weir, which was located at the time of the diversion, collapsed. The Shinano River repair work then led to the construction of a movable weir to replace the Jizai-weir. In 1931, all construction was completed and the Okawazu Diversion became functional.

The construction of the Okawazu Diversion not only reduced flood damage, but also led to a reduction in the width of the river and an increase in farmland and urban areas in the downstream areas where the water volume had decreased. It is clear that the river played a very important role in the development of Niigata.

In recent years, the wash weir (on the Shinano River side) was reconstructed in 2002 and the movable weir (on the Okawazu Diversion side) in 2014 to replace the aging weirs. Currently, various construction works, known as the "2025 Great Repair," are underway.

Why don't you take a look at the Okawazu Diversion, which has greatly contributed to the development of modern Niigata, and think about the history of Niigata with your own eyes?

Spots where you can experience the Okawazu Diversion

Shinano River Okawazu Museum

Courtesy of the Shinanogawa Okawazu Museum

Visitors can learn about the history of the Okawazu Diversion and the construction work that was done 100 years ago through a video theater, simulations, and even an actual trolley.
From the observation room on the fourth floor, visitors can enjoy a panoramic view of the Okawazu Diversion.

Old washing weir

Courtesy of the Shinanogawa Okawazu Museum

The former Okawazu Sewer (on the Shinano River side), which has been in use since 1922, remains in its original state. After the completion of the new weir, the area was developed as a plaza, and visitors can pass under the gate.
It is a nationally registered tangible cultural property.

Okawazu Branch Canal 100th Anniversary Memorial Site (open in new window)
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