Carved into the landscape, the Ota River Flood Control Channel, also known as the 太田川放水路, stands as a testament to Hiroshima’s resilience. The Ota River Flood Control Channel isn’t just a waterway. It’s a story of a city grappling with nature’s fury and a symbol of its unwavering spirit. The Ota River Flood Control Channel flows approximately 9 kilometers, diverting a significant portion of the Ota River’s flow away from the heart of Hiroshima. This engineering marvel, nearly 300 meters wide, plays a crucial role in protecting the city from the devastating floods that have marked its history.
Hiroshima’s growth, from a castle town to a bustling metropolis, occurred within the Ota River delta. The city, vulnerable due to its low-lying terrain and the significant tidal variations of Hiroshima Bay, faced a constant threat from both floods and high tides. Historically, the Ota River, prone to flooding, posed a constant threat to the city. Records show major floods occurring approximately every four to five years during the Meiji period, often sweeping away bridges and causing widespread damage. The seven branches of the Ota River, before the construction of the Ota River Flood Control Channel, struggled to contain the river’s powerful currents during flood seasons. Severe floods, dating back to 1654, are documented. More recent, devastating floods occurred in 1796, 1859, 1886, 1919, and 1928. These events highlighted the urgent need for a comprehensive flood control solution.
Construction on the Ota River Flood Control Channel, initially planned as the Yamate River Diversion Channel, began in 1932. However, World War II brought the project to a halt. By 1944, only the dredging near the river mouth and some embankment work had been completed. The project, resurrected in 1946 as part of Hiroshima’s reconstruction plan, was not without its challenges. Land acquisition disputes and protests by local fishermen and residents delayed the project significantly. It wasn’t until the late 1950s, after resolving numerous compensation issues, that construction finally resumed in earnest.
The Ota River Flood Control Channel was officially completed in 1968. Two strategically placed floodgates, the Eba and the Osaki, regulate the flow of water between the flood control channel and the old Ota River. During normal conditions, the Osaki gate is fully open. This allows water to flow into the old river channels. These supply water to the city’s inner rivers. However, during floods, the Eba gate opens and diverts the surge into the flood control channel. This protects the city center.
The Ota River Flood Control Channel’s effectiveness was quickly proven. In July 1965, just two months after its opening, a major flood hit Hiroshima. The channel performed flawlessly, preventing any significant damage. Even during the largest floods after its completion, in 1972 and 2005, the channel minimized the impact. The Ota River Flood Control Channel, more than just a flood control measure, has transformed Hiroshima. It has enabled the development of riverside parks and green spaces, enhancing the city’s beauty and livability. It has allowed Hiroshima to flourish, free from the constant fear of devastating floods. As you stand here, beside the Ota River Flood Control Channel, remember it’s a tribute to human ingenuity and a symbol of hope for a city reborn from ashes.