In Mabi, Kurashiki City, the banks of the Oda River and its tributaries, including the Takama River, breached during the July 2018 Heavy Rain Event, flooding a wide area and causing extensive damage.
About three and a half years after the disaster, in February 2022, lights and activity have returned to the town.
However, even now, large dump trucks and other vehicles frequently travel through Mabi on weekdays, as construction work to improve disaster preparedness continues.
Named the “Mabi Emergency Flood Control Project,” the large-scale construction undertaken by the national government, Okayama Prefecture, and Kurashiki City aims for completion by March 2024 (the end of fiscal year 2023).
This article introduces an overview of the “Mabi Emergency Flood Control Project” and the progress of construction as of February 2022, including an interview with Yasuhiko Hamada, director of the Takahashi River and Oda River Emergency Flood Control Office.
The information presented was current when this article was published in March 2022. Please note that it may differ from current information.
What Is the “Mabi Emergency Flood Control Project”?
The “Mabi Emergency Flood Control Project” is the collective name for the structural and non-structural measures being implemented in response to the July 2018 Heavy Rain Event.
The main projects are as follows:
- Oda River Bank Restoration Work (completed June 14, 2019)
- River Channel Excavation Work (completed June 10, 2021)
- Levee Reinforcement Work
- Oda River Confluence Relocation Work
The national government, Okayama Prefecture, and Kurashiki City are working together to accelerate improvements. In particular, the Oda River Confluence Relocation Work is being carried out under the Special Emergency River Disaster Prevention Project, with the original completion deadline of fiscal year 2028 brought forward to fiscal year 2023.
Because these are river construction projects, the focus is often on “structural measures,” but another feature is the implementation of non-structural measures aimed at ensuring that no one is left behind when evacuating.
Oda River Bank Restoration Work (completed June 14, 2019)
Photo courtesy of: Takahashi River and Oda River Emergency Flood Control Office
After the levee breached during the July 2018 Heavy Rain Event, a temporary levee was built using sandbags and other materials.
This work involved removing it, rebuilding the embankment, and restoring the levee.
This work was completed on June 14, 2019.
Photo courtesy of: Takahashi River and Oda River Emergency Flood Control Office
River Channel Excavation Work (completed June 10, 2021)
This work involved excavating the Oda River channel to increase the area available for water to flow through.
This work was completed on June 10, 2021.
Levee Reinforcement Work
This work reinforces and widens the levees along the Oda River, which runs across Mabi.
- Widening the levee crest (the width at the highest point of the levee, often a road) from about 5 meters to 7 meters
- Making the levee slope gentler (approximately a 1:3 slope)
- Installing drains as needed to quickly remove seepage water
The most readily apparent change is the widening of the levee.
There was already a road on the Oda River levee, but before it was widened, cars could barely pass each other. After the widening, the levee became broad enough for cars to pass each other easily.
Incidentally, the large volume of soil (308,000 cubic meters) produced by the river channel excavation is reportedly being mixed with soil from the Takahashi River and also used to reinforce the levees.
In a sense, you could call it “locally produced and locally consumed.”
Relocation of the Oda River Confluence
One of the key elements of the “Mabi Emergency Flood Control Project” is the relocation of the Oda River confluence.
One cause of the Oda River flooding during the July 2018 Heavy Rain Event is believed to have been the “backwater effect,” in which the Takahashi River blocked the flow of the Oda River.
This major project aims to move the confluence with the Takahashi River downstream and create a slope to improve the flow of water.
As of February 2022, when we visited, construction was progressing toward completion in March 2024 (the end of fiscal year 2023), and the finished project was gradually taking shape.
Here are photos showing the area from Minamiyama Bridge in Mabi, the starting point of the relocation work, to the vicinity of Kurashiki Ohashi Bridge in Yanaihara, Funao.
Photographed in late February 2022
It was once a river, but work on the Takahashi River about 100 years ago turned it into a reservoir. After the diversion work is completed, it will become a river again.
It is planned to serve as a park in normal times, and as a flood-control center in emergencies, storing supplies and providing facilities for directing operations from the front.
Because water from the Oda River will flow through here, the road will eventually be removed and replaced by a bridge.
Non-structural measures
Large-scale river works, rare even nationwide, are underway, including the diversion of the Oda River at its confluence.
“With measures like these in place, we’ll be safe now.”
Some people may think so.
In fact, the design aims for a state in which the area can withstand rainfall equivalent to that of the July 2018 Heavy Rain.
“People expect ‘absolute safety,’ and of course I’d love to say that this makes us safe. But many recent disasters have occurred because events exceeded the capacity of facilities, so we can’t say there’s absolute safety.”
Yasuhiko Hamada, director of the Takahashi River and Oda River Emergency Flood Control Project Office, explains.
It will be safer than in 2018, but “first, get to safety.”
The office is clearly communicating this message and holding information sessions for residents, while also providing thorough explanations as the Takahashi River and Oda River Emergency Flood Control Project Office.
The most accessible initiatives are supporting residents in creating their own “My Hazard Maps” and “My Timelines,” and promoting their use. These activities are called “non-structural measures” and are being carried out alongside “structural measures” such as levee construction.
However, completing in five years a project that was originally expected to take ten is no easy task.
In the second half of this article, we spoke with Yasuhiko Hamada, director of the Takahashi River and Oda River Emergency Flood Control Project Office, Chugoku Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, which oversees the construction, about the progress of the work and other topics.
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