P.S. Mitsubishi Construction (PSM) is Japan’s largest general construction company in the field of prestressed concrete construction, a construction method known for its strong performance in terms of structural strength and durability. Having undertaken many projects using the related technology, the company has a stellar track record of delivering various public works projects for recovery and reconstruction from the Great East Japan Earthquake , providing measures against catastrophic natural disasters and promoting the national resiliency improvement policy focusing on deteriorating infrastructure.

PSM is currently engaged in a regional disaster resilience project in Iwate Prefecture. In August 2016, Iwaizumi Town in the northeastern part of the prefecture was hit by Typhoon No. 10 (Lionrock), resulting in the largest flood flows on record and the flooding of the Omoto and Shizu rivers, two major waterways running through the town. The massive flood brought grave damage to the region, claiming a total of 29 victims, including both fatalities and missing persons, and submerge large areas of the basin, where flooting occurred to 723 houses above floor level and 121 houses below floor level.

In this project, PSM has won a contract for river improvement for the designated disaster zone, a section of the river spanning around 3.5 km, with the aim of preventing river flooding even in an event with similarly intense rainfall levels. The project plan is composed primarily of the dredging and excavation of river channels to expand the water discharge capacity along with a number of other processes, such as downstream extension of the revetment, embankment elevation, and bridge replacement.

Deputy Civil Engineering Division Head Hitoshi Suzuki explained the difficulties involved with the disaster resilience projects. “Usually, an invitation to bid for river improvement contracts is published when necessary preparations have been made to acquire land and to decide construction methods, a key prerequisite to smooth progress according to the client’s plan,” Mr. Suzuki noted. “ Meanwhile, in the case of disaster resilience projects, an invitation for bid is announced immediately after the occurrence of the disaster, when the land is quite often yet to be acquired and construction methods are yet to be decided. This situation often hampers prompt and efficient implementation of work plans.”

He continued: “For example, a delay in land acquisition can result in compromised efficiency, specifically by popularizing the initial plan to start from the downstream side and forcing the construction to start from a less favorablre point. Also, construction methods and areas are constantly changing, depending on the situation. In addition, for land purchasing plans, consideration needs to be given not only for construction areas but also for logistics roads. Disaster resilience project contractors need to have expertise and technical capabilities to respond to such challenging issues with flexibility and must work closely with the client to achieve smooth progress with the project.”

River improvement projects require high levels of skills in order to effectively handle an array of environmental conditions related to river flow velocity, depth, embankment height, and other factors. At the same time, consideration should be given to building structures located in the river basin, such as schools, municipal offices, and commercial facilities, which may pose a major issue. In response to all these challenges and issues, PSM was able to offer appropriate advice to its clients.