Countermeasures against floods that exceed design levels based on topographical and historical analyses of the September 2015 Kinu River flooding

Study region: The Kinu River basin receiving serious damage in September 2015 because of the heavy rainfall disaster that hit the districts of Kanto and Tohoku in Japan. Study focus: This paper provides future flood risk management for floods that exceed design levels (FEDL) based on past flood control systems and land use considering the natural topography in the area that was inundated by flood water from the Kinu River. New hydrological insights for the region: The results of the literature research reveal flood management methods for preventing inundation of the city of Mitsukaido, such as drainage using a discontinuous embankment and a low-lying backswamp. In addition, the areas inundated by this flood were mainly those around a high-altitude natural levee, and residential land in the backland lowland area was developed after the Meiji period (1868–1912). Furthermore, a field survey revealed that many of these flood management systems are not functioning completely because of artificial modification. Identifying locations of potential flooding in areas of low population density is necessary as a countermeasure against FEDL. It is also important to recognize microtopography such as natural levees or backswamps, to induce land use based on the different flood risks of these topographies, and to utilize historical flood control systems as countermeasures against FEDL.