An economic value for ecosystem-based disaster risk reduction using paddy fields in the kasumitei open levee system

In this article, we examined the value of the traditional Japanese flood control measure that uses a discontinuous levee (kasumitei). By avoiding the use of flood-prone lowlands for inhabitation and allowing floodwater movement through the kasumitei, the cost of building damage can be reduced, and water supply to wetlands can be increased. The purpose of our study was to quantify flood damage cost reductions and the potential gains for wetland species as part of an ecosystem-based disaster reduction initiative. The study was conducted in the Amano River basin in central Japan. First, we applied a drainage model and calculated the flood damage cost reduction in the floodplain from an evaluation of inundation depth differences. As part of an analysis of potential wetness, we identified areas where 1 m of flooding was predicted in rice paddies near kasumitei. We also quantified a topographic wetness index, the ratio of lowlands, and the ratio of poorly drained soil types, all of which would be beneficial to wetland species. We also investigated land-use change in the area and the relevant financial support framework. The results showed that a simulated closed levee system causes greater inundation and exposure to residents, and the value of paddy areas near kasumitei was calculated to be 43,830 JPY/1000 m²/year at the maximum. Even though the paddies tend to be poorly drained, these areas have been continuously used as paddies for the past century even under development pressure. The economic value and habitat potential of kasumitei levee systems have not been considered as part of any previous flood-management policies. We propose these existing flood control areas to be considered in the financial support framework in the context of river basin and ecosystem-based disaster risk reduction management.