Author(s): Kazuaki Ohtsuki; Kota Tomaru; Sakiko Yaegashi; Takashi Nakamura; Kazuki Karasawa; Kota Tawa; Rei Itsukushima

Linked Author(s): Kazuaki Ohtsuki

Keywords: Nature-based solutions (NbS); Alluvial fan rivers; Floodplain; Biodiversity; Channel widening

Abstract: This study explored nature-based solutions (NbSs) for managing flood risks and supporting biodiversity in Japan's alluvial fan river floodplain, which is susceptible to sudden flooding. This study applied a 1D-2D flood simulation model to the Kamanashi River basin to evaluate three interventions in the floodplain area: widening of channel width, flood diversion to agricultural lands, and secondary levees. River widening has proven to be effective in reducing flood depth and damage by enhancing drainage in stagnant areas. Secondary levees also effectively dispersed the floodwater and reduced the depths in external flooding scenarios. Flood diversion to agricultural lands, however, increases urban flood risks, highlighting the need for careful placement of diversion sites and embankments to prevent unintended harm to urban areas. Ecologically, river widening facilitates biodiversity by creating sandbars that provide essential habitats for floodplain-dependent species with minimal species loss in sandbar-formed areas. However, in areas without sandbars, a slight decrease in species diversity was observed, suggesting that habitat conditions should be carefully managed. Overall, this study recommends river widening as a primary flood control measure because of its dual benefits for flood mitigation and biodiversity. Future research should examine the ecological effects of agricultural land diversion and the impact of double levees. A multistrategy approach may offer a balanced solution for optimizing flood control and ecological preservation.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P2114-cd

Year: 2025