Author(s): Kazuaki Ohtsuki; Kota Tomaru; Sakiko Yaegashi; Takashi Nakamura; Kazuki Karasawa; Tawa Kota; Rei Itsukushima
Linked Author(s): Kazuaki Ohtsuki
Keywords: Nature-based solutions (NbS) Alluvial fan rivers Floodplain Biodiversity Channel widening
Abstract: This study explores nature-based solutions (NbS) for managing flood risks and supporting biodiversity in Japan's alluvial fan rivers floodplain, which are susceptible to sudden flooding. The study applied a 1D-2D flood simulation model in the Kamanashi River basin to evaluate three interventions in floodplain area: Widening of channel width, flood diversion to agricultural lands, and secondary levees. River widening proved effective for reducing flood depth and damage by enhancing drainage in stagnant areas. Secondary levees also effectively dispersed floodwater and reduced depths in external flooding scenarios. Flood diversion to agricultural lands, however, increased urban flood risks, highlighting the need for careful placement of diversion sites and embankments to prevent unintended harm to urban areas. Ecologically, river widening facilitated biodiversity by creating sandbars, which provided essential habitats for floodplain-dependent species, with minimal species loss in sandbar-formed areas. However, in places without sandbars, a slight decrease in species diversity was observed, suggesting that habitat conditions should be carefully managed. Overall, the study recommends river widening as a primary flood control measure due to its dual benefits for flood mitigation and biodiversity. Future research should examine agricultural land diversions’ ecological effects and the impact of double levees. A multi-strategy approach may offer a balanced solution, optimizing flood control and ecological preservation.
Year: 2025