Author(s): Meng-Chi Hung; Chuan-Yi Huang; Chang-An Hsu

Linked Author(s): Meng-Chi Hung

Keywords: Instream flow incremental methodology (IFIM); Instream flow needs (IFN); Weighted Usable Area (WUA); Spurdike; Refuge pond; Floodplain excavation

Abstract: This study attempts to employ instream flow incremental methodology (IFIM) for evaluating the impact of flood protect measures on fish microhabitats instead of determining the instream flow needs (IFN). The downstream reach of Fengshan River Bridge in Northwest Taiwan was used as a case study. The swimming- type fish Acrossocheilus paradoxus and benthos fish Rhinogobius candidianus were selected as indicator species. A two-dimensional hydraulic model (SEC-HY21) with fine-resolution grids (10 m²) is used to simulate flow fields. Following instream flow incremental methodology (IFIM) procedures, index species habitat suitability curves for velocity and depth are incorporated into flow field simulations to derive spatial weighted usable area (WUA) distributions. The flow fields were simulated with flow discharge starting from zero and increasing step by step until the WUA reach ing its maximum value. Comparing the WUA of scenarios with or without spurdikes installed to analyze their effects on fish habitat quality. Additionally, the swimming fish A. paradoxus is used as index species to assess the protection effect of refuge ponds and floodplain excavation during floods by analyzing differences in velocity suitability distributions within a river contract ion.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.264

Year: 2026