Evaluation of stream habitat suitability using the HMUs clustering method and habitat diversity index

The objectives of this study were to classify streamflow patterns into Hydro-Morphological Units (HMUs) using hydrodynamic factors and to evaluate stream habitats based on these HMU clusters. A 2.9 km reach of the Bokha stream was selected as the study area, where aquatic habitat enhancement is required. Stream velocity and water depth were simulated using the HEC-RAS 2D model. Based on the simulation results, the stream flow patterns were categorized into five HMU types—pools, riffles, rapids, ruffles, and runs—according to estimated probabilities derived from their respective hydrodynamic boundary ranges. Spatiotemporal analysis indicated that HMUs such as ruffle and run closely corresponded with observed fish habitat characteristics, suggesting their suitability as indicators for habitat evaluation. To quantitatively assess habitat diversity, the Normalized Shannon–Weaver Index was calculated, yielding values of 0.93 at the minimum ecological streamflow (0.48 m³/s) and 0.88 at the maximum Weighted Usable Area (WUA) flow (6.9 m³/s). Overall, the proposed approach provides a robust framework for stream habitat evaluation and contributes to the identification of streamflow ranges that are both ecologically meaningful and practically feasible, thereby supporting sustainable stream management strategies.