Estimation of least ecological streamflow through long-term habitat evaluation using stream hydrodynamics and water quality factors

ABSTRACT The objectives of this study were to evaluate aquatic habitat suitability considering stream hydraulics as well as water quality and to propose a stream ecological flow rate for Zacco platypus in the Banbyeon Stream of South Korea. Stream water temperature and dissolved oxygen (DO) in addition to streamflow velocity and depth were simulated using the Hydrologic Engineering Center-River Analysis System (HEC-RAS) from 2010 to 2020 and then used to estimate weighted usable area (WUA) as the proxy indicator of stream habitat suitability. The continuous above-threshold (CAT) analysis revealed several anomalous drops in WUA as the combined effect of water temperature rise and streamflow reduction. A WUA/WUAmax ratio of about 24% seems to be a threshold level below which water temperature rises more rapidly as streamflow decreases. This is equivalent to a streamflow rate of 3.6 m3/s and is proposed as the least ecological streamflow to sustain minimal aquatic habitat suitability.