Comparison of environmental flows from a habitat suitability perspective: A case study in the Naeseong-cheon Stream in Korea

Environmental flow is the amount of water flow required to maintain the health of a river ecosystem. Environmental flow includes both optimal flow and minimum flow. The former is the amount of flow that guarantees the complete function of a stream ecosystem, whereas the latter is the amount of flow below which the stability and health of a stream ecosystem cannot be maintained. This study attempts to compare environmental flows computed by various environmental flow methodologies, including hydrological methods, hydraulic rating methods, and habitat simulation methods. For the habitat simulation method, physical habitat simulations were carried out using habitat suitability curves for Zacco platypus. The study site is a 20-km-long reach of the Naeseong-cheon Stream downstream from the Youngju Dam in Korea. The Naeseong-cheon Stream is a moderately sized stream (order 8) with a normal flow of 4.1 m³/s. It was found that environmental flows vary greatly depending on the selection of methodologies. Specifically, the minimum flows by the hydrological methods were significantly smaller than those by the hydraulic rating methods or the habitat simulation methods, and the optimal flow by the hydraulic rating method is much larger than those by the other two methods. Physical habitat simulations for various minimum flows revealed that the minimum flow by the hydrological methods might fail to provide the minimum requirement for an aquatic habitat.