Effect of Probability Distribution-Based Physical Habitat Suitability Index on Environmental-Flow Estimation

Habitat suitability index (HSI) is a fundamental factor in ecological river-restoration projects for assessing fish habitat to create inhabited environment for aquatic organisms. An accurate estimation of HSI requires long-term-monitored data including flow velocity, water depth, and bed materials; however, this is not easy to collect, and the dataset comprises local characteristics. Therefore, it is difficult to present a generalized method of HSI estimation with limited local and temporal data. In this study, the probability distribution was applied for HSI estimation with limited data measured in the tributaries of Han and Geum Rivers in South Korea. Log-normal distributions were applied to the water depth and velocity data of aquatic habitat for Zacco platypus, and then the developed log-normal distributions were used as the HSI. The HSIs developed by applying the log-normal distribution were compared with the HSIs developed using the instream flow and aquatic system group (IFASG) method. By using the log-normal-distribution-based HSIs, the environmental flows estimated through the physical-habitat-assessment models based on instream flow incremental methodology were also compared with the IFASG-based results. The environmental flows were determined to be similar within an optimal range in both cases of the tributaries of Han and Geum Rivers.