Identification of preferential target sites for the environmental flow estimation using a simple flowchart in Korea

Since the 1960s, rapid urbanization has caused serious deterioration in the quantity and quality of instream flows in South Korea. As demands for healthy instream ecology, landscape, and water-friendly environments have increased, the government has revised the relevant legal codes. In 2017, the environmental flow, defined as the minimum flow to conserve the health of aquatic ecosystems, has been endorsed in the Water Environment Conservation Act. However, owing to the lack of established criteria for the selection of target sites, the implementation of environmental flow is still in its early stage. This study suggests a simple flowchart to identify the preferential target sites for environmental flow estimation. First, deterioration in the health of aquatic ecosystems is identified by comparing the monitored Fish Assessment Index (FAI) with the standard suggested by the Ministry of Environment. Thereafter, the conditions of discharge and water quality of the instream flows are assessed. In the discharge analysis, linear regression is used for three flow metrics to analyze the interannual variability of discharge. Discharge deficiency is evaluated by comparing the drought flow (Q₃₅₅) and the 10% mean annual flow. The load duration curve (LDC) is used in the water quality analysis. A case study is conducted for the Bokha-cheon Stream to test the flowchart, followed by a nationwide application. From the results, more than 70 sites have been identified as target sites for the estimation of the environmental flow in the five major river basins of Korea.