Articles | Volume 21, issue 11
Research article
14 Nov 2017
Research article |  | 14 Nov 2017

Assessment of integrated watershed health based on the natural environment, hydrology, water quality, and aquatic ecology

So Ra Ahn and Seong Joon Kim

Abstract. Watershed health, including the natural environment, hydrology, water quality, and aquatic ecology, is assessed for the Han River basin (34 148 km2) in South Korea by using the Soil and Water Assessment Tool (SWAT). The evaluation procedures follow those of the Healthy Watersheds Assessment by the U.S. Environmental Protection Agency (EPA). Six components of the watershed landscape are examined to evaluate the watershed health (basin natural capacity): stream geomorphology, hydrology, water quality, aquatic habitat condition, and biological condition. In particular, the SWAT is applied to the study basin for the hydrology and water-quality components, including 237 sub-watersheds (within a standard watershed on the Korea Hydrologic Unit Map) along with three multipurpose dams, one hydroelectric dam, and three multifunction weirs. The SWAT is calibrated (2005–2009) and validated (2010–2014) by using each dam and weir operation, the flux-tower evapotranspiration, the time-domain reflectometry (TDR) soil moisture, and groundwater-level data for the hydrology assessment, and by using sediment, total phosphorus, and total nitrogen data for the water-quality assessment. The water balance, which considers the surface–groundwater interactions and variations in the stream-water quality, is quantified according to the sub-watershed-scale relationship between the watershed hydrologic cycle and stream-water quality. We assess the integrated watershed health according to the U.S. EPA evaluation process based on the vulnerability levels of the natural environment, water resources, water quality, and ecosystem components. The results indicate that the watershed's health declined during the most recent 10-year period of 2005–2014, as indicated by the worse results for the surface process metric and soil water dynamics compared to those of the 1995–2004 period. The integrated watershed health tended to decrease farther downstream within the watershed.

Short summary
The Korean government has tried to create and is tasked with implementing programs designed to repair the damage already done to the environment in the Han River basin. However, there is an absence of an integrated approach method for considering water supply, water quality improvement, and natural ecosystem maintenance. The objective of the study is to conduct integrated watershed health assessment of the natural environment, hydrology, water quality, and aquatic ecology of the Han River basin.