| Abstract: | Watershed health, including the natural environment,
hydrology, water quality, and aquatic ecology, is assessed
for the Han River basin (34148 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 subwatersheds
(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
to those of the 1995–2004 period. The integrated watershed
health tended to decrease farther downstream within the watershed.
surface process metric and soil water dynamics compare |