Evaluation of Watershed Healthiness based on Hydrology, Water Quality and Ecological Status Using SWAT and InVEST

This study assessed the status of the watershed health in the Geum River Basin (9,645.5 km2) by applying SWAT (Soil and Water Assessment Tool) and InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs). The watershed has 62% forest, 15% rice paddy, 11% upland crops, and 5% residential land uses. The streams in this watershed have been dried mainly by the forest growth and increase of groundwater use during the past 50 years. The watershed healthiness was calculated using multi-variate normal distribution from 0 (poor) to 1 (good) based on watershed hydrology and stream water quality results of SWAT and ecological status results of InVEST. Before evaluation, the SWAT model was calibrated and validated using the daily inflows and storage of two multi-purpose dams and three weirs for 11 years (2005-2015) and using monthly stream water quality of three monitoring stations in the basin. For dam and weir inflow, the Nash-Sutcliffe efficiency (NSE) was 0.55~0.77, and the coefficient of determination (R2) was 0.62~0.81. For stream water quality, the R2 of Suspended Solid (SS), Total Nitrogen (T-N), and Total Phosphorus (T-P) was 0.67~0.94, 0.59~0.79, and 0.61~0.79, respectively. The ecological status of watershed was simulated by the InVEST model linked to the SWAT results. For 30 years (1985~2014), the spatio-temporal change of watershed healthiness was analyzed on a decade basis considering watershed hydrology, stream water quality, and ecological status.