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Analyzing Long-Term Changes in Water Discharge and Soil Condition of Ogouchi Reservoir Catchment

Author(s): Charles John C. Gunay; Chika Nakagawa; Katsuhide Yokoyama

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Keywords: Forest maintenance; SWAT model; Ogouchi Reservoir; Hydrograph separation; Decadal validation

Abstract: Through effective and sustainable management, forests can contribute in soil and water resources conservation by reducing the intensity of floods and soil erosion. To clarify this relationship, modeling of long-term water discharge and quantitatively analyzing its influence to changes in watershed condition is necessary. In this study, SWAT model was used to simulate long-term water discharge of Ogouchi Reservoir catchment in Japan. Model calibration was performed by varying sensitive streamflow parameters: Cn2 (SCS Curve Number) and Sol_Awc (soil available water capacity). Subsequently, model performance was evaluated every 10 years in an attempt to develop decadal trends which will describe the response of forest soils to the 56-year flow variations in the watershed. Using statistical indices and recursive digital filter method for model validation, it was found that SWAT accurately reproduced both the monthly streamflow components, surface runoff and baseflow, at wet periods where there is moderate to high flow. The high accuracy proved the applicability of SWAT in long-term discharge analysis of a steep and forested watershed like Ogouchi. Moreover, the trend of optimal Sol_Awc factors revealed that there may be significant change in soil condition from decade B (1969-1978) to decade F (2009-2015) which exhibits the positive effect of forest management policies implemented from the past years.


Year: 2020

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