[A-HW27] Biodiversity, nutrients and other materials in ecosystems from headwaters to coasts

[AHW27-P07] Estimation of SS loading from an Upland Agricultural
Temperate Catchment using SWAT

*Francis Jhun Tin-ao Macalam^1,2, Kunyang Wang¹, Shin-chi Onodera¹, Mitsuyo Saito¹, Yuko Nagano³, Masatoshi Yamazaki⁴ (1.Graduate School of Advanced Science and Engineering, Hiroshima University, 2.Department of Environmental Science and Technology, College of Science and Mathematics, University of Science and Technology of Southern Philippines, Cagayan de Oro City, 9000, Philippines, 3.Japan Forest Technology Association, Rokubancho, Chiyoda-ku, Tokyo 102-0085, Japan, 4.PASCO Corporation, PASCO Meguro Sakura Bldg, 1-7-1 Shimomeguro, Meguro-ku, Tokyo 153-0064, Japan)

Keywords:Chikugo river, SWAT Model, Sediment loading, Mountainous catchment, Soil Erosion

The Chikugo river, the longest river on Kyushu Island, originates on Mount Aso and flows into the Ariake Sea, serving as a critical freshwater resource for agriculture, industry, and ecosystems. Due to its mountainous topography and extensive agricultural land use, the catchment is susceptible to soil erosion and sediment transport, especially during typhoons and heavy rainfall events. Understanding suspended sediment (SS) loading is crucial for effective watershed management and erosion control. This study applies the Soil and Water Assessment Tool (SWAT) to estimate SS loading and evaluate hydrological processes affecting sediment transport in the Chikugo river basin from 2007 to 2021. Model calibration and uncertainty analysis were conducted using the Sequential Uncertainty Fitting Version 2 (SUFI-2) approach, demonstrating strong model reliability in simulating streamflow and sediment dynamics. Sensitivity analysis identified surface runoff, channel flow, and sediment transport parameters as key drivers of SS loading, highlighting the impact of land use and rainfall variability on erosion processes. The study findings provide valuable insights into sediment mobilization, deposition, and transport mechanisms, which are essential for developing sustainable land and water management strategies. By improving sediment load estimation, this research contributes to better erosion mitigation, reservoir sedimentation control, and water quality management in similar temperate catchments. The results serve as a scientific basis for policymakers and stakeholders to implement effective soil conservation measures and sediment management practices in agricultural and mountainous watersheds.