wcm.02.2025.200.206

The Sumani Watershed plays a critical role in maintaining hydrological balance and water resource management. This study evaluates the effects of different land use compositions—forests, agriculture, settlements, and rice fields—on surface runoff using the Soil Conservation Service Curve Number (SCS-CN) model. Rainfall and soil properties, such as texture, organic matter, and infiltration rates, were analyzed to determine their impact on runoff generation. Soil samples showed that forests had the highest infiltration rate (up to 81 mm/h), significantly reducing surface runoff, while settlements with compacted soils had the lowest infiltration rate (28.97 mm/h), contributing to the highest runoff. SCS-CN analysis revealed that settlements contributed 77% runoff, compared to only 35% in forested areas. These findings emphasize the importance of sustainable land management practices, such as reforestation and improved soil conservation techniques, which can potentially reduce surface runoff by 30% in critical areas. This research contributes valuable insights for the development of sustainable land-use strategies and watershed conservation planning, particularly in tropical regions.