Changes in land use have occurred in several areas in the watershed, from green-covered land to oil palm plantations
and settlements. This change is supported by high rainfall, which can increase soil erosion or the rate of erosion and
cause river shallowing due to sedimentation. This study aims to determine the extent and distribution of soil erosion
and sedimentation on the small flat watershed. Erosion rate was calculated using the Universal Soil Loss Equation
method based on the Geographic Information System. The result shows that the erosion rate in the study area reached
32,094.82 Mg·ha–1·yr–1. The level of soil erosion hazard in this area was dominated by the low category of 55.93%
with an area of 279.35 km2, followed by the low-moderate (16.61%), moderate (16.99%), high-moderate (6.84%), and
high (3.63%) categories. The interactions between USLE parameters significantly affect the annual average level of
soil loss. On the small flat watershed, the soil loss for the light and very light categories is usually related to conservation practices and protected areas. Based on the flow bed shear stress above the critical value, the sediment grains move,and sediment transport occurs. The sediment transport flow capacity along the bed varies directly with the difference in shear stress. The findings of this research can help prepare land use scenarios that reduce erosions and sedimentations.The small flat watersheds are a key consideration when utilizing flow connectivity, erosion, and sedimentation functions as enhancement tools in water catchment scale modeling.
Key Words: Geographic Information System; sediment transport; small flat watersheds; soil erosion; USLE.