Comparison of Sedimentation Rate Analysis of Lake Tondano using Empirical Methods and Direct Measurements

Sedimentation in the Lake Tondano watershed was assessed by comparing estimates from the Universal Soil Loss Equation (USLE), Revised Universal Soil Loss Equation (RUSLE), and Modified Universal Soil Loss Equation (MUSLE) with direct field observations from ten major inlet rivers. The analysis combined rainfall, soil, slope, and land-use data with laboratory measurements of sediment concentration. The calculated Erosivity (R) values were 1,703.14 MJ.cm/ha.jm/yr for USLE, 1,566.54 MJ.cm/ha.jm/yr for RUSLE, and 1,648.00 for MUSLE. The watershed had an average soil Erodibility (K) of 0.20, an LS factor of 0.496, a land-cover factor (C) of 0.241, and a conservation-practice factor (P) of 1. Using these parameters, the estimated annual sediment volumes were 46,081.70 m³/year with USLE, 73,588.18 m³/year with RUSLE, and 44,589.68 m³/year with MUSLE. Measurements from the inlet rivers showed sediment concentrations between 1.33 and 14.58 gr/m³, while peak discharge reached 662.31 m³/s. Among the three empirical approaches, the MUSLE estimate was closest to the direct measurements. Its closer agreement with the field data is consistent with the model’s use of runoff-related variables, which are particularly relevant under the high-rainfall and strong-runoff conditions of the Lake Tondano watershed. These findings provide a basis for improving sediment-control and watershed-management efforts in Lake Tondano, where changes in land cover have contributed to increased erosion and sediment accumulation.