Landslides, debris flows, and other secondary disasters caused by earthquakes threaten the safety and stability of river basins. Earthquakes occur frequently in Japan. Therefore, it is necessary to study the impact of earthquakes on sediment transport in river basins. In this study, considering the influence of reservoirs, the Soil and Water Assessment Tool-calibration and uncertainty program (SWAT-CUP) was employed to analyze the runoff parameter sensitivity and to optimize the parameters. We manually corrected the sediment transport parameters after earthquake, using the Soil and Water Assessment Tool (SWAT) model to assess the process of runoff and sediment transport in the Atsuma River basin before and after the 2018 Hokkaido Eastern Iburi Earthquake. The applicability of the SWAT model to runoff simulation in the Atsuma River basin and the changes of sediment transport process after the earthquake were studied. The research results show that the SWAT model can accurately simulate the runoff process in the Atsuma River basin, the Nash–Sutcliffe efficiency coefficient (NSE) is 0.61 in the calibration period, and is 0.74 in the verification period. The sediment transport increased greatly after the earthquake and it is roughly estimated that the amount of sediment transport per unit rainfall increased from 3.5 tons/mm/year before the earthquake to 6.2 tons/mm/year after the earthquake.

In many parts of Southeast Asia, opencast hydraulic tin mining has been carried out since the colonial era. Regardless of its scale, this mining method has significantly affected microtopography and left extremely degraded soil surfaces, where vegetation can hardly grow. Therefore, the identification of a feasible method for the rehabilitation and reforesting of these areas is a long‐term issue. In this study, we aimed to clarify the subsurface geological (soil properties and distribution) and hydrological conditions at a post‐tin mining site on an Indonesian island using an electrical resistivity survey combined with microtopographic information. The electrical resistivity survey of the study site provided information about the distribution of bedrock and sandy and clayey soils, reflecting mining activities. Furthermore, direct and continuous groundwater level monitoring showed the ranges of groundwater fluctuation depending on the soil and climate conditions. Our study demonstrates that subsurface assessment by electrical resistivity survey can provide essential information, contributing to the development of feasible plans for reforestation or transformation to agricultural land at post‐tin mining sites through the improvement of physical conditions and soil fertility.