This paper explores the use of ¹³⁷Cs derived from Chernobyl as an indicator of sediment supply and transport within small agricultural catchments by analyzing the depth distribution of radionuclides, with a focus on post-Chernobyl changes in the activity concentration of radionuclides. To this end, depth-incremental sampling was carried out along routes of sediment transport within a small agricultural catchment subject to intense radioactive contamination in the Tula region. Some points were set to repeat the position of those made 27 years earlier and to understand the dynamics of deposition and the ¹³⁷Cs content in the sediment load. It has been suggested that a decrease in the activity concentration of ¹³⁷Cs can be used as an indicator of the relative age of deposits. Assuming this, the pattern of erosion product deposition on the sides and bottom of the dry valley was determined. This pattern was found to be stable and consistent with the observed geomorphic features and climate trends: the rate of accumulation in the valley bottom over the past 27 years has dropped almost twice, coinciding with a decrease in snowmelt runoff during springtime and no increase in intense rainfall. Grain-size analysis of the collected samples showed that selective transfer of clay particles may occur, but over a short delivery distance, it is unlikely that the sorting process will significantly alter the downward trend of ¹³⁷Cs concentrations. The proposed approach has the potential to significantly improve the accuracy of sediment budget estimations and environmental quality assessments.