Abandoned tidal channels as rapidly infilling sedimentary reservoirs in a macrotidal flat with implications for blue carbon potential

Sedimentary systems in coastal environments function as important reservoirs for material storage, including organic carbon. In tidal settings, actively migrating tidal channels are commonly recognized by persistent sediment reworking, conditions unfavorable for the long-term sediment preservation. In contrast, abandoned channels have been identified as potential blue carbon storages. However, mechanisms governing their formation and rapid infilling remain poorly quantified, particularly beyond a seasonal influence. This study examines how rainfall-tide interactions control tidal channel morphodynamics and abandoned channel formation in the semi-enclosed macrotidal Dokgotri tidal flat on the west coast of Korea. Multi-temporal UAV-derived digital elevation models (DEMs) from 2022 to 2025 were used to quantify channel mobility and erosion-deposition patterns, combined with precipitation and tidal level data. GPS-based topographic data and sediment cores were used to support the analysis of sedimentation associated with different channel migration modes. Results show that channel migration and depositional responses depend on the timing of rainfall relative to tidal stage rather than on seasonality alone. Rainfall events coinciding with low tide promote enhanced channel migration and depositional dominance of the tidal flats, while rainfall during high tide results in erosional trends with limited channel mobility. Chute cutoffs, a key mechanism for channel abandonment, occur not only during the summer but also during non-summer periods when channel sinuosity approaches a threshold configuration. After chute cutoff events, stream piracy redistributes flow within the channel network, leading either to continued reworking through flow reoccupation or to isolation which results in channel abandonment. Abandoned channels that remain isolated exhibit sustained depositional dominance and rapid infilling, supported by sediment core data. In contrast, consistently active or repeatedly reoccupied channels experience continuous sediment reworking and show low potential for long-term sediment preservation. These results indicate that although highly dynamic channel zones may be unfavorable condition for carbon preservation, the frequent formation of abandoned channels by channel adjustment provides recurring chances for sedimentary reservoir development. This process-based perspective highlights how chute cutoff, stream piracy, and subsequent infilling control sediment storage in macrotidal settings and demonstrates their relevance to blue carbon potential and coastal carbon mitigation strategies with highly dynamic tidal environments.