Effective discharge for sediment transport and its geomorphological significance in karst catchments

As a key factor in shaping channel morphology, effective discharge (Q_e) can quantitatively link water discharge to geomorphic processes. However, a better understanding of Q_e estimation and its geomorphic impacts is still challenged by the diversity of values identified for various catchments. To address this issue, the objectives of this study were to calculate Q_e using both analytical and class-based approaches in 8 karst catchments during 2003–2023 based on monthly water discharge and sediment load, and further to evaluate the effect of Q_e on channel adjustment. Results showed that water discharge and sediment load in each catchment exhibited significant seasonal variations, and annual sediment load was generally governed by the period from June to September. The Q_e obtained by two methods differed considerably. The recurrence interval of Q_e ranged from 1.37 to 4.07 and 1.04 to 10.15 years obtained by the analytical and class-based approaches, respectively. The Q_e was also closely related to sediment transport and deposition processes, and thus the channel morphology. Specifically, the proportion of discharge required to transport 50 % of the suspended sediment ranged from 20 % to 67 %, while the proportion of duration required for this transport ranged from 22 % to 69 %. The decreased Q_e could cause channel aggradation, while increased Q_e led to channel incision. This study can provide a new perspective for better understanding the linkage between hydrology and channel morphology, and offer valuable information for effectively controlling sediment delivery in karst catchments.