Multidisciplinary approach to sediment connectivity between debris-flow channel network and the Dolra River, Mazeri Valley, Southern Caucasus, Georgia

The Mazeri Valley in the southern Caucasus Mountains, Georgia, is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the population and infrastructure. In this regard, we report a tree-ring-based chronology of the debris-flow activity on a large cone to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and a bedload river in this remote area under global climate change and glacial retreat. The 161 sampled trees demonstrated the appearance of 12 significant events over the last 65 years, with all of the events involving possible sediment input into the stream system of the Dolra River. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Surficial sedimentary characteristics, such as morphometric indices, have enabled the discrimination between sediments from the debris-flow activity and river dynamics (alluvium inputs). Finally, most of the reconstructed event-years are characterized by at least one month of above-average rainfall.