Late Holocene Sedimentary Records of Recurrent Debris Flow Hazards in Tbilisi, Georgia

The 13 June 2015 Vere River disaster, which caused multiple fatalities in Tbilisi, exposed the extreme vulnerability of Georgia’s capital to debris flow processes generated in the steep, landslide-prone headwaters of the Vere basin. Although damaging flash floods occur frequently in the Vere catchment, the recurrence of debris flow events prior to the start of instrumental observations has remained unknown. To determine whether the 2015 event was exceptional or part of a persistent natural regime, we conducted an integrated geomorphological, sedimentological and chronological analysis of the basin.

High-resolution UAV and satellite imagery, combined with field mapping, were used to identify paleo debris flow and landslide deposits along the main channel and its tributaries. Flow directions and sediment pathways were reconstructed from palaeocurrent indicators, including clast imbrication, allowing depositional units to be linked to specific source areas.

Radiocarbon dating of organic material from multiple stratigraphic sections within individual depositional complexes provides a chronology of major sediment-delivery episodes. The results reveal repeated debris flow events during the Late Holocene. It demonstrates that the 2015 event can be intrinsic to the long term behavior of the Vere basin rather than a rare anomaly. Because the Vere River drains directly into the densely urbanized centre of capital city of Tbilisi, this palaeohazard record has critical implications for hazard assessment and confirms that future catastrophic events are expected unless exposure is reduced.