Geoinformation technologies in the evaluation of short-term geomorphic change: An example of Damdere debris flood area (Bulgaria)

A debris flood is a hazardous hydrogeomorphic process that can change the topographic surface in a short time due to a high streamflow and a large volume of sediment transport. Large areas of the Eastern Rhodopes Mountains (Bulgaria) are susceptible to erosion, debris flows, and debris floods due to loose earth masses, rare vegetation, and alternating dry and wet periods with extreme rainfall. The study area is located in the lower part of the river Damdere catchment and covers the area around the check dam. Studying the geomorphic changes of the debris flood areas can provide information about the behavior of the event, and contribute to the development of mitigation measures. In the current research, the data are obtained using terrestrial laser scanning (TLS) during two campaigns (in October 2019 and August 2021). After processing the raw TLS data, two pairs of ground point clouds have been obtained- for the area immediately before the check dam and for the one after the dam. To evaluate the changes in the topographic surface, two approaches are applied: (1) measuring the distance between the successive point clouds (M3C2 algorithm) and (2) measuring the differences between the digital terrain models in geographic information system environment (DoD method). Both approaches have shown similar results and indicated active hydrogeomorphic processes. The relatively large volume of deposition after the check dam is an indicator for the decrease in the retaining capacity of the check dam, which is a prerequisite for the increase of a flood risk.