DEBRIS FLOWS IN THE WATERSHED OF THE BOROVITSA RIVER, THE EASTERN RHODOPES

ABSTRACT. The territory of the Eastern Rhodopes is defined in the specialised literature as highly affected by debris flows. These events propagate usually in deep erosional forms and can be defined as a rapid movement of highly liquified earth masses, caused by intense rainfall and snowmelt. Despite the built anti-erosion facilities and the mitigation measurements in the Eastern Rhodopes, there are still large areas of deforested and eroded slopes, which are a prerequisite for the propagation of debris flows. Large parts of the slopes in the watershed of the Borovitsa River are such areas. This article analyses small watersheds of the left tributaries of the river, after the Borovitsa Dam. The study is focused on the morphometric parameters of the watersheds and characterisation of the deposits. The presence of loose Paleogene volcanic materials, slope gradients between 15º and 30º, and sparse vegetation define the areas with the occurrence and propagation of debris flows. The results of the morphometric and grain-size analyses provide information on the energy of the flow and allow to delineate the zones of feeding, transport, and accumulation of the material.