Debris flows in Kresna Gorge (Bulgaria)-geomorphological characteristics and weather conditions

Abstract

Over the last decades, numerous extreme climate events such as extreme temperatures, droughts, heavy precipitation, and storms associated with climate change have been recorded in many countries, including Bulgaria. As a result, geomorphological hazards such as landslides, debris flows, mudflows, high-speed soil erosion, etc. often occur on the territory of the country. The debris flow is one of the most common hazardous processes in small catchments of the main river basins in Bulgaria. The Kresna Gorge located in the middle part of Struma River valley is a typical area with such processes which often cause the damages to the E79 international highway. The purpose of the present study is to characterize debris flows in Kresna Gorge (southwestern part of Bulgaria) by comparative analysis between the two events (occurred on May 24, 2009 and July 28, 2019). In order to achieve the aim of the study the geomorphological features and flow type of 2019 event were identified and the results were compared with the previous publications which investigated the event on May 24, 2009. In the present paper, the sediments and the type of transportation of the investigated event (July 2019) were determined by grain-size and clast-shape analysis. The impact of weather conditions on debris flow occurrence was shown by the analysis of the synoptic conditions on the day before the event. The results of the study bring to clarifying the geological-geomorphological and meteorological factors for the occurrence of debris flow and are important for geomorphological hazard management.

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

“…These values indicate irregular distribution of the precipitation and cases of high precipitation for a short period which is a prerequisite for the occurrence of debris flows and debris floods. Similar results are obtained for the region Kresna Gorge (Western Bulgaria) by Krenchev et al (2021), which gives reason to assume that daily precipitation above 20 mm could be considered as a threshold value for active hydrogeomorphological processes (debris flows/debris floods). Having regard to the peculiarities and differences in land cover and hydrological conditions, further investigations are needed to specify the impact of weather conditions on short-term geomorphic change.…”

“…Most of the publications about hydrogeomorphic processes in Bulgaria and particularly about debris flows consider the conditions and triggering factors for these hazardous events as well as the sedimentological properties of the deposits (Baltakova et al, 2018;Dobrev & Georgieva, 2010;Kenderova et al, 2013;Krenchev et al, 2021;. Only a few publications in Bulgaria emphasize on the types of the events (debris flow, debris flood, mud flow, etc.)…”

Peculiarities of the materials involved in the debris flows in Kresna Gorge, Southwest Bulgaria

“…Именно този проблем насочва вниманието в настоящото изследване на условията, при които възниква това явление. Досега има неголям брой публикации по тази тема (Dobrev, 1999;Dobrev, Georgieva, 2010;Krenchev et al, 2021).…”

“…Специфичната плътност при тях е ниска -варира от 2,58 до 2,65 g/cm 3 . Krenchev et al (2021) публикува изследвания върху 4 броя проби с номера 858, 859, 860 и 861, взети от района на кално-каменен порой в северната част на Геоморфоложка, тектонска и геоложка характеристика на района В геоморфоложко отношение районът на настоящото изследване представлява проломен участък, оформен от врязването на р. Струма през издигнат тектонски блок, известен още като Кресненски хорст (Zagorchev, 1970(Zagorchev, , 1975. Този участък, известен като Кресненски пролом (а също и като Кресненско дефиле), е оформен от своя страна в резултат от врязването на реката в по-слабите и тектонски обработени зони със суб-меридионално направление.…”

“…Проби са вземани и от учени от Софийския университет -през 2014 и 2021 г. Krenchev et al, 2021). Пробовземанията са осъществени след различни прояви на кално-каменни порои в северната част на Кресненския пролом.…”