Flood Formation Mechanism of the Devastating Flood in the Town of Miziya, Bulgaria in August 2014

Acta Universitatis Palackianae Olomucensis – Geographica, Vol. 45, No. 2, 2014, pp. 99-120 99 FLOOD FORMATION MECHANISM OF THE DEVASTATING FLOOD IN THE TOWN OF MIZIYA, BULGARIA IN AUGUST 2014 1 1 Daniela Zlatunova , Panka Babukova 1 Department of Regional and Political Geography, Faculty of Geology and Geography, Sofi a University St. Kliment Ohridski, 15 Tsar Osvoboditel Bul. 1504 Sofi a, Bulgaria [email protected], [email protected] Abstract The publication aims to study the factors involved in the formation of the devastating fl ood in the town of Miziya in the Republic of Bulgaria in August 2014. The natural and anthropogenic fl ood formation factors in the river basin are researched in details. The fl ood formation mechanism is researched and the main conclusions about the situation and future fl ood risk management in the basin are developed. The following scientifi c research methods are used in the publication: differentiated approach, complex (combinatory) approach, geographical scientifi c approach (chronological and chorological), mathematical-statistical method and spatial analysis method. Key words: fl ood formation mechanism, spatial analysis, Miziya, Bulgaria. INTRODUCTION in future, it is necessary to plan and implement adequate measures. However, the defi nition of As a result of heavy rains in the period from the measures depends on a detailed analysis of the 31 July to 2 August 2014 the level of the Skat River fl ood’s formation mechanism in Miziya. Therefore, increased and on 2 August 2014 it fl ooded the town the aim of the publication is to investigate and of Miziya. The water level remained unchanged clarify the fl ooding formation mechanism, includ- until the afternoon of 5 August 2014 when it began ing the natural and anthropogenic factors, which to drop slightly. As of 7 August 2014 the water level caused the fl ood in Miziya in the period 2–7 August dropped and the river resumed its normal course. 2014. The streets of the town are positioned higher than the housing and yard areas, therefore the yards THEORETICAL BACKGROUND remained under water. The research is based on the concept that the river Meanwhile, the tributaries of the Skat River also basin is a system (Figure 1) with a certain ratio of overfl owed and caused fl oods – the Barzitsa River organisation, which is widely recognized as the most (right tributary) and the Barzina River (left tribu- fundamental landscape unit for the water cycle, the tary). The areas between the rivers were fl ooded. cycle of sediments, and dissolved geochemical and biogeochemical constituents. Catchments integrate Flood damage was devastating – two human casual- all aspects of the hydrological cycle within a clearly ties, many houses were destroyed or uninhabitable defi ned area in a way that can be studied, quanti- and numerous citizens of the town of Miziya were fi ed and acted upon (Wagener et al. 2004). Drain- affected. To avoid such disastrous consequences age basins are commonly viewed by scientists as AUPO Geographica Vol. 45 No. 2, 2014, pp. 99-120 100 Flood formation mechanism of the devastating fl ood in Miziya, Bulgaria in August 2014 Figure 1 Drainage Basin System. Source: Wagener et al. 2004; own processing. open systems. Inputs into these systems include A number of factors infl uence the input, output, precipitation, snow melt, and sedimentation. and transport of sediments and water in a drainage Drainage basins lose water and sediment through basin. Such factors include topography, soil type, evaporation, deposition, and streamfl ow. We need bedrock type, climate and vegetation cover. The to understand, manage and/or deal with the space- geology, climate and disturbance regimes of an area time variability of catchment responses to climatic infl uence the shape and condition of a watershed. inputs (water and energy) on the land’s surface. Understanding the spatial and temporal variability Human activities can modify the natural disturbance of the hydrological processes aggregated to the regimes by changing the timing and intensity of catchment scale, as well as their extremes and their these natural processes. For example, urbanization scaling behaviour in time and space, is important and roads increase impervious surfaces and change for a number of applications, such as fl ood estima- the routing of water. These conditions can increase tion, drought mitigation, water resources systems fl ood peaks and landslide frequency above the range analysis, etc. (Murugesu 2005). The complex cause- that would be expected in undeveloped conditions. effect relationships between the climatic, mete- Conversely, dams and other water impoundments can orological, hydrographic, orographic, geological, reduce fl ood peaks and interrupt sediment supply, soil-vegetation and other factors are important in impacting the aquatic system by limiting the creation this respect. of side-channels or delivery of spawning gravels. AUPO Geographica Vol. 45 No. 2, 2014, pp. 99-120 Flood formation mechanism of the devastating fl ood in Miziya, Bulgaria in August 2014 101 Figure 2 Geographical location of the Skat River Basin. Source: GIS spatial data of the territory of Bulgaria and the Skat River Basin; own processing. AUPO Geographica Vol. 45 No. 2, 2014, pp. 99-120 102 Flood formation mechanism of the devastating fl ood in Miziya, Bulgaria in August 2014 METHODS AND MATERIALS This geographical location predetermines the unique plain structure of the river basin and has Flood formation and the systemic approach have a specifi c moderate continental climate, unstable a direct relationship because both are systemic water regime and small run-off values (0.5–1.0 and non-linear (Ohlsson and Turton 1999). The l s−1 km−2). Rain water is almost exclusively lost as basic principle of any systemic study is connectiv- evaporation and only small insignifi cant amounts ity. A system is a set of elements with connections form the surface and underground waters. Simul- between each other. Any system is composed of taneously, the geographical location of the river subsystems; each being autonomous and open, basin determines the formation of torrential rain- directly interrelated and integrated with its envi- fall and fl ash fl oods. ronment (Laszlo and Krippner 1997). The systemic approach is used in this study to analyse fl ood Climate factors formation mechanisms and improve our understanding of the complex interactions between the Atmospheric circulation factors. The torrential rainfall factors determining the formation and expression events, which form fl oods and cause rivers to over- of fl oods. The spatial analysis method takes a cen- fl ow, occur in several types of synoptic-meteorolog- tral place in the examination of the fl ood forma- ical systems: Mediterranean, Atlantic, Continental tion factors and mechanisms, using GIS as a tool and Combined (Table 1). for analysis. Precipitation. The Skat River valley is one of the least The following information has been used: spatial humid areas in Bulgaria. The average annual precip- data (maps of reconstructed property, updated in itation values are insignifi cant, from 450-500 mm in 2013 – 57 maps “.zem” documents; orthophoto the Danube plain up to 650-700 mm above the hilly map of Bulgaria updated in 2011 – 129 map sheets; slopes of Veslets. digital terrain model of the territory of Bulgaria in 2011 – block 2, block 7 and block 8; borders of the The continuous rainfall in the period from 31 July to underground water bodies in the Skat River catch- 2 August 2014 affected the whole Skat River Basin. ment); map materials (topographic maps of Miziya According to data from the National Hydromete- region, scale 1:5,000; geological map of the Skat orological Institute of the National Academy of River catchment, scale 1:100,000; soil map of the Science and the Executive Agency “Combat hails”, Skat River catchment, scale 1:200,000); hydromete- precipitation values for this period were between 70 orological data (precipitation and water level values and 217 mm (Figure 3). The higher precipitation of the Skat River). values were recorded in the village areas of Malo- rad, Ohoden and Banitsa (167-217 mm), as well as ASSESSMENT OF THE NATURAL FAC- in the southern part of the Skat River Basin (110- TORS INVOLVED IN THE FORMATION 125 mm). The lowest recorded precipitation values OF THE MAXIMUM RUN-OFF AND are in the northern part of the basin (in the area of FLOODING OF THE SKAT RIVER Miziya town 76 mm). Geographical location Maximum precipitation values were recorded between 16:00 h, 31 July 2014 and 09:00 h, 1 August The Skat River fl ows through northwestern Bul- 2014 (NINKS-HM Ltd. 2014). garia and is the major tributary of the Ogosta River (Figure 2). The Skat River originates 505 m The torrential rainfall in the period from 31 July above sea level, at coordinates 43° 15′ 4.139″ N and 2014 to 1 August 2014 was assessed as extreme for 23° 37′ 28,134″ E. The river discharges into the the following reasons: Ogosta River 25 m above sea level, at coordinates • Comparison of rainfall values from 1 August 43° 43′ 24,156″ N and 23° 51′ 44,109″ E. and 2 August 2014 with the relevant average AUPO Geographica Vol. 45 No. 2, 2014, pp. 99-120 Flood formation mechanism of the devastating fl ood in Miziya, Bulgaria in August 2014 103 Table 1 Atmospheric circulation systems for formation of torrential rainfall events. Source: Zyapkov 1997; own processing. Characteristics Mediterranean (M) Atlantic (A) Continental (C) Combined Total number 236 218 100 56 Wind direction (%) SW 60.2 NW 80.3 NE 2.0 W 38.1 W 17.4 N 69.0 S 1.7 N 2.3 NW 29.0 Cyclones (%) 98.3 62.8 27.0 MAC 35.7 Anticyclones (%) 0.4 34.9 42.0 MC 37.5 Mixed (%) 1.3 2.3 31.0 MA 12.5 Cold fronts (%) 26.3 98.2 100.0 MC Warm fronts (%) 72.7 1.8 – Other monthly values for the periods 1961-1990 and Soils are represented by two types: loess complex 1981-2010 showed that the rainfall in 2014 sig- (loess, loam) and sediment formations (made up nifi cantly exceeded the average monthly values of clays, clay limestone, marl, compacted clay rocks of all stations, except for Ostrov.

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