On the Flood Forecasting at the Bulgarian Part Of
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BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 THE INFLUENCE OF THE CLIMATICAL, PSYHICAL AND GEOGRAPHICAL FACTORS GENERATING FLOODS IN THE SMALL HIDROLOGICAL BASINS LOCATED IN THE WESTERN PART OF THE CARPATHIAN MOUNTAINS Felicia POPOVICI NATIONAL INSTITUT OF HIDROLOGY AND WATER MANAGEMENT Bucharest, Romania Abstract The purpose of this paper is to present the influence of the climatic, physical and geographical factors (precipitations, geology, soil, vegetation, anthropogenic impact) to the maximum discharge, factors who generate the floods in small basins situated in the west part of Oriental Carpathians, Romania. For the period of study (1975 – 2000), is very important to analyse: - the maximum discharge which are produced; - the more important elements of floods; - the characteristics of the precipitations and runoff coefficients which are produced in the basins considered.(Gurghiu, Tarnave, Sovata, Bistra , Hodos, Homorodul Mare si Homorodul Mic, Rastolita.) Tables and graphics are coming to illustrate with accuracy the relationships between the characteristics of the rainfalls and geographical conditions of the main floods produced in these basins. The reason of these analyse is to determine useful parameters for the prediction and forecast of the floods in small basins, because these basins have a high speed reaction to the inputs elements (precipitations and its characteristics). Geological conditions From the paleo-geographical evolution standpoint, the studied zone is characterized by a late magmatism manifested along the great transversal fault Oas – Tusnad, since Miocene to Pleistocene. The most intense and recent volcanic activity has been recorded in the Caliman-Harghita area. The eruptions occurred within the inferior Pliocene-Pleistocene cycle, when the volcanic structures erected. The strato-volcanic structure ( made of lava and piroclastite ) prevails among the specific effusion structures. In the eastern part of the Transilvanian Depression (upper reach of Mures and Olt rivers) there are isolated sedimentary basins, namely the depressions of volcanic barrage ( dam ) Giurgeu and Ciuc. We can observe the geology of zone in the following map: (Fig 2) Droughts and Floods 1 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 Legend: A = TOPLITA B = RASTOLITA C = BISTRA D = GURGHIU E = TARNAVA MICA F = SOVATA G = TARNAVA MARE H = SICASAU I = HODOS J=HOMORODUL MARE K = HOMORODUL MIC Sedimentary formations Aluvial deposits Pannonian (Pn) Extracarpathian Sarmatian (Sm) Andesits, Piroclastits Diorits and Basalts Upper Precambian (B) Figure 2 – Geological Map (after Romanian Atlas 1978) Lithological structure The studied volcanic area contains mainly impermeable or weakly permeable rocks. It is characterized by an intense drainage of the surface and shallow ground waters, due to the great slopes. In the compact volcanic area (andesites, basalts) the water resources are low, however the piroclastites offer great possibilities of water retention (when their stratification includes clays and cemented rocks). The regeneration of the shallow waters is more intense on the western slopes of the western Carpathian Mountains (rich precipitations). Psyhical and geographical conditions Relief The volcanic relief of the studied area is distinguished by successive eruptions and has both petrographical and structural character. It has specific shapes generated either by the various agglomerations of lava reaching the surface, or by the direction of the various erosions within the volcanic skeleton. The andesites lava (hard and compact, sometimes with stratification) shows as dome shapes, while the volcanic agglomerations show as plateaus generating a more varied relief, alike to the one formed by conglomerates ( scarps, towers,needles ). The volcanic chain Oas - Caliman – Harghita (considered as the longest of Europe) has a variety of relief forms, due to the mineralogic composition of the rocks, to the eruption type or to the age of the Droughts and Floods 2 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 volcanos. The wide plateau in contact with the Precarpathic Transilvanian area, is dominated by associated domes, made of an alternation of andesite and piroclastite lavas with more pronounced slopes and monoclinal stratification. On top, the central part of these domes corresponds to the volcanic craters. The alteration process of the feldspats contained in the andesites has created pans and lapies on some surfaces and the more intensive kaolinization allowed small depressions to be formed, of doline type. In the Caliman Mountains, there are caves with lymonitic structures ( stalactites, stalagmites and drip curtains ) and in the Caliman - Gurghiu - Harghita (1.600 - 2.100 m) group, the best preserved morphology is the volcanic one. From the structural standpoint, the area has two complex parts: the volcanic-sedimentary base ( Pliocene ) due to the accumulation of volcanic products, and the upper part represented by volcanic cones formed during the last phase of the volcanic erruptions. Legend: A = TOPLITA B = RASTOLITA C = BISTRA D = GURGHIU E = TARNAVA MICA F = SOVATA G = TARNAVA MARE H = SICASAU I = HODOS J = HOMORODUL MARE K = HOMORODUL MIC RELEF DEVELOPED ON THE VULCANO FORMATIONS Mountains (1600-1900m)→on vulcano neogen formations:volcano cones, craters. Mountains (800-1200m)→from defragmentation of the piroclastites plateaus and neogene lava INTERMOUNTAIN DEPRESSION Tectonics and volcanic barrage depression with hill aspect or aluvial plateau aspect RELIEF OF HILLS AND PLATEAUS Relief developed on the neozoic monoclinale formations or affected by diapires folds and domes Hills (400-700m)proceeding by the fragmentation of the plateau with actifs versants Relief developed on the neogene and sedimentary formations very strong affected by folds, with accentuate tectonic mobility. Hills (400-900m) fragmentated in summits and massifs which are liable to the denudation SUBCARPATHIANS DEPRESSIONS AND HILLS DEPRESSIONS Differential erossion depressions with hilly aspect Figure 3 – Geomorphologiclal Map (after Romanian Atlas 1976) Droughts and Floods 3 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 The erosion has formed countless depression basins, often represented by relief inversions.The valleys from the western part of the Carpathians are narrow, with pronounced slopes and irregular longitudinal profile; the main valleys are wider, having flood plains and terraces in the rocks or in alluvial deposits, while the largest valleys have an either longitudinal development ( Mures and Olt in the Giurgeu Depression and Ciuc Depression) or cross sectors with local narrowings, straits and gorges.( Mures in the Toplita – Deda Strait ). The highest go from 1750-2100m : Pietrosu Peak, in the Calimani Mt 2.102m, Saca Peak in Gurghiu Mt, 1.777m and Harghita Madaras Peak, in Harghita Mt. -1800m. In the next picture - Fig 3 – is attached the geomorphological map (after Romanian Atlas 1976) for more details. Soil The soils of the mountain area Caliman – Gurghiu - Harghita have been formed in a wet and relatively cold climate; they have a generally small depth and a more or less skeleton character. The main feature of the soil cover is the vertical division into zones; however this succession of altitudes, determined by the climate, is much influenced by rocks and relief. The studied area represents the domain of the brown – acid soils and andosols. In the lower part of the mountain, corresponding to the area of the leafy trees or mixture ( leafy and coniferous ), there are brown soils, as well as brown slightly debasified soils, rendzinas, lithosols. In the upper part of the mountain, specific area of the coniferae and sub-alpine zone ( juniper area ), brown-acid and brown podzolic soils can be found, along with the andosols, and over restricted areas, there are lithosols as well. In the depression area constituting the transition to the Transilvanian sub-Carpathians ( lower Gurghiu valley, Praid-Sovata, Odorhei, Homoroadelor corridor ) there is a large variety of soils. The highest areas have brown soils (slightly and moderately debasified), brown-luvic, white luvic soils, while the low plains and the weakly drained flood plains have alluvial soils in various degrees of gleyzation – due to the high humidity, peat soils and humic gley.) In the Fig 4 is the map of the soils, which are showing the types of the soils for the area studied. The map was realised after Romanian Atlas –1978. Vegetation The analyzed hydrological basins are vertically divided into zones according to the vegetation structure. The vegetation - especially the forest – has a very important role in the process of the runoff generation : the arborescent vegetation helps forming more permeable soils than in the free areas ( lawns or reclaimed lands ). The vegetation has a direct influence on the soils endurance to erosion, both by the litter and by the roots knitting system maintaining the humidity from infiltrations. The forest creates a specific microclimate, characterized by the snow melting delay, thus increasing the period of the high waters along with the runoff decrease and intensification of infiltrations. Rivers regularization is carried out through the underground water supply, even during the periods without precipitations. On the deforested surfaces the phenomenon happens in the reversed way. In the Fig 5 is the map of the vegetation –forests-after Romanian Atlas –1975 at scale 1:1.000.000 Droughts and Floods