Carpathian Journal of Earth and Environmental Sciences, February 2011, Vol. 6, No. 1, p. 119 - 132 THE MOST IMPORTANT HIGH FLOODS IN VASLUI RIVER BASIN - CAUSES AND CONSEQUENCES Gheorghe ROMANESCU1, Ionut JORA2 & Cristian STOLERIU1 1University „Al.I.Cuza” of Iasi, Faculty of Geography and Geology, Department of Geography, Bd.Carol I 20A, 700505, Iasi, Romania, [email protected], [email protected]. 2Prut Water Headquarters, Iasi, Str.Vascauteanu, 10, Iasi, Romania, [email protected]. Abstract: The frequency of flooding phenomena in Romania has significantly increased and the extreme catastrophic events became more frequent. Most of the rivers in the Eastern part of Romania are influenced by the excessive continental climate. That is why torrential rains are frequent and the possibility of high floods occurrence is extremely high. The Vaslui river is not an exception, and this is the reason why a series of measures to prevent floods have been taken in this river basin. The most efficient constructions for diminishing high floods consisted in damming the main water courses on certain sectors, building up of an accumulation in Solesti and slope forestation. The measures have as a main purpose the diminution of the negative impact on the town of Vaslui. The maximum flows in the Vaslui river basin can be recorded in any season, but most frequently they register during spring, sometimes at the end of winter, when snow melting is accompanied by high amounts of rain. Keywords: high floods, maximum flow, reference flow, water volume, barrage. 1. INTRODUCTION obtained from the Prut Water Headquarters in Iasi. The facts revealed by the data processing are For the last few years, catastrophic floods compared and corroborated with the data existent in have occurred in Romania every two years. The the literature in the field, especially in the literature importance of the main high floods on the Vaslui referring to the Moldavian Plateau river is pointed out, and their consequences, as well as the measures necessary to reduce the effects. 2. REGIONAL SETTING The main characteristic of the rivers in the Eastern part of Romania is the uneven flow, with Vaslui River represents one of the most extremely high flows during high waters. As a result important hydrographic elements of Vaslui County. of the fact that the Vaslui river has often over flown The Vaslui river has its source under the Repedea – its banks, measures of regularization of the river Paun plateau, at 340 m altitude, and the river flows course and barrage construction in order to diminish into the Barlad river, at 80 m altitude. As a left the high floods have been taken. From this point of tributary to the Barlad river, the Vaslui river is view the Vaslui river basin is insured and the situated in the Eastern part of Romania. The area of frequency or intensity of the floods has diminished the hydrographical basin represents 9.58 % of the significantly. Nevertheless, the phenomena with Barlad river basin, which is the greatest river basin hydrologic risk start to have a special importance for and the longest river in the Siret river basin (Fig. 1). the small river basins, tributaries to the main course. From a morphologic point of view, the Vaslui The intrinsic connections between the amount river basin is situated in the central-eastern part of of precipitation (especially those with torrential the Moldavian Plateau, more precisely in the central character), and the occurrence of the flood - eastern part of the Central Moldavian Plateau. It is phenomena are pointed out. Therefore, the climatic limited by the Rebricea and Telejna river basins to data stored at the Moldova Meteorological Center in the west, by the Crasna river basin to the east, and Iasi have been correlated with the hydrological data by the Bahlui and Jijia river basins to the north 119 (Amariucai et al., 2004, Atlas of Water Cadastral It has a length of 81.0 km and a basin area of Survey in Romania, 1992, Bacauanu et al., 1980, 692 km2 (Atlas of Water Cadastral Survey in Panaitescu, 2007, Ungureanu, 1993). Romania, 1992). The total length of the water courses in Vaslui county, except the Prut river, is appreciated to be 1 960 km, with a density of 0.37 km/km2, unevenly distributed. The hydrographical network density is about 0.32 km/km2, superior to the country average (0.33 km/km2). The combined water courses have a length of 218 km. The Vaslui river course is subsequent, and the reception basin is asymmetrical to the right (73% of the total area), a characteristic which is also met in the case of other Barlad tributaries such as Crasna. The asymmetry is caused by the decrease of altitude of the Barladului Plateau towards the Prut river basin. In the superior basin the slopes are 10‰, and in the inferior course they decrease to average values of 3‰ (Panaitescu, 2007). The water share is not proportional to the area of the basin, as it is a typical silvosteppe river, with very reduced flow and a low discharge. 3. MATERIALS AND METHODS The methodology related to the maximum runoff is closely related to the issues that will be Figure 1 Geographical location and mathematic further outlined (Romanescu & Lassere, 2006). In coordinates of the Vaslui river basin (Romania) the present study the hydrology specific methods have been used, especially those referring mainly to Table 1 Characteristics of the water courses and river high floods and high waters. From this point of basins view, the following parameters have been analysed: Data on the water Data on the river - maximum flow (Qmax, m3/s); course basin 3 Altitude - reference flow (Qb, m /s) – the flow where the (m) high flood starts and ends; - increase time (Tc, hours or days) – represents ) Water 2 the time period in which the flows increase from the course value of the reference flow to the maximum flow; - decrease time (Td, hours or days) – represents the Area (km Area Length (km) period of time in which the flow decreases from the Upstream Upstream Downstrea Average slope(‰) Confluence position Sinuosity coefficient Sinuosity coefficient Average altitude(m) maximum value to the value of the reference flow Forest cover area (ha) Forest cover (always Td > Tc); total time (Tt, hours or days) – Vaslui L 81 340 80 3 1.28 692 233 14,122 represents the duration of the high flood, Tt = Tc + Td; Carbunaria r 7 340 196 21 1.15 15 289 1,187 - water volume (W, m3), flown in an hour, a day, Tabara r 10 380 178 20 1.16 23 276 1,222 a season or a year – results from the multiplication (Valcele) between the average water flow in the specific time Pocreaca r 9 360 152 23 1.18 15 273 93 and the duration of the period. The total volume of Coropceni L 6 380 150 38 1.10 10 95 the high flood (Wt) can be calculated, as well as the Ciortesti L 7 270 135 19 1.52 22 258 266 volume during high flood increase (Wc) and volume Dobrovat r 27 330 122 8 1.16 185 248 6,412 Lunca r 16 335 118 14 1,12 45 246 232 during high flood decrease (Wd). These are Rac (Iaz) L 14 380 111 19 1.42 30 244 346 calculated using the following formula: W = Qmed x T, (Sorocovschi, Buta, 1994), in which: Qmed – Glod r 7 330 109 32 1.03 10 243 3 Feresti r 14 330 99 17 1.44 69 217 460 average flow (m /s);T – time (seconds); Munteni r 6 155 98 10 1.05 19 235 237 - flown layer (h, mm) – represents the thickness Delea r 14 222 92 9 1.18 19 160 of the water layer obtained if the high flood volume l-left; r-right is evenly distributed over the whole surface of the 120 river basin generating it. This is calculated using the Analyzing the causes of the highest annual following formula: h = W / (1000 x F), in which: W maximum flows, lead us to the conclusion that – high flood volume (m3); F – river basin area (km2) rainfall has a main role in producing them, either upstream the section in which the measurements alone or accompanied by snow melting. have been taken (Minea & Romanescu, 2007); Consequently, when calculating the maximum - shape coefficient of the high flood (y) – flows, the starting point is represented by the represents the numerical characteristic of the high analysis of the annual maximum flows (Fig. 2). flood shape and it always has a value under 1. This is XII II II IX IX calculating using the following formula: y = (h x F) / 3% III 2%2% III VIII 9% 7% 13% [3,6 x Tt x (Qmax - Qb)], in which: Tt – total time VIII 17% 3% 7% VII (ore) (Smith & Ward, 1998). 6% The maximum flow, the increase time, the total VII 15% IV time and the high flood volume are the main IV 22% VI 17% elements defining the high flood hydrograph and 22% represent the basis for its calculation and VI V V construction. 23% 10% 22% Satu Nou Codaesti 4. RESULTS AND DISCUSSIONS IX XI I II IX 4% 4% VIII 4% 4% 13% 8% VIII III Due to its flooding potential, Vaslui River has 4% 31% III been strongly regulated with hydrotechnical works VII 21% VII 4% with the purpose of diminishing the catastrophic 8% events (Panaitescu, 2007). VI 17% The maximum flow is extremely complex, VI IV being influenced by a multitude of factors: the river 21% 13% IV V V 18% basin shape and size, lithology, vegetation cover 13% 13% degree, slope inclination and river bed, flood plain Solesti Codaesti (Dobrovat river) width and configuration, presence of lakes etc.