Hydrological risk phenomena in the Basca Rozilia river basin

Lidia Sǎlǎjan, Petre Stanciu The National Institute of Hidrology and Water Management, Everything that mankind could not conquer or explain has been put on hazard. Hazard consists of two major components: one is related to the repeatability of a phenomenon and its main determining causes, the other one is related to its random character, having no connection with the past, component that give the hysteresis state of the studied system. In the first part of this presentation there are analyzed the main risk factors such as: general presentation of the river basin, the definition of flood, the main characteristics of a flood, the geographical position of the river basin and its main rivers, the human impact in the hydrological water flow regime. In the second part there are analyzed the three historical from 1975 and 2005 recorded on the Basca river at the Varlaam gauging station on the Basca Mare river and on the Basca Mica river, and the other one at the Basca Rozilia gauging station on the Basca river. After that, an evaluation of the negative effects are analyzed and actions to take in order to diminish the hydrological dangerous effects in this river basin are also suggested. The Basca Rozilia river basin Geographical location - is situated in the South – Easthern part of the country within the Curvature Carpathians Limit: -In the North – Western part is limited by Intorsurii Mountains ; -at North by Vrancei Mountains and Zabala River ; -at East with the Vrancei Mountains and the Sub-Carpathians ; -in South only with the Sub-Carpathians ; -and towards West by the Buzau River Morphometric characteristics

The Basca Rozilia river basin is formed by the junction of the Basca Mare and Basca Mica rivers, this is the left of Buzau River, having a length of 71,4 km and a surface of 776 square km. Basca Mare has its sources in the North of Lacauti at an altitude of 1776 m from Vrancei Mountains and Basca Mica under this peak, from where it lies toward South. The relief, the geological structure and the climate condition the natural shape of the hydrographic network with a permanent flow regime.

The Basca Rozilia river basin- morphometric characteristics

Length Square Main river Tributary (Km) (Kmp) Basca Mare 60.5 424 Holomul 7 20 Ghiurca Mare 8 23 Slobodul 5.82 10 Potacu 10 18.5 Basculita 10 28 Cernat 5.70 11 Milei 6 15.4 Ciresul 9 32 Saros 7 15.2 Darnaul Mare 10.2 21.5 Corongos 5.67 13.2 Basca Mica 43.9 235 Giurgiu 6.50 15.6 Sapte Izvoare 6.63 15.5 Brebu 5.86 11.2 Basca Unita 71.4 759 Paltinis 9 24 The Basca Rozilia river basin

• In the Bâsca river basin, the hydrographic network is well organized and has a permanent flow regime. • The torrential organisms have developed on the slopes of the valleys in the depressions due to uncontrolled deforestations. • Within the mountain area of the internal and external flysch comprising the Bâsca Rozilia river basin, the prevailing rocks are: conglomerates, grit stones and limestone, favouring the infiltration through sreaming and superficial flow. • The steep slopes contributed to the organizing of the hydrographic network and the limestone rocks in the flysch area favoured the presence of flows with a semi-permanent flow regime, becoming dry every 2-3 years.  The Bâsca Rozilia river basin is situated in the mountain area, with rural human settlements, such as scattered villages, situated on the river meadows and depressions. Thus, in the north-weastern part of the river basin, there is Comandău village (45059'19'' north latitude and 26027'52’’ east longitude; In 2002 Comandău counted a population of 1018 inhabitants.

 Gura-Teghii is a village in the Buzău county (45o20’ north latitude and 26o25’ east longitude), situated at the junction of Bâsca Mică and Bâsca Mare rivers, creating a beautiful valley, cut in the rocks, but with ideal sandy beaches. According to the population census, in 2002, it had a population of 3884 inhabitants.

RISKS IN THE BÂSCA ROZILIA RIVER BASIN

 The risks are not limited in space and time, they can occur anytime, affecting all the natural, social and technical terrestrial geostructures at local, regional and global level;  The drought and the floods represent important risk phenomena, being linked to the assurance calculation which represent the safety anticipation in that area.  The risk elements can be found in the areas with different vulnerability degrees and comprise: “population, buildings, economic activities, public services, utilities, infrastructure which are prone to risks in a particular area” (Crozier, 1988).  In the Bâsca river basin, the floods are the most frequent, causing major damage with serious consequences. They are mostly due to the global climate evolution and to the anthropogenic factor.  Due to significant variations in time and space of the temperature and other climatic elements, the floods can occur anytime, but particularly during the interval April- September.  The geological structure and the lithologic composition of the area in the mountain area, due to rocks impermeability, does not allow a massive soil infiltration, reducing to minimum the role of the underground drainage, but also represents a major vulnerability due to the big slope energy, which causes landslides and torrents. RISKS IN THE BÂSCA RIVER BASIN

 The vulnerability and resilience assessment represents a complex process, because it implies the presence of human communities at risk.  In this area, there have been identified both slope and minor riverbed processes, especially in and on the Păltiniş Valley, resulting from floods and the thaw-frost phenomenon.  The villages gather on the valleys, mostly at the slope base, the main communication ways are not close to the sources, the most frequent being the forest roads. In this area, the population is scarce and old very poor.  The population resilience analysis revealed that at the administrative units and domestic level, the incomes are insufficient for a decent living, the balance of these values being negative in most of the cases.  The resilience represents the human capacity of recovering to the initial stage, after having suffered losses in a disaster.  The causes of these risk phenomena in the Bâsca river basin are: the temperatures, the precipitation, the thaw-frost phenomena and the anthropogenic actions. The factors that determine the risk phenomena - Precipitation- The precipitation regime under the aspect of the annual amounts varying between 800 and 1200 mm in the mountain area represents a series of particularities connected to the general air mass circulation and the natural environment. The precipitation amounts lower from north to south, as a result of the wet western air masses, or the depression areas where larger amounts of precipitation are recorded due to the thermal advection. The average multiannual rainfall amount at the Lăcăuţi meteorological station over a 50-year period was of 65 mm, in 2005, the maximum precipitation amounts which produced floods over the interval May-September were of 120-220 mm at Lăcăuţi, and of 150-280 mm at Penteleu. At the Lăcăuţi meteorological station, these values are graphically represented by percentages.

The fluctuation in 2005 of the monthly The percentage of the monthly rainfall amounts rainfall compared to an average year recorded in 2005 (multiannual mean monthly rainfall) at the compared to the( multiannual meam monthly Lacauti meteorological station ). values). Variation of rainfalls over the period 1971-1980 at the Lacauti meteorological station The factors that determine the risk phenomena -Temperatures-

• The Bâsca river basin is located in a mountain climate with mean annual temperatures of 4-6o C. • On the basis of the statistical data analysed at two meteorological stations over the period 1961-1990, the minimum temperature in January if of -35,5oC (Intorsura Buzaului) and of -28,7oC (Lacauti). The maximum temperature at Întorsura Buzăului is of 34,2oC and at Lăcăuţi of 27,2oC both recorded in July. • The frost-thaw phenomenon occurs when the air tempertures drop below 0oC, the average date of the first day with frost is 1st of October in the mountain area, and the average date of the last day with frost is 1st of May. Distribution of mean monthly temperatures over the period 1971-1980 at the Lacauti meteorological station. Water shortage – major cause of environmental effects

The water shortage is due to the lack of precipitation over a long period of time. This lack may produce hydrological and pedological effects. The of inferior order in the Bâsca Rozilia river basin have a semi-permanent flow regime. The water reserve shortage is characteristic in this basin and it produces during the winter, mostly in the period December- February, due to low temperatures. Sometimes, this deficit is not a consequence of the water shortage from the snow cover but the negative temperatures recorded during the winter, which do not allow release of water from the snow cover. Thus, the water is preserved and suddenly, in spring, together with the rainfalls, it brings its contribution to the occurrence of floods and high waters. The mean monthly multiannual flow

From the hydrometric data analysis, it was concluded that the very low mean monthly multiannual discharges are in the intervals January– February and October–December. They will grow in March–September when flash floods may occur.

Mean monthly multiannual flow ESTABLISHING OF THE MINIMUM, MEAN AND MAXIMUM YEAR OVER THE INTERVAL1973 – 2005 • Knowing of the maximum flow value is very important, taking into account the various negative effects produced by flash floods and high waters. The maximum flow usually occurs in spring when the fluvial organism supply is very rich (the melting snow layer combined with spring rainfalls). The safety of hydrotechnical structures, crops, and human settlements depend on it. • Knowing of the minimum flow value and the maximum one is crucial. The water of the rivers is very important for agriculture, pisciculture, water supply for population, hydrotechnical structures, filtering stations). • For the hydrological characterization of the water resources in a river basin, it is very important to establish, from a data series the minimum, mean and maximum year.

Establishing of the minimum, mean and maximum year at the Varlaam hydrometric station on the Bâsca Mică river Solid flow – risk quantifier • The solid flow can be consider a quantifier of the flash flood and high water state effect, through its size, giving pretty eloquent information on the anthropogenic actions upon the studied environment (deforestations, chaotic agriculture) and of the lithologic context of the area. • In the Bâsca river basin area, the Bâsca Mică and Bâsca Rozilia rivers represent the area with the largest amounts of suspended sediments due to the lithologic structure and the slope energy conditions, favoring slope and riverbed erosion. • The vertical zonality of the mean solid flows is emphasized by the analysis of the variation between the mean altitude and the mean specific to small basins (Bâsca and Slănic).

1991 I II III IV V VI VII VIII IX X XI XII

mean 159 108 5,37 11,5 32,1 73,1 440 12,7 4 2,89 2,7 1,09

maximum 2,31 1,29 27,9 22,7 181 369 19800 174 210 25 252 1,60

data 13 24 25 21 30 30 18 19 19 3 18 1

miinimum 0,8 0,9 1,18 3,95 6,15 12,5 6,20 1,98 1,02 1,04 0,975 0,9

data 31 1 1 6 2 - 3 28 26 31 16 31 3 9

1975 I II III IV V VI VII VIII IX X XI XII

mean 0,847 0,139 0,528 1,29 18,1 11,0 161 6,16 1,06 8,22 0,464 0,364

maximum 5,66 0,246 2,92 11,7 610 348 16400 36,5 10,3 335 0,756 0,820

data 1 1 13 23 28 4 2 20 4 20 29 19

minimum 0,185 0,06 0,043 0,055 0,3 1,09 0,425 0,376 0,95 0,376 0,316 0,140

data 19 6 2 30 1 14 6 31 28 1 16 5 The correlation between mean altitude and mean solid discharge on the Buzau river HYDROLOGICAL RISKS IN THE BÂSCA ROZILIA RIVER BASIN

 The floods are flow processes along the river beds of large water amounts, exceeding the natural banks and the dikes and overflowing the flood plains, invading large land surfaces used by the man.  Knowing the cause and the way in which floods occur, enable us to prevent and mitigate the negative social, economic and ecologic effects they may cause.

 The high floods occur after heavy rains, quick snow melting or the occurrence of these two phenomena at the same time. They are generated by the basin surface flow towards the riverbeds, where rapid growths of levels and discharges may occur.  Function of the time distribution of the precipitation, these ones are divided into: simple high floods (ccharacterized by a single peak) and compound (with many peaks).  The occurrence of high floods and their characteristics are also determined, besides the climatic conditions, by other factors such as: permeability, himidity level,soil temperature, vegetation, riverbed and slope plants, shape and surface of the reception basins and the riverbed characteristics. Flood at the Varlaam hydrometric station Flood at the Varlaam hydrometric on the Basca Mica river (July-1975) station on the Basca Mare river (July - 1975)

growth time 15 hours growth time 21 hours decrease time 45 hours decrease time 90 hours

high flood duration 60 hours high flood duration 111 hours maximum discharge 392 mc/s maximum discharge 600 cm/s high flood volume 25 mil cm high flood volume 48 mil cm form coefficient 0.29 form coefficient 0.20 basic discharge 14.5 cm/s basic discharge 22.5 cm/s basin surface 235 km2 basin surface 434 km2 flow coefficient 0.42 flow coefficient 0.45 specific discharge 1668 l/s&km2 specific discharge 1382 l/s&km2 Flood at the Varlaam hydrometric station on the Basca Mare river (July - 1975) The composition of flood waves at the Basca Rozilia hydrometric station Basca Roziliei (July -1975)

growth time 24 hours decrease time 99 hours high flood duration 123 hours maximum discharge 940 cm/s high flood volume 75.8 mil cm form coefficient 0.18 basic discharge 20 mc/s basin surface 759 km2 flow coefficient 0.43 specific discharge 1328 l/s&km2 Flood at the Varlaam hydrometric station Flood at the Varlaam hydrometric station on on the Basca Mica river (July - 2005) the Basca Mare river (July - 2005)

high flood duration 30 hours growth time 30 hours growth time 12 hours decrease time 117 hours decrease time 18 hours high flood duration 147 hours maximum discharge 128 cm/s maximum discharge 135 cm/s high flood volume 5.5 mil cm high flood volume 33 cm form coefficient 0.39 form coefficient 0.50 basin surface 235 km2 basic discharge 25 cm/s rainfall amount 48 l/m2 basin surface 434 km2 flow coefficient 0.47 flow coefficient 0.26 specific discharge 545 l/s&km2 specific discharge 311 l/km2&s basic discharge 4.59 cm/s Flood at the Basca Unita hydrometric station on the Basca Roziliei river (July-2005)

The composition of flood waves at the Basca Roziliei hydrometric station (July –2005)

growth time 18 hours decrease time 165 hours high flood duration 183 hours maximum discharge 173 cm/s high flood volume 38.2 mil cm form coefficient 0.42 basic discharge 17.5 cm/s basin surface 759 km2 flow coefficient 0.52 specific discharge 228 l/s&km2 CHARACTERISTICS OF THE ANALYZED FLOODS

For the analysis of the 1975’s and 2005’s high floods, the summer floods were selected to calculate the mean precipitation amounts for the Bâsca river basin, with values between 120 and 180 mm .

The flood occurred in July 2005 on the Bâsca Mică river is one of the most eloquent form the point of view of the anthropogenic influence upon the Bâsca Mică river basin, being translated into a duration of 30 hours, a growth time of 12 hours, in comparison with the flood occurred in July 1975 on the same river which lasted 60 hours, with a growth time of 15 hours, in the conditions in which the rainfall recorded in the basin in 1975 had about the same duration with the 2005’s one, but with a higher intensity, pointing out the decrease in slope concentration times due to the destructive anthropogenic influence.

Due to rain advancing in the Bâsca river basin, it can be noticed that at the level of July 2005, although the floods on the Bâsca Mică and Bâsca Mare rivers, had maximum discharges of 150 cm/ s, at the Bâsca Rozilia hydrometric station, a double discharge was not recorded but a higher flood duration, which is due to the 2-3 hour offset of the hydrometric stations on the Bâsca Mică and Bâsca Mare rivers, compared to the and the fact that there is a 1-2 hour delay in the Bâsca Mică basin reported to the rain nucleus formed on the Bâsca Mare river.

During the flood of July 1975, in the same river basin, it can be noticed that the flood waves on the Bâsca Mare and Bâsca Mică rivers have a small 2-hour offset due to the fact that at higher discharge values, the speed increases and the rain nucleus falling evenly on the basin, the offset does not occur any longer when the flood breaks out. Thus, the discharge produced on the Bâsca river and recorded at the Bâsca Rozilia hydrometric station was of 940 cm/s, representing the historical discharge in the Bâsca river basin. Characteristics of the flood waves in the summer period of the years 1974, 1975, 1991 and 2005.

1974 June 1975 July 2005 July 1991 July Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Bâsca Mică Mare Unită Mică Mare Unită Mică Mare Unită Mică Mare Unită

Growth time 12 21 21 15 21 24 12 30 18 15 27 18 Decrease time 48 84 105 45 90 99 18 117 165 45 93 117 High flood 60 105 126 60 111 123 30 147 183 60 120 135 duration Maximum 114 300 345 392 600 940 128 135 173 359 227 537 discharge High flood 7,72 38,4 47,8 25 48 75,8 5,5 33 38,2 25,3 24,3 50,6 volume Form 0,28 0,34 0,3 0,29 0,2 0,18 0,39 0,5 0,42 0,33 0,25 0,19 coefficient Basic 11,5 14 21 14,5 22,5 20 7,59 25 17,5 8,5 11,5 11,5 discharge Specific flow 485 691 4,87 1668 1382 1328 545 311 244 1528 535 708 Discharge 0,30 0,59 0,45 0,42 0,45 0,43 0,47 0,26 0,56 0,32 0,48 0,67 coefficient CONCLUSIONS Measures for flood prevention and mitigation - Carrying out of works to retain and slow the water flow on the slopes, tributaries or torrents, coming from heavy precipitation amounts or snow melting. These works could be:  forestation or reforestation of the slopes, creation of certain types of vegetation covers to favor the infiltration and reduce runoff on the slopes, construction of retention dams in the valleys, modification of the lower course of rivers through building dikes and canals and carrying out of temporary basins on certain flood plain sections;  establishing of the flood plains to know better the interdiction areas, in accordance to which no building can be raised in the flooding canal;  giving up the generalized embankment of the major riverbeds and the flood plains and encouraging the construction of polders during the flood periods;  carrying out of anti-erosion works in the reception basins of the rivers and the declogging of the minor riverbeds;  Firm involvment of the authorities of the local and national administration in order to apply the flood prevention, protection of population and environment;  Upgrading of the information system, enabling the warning in case of occurrence of severe hydrometeorological phenomena;  Education of the population for the protection of riverbeds against pollution with solid and waste, information and teaching them how to act in case of floods. CONCLUSIONS Measures for landslides prevention and control They are made according to the following criteria: soil structure, climatic conditions, agrotechnical and agrosylvan methods to mitigate landslides.

• On the steep slopes with a clay layer at the surface, surface horizon with a texture made up of clay, it is recommended that ploughland should be made along the slope line, use of plant species demanding a large water consumption.

• Among the most important agrosylvan methods is to carry out protection curtains along the slope line, using species of trees with ramified roots, with the role of consolidating and reinforcing, and from the agrotechnical point of view and planting of orchards of fruit trees with higher densities towards the sliding base.

• Among the modern methods of consolidation of areas prone to landslides is the reinforcing of the of the terrain towards the sliding base with tensar grilles and carrying out of a horizontal drainage allowing the flow of water afflux and not permitting it to reach the sliding bed, doubled by carrying out of vertical drains all along the surface of the slope prone to landslides. THANK YOU VERY MUCH FOR YOUR ATTENTION!