The analysis of flash floods produced in the upper course of the Jijia river.
This paper seeks to identify both the causes of flash floods and floods and their integrated management, in order to limit the damages and to solve the problems occurred following these calamities in the upper Jijia river basin.
The main objective of this paper is also to identify the space and time dimension of risk hydrological phenomena (flash floods and floods).
The upper Jijia basin, with an area of approx. 300 [km.sup.2], is located in the northern Moldavian Plateau. The western part of the basin overlaps Suceava Plateau (Ibanesti Hill, Bour Hill, Lozna Saddle) (fig. 1). The Jijia tributaries exceeded the heights line reaching the Siret river basin in the Lozna saddle, where they collected waters until the terrace level of 8-10 m.
The rest of the basin (the central and eastern parts) belongs to another subunit of the Moldavian Plateau, namely the Jijia Plain. 3 4
3. Data and Methods
The data based on which the study herein was drawn up were the flow values measured at the Padureni hydrometric station on the Buhai River (the period 1980-2012), the Dorohoi station on the Jijia River (the period 1959-2012) and those on the Iezer reservoir, the climatologic and meteorological data (INHGA, 2010).
Regarding the maximum liquid and solid discharge analysis, the methods used were specific to this domain, found both in the specialty literature as well as within the surface hydrology compartments of INHGA (National Institute of Hydrology and Water Management--the surface hydrology--serban, Stanescu, Roman, 1989).
4. Physical and Geographical Features of the Upper Jijia Basin
Relief: The western part of the basin is hilly (Bour Hill--472 m, Ibanesti Hill--385 m), while the eastern part of the region is represented by a quasi- horizontal low region, the Botosani-Dorohoi Depression (average altitude of 200 m); the relief energy is reduced, with an average of 30-40 m.
The monocline of the Romanian Badenian layers, with a general orientation to the South-East, as well as the alternation of hard layers with soft layers are the ones determining the presence of cuestas and structural valleys (consequent, subsequent and obsequent). The landslides of different types and ages are specific of the studied area, and the water courses have riverbeds like small canyons counteracting the gentle lines of the relief (Tufescu, 1977). The depth erosion has caused the formation of the Ibanesti ravine in the hill bearing the same name, creating the appearance of badlands.
Geology: The studied area is characterized by an old Precambrian foundation, consisting of crystalline schists and a Palaeozoic, Mesozoic and Neozoic sedimentary superstructure, above which there is a thin cover of more recent quaternary formations, represented by loess clays where the waters coming from rainfall or snowmelt deeply infiltrate (Tufescu, 1977).
According to the tectonic ratio, the measurements performed on the actual movements of the crust currently show an elevation in the contact area with the Siret hills and a descending crust in the Ia.si area (subsidence area) (Tufescu, 1977).
Vegetation: The durmast forests are common in the north--western part of the upper Jijia basin, while the beach and mixed forests are common in the south-western part of the basin (fig. 2). In the rest of the basin (the central and the eastern part) the forests were massively cleared, and the natural vegetation is found on reduced surfaces as meadows and grass lands with perennial grasses.
The place of the natural vegetation has been taken by vineyards, orchards (plum, sour cherry, cherry, apple, pear, quince and walnut trees) and agricultural crops (wheat, rye, barley, corn, potatoes, sugar beet, sunflower) (Tufescu, 1977).
Hydrography: In the upper basin, the Jijia River receives as main tributaries the Buhai River on the right and the Paraul lui Martin Stream on the left, with a length of 10 km. The Buhai River has a length of 18 km and its main tributary is the Paraul intors Stream. This stream flows on the South-North direction from the Vaculesti village until its discharge into the Buhai River (Tufescu, 1977).
The supply waters of the rivers in the upper Jijia basin is 86% pluvionival, hence the high dependence of the discharge on the climatic factor.
Besides the heavy rains, the flash floods occurrence was caused by: the rock friability, the high degree of torrentiality and the nearly circular form of the basin, allowing the fast concentration of liquid and solid flows.
5. Flash Floods and Floods--as Extreme Phenomena
The main cause of the historical flash floods occurrence in 2010 was the precipitations. We refer to the ones fallen between June 18-July 9, 2010 (the cumulated quantity of water in this period exceeded 370 mm), as well as the heavy rain from June 28, 2010, which quickly triggered flash floods causing serious damage. The most damaged area by the floods was the Dorohoi town.
The atmospheric instability was due to the contrast between the tropical mass from the East of Romania, being very hot throughout the troposphere column, and the cold altitude core blocked over our country, as well as to the humidity advection, and the retrograde cyclone from the Black Sea.
The numerous ponds of the Jijia plain, being attested in documents since the 15th century, were especially built for the accumulation of water during the floods and its use during periods with lower precipitations, which are larger, e.g. the pond near Dorohoi--Iezer (430 ha).
6. The Analysis of Mean Pressure Field Deviations for the Period June 18-July 28
The climatologic aspects were obtained from the reanalysis data from the North Atlantic Oscillation (NOOA-NCEP/NCAR), followed by an analysis of the mean pressure field deviations of 1000 hPa (fig. 3) and 500 hPa from the period June 18-July 28 (Hustiu, 2011).
This interval was analyzed in order to find out the cause of these precipitations from the central-eastern and south-eastern parts of Europe, and the data related to the precipitation deviations from the monthly averages were obtained from the Climate Prediction Center (CPC) and the North Atlantic Oscillation (Hustiu, 2011).
The pressure field at sea level (SLP) was obtained from the National Center for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR), for 750 mmHg = 1000 hPa, 1hPa (hectopascal) = 100 Pa (Pascal), 760 mmHg = 1013.25 hPa) (2010, Patrut).
7. Mesoscale Structures that Produce Flash Floods in the Moldavian Plateau
The synoptic scale reveals two baric systems, one high pressure system over Central Europe and one retrograde system North of the Black Sea. The first is associated to a mobile anticyclone detached from the Azores Anticyclone, while the well-shaped cyclone formed over the Gulf of Odessa, on the morning of June 28, disintegrates partially (Hustiu, 2011) (fig. 4).
On June 25, the dorsal of the north-eastern basin of the North Atlantic advances towards Central Europe, determining extreme phenomena (exceptional precipitation quantities, hail, two tornadoes near Ibanesti and Dorohoi).
8. The Importance of Warnings in the Management of the Dangerous Hydro-Meteorological Phenomena
Following the elaboration of the meteorological forecast on June 28,2010, two hydrological warnings were issued on June 28, 2010, and June 29, 2010, for the upstream part of the Jijia River, when Code Red was declared because the Danger Levels were exceeded at the hydrometric stations: Padureni on the Buhai River, Hcm = (350+180), and Dorohoi on the Jijia River, Hcm = (600+270)--Risk of major flash floods, with the direct threat to the safety of persons and goods (INHGA, 2010).
9. The Flash Flood from the Period June 28-June 29, 2010
The analysis was performed on the upstream part of the Jijia River and the data from the following hydrometric stations were analyzed: Dorohoi (F=238 sq.km, Hmed = 262 m) on the Jijia River and Padureni (F=54.2 sq.km, Hmed = 165 m) on the Buhai River, tributary of Jijia on the right. The analysis of annual maximum flows for the operating period of the Padureni hydrometric station on the Buhai River highlighted the years with the highest values: 2010-85.0 mc/s, 1991-85.0 cm/s and 1991-68.0 cm/s. The flash flood occurred in 2010 (June 28/29, 2010) on the Buhai River at the Padureni hydrometric station was a historical flood, having a 3% excess probability, a maximum flow rate of (85.0 mc/s), precipitations of (164 mm), a total volume of (3.5 million mc), total time of (32 hours), a concentration duration of the precipitations per basin of (6-7 hours), form coefficients of (0.35-0.49), (fig.7a) (Cadastre of Maximum Flows, 1988, and Hydrological study in the Jijia river basin, 2011). At the confluence of the Buhai River with its tributary, Paraul intors, it had a flow rate of 190 mc/s with a 1% excess probability, being a flash flood that occurs once every 100 years (Hydrological study in the Jijia river basin, INHGA, 2011).
Upstream of the Dorohoi hydrometric station, the remuu phenomenon occurred resulting in the attenuation of the flash flood wave and the mitigation of effects downstream. The Dorohoi hydrometric station on the Jijia River revealed a (2%) excess probability with a maximum flow of (190 mc/s), total time (149 hours) and a form coefficient of (0.29-0.41) (fig. 7b), precipitations of (220 mm) at Dorohoi and (190 mm) at Iezer lake, (Cadastre of Maximum Flows, 1988).
10. The Insurance Curve for Maximum Flows at the Padureni Hydrometric Station on the Buhai River
In the hydrological practice, the most important insurance curves are performed according to the distributions of the types Weibull, Kritki Menkel, Pearson III. For the maximum flow analysis, we obtained the maximum flow values for the operating period from the Padureni hydrometric station. By considering the modifications from 2010, 1991 and 1998, we obtained a 1% insurance access flow of 110 mc/s and used a Cs=3 Cv (Drobot and Serban, 1999).
11. Effects of Flash Floods from June 28, 2010-July 03, 2010 on the Upper Course of the Jijia and Buhai Rivers
In the Buhai hydrographical basin, on the direction (Dersca-Padureni-Dorohoi) the flooded surface was of 4.07 square kilometers, the length of the damaged sector was of 18 km, as well as the infrastructure (25 km community road DC, 63 footbridges and a bridge) (2010--Damages and Features of the flash floods from June and July). During the events, measures were taken to evacuate the affected people, as well as to pay the intervention costs in emergency situations for the immediate recovery of the area, to help people and animals, as well as to reconstruct the houses. On the Hiliseu-Horia-Dorohoi- Rauseni direction, the flooded surface was of 61.53 square kilometers, the damaged sector had a length of 135 km, the infrastructure was damaged (200 m of national road--DN29A, 1 km of the county road--DJ291, 8 km of the community road--DC 78 and 79). In total, 11 km of streets, 11 bridges and footbridges, the Dorohoi railway station--1 km of railways, 10 km of the sewage network were damaged.) During the floods, emergency measures were taken, supporting costs with the relocation and the health of the population and with the area recovery and the housing reconstution (Synthesis, 2011).
On the upper course of the Jijia River, following the floods from June 28 --July 3, 2010, the following damages occurred in the localities (Pomarla, Dorohoi, Lozna, sendriceni, Dersca, Hiliseu- Horia and Broscauli): 7 deceased persons; damaged houses (422), destroyed houses (45) and collapsing houses (367); evacuated persons (3776) and (2715) persons that returned; unincorporated areas (ha)--agricultural (1024) and grass lands and meadows (1521); damaged wells (1492) and drained wells (2029); Source: The effects situation on July 17, 2010--The Committee for Emergency Situations, City Hall and the County Council and S.G.A.-Botosani (2010--Damages and Features of the flash floods from June and July, 2012, Order).
12. Reconstruction Measures and Proposals to Mitigate the Flood Waves
The flash floods from June-July 2010 caused damages, deaths, affecting houses, unincorporated areas, wells and infrastructure. The damaged houses were rebuilt; the maximum levels of the flood waves were rebuilt on the upper course of Jijia (at the Padureni hydrometric station, at the Iezer reservoir and at the Dorohoi hydrometric station). Comparisons were made between the status of the rivers during the flash floods from 2010 and the one from November 2012, revealing differences between the extreme values (Synthesis, 2011).
The causes of historical flash floods occurrence in the upper course of the Jijia basin were the cumulated precipitations of over 370 mm and the heavy rains in the Buhai river basin from the period June 28-29, 2010. These were due to the atmospheric instability existing over Romania, as well as to the humidity advection caused by the retrograde cyclone formed above of the Black Sea.
Following the research performed in the office, by analyzing the existing data and studies, we found that the flash floods and the floods from June--July 2010 occurred on the upper course of Jijia were historical flash floods both at Padureni as well as Dorohoi (Cadastre of Maximum Flows, 1988). The maximum flow history and analysis reveals that the flash flood occurred in 2010 on the Buhai River was the worst.
The precipitations that caused it were higher than the 1% probability (110 mm), with precipitations of 170 mm, determining us to believe that it is a flash flood with a 1% probability.
At the Dorohoi hydrometric station on the Jijia River, the flow was of 190 mc/s with a 2% excess probability and precipitations of 220 mm. Measures and proposals taken following the floods occurred on the upper course of Jijia, in 2010, were the rebuilding of the damaged houses, roads, bridges and the fitting of the riverbeds (serban, Galie, 2006).
Riverbed cleaning and control works, the afforestation of slopes to reduce the erosion process and to reduce solid flows, as well as the construction of temporary reservoirs to retain water upon flash floods are necessary in order to mitigate the occurrence of such phenomena in the studied area (serban, Galie, 2006).
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lidia. salaj an@yahoo. com
University of Bucharest
University of Bucharest
MARIA ALBU DINU
University of Bucharest
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|Author:||Salajan, Lidia; Gaina, Aurel; Dinu, Maria Albu|
|Publication:||Geopolitics, History, and International Relations|
|Date:||Jan 1, 2014|
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