Olt River Basin - Inundatii

Where is it located?

Olt River takes its source from Hasmasul Mare Mountains, in the Eastern Carpathians, at an altitude of 1,440 m, with a hydrographic network of 9,172 km long and the outlet to the Danube River in Islaz (Teleorman county). Olt River Basin is delineated to the North and North–West by Mures River Basin, to the West by Jiu River Basin, to the South by the Danube River, to the East and South–East by Arges River Basin, and to the North–East by Siret River Basin.

On Olt, there are around 30 reservoirs, and the hydrographic network, though variable, having between 1.4 km / sq. km in the area of Fagaras Depression and 0.156 km / sq. km in the lower section of Olt, with an average of 0.410 km / sq. km, can be considered dense. Together with the main water course, Olt River Basin is crossed by major tributaries, such as Raul Negru, Cibin, Lotru, Oltet. As a result of the high variation of its feeding sources, Olt River has a compensated and well-balanced hydrological regime. The average altitude is between 750 m in the high-laying area and 18 m in the confluence area.

Relief of the river basin

Olt River Basin includes all major landforms: mountains (31%), hills (53%) and plains (16 %), with altitudes varying between 2,544 m (Moldoveanu Summit in Fagaras Mountains) and 50 – 100 m to the plain area. The physical and geographical framework of Olt Basin is highly varied, featuring the existence of several specific sectors, which is reflected also in the hydrological flow formation of Olt and its tributaries.

Depending on the particularities of its flow, on the morphology of the valley opening up in many flatlands drained by the river, there can be distinguished three specific sectors: the Higher Olt (up to Racos), the Middle Olt (Racos – Ramnicu Valcea) and the Lower Olt up to its mouth.

Higher sector: included between the spring and downstream the confluence with Homorod River, it has an area of the catchment of 6340 km2 and crosses two distinct areas: Ciucului Depression and Barsei Depression. The average altitude varies between 600 and 750 m. On this sector, the basin has an increased symmetry, with water courses which are almost perpendicular to Olt river.

Olt middle sector: after the confluence with Homorod, Olt enters Fagaras Depression. Oltului Valley is wide, with an average slope of 1‰. In this area, the basin has an increased asymmetry of the system to the right. After the confluence with Cibin River, Olt enters the gorge, where the valley narrows, slopes are steep, with the area of the catchment reaching 15,340 km2 in Ramnicu Valcea. Olt lower sector: after leaving the gorge, Olt crosses the hilly area of the Sub-Carpathians and the plain area, with well-defined terraces up to its outlet to the Danube. The plain area is characterized by many non-permanent water courses, representing around 15.3% of the total length of water courses in Olt River Basin. Also in this area, there is the basin sector where there are the Danube direct tributaries.

Climate of the river basin

In climate terms, the territory managed by Olt RBA has a wide variety, from continental – moderate with Atlantic influences to the North of the basin, to sub-Mediterranean and continental, in the rest of the basin.

The climate of region is determined by its geographic position, by the general circulation of air masses and by the characteristics of the subjacent area. As a consequence of genetic factors, the climate of Olt River Basin belongs to the temperate continental climate specific to Romania. Soils, vegetation and fauna are natural elements making up the pedobiogeographic complex closely related to climate conditions and specific landforms.

Total water resources

Depending on the specific elements of its flow, on the morphology of the valley opening up in many flatlands drained by the river, there can be distinguished three specific sectors: the Higher Olt (up to Racos), the Middle Olt (Racos – Ramnicu Valcea) and the lower Olt up to its mouth.

Olt River Basin is made up, at its turn, of the following:

Olt river higher sector

Ranging between the spring and downstream the confluence with Homorod River, it has an area of the catchment of 6340 km² and it crosses two distinct areas: Ciucului Depression and Barsei Depression. The average altitude varies between 600 and 750 m. On this sector, the basin has an increased symmetry, with water courses which are almost perpendicular to Olt river.

Olt river middle sector

After the confluence with Homorod, Olt enters Fagaras Depression. Oltului Valley is wide, with an average slope of 1‰. In this area, the basin has an increased asymmetry of the system to the right. After the confluence with Cibin River, Olt enters the gorge, where the valley narrows, slopes are steep, with the area of the catchment reaching 15,340 km² in Ramnicu Valcea.

Olt river lower sector

After leaving the gorge, Olt crosses the hilly area of Sub-Carpathians and the plain area, with well-defined terraces up to its outlet to the Danube. The plain area is characterized by many non-permanent water courses, representing around 15.3% of the total length of courses in Olt River Basin. Also in this area, there is the basin sector where there are the Danube direct tributaries.

Olt river receives the waters of a coded hydrographic network totaling 622 water courses (with areas larger than 10 km²) with a length of 9872 km (12.5% of the total length of the coded network in the country, having a density of 0.41 km/km², higher than the national average – 0.33 km/km²). To the left, Olt river receives 99 tributaries, among which the most important are: Fisag, Raul Negru, Barsa, Homorod – Ciucas, Sercaia, Topolog, Cungrisoara, Iminog. To the right, Olt river receives 80 tributaries, among which the most important are: Baraolt, Cormos, Homorod, Cibin, Lotru, Olanesti, Bistrita, Luncavat, Pesceana, Oltet, Teslui, Vladila, Crusov.

The hydrologic network structure includes 7 hydrological stations: Miercurea Ciuc, Sfantu Gheorghe, Brasov, Sibiu, Ramnicu Valcea, Horezu and Slatina, including 104 gauge stations. In Olt River Basin, there are 35 major reservoirs, with a complex use. The most important reservoirs are on the rivers: Olt, Lotru, Cibin, Tarlung, Sadu, Frumoasa, Homorod – Ciucas.

In Olt River Basin, there are many freshwater natural lakes, among which the most important are glacial (Urlea, Podragu, Doamnei, Avrig, Balea, Iezerul Mare), and Sf. Ana has a volcanic nature. Surface water resources of Olt River Basin, from inland rivers, are of 5300 mil. m3, and the underground water resources are of 862 mil. m3.

Description of existing flood protection works

Olt River Basin has a complex system of hydrotechnical works with a role in the quantitative management of water resources, including many diversions for feeding volumes of water from one river to another. Flood protection works existing at the level of the whole Olt River Basin include river regularizations, embankments, bank reinforcements, as well as complex reservoirs, permanent and non-permanent.

In Olt River Basin, there are 159 accumulations, of which: 5 dams with reservoirs, on the tributaries, for the population’s water supply – managed by Olt RBA and 13 dams with non-permanent reservoirs for flood alleviation; 27 dams with reservoirs, on Olt River, with a complex use (power generation, industrial water supply and irrigations) – managed by Hidroelectrica S.A.; 10 dams with reservoirs, on the tributaries (Lotru and Sadu), with a power-related use, of which Bradisor reservoir is also used for population’s water supply – managed by Hidroelectrica S.A.; 108 dams with reservoirs, with a fishery, leisure use and of local interest– managed by other holders.

Olt River Basin is one of the basins fitted with hydrotechnical works with a flood protection role. The chain of reservoirs, with a hydro-power use and water supply on rivers Olt, Sadu, Lotru, diversions of existing high waters and non-permanent dams in Olt River Basin ensure a better flooding management, by its alleviation, resulting in the significant reduction of discharges for downstream water courses.

The arrangement scheme for Olt River Basin has been designed so as to ensure the flood protection of the main localities / municipalities in Olt River Basin: Balan, Miercurea Ciuc, Sfantu Gheorghe, Brasov, Sacele, Fagaras, Sibiu, Avrig, Agnita, Ramnicu Valcea, Dragasani, Slatina, Caracal, localities with a population over 803,234 inhabitants.

Flood records

The river basin managed by Olt RBA was affected by floods in 1930, 1932, 1948, 1955, 1970, 1972, 1975, 1991, 1998, 2000, 2007, 2014. During the period 1930 – 1970, the most significant floods in Olt River Basin occurred in 1932 (April) and in 1948 (June).

After 1970, the major floods occurred in: 1970 (May), 1971 (July), 1972 (October), 1973 (March), 1975 (July), 1991 (May-June, July), 2005 (May, July-August).

A brief description of the regime of major floods is as follows:

1970: Floods occurred in May because of long-lasting heavy rains, as well as because of how the main weather elements developed the previous months, exceeding critical thresholds, causing overflowing of most rivers in Olt River Basin. Large amounts of water recorded on extended areas overlapped, given a very deep hydrological front.

1972: Floods occurred in October (3 – 11 October) because of rainfalls exceeding by far the average of annual precipitations. In the lower basin of Olt, there were the most significant amounts of precipitations as rain and snow.

1975: Floods occurred in July (1 – 10 July), given that the maximum intensity of heavy rainfalls was recorded during the first 3 days. On the first day, quantities of precipitations were recorded in the whole basin, with the highest values being recorded in the middle and lower basin. The next day, there were larger amounts of water in the higher and middle basin on an already water-saturated soil, speeding up the runoff towards the lower basin, causing the flooding and washing of areas in the Lower Olt. At the confluence of Homorod with Olt, levels grew to 2 m from the ground surface, so that in Hoghiz area, the tree tops were no longer noticeable. In Ramnicu Valcea, levels exceeded the flooding level, remaining over this level for 6 days and 7 hours.

1991: During the periods 26 May – 5 June 1991 and 2 – 7 July 1991, on the tributaries of the Lower Olt, there were large amounts of precipitations, with dangerous phenomena being recorded, namely major increases of discharges within short periods of time. On the tributaries of the Lower Olt, in Valcea and Olt counties, the floods from 1991 affected around 36,000 ha, 1,700 households, 800 km of roads, 15 industrial objectives and public institutions, 60 bridges. River sectors where the aforementioned damages were recorded included: Hinta river in Govora, Paraul Sarat in Ocnele Mari, Ramesti river and Ursanilor Stream in Horezu, Salatrucel river in Berislavesti, Taraia river in Polovragi, Oltet river in Alimpesti, Morunglav and Bals, Lotru river in Voineasa and Voinesita, Beica river in the area Carlogani – Plesoiu.

2005: In July – August 2005, large amounts of precipitations were recorded in the entire basin, with dangerous phenomena mainly on the tributaries of Olt in the lower basin.

Contact Olt RBA

Address: Strada Remus Bellu, nr.6, cod 240156

Central office phone: 0256 491848; 0256 491 843; 0256 491849

Management Secretary’s Office: 0256 492097

Fax: 0256 491798

E-mail: dispecer@dab.rowater.ro