Olt River Basin
Olt River Basin has an area of 24,050 km² (representing around 10% of the national territory) and a total length of 9872 km, of which the length of Olt river is of 615 km, crossing six main counties, namely: Harghita, Covasna, Brasov, Sibiu, Valcea, Olt.
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
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 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
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
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.
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.
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:
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.
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