THE DANUBE RIVER IN THE LOWER SECTOR IN TWO HIDROLOGYCAL HYPOSTASES –HIGH AND LOW WATERS
P. Gâştescu , Elena Ţuchiu
Abstract. The Danube River in the lower sector in two hydrological hypostases-high and low waters. The lower sector of the Danube, with the exception of the Iron Gates gorge, is characterized through an asymmetric development under morpho-hydrographical aspect, with a floodplain, developed on the left (between Drobeta-Turnu Severin and Calaraşi) in Romania, with unequal extensions of 5 km at Greaca, 12 km at Calaraşi and fragmented by narrowing at Islaz, Zimnicea, Giurgiu, Olteniţa. From Calaraşi to Brăila, the floodplain has the largest expansion, being between the arms of the Danube, which form, in natural conditions, two wetlands of Mesopotamian type, known as Romanian hydronyms Balta Ialomiţei (Borcea) and Balta Brăilei. The total area of the Danube floodplain including the delta is 9230 km2, respective 4% from the Romanian territory. In natural conditions, before the embankment and drainage works (1960), the Danube floodplain and delta was an amphibious territory consisting of lakes, streams, backwater, eutrophic marshes, willow and poplar forests on fluvial banks being flooded at spring-summer high water 93% (hydrograde 8). It is estimated that at 1.5 m thick layer of accumulated water for 1-2 months a year, the volume of water stored was about 4.3 km3, contributing to attenuation of floods and at the same time to water renewal of lakes, alluvial and cleaning of ecotonal area. Also, the Danube floodplain and delta is an important area of genetic capital for reproduction of many fish species. The famous hydrobiologist Grigore Antipa studied the floodplain and the delta, scientifically arguing through its work from 1910 (The flooding region of the Danube) the role of this flooded area in biological functionality and productivity.
The anthropogenic interventions in various aspects, on the main artery - "free space", on the tributaries and throughout drainage basin, in correlation with climate changes have caused changes of discharge regime, especially in high water phase causing major material damages due to flooding (in 1970 and more recently in 2006, 2009), but also during low water phases (1921,1947,1954).
Key-words: Danube, lower sector, floodplain, hydrological regime
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