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