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The Danube River runs over territories
of 10 states and is the second-largest river in Europe. Its length makes 2.875
km; area of the basin is 817.000 sq. km and annual discharge is 200 cubic
kilometers. At the inflow into the Black Sea the Danube River forms an extensive
delta with the area more than 5.600 sq. km. Such an area size of the delta
is formed, first of all, by river sediments transported by the Danube into
the Black Sea (about 50.000.000 tons yearly).
The head of the Danube delta is a place of the river’s division in two largest arms – Kilia arm (left) and Tulcea arm (right). The Kilia arm forms over its length (116 km) two internal deltas and one external (marine or Kilia) delta. The length of the arm is only 17 km and then it divides into Sulina (69 km) and George (109 km) branches.
Present-day delta of the Danube began to form about 5000 years ago. Now the most dynamic delta reach is the marine Kilia delta, which has arisen in the middle of the 18th century. Since then its area has increased up to 370 sq. km. And this process proceeds now, i.e. the area of the European continent constantly grows owing to the Danube River.
The delta of the Danube has rare natural resources: abundance of moisture, mild climate and fat soil facilitate development of diverse of flora and fauna here. Numerous fish species including such valuable as sturgeon and Danube herring live there in watercourses and water bodies. The aspiration for preservation of unique nature of the Danube delta resulted at establishing of biosphere reserve here.
The natural complex of the Danube delta is formed under the influence of occurring here hydrological, morphological, hydrochemical, biological and other processes; thus the hydrological and morphological processes. The major feature of these processes is that they proceed at interaction and under joint influence of the river and sea. From the middle of the 19th century anthropogenic factor influences significantly on the nature of the Danube delta too.
The hydrology of the Danube reflects integrated influence of natural conditions in the river basin on hydrological and morphological processes in the delta. Waters flow and river sediments, their volume and inconstancy determine much of the history of the Danube Delta formation
Among the sea factors the greatest influence upon hydrological processes in the delta is exerted by fluctuations of the sea level. Dynamic interaction of waters of the river and sea forms specific regime of the delta’s level of the Danube. As a result of mixture of river and sea waters in the littoral area of the sea the water masses with peculiar hydrochemical and hydrobiological characteristics are formed. Sea wave and currents determine to a considerable extent the dynamics of marine delta.
Climate of the Danube delta is also affected by the hydrological regime influence as In particular, strong east winds, typical for this region, cause significant rises of water levels and facilitate salt-water encroachment into the arms of the delta. Mild winters determine irregularity and instability of ice phenomena in the Danube delta.
Anthropogenic influence on the nature of the Danube delta can be direct and indirect. The indirect influence is the change of Danube Delta hydrology of the Danube delta as a result of water management measures in its basin. For example, the irretrievable withdrawal of water for domestic needs results the water level falls and, increasing of the influence of the sea. Construction of water reservoirs “Gerdap-1” and “Gerdap-2” has caused reduction in sediments flow to the delta and affected intensity of processes of delta building up.
Since 1857 hydraulic engineering works have been carried and fulfilled within the limits the Danube delta that directly influence its hydrology. Thus construction of protection embankments along the arms of the delta has resulted the reduction of the catchment area in the delta and has caused additional rise in flood levels. Dredging and armstraightening works done to improve the conditions of navigation have caused re-distribution of water flow and sediments along the delta arms, changed regime of levels and dynamics of the marine delta, increased range of sea waters penetration. Regulation of exchange between different waters of the Lower Danube Lakes has resulted in reduction of amplitude of oscillation of water levels in lakes and increase of mineralization.
Thus, water management measures, which have been used both in the Danube basin and in its delta, cause changes in hydrological and morphological processes and lead to reorganization of all the natural complex of the Danube delta as a whole. This reorganization often has undesirable character and is at present the reason of serious ecological and socio-economic problems in the region. The problems are following: conservation and restoration of biodiversity of the delta, ecological situation in the Lower Danube Lakes and artificially demineralized Sasyk Lake; ensuring reliable water supply to the population, developing of a transit navigable channel Danube - Black Sea. There are also other important issue required urgent solutions.
At the same time studying of hydrological, morphological and hydrochemical processes, especially in the context of their influence on the nature of the Danube delta, is still insufficient. Therefore any researches, which will help to reduce the number of “white spots” in our knowledge of the Danube delta, are sincerely welcome!
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Registered in the Ukraine Number AA425654
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