The Danube delta begins at the first bypass of the Danube with the Ismail river island. It is included into the Lobate type of the Weltdeltas, and in so far from the dimensions in calculation to be taken, the Danube delta the 23 place, the world rank list occupies.

Those about 300 watercourses secure, in the delta, an average multi-annual river of 6430 cubic meter/seconds. Maximum value was registered 1897, when it reached 17,900 cubic meter/seconds, and minimum value was registered at 1280 cubic meter/seconds, 1942. The conditions of the level, the delta occurring, show a Polyphasisches behavior, with repeated rises and reductions in cycles, with extent and duration, which change from year to year.

The quasi-permanent fluctuations of the water level demand the typical hydrologic - indication of the Deltas. The most frequent most levels are registered in spring and in early summer, and the most frequent low level in autumn and winter are registered. The hydrologic - net will represent by the Chilia, Tulcea, Sulina and Sf. Gheorghe of arms, by channels and watercourses, with a total length of 3500 km. The Chilia arm with many bypasses and islands is the youngest and longest arm, more achievement-able as other one, because it transporiert the largest quantity of the water and alluvialer deposits.

It begins at mile (M43), where the Ismail flussinsel is put and the Deltas secondary up to the delta of the Stambulul Vechi (old persons the Istanbul) stretches arm of the Chilia. Those lengthens amounts to 121 km. Arm secures at present a flowing of 55% for the Danube at the surface of the Delta's. The specific character of the arm is given by the two differences, first is between Pardina (the 76Km) and Chilia Veche (the 46Km), and second between the 38Km and Periprava (the 22Km). These bypasses, with that islands between them, represent old secondary Delta's of the Chilia of arm.

Downstream Vilcov is the point of the secondary Delta's Chilia, which at the end of the Xviii ten themselves century to form began, nowadays it around an area of 400 km² rose, with a rising average Rhytmus of 1,8 Km² per year. Most of the Chilia's secondary Delta's surfaces are to be found in the Ukrainian area. This arm is used more important ports for fluviale navigation, the Ismail and Vilcov Vilcov-Haefen, who are into the Ukraine.

The Tulcea arm begins at the M43 (the Ismail flussinsel), which only 17 km is long, and at present - it secures a flowing of 45% the total TLA dung of the Danube. Between M41 and M37 it forms a Meander curl, which reaches its high point in Tulcea, where it amounts to the maximum depth (38m). The Sulina arm begins to the Sf. Gheorghe island, which can be found at M34. At first the arm 84 km was long; it wound itself and shallow. The arm released for the navigation on the basis of Danube European Kommission's studies (1856), condition of which the improvement of the Meandern affected and the deepened of the flussbetts during 1857-1902 (the Ausbaggern was preferred, which with 1857, and cutout of the curls of the Meandern 1868) affect has.

The mechanism was arranged 1902 terminated, when the Sulina arm was shortened around 21 km, perfectly, and transformed into an embarking channel for oceanic ships. This renewal was the first anthropische mechanism with main effects in the transformation of the structure and the deltaischen system functions. Consequently the length from 84 km to 63,7 km became, and the river of the water reduces, and Alluvienmenge became larger from 7-8% to 18,8-22% (nowadays) which for Chilia's arm a disadvantage is because it before 70% transported.

Downstream the Sulina Stadtes, continues the arm, with by condemnations protected a channel, for navigation security built, which penetrates nearly 8 km in the sea. At the delta of the channel sandige and muddy deposits are accumulated, which form there a Baecken, which must be constantly dragged to permit in order to secure a minimum necessary depth from 11m to, in order entrance for sea ships. The Sf.Gheorghe arm begins its total length at the island with same name (M34), amounts to 110 km, and it transports approximately 23% of the Tulcea's of branch river. It does not show fluctuations. Downstream 85 km, wind themselves to 7 Meander curls, which large changes between 85 km and 64 km exhibit, admit as the Murighiol Meander, to a considerable degree. Between 1983 and 1985 this Meander was cut off, in order to shorten the navigable way. The arm ends to that with eimem small secondary delta, area is at present 13 Km². The delta began its education process at the beginning of the last century, develops with an average multi-annual Rhytmus of 0,07 Km² per year. Before that arm delta on its right side dissolves another arm, which in its revolution in Garla de Mijloc and Garla Turceasca giving ELT, which flows into a gulf, Meleaua Sf. Gheorghe gennannt itself, due to this entwicklte itself the Sacalin island (19Km nowadays). The barrier of the Sacalininsel blocks the secondary delta, Sfantu Gheorghe.

Further hydrographic elements are: Sahales are old arms of the Danube, which became to leave within the Deltas. They were transformed correctly on Vidrascu's map represented, dating from the beginning of the century, later these into channels. The Sireasa, Sontea, dad dia., Iacob, Adanca, Pardina, Repedea, Gotca, Poliacova, Bratusca, Statului of sahales were used, in order to arrive between the Chilia and Sulina arms. From all these existed still at present Sontea and the three latters, the others were transformed perfectly or due to the insulations and dewaterings disappeared. Between the Sulina and Sfantu Gheorghe arm gave it to two large sahales, Litcov and Macovei both over by hydraulictechnical functions to be arranged.

Rivers are natural connection Arterien between arms and stagnating aquatoriume within the Deltas. Between the Sulina and the Sfantu Gheorghe arm, Eracle, Lopatna, Matita, Sulimanca, the Magearu of watercourses are maintained. Between Sulina and Sfantu Gheorghe gives it to Perilovca, Vatafu, Busurca, Imputita of watercourses, and southward the Sfantu Gheorghe of arm gave it to the Dunavat, Dranov and Cernatel, furnished under the guidance of Gr. Antipa, already at the beginning of the century.

The most watercourses and sahales cover 9959 hectars! (2,5%), of those small only 7800 hectars! represented. Stagnating ones aquatorien are sumps, ponds, pilot water, lakes and lagoons; fill the depressions under 0m in the western part (fluviales delta), and under -0,5m in the eastern part (sea-delta) where them are combined in a lakustrisches complex, out; these complexes represented 1964, 31260ha! (9,3%) and only 25800 hectars! (8%) in 1990, because of the dripping off process for agriculture and silviculture mechanisms.

Sumps are deltaische seas with large areas and depths, which experience different stages dewaterings at present. The main sumps are Fortuna (977 hectars!), Matita (644) hectars!), Babina, Merhei (1057ha!), Obretin (between the Chilia and Sulina of arms), Gorgova (1377 hectars!), Isac (1101 hectars!), Puiulet, Puiu, lumens (1367 hectars), Rosu (1445 hectar between Sulina and Sfantu Gheorghe) and Dranov (2170 hectars - southern of Sfantu Gheorghe). Ponds, weiher are to have been strongly withdrawn, many of them reduced, in order by the mineral and biogenous deposits by sumps have been formed.

The Sulina of arm the most important ponds are northern: Tataru, Mester, dad dia., Nebunu, Baclanesti, Babinti, Rosca, Buhaiova, and south of Sulina gives it the following ponds: Iacub, Cuibida, Pojarnic, Rosulet, Uzlina. Staugewasser are ponds into a high stage of the deposits, particularly biogenous deposits are. In the summer Staugewasser will strike by submerged swimming vegetation, which lets them look like sumps. In shallow water they drain. Lakes will narrow extended and, and will become by that to block the little deltaischen gulfs, by sandige barriers in ascending development, deformed. If deltaische barriers reach the stage of the Involution, lakes, are first open by Pfoertchen which gradual becomes larger. That is like Zatonul Mare and Zatonul Mic, in the south of the Deltas, was formed. Lagoons are formed broad Aquatorien by blocking Dobrudja gulfs by a set of sandigen barriers.

Razelm is the largest lagoon, Sinoe (115Km²) Golovita (85Km²) and Zmeica (60Km²) follow thereafter. Lagoons are enriched with water that the Sfantu Gheorghe arm comes by the Dunavat and Dranov of channels south the Razelm lagoon gives it the small lagoons in the Periteasca Leahova complex. The connections between the flowing and stagnating Aquatoriums become, from polyp hare - conditions of the flowsent water based on the Danube depending. In spring, if the rivers alluvialen, with cloudy water and deposits and close materials are loaded, that grows water level and the water penetrates in the channels, watercourses and sahales within the Deltas, which enriches the sumps, ponds and pilot water with water and nutrients.

That is the replenishment Interval, which reaches the maximum frequently at the end of the monthly May and during this period, and can up to five thousand million cubic meter of water in the delta increase. The Stagnations Interval of the water in, follows a process of the alluvialen deposit, decantation mentioned, delta where annually approximately 1 million tons of sediment deposit take place in the delta. The more largely the rivers, the longer the stagnation Interval. The specific acceptance of the rivers, to late summer and autumn, determines the acceptance of the rivers on arms and at the same time the release of the emptying Intervals of the Deltas. Water flows by watercourses and channels, and flows together with the arms of the river, the difference between the cloudy water and the pure water of the Deltas will be offesichtlich.

Due to frequent Schwankungendes of water level on the Danube, during eienes, can meherere cycles of the emptying of inundation day nation yearly develop.