global changes, sea level rising and the danube delta - GeoEcoMar

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N. Panin - Global Changes, Sea leyel Rarng and the Danube Delta -fu"r' f'o63na-$inoie N/_{**detta a% 3.$1.5 K yr. BP and important sediment accumulation. At present the subsidence ofthe coastal zone nearby the Danube Delta rs appreciated to 1.$1.8 mm/yr. The present-day variations of the Black Sea level depend on seasonal, multiannual or eustatic changes of sea water balance as well as on the deformation of free water surface under the influence of different external g\ n I n d c r e r{" gua. a sY. eEtl0 St.George ll Delta Fig. 2 The Danube Delta evolution during the Horocene and correspondent coastline position changes (panin & E. and G. lon, 1997) t t I .,. I t ','n ..,,'* lr ::;I., f, 'ln J* f E { ''t IOrCeS. During the last century the maregraphic observations have shown the tendency of rising by 1.S-4 mm/year of the refative sea level (2.S95 mm/yr. - Selariu, 1972; 3.71 nT{yr. at $ulina, 2,67 mmlyr. at Constaniza - Bondar, 1989). 22 G EO-ECO.M ARIN A, 4/1 999 National lnstitute of Marine Geatogy and Geo_ecotogy Proc lntem. workshop on 'Modern and Ancient Sedimentary Environmeiis and processes ,, in Moeciu, Romania, oct. g-15. 199g ,,t ,l oi v h
N. Panin - Global Changes, Sea Leyel Rislng and the Danube Delta DanubeS€dimentDischargeatVaduOiihydrographicatation.Km.24T (1961.1996) yF54,285x-105108 R'? : o 1492 1 955 1 900 I 965 1970 1 S75 Fig. 3 The River Danube mean annual sediment discharge variation at Vadu Oii hydrographic station (Kn 247). and important sediment accumulation. At present the energy is of approximately 2,000 kWh/m (Spdtaru, 1984, subsidence ofthe coastal zone nearby the Danube Delta 1e92). is appreciated to 1.5-1.8 mm/yr. The atmospheric circulation and other hydrological The present-day variations of the Black Sea level and morphological factors determine in the Black Sea a depend on seasonal, multiannual or eustatic changes of general cyclonic water circulation with numerous sea water balance as well as on the deformation of free secondary and smaller scale eddies. In the north- water surface under the influence of different external western and western areas of the sea, this current, is forces. flowing southward towards the Bosphorous. Within the During the last century the maregraphic observations Danube Delta coastal area, there is, even during quiet have shown the tendency of rising by 1.5-4 mm/year of periods, a generally southward current characterised by the relative sea level (2.595 mm/yr. - Selariu, 1972; 3.73 5-50 cm/s velocity depending on the water supply of mm/yr. at Sulina, 2,67 mmlyr. at Constantza - Bondar, rivers and the Coriolis Force. In addition to this current, 1e89). the winds, of different velocity and stability, generate a Amongst the short-term deformational oscillation of complex current system generally roughly corresponding the sea water surface seiches, wind surges and tides are to the wind direction, influencing the direction and to be mentioned. The seiches in the north-western and spreading of the river jet-like wedge. western areas of the Black Sea have periods from few As regards the Danube Delta seashore, the minutes to 13 hours and amplitudes from few longshore sediment drift is directed towards south. lts centimetres to 2.0 m. The storm surges from northern, intensity is high enough to transport the coarse-grained north-eastern, eastern and south-eastern directions discharge of the Danube many tens of km south of the induce sea level set-up of up to 1,2-1.5 m. The tide in distributary mouths along the shore. Local perturbations the Black Sea has insignificant values (amplitudes of Z- of southward littoral sediment movement are induced by 11 cm, average period of 12.25 h) (Bondar et at., 1973: different anthropogenic structures built on the shoreline Sorokin, '1982). (e.9. the eddy circulation south of the Sulina jetties) (Almazov ef a/., 1963; Bondar et al., 1973). d. Waves, currents and longslrore sediment drift system 3.2. The present-day state of coastal degradation The wave regime in the western and nodh-western At present the Romanian Danube Delta coast parts zone of the Black Sea basin can be characterised as follows (Cristescu, Diaconu, ',|980): can be divided into 11 sections with specific dynamic tranquil (smooth) sea and equilibrium characteristics. These sections are the (waves below 0.2 m) represents 49.1o/o of the whole bulk foilowing (Panin, 1976; Giosan et at.,1997) (Fig. 4): of data concerning the waves, wind waves - 33olo and swell, 17.9o/o. The most frequent wind waves are 1. Baia de Nord or Baia Musura (Northern Bav recorded or along NE direction, corresponding to the Musura Bay), situated north of Sulina prevailing distributary, li km wind direction, while from east are recorded long,.with a very low, marshy coast. A tendency almost of 40o/o of swell waves. The mean and maxrmum clogging by the sediment input of Kilia distributarv heights is of wind and swelt waves (5.2 m at Constantza. reported. 7.0 m at Sulina at the jetties end) are higher for the eastern direction for which the wind fetch is maximum. The energy of storm waves reaches important _ 2. Sulina values: e.g. on 17-th of February 1979 there was a storm characterised by 12,242 kWh/m, while usually the section, South of Sulina distributary, about 8 km long, with a complex barrier beach, teO by tne eddy-like cunent generated by Sulina jetties, as well as artificially, with the sand dredged from the port of Sulina. GEO-ECO-MARINA. 4/1 999 L-t National lnstitute of Marine Geology and Geo_ecology Proc. Intem- workshop on "Modern and Ancient Sedlmentary Environmeiis anabrocesses,,ln Moeciu, Romania, oct. g-1s. lgg1
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global changes, sea level rising and the danube delta - GeoEcoMar

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