Impact of human activities on the evolution of the Romanian Black Sea beaches

Hydrotechnical works along the Danube and its main tributaries

The hydrotechnical works with the greatest influence are the dams built on the Danube (Portile de Fier I and II). They retain the sediments transported from upstream, creating a sedimentary deficit in the littoral zone. Thus, after the construction of the Portile de Fier I Dam in 1970, the total sediment discharge has diminished by approximately 30–40% ( Panin 1996). The sediment retention in the dam lakes is even higher, but the Danube partially compensates for the sedimentary deficit by eroding the riverbed ( Panin 1996).

The construction of dams on the Danube’s main Romanian tributaries has rendered their sediment loads insignificant. The rectification works that have been carried out on the Danube distributaries during the past 130 years have altered the distribution of liquid and solid discharges. As a result of all these changes, the sediment load brought by the Danube into the Black Sea littoral zone has been drastically reduced from approximately 65 × 10⁶ t in 1858 to 38 × 10⁶ t in 1988 ( Panin 1996; Giosan et al. 1997 ).

Harbour and other coastal engineering works

Engineering works in this category include: the jetties that protect the Sulina Navigation Canal; the protection jetties of the Midia; Constanta South and Mangalia harbours; and the littoral protection works (groynes and breakwaters) from the tourist beaches.

The two parallel jetties at Sulina, with a length of approximately 8 km, have modified the distribution of marine currents. The sediments transported by the Chilia Distributary and by the longshore current from the north cannot pass the harbour system and are either deposited in Musura Bay or redirected offshore. Moreover, the alluvia brought by the Sulina Distributary enter the littoral system a long distance from the shoreline. The presence of these jetties at Sulina induces the appearance of an anticyclonal current immediately south of the jetties ( Panin 1996; Giosan et al. 1997 ). The sedimentary deficit is even more intense because of the dredging of the Sulina bar and the dumping of this material approximately 4 km south-east of the end of the jetties.

The Midia, Constanta South and Mangalia Harbour jetties represent obstacles for the longshore current. The most important is the Midia Harbour jetty, which interrupts the southward transport of the Danubian sediment by the longshore current. Thus, these sediments are either deposited north of the harbour, or redirected offshore. Because of this, the entire southern sector of the Romanian littoral zone is almost completely deprived of Danubian sediments. Furthermore, these harbour jetties induce anticyclonal currents, thus altering sediment transport.

In tourist areas, coastal protection engineering works were built in order to halt the erosion. Unfortunately, as observed worldwide, this solution does not solve the problem, being only a local solution, as the erosion always migrates downdrift.

Introduction of opportunistic species in the Black Sea basin

The introduction (on the keels of ships) of opportunistic invertebrates that have had an explosive development in the Black Sea basin, have induced changes between the mineral and organogenic fractions of beach sediments. One such species is Mya arenaria, described for the first time in Romania in 1972 ( Gomoiu & Skolka 1996). Over time, massive accumulations of shells become an important source of sediments after their reworking by waves and currents.

Direct intervention on beach sediments

The direct intervention on beach sediments has mainly been the collection of the coarse organogenic fraction (shells and shell fragments) from the tourist beaches. This is only partially compensated by the artificial sediment nourishment.

Northern sector

The littoral zone in front of the Danube Delta can be divided into three major subsectors: (i) northern (between the mouths of the Sulina and Sf. Gheorghe distributaries); (ii) central (Ciotic–Periteasca); and (iii) southern (Portita–Cap Midia). These zones are differentiated by the distance from the source of Danubian sediments (as discussed before) and also by their orientation from the predominant wind and wave directions.

The importance of the shoreline orientation is obvious in the northern subsector (Sulina–Sf. Gheorghe; Fig. 1). Here, the predominant winter winds are from the north-east ( Ciulache 1991). They generate destructive high waves that have an almost transversal incidence on the shoreline. The drastic reduction in the quantity of sedimentary material that enters the littoral system is accompanied by high transport and reworking capacity of the marine factors. The disruption of the natural sediment dispersion after the building of the Sulina jetty system increases the sedimentary material deficit for these beaches. The result is an almost general accelerated retreat of the shoreline with recession of up to 20–25 m per year, which continues the historical trend of evolution of the Sulina Delta ( 2, 3). Locally, the building of the Sulina jetties has, however, induced an important accumulation of sediments. In Musura Bay, because of the forced sedimentation of the alluvia brought by the Chilia Distributary, the water depth drastically decreased from approximately 8 m at the beginning of the century to approximately 3 m in 1998. At the northern extremity of Sulina beach, the accretion is due to the anticyclonal current that appeared south of the jetties. In the southern part, the amplitude of the shoreline changes is lower ( Fig. 4).

The central subsector has an east–west orientation (Perisor–Periteasca; Fig. 1), and is, therefore, somehow more protected from wave action. As long as the sediment load brought into this area remained high, the Perisor– Periteasca beaches were in accretion. Today, the accretion continues only in small areas ( 5, 6), the rest of this subsector being relatively stable.

The southern subsector (Portita–Periboina; Fig. 1) is characterised by a small input of Danubian sediments, which is compensated for by an accentuated production of organogenic detritus. The shoreline orientation is northeast–southwest. The wave energy is much more important there than in the central subsector but less important than in the northern one. Therefore, the Portita and Periboina beaches suffer a mild process of erosion. The extent of shoreline retreat does not exceed several metres per year.

Southern sector

As in the northern sector, the southern part of the Romanian littoral zone being eroded. The infiltration of meteoric waters to the Villafranchian clay level induces important cliff slides. The direct wave activity on the base of the cliffs is also causes erosion, although to a smaller degree.

The littoral bars are characterised by an important sedimentary deficit that has induced continuous erosion and the general increment of beach-sediment grain size through the washing of the finer fraction ( Grigorita & Ariciuc 1995). The tourist beaches, especially Mamaia and Eforie, are also degrading rapidly because the harbour jetties from Midia and Constanta South practically block all the sedimentary material brought to this sector by the longshore current. The coastal protection engineering works that were meant to stop this phenomenon have moved the erosion downdrift.