Flow Variability of the Lower Danube River: An Up-to-Date Overview

This chapter provides an up-to-date overview of the flow variability of the Lower Danube River, on a length of about 1,000 km, from the entrance in Romania (at Baziaș) to the beginning of the delta (at Ceatal Izmail or Ceatal Chilia, in Romania). It highlights the spatio-temporal variation of the average, maximum and minimum annual and monthly discharges of the Danube River, at several gauging stations located on the Romanian bank of the river. The analyzed periods range from 44 years (1976–2019) to more than 170 years (1840–2012). Between Baziaș and Ceatal Izmail, the multiannual discharge of the Danube River increased by almost 1,000 m3/s (from 5,551 to 6,516 m3/s, during the period 1840–2012), as a result of tributaries’ contribution from the riparian countries (Romania, Serbia, Bulgaria, Republic of Moldova, Ukraine). The flow regime of the Lower Danube River shows the highest discharges in spring and early summer (April–June, with the peak in April) and the lowest discharges in late summer–autumn (August-November, with minimum in September). During the period 1931–2019, the highest maximum discharges occurred during the historical flood in 2006. They reached 15,800 m3/s at Baziaș and 15,900 m3/s at Ceatal Izmail, but at some intermediate gauging sections the discharges exceeded 16,000 (e.g. 16,300 m3/s, at Giurgiu, 16,200 m3/s, at Oltenița). During the same period, the minimum discharges decreased up to 1,040 m3/s at Baziaș (in 1949) and 1,790 m3/s at Ceatal Izmail (in 1947). The two large dams and reservoirs built on the Lower Danube River within the hydroelectric and navigation systems Iron Gates I and II, did not significantly impair the water flow of the Danube River, but mostly the sediment flux.