ИСТИНА

Socio-economic complex, natural objects and systems at the Don River mouth are affected by a series of dangerous hydrological phenomena. These are inundations during the spring flood and accidental water discharges from the Tsimlyansk reservoir, storm surges, heavy rain flooding in urban areas, water shortage, wind ebbs, dangerous ice and morphodynamic phenomena, deterioration of water quality. Flood situation is developing in the last decades in the conditions: 1) reducing the average (from 27.4 to 21.5 km3/year) and maximum (3.5 times) water runoff of the river, 2) artificial redistribution of flow between months 3) forced channel erosion (its average value is approximately 0.5-0.8 m), 4) sea level rise (at a rate of 1-2 mm/yr) and the total intensification of marine factors, 5) a series of protective measures, including the creation in 1952 of the Tsimlyansk reservoir. As a result, the date of maximum water flow has changed; maximum water levels has decreased by 0.5-2.5 m; frequency and magnitude of flooding has decreased too. If in 1917-1951 the frequency of flooding the floodplain was 86%, now it is only 17%. The average duration of flooding was reduced from 50 to 14 days, the total area - from 1110 to 920 km2. On the contrary, surge phenomena not only retained their hazardous characteristics, but also increased the frequency and magnitude. Only in the last 20 years, four large-scale surges flooding occurred in the Don river mouth. Strong surges repeat an average of 1 every 10 years. The problem of water shortages and maintaining favorable navigational depths has to some extent been solved after the creation of the reservoir and in the context of sea level rising. Influence of wind ebbs is not weakened; water quality has deteriorated, the salinity has increased.