ИСТИНА

Flooding is very much widespread disaster phenomenon for many territories, and the Krasnodar region is not exception. Since XVIII century there were about 200 cases of catastrophic inundations on the Kuban River, main waterway of the Krasnodar region. Because of low elevations of land, gentle surface slopes and other factors the Kuban River delta more than once was flooded with either river or sea waters. The reasons of catastrophic rises of a water level in the Kuban delta are flood flow, ice dams and storm surges. Very much frequently the ice-clogging inundations are formed during a high water period on the river and simultaneously forming in river channel or at the nearshore zone ice dams. Besides the deltaic land flooding may occur due to heavy rains when fast water infiltration or evacuation are difficult, as it was, for example, in 1972, 1973 and 1998. Water run-off inundations are formed in case if water discharges (Q) in the river exceed its channel capacity. As a result, the flooding of flood-plain and economic and social objects, located on it, begins. Large Q may be observed on the Kuban lower reaches at any time during the year, but it is especially frequent since May till August. Downstream two main delta branches of the Kuban River, the Protoka and the Kuban itself, Q in the warm season (because of natural and anthropogenic losses) reduce. But in the cold season Qmx along the Kuban branch increase due to inflow of water from small tributaries. During time the Kuban River and delta branches capacities and elevations of flood-plain flooding changed. Reasons are construction of artificial levees and dredging works. However, because of periodic underscouring and destruction of levees during Qmx, they did not solve completely a problem of flood control. Reliable protection of the Kuban lower reaches from runoff inundations became possible only due to construction of reservoirs and, mainly, the Krasnodar reservoir (in 1973). Its construction has resulted in reduction of Qmx from 1140 to 850 m3/sec. and suspended sediment load from 6,84 to 1,51 mln. t/yr., to intensification of erosion processes in tailrace canal and, as consequence, to drop of water levels in the Kuban River and the upper parts of two its delta branches. In delta natural and anthropogenic factors promote greater decrease of Q. As a result, runoff inundations in the delta in 1973-2001 were not observed at all, and frequency and duration of flooding of surface section between banks of the channel and embankments has essentially decreased. In 1990th the situation with prevention of runoff inundations again began to be worsened. It was connected with the strong physical deterioration of the machinery and elements of hydraulic engineering and irrigational constructions. Besides the channel capacity reduced, for example, on the Kuban River from 1500 to 1200-1300 m3/sec., and mean and maximum Q increased since 1987 due to climatic influence. However, the events in summer 2002 have shown, that flood protection system on the Lower Kuban is still capable to prevent runoff flooding. Despite of catastrophic character of the rainfall flood in June-July 2002, when flow into the Krasnodar reservoir amounted to 1940 m3/sec., and removing water in tail-water pool 1300 m3/sec., only in one case, on the middle reach of the Protoka branch, breaking of embankment and insignificant flooding of delta lands have taken place. Ice-clogging inundations. Reasons of the ice dam formation in the Kuban river delta and caused by them flooding are the winter floods, unstable ice cover and presence of numerous obstacles to ice movement. Because of complex character and large number of the reasons of ice dam formation the struggle with ice-clogging inundations is difficult. The decrease of danger of ice-clogging inundations was promoted by construction of flood storage basins, regulating of winter flood flow, increasing water temperature in tailrace canal and changes of regional climatic conditions, for example, the warming in January from middle of 1970th. As a result, frequency of ice-clogging phenomena in the delta has decreased in 2-5 times. At some gauging stations ice dams have ceased to be observed at all (Tikhovskyi, Serbin, Troitskaya, Varenikovskaya, Demin Erik). Also duration of the period with the ice phenomena and their probability have decreased. However, ice-clogging inundations still are the single type of flooding, connected with the river regime and periodically bringing the threat to a nature, population and economy of the delta. A complex of measures against ice dams and inundations, caused by them, in present day includes the following: 1) construction of check dams, dredging works and channel clearing; 2) actions for operative decrease of water discharges upstream ice dam; 3) pyrotechnic and mechanical destruction of ice cover in places of expected channel clogging and, certainly, ice dams. The organization in the winter period of aeromonitoring of hydrological conditions and increase of number of hydrological gauging stations might render the essential help in control of ice dam flooding. Storm surge inundations are connected with the sea storm surges, caused by strong northern, western and northwestern winds. Frequency of these winds is insignificant, and storm surges here are observed very seldom, 5 times a year. Strong surges, resulting in rise of a water level by 1 m and capable already to cause a flooding of coastal areas, have frequency once a year. Surges, resulting in catastrophic flooding, are observed here extremely seldom - once in 50 years, for example, in 1739, 1801, 1840, 1892, 1914 and 1969.