Causes and systematics of inundations of the Krasnodar territory on the Russian Black Sea coast
Authors: Alexeevsky N. I. , Magritsky D. V. , Koltermann K. P. , Krylenko I. N. , Toropov P. A. 
Published: January 2016

Abstract. We analyse inundation situations on the Black Sea coast of Krasnodar territory for the period from 1945 until 2013 and describe the main types of inundations at the coast. Synoptic factors of the formation of extreme rainfalls and rainfall floods, features and regularities of the downstream flood wave transformation in the rivers are studied. Assessments of seasonal and maximum flow of the Black Sea Coast rivers for the period for which hydrometric measurements describe regularities of change of the occurrence of inundations and their characteristics on the coastal terrain, within a year and on perennial time scale. Most catastrophic and exceptional inundations arise in the summer and in early autumn. Small inundations during the remaining year reflect the seasonal distribution of river flow and floods in the Black Sea Rivers. Extensive and sometimes extreme precipitation dominates the river flow regimes. The seasonal distribution of small and moderately dangerous inundations reflects, on average, a water regime of two groups of rivers of the coast – to the north of the Tuapse River, and to the south. To the north of the Tuapse River, floods prevail from November until March (to 70 %). They result from precipitation and winter snowmelt during frequent thaw periods. High waters in the cold season of the year often overlap with each other, forming a multipeak high water with 2–3 weeks in duration. In the summer and in early autumn a steady low flow is observed. The total amount of runoff increases both in a southeast direction, and with the altitude of the river basins. Inter-annual variability of mean annual runoff, as well as maximum runoff, on the contrary decreases in the southern direction and with an increasing area of a river basin. The coastal high waters of the rivers of the Sochi part are typical at any time of the year, but more often floods in the cold season result from incessant rains, and thawing snow. Annually up to 25 floods are observed. The principal reason of such distribution is the increase of extreme rainfalls in the warm season. Orographic features of the coast and detailed features of rainfall cover only a small number of local river basins and a limited area. The geographical correlation of individual rainfall and subsequent floods ceases to be statistically significant for the distances over 40–60 km. The annual flow cycle is mainly determined by strong winter and spring, and weak summer flows: Despite a characteristic distribution of floods and of water flow within a year, almost 71 % of all catastrophic and exceptional inundations took place in July – August (71 %) and in October – November (29 %). The characteristic features of dangerous floods are their rapid formation and propagation, a significant increase of water level (up to 5–7 m and more) and multiple increase of water discharges. An appreciable increase of the number of inundations in the period from the early 1970s until the early years of the 21th century was noted. Quantitative assessments of risk, hazard and damage for the population and economic activities from accidental inundations in the valleys of the Black Sea coast rivers show that economic and social losses from inundations at the Black Sea coast of the Krasnodar territory are one of the highest in the Russian Federation. The basic conclusion from recent inundations is the need to consider not only the lower reaches and mouths of the Black Sea coast rivers where the main part of the social and economic development of the coast is concentrated, but also total river basins and catchments. Further, we provide an analysis of the efficiency of the measures applied at the coast to fight inundations and their aftereffect.