ИСТИНА

The deltas of the Volga, Ural, Terek, Sulak, Samur, Kura, Sefidrud and Gorganrood are an important and unique parts of the coast of the Caspian sea. A distinctive features of the Caspian deltas are a continuous, large-scale and relatively rapid changes in their size, meso- and micro-relief, soil and vegetation land-cover, shape and position of the sea shores, water objects and regime, and another. These changes threaten the population and the unique delta ecosystems, form the economic damage, limit the use of natural resources. Large-scale fluctuations of the Caspian sea level, changes of water runoff and sediment load of rivers, economic activities and hydraulic engineering in river deltas are the main factors of these disorders. For example, sea level in the period from 1929 to 1977 decreased at 3.13 m, in 1978-1995 it rose at 2.35 m, in 1996-2012 again decreased at 0.91 m. The runoff of suspended sediments of the Volga decreased at 48%, Terek - 22% of Sulak - 88%, Kura - by 58%. Significant climatic and anthropogenic changes in the values of the annual water flow of the rivers, and its redistribution between months and hydrological seasons (under the influence of large reservoirs) took place in the second half of the XX century and the beginning of the XXI century. In the deltas of the Volga, Terek and Sefidrood drainage systems and large hydrotechnical objects were created. There are many such examples. They are implemented on a background of intense natural processes of delta-forming. As a result, morphological structure and hydrographic network of the deltas of the Terek and Sefidrud rivers have changed beyond recognition; the size of the deltas of the Sulak and Kura rivers has decreased by 1995 (during sea-level rise) at 38% and 41%; Samur River delta has lost a considerable amount of river water and sediment, etc. In all the deltas water regime has changed significantly. At first glance, these changes do not contain any regularities. But they exist. To identify and explain these regularities, to determine their factors is a very important and actual task. Its solution helps to get a tool to predict the reaction of river deltas on the sea-level rise, climate and anthropogenic changes in the value and regime of water flow and sediment runoff of rivers, and other impacts. In relation to the river deltas of the Caspian sea, the authors of the report this task successfully solved. For example, understanding the different reaction of river deltas and their elements to the same sea level change, the role of morphology of mouth seaside, sediment runoff in such reaction was obtained. An important result is the regularities of the evolution of the hydrographic network of the deltas and its individual elements. This work was supported by the Russian Foundation for Basic Research (grants No. 11-05-00199 and 14-05-00949). Continued studies of the deltas is being financed through a grant from the Russian science Foundation No. 14-17-00155.