The river network of the Selenga Delta at present

The Selenga Delta is located in Eastern Baikal within the Ust-Selenga depression of the Baikal rift zone. Its estimated age is 500 thousand years. The mouth area of the Selenga is of the open-type with delta shore and lobate delta protrusion. The delta was formed by long-term interaction of the system «Lake Baikal - the Selenga River» and is a unique accumulative plain with a number of specific natural features. The ecosystem of the delta of the Selenga filters water stream coming from the river basin. A comparison of multi-temporal cartographic material (sailing directions of the Selenga River and Lake Baikal topographic survey of 1908, 1949, 1986, 2001; 1:100 000 scale topographic maps of 1956, 1986, 1998; and modern satellite images) was made. Since 2003, annual field researches have been carried out. Experimental work on the network of hydraulic sections and observation points include section binding, riverbed survey, hydrometric measurements, riverbed erosion observations, geological and geomorphological work. The main factors in the formation of the delta at present are meteorological conditions, bedrock, economic activities related to bank protection, and modern tectonic movements. The role of these processes is different in separate areas of the Selenga Delta. The completed construction of the Irkutsk hydroelectric power station in 1959 coincided with a high-water period and led to a catastrophic rapid rising of Lake Baikal. By 1962, the level was 266 cm above zero of the graph. The peak level was observed till 1972. This long period significantly contributed to the re-formation of the shores of Lake Baikal and the restructuring of the river network in the Selenga River delta. Prolonged high levels of Lake Baikal and the high level of the water table in the delta of the Selenga River resulted in the flooding of large areas of sub-aerial part of the delta, formation of new channels, and redistribution of the runoff. At the present stage the annual amplitude fluctuations in Lake Baikal are within the range of 1 m, which is limited by Irkutsk power plant. The morphogenesis of the mouth area is accompanied by changes in the channel network parameters, redistribution of the water and sediment runoff. Changes of the channel network are most clearly manifested in the high water period; it is typical for high-water flow distributaries. Lateral erosion largely occurs in the Lobanovsky sector. The changes of the channel network and the altitude points of the sub-aerial surface of the delta are most clearly shown in hypsometric models designed according to the data of the topographic maps of different periods. By comparing hypsometric models we obtained the accumulation and erosion processes in the delta. At the present stage, the levels up to 459 meters above sea level move into the central part of the delta. The boundaries of the morphodynamic areas were allocated by the dynamics of the shoreline and by various hydromorphological elements. Three sectors of the Delta were identified: Lobanovsky, Sredneustevsky and Selenginsky, named after the large branches of the delta. The tendencies of development of the riverbed processes and the dynamics of the distribution of water flow and sediment in the channel network of the delta were obtained.

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