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Inundation of the Aydar-Arnasay depression (1969-1970)

Increase of collector-drainage water from the Golodnaya Steppe and experimental discharges from the Chardara reservoir to the Aydar-Arnasay depression in mid-to late 1960s gave rise to instant formation of the Aydar-Arnasay lakes. Drainage water surpluses from the Arnasay lakes were discharged to the Aydar depression (Nasrullin, Chembarisov et al. 2007). According to Gorelkin’s estimates (1976) the lakes’ water surface amounted to 110 km² and the volume to 300 million m³ by 1969.
During the archives’ analysis it was concluded that the Aydar-Arnasay lakes system mainly fed by the collector-drainage water from the Golodnaya Steppe eventually formed in the extremely wet 1969 as a result of 21 km³ water discharges from the Chardara reservoir. Inundation of the Aydar-Arnasay depression precluded huge damage in the downstream part of the Syrdarya River on the Kazakh territory (Mahmudova 2004a). At the same time, a substantial part of Uzbek grasslands was flooded and restructuring of the Arnasay lakes’ hydrographic network took place, including flooding of the Aydar depression and its connection with the Tuzkan lake in 1970.
Having examined the different archive materials and scientific national reports concerning the respective topic, the author assumed that the inundation of the Aydar-Arnasay depression became a crucial period of early formation of these lakes and therefore 1969-1970 can be identified as an important development stage of these lakes.

4. Lakes for residual water (1970-1993)

CEU eTD Collection
For current research we should emphasize that inflow of collector-drainage water from the Golodnaya Steppe was the primary inflow component of AALS water balance during 1970-1993. In the 1970s 98% of the water mass was concentrated in the Aydarkul and Tuzkan lakes while the Arnasay lakes characterized by the regime of collector-drainage network did not concentrate a large water volume (Ivanov and Nikitin 1978).
Most of the literature analyzed (Mahmudova 2004a; Ivanov and Nikitin 1978; Gorelkin, 1976 and 1977; Kamilov, 1973) showed that the Aydar-Arnasay lakes had a particular hydrological regime during 1970-1993 basically due to collector-drainage water. Besides, the main function of these lakes was the accumulation of this residual water from the irrigation. Thus, based on the literature review, the author concluded that this period of time can be

treated as a milestone in the AALS evolution and classified as the one of the historical stages. Figure 4 demonstrates the Aydar-Arnasay lakes system in 1993.

Figure 4. The Aydar-Arnasay lakes system in 1993 (adopted from Google Earth and modified by the author)

In addition, the bulk of the national reports examine some general trends of the AALS development in 1970-1990. After the careful review of these reports and translation of the relevant issues the author combined the following conclusions:

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  The main function of the AALS during 1970-1993 is to store collector-drainage water coming from the Golodnaya Steppe irrigation areas;
  
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  In the 1970s constant decrease of lakes’ level, increase of mineralization and concentration of biogenic substances resulted in gradual eutrophication of the Arnasay lakes (Ivanov and Nikitin 1978);
  
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  CEU eTD Collection
  During 1975-1977 such water quality characteristics as water purity, coloration and oxidation, concentration of biogenic and organic substances sharply changed. In 1975 and 1976 during the summer period an increased number of phytoplankton was observed in the Tuzkan lake (Ivanov and Nikitin 1978);
  
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  In the 1970s practicing of the low-mineralized water discharges from the Chardara reservoir was the crucial issue for maintenance of the lakes’ regime during the summer period as well as for favorable conditions during the winter period (Nikitin 1991);
  
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  In case of not having the water discharges from the Chardara reservoir the gradual fall of the AALS level and growth of mineralization would be continued;
  
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  Increase of mineralization will cause decrease of the lakes’ freezing point to - 0,3- 0,6˚C. Therefore, the probability of more intensive cooling before freeze-up period will take place. The formation of freeze-up under the low level of lake will have influence on hydrochemical regime of lakes and increased content of organic substances could probably give rise to suffocation killing fish species (Giniatulina, Mullabaev et al. 2004).
  

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