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Turgunov Daniyar Mannapjanovich, Khikmatov Fazliddin Khikmatovich, Prof. Dr., National University of Uzbekistan named after Mirzo Ulugbek, lecturer, of the Faculty of geology and geography, Tashkent city, Uzbekistan E-mail: d.turgunov1987@gmail.com
ESTIMATION OF THE LOW-WATER NORM IN THE MOUNTAIN 1RIVERS OF CENTRAL ASIA
Abstract: The article considers the issues of calculation of the flow norm for the basins of Syrdarya and Amudarja mountain rivers. The low-water years and norms for the low-water years are determined for these rivers. For the first time the notion of "lwo-water factor" was introduced, and its values were estimated for different types of the river alimentation. The formula for calculation of the low-water norm is proposed.
Keywords: river, catchment area, river flow, flow norm, low-water years, catastrophic low-water years, low-water, low-water factor, low-water norm, Schults' factor, low-water estimation.
Introduction. As it is known, the river flow is char- Data. For reaching this goal, 39 mountain rivers on
acterized with internal variability. Alternation of the the territory of Central Asia were selected. The data on
high-water and low-water years can be observed on the rivers. These changes are related to climate factors and are not subjected to the certain regularities. However, the river flow values vary within certain mean value -flow norm. Regarding interannual variability it can be noted that the values of variation frequency are different. According to studies of I. P. Druzhinin, G. P. Kalinin and D. Ya. Ratkovich, it was concluded that the periods of the river flow changes are characterized with 2-3, 5-7, 10-12, 22-28 - year frequency [7].
For the solution of numerous theoretical and applied problems related to the river flow use, the proper estimation of the river flow norm is very important. Thus, on the base of calculated value of the river flow norm it is possible to distinguish the low-water years recorded on the rivers and to calculate the low-water norm for these years. The low-water norms calculated in this way will make the estimation of the water safety degree for the recorded low-water years possible, which facilitates the rational use of the river flow. Problem of the estimation ofthe water safety degree of the years is one of the less studied problems in hydrology. Basing on the above mentioned, it can be concluded that the estimation of the low-water norm on the rivers is the main purpose of this study.
the mean monthly and mean yearly flow values were collected at hydrological gauging stations with the natural hydrological regime.
Results and discussion. Basing on data of the mean monthly flow values the factors of V. L. Schults (S) were calculated, and rivers were distinguished by four types of river alimentation sources: 1) glacial-and-snow (S > 1,0); 2) snow-and-glacial (0.99 > S > 0.26); 3) snow (0.25 > > S > 0.18) and 4) snow-and-rain (0.17 > S > 0.001) ones (Table 1).
Regarding the main goal of this study, the mean long-term flow values( Qlme) in the low-water years for the studied rivers were calculated with the following formula:
n
^lQlow
Ql = --, (1)
n n
where: ^ Q - sum of the mean yearly flow values re-
corded inlow-water years; n - number of the low-water years [5].
For the definition of the low-water years the modular ratios of the mean yearly flow values [4] were used. Their values were calculated with the following formula:
~ (2) Qo
k = Q,
where: Qi- mean yearly flow values, m3/s; Q - flow norm, m3/s.
As it follows from the formula given above, if Ki < 1, then the river flow in the given year is less than the norm and, on the contrary, if Ki > 1, then the given year is expected to be high-water one. It should be noted that with the values of the modular ratios in the range of 0.93 < Ki < 1.07 it is assumed that the flow value is near the norm. That is why, for singling out the low-water
Table 1. - Mean long-term values of the
years as criteria, the modular ratio values were used Ki < 0.92 [2, 3, 5 ].
Mean yearly flow values (Q_ms) for the revealed low-water years, as well as the values of the flow norms (Qo) for the long-term period were calculated for the studied rivers. Calculated values of Q and Q made it possible to calculate low-water factor (Ko) as their correlation (Table 1).
low-water factor (K ) for mountain rivers
Point № River-station F, km2 Qn, m3/s W ß _ y yVII-IX W ' v III-VI QM К0 = ^ 0 Qo
1 2 3 4 5 6
Rivers with glacial-and-snow питания
1. Sokh - Sarykanda 2480 45.41 2.52 0.92
2. Zeravshan - Dupuli 10200 156.5 1.58 0.83
3. Koksu - Kurbankul 174 2.59 1.16 0.84
4. Oigain - river mouth 1010 28.7 1.03 0.78
5. Maidantal - river mouth 471 18.6 0.93 0.81
6. Pskem - Mullala 2540 77.4 0.78 0.81
Mean value 0.83
Rivers with snow-and-glacial alimentation type
7. Aksuv - Khisorak 755 11.8 0.64 0.77
8. Zaaminsu-Duoba 546 1.909 0.53 0.71
9. Chatkal-Khudaidotsai 6580 110.6 0.50 0.75
10. Chilarma - river mouth 103 3.1 0.45 0.74
11. Yakkabag - Tatar 504 5.95 0.43 0.72
12. Uriklisai - Ismani river mouth 149 0.704 0.42 0.68
13. Chimgansai - Chimgan canal 23.3 0.3 0.39 0.67
14. Nauvalisai - Sidjak 99.4 3.83 0.38 0.70
15. Sherabad - Derbent 949 5 0.34 0.73
16. Ugam - Khodjikent 869 22.8 0.33 0.76
17. Akbulak - river mouth 886 19.4 0.32 0.74
18. Kyzylcha - Iertash river mouth 51.6 1.05 0.31 0.70
19. Jinnidarja - Dzhauz 152 1.49 0.31 0.66
20. Yangikurgansai - Yangikurgan canal 33.7 0.67 0.3 0.60
21. Tankhazdarja - Kattagan 435 3.98 0.29 0.69
Mean value 0.71
Rivers with snow alimentation type
22. Uradarja - Bazartepa 1250 4.26 0.25 0.66
23. Gavasai - Gava 657 6.049 0.25 0.69
24. Karadarja - river mouth 2340 24.84 0.24 0.69
25. Sangardak - Kingguzar 901 15.8 0.23 0.76
26. Shaugaz - Karatash 65.8 0.469 0.22 0.64
27. Amankutan - Amankutan 57.8 0.969 0.21 0.64
28. Sanzar - Kirk 570 1.982 0.21 0.69
1 2 3 4 5 6
29. Chadaksai - Zhulaisai 350 3.75 0.19 0.66
Mean value 0.68
Rivers with snow-and-rain alimentation type
30. Abzhasai - Abzhas 70.5 0.6 0.17 0.68
31. Nishbash - Nishbash 141 2.76 0.16 0.68
32. Akhangaran - Iertash river mouth 1110 19.9 0.15 0.70
33. Kashkadarje - Varganza 511 5.24 0.15 0.69
34. Dukantsai - Dukant 201 4.89 0.14 0.65
35. Karabau - Samarchuk 166 3.19 0.13 0.71
36. Khalkadjar - Bazarjoy 577 6.4 0.11 0.72
37. Biglyar - Biglyar 180 0.609 0.10 0.56
38. Kichik Uradarja - Gumbulok 1570 1.43 0.09 0.55
39. Akdarja - Agalyk 70.9 1.04 0.07 0.63
Mean value 0.66
On the base of calculated values their mean values were estimated according to the river alimentation type. For the rivers of I type, i.e., for the rivers with the glacial-and-snow alimentation type Ko = 0.83, II - for the rivers with snow-and-glacial alimentation type Ko = 0.73, III -for the rivers with the snow alimentation type Ko = 0,68 and for IV type - i.e., for the rivers with snow-and-rain alimentation type Ko = 0.66.
1
The analysis of the obtained results has shown that the different values of the low-water factors (Ko) on the studied rivers depend on the sources of their alimentation. Taking this regularity into accout, we have studied the relationship between the low-water factor Ko and Schults' factor (S), which determines the type of the river alimentation source (fig. 1).
-0,0443x2 + 0,2219x + 0,6296 R2 = 0,6873
0,9 0,8 0,7 0,6 0,5 0,4
r = 0 ,83 ....P
• f.. •
% • • •• • •
> p
0
0 0,2 0,4 0,6 0,
1 1,2 1,4 1,6 1,
Schults factor , ô
2 2,2 2,4 2,6
Figure 1. Graph of correlation between low-water factor (KJ and Schults' factor (ô)
From this it follows that the flow of rivers with the glacial-and-snow alimentation type is regulated (normalized) in the long-term period with the melting water of glaciers and perennial snow, and in the result of this the deepening of the low-water situation in the low-water water are not observed.
As it is seen from the graph, the correlation between the low-water factor (Ko) and Schults factor (S) is characterized with curvilinear relation which is described with the following equation:
K = -0.0443-S 2 + 0.2219-S + 0.6296
(3)
Pairing correlation factor determining closeness of relationship and accuracy of the regression equation (3) is 0.83 ± 0.034.
y
Summarizing all mentioned above, the low-water norm (QlO, M3/c)for the river flow can be calculated with the following formula:
QO = K0 ■ Qi, (4)
where: K - low-water factor; its value is estimated in
o 7
accordance with the type of the river alimentation; Q. -mean yearly discharge value, m3/s. It is necessary to note that the low-water norm can be estimated not only for one year, but also for the whole long-term period.
Conclusions. On the base of results of studies, the following conclusions and proposals have been made:
1. The ratios between the mean yearly discharge values for the low-water years (Qlme) and the flow norm (Qo) are estimated for the whole long-term period calculated.
2. For the first time on the base of the mean values of calculated ratios the notion of "low-water factor" (Ko) was introduced, and its mean values were estimated for each alimentation type according to V. L. Schults classification.
3. Statistical assessment of closeness of relationship between low-water factor (Ko) and Schults's factor was carried out. It is recommended to use the regression equation derived with sufficient degree of relationship closeness in hydrological calculations for the planning of different water economy activities. For example, with the use of Schults's factor the low-water factor can be estimated for the unstudied rivers;
4. Design formula was proposed for estimation of the low-water norm (Qlo, m3/s) with the use of the low-water factor;
5. For the riverswith the glacial-snowalimentation type the values of low-water factor Ko vary within 0.78-0.92; for the rivers with snow-glacial alimentation type the low-water factor value varies within 0.60-0.77; for the rivers with snow and snow-rain alimentation type it varies within 0.64-0.76 and 0.52-0.72, respectively;
6. The proposed design formula ( QlO = KO • Qi, ) makes it possible to estimate the low-water norm for individual year or in average for the long-term period. The practical value of this norm is manifested in the following:
- it is used for the assessment of the water safety observations on rivers in the low-water years;
- it is used in the low-water years for the most rational use of the water resources of water storages in the mountain river beds;
- it is used for definition of the limiting values of the water intake to irrigation canals;
- with the use of the calculated low-water norm and cyclicity of the river flow variations the planning of agricultural crops seeding on irrigated areas is feasible;
7. If to take into consideration that the results of conducted studies are characteristic for all mountain rivers on the territory of Central Asia, then the values of the design formulas proposed above become more ponderous.
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