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Rakhmonov K.R., PhD associate professor lecturer
Terrestrial Hydrology Department National University of Uzbekistan named after Mirzo Ulugbek
Uzbekistan, Tahkent Uteniyazov A.S. magister student
Karakalpak State University named after Berdakh
Uzbekistan, Nukus Allashov Z.J. project chief engineer Land Planning Department of the Republic of Karakalpakstan "Uzdavyerloyiha" State Scientifically-Design Institute
EROSION ACTIVITY INDICATORS OF MIDDLE ZARAFSHAN BASIN
RIVERS
Annotation: The article identifies indicators of erosion activity of rivers and streams in the middle part of the Zarafshan River. For this purpose, the turbidity of river and stream water was calculated as the flow of sediments (in units of weight and volume), washing modulus and washing layer, erosion meter, etc. As a result, erosion processes were accelerated in Tusunsay, Omonqutansay and Urgutsay basins.
Key words: river basin, river, flow rate, water flow, turbidity, flow modulus, erosion meter.
It is important to investigate water erosion from river basins and their products - the formation of suspended riverbeds. Research in this area has a key role in determining the laws of water erosion and the formation of riverbeds, in the design of water management systems and hydraulic structures, their effective operation. In this regard, it is important to study in depth the regime of suspended tributaries of the middle reaches of the Zarafshan River, to draw appropriate conclusions and develop the necessary recommendations in this regard. The first scientific and theoretical views on the study of water erosion processes in river basins were studied by B.V. Polyakov, K.S. Kabanova, N.I. Makkaveev, V.L. Shuls, A.V. Karaushev, G.N. Khmaladze. Later researches in this direction were continued by O.P. Sheglova, Yu.N. Ivanov, H.M. Mahsudov, A.R. Rasulov, Z.S. Sirliboeva, F.H. Hikmatov and others. It should be noted that almost all of the above-named scientists have focused on assessing the suspension of large mountain rivers and the intensity of water erosion in their basins. More precisely, in these studies, the rivers that form directly in Uzbekistan and adjacent areas are relatively little studied. This situation requires
the study of the problem associated with the formation of suspended sediments and the intensity of soil washing on the example of rivers and streams of the Republic, based on new hydrological data.
The main purpose of this work is to create conditions for maintaining the intensity of soil accumulation, i.e. erosion, under the waters of the Central Zarafshan basin of Uzbekistan.
Based on the purpose of the work, 7 hydrological posts were selected for observations on rivers in the Middle Zarafshan basin. Based on the data on water (Q) and suspended runoff (R) consumption observed at the selected hydrological posts, indicators such as turbidity, runoff volume, washout modulus, washout layer, erosion meter were determined for each river and river basin. The extreme, i.e., average, maximum, and minimum values of each indicator were calculated based on the data observed in 1961-2020.
Data on the selected hydrological monitoring sites for the study of the intensity of soil leaching from river basins are given in Table 1. It can be seen from this table that the largest of the average heights of the observed hydrological posts relative to sea level in the water and suspension runoff flows belong to Biglyarsoy (1340 m). Measurements of water consumption in this stream began in 1964 and continue to this day. At the Yangi-Akchob hydrological post of Biglyarsay, the discharge of suspended sediments was observed in 1974-2001.
In contrast, the most studied streams in the basin are the Utgutsoy and Biglyarsoy. Although the catchment area of these streams is not large, the duration of the years in which water consumption was measured is more than 50 years, i.e., the measurement of water consumption in these streams began in 1950 and 1964 (Table 1).
The longest observed value of the consumption of suspended streams in the rivers and streams of the middle part of the Zarafshan River also belongs to the Karaogach (Mavlon) river, which collects water from an area of 34,7 km2. Measurements of the consumption of suspended solids in the river were recorded during 1979-2016.
Table 1. Water and water floating consumption in rivers and streams in the
middle part of the Zarafshan basin
№ River observation point Years of observation
Q, water consumption R, floating consumption Number
Q R
1 Urgutsoy - Urgut town 1950-89, 2006-2020 1966-1989 55 24
2 Omanqutansoy -Oman-Qutan village 1970-2020 1971-75, 1977-92 51 21
3 Oqdaryo-Ogaliq village 1985-2020 1985-2020 36 36
4 Tusunsoy - Qoraqiya village 1963-1990 1966-1975, 19771991 28 25
5 Qoraog'ash - Mavlon village 1978-2020 1979-2020 44 42
6 Maydon - Olmaota village 1982-2005 1983-2005 24 23
7 Viglyarsoy-Yangi-Oqshob village 1964-2020 1974-2001 57 28
The turbidity of river water (p, g/l) was calculated using the following expression based on the values of water consumption and suspended runoff measured in them:
R
p = q
Turbidity flow values were determined in two different units of measurement:
a) in units of weight: Wrg = 86,4 • T • R, tons,
b) in the unit of volume:
w w™ Yr
One of the main indicators of river erosion activity is the washing modulus (Mr, t/km2), taking into account the basin area (F) mr =
determined using the expression.
The modulus of leaching of soils from river basins (hR, mm) was determined as follows:
wr v
r = ~~pv
The determined values of the wash layer allowed to calculate the erosion meter (he, year) specific to each river basin using the following expression:
1,0 m
h e =~h— h r
The results of the calculations are summarized in the table 2.
Table 2. Indicators of erosion activity of the Middle Zarafshan rivers
Erosion activity indicators
№ River observation point s e Water consumptionQ, m3/s n, io çp m us £ idi Nutrients flow Washing module Mr, t/km2 year m s pi h r Erosion meter, he, year
Va a ^ o c, cg ,R ati lo E s à t, s £ Wrg 103 t Wrv 103 m3 M g in s a £
max 1,34 0,51 0,38 16,0 10,7 641 0,427 2342
1 Urgutsoy -Urgut town min norma 0,03 1 0 0,00 4 0,06 8 0,06 2 0,04 2,51 133 0,0017 0,089 588235 11236
l 0,38 6 2 0,10 6 5 0,27 5 3 3,34 3 2 2,22 9
max 1,99 1,20 0,60 37,8 25,2 655 0,436 2294
Omanqutan min 0,19 0,00 3 4 3 3,82 0,0003 4000000
2 soy -Oman-Qutan village norma l 0 0,97 6 7 0,18 4 0,03 7 0,18 9 0,22 1 5,80 0,14 7 3,87 100 0,067 14925
Max 3,04 0,31 0,10 9,77 6,51 138 0,092 10870
3 Oqdaryo - Ogaliq village min norma l 0,37 3 1,03 0 0,00 3 0,08 1 2 0,00 8 0,07 9 0,09 5 2,55 0,06 3 1,70 1,34 35,97 0,001 0,024 1000000 41667
max 7,9 42,0 5,32 132 883 1484 0,989 1011
Tusunsoy - min 0,70 0,00 0,00 5 0,08 0,141 0,0001 1000000
4 Qoraqiya village norma l 1,56 4 2,11 6 1,53 0,12 6 66,5 4 44,3 74,5 0,050 0 20000
max 0,94 0,11 0,12 3,56 2,37 103 0,068 14706
5 Qoraog'ash - Mavlon village min norma l 5 0,06 2 0,30 1 3 0,00 1 0,02 7 0 0,01 6 0,09 0 0,03 2 0,85 1 0,02 1 0,56 7 0,922 24,5 0,001 0,016 1000000 62500
max 1,36 1,0 0,72 31,5 21,0 505 0,336 2976
6 Maydon - Olmaota village min norma l 0,13 8 0,66 9 0,00 1 0,10 6 5 0,00 7 0,15 8 4 0,03 2 3,34 3 0,02 1 2,23 0,513 53,5 0,0003 0,036 3333333 27778
max 2,25 0,37 0,16 11,7 7,80 65,0 0,043 23256
7 Viglyarsoy - Yangi-Oqshob village min norma l 0,11 0 0,60 1 0 0,00 1 0,04 0 4 0,00 9 0,06 7 0,03 2 1,26 0 0,02 1 0,84 0 0,178 7,00 0,0001 0,005 1000000 0 200000
Note: Q - water consumption, R - Floating consumption, r - turbidity,
MR - washing module, hR - washing layer, he - erosion meter.
As can be seen from the table, erosion processes are accelerated in the rivers Tusunsoy (Karakiya), Omanqutansoy (Omanqutan) and Urgutsay (Urgut). For example, the leaching modulus (Mr) determined for maximum values in Tusunsay is 1484 t/km2, while in Omanqutansoy it is 655 t/km2. According to these values of the wash modulus, the annual wash layer (hR) from the river basins is 0,989 mm and 0,436 mm, respectively.
It is known that the average perennial water consumption in the Urgutsoy River in 1966-1989 was Q = 0,386 m3/s, and the average perennial value of suspended sediment consumption was R = 0,106 kg/s. The washing modulus determined on the basis of these average perennial values of water and suspended runoff consumption observed in the river was Mr = 133 t/km2-year. The mean perennial wash layer was hR = 0,089 mm. The identified washout layer made it possible to calculate the average perennial erosion meter, and the average perennial erosion meter detected for this river basin was he = 11236 years. This means that the surface area of the Urgutsoy basin decreases by one meter on average during 11236 years.
The amount of erosion meter calculated on the basis of the maximum values of the tributaries of the Urgutsoy River is 2342 years, while the minimum value increases sharply to 588236 years.
Among all the studied rivers, the process of water erosion on the surface of the basin of the river Koksaroysay (Koksaroy) is relatively slow. It would take 249968 years for the surface of this river basin to fall by an average of one meter. The reason for this can be explained by the natural conditions of the river basin, more precisely by the geological structure, relief, soils and vegetation condition of the basin.
In summary, the modulus of soil leaching (Mr) from the catchment areas of the rivers of the Middle Zarafshan Basin varies from 7,0 to 133 t/km2. According to these values, the washing layer (hR) from the river basins has values in the range of 0,005 - 0,089 mm. It should be noted that these figures are preliminary results and require clarification in future studies, based on calculations performed on the basis of homogeneous hydrological series.
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