Long-term dynamics of water loss of the Amu Darya river. Case study Lebap Province, Turkmenistan



1. INTRODUCTION

Amu Darya is the largest river in Central Asia. Its length is from the sources of the river. Pyanj is 2540 km, the catchment area is 309 thousand km2 (excluding the catchment area of the Zeravshan River). She receives the name Amu Darya when p. Panj flows into the river. Vakhsh. Three large right tributaries (Kafirnigan, Surkhandarya and Sherabad) and one left (Kunduz) flow into the Amu Darya in the middle reaches. Further down to the Aral Sea, tributaries are absent. Basically, the river is replenished with melt water, so the maximum costs can be observed in the summer, and the minimum — in January-February. Such a flow regime during the year is favorable for the use of river water for irrigation. Flowing through the plain, from Kerki to Nukus, the Amu Darya loses most of its flow in the form of evaporation, infiltration and selection for irrigation. Amu Darya is the first in the world in sediment transportation. The main runoff of the river. Amu Darya is formed on the territory of Tajikistan (about 72.8 % — excluding the Zerafshan River). Then the river flows along the border between Afghanistan and Uzbekistan, then it crosses Turkmenistan and returns to Uzbekistan, where it flows into the Aral Sea. About 14.6 % of the river’s water Amu Darya is formed on Afghan territory and in Iran. About 8.5 % of the Amu Darya flow is formed in Uzbekistan.

Water flow changes along the course of the river. These changes depend on the flow of groundwater into the river in the zone of runoff formation, the influx of return water in the transit region, which varies with water level and runoff losses in the lowest zone of the delta. Some losses occur due to evaporation and filtration in river beds.

Observation is the most reliable measure for assessing losses; water balance calculations are only a rough estimate.

1.1. The importance of the research topic

At present, it is very difficult to determine the channel losses in the lower reaches of the river. Amu Darya below Kerky. Recent five-year observations in this part of the river showed that losses vary from 7.0 to 13.0 km3 / year. This is comparable to 20–40 % of the total volume of water withdrawals into canals. Even taking given the losses due to evaporation, filtration and channel stocks, there is a huge imbalance. Its reasons are inexplicable, since the general climatic and hydrological factors do not contribute to such losses. A more thorough study of this problem in the near future is needed. In addition to recording observational data, many control measurements of channel losses should be made. Actual water losses due to evaporation in former riverbeds, floodplains and natural depressions should be estimated using remote sensing methods. Based on these measurements, it is possible to prepare proposals to reduce runoff losses in the Amudarya river basin, exceeding 3.5–5.0 km3 / year.

1.2. Research question

The main issue is the similarity of actual data with the actual water consumption in the Amu Darya river basin for 19 years, as well as with the loss of water on the Amu Darya river for natural conditions.

1.3. Purpose of the study

Purpose of the study is an analytical study of the water balance of the Amu Darya River with the determination of the long-term dynamics of water losses.

1.4. Research objectives

— to study of the Amu Darya river basin;

— collect and review of the Middle River Department “Amudarya” data for 20 years

— analysis of stocks of materials and data on the distribution of water resources in the Amu Darya river basin

— conduct a survey of water supply facilities;

— develop water balance calculations.

— draw up a water loss schedule over 20 years

1.5. Research methods

Research Methods: Review of geographical and climatic conditions. Analysis of the general literature. Data collection in water intakes and hydrometric stations, literature review, data processing and analysis.

1.6. Scientific and practical values topic

Scientific values

The research results will determine the channel losses in the lower reaches of the Amu Darya river below the city of Kerki.

The results of the study will shed light on the dynamics of water loss in the alignment over the past 20 years.

The results obtained in the thesis can be used in simulation models of river flow dynamics.

Practical values

The results of the analysis of the long-term dynamics of water losses taking into account climatic data will be useful for developing a strategy for the efficient use of water resources

2. Literature review

2.1 Geographical location and description of the natural conditions of the region

Fig.1. Map of Amudarya river basin

The Amu Darya River is the largest river in Central Asia, passing through the territory of northern Afghanistan, Tajikistan, Turkmenistan, a significant part of Uzbekistan and a small area in the upper reaches of Kyrgyzstan. The catchment area is 309 thousand km2, the length of the river from the upper sources of the Panj exceeds 2540 km. Its main components are the Vakhsh and Pyanj tributaries, from the confluence of which the river takes its name. Downstream, the Amu Darya receives tributaries Kafirnigan, Surkhandarya, Sherabad on the right and Kunduz, on the left from the territory of Afghanistan. Below the Kerky site, the river has practically no influx, with the exception of discharge of collector-drainage water into it. The river has mixed snow-glacier nutrition with a natural runoff hydrograph (Fig. 1), which clearly coincides with the need for irrigation, when the maximum flow rate — 77–80 % falls on April-September and a minimum on October-February. From the Kerks to the delta, mainly the Amu Darya loses its runoff, although its interaction with groundwater depends on the water content of the year. The Amu Darya is a transboundary river — its upper reaches lie mainly on the territory of Tajikistan — 72.8 % of the catchment area: the left bank of the Panj and partially — 300 km along the Amu Darya. Further from the confluence to Mukrov, it passes along the border with Afghanistan, the formation zone occupies 14.6 % of the total catchment, first between Tajikistan, then Uzbekistan and Afghanistan, then through the territory of Turkmenistan and, starting from Tuyamuyun, passes to the territory of Uzbekistan. Within the Amudarya catchment area, 8.5 % of the catchment area lies in Uzbekistan and 4.1 % in Kyrgyzstan. In addition to the existing Aral basin, there are a number of watercourses previously associated with the Amu Darya and now gravitating to it or associated with the economic use of its waters. These are the rivers of the basins of Kashkadarya, Zarafshan, Murghab, Tedzhen, Atrek and the rivers of northern Afghanistan (Hulm, Balkh, etc.). The main water resources of the basin — the recorded surface runoff — are determined by the data of hydrometric stations located near the river exit from the mountains. Figure 2 shows the location of the main gauging stations on the Amu Darya River and its main tributaries.

Fig. 2. Linear scheme of middle stream of Amudarya river

According to the conditions of channel stream transformation, formation and unloading of groundwater in the middle and lower reaches of the Amu Darya, 4 sections are allocated. They are located between the Kerky-Ilchik gauging stations, Ilchik-Darganata, Darganata-Tuyamuyun, Tyuyamuyun-Samanbai gauging stations. In the Kerky — Ilchik section, the resulting channel balance according to long-term data indicates the average annual loss. Filtration losses from the river bed occur on the left bank. The bulk of the filtration losses in the channel due to the difficult conditions of the outflow from the valley can be spent only on the total evaporation from the groundwater level and on wedging out into the collector-drainage network. Here, the main form of filtration is its formation in the form of a sub-bed stream. The length of the plot is 295 km. The floodplain is 4–5 km wide. Slope 0.00024.

River runoff is characterized by strong seasonality, with peak flows occurring in summer, peaking in July, when glacial melting peaks, as shown in Figure 3. The minimum river runoff occurs in January-February. Only the inflow of the Kafirnigan River has a slightly different discharge, with a maximum discharge in May, since this river is more controlled by melting snow, rather than melting glaciers.

Fig. 3. Monthly average discharge

The Ilchik-Darganata section is a zone of pinch-out of the channel under the river into the river, which is facilitated by the deepening of the narrow river valley embedded in low-permeable bedrock. The river is a natural drain of groundwater in the surrounding areas. Possible entry into the channel of groundwater from both banks and wedging out of the channel bed. The length of the plot is 140 km. The width of the floodplain is small, sometimes practically absent. Slope 0.00022. Collector influx exceeds water intake. On the Darganata-Tuyamuyun site, the Tyuyamuyun hydroelectric facility is located. It is characterized by losses due to evaporation from the reservoir, losses in the riverbed, but at the same time, by filtration inflows in the Ruslovoye reservoir (at high levels in the reservoir, outflow to underground waters is observed, at low levels — discharge into the reservoir from underground horizons).2.2 Water intakes from rivers

The list of water withdrawals from the MAB rivers is given in the Appendix, in table 2. Until 1992, the distribution of water resources of the Amu Darya among the four republics of Central Asia was carried out on the basis of the General Scheme for the Development of Water Resources in the Amu Darya Basin. The division was approved by the decision of the USSR Ministry of Water Economy No. 566 in 1987 on the basis of the resolution of the USSR State Planning Commission No. 563р for 1987. The proportion of surface water allocated to each state according to this decision was (in percent of the projected runoff along the Amudarya river trunk): Kyrgyzstan — 0.6, Tajikistan — 15.4, Turkmenistan — 35.8, Uzbekistan — 48.2. Today, the distribution of water in the Amu Darya basin is carried out according to established limits on water withdrawals. The actual distribution for 1993–2004 is shown in table 1.

Table1

Actual water withdrawal from the IBA (1993–2004), km3

	1993-1994	1994-1995	1995-1996	1996-1997	1997-1998	1998-1999	1999-2000		2000-2001	2001-2002	2002-2003	2003-2004
Kyrgyzstan	0.15	0.48	0.13	0.16	0.17	0.45	0.45	0.45		0.43	0.45	0.50
Tajikistan	7.32	7.01	7.41	7.51	7.03	7.37	7.87		7.51	7.20	6.74	7.62
Turkmenistan	22.76	21.15	21.46	21.02	21.99	21.89	17.23		13.73	19.31	21.47	22.35
Uzbekistan	21.32	22.26	24.17	22.36	23.56	25.08	18.40		17.33	20.75	22.86	23.05
Total	51.55	50.55	53.20	51.06	53.03	54.79	43.95		38.71	47.71	51.57	53.5

2. 2 Return flow

Currently, there are four areas in which water is removed, distributed and used for collector-drainage flow (CDW): — use of part of the CDW for irrigation directly in the places of its formation (ZP); — the withdrawal of part of the CDS beyond the boundaries of irrigated lands to natural depressions (evaporators) or lakes; — discharge of part of the CDS into rivers (such a discharge can also be carried out from lakes); — supply of CDS to the delta and the Aral Sea. The return flow discharged into the rivers, in addition to the waste water coming from the irrigated massifs, includes discharges from the irrigation network (for example, from the Vakhsh canal), municipal and industrial effluents, as well as the flow of drainage water in the form of filtration into the river (the last component is taken into account when modeling as channel filtration losses with the opposite sign). Between the volume of formed CDS in the RF and the water intake in the RF, one can trace some regularity characteristic for each planning zone. To calculate the return flow entering the Amu Darya river, it is necessary to take into account the transformation of these values when passing through salt lakes, the flow of part of the water supply from neighboring basins that are not included in the IBA, etc. Thus, the return flow from the irrigated territories of the Surkhan-Sherabad massif account for a large proportion of the formation of the Amu Darya flow., river basins Kashkadarya — Southern collector and Sultandag discharge, Zarafshan — Main Bukhara collector and Parsankul discharge (Bukhara ZP), from the Turkmen Coastal Irrigation Area (Lebap ZP) entering the large pool of the Amu Darya. Some of the costs of CDS by decade are shown in table 2

Table 2

Collector-drainage flow

Name of collectors	I dec			II dec			III dec
	Avg.dec flow	flow	Stock growing	Avg.dec flow	flow	Stock growing	Avg.dec flow	flow	Stock growing
GLK	15,10	13,05	601,99	15,67	13,54	615,53	14,51	13,79	629,32
Gravity Farab	3,50	3,02	109,23	3,48	3,01	112,24	3,40	3,23	115,47
GDK	2,00	1,73	54,55	2,00	1,73	56,28	2,00	1,90	58,18
Halach	10,07	8,70	341,31	9,62	8,31	349,62	9,40	8,93	358,55
Burdalyk	1,70	1,47	52,14	1,69	1,46	53,60	1,60	1,52	55,12
Charshanga	3,00	2,59	102,50	3,00	2,59	105,10	3,10	2,95	108,04
Hojambaz	3,83	3,31	114,52	3,82	3,30	117,82	3,80	3,61	121,43
Mekan	0,46	0,40	15,20	0,45	0,39	15,59	0,40	0,38	15,97
Porsankul	21,69	18,74	1108,60	23,01	19,88	1128,48	0,00	0,00	1128,48
South Karshi	5,75	4,97	511,11	0,00	0,00	511,11	0,00	0,00	511,11
Total:	67,10	57,97	3011,16	62,74	54,21	3065,37	38,21	36,31	3101,69
Without Charshanga	64,10	55,38	2908,66	59,74	51,62	2960,27	35,11	33,37	2993,64

2. 3 Water loss

In the 60s of the last century, V. Schulz estimated the loss of water from the Amu Darya River at 7.6 km3 [1]. In the design studies of the Central Asian branch of the Hydroproject (1971) in the General scheme for the integrated use of water resources of the river. Amu Darya [2] losses from the river were estimated at 7.8 km3 per year (for the conditions of a long-term average year). At the same time, water losses were estimated at 1.2 km3 in the section from the confluence of Vakhsh and Pyanj to Kerki, 6.6 km3 in the Kerki-Chatly section (4.7 km3 for evaporation, 0.3 km3 for filtration, 1.4 km3 and 0.2 km3 for unaccounted water intake were referred to the accuracy of flow accounting). At the beginning of the 80s, when the Amu Darya scheme was refined, the estimate of losses was slightly reduced [3]. For a dry year (90 % coverage), losses were assumed to be 2.9 km3, including in the lower reaches of 1.96 km3 (or 7.2 % of the flow in the Tuyamuyun site). In connection with the commissioning of the Tuyamuyun hydroelectric facility (reservoirs were filled in the mid-80s) and changes in the river regime in the lower reaches, the task was to revise the channel balance of the river and clarify losses (including an assessment in the reservoirs of the Tyuyamuyun hydroelectric complex). Such studies, having a powerful expeditionary base, were carried out from the mid-80s to the mid-90s in SANIIRI, in the Department of Integrated River Flow Management. The studies included field measurements, their processing, and computer simulation of the processes of loss formation [4]. According to the results of studies, losses from the river, on average for the period 1981–1988, were estimated at 8.6 km3, including 3.8 km3 (or 13.2 %) below the Tuyamuyun site. Losses for 1989–1990 amounted to 7.3 km3, but since 1991 they began to increase again. At the same time, it was concluded that the losses in the Revised Gensham of the Amu Darya were underestimated, in particular, due to the lack of consideration of the filtration component, which during the passage of the clarified stream (below the Tyuyamuyun hydroelectric complex) can account for a significant part of the losses. A hypothesis was developed [4], according to which the river from Kerky to Darganata was divided into two sections according to the conditions of formation of the filtration flow: Kerki — Ilchik and Ilchik — Darganata.

The first section was characterized by filtration losses, the second by filtration channel inflow, depending on the magnitude of filtration losses in the first section. The third section (Tuyamuyun — Samanbai) was characterized by filtration losses. Dependencies were obtained combining channel filtration with hydraulic parameters and flow turbidity (the lower the turbidity, the higher the loss). The use of filtration dependencies, formulas for calculating the turbidity of the flow, and also the morphometric dependences of Kh. Ismagilov in the SANIIRI [4] models made it possible to calculate losses from the river, both for filtration and evaporation, for any watering year, season, month. The hypothesis of the presence of filtration losses from the Amu Darya River, first posed by V. Kunin [5] and A. Proskuryakov [6], was confirmed not only by SANIIRI, but also by the Hydroproject, according to which the Tyuyamuyun — Chatly section in the late 60s and early 70s of the years an underground outflow of about 1.4 km3 per year was established [7]. Clarification of channel losses of the Amu Darya River is a task that is periodically solved in the region for several decades, and since the mid-80s — using computer simulation. The loss assessment was studied on the channel dynamic model of the Amu Darya river, developed at the SIC ICWC, which calculates losses by components (evaporation, filtration, etc.) with a step of a day, a decade. Modeling the water regime of the Amu Darya river on a riverbed model represents a schematization of the processes of river flow movement taking into account the “run-up” time and the use of empirical particular laws of flow formation and transformation characteristic of the middle and lower reaches of the river. The empirical parameters and coefficients were calibrated according to the available information for the period from 1970 to 1995 according to the criterion — the smallest total value of the residuals of the water balance. Table 3 shows the SIC ICWC data on the relative losses from the Amu Darya river (as a percentage of the river discharge at the beginning of the estimated section) for different seasons and sections of the river, depending on the expenses passing along the river. The data are obtained by the results of numerical calculations for years and seasons of different water content, are enlarged and show the expected range of calculated values. There is a slight increase in relative losses at minimum and maximum costs.

Table 3

Losses of water from the Amu Darya River (as a percentage of the flow of water in the river) by sites and seasons

Water discharge in the river, m3 / in the river, cubic meters / sec				Water loss %
				Middle course			Downstream
				Vegetation	Inter-Vegetation		Vegetation	Inter-Vegetation
< 500				3…6		2…5
500–1000				2…5		1…3	6…12	6…8
1000–2500				2…4		1…3	6…10	6…7
> 2500	3…6	2…4	8…14	7…9

Calculations show that during periods of special low water occurring for more than one year, the relative losses in the lower reaches of the Amu Darya can reach 19... 21 %, which is 15 % more than the average long-term data. Thus, the increase in relative losses in low water 2000–2010 was associated with a slight increase in the filtration component caused by a drop in the groundwater level in the pre-channel zone.

3 MATERIALS AND METHODS OF RESEARCH

3.1 Materials and methods:

— Assessment of the water balance of the average river flow

— Analysis of stocks of materials and data on the distribution of water resources in the Amudarya river basin

Methodology of research:

The study of water balance is based on the use of the law of conservation of matter. It consists in the fact that for any volume during any period of time, the difference between the total water supply and p31 water consumption is equal to the change in its supply in this volume. Therefore, in general, the method of water balance involves a direct measurement of the reserves and flows (flow) of water, however, in some cases, with the right choice of volume and time period for which the water balance is calculated, some elements can be obtained by indirect calculations.

The equation of water balance of a natural object (on example, a river basin or reservoir) shows the ratio of the arrival, discharge and changes in water reserves for a given land plot or for a given reservoir. In the general case, the incoming part of the water balance equation of any object is atmospheric precipitation P falling in the form of rain and snow onto the land surface, surface and underground influx of water Qsi and Qui from outside into the pool or reservoir. The consumable part includes the evaporation of E from the surface of the object, the surface Qso and the underground drain Quo (more precisely, the outflow), leaving the object. The excess of the incoming part of the water balance over the expenditure causes an increase in the total water reserves in the DS facility; the inverse ratio of income and expense leads to a decrease in these reserves. All components of the water balance are determined with some measurement and calculation errors.

Therefore, in the water balance equation, in addition to its components, the term of the residual r is included. Therefore, the water balance for any object and for any time interval in general form can be represented by the following equation:

P+QSI+Qui –E–Quo–DS = о. (1)

3.2 Types of water balance equation

In relation to a wide variety of water-balance calculations, equation (1) can be simplified or complicated depending on the availability of initial data, the purpose of the calculation, the type of water body (river basin or administrative region, lake or reservoir, etc.) and its size, hydrographic and hydrological characteristics of the object, the duration of the calculation period and the phase of the hydrological regime (high water, low water), for which compilation of water balance.

On large river basins, the balance components Qui and Quo insignificant in comparison with other components; therefore, they are usually not taken into account (underground water exchange with adjacent basins is assumed to be zero). The inflow of surface water into a river basin with a clearly defined watershed from an adjacent territory cannot take place (unless artificial transfer of water from another region is carried out) and therefore Q «included in the equation of the water balance of the river basin. Thus, equation (1) for the river basin takes the following form;

P — E — Q — DS –n = 0. (2)

Where Q is the river flow from the pool.

Depending on the task, the terms of equation (1) can be detailed. For example, when compiling water balances for short periods of time, the change in the total DS water reserves in a small river basin can be subdivided into the change in moisture reserves in the DM soil, in the aquifers of the DG, in the ASt lakes and reservoirs, in the DSl, river channels, in the DSch and glaciers in the snowy roof DSgl- The water balance equation takes the form

P+Qs i + Q u i — E — Q s o — Q u o — DM — DG — DSl — DSgl — DSs n –n=0

where Qsi is the transfer of surface water from other basins.

3.3 Features of water balance equations for various time intervals

The water balance can be calculated for any time interval.There are long-term average water balances and balances for specific periods (for a single year, season, month or several days). Such balances are sometimes called current or operational water balances. Water-balance calculations for many years and for specific periods have their own characteristics.

The average long-term water balances are usually per annual cycle (per calendar or hydrological year), although they can be calculated for any season or month. The preparation of average multi-year balances for the year is the simplest task, since it is possible not to take into account changes in moisture reserves in the basin DS, the measurement and evaluation of which causes the greatest difficulties. Over the course of a long period, the positive and negative changes in water reserves occurring in individual years are mutually compensated and their value at the end of a long-term billing period can be equal to zero.

The reverse is the case when calculating the water balance for short periods of time for which DS = 0 the shorter the time interval for which the balance is calculated, the greater accuracy is required when measuring or calculating balance elements, the more differentiated it is necessary to consider DS, and usually other balance elements, the more complicated is its equation and the more difficult it is to close it with the least residual. Component DS must be taken into account when calculating the average multi-year water balances for individual seasons or months.

3.4 Closing the water balance equation .

In order to close the water balance equation, all of its elements should be measured or calculated as independent as possible. Measurements and calculations of elements of the water balance are made in any case with a certain error due to the imperfection of measurement and calculation methods.

Therefore, the water balance equation, even if all its elements are measured or calculated by independent methods, usually does not close (does not balance). The discrepancy m) is defined as the residual term in the water balance equation and includes errors in the determination of individual ebb elements, as well as elements unaccounted for by the equation. A small value of t) indicates a balance in the water balance.

If any element of the balance cannot be obtained by direct measurement or calculation, it can be determined from the water balance equation as a residual term;. In this case, it also includes the discrepancy of balance, which may be even greater than the value of this element.

This technique, as you know, is shaded in hydrology when from the measured values of one element, the values of another element are determined using empirical or semi-empirical formulas. The value calculated in this way will include the error due to the imperfection of the formulas and the measurement error.

3.5 Methods for calculating the basic elements of water balance

The initial materials for calculating the elements of the water balance of river basins over a multi-year period are observations of a network of stations for precipitation and runoff. The data of these observations are published in the form of hydrological and meteorological yearbooks, bulletins and other publications.

To draw up the water balance for individual years, seasons, months, additional data on changes in moisture reserves in the pool is required. These data are determined by the results of observations of soil moisture, fluctuations in water level on lakes, fluctuations in level underground filming.

To calculate the water balance of small areas with a specific balance structure (mountain-ice basins, forests, irrigated lands, etc.) in most cases, it is necessary to organize special observations according to a special program, for example, glacier melting, interception of precipitation by woody vegetation, and zone humidity aeration, etc.

For the calculation of Evaporation, data from evaporation plants and observations of meteorological stations on temperature and humidity, wind speed, cloud cover and solar radiation are required.

3.6 Maps and Atlases

In the absence of precipitation, runoff, or evaporation, in some cases, regional maps and atlases of mean long-term values of these balance elements may be useful. According to such maps constructed in contours, the average values of precipitation, runoff, or evaporation for any territories can be easily determined by planimetry.

It should be noted here that for of water balance goals, maps of annual precipitation, source evaporation standards should be linked to each other, i.e. the difference in precipitation, evaporation and runoff determined from the сorresponding contour maps for a given river basin should be zero in accordance with the equation of the river basin water balance over a long-term period

P — F — Q = 0.

IV EXPECTED RESULTS

Expected results

It is expected that the water balance of the Amu Darya river basin will develop from the Atamurat gauging station to Dargan-Ata during 2000–2019, and long-term dynamics of water losses will be revealed.

References:

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5. Kunin V. I. The origin of the underground waters of the Karakum. News of VGO. Volume 79, Issue 1, 1947.
6. Proskuryakov A. K. Water balance p. Amu Darya on a site from Kerky to Nukus. Gidrometeoizdat, 1953.
7. Svetitsky V. P. To conduct research and draw up a modern and prospective up to 2000 water balance of the Aral Sea basin. Research Report. SANIIRI. Tashkent, 1985.
8. «Southern Aral Sea — New Perspectives» edited by prof. V. A. Dukhovny, Jupe de Shuter, Tashkent, 2003,
9. INTAS-RFBR-1733 project «Assessment of the socio-economic consequences of the ecological disaster — the drying up of the Aral Sea», 2002
10. Dukhovny V. A., Sokolov V. I. «Integrated water resources management in the Aral Sea basin», Collection of scientific works of SIC ICWC. Favorites for 1992–2002. Tashkent, 2002, p.