CC BY
9
Section 4. Agricultural sciences
https://doi.org/10.29013/ESR-21-1.2-20-24
Zakirov M.M., Begimkulov D.K., Gulomov G.D., Khudoyberdiev T.M., Tashkent State Technical University, "Uzbekhydrogeologiya" State Institution Tashkent, Uzbekistan
E-mail: mzakirov1957@mail.ru
THE ENGINEERING AND RECLAMATION STATE OF MIRZACHO'L AREA OF SIRDARYO REGION
Abstract. The article examines land degradation in the drylands as a result of various factors, including climate change with human activities. At the same time, the particularity of the problem of desertification, which was an integral part of land degradation, is examined. In general, "Land degradation" is considered as a decrease or loss ofbiological and economic productivity of irrigated land or areas under the influence of natural and anthropogenic factors.
Soil degradation of Mirzacho'l is currently caused by:-depletion of the surface soil layer due to wind and water erosion and induced-changes in soil chemistry and biological environment caused by acidification, salinity or pollution-accelerated loss of nutrients from mineral and organic soil matter and loss of organic matter itself-soil compaction and loosening due to infrastructure development and housing development.
Keywords: degradation, hypergenesis, groundwater, desertification, reclamation conditions, hy-drogeological and engineering geological conditions.
Introduction. Desertification and drought holds citizen of the Republic is its consumer, although not
special place among modern global problems of everybody realizes it. 98% of the products we con-
mankind, which impede sustainable development of sume originate from these lands [1; 2; 3]. economy, that was reflected in regional researches on Desertification means land degradation in arid
estimation ofhydrogeological and meliorative condi- areas due to various factors, including climate change
tions of territory and study of predicted groundwater and human activities. At the same time, particular
resources of Neogene-Quaternary deposits in view importance is given to the problems of desertifica-
of water management conditions change on area of tion, of which land degradation is an integral part. Mirzacho'l of Sirdaryo region. And groundwaters of Soil degradation of Mirzacho'l at present is
Mirzacho'l are an exhaustible resource, and every caused by: - depletion of the surface layer of soil due
to wind and water erosion and caused by; - changes in the chemical composition of soil and biological environment caused by salinization or pollution.
Research subject. Irrigated areas of Mirzacho'l belonging to Sirdaryo region were the research subject. Here significant rise of ground water of 1.5-3m and more is observed, in comparison with natural conditions of 5.0-10m in 1960. The flooding caused in the last decade by groundwater rise in considerable areas of Mirzacho'l, mainly due to irrigation system operation rules violation, creates additional difficulties both in development and in construction of engineering structures, underground utilities and drainage.
Purpose and method of the research. Sirdaryo region's natural, anthropogenic and economic conditions have an approximately uniform natural and soil-reclamation environment for the desert zone of Mirzacho'l [9; 10, 13-15].
The purpose of the research is to study soil-reclamation state of irrigated soils and grounds taking into account natural conditions and anthropogenic factors. For achievement of the purpose, the following tasks have been set: - to identify causes, regularities of formation and geographical distribution of saline soils and grounds; - to establish regional peculiarities of salt accumulation; to assess reclamation state of grounds in Sirdaryo region.
There is an all-round increase of ground water level on the studied territory. If we take into account that the groundwater recharge area ofMirzacho'l as a whole, is through precipitation and infiltration from irrigation canals. And it should be noted that in the central and eastern parts of the studied area there is no groundwater recharge, except capillary rise and evaporation. Similar conditions have been mentioned in works ofdifferent authors in different years [8; 9; 16].
Approximately the same approach was adopted in Russia even earlier [2]. However, the set of physical degradation indicators was a little wider here. In addition to those mentioned above, porosity, filtration coefficient, reduction of soil thickness and others were used here.
Some Russian agencies (e.g., State Committee on Land Resources and the Ministry of Ecology) recommend using their methods for assessing physical degradation of soils [3], the idea of which is approximately the same-assessment of soil deterioration with respect to some initial condition.
In fact, the only sources of information for judging the presence ofphysical degradation and subject to hypergenic changes are the results of comparative observations in non-irrigated and irrigated areas of long-term field engineering and geological studies accompanied by experimental experiments. Based on these sources of information, we consider it important to systematize the processes in soils related to hypergenesis and physical degradation, to establish its causes, a clearer diagnosis, possible areas of distribution and the search for ways to prevent it.
Discussion of results. The article uses the results of mining and test-filtration studies of irrigated and newly irrigated areas of Mirzacho'l, pertaining to Sirdaryo region. Based on these comparative studies conclusions will be drawn about changes in physical properties, which we interpret as degradation and hypergenic changes in soils. The results of macro- and micro morphological and textural structure of soils and individual soil aggregates, structural-textural composition, water resistance of aggregates, porosity, about the ratio of vertical and horizontal pores -anisotropy are used as indicators of these processes.
According to the guidelines for hydrogeological and engineering geological investigations [1; 4; 5; 6; 7], the lithological composition of rocks in the outcrop and their stratigraphic position are recommended to be described with little detail. The order in which rocks are described is as follows: a) petro-graphic name; b) mineralogical composition of the rock; c) rock colour; d) impurities and rock cement; e) density; f) structure and texture; g) layering and various features associated with the rock formation conditions; h) inclusions; i) fractured rock; j) fauna and flora; k) assumed age.
The colour of a rock can often indicate the genesis of the rock and its properties. Therefore, in our studies, the bright red hues due to the presence of anhydrous iron oxide (Fe2O3) or hydroxides (2Fe2O3 . . H2O) and gypsum (CaSO4 . 2H2O) indicate continental conditions of formation, rather dry and hot climate. It should be taken into account that rocks in fresh fracture often have a colour or hue that differs from the colour of rocks on the surface. This last circumstance is caused by weathering processes: oxidation, reduction and decomposition of the main rock-forming minerals.
Many features of rocks were identified by eye and to the touch; e.g: Sandy and clayey rocks were identified by touch by rubbing or rolling; ferruginous rocks were identified by the rusty colour of the rock; mica was identified by glistening mica plates; the presence of water-soluble salts by the content of potassium and sodium hydrates in the soils which contributed to the so-called "puffed" separates of bright white in the section, representing a loose, dusty medium.
Soil density was described as follows: sands and sandy loams are classified as loose, compacted (caked), clays, clay loams in terms of ductility, plasticity.
When describing rock structure and texture, the shape, location and size of the constituent minerals are noted.
If there are different grain sizes in the rock, the secondary formations are described as different grains. Grain sizes are determined by means of a pie chart and, with some skill, can be determined by eye.
To determine the filtration coefficient of non-water-saturated soils, i.e. soils in the aeration zone, the water infiltration method is used in a sump. The point of the method is to create a vertical filtration flow through the dry soil down from the bottom of the sump and to measure the cross-sectional area of the flow and the flow rate. Water is absorbed into the dry soil and moves in it not only by downward forces of gravity, but also by capillary forces, which can act in all directions. As the depth of wetting increases, the rate of change of the wetting figure slows down and
the flow rate of water for infiltration from the sump stabilises. Therefore, this method only approximated the value of the filtration coefficient, but with an accuracy that is quite acceptable for practical purposes.
Experimental and filtration studies of the filtration coefficient of various genetic types (in our case a QIV sd and ap Q gl of Quaternary age) of saline sandy loam and sandy loam soils have shown that the filtration coefficient is determined by a natural combination of their composition, state and nature of structural relationships.
Conducted comprehensive research in the territory revealed that groundwater has a multifaceted influence on the formation of secondary salinity zones in the soil section. In the studied reference areas ground waters occur at depths from 0.5-0.75 to 2.0-2.5 m. Depending on the general salinity the ground waters of the territory have-medium salinity from 5 to 15 g/l; - high salinity from 15 g/l and more. According to the chemical composition, groundwater is mainly chloride-sulphate-sodium-magnesium, and rarely sulphate-potassium-sodium.
An increase in the "critical" groundwater level with increased salinity drastically worsens the soil-reclamation conditions. This in turn is a consequence ofinten-sification of desertification processes and secondary salinization. In addition, groundwater is not discharged in the operational and reclamation periods to the drainage systems. The provision of surface natural runoff to drainage systems is not yet effective enough. On the background of groundwater table increase of Mirzacho'l there is widespread deterioration of reclamation state of soils due to secondary salinization. This is caused by the impact of large canals and irrigation systems contributing to increase ofgroundwater table. Salinization leads to the formation of gypsum horizons at depths of about 0.75-1.0 to 1.5m (Table 2). It is interesting that private farms (Khavast, Mirzaabad and Bayaut districts) extract the gypsum horizon and set up mini greenhouses at a depth of1.0 - 1.5m.
The data shown in (table 2) show that the quantitative values of the dense residue are very wide rang-
ing from slightly saline from 0.35 - 0.485 % to highly saline 2.02 - 2.65 %.
The composition of water soluble salts in saline soils is very diverse but in this case these salts are combinations of only three sodium (Na+), magnesium (Mg++) and calcium (Ca++) cations and four chlorine (Cl), sulphate (SO4) and hydrocarbonate (HCO3) anions. It is obvious that the following salts can be formed from them: NaCl, Na2SO4, NaHCO3, MgCl2, MgSO4, Mg(HCO3)2, CaCl2, CaSO4 and Ca(HCO3)2.
Thorough study of saline soils of the territory of Sirdaryo region allowed to reveal their different sensitivity in relation to water. On the studied territory everywhere depending on texture, structure, content and composition of secondary formed salts (amorphous silica -SiO2, gypsum - CaSO4. 2H2O, etc.) dense saline zone at depth from 0.75 - 1.0 to 1.5m is established (tab. 2). The formation of the zone is probably due to capillary rise of saline groundwater and due to the influence of arid climate a dense zone of secondary salts appears. This zone negatively affects the reclamation state of irrigated area soils. In our case, according to schedule of water discharge change from time, sandy loam, being strong enough in saline state, in the process of leaching in different degree is additionally hydrated, decompacted and sharply deconsolidated, passing from initial, their meliorative condition is improved.
And on sections of settlements and central homesteads of district, the relationship of soils with water
leads to leaching of salts, coagulation-crystallization structural connections in sandy loam are weakened and broken that leads to sharp decrease of strength and change of deformation behavior of soils.
Conclusion. Hydrogeological conditions of the study area contribute to the fact that the formed groundwater in the "critical" state, as well as a large amount of surface irrigation water used for irrigation does not have sufficient outflow and is spent mainly on evaporation and transpiration, which creates the preconditions for the development of secondary salinization, especially intensive on the poorly drained areas.
The unsatisfactory meliorative condition of irrigated soils in the prevailing part of the territory is largely due to significant shortcomings in the operation of irrigation, especially collector-drainage network. Technical imperfection of irrigation and drainage systems, irregular and uncontrolled water use causes huge overuse of irrigation canals. The salt balance on non-drained and insufficiently drained lands changes towards salt accumulation, which is associated with evaporation of saline groundwater close to the surface.
Irrigated territories of Mirzacho'l in Sirdaryo region are salinized in different degree with weak, middle, in some places strong salinization. Ameliorative well-being of irrigated lands in irrigated part of investigated territory is unstable, i.e. in these lands groundwater remains moderately (3-10 g/l) and strongly (> 10 g/l) mineralized.
References:
1. Адылов А. А. Инженерно-геологические исследования. - Т., ТГТУ 2016. - 156 с.
2. Гофурова Л. А., и др. Деградация почв. Учебное пособие. - Ташкент. НУ, 2012. - 218 с.
3. Березин П. М. Физическая деградация почв / П. М. Березин, И. И. Гудима // Деградация и охрана почв. - М.: Изд-во МГУ 2002. - С. 168-196.
4. Ахмедов А. У., Парпиев Г. Т. Орошаемые почвы Сырдарьинской и Джизакской областей. - Ташкент, ФАН, 2005. - С. 122-157.
5. Ахмедов А. У, Гофурова Л. А. Оценка современного почвенно-мелиоративного состояния Голодной степи // Владимирский земледелец. Владимир. 2019. - № 4. - С. 7-12.
6. Деградация и охрана почв / Под ред. Г. В. Добровольского. - М.: Изд-во МГУ, 2002. -654 с.
7. Закиров М. М., Худойбердиев Т. М., Агзамова А. И., Бегимкулов Д. К., Очилов Г. Э. Особенности изменчивости гидрогеохимического режима для оценке современного мелиоративного состояния грунтовых условий голодной степи / Конференция____- Таш ГТУ 2020.
8. Затенацкая Н. П. Закономерности формирования свойств засоленных глин. - М., Наука, 1985. -145 с.
9. Ковда В. А. Проблемы опустынивания и засоления почв аридных регионов мира - М.: Наука, 2008. - 415 с.
10. Ломтадзе В. Д. Инженерная геология. Специальная инженерная геология. - Л., Недра, 1984. - 511 с.
11. Лопатовская О. Г. Мелиорация почв. Засоленные почвы: учеб. пособие / - Иркутск: Изд-во Иркут. гос. ун-та, 2010. - 101 с.
12. Новаковський Л. Я. Консервация деградованных и малопродуктивных земель Украины / Л. Я. Но-ваковський, А. П. Канаш, В. О. Леонець // Вестник аграрной науки. 2000. - № 11. - С. 54-59.
13. Сергеев Е. М. Грунтоведение. - М., МГУ 1983. - 389 с.
14. Теоретические основы инженерной геологии. Физико-химические основы. Под ред. Е. М. Сергеева. - М., Недра, 1985. - 288 с.
15. Пулатов К. П. Закономерности формирования, распространения и региональный прогноз проса-дочной и послепросадочной деформации лессовых пород на вновь орошаемых территориях аридной зоны. На прим. Юго-Западного Узбекистана. Автореф. диссертация на соискании доктора геол.-минерал.наук. - Ташкент, 1991. - 42 с.
16. Хасанов А. С. Условия формирования химического состава подземных вод Голодной степи. - Ташкент, Фан, 1968. - 95 с.
