HYDRAULIC EFFICIENCY OF UNLINED AND LINED OPEN CHANNELS

ABSTRACT

Currently, the problem of water shortage is getting worse every day. Sudden changes in atmospheric air also affect water reserves. With the world population expected to reach 10⁹ by 2050, the world's water consumption will exceed 3.7 trillion cubic meters. In the last 15 years, the annual volume of water per capita in Uzbekistan has decreased from 3048 m³ to 1589 m³. Based on these problems, the article made a theoretical analysis of the work to be done on water loss and its prevention. Empirical and analytical methods of determining water loss due to filtration in open riverchanels were studied. Analyzes of hydraulic efficiency, service life and construction costs of covered open channels, types of covering material were presented. The coatings with the least water filtration, the longest service life, and the most hydraulically efficient properties were compared. Based on the obtained results, conclusions are drawn on the convenient construction of uncoated and coated open watercourses.

АННОТАЦИЯ

В настоящее время проблема нехватки воды обостряется с каждым днем. Резкие изменения атмосферного воздуха также влияют на запасы воды. Ожидается, что к 2050 году численность населения мира достигнет 10⁹ человек, а потребление воды в мире превысит 3,7 триллиона кубических метров. За последние 15 лет годовой объем воды на душу населения в Узбекистане снизился с 3048 м³ до 1589 м³. На основании этих проблем в статье сделан теоретический анализ предстоящих работ по устранению и предотвращению потерь воды. Изучены эмпирические и аналитические методы определения потерь воды за счет фильтрации в открытых руслах рек. Приведены анализы гидравлической эффективности, срока службы и стоимости строительства крытых и открытых каналов, видов укрывного материала. Сравнивались покрытия с наименьшей фильтрацией воды, наибольшим сроком службы и наиболее гидравлически эффективными свойствами. На основании полученных результатов сделаны выводы об удобном строительстве открытых водотоков без покрытия и с покрытием.

Keywords: Filtration, coating, open chanel, hydraulic efficiency, Geomembrane.

Ключевые слова: Фильтрация, покрытие, открытые каналы, гидравлическая эффективность, геомембрана.

Introduction. Today, the increasing water shortage in the world community and the development of new directions for solving water management problems are considered urgent issues. Many scientists of the world and our country have carried out theoretical and practical work on the issues of calculating and reducing the loss of water as a result of the filtration process [1,2]. As a result of the conducted research, theoretical and practical solutions of new directions of calculating the filtration process and solving problems of its reduction are being further developed [3,4].

Water loss in open water structures occurs as a result of evaporation into the atmosphere, seepage into the ground, and filtration in hydrotechnical structures in open basins. The loss of water through filtration in hydrotechnical structures in open valleys is insignificant and is usually not taken into account in calculations. Evaporative water loss is measured by the layer of water evaporated from the entire area of the water window in open water structures. Depending on climatic conditions, these losses range from 300 to 800 mm per year. The main water loss in open floodplains is caused by seepage into the ground, which can lead to a loss of up to 50 % of water [6,10].

Concrete, reinforced concrete, asphalt-concrete, soil-sheeting, concrete-sheeting, bitumen and geomembranes have been widely used in the past 30-35 years to combat filtration in open watersheds [11,12].

Reducing the loss of water due to filtration in open water structures is an important current issue of the world and our country's water management today.

In the article, the loss of water as a result of filtration in open valleys is calculated, and it is aimed to solve the problems of water shortage, soil salinity, swamping by reducing filtration.

The main tasks of the work are to determine the hydraulic efficiency of coated and uncoated streams to reduce filtration, to study the types of coating, and to choose the most convenient coating material by comparison.

Research object and method. In order to study the effective operation of open channels, we will consider the advantages and disadvantages of open channels without coating and with different types of coating (Fig. 1).

Figure 1. open chanel without coating and with various coatings

The hydraulic efficiency of open watercourses is an important indicator, which takes into account unnecessary water losses due to filtration during transportation. The hydraulic efficiency of open watercourses is said to ensure minimum water loss and maximum water permeability during water transport. We used various empirical formulas to determine hydraulic efficiency.

We used N. Deskelesky's formula to express the hydraulic efficiency index -  of open riverchanels with two parameters:

                                                                     (1)

here,  - the transport efficiency parameter describing the technical condition and permeability of the open riverchanel,  - the parameters of water distribution and use [3,4].

M.A. that the indicator of hydraulic efficiency of open riverchanels is the ratio of the average speed of water movement to the speed in the most hydraulically favorable cross section. Having studied the researches of Latishenkov, we determined:

                                                         (2)

The limit value of the hydraulically most favorable section was determined by the empirical formula proposed by R.R. Chugaev [7,8,]:

                                               (3)

here, m- slope coefficient of the trapezoidal channel.

Continuous water losses in an open channel with soil were determined using the following formula for a trapezoidal open channel [9, 10, 12]:

                                                            (4)

Results of research. Based on the research conducted using the formulas given above, it was found that the loss of water to the ground as a result of natural filtration in uncoated open channels increases depending on the water consumption and the length of the open channel, and leads to a decrease in the hydraulic efficiency of the open channel (Fig. 2 ).

Figure 2. Loss of water per 1 km as a result of natural filtration in open valleys, %

The hydraulic performance indicators of reinforced concrete, asphalt concrete, bitumen and geosynthetic materials used to prevent water loss were calculated (Fig.3).

Figure 3. Hydraulic efficiency of open chanels with different coatings, %. 1. Geomembrane; 2. Polymer sheeting; 3. Concrete and reinforced concrete; 4. Asphalt concrete; 5. Bitumen

When choosing the type of coating, we compared the coating materials in terms of the efficiency of use and prevention of water loss during transportation, and the results of the comparison are presented (Fig. 4).

Figure 4. Yearly changes in the hydraulic efficiency of open waterchanels with different coatings; 1. Geomembrane; 2. Polymer sheeting; 3. Concrete and reinforced concrete; 4. Asphalt-concrete; 5. Bitumen

According to the results of the comparison, when choosing a covering material for open watercourses, we found that the service life of Geomembrane is longer than other types of covering, but the high project and construction costs reduce its economic efficiency. the importance of preparation was determined.

Conclusion. Through the conducted research, it was found that the filtration index increases as the water consumption increases in open basins. The fact that water loss due to filtration can be reduced by improving the physical and technical properties of the local soil in the open riverchanel and by covering the bottom and side walls of the open riverchanel with anti-filtration coatings was studied through hydraulic calculations. Calculations have shown that coatings reduce water loss, improve water quality, and increase irrigation efficiency and service life. Taking into account that the coatings are made of different materials, we determined and compared their hydraulic efficiency. Covering open watercourses with coatings requires a number of additional costs from a technical and economic point of view, therefore it is advisable to choose a coating with the least water loss and the longest service life. Also, coatings can be different and their selection is made taking into account various factors, including potential benefits, technical economic costs and environmental impact. According to the results of the study, it was necessary to consider new structural, technical and technological solutions for the design and construction of pavements. The use of such solutions increases the hydraulic efficiency of anti-filtration coatings, ensures waterproofing, increases reliability and makes it possible to use local raw materials.

We recommend the use of geomembrane coatings based on local raw materials in order to reduce the economic costs related to the design and construction of the compared coatings, and to increase the hydraulic efficiency.

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