Summary of research project: |
Objective and technical fields:
Elaboration of measures on reduction of water consumption and diversion norms through rational use of surface and ground waters for irrigation, optimization of the operational regime of vertical drainage wells, increase of participation of ground waters in sub-irrigation, reduction of water expenditures for physical evaporation.
Scientific and technical approach:
Raising the efficiency of irrigated lands and their water supply on the basis of the rational use of ground waters for irrigation and sub-irrigation.
Environment characteristics:
Environmental characteristics of “Ikan” cotton state farm are typical for the most part of Arys-Turkestan irrigation scheme. Climate is sharply continental. Average annual temperature is 13-15oC, maximum temperature is 40-45oC, minimum temperature is 20-25oC. Average ten-days period temperature above 14oC remains for 6 months since the middle of April till the middle of October. Evaporativity is 1200-1400 mm. Total precipitation is 150-250 mm, average annual precipitation is 195 mm. Relative air humidity is 50-60%, it rises up to 85% in winter and falls down to 20% in summer. The territory of the cotton state farm is located on a foot-hill plain. Relief is slightly corrugated. Inclination is 0,0002-0,0006. Soils are made of a multilayer quaternary deposit. The upper layer is made of heavy and middle loams, than of sandy and condensed loams. They depth varies from 0,8 m to 2,0 m in the northern-eastern part of the scheme, it gradually rises in the south-west direction reaching 20 m near the borders with dry-farming lands. Gravel-shingle proluvial-alluvial deposit is the deepest, its depth varies from 10 to 30 m within the irrigation scheme. Gravel-shingle deposit has mostly a loam - sandy loam filler and separate lens-shaped sand interlayers. Sections are found where gravel-shingle deposit is divided into several layers by lens-shaped clay 3-5 m deep. Absence of a solid clay interlayer guarantees hydraulic connection between water-bearing layers of a quaternary deposit.
Negative confining bed is a tertiary-cretaceous deposit. It includes red-colored gypsum-bearing clays with of conglomerate, limestone and sandstone interlayers. The quaternary deposit is made of highly complicated alternation of layers with different permeability properties. Coefficient of permeability of loam is 0,2-0,5 m/day, of sandy loam is 0,5-1,2 m/day, of sand is 1,0-2,5 m/day. Coefficient of permeability of the gravel-shingle deposit is 20-50 m/day (with a loam filler), 40-80 m/day (with a sandy loam filler), 80-150 m/day (with a sand filler). Coefficient of hydraulic conductivity is 300-2000 m2/day. Specific yield coefficient is 0,1-0,12 for loam, 0,12-0,15 for sand and sandy loam, 0,13-0,18 for gravel-shingle. Ground water salinity of the cover deposit is mostly 1,0-3,0 g/l, sometimes it is 0,5-1,0 g/l or 3-5 g/l; ground water salinity of the gravel-shingle deposit is 0,5-1,5 g/l, sometimes it is 1,5-2,0 g/l. The type of salinity is hydrocarbonate-calcium or hydrocarbonate-sulphate, calcium-magnesium-sodium. «Adjusted» sodium-adsorption ratio (SAR) varies widely: it is 2,0-14,0 for ground waters and 2-9 for drainage waters. In the first case SAR of ground waters does not exceed permissible limits on the third part of the irrigated territory, in the second case - less than 20% of vertical drainage wells abstract waters which have SAR exceeding permissible limits. Soils are heavy and middle loam. Coefficient of permeability is 0,2-0,5 m/day. Area of non-salinized soils is 65-70% of the irrigated territory. Spotty salinity is on 20-25%, middle and slight salinity if on 5-10% of the irrigated territory. The type of salinity is chloride-sulphate.
Parameters of Pilot Projects and Technical Solutions:
Gross irrigated area is 12 000 ha, net irrigated area is 8 500 ha, efficiency of land use is 0,7. The farm is specialized on cotton growing and cattle breeding. Water is supplied by distributors P-23, P-24, P-25, P-26, P-28. The length of simultaneously operating canals is 80-100 km, on the whole it is app. 200 km. A third of canals has a seepage-preventing lining. Efficiency of the system is 0,75. Number of vertical drainage wells is 60. Discharge of wells is 20-45 l/sec, designed discharge is 50-60 l/sec.
Methodology:
Formation of shallow and deep ground waters; water and salt movement; measurements of water-salt balance elements of an aeration zone; shallow and deep ground waters used for sub-irrigation and irrigation with pumping by vertical drainage wells were studied Main distributors in the farm were provided with water metering equipment, irrigated lands were equipped with an observation network. The problem was solved on the basis of the systems analysis of the results and use of the data gathered by operational water and agricultural institutions.
Results:
The cotton state farm was established at the end of the thirties on the basis of use of Ikan-Su river flow. Yield of grown crops depended on the volume of water in the Ikan-Su river and varied widely: cotton - 1-2 t/ha, cereals - 1,5-3 t/ha, maize - 2-4 t/ha. After putting into operation of Arys-Turkestan Canal yield of the grown crops began rising. At the end of the sixties and at the beginning of the seventies (1969-1971) yield became stable at the level of 2,2-2,4 t/ha for cotton, 2,5-3 t/ha for cereals, 4-5 t/ha for maize. Later on the irrigated area in Arys-Turkestan Canal zone increased up to 65 000 ha (design 54 000 ha). In dry and hot years deficit of irrigation water reached 30% and yield decreased by up to 2 times especially for second crops. It precipitated construction of vertical drainage wells to cover the deficit in irrigation water and improve the reclamation situation on irrigated lands. On the lands of «Ikan» cotton state farm the system of 60 vertical drainage wells was built which allowed:
- to control the rate of soil desalinization and depletion rate of ground and head waters;
- to reduce water consumption norms through regulation of the regime of shallow ground waters and degree of their participation in sub-irrigation at various stages of crop development;
- to increase sufficiency of water supply of irrigated lands through use of drainage waters for irrigation and control of deep ground waters;
- to create negative salt balance on the meliorated territory through strengthening of ground water overflow from cover loam to a pumped water-bearing layer.
As a result of the operation of vertical drainage system (the construction began in 1974 and finished in 1986) the area of saline lands decreased from 2000 ha down to 600 ha (1989), salinity of ground waters on the most part of the territory (app. 90%) decreased down to 2 g/l. Salinity of drainage waters (comparing with the first month of pumping) increased by 0,2-0,5 g/l on the lands with no salinity and by 0,5-1,0 g/l on saline lands. Maximum salinization of drainage waters was in autumn when overflow of shallow ground waters from cover loams to a pumped layer and inflow of deep ground waters from adjoining territories strengthened. In the period of the vertical drainage operation (1988-1992) salt regime of ground and drainage waters became stable. With water abstraction equal to 55-65 mln. m3 50% of irrigation water or 24-30 mln. m3 were lost for filtration (from the irrigation network and irrigated fields). If inflow and outflow of deep ground waters are equal they should be considered as operational reserves which could be used for sub-irrigation and irrigation though their pumping by vertical drainage. For reduction of operational expenditures operational regime of vertical drainage wells were synchronized with the water supply and irrigation regimes. At the end of April and at the beginning of May vertical drainage wells located in the south-west part of the irrigation scheme started operation where the depth of water table was 1,0-1,5 m. At the end of May and at the beginning of June vertical drainage wells began operation in the middle section of the irrigation scheme where the depth of water table was 1,5-2,0 m. In July the rest of vertical drainage wells began operation to cover irrigation water deficit. In highly water supplied years 1-13, in dry years 15-17 mln. m3 were pumped.
The number of operating wells was determined with due regard for the water sufficiency of the year and the degree of possible participation of ground waters in sub-irrigation. Average annual volume of pumped ground waters for irrigation guaranteeing stabilization of operational reserves of ground waters and reclamation improvement on irrigated lands should not exceed 10-15 mln. m3. The possibility of this solution is corroborated by the salt balance which shows that 30-35 th. t of salt were brought in to the irrigation scheme with precipitation, ground and irrigation waters; and 25-30 th. t of salt were removed with outflow of ground waters and drainage outflow. Difference of 5 th. t corresponds to 0,4 t/ha. With the existing level of an aeration zone salinization equal to app. 0,12% (permissible limit is 0,3%) and ground waters equal to 1-3 g/l, secondary salinization will not happen (for the next decades) if the existing principle of water and salt exchange between an aeration zone and shallow ground waters, and between shallow and deep ground waters remains. If less than 10 mln. m3 of deep ground waters are pumped, salt will be mostly in the topsoil, therefore soil efficiency will decrease even with low salinization of lower layers of an aeration zone (up to 0,2%) and ground waters (less than 3 g/l).
Depending on the sufficiency of water supply of the year, depth of the cover deposit and regime of shallow ground waters, irrigation norms varied within the following limits: 4,0-8,5 th. m3/ha for cotton, 4,5-10 th. m3/ha for lucerne, 3-7,5 th. m3/ha for maize, 2,0-4,5 th. m3/ha for winter wheat. Ratio of the duty of water and precipitation (8,0-9,0 th. m3/ha) to the total evaporation (8,0-8,5 th. m3/ha) varied from 0,94 to 1,13. The negative salt balance was formed by overflow of waters from the cover deposit to a pumped layer and diversion of drainage waters (6-8% of the duty of water) out of the borders of the irrigation scheme. In the following years (1995-1997) the vertical drainage system stopped operation, therefore water-salt balance formed with growing salt accumulation due to salt inflow with irrigation waters and subsurface flow from the higher territories. For this period drainage outflow (of collectors, surface drains) rose up to 10-12% of the water abstraction.
The main result of the researches was improvement of the reclamation situation and stable yield which is high or the main crops of this zone (2,4-2,6 t/ha of cotton, 2-2,5 t/ha of cereals, 8-10 t/ha of lucerne) with the reduction of water abstraction from 8-10 th. m3/ha down to 6,5-7,5 th. m3/ha. Annual water consumption norm was reduced through synchronization of the operational regime of the vertical drainage system. Economic efficiency of determination of water consumption and diversion norms was 200-250 ruble/ha on the net income in 1983-1985 prices.
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