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Objective and technical fields:
Definition of drainage effluent use efficiency for irrigation in the places of its origin and drainage outflow management in order to decrease it; irrigated lands water supply improvement by means of groundwater pumping rate for irrigation management.
Scientific and technical approach:
Determination of groundwater formation conformities and development of technology of their maximum utilization for irrigation by means of vertical drainage system operation arrangement.
Meaning of investigations: development of system of measures on irrigated lands productivity increase and their water supply improvement.
Environment characteristics:
Pilot plot is located within alluvial valley and zones of depositions removal forming high plain with slope 0.002-0.005. Cover layer is represented by heavy and middle loam, which transits to sandy loam, sand and clay and underlaid by pebble-gravel depositions. Cover thickness varies from north-east to south-west from 0.8-2.0 m up to 20 m. Gravel - pebble depositions thickness is 10-30 m. Unpermeable layer is clay with gipsum. Loam permeability coefficient is 0.2 -0.5 m/day, sandy loam - 0.5-1.2 m/day, sand - 1.0-2.5 m/day, gravel-pebble from 20-50 to 80-150, which depends on filling material. Transmissivity coefficient is 300-200 m2/day. Water specific yield coefficient for loam is 0.1 -0.12, sandy loam and sand - 0.12-0.15, pebbles - 0.13 - 0.18. Groundwater salinity is from 1.8 -3.0 to 0.5-1.5 g/l. Chemical composition is hydracarboneous - calcium, sodium-absorbing coefficient (SAR) of drainage effluent varies in wide range from 2 to 6. To the end of growing period it can increase up to 10. When irrigated lands border with uncultivated ones groundwater inflow to irrigated lands is strengthened.
Soils are represented by heavy and middle loam. Permeability coefficient varies within broad range from 0.2 to 0.5 m/day. Most part of territory (60-65 %) is non-salinizated. On the one -third of the scheme spot salinization is noticed. About 5-10 % of lands are middle salinizated. Salinization type is chloride-sulfate.
Parameters of Pilot Projects and Technical Solutions:
Irrigated area is 12.000 ha (8.500 ha net). Land use efficiency is 0.7. State farm occupation is cotton growing and cattle breeding. Water supply is performed by distributors R - 23,24,25,26,28. Canal length is 80-100 km. Head water-intake discharge is 2.-8 cu.m./sec. System efficiency is 0.75. Collectors’ density is 3 -5 m/ha. Sixty vertical drainage wells have depth 25 -35 m. Screen length is 15 -20 m. Well discharge is 20 -45 l/sec. against expected discharge 50 -60 l/sec.
Methodology:
Field observation of water and salt movement, water-salt balance contents measurement for unsaturated zone, groundwater and irrigated lands as a whole. On five sites, situated in different hydrological conditions, observations were carried out on soil water-salt regime and groundwater under irrigation by drainage effluent. Main distributors were equipped by means of accounting and irrigated areas by observation network. Methodologically task has been solved by multicriterial analysis of field investigations.
Results:
State farm was established at the beginning of 30-es at expense of Ikan-Su river flow. Before the Aris-Turkestan canal construction reclamation situation was good. Crop yield depended on the Ikan-Su river water supply and varied in broad range: cotton 1.0 - 2.0 t/ha, grain 1.5 -3.0 t/ha, corn 2.0 - 4.0 t/ha. After canal completion new lands were developed. Groundwater level increased and this led to land waterlogging and secondary salinization. After drainage system construction over area of 800 ha with specific extent 35 -40 m/ha reclamation situation was improved. Within dry years (1974 -1975) water consumption use deficit was 30 % and yield was sharply decreased. That is why decision about vertical drainage construction was adopted. Till 1976 VDS of 60 wells was completed, which gave opportunity:
- to increase irrigated land water supply at expense of drainage water maximum use;
- to regulate groundwater level, water and salt movement;
- to manage unsaturated zone soils and groundwater desalinization at expense of groundwater level lowering rate change;
- to create reserve volume for accumulation of irrigation water, formating within the irrigation network;
- to eliminate spotted soil salinization and provide reclamation background regularity within irrigated area;
- to provide negative salt balance formation within unsaturated zone all over the irrigated area at expense of groundwater overflow from cover sediments to the aquifer.
After VDS completion salinizated soils area was cut down from 2.000 to 600 ha, groundwater salinity was less than 2 g/l over 80 -85 % of area. Pumped water volume varied within 15 -17 mln/cu.m (30 % of water intake) for groundwater level decrease from 1 -2 to 3 -4 m. During 25 -30 years soil water-physical properties changed negligibly: volumetric mass growth was 0.06 - 0.08 g/cu.m soil -absorbing complex was improving at expense of calcium stability (60-65 %) and certain reduction of potassium content (5%). Within 1986 -1990 water supply plus drainage outflow plus precipitation (8.0 -9.5 th. cu. m/ha) to total evaporation (8.0 -8.5 th.cu.m/ha) ratio was 0.94 -1.18. Drainage water use for irrigation permitted to improve reclamation situation and stabilize cotton yield at the level of 2.4 - 2.6 t/ha under its share in crop rotation 45-50 %. Main result of investigation is irrigated lands water supply increase, reclamation situation improvement (60 -70 % irrigated lands became non-salinizated), yield growth 10 -20 %. Economic efficiency of in -farm drainage water use for irrigation is 150- 20 rouble/ha. Since the beginning 1990 the gap between pumping and power equipment and agricultural products price started to grow, which led to VDS degradation and further conservation. (B+Oc): (T+N) ratio reduced to 0.75 -0.96 and water - salt balance became positive.
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