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Objective and technical fields:
Definition of vertical drainage efficiency under artesian water inflow. Soil water-salt regime management and old developed lands productivity improvement on background of conjunctive operation of vertical and horizontal drainage.
Scientific and technical approach:
Prevention of soil salinization and water-logging and irrigated land productivity improvement is based on drainability strengthening of the territory with perfect type of drainage.
Development of optimal soil reclamation regime and drainage operation providing water and labour saving per production unit.
Environment characteristics:
Climate is sharply continental. Average annual temperature is 13.6 oC, in July 29.5 oC, maximum temperature is 44 oC, minimum is –24 oC.
Annual precipitation is 97-124 mm, moistening coefficient is 0.084, hydrotermic coefficient is 0.107, aridity coefficient is 16.5.
Relief: Slightly corrugated plain.
Lithology: Loam (6-18 m), gravel-pebble-sand (40-60 m). Cover loam’s permeability coefficient is 0.17-1.0 m/day; vertical permeability coefficient is 0.22-0.48 m/day. Gravel-sand layer permeability coefficient is 12.98-18.5 m/day.
Soils: Sandy loam and middle loam. Average weighted full field moisture capacity is 21.8 %; water specific yield is 0.19; solid phase density is 2.6 g/cu.cm; density is 1.43 g/cu.cm; porosity is 0.48.
Artesian water head is higher to compare with groundwater level on 0.2-0.6 m. Groundwater average salinity is 3.0 g/l (60.2 %), 3-5 g/l (35.8 %) and 5-10 g/l (3.96 %).
Chemical composition is sulphate-chloride. Artesian water is fresh (0.4-0.8 g/l).
Soils are mainly non-salinizated (92.7 %), slightly and middle salinizated (7.3 %). Main crops are cotton (60-65 %), alfalfa (5-10 %), vegetables, corn for silage
Parameters of Pilot Projects and Technical Solutions:
Pilot site's area is 565 ha. There are 5 vertical drainage wells with depth of 32.5-48 m, diameter - 900 mm, screen length - 11.85-23.49 m, porosity - 20 %. Well's discharge is 10-40 l/sec, specific yield is 3-8 l/sec/m. Water supply is executed through mains Gambay, Dekhkanabad and Kum with discharge 1-1.5 cu.m/sec.
Drainage network - open drains and collectors. Distance between drains is 200-250 m, depth is 2.5-3.0 m, depth of collectors is 3.0-3.5 m. Total extent of collector-drainage network is 11.65 km including 1.8 km of drains. Drain's density is 20.3 m/ha, within the control site - 45 m/ha. Drains are covered with vegetation and have low efficiency.
Methodology:
Field investigations of vertical and horizontal drainage operation, soil water-salt regime change, ground and artesian water regime and crops growing process.
Site was equipped by piesometers, water-meters and devices for observations on water-salt balance elements.
Results:
Five vertical drains were operated during 1970-1980 with average monthly discharge 30 l/sec (non-growing period) and 158 l/sec (growing season). All pumped water was used for irrigation (53.9-414.41 th.cu.m per month or 3266-5012 th.cu.m per year). Operation efficiency was 0.41-0.64. Electric energy expense was 0.13-0.28 kWt for 1 cu.m of water.
Average drainage modulus (1970-1980) was from 0.054 (April, May, October, December) to 0.245 (March, April, July, September) l/sec/ha.
Groundwater level during growing season was 1.85-2.36, in autumn-winter time it was 1.63-2.74 m. Under vertical drainage operation artesian head gradually decreased from 0.6-0.7 m during autumn-winter period to 0.1-0.4 m during growing season. Drainage modulus of open drains within of vertical drains zone of influence are 0.08-1.40 l/sec/km and outside of this zone - 0.05-2.74 l/sec/km. Groundwater level was on depth: more than 3 m (7.2-24.2 % of area); 2-3 m (50-74 %); 1-1.5 m (9.7 %). Thus necessary area drainability was established by vertical drainage system operation regulation. Within pilot site cotton was irrigated 5-6 times by norm 870-2090 cu.m/ha. Irrigation was performed under moisture content 56-66 %.
Irrigation interval was 16-28 days. Corn was irrigated 3-4 times by norm 800-1100 cu.m/ha; irrigation norm was 3000-4000 cu.m/ha during growing season.
Irrigation norm for 1 ha was 7700-8349 cu.m/ha, including 6255-7039 cu.m/ha during growing period. Overflow from unsaturated zone to groundwater was 566-2044 cu.m/ha.
Groundwater stock was as follow (cu.m/ha): 1972 - 160; 1973 - 280; 1974 - 20; 1975 - 40.
Total drainage outflow was 5-7.75 th.cu.m/ha or 0.155-0.217 l/sec/ha. Open drains' share was 22.2-28.7 %. Total water stock changed from 592 to 968 cu.m/ha.
Irrigation water salinity was 0.5-1.0 g/l. Chemical composition was sulphate-chloride-hydrocarbonate-calcium-sodium.
Pumped water salinity varied from 0.63 to 1.54 g/l. Chemical composition was sulphate-hydrocarbonate-magnesium-sodium.
Groundwater was fresh (0.4-0.8 g/l).
Soils are slightly salinizated on 41 ha (7.3 %), non-salinizated on 524 ha (92.7 %).
During two years (1970-1972) water duty was 7700-8349 cu.m/ha (6445-7039 cu.m/ha during growing season) salt removal from 1 m-layer was 3.75 t/ha, from 3 m-layer - 46.5 t/ha.
Annual drainage outflow to water duty ratio is 0.62-0.97 (0.42-0.67 within growing season and 1.05-2.47 in autumn-winter period). Annual water duty to total evapotranspiration ratio (B:ET) during 1970-1973 was 0.98-1.0 and 1.06-1.31 (with regard to precipitation).
Cotton yield (average over site) increased from 2.79 (1970) to 3.5 (1975) t/ha.
Water expense for 1 t cotton decreased from 2877 to 2220 cu.m.
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