Summary of research project: |
Objective and technical fields:
Determination of hydrogeological conditions and causes of unfavorable reclamation state of irrigated lands through hydrogeological surveys as well as assessment of vertical and horizontal drainage efficiency, development of recommendations on improvement of reclamation state of irrigated lands. Determination of reclamation efficiency and work capacity of different drainage types and structures. Management by soil water-salt regime.
Scientific and technical approach:
Salinity control and soil and water productivity increase, which are based on drainability and leaching strengthening. Importance of the study consists in scientifically grounded measures on improvement of water use, management by soil water-salt regime under conditions of fresh river water shortage. Development and justification of drainage types and structures in order to use return waters in irrigation.
Environment characteristics:
Environment conditions of the pilot plot are typical for the most part of Isfara-Lyakkan valley. The plot is located in a zone of salt accumulation, in the middle right-bank part of Isfara river. Isfara-Lyakkan valley is an inter-mountainous hollow. Relief is smooth, height above sea level is 800-900 m. The climate is sharply continental, average annual precipitation is 146 mm, evaporativity is 1200 mm/year. It is typical for desert zone. Average annual temperature is 12,5oC. Lithology: there are clays, their thickness is 3-9,5 m, followed by detritus, pebbles and sands with total thickness equal to 30 m. In upper layer loam and sandy loam with clay interlayers prevails, thickness is 0,5-3,7 m.
Ground waters are bedded at a depth of 1-2 m, piezometric head in lower layer is 0,3-0,6 m higher than land surface, i.e. difference of piezometric head and ground water level accounts for h = 2,1-3,1 m. During growing period ground water level rises to 0,5-1,0 m. In all wells there is free discharge. Rate of free discharge at a well depth of 15 m is 1l/sec, specific discharge is 1,5 l/sec/m. Permeability coefficient of top soil is 0,1 m/day. Permeability coefficient of lower layer is 15 m/day. Conductivity is T=500 m2/day. Average gradient of sub-artesian flow to the plot is i=0,01. Width of flow front within the plot is W=520 m. Difference of piezometric head and ground water level under high position of latter one is h = 1 m. Discharge of ground waters inflowed to the plot is 2600 m3/day. Discharge of rising overflow from lower sub-artesian layer to upper layer is g = 125 m3/day/ha, to the whole territory of 18 ha is g = 2250 m3/day.
Soils of the plot are slightly- and middle- salinized as a result of ground water evaporation. Content of chlorine ion is 0,08-0,26%, toxic sulphate ion is 0,46% by weight. Weighted average salinity of ground waters varies from 1,2 to 5,0 g/l. Salinity of artesian waters is 1,2-3,0 g/l.
Parameters of Pilot Projects and Technical Solutions:
Total area of the plot is 20 ha. Length of subsurface horizontal drainage is 1060 m. Drain spacing is 120 m. Depth of drain is 2,2-2,4 m. Pipes are asbestos-cement. Filters are sandy-gravel. Observations of ground water regime were conducted by 14 wells. There are 7 wells for observation of piezometric head of artesian horizon. Depth of such wells is 20-85 m. There are 11 relief wells, their depth is 15,0 m, drilling diameter is 500 mm.
Methodology:
Objective of the study is to approbate under field conditions the technical solutions made on structures and parameters of drainage and the other reclamation works through control of environmental-reclamation efficiency of implemented measures. Field studies and observations of the ground water regime, hudrogeological studies conducted in irrigation and drainage networks for quantitative assessment of water supply and drainage outflow. Regular observations of soil water-salt and ground water regime, all the elements of water-salt balance in connection with irrigation and leaching scheduling. The plot was equipped with water-salt meters and piezometric network to keep regular observations. Systems analysis of the results of observations and studies by graph-analytic and statistics methods while applying mathematical and analogous modeling was used.
Results:
There is difficult reclamation state of irrigated lands on 19200 ha. Area of salinized lands is 3,7 th.ha. There are 3,2 th.ha, which are in unsatisfactory condition, including 2,5 th.ha of water-logged lands. This caused death and depression of stone fruit gardens. The Isfara-Lyakkan valley is characterized by low natural drainability. There is no flow in some areas, particularly in zones of backwater within collectors, and ground waters are recharged from artesian horizons. 1230 ha of irrigated lands are under secondary salinization. The soils are middle- and heavy- salinized. 2700 ha are slightly salinized. Artesian water spreads on 1650 ha, the head over land surface is 0,3-4,0 m. Isfara irrigation system is lowly supplied by water and has low efficiency (0,52-0,63). Shortage of water in Isfarinka river is compensated by use of return waters (36-42 mln.m3/year or 25% of river intake), which irrigate 17% of lands. The largest share of return waters (80-94% of water supply) is used in Lyakkan part for irrigation of most unfavorable lands. Water supply in farms, depending on water availability, accounted for 11,2-14,6 th.m3/ha or, on the average, 12,5 th.m3/ha. The highest figures of water supply (about 17,5 th.m3/ha) are in Lyakkan part of the valley. Total water intake in the valley is 195 mln.m3/year or, on the average, 19,1 m3/ha (gross). The main inlets are collectors K-1 and K-2. There are 103 vertical drainage wells in the valley. 46-69% of the wells are operated. From 472 th.t of salts entering the valley 395 th.t or 84% come from Batken district of Kyrgyz Republic. 150 th.t or 32% of salts enter with ground waters. Analysis of general salt balance shows, that measures implemented in the valley do not influence the reclamation state of lands. In order to improve reclamation state of the Isfara-Lyakkan valley a set of measures on application of water saving irrigation technologies, change of crop patterns and capture of underground flow from Paran natural landmark is needed for reduction of salts entering from Kyrgy Republic. To leach the salinized lands, quantity of which increases due to salts entering from Batken district, it is necessary to use fresh water from Isfarinka river or from Tocktogul reservoir in the amount of 35,2 mln. m3/year. The study shows, that construction of drainage systems will promote improvement of reclamation state in combination with other measures on reconstruction and reduction of return water share. Combined drainage structure was studied in the pilot plot. Result of the study show, that combined drainage can be constructed in the Isfara-Lyakkan valley on 1650 ha. The distance between reinforcing wells is 60 m, depth is 15-30 m. It is determined, that drain spacing increases by 2-4 times under combined drainage use. Besides, it is recommended to construct systematic horizontal drainage. Depth of drain is 3,0-3,5 m. Drain spacing depends on geofiltration planning of the territory. Drainage norm under combined and horizontal subsurface drainage is 1,8-2,2 m.
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