Summary of research project: |
Objective and technical fields:
Determination of hydro-geological conditions and justification of measures on improvement of the environmental-reclamation situation in the Isfara-Lyakkan valley. Choosing and calculation of the parameters of drainage structures and types, development of recommendations on improvement of environmental-reclamation state of irrigated lands.
Scientific and technical approach:
Salinity control and improvement of available water supply, which are based on drainability strengthening. Importance of the study consists in scientifically grounded measures on improvement of water use, management by soil water-salt regime and development of types and structures of drainage.
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 headand ground water level under high position of latter one is h = 1 m. Discharge of ground waters flowed to the plot is 2600 m3/day. Discharge of rising inflow 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. Length of a surface drain is 750 m. Length of irrigation network of the plot is 540 m. Efficiency of the network is 0,52-0,63. Actual water supply is 14500-1600 m3/ha. Salinity of irrigation water is 1-2 g/l. 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:
Results of the studies showed, that existing irrigation system, irrigation technique, methods and drainage network constructed in 1980-1990 did not improved environmental-reclamation state of irrigated lands. Unsatisfactory operation of collector-drainage network is connected with its shallow depth (2-2,2 m) and backwater in collector-inlets caused by intake of return waters for irrigation, incorrect placing of the network according to direction of the main ground water slope and lack of capture drains or their placing at an angle to the stream. The other reason of low efficiency is connected with large infiltration recharge by inflow from upstream lands and artesian horizons, which is accounted for 1,5-2,5 l/sec/ha. The observations of drainage water discharge were conducted after construction of subsurface drainage in the pilot plot. Inflow per 1 km of subsurface drain accounted for 23,3 l/sec, drainage modulus was 2,49 l/sec/ha (0,022 m/day), including 0,97 l/sec/ha of infiltration recharge by irrigation water and 1,52 l/sec/ha of inflow from artesian horizons. Mentioned data show, that due to underground inflow from artesian horizons and upstream lands an infiltration recharge is very high (0,021 m/day). Infiltration recharge by irrigation water is only 30-32% of total amount. Specific inflow per 1 km of surface drain and collector laid in detritus-pebble soils accounted for 14 l/sec/km in winter and 65 l/sec/ha in July-September. Average drainage modulus during growing period was equal to 2,2 l/sec/ha (0,019 m/day). Average annual drainage modulus was 1,5 l/sec/ha (0,013 m/day) and maximum value was 3,1 l/sec/ha. These values provided satisfactory reclamation state.
Ground water level during studies was 1,8-2,3 m, that is 0,3-0,5 m deeper than initial one. Productivity of forage crops increased by 5-7%, productivity of stone fruit gardens increased by 3-5%. Use of vertical drainage is ineffective under conditions of Isfara-Lyakkan valley. This is confirmed by the results of pumping with the group of observation wells in Lyakkan valley. Long-term (3 month) pumping with the group of observation wells showed, that while pumping from pebble horizon contained artesian waters decrease of ground water depletion was less than 0,6 m at a distance of 110 m between central wells. Ground water depletion in the wells was equal to 26-28 m and fastly reached its initial state after pumping completion. Only after construction of horizontal drainage situation was improved. Discharge of drain, which length is 1200 m, accounted for 27,7 l/sec/km. Drainage modulus was, on the average, 1,4 l/sec/ha per year and varied from 2,3 l/sec/ha in August-September to 1,05 l/sec/ha in January-April. Taking into account above mentioned, the following conclusions on the most efficient measures for environmental-reclamation state improvement under conditions of Isfara-Lyakkan valley can be made:
1. In the plots with artesian waters, total area of which is 1650 ha, combined drainage should be constructed. Parameters of combined drainage are the following: depth of reinforce wells is 15-30 m, pipe diameter is 144 mm, depth of drain is 3,0-3,5 m, diameter of horizontal drain is 0,5 m, drain spacing is 70-430 m.
2. Construction of subsurface and surface horizontal drains at a depth of 2,7-3,0 m, without backwater. Placing of drains at an angle to the ground water flow. After construction drainage modulus in the plots with artesian waters will be 1,3-1,8 l/sec/ha and 0,3 l/sec/ha (0,0026 m/day) without artesian recharge.
3. Vertical drainage should be considered as additional measure, particularly under conditions of settlements density and for partial capture of ground waters.
|
