CA Water-Info

Map | Search | -

Operation of combined drainage system; evaluation of performance and efficiency

Operation of combined drainage represents a complex of technique, organizational and economic measures ensuring keeping of combined drainage in serviceable condition, its regular inspection, carrying out of scheduled preventive maintenance, regulation of soil water regime, management and control of the preparation of combined drainage and its elements for operation during the growing season, etc.

Key objectives of combined drainage use are as follows:

  • Maintenance in serviceable (proper) condition, taking measures aimed at prevention of damage of combined drainage and its particular elements;
  • Improvement of technical level and functionality of combined drainage and its elements.

The most urgent issues are those associated with the use of combined drainage. Proper use enables increasing interrepair time for the elements of combined drainage, smoothing the impact of natural factors on reclaimed lands.

To use combined drainage properly it is necessary to implement regular inspections, servicing and current repair works, i.e. the components of operational works that cohere with the general concept maintenance and enable considerably reducing down the cases of failure of combined drainage components and properly allocating their repair expenditures. At that, to get the highest effect of inspection and maintenance of combined drainage it is necessary to have clear order of priority of the performance of given operations, which is based on the principles of the complexity of work execution, consideration of the importance of the technical objects of the system for ensuring its general sustainable functioning.


Combined drainage is also promising under the conditions of heterogeneous structure of soils formed by poor-permeable (0.01-0.5 m/day) covering fine-grained soils with a thickness from 5 to 15 m and highly permeable (more than 10 m/day) subsoil with confined or non-confined groundwater. Combined drainage cannot be used with thin covering fine-grained soils, because its horizontal element (3-4 m deep) is laid directly into highly permeable subsoil, which avoids the necessity for laying its vertical element (wells-amplifiers). With the thickness of covering fine-grained soils of more than 15-20 m, its geofiltration resistances and hydraulic losses become higher. Under the conditions of low-permeable covering fine-grained soils (below 0.1 m/day), when the drainage capacity of the horizontal network is negligible and it can be substituted by a nonperforated dummy water conduit, which will transport drainage effluent from out-blowing wells.

Main features of combined drainage required at considering its possible application on objects:

  • specific yield of wells-amplifiers, l/s per 1 m of head - 3-3.5
  • area served by one well, ha - 7-15
  • specific length of the horizontal network, m/ha - 10-25
  • well drilling diameter, m - 0.5
  • filtering material- sand and gravel mixture.

Analysis of these tests comparing with the works earlier carried out by the Central Asian Research Institute of Irrigation (SANIIRI) in this zone enable emphasizing the following advantages of combined drainage:

  • Cheapness of the construction:
    • the construction of combined drainage systems will cost twice as low as the construction of closed horizontal drainage;
    • saving of electric power;
    • operation of vertical drainage will require 700-800 kW/h of electric power per hectare of the drainable area. Combined drainage will save consumers from these costs, which is very important under general character of deficit of energy and power resources.
  • Cheapness of use:
    • the expenses for the use of combined drainage systems are 3-5 times lower than the expenses for the use of vertical drainage and 1.5-2.0 times lower than that of horizontal one;
    • simplification of use;
    • combined drainage as opposed to vertical one does not require complex energy-power equipment, and risk of its siltation is much lower as compared to horizontal one.
  • Acceleration of desalinization rates:
    • owing to optimization of land reclamation regimes, desalinization of soils with combined drainage occurs 1.2-1.5 times faster than with closed horizontal drainage and at the same rate as with vertical drainage.


Selected bibliography