Operation of horizontal drainage system; evaluation of performance and efficiency

Operation of horizontal drainage system; evaluation of performance and efficiency

The operability of the closed horizontal drainage largely depends on regular carrying out of the maintenance works at supra-drain border check, surface inlets, and outfall structures. When using closed horizontal drainage, a particular attention should be paid to the safety of the surface inlets, outfall structures and backfilling of the supra-drain border checks.

It is absolutely forbidden to:

destroy the leakproofness of the group of surface inlets, perforate them for discharging surface waters;
unnecessarily take the surface inlets’ covers off;
litter the surface inlets with various things and rubbish;
stop up the drainage pipe holes in surface inlets;
discharge irrigation water to the supra-drain border check with unconsolidated backfill soil;
carry out willful filling-up of considerable backfill deformations (funnels, tunnels, gullies by structures, etc.);
litter the outfall structures with various things and rubbish;
organize discharge of surface (irrigation) water to an open collector above the outfall;
take off and take out the rings of drainage pipes (asbestos-cement or plastic) from the outfall structure outgoing to an open collector;
burn weed vegetation in open collectors.

It is absolutely forbidden to carry out irrigation and all the more discharges of irrigation water to supra-drain border checks if the consistency of the backfill soil does not approach the consistency of the backfill soil of natural consistency. During this period, supra-drain border checks are enclosed by the 0.6-1.6 m ditches made by ditch diggers at a distance of at least 5.0 m from the edge of the closed horizontal drainage trench.

Supra-drain border checks are allowed to be put into use in the following cases:

when laying drains by semi-mechanical means – in the second year after the construction;
when laying drains by trench-digging machines – in two-three years after the construction;
when laying drains by trenchless or fissure-cutting machines – immediately after the construction.

Development of supra-drain border checks for agricultural purposes is permitted immediately after the construction of drains and carrying out backfill soil compaction works (by their combined prewatering or other methods).

In the process of backfill soil self-compaction on supra-drain border checks as well as in the case they are not used for agriculture, one should carry out land clearance operations (ploughing, harrowing) two-three times a year in order to prevent the growth of weed vegetation, fill the passage ways of earth-boring dung beetles, formed cracks, especially longitudinal ones between the ground of natural consistency and made-up ground.

Before supra-drain border checks are put into agricultural use, experimental leveling is required to be made on them by using longspan levelers.

First vegetative irrigations on supra-drain border checks should be performed in daytime under the supervision of irrigation (mirab). At that, longitudinal shorter furrows at most 50 m long need to be cut, and irrigation water should be supplied through those at lowest flow rates of 0.1...0.3 l/s. If a remarkable backfill deformation (solution sinkholes, tunnels, etc.) occurs on the supra-drain border checks during the irrigation process, irrigation water supply to this site should be stopped. The chief of the division and hydraulic engineer (land reclamation specialist) of the given farm should be informed about this incident in order to find out the cause of the deformation and take necessary measures.

Transverse furrows are not advisable to be made since irrigation water stagnation may arise because of uniform backfill soil self-compaction on supra-drain border checks. In addition, it is difficult to stop irrigation in the case of occurrence of substantial backfill deformations; therefore, certain difficulties are made in the accomplishment of agricultural works (necessity to cut additional irrigation network and enclosing of the supra-drain border check area where the deformation has arisen; field cultivation conditions aggravate, carrying out of next vegetative irrigations, etc.).

Dangerous place should be enclosed or warning signs should be put on the supra-drain border check with considerable deformation for the purpose of preventing getting people, machines or cattle there.

Control over the cutting of temporary irrigation network should be carried out. Cutting of temporary irrigation network along a supra-drain border check or in immediate proximity to it is not allowed. A permissible distance from the closed horizontal drainage trench boundaries is at least 5 m.

Planting of trees, shrubs, and sowing of crops with deep rootzone is not allowed on a supra-drain border check or in immediate proximity to it at the points of intersection of the irrigation network with closed drains, where backfill has not compacted yet. The minimum permitted distance from the trench boundary is four-fold depth of drain or at least 10 m.

Surface inlets have to be kept in clean condition; the drain sump should be cleaned from rubbish and silt; minor repair of their above-ground part should be carried out as appropriate.

To provide better visibility of the surface inlets, their above-ground part must be whitewashed in spring as well the plants should be cut and the area around those within a radius of at least 0.5 m should be cleaned.

The surface inlets that slightly excess over the land surface or even at the same level or lower than it should be enclosed or warning signs (board) should be put indicating their presence in a given place in order to prevent runover of agricultural machines on them or getting cattle there as well as prevent any accident.

To eliminate the probable silt deposition in the piped line, preventive flushing of those should be carried out by supplying water with hose pipes to the surface inlet from the flume network, and by means of a movable pumping unity or from a tank in the case of absence of falls of irrigation canals’ sides.

Preventing flushing should be executed most often, 2-4 times a year, during the growing seasons of the first two-three years after the construction of drainage and at available groundwater table in the zone of placing a closed drain. After the termination of this period, preventing flushing should be carried out once at the end of a growing season or as and when required.

Source: Yakubov, Kh.I., Baturin, G.E., Gorshkov, N.I. Rules for the organization and arrangement
of operation of closed horizontal drainage in farms. Tashkent, 1983