Dear Bouderbala

Greetings

Please find attached relevent information with a comprehensive details.

Drainage

Irrigation is the most effective means of stabilizing agricultural production in areas where the rainfall is either inadequate for meeting the crop requirements or the distribution is erratic. Before the introduction to an area of large quantities of water through irrigation, there exists a water balance between the rainfall on the one hand and stream flow, groundwater table, evaporation and transpiration on the other. This balance is serously disturbed when additional quantities of water are artificially spread on the land to grow agricultural crops, introducing (Plates 3, 4a, 4b) additional factors of groundwater recharge from seepage from canals, distributors and field channels, most of which are unlined, and from the irrigation water let on to the fields over and above the quantities actually utilized by the crops, etc. As a result of these, the groundwater table rises. There are numerous instances throughout the world, where consequent upon the introduction of canal irrigation, the water table has risen considerably within 10 years to less than 2 m. Once the groundwater table is close to the soil surface, due to evaporation from the surface, appreciable movement of the groundwater takes place resulting in the accumulation of salts in the root zone. A schematic relationship between depth of groundwater and evaporation from the soil surface is shown in Figure 7. This relationship is significant and shows that there is a critical depth of water table above which there is a sharp increase in the evaporation rate and therefore soil salinization. In general, the critical depth of water table ranges between 1.5 to 3.0 metres depending on soil characteristics, root zone of crops, salt content of groundwater, etc: To ensure a salt-free root zone, evaporation from the groundwater must be prevented thus keeping the groundwater table below the depth that will cause rapid soil salinization. Provision of adequate drainage measures is the only way to control the groundwater table. Subsurface drainage problems may also arise due to the presence, at some soil depth, of a clay barrier, a hardpan, bed rock, or even a subsoil textural change.

In many areas drainage problems also arise because of the accumulation and stagnation of rainfall or excess irrigation water on the soil surface. Surface drainage problems usually arise due to slopes that are too flat or to slow water penetration because of structural instability of the soils or to uneven land. Temporary water stagnation in standing crops results in problems of aeration, disease, weed control and nutrient supply. Proper land shaping and provision of surface drains are needed to solve the problems of surface water stagnation. The experience of some countries in tackling drainage problems and the nature and properties of various drainage materials are described in two FAO publications (FAO, 1971a; 1972).

Plate 3 An unlined field channel; such channels are highly conducive to water loss through seepage

Figure 7 A schematic relationship between the depth of groundwater and relative evaporation rate from soil surface

Plate 4a Lining a field channel to reduce water loss

Plate 4b A canal lined to reduce water loss

i. Surface drainage

In surface drainage, ditches are provided so that excess water will run off before it enters the soil. However the water intake rates of soils should be kept as high as possible so that water which could be stored will not be drained off. Field ditches empty into collecting ditches built to follow a natural water course. A natural grade or fall is needed to carry the water away from the area to be drained. The location of areas needing surface drainage can be determined by observing where water is standing on the ground after heavy rain. Field ditches and collection or outlet ditches should be large enough to remove at least 5 cm of water in 24 hours from a level to a gently sloping land. The capacity of a drainage system should be based on the amount and frequency of heavy rains. How quickly water runs into ditches depends on the rate of rainfall, land slope and the condition of the soil surface including the plant cover. The area that a ditch can satisfactorily drain depends on how quickly water runs into the ditch, the size of the ditch, its grade or slope and its irregularity. The latter is measured by the roughness and the contents of debris and growing vegetation in the ditch. In relatively level areas (slope < 0.2%) a collecting ditch may be installed along one side and shallow v-shaped field ditches constructed to discharge into this collecting ditch. Field ditches used to discharge water into collecting ditches should be laid out parallel to each other 20 to 60 m apart. They should be 30 to 45 cm deep depending upon the depth of the collecting ditch. Care should be taken to avoid sharp curves in the ditches to lessen erosion of the banks. Before planning a detailed surface drainage of an area a standard handbook on the subject should be consulted (for example, ILACO, 1981).

ii. Subsurface drainage

If the natural subsurface drainage is insufficient to carry the excess water and dissolved salts away from an area without the groundwater table rising to a point where root aeration is affected adversely and the groundwater contributes appreciably to soil salinization, it may be necessary to install an artificial drainage system for the control of the groundwater table at a specified safe depth. The principal types of drainage systems may consist of horizontal relief drains such as open ditches, buried tiles or perforated pipes or in some cases pumped drainage wells (Plate 5).

a. Open ditches: Open drainage ditches are advantageous for removing large volumes of either surface or subsoil water from land and for use where the water table is near the surface and the slope is too slight for proper installation of tile drains. Where subsurface tile drains are uneconomic or physically impossible, as in many heavy clay soils and where the topography is nearly flat, open drains may be the only practical means of draining the land. Open ditches also serve as outlets for tile drains where their depth is sufficient and other conditions are favourable. The chief disadvantage of open drains is that they occupy land that might otherwise be put to cultivation; open ditches across cultivated fields also obstruct farming operations and are a danger to the livestock and are more costly to maintain than the subsurface covered drains. Open drains become ineffective due to growth of weeds, collapse of banks resulting in partial filling with soil material, etc., and must be periodically cleaned.

b. Mole drains: these are channels left by a bullet shaped device pulled through the soil, they have been used successfully for shallow subsurface drainage of heavy clay soils in many, relatively humid, parts of Europe but have been found impractical with soils of coarser texture. Mole drains are generally cheaper to install than tile or plastic tubings but may last only for two or three years. In addition to being temporary, mole drains are generally shallow and have not been used extensively where salinity build up from the groundwater table is a major problem.

c. Other subsurface drains: These include any type of buried conduit with open joints or perforations that collect and convey excess water from the soil. The conduits may be made from clay, concrete, plastic or other synthetic material but clay and concrete tiles have been the most widely used. Clay tiles are generally manufactured in 30 and 60 cm lengths and have an inside diameter of 10 to 25 cm. They are made from surface clay or shale, which is pulverized, extruded through a die, dried and then burnt in a kiln. Clay tiles are not affected by acid or sodic soils but those made from surface clay or poorly burnt tiles are subject to deterioration by freezing and thawing action. Good quality clay tiles have been found to last indefinitely in the soil. Concrete tiles are made from sand and gravel aggregate and steam or water-cured to obtain the desired strength. Concrete tiles are resistant to freezing and thawing but may be subject to deterioration in acid and sodic soils. For such soils the tiles should be made with cement having a special chemical composition. Water enters the tiles at the butt joints or spaces between adjacent sections. Both clay and concrete tiles may have fitted ends and be perforated for easier entry of water. All drain tiles should meet standard specifications.

Since the nineteen sixties, thermoplastic tubing has become a common drain material. High density polyethylene and polyvinylchloride are the two most common materials. The plastic tubing is corrugated and, unlike clay or concrete tiles, flexible and will deflect vertically when soil is backfilled in the trench. As it deflects, the sides of the tubing move outward horizontally into the surrounding soil. The circular tubing changes to a slight oval shape, which becomes stabilized because the soil on the sides of the tubing resists the further outward movement. Corrugations in the tubing provide sufficient stiffness to resist the initial soil load. They also reduce the amount of plastic required to make the tubing as well as provide flexibility which permits the smaller size tubing to be coiled into a compact package. Plastic drain pipes are generally available in 8 to 30 cm diameters and usually come in rolls of 75 to 80 m long depending on the diameter of the tubing. Corrugated plastic tubing weighs only 1/25 of a concrete or clay tile, resists practically all soil chemicals and can be installed in continuous lengths. Compared to concrete and clay tiles, greater care is required in placing soil around plastic- tubing because of deflection. Water enters the drain tube through sawed slits or cut holes spaced uniformly around and along the tube.

Plate 5 Laying a tile drain

iii. Filter materials

These are sometimes placed around subsurface drains primarily to prevent the inflow of soil into the drains which may cause failure, and/or to increase the effective diameter or area of openings in the drains which increases inflow rate. Two types of materials are generally used:

- thin sheets such as of fibre glass or spun nylon, and

- sand and gravel envelopes or other porous granular materials.

The thin sheet filters may be sealed on to the plastic tubing at the manufacturing site or they may be installed above and/or below the drains as they are being laid. Granular materials should be placed above or below the drains during installation. Such materials must have the proper gradation of sizes to prevent the inflow of soil.

The principal factors affecting the costs involved in installing subsurface drainage systems in large areas are the spacing and depth of drains. Many mathematical equations have been developed to arrive at the optimum depth and spacing for drains but in practice these have found limited application because of the difficulty and high cost of obtaining soil hydraulic conductivity data and related soil and crop interactions. For these reasons the depth and spacing of drains are based largely on experience and judgement (Schwab et al., 1966).

Subsurface tile or plastic drains are relatively permanent when correctly installed and protected. Large-scale subsurface drainage systems have been in operation in the western United States for nearly fifty years. Extensive installations for water table and salinity control are now being made in many countries including Iraq, Egypt, Australia, etc.

iv. Pump drainage

The chief drawback of gravity drainage systems is their inability to lower the water table to an adequate depth. Pumping groundwater in areas where a suitable permanent aquifer exists is often an effective means of lowering the water table. A decision to pump groundwater for drainage is generally favoured by adequate depths and permeabilities of the water bearing formations, by high values of pumped water for irrigation and by low power costs (see section 4.8.1 on drainage of sodic soils). To determine if pumping would be effective, pumping tests have to be carried out in test wells to determine the feasibility and area of influence by measuring water levels in adjacent observation wells or piezometers. Spacing, depth, and capacity of the pumped wells and other operational details also need to be evaluated from these tests.

v. Maintenance of drainage systems

After a subsurface drainage system has been installed, a suitable map should be made and filed with the property deed. The map should show the location of all ditches and subsurface drains, tile size and grade, depth and spacing. Any subsequent changes should also be recorded on the map. The record is of considerable value to the present and future land owners when the drainage system might need repairs or maintenance.

A subsurface drainage system normally requires little maintenance if it is properly designed and installed. The outlet ditch should be kept free of the sediment and the tile outlet should be protected against erosion and undermining.

If a drain line becomes filled with sediment or roots the line should be uncovered at some point downstream to locate the obstruction. If the line is not completely clogged and water is available the sediment can sometimes be flushed out. A suitable plug, swab or a rigid rod can be used to remove the blockage. A high pressure water jet may be needed to clean out some lines. Often it is more economic to replace the entire plugged section.

Roots of nearby trees can also block subsurface drains. For this reason shrubs and trees growing adjacent to a tile line should be removed. If the tile lines become filled with roots, it is best to dig up and replace the clogged section and remove the troublesome trees at the same time.

The maintenance of open collecting ditches is most important and it is difficult. Weed growth must be controlled and the caving in of the sides requires continuous attention in order that the entire drainage system continues to work efficiently.

PFA

Please find attached the relevant information for you.

Thank you so much Pr. Kulvir and Pr. Niels for these documents.

They are really very interesting.

thanks

DearAbdelkader,

You could find a manuscript on dry drainage as an environmental solution in salty soils. Dry drainage could be used in combination of conventional drainage systems (subsurface drainage systems) to reduce its environmental impacts).

Dear: Dr. Abdelkader

Sorry I don't have any related research until now

Thanks Dr. Soltani for your paper and thank you Dr. Abobatta for your answer.

Dear Abdelkader,

You can find some links to papers in the following site:

https://engadvisorsprofiles.cc.umanitoba.ca/user/ramanathan_sri_ranjan/

http://dx.doi.org/10.13031/trans.56.10370

Thank you Dr. Ramanathan for the links

thanks so mutch Dr.

** http://unesdoc.unesco.org/images/0000/000057/005702eo.pdf

** http://articles.extension.org/pages/63502/solutions-to-soil-problems:-high-salinity

GOOD LUCK

Thank you for these documents Dr. Samra

Best Regards

We have used tile drainage with drainage control structures installed at the outlet to pump waterback through the tiles to subirrigate. Our EM-38 surveys before and after one growing season showed considerable flushing of the salts below the root zone.

You will need to identify the source of the salinity. If it is from the water table below, then sufficient irrigation depth should be applied to prevent capillary salinization. Drainage systems will also help remove the water to create a capillary barrier below the rootzone.

If the source of the salts is through lateral seepage, then interceptor drains could isolate the field.

Thank you Dr. Ramanathan for your interesting ideas

Best Regards