First considerations about the agricultural-type drainage


164a

Information provided by Josep Madurell of drenotube® (Fumoso Industrial S.A.).

A drainage is a device which works according to the type of soil on which it is installed, that is to say, if we put a pipe of higher section, it is not going to collect more water, and thus we can find the paradox that due to the hydraulic transmission of the soil it is oversized.

The determinants for a right design are besides the right identification of the soil, the geometric disposition of the drainage system (depth of the trench, the slope, the distance and position of the drainage lines) and the type section of the drainage system.

The agricultural sector is peculiar when we talk about drainage; in general, there are 2 groups:

a) The person who makes himself his drainage, according to his custom, knowledge, means and experience.

b) The person who subcontracts him, total or partially. Here it is included from the industrialist who with large machinery can generate at the end of the day several km of finished drainage, up to the excavation industrialist who also provides and puts the gravel.

a.1) Agricultural auto construction drain

Due to the variety in geometry and the used materials (bags of grains, plastics, surrounding stones and of the soil itself, straw, remains of concrete, etc.) we can’t determine a common denominator except for the plastic pipe of the drainage and that the cost is as low as possible.

It is very strange to use a geotextil filter, although it is obligatory its use in civil works and buildings, and in this case, there is a lack of technical rigour of the projects.

They trust more on the opinion or information of the neighbours, friends or on their own experience, more than on tests, quality certificates, CE marking, etc…. Except for the cases of the farmers who really have a serious problem of drainage and who have tried several things which haven’t worked.

b.1) Industrialised agricultural drain

The type section is generally:

• Width of the trench: 15 cm.

• Depth 1m aprox.

• SN2 Single or two-layer pipes (the cheaper and simpler possible).

• Diameter from 50 or 63 mm, with or without geotextil/coconuts fibres (cover of the pipe drain pipe)

• Filling of the trench with loose gravel.

• They are installed with a distance from 5 to 10 m as maximum.

THIS TYPE OF DRAINAGE IS THE ONE WHICH MORE MEASUREMENT GENERATES: IT IS EASY THAT AN INDUSTRIALIST INSTALL MORE THAN 500 KM IN A SEASON. THERE ARE IN ORIENTAL ANDALUSIA AND PAMPLONA.

164b

Advantages: quick installation and price.

Inconvenient: you need to clean the field to walk, minimum measure so that the industrialist can carry out the work; doubtful durability: before 5 years the drainage is done again, removed and then the work is done again.

Technical problem: as it isn’t used geotextil, the loose gravel and the pipe finished obstructed/blocked off with soil by the dragging of the fine elements of the water.

b.2) Agricultural drain performed on the soil

The type section is generally:

• Width of the trench: from 30 to 80 cm.

• Depth 1m aprox.

• SN2 Single or two-layer pipes (the cheaper and simpler possible).

• Diameter from 63 to 160 mm, with or without geotextil/coconut fibres (design of the drain pipe with cover).

• Filling of the trench with loose gravel/gravel/stones depending on the availability.

• They are installed with a distance from 5 to 15 m.

164c

Advantages: installation that can be done anywhere, higher price.

Inconvenient: slow execution, with performances from 150 to 250 m/day. Doubtful durability.

Technical problem: as it is no used the geotextil to protect the filtering material this and the pipe ended obstructed/blocked off with soil by the dragging de fine elements of the water. Besides of being a manual job, it is subjected to the heterogeneities proper of the on site works.

THIS TYPE OF DRAINAGE IS THE MOST COMMON, AND IT FINISHED LIKE IN THE PICTURE, BLOCKED OFF WITH SOIL OR IF IT HAS A COVER, THE FINE ELEMENTS FILL THE GRAVELS UP TO THE GEOTEXTILE IN ONLY FEW YEARS.

References

– Information provided by Josep Madurell of drenotube® (Fumoso Industrial S.A.).

– SCS NAt.Engi. Handbook sec 16 DRAINAGE OF AGRICULTURAL LAND

>>> For the design of drainage, it is calculated the capacity which has the hydraulic section of a drainage pipe, according to the slope with which it is installed, the kind of material and the geometry according to Manning, but it is not common to take into account if we will fill or not the pipe. It usually happens that when there is a doubt, it is installed a large pipe which is a mistake because it works worse and it represents an extra cost.

It is recommended to read: www.agua.uji.es/pdf/PRESRH08-11.pdf

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