Drainage of Agricultural Lands

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Abu Bakar Soomro

Basic Concept • Drainage is the removal of excess water from the land or

from the root zone of crop.

• Sustained accumulation of water over land leads to water logging, which necessitates land drainage.

• Over irrigation and excessive precipitations are most general causes of waterlogging.

• Pakistan has well distributed structures of main and link canals. Seepage losses from canals is also contributing to rise of water table.

• In these situation drainage of water is necessary to create favorable conditions for plant growth.

Benefits/Purposes of Land Drainage • Reclamation of the waterlogged soil in order to make it feasible for agricultural use

• To enhance movement of capillary moisture.

• To improve soil structure.

• Provide aeration within the rootzone.

• Make the soil warmer.

• Prevent the erosion hazards.

• Minimize effect of drought conditions.

• Prevent freezing out.

• Improve physical condition of the soil to allow farm operations.

• Improve the drainage conditions of the agricultural land and allowing soil air and moisture favourable for agricultural production.

Land Drainage Requirements

Land drainage is very important for proper agricultural production.

Proper agricultural drainage requires that several factors should be well known before designing a drainage system.

These parameters are soil type, rainfall, soil salinity level, watertable depth, groundwater quantiity, topographic conditions and groundwater quality.

Types of Drainage Systems

Surface or Open Drainage systems

• The surface drainage is achieved by land forming and smoothing for removal of isolated depressions, or by construction of parallel ditches.

• Ditches and the furrow bottoms are gently graded and discharged into the main drains at field boundary.

• Although the ditches and furrows are projected primarily to convey the excess surface runoff, there is also some seepage through soil to ditches, depending on position of existing watertable which is relevant to bed of the draining channels..

Pipe Drainage Systems

A pipe drain is basically a pipe buried in soil (regardless of material, size or shape) which receives excess groundwater and then conveys to control the existing watertable at any desired depth.

The advantages of pipe drainage are: • The land can be farmed over the drain without loss of the farming area.

• Maintenance requirements are the minimal if system is properly

designed and constructed.

• Pipe drainage system is installed in soil below the plough layer (normally > 0.70 m depth), and it has the advantage of interference with the farm operation.

• Types of Pipe Drainage System

• Pipe drainage systems may be divided into

• (i) Singular systems (ii) Composite systems.

Singular systems

In this drainage system, the field drains comprise

of buried perforated pipe laterals which

discharge into the open ditch collector drains.

Composite System In the composite pipe drainage system, the

collector drain also consists of closed pipe that

in turn discharges into the open main drain

either by pumping or by gravity.

Vertical Drainage System

A well, pipe, bore, or pit in porous, underground strata into which the drainage water can be discharged without any contamination in groundwater resources.

It provides outlet for the drainage water from a surface or subsurface drainage system.

The efficiency of vertical drainage is dependent upon many factors like physical properties of the subsurface aquifers and hydrologic conditions of the site.

Vertical drains should penetrate the aquifer which is absorbing the drainage flow.

Mole Drain

Mole drain is basically an unlined underground drainage water channel, which is formed by pulling solid object, usually the solid cylinder with wedge shaped point located at the end, through the soil at proper slope and depth, without a trench.

Mole drainage is applied under very specific conditions, mainly in the stable clayey soils.

The mole drainage is rapid removal of the excess water from surface layers, rather than at controlling of watertable only.

However, mole drain has a life span of only a few years and has to be renewed frequently.

• Waterlogging refers to the saturation of soil

with water. Soil may be regarded as

waterlogged when the water table of the

groundwater is too high to conveniently permit

an anticipated activity, like agriculture.

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