IDE 354 ppt final

Degree : Agricultural Engineering
Course No. - IDE 354
Course Title : Drainage Engineering
Academic Year- 2014-15
Presented by
Course Instructor : Er. G. G. Kadam
Assistant Professor
Department of Irrigation and Drainage Engineering
Dr. Budhajirao Mulik College of Agricultural Engineering and
Technology, Mandki-Palvan,
Tal.Chiplun,Dist. Ratnagiri- 415 641 (M. S.)

• Irrigation and Drainage : Irrigation can be defined as
addition of water in the field, or artificial application of
irrigation water to crop is called as irrigation, while
removing the excess quality of water from the agricultural
land is the drainage.
• Waterlogged Lands : An agricultural land is said to be
waterlogged, when the high water table (depth of watertable
is less than 2 m from ground surface) affects its
productivity.
• Excess quality of water : It is defined as the defined as the
quality, which is not required by the plant/crop is called as
the excess quality. In other words, it can be defined as the
additional quantity of water in the root zone, which
enhances soil moisture from field capacity to saturation
condition, which afterwards creates the suffocating action in
the root zone. It is also defined as the additional quantity of
water, which disturbs the ratio of soil water and air.
• Surface Drainage : Removal of excess quantity of water
from the root the zone or beneath the soil surface is called as
the surface drainage.

Categorization of Waterlogged Areas
The working Group on Problem Identification
ill Irrigated Areas, constituted by the Ministry of
Water Resources, Govt. of India (MOWR,1991)
adopted the following norms for identification of
waterlogged areas.
• Waterlogged areas : Water table within
2 m from the land surface.
• Potential area for waterlogging : Water table
between 2 – 3 m from the land surface.
• Safe area : Water table below
3 m from the land surface

PROBLEMS CREATED BY WATERLOGGING
• Ill aeration of plants.
• The primary tillage operations such as tilling, ploughing, etc. cannot
be easily carried out in wet soils. In extreme cases, the free water may
rise above the surface of land, making the cultivation operation
impossible and lowering the soil temperature. In ordinary language,
such land is called a swampy land.
• Some water loving plants like grasses, weeds etc, grow profusely and
luxuriantly in waterlogged lands, and compete below and above the
ground with the regular crops which results in making hurdles in
growth of crop and decrease in productivity.
• Salinity is the cause of waterlogging, explained as: if the watertable
has risen off, or if the plant roots happen to come within the capillary
fringe, water is continuously evaporated by capillarity. Thus a
continuous upward flow of water from the watertable to land surface
gets established, which resulting in the deposition of salts in the root
zone of crops. The concentration of these alkali salts present in the
root zone of crops has according effects on the roots, which reduces
the osmotic activity of the plants and checks the plant growth and the
plant ultimately fade away. Such soils are called saline soils.

Causes of Waterlogging
1. Over and intensive irrigation : When policy of intensive irrigation is
adapted the maximum irrigable area of a certain region is irrigation.
This may lead to too much of irrigation, resulting in more percolation
and subsequent but slow rise in watertable. For this reason, to avoid
waterlogging, the policy of extensive irrigation (i.e. irrigation spread
over wider region) should suppress the policy of intensive irrigation.
2. Seepage of water from the adjoining high lands. Water from
adjoining high lands may seep into the sub soil of the affected land and
may raise the watertable, sometimes occur water stagnation in low
lying areas.
3. Seepage of water through canals: Water may seep through the bed
and sides of the adjoining canals, reservoirs, etc. situated at a higher
level than affected land, resulting in build up to of high watertable.
4. Impervious obstruction : Water seepage below the soil moves
horizontally (i.e. laterally) but may find an impervious obstruction,
causing the rise of watertable on the upstream side of the obstruction.
Similarly an impervious stratum may occur below the top layers of
previous soils. In such cases water seeping through the previous soils
will not be able to go deep, and thus quickly resulting in high
watertable.

5. Inadequate natural drainage: Soils having less permeable sub
stratum (such as clay) below the top layers of pervious soils, will
not able to drain the water deep into ground, and hence resulting in
high water level in affected soil.
6. Inadequate surface drainage: Excessive storm water falling over
the land and excess irrigation water should be removed and should
not be allowed to percolate below .If proper drainage is not
provided the water will constantly percolate and will raise the level
of underground reservoir.
7. Excessive rains : Excessive rainfall may create temporary
waterlogging and in absence of good drainage, it may lead to
contribute watertable built-up and continued waterlogging.
8. Submergence due to floods : If land is continuously submerged by
floods, water loving plants like grass, weeds etc. may grow which
obstruct the natural surface drainage and thus increasing the
chances of temporary waterlogging.
9. Irregular or flat topography : In steep terrain, the water is drained
out quickly. On flat or irregular terrain having depression, the
drainage is very poor. All the factors lead to greater detention of
water on land and hence more percolation and increases watertable.

Main causes of soil salinity and sodicity
Irrigation with water of low salinity but with dominant
HCO3 anion and migration of sodic salts in arid
climate prominently.
1. Irrigation mismanagement
1. Poor land leveling.
2. Leaving land fallow during dry periods especially
in regions of shallow water table.
3. Improper use of heavy machinery resulting in soil
compaction.
4. Leaching without adequate drainage and
5. Adoption of improper cropping patterns crop
rotations. In irrigation agriculture, scientific water
and land management is the key to avoid
waterlogging and salinity problems.

Causes of Waterlogging and Salt Problems
1. Climate Factor : Erratic rainfall distribution within a short wet season
followed by a long dry season is the specific features of a monsoon
climate. Heavy monsoon rain cause accumulation of runoff. Its ill effects
are more severe in flat terrains and low lying areas, even during a
relatively smaller rainfall in some of the non-monsoon months. In the
absence of drainage, natural or man-made, the accumulated water gets
more opportunity time to percolate down and causes the water table to
rise. In heavy textured soil or black cotton soils, due to excess wetness of
the soil, delay in the sowing of winter crop after the withdrawal of
monsoon is a common feature in ill drained soils, which reduces the crop
yield. High evaporation and evapotranspiration in the dry season increase
the salt concentration on the soil surface and beneath the soil (in the root
zone).
2. Lack of Catchment Area Protection : Deforestation, overgrazing,
unplanned urbanization and faulty cultivation practices cause soil loss due
to erosion. Waterlogging over the downstream lands, siltation and pollution
of downstream natural streams reducing the capacity of man-made surface
drains and reservoirs, and help to deteriorate the water quality. The
intensity of the flood hazard increases if the carrying capacity of natural
stream has reduced due to siltation.

3. Adverse Topography: Area with adverse topography are known by different local
names such as a Bhal (as flat as the forehead) lands in Gujarat, Diara (concave) and,
Tal and Chaur (floor plains of low elevation) lands in Bihar and Uttar Pradesh. There
are low lying lands with severe restriction of natural drainage in several parts of India.
Examples are the large area in the Indo-Gangetic plain, the delta regions of the seas and
the below sea level cooperative rice farms in the Kuttanad region of Kerala. In many of
such low lands or land with adverse topography, the monsoon cultivation season is lost
due to high level of land inundation following incessant heavy rains, floodwater
accumulation and backwater flow.
4. Canal seepage : Seepage from unlined or lined but ill-maintained canal in the irrigation
areas long duration wet and sometimes marshy condition in the adjoining agricultural
lands ultimately results in rise in water table and development of salinity and alkali
conditions. This is a major problem in irrigated agriculture due to which not only the
valuable irrigation water is lost but also the water that is loss causes other problems like
salinity and alkalinity.
5. Injudicious use of Irrigation Water : Field to field irrigation and over-irrigation due to
uncertainly in the release of canal water both in time and in quantity, are the examples of
injudicious use of irrigation water. Besides, unconsolidated lands, inadequate land
preparation, mostly ungated and many unauthorized outlets and an absence of scientific
rostering of canal water lead to poor irrigation efficiency. These, an turn, cause
temporary surface waterlogging and watertable rise.

6. Other Man-made Causes: Unplanned construction of roads, rail lines
and railway embankments and under capacity culverts lead to
restriction in the natural flow of water, results in waterlogging.
Adoption of unscientific cropping practices such as growing more
water requiring crops against the planned cropping pattern in a canal
irrigated area results in applying more than the anticipated quantity of
water over relatively smaller areas. This causes excess water problem
in certain parts and water deficit over the other parts.
7. Poor Water Quality: Brackish ground and surface water, when used in
irrigation for want of adequate quantity of freshwater, adds
undesirable salts to the agricultural lands. Disposal of untreated
municipal and industrial effluent on the land and into the natural
streams causes surface and groundwater quality problems.
8. Inherent problem with the soil : High salt content in the soil due to
properties of the parent rock material, poor water transmission
characteristics in heavy soil and high evapotranspirative water demand
in a major part of the year lead to salinity and alkali problems. This is
more conspicuous in the semi-arid regions.

9. Lack of Proper Prioritization : Land development and reclamation,
construction of field drains and drain maintenance, are not
considered as priority items of work in an irrigation command area.
The working funds for such works are always limited. Many of these
works are planned but are not executed adequately and in time.
This leads to the development of waterlogging and salt problem,
which become expensive to tackle at a later stage.
10. Lack of Monitoring : Monitoring of the gradual changes in the
health of the land and the water resources are seldom done
routinely in any command area after the introduction of irrigation
.Problems of drainage (watertable rise) and salinity become known
when it is too late and the remedy becomes expensive.
11. People participation : Absence of a cooperative/participatory
approach by the irrigation water user to manage the water resource
at the farm level and developing suitable management alternatives
to tackle the upcoming problems leads to gradual degradation of
the physical and the chemical environment of the agriculture land.

12. Lack of Policy Guideline : The Ministry of water resources,
Government of India, has brought out a National Water
Policy in 1987, which was subsequently revised in 2002. This
policy has recognized water as a scarce resource and
considers its planning and management as matters of utmost
urgency for its optimal, economical and equitable use. On the
other hand, the National Land Use and Wastelands
Development Council, under the chairmanship of the Prime
Minister, have adopted, in Toto, National Land Use Policy
Outline drafted and submitted by the National Land Use and
Conservation Board in 1986. The Council's meeting also
stipulated 19 action points to be pursued by various state
Land use Boards constituted mostly under the chairmanship
of the Chief Ministers. Unfortunately, presumably because
the National Land Use Policy outline was not a document
formally endorsed by the Parliament. However, all the Union
Ministries related to use and management, including the
Ministry of Water Resources and ICAR were among the
parties when this policy outline was adopted. There has been
little interactive development in taking cognizance of various
lines and directives given in this Policy Outline.

Waterlogging Control
1. Living of canals and watercourse : Attempt should be
made to reduce the seepage of water from the canals and
watercourses. This can be achieved by lining them. It is
very effective method to control waterlogging.
2. Reducing the intensity of irrigation : In areas where
there is a possibility of waterlogging, intensity of irrigation
should be considerably reduced. Only a small portion of
irrigable land should receive canal water in one particular
season. The remaining areas can receive water in the next
season.
3. By introducing crop rotation : Certain crops require
more water and other require less water. If a field is always
sown with a crop requiring more water, the changes of
waterlogging are more. In order to avoid this, a high water
requiring crop should be followed by the one requiring less
water and then by one almost no water. Rice may be
followed by wheat and wheat may be followed by a dry
crop like cotton.

4. Optimum use of water : It has been said earlier that only
a certain amount of water gives best results. Less than that
or more that reduces the yield. But most of our cultivators
are unaware of these techniques and they feel that by using
more water they can increase their yields. Therefore, they
try to use more and more water. This can be checked by
educating the cultivators through proper propaganda.
Moreover, revenue should not be charged on the basis of
irrigated area, but should charge on the basis of quantity of
water utilized. A strict watch should be kept at the outlet in
order to stop undue tapping.
5. Providing intercepting drains : Intercepting drains along
the canals should be constructed, wherever necessary and
the constructed drains should be maintained properly.
These drains can prevent the sub-soil water from reaching
the area likely to be waterlogged.

6. Provision of an efficient drainage system : An
efficient drainage system should be provided in order to
drain away the storm water and the excess irrigation
water. A good drainage system consists of surface
drains, sub-surface drains as well as interceptor drains.
7. Improving the natural drainage of the area : To
reduce percolation, it is necessary that water should be
allowed to stand for a longer period. Some relief in this
direction can be obtained by removing the obstruction in
the path of natural flow. This can be achieved by
removing bushes, rubbles, etc and maintaining the
proper slopes of the natural drainage lines.
8. Introduction of lift irrigation : Lift irrigation utilizes
the underground water for irrigation. It therefore helps
in lowering the watertables through tube-wells. Canal
irrigation may be substituted by lift irrigation, in areas,
which are likely to be waterlogged.

Purpose of Drainage
1. To provide a good environment that is suitable for
the maximum growth of plants.
2. To increase production/productivity and to sustain
yields over long periods of time.
3. Main reasons that poor drainage causes a
decrease in crop production is the fact that the
plant roots have only a limited amount of soil in
which plant is growth. This means that the plant
root system is not adequate to supply the top of
the plant with the food it needs. Plants do not do
well under such circumstances.

Effect of Poor Drainage on Soil and Plants
1. Water fills the soil pores and displaces air and
obstructs the gases, which are given off by the
roots.
2. The soils become blocked and inefficient for the
exchange between gases in the soil and in the
atmosphere.
3. The oxygen content in the soil is less.
4. Extremely slow rate of diffusion of gases is
observed through such soils.
5. In waterlogged soil, gas exchange is confined t a
fraction of the top inch of soil, below this oxygen
is non-existent.

6. After the dissolved oxygen in waterlogged soils has
been consumed, anaerobic decomposition of
organic matter takes place. This results in the
production of reduced organic compounds, such as
methane or marsh gas, methyl compounds and
complex aldehydes.
7. Because of the decline in rate of decomposition,
nitrogen tends to remain locked up in the organic
residues.
8. The decline in the rate of transpiration, the decay
of roots and lack of formation of new roots takes
place.
9. Adverse effect on the uptake of nutrients by plants.
10. Health hazard is created by increase in population
of mosquitoes, which breed in ponds and small
puddles in the field.

Benefits of Drainage
1. Drainage removes excess water and helps the roots to
grow into the increased soil volume. Consequently, more
nutrient becomes available to the plant and its anchorage
with soil improves to support against lodging under wet
soil and high wind conditions.
2. Due to hot summer temperature, water that is ponded
because of irrigation or rainfall kills planted grasses or
legumes. Drainage with proper grading reduce the
damage due to scalding (burning due to hot water)
increase the yield.
3. If the fields are properly graded and outlets and ditches
foe the disposal of water are provided, this situation will be
remedied and more healthful and pleasant environments
for human habitation will be created.
4. Optimum soil temperature is needed for healthy
germination of seeds. A high water table results in a soil
that does not warm up readily in the spring. Germination of
crops is delayed and the seed may infect rot before it
germinates. The drained soils become warmed soil.

5. The unfavourable root environment exists in the areas of high
watertable. Plant diseases are more active under these conditions.
Fungus growth is particularly prevented.
6. Drainage creates congenial root environment, which is essential for
the growth of beneficial soil bacteria, which convert soil organic
matter and fertilizer to available plant food.
7. Drainage brings the field to the capacity (working condition) sooner
and keeps so for a longer time. Field operations become easier and
less time labour consuming. In wet and heavy soils, field operations
are not only difficult but also destroy the soil structure.
8. Removal of excess water by drainage reduces the specific heat of the
soil-water system. A warmer and more favourable soil temperature
regime extends over a longer period. This accelerates bacterial activity
and plant growth.
09. Plant availability of Nitrogen of the applied fertilizer increase in well-
drained soils and loss of Nitrogen due to denitrification in
minimized. If the soil is heavy, saline-sodic and waterlogged, the
positively charged ammonium ions of the fertilizer fail to adsorb on
the negatively charged soil clay complex in the presence of stronger
cations and ammonia volatilization loss occurs. Some ammonia,
however, get lost through the leachate of the subsurface drainage
system during the initial period reclamation of heavy and salt affected
soils. But once reclaimed, such losses are completely avoided.

10. Harmful salts are washed away and leached out of the
root zone by the drainage system, maintaining
favourable salt-water balance in the agricultural
land.
11. Drainage helps early planting due to improved soil-
water regime and as a result longer effective
photoperiod becomes available to the plant for its
growth.
12. Drainage is not crop-specific and a good variety of
crop can be grown successfully in well-drained
agricultural lands.
13. Waterlogged and ill-drained soils are the breeding
grounds of agents that cause disease to men and
livestock such as malaria, dengue, foot rot and liver
fluke. Mosquitoes breed profusely in stagnated water
bodies and affect the livestock and human beings.
Drainage removes these problems.
14. Drainage is essential for salinity-alkalinity control
in arid/semi arid regions.

Inter-relationship of Irrigation and Drainage

The appropriate choice of drainage criterion will
depend on the following set of conditions:
• Hydrological conditions : Which determine the quality
of excess water to be drained within a specified time.
• Agronomic conditions : Which depending on the crops
and specific soil conditions, determine the permissible
upper limit of the root zone's soil moisture content and
it/s duration.
• Soil conditions : Which determine the relations
between aeration and moisture content, groundwater
level and soil moisture content and groundwater level
and capillary rise.
• Economic conditions : Which determine the cost-
benefit ratio, i.e. the ratio between the costs of installing
a drainage system and the benefits derived from less
frequent and less severe yield depressions.

Drainage Properties of Soils
A soil may need artificial drainage for either or
both of the following two reasons:
1. Where there are high water tables that
should be lowered.
2. Where excess surface water cannot move
downward through the soil as over the
surface of the soil fast enough to prevent the
plant roots from suffocating.

• Hydraulic conductivity : The hydraulic
conductivity of a soil represents is average water
transmitting properties, which depends mainly on
the number and the diameter of the pores present.
• Homogeneous soil : If the number and diameter
of the pores are distributed uniformly, the soil is
said to be homogenous.
• Isotropic soil : If the hydraulic concavity is same
in all direction the soil is said to be isotropic.
• Anisotropic soil : Soil commonly shows certain
stratification so that K in one direction is greater
than in another. A soil in which hydraulic
concavity at any point has perfect direction is
called anisotropic soil
• Heterogeneous Layer : If the anisotropy varies
from point to point in a given layer the layer is
said to be heterogeneous layer.

Negative effects of poor surface drainage on
agricultural productivity :
1. Inundation of crops, resulting in deficient
growth.
2. Lack of oxygen in the root zone, hampering
exchange of gases and uptake of nutrients.
3. Insufficient accessibility of the land
mechanized farming operations.
4. Low soil temperatures in spring time
(temperate zone) affect the germination.

Design of surface drainage system has two
components:
1. The shaping of the surface by land forming,
which ICID (1982) defines as changing the
micro-topography of the land to meet the
requirements of surface drainage or irrigation:
2. The construction of open drains to the main
outlet.

Land Forming for Surface Drainage
The construction of a surface drainage system, in the
sense of a system of channels to convey surface water, is
usually not sufficient to guarantee the timely excess
surface water. Water is likely to remain stagnant on the land
in shallow depression. Therefore, in addition to the
construction of channels, the micro-topography of the land
nearly always has to be changed. This operation is referred
to as land forming.
In planning land-forming operations, one should
take into account the time over which excess water has to
be removed from the soil surface, the specific cultivation
needs of various crops and crop rotations and the use of
mechanized farming equipment.

A) Land Smoothing
Land smoothing means the operation of producing a plane
surface with a uniform slope without changing its general topography.
The smoothing operation eliminates small differences in elevation and
continual slope from all points in the field to a surface field drain.
Land smoothing on irregular topography improves surface drainage,
corrects many difficulties in drainage and allows efficient
mechanization. It is also the finishing operation for land grading and land
forming practices to correct minor surface irregularities.
For proper land smoothing, the soil has to be dry and crumbling.
The operation can best be performed once a year after completion of other
tillage operations for seedbed preparation.
In a land smoothing job, the depth of grading is controlled to
prevent exposure of unproductive sub soil. It is not necessary to grade the
field to a uniform slope over the entire field length.
Land smoothing is the cheapest and yet one of the most productive
surface drainage practices. The work can be done with an old type of
wooden drag behind a farm tractor as well as with more sophisticated
equipment like land levelers and land planes.

B) Surface Grading
Land grading is the process of process of forming the surface
of land to predetermined grades, so that each row or surface slopes
to a (field) drain.
Land grading for surface drainage consists of forming the
landscape by cutting, filling and smoothing it to planned continuous
surfaces.
It is a one-time operation, carried out by such machines as
bulldozers and scrapers and involving the transport of each according
to specified cuts and fills based on the predetermined grades.
Land grading for surface drainage differs from land leveling for
irrigation in that, for drainage no uniform grade is required.
Grade in the direction of drain must be continuous with a
minimum of 0.05%, preferably 0.1% and maximum of 0.5%.
The maximum permissible row length is determined by the
grade, the permeability of the soil, and the erosion hazards.
In areas with little or no slope, grades can be established or
increased by creating a uniform grade between the parallel drains or by
creating an artificial ridge midway between the parallel drains.

Grading operation involves a number of steps:
• Site preparation : On cleared land, this can be done with
regular farm equipment. It mainly involves removing or
destroying vegetative matter and other obstacles. Ridges
or rows are leveled. Surface should be dry, firm and well
pulverized to enable the earthmoving equipment to
operate efficiently. The field is surveyed after preparation.
• Rough grading : This can be done with several types of
equipment.
• Finished grading : It is most efficiently done with land
plane (a bottomless scrapper). Several passes are usually
made at angles to one another. Drags and furrows can be
used for smaller fields and for final smoothing.

Information to be Obtained from Drainage Surveys
If the results of the reconnaissance survey are
favourable, it is followed by detailed drainage surveys for
preparing plans and estimates.
The principle information needed on a drainage
survey is as follows:
1. A map of area showing watershed location, areas and
vegetative cover of the area tributary to each drainage
ditch. The map should also show location of the outlet
ditch, roads, railway lines and other physical features,
which will affect the design of the proposed drainage
system.
2. Profiles on the centre line of the proposed drainage
ditches and tile mains.
3. Topographic map of the area to determine the general lay
of the land for designing the drainage system. Elevation of
low points, which need drainage, is of special importance.

4. Outlet conditions : adequacy of capacity, high
water elevations and frequency of floods.
5. Physical properties of soil affecting drainage
requirements, infiltration capacity of the
surface and permeability characteristics of
lower horizons.
6. Amount of soluble salts in the soil to be
leached.
7. Determination of exchangeable sodium (High
percentage of exchangeable sodium creates
imperviousness).

Factors affecting Drainage
1. Topography of the affected area and the
adjoining watershed which contribute flow
into the problem area.
2. Soil characteristics
3. Rainfall and other climatic factors
4. Crop factors.

Types of Lands Requiring Drainage
Land under following conditions requires drainage in order to
achieve a high level of agricultural productivity.
1. High watertable : The watertable is within or near to the root zone. A
watertable within 1.5 m is usually not desirable.
2. When water stands on the land surface for a long period :
Tolerance of crops to standing water varies widely i.e. 2 to 4 hours for
sensitive vegetables such as potatoes at the tube setting stage, about 1
day for maize and small grains and 4 days or more for water tolerant
grass crops.
3. In region where the annual evaporation exceeds annual rainfall :
Soil salinity and alkalinity and rise of groundwater level due to excess
irrigation water are the problems of the region. Drainage aids in
leaching of salts, reduces the chance of accumulation and removes
excess irrigation water.
4. Excessive soil moisture content : Soil moisture content above the
field capacity for a considerable length of time is harmful to crops.
5. Humid regions with continuous or intermittent heavy rainfall.
6. Flat lands with fine textured soil.

Common Techniques Used to Drain Excess Water
a) Surface Drainage, b) Sub-surface Drainage and c) Tube Well Drainage.
A) Surface drainage can be described as (ASAE,1979) the
removal of excess water from the soil surface in time to prevent
damage to crop and to keep water from ponding on the soil surface
or in surface drains that are crossed by farm equipment, without
causing soil erosion. Surface drainage is a suitable technique
where excess water from precipitation cannot move freely over
the soil surface to a (natural) channel. The water may be from
excess rainfall, over -irrigation, losses from conveyance channels
and storage systems, or seepage from areas at higher elevations.
Flat or level land having impermeable sub-soils with shallow
top-soil frequently requires surface drainage because pipe
drains are not practical or economical. Open drains are
advantageous for removing larger volumes of either surface or
substance water, including storm water from land where the water
table is near the ground surface. Open drains are essential for
disposing of storm water also.

Disadvantages :
1. Open drains cut away the farm area into
fragments and interfere with the movement of
machinery. They also waste considerable area
of the farm land. Efforts should be made to
reduce the number of relief drains as far as
possible.
2. They require frequent cleaning.
3. They harbour and distribute obnoxious
weeds.

Surface drainage broadly comprises of the following:
1. On farm drainage system (relief drains) consisting of graded
channels that collect excess water from fields.
2. Intermediate drains (collector or carrier drains) which are link
drains between the various field drains and sub main drains or
main drains.
3. Main drains or Main/sub-main drains are excavated or natural
drains, collecting water from link drains or directly from field
drains.
4. Interceptor drain, also called seepage drains which are located at
foothills to intercept seepage from hill sides/earthen reservoirs,
canals and intercept surface/subsurface flow.
5. Land grading and smoothing to produce a level or gently sloping
land surface, including a number of cultivated fields, which many
times are irregular, consisting of randomly distributed elevated
areas and depressions. It results in ponding of water, inefficient
irrigation, interrupted surface drainage, difficulties in mechanized
field operations and consequently, non-uniformity and reduction in
crop yield. The construction of the drain is always started at the
outlet and progresses upstream.

B) Subsurface drainage is the removal of excess soil
water in time to prevent damage to crops, because of a
high groundwater table. Subsurface field drains can
be either open ditches or pipe drains. Pipe drains are
installed underground at depth varying from 1 m to
3 m. Excess groundwater enters the perforated field
drain and flows by gravity to the open or closed
collector drain.
C) Tubewell drainage can be described as the control
of an existing or potentially high groundwater
condition. Most Tubewell drainage installation
consists of a group of wells spaced with sufficient
overlap of their individual cones of depression to
control the watertable at all points in the area.

Drainage Coefficient
• The rate of drainage is a key factor in establishing
the needed capacity of a drainage system.This rate,
expressed as the depth in centimeters of water
drained off from a given area in 24 hours, is called
the drainage coefficient or drainage design rate.It
may also be expressed in terms of flow rate per unit area,
as cubic meters per square kilometer per 24 hours, or in
terms of the flow rate per unit of area, which varies with
the size of the area.
• Drainage coefficients are selected with respect to the
degree of protection to be provided for various crops.For
average small drainage projects the drainage
coefficient would range from 6 to 25 mm.

Classification of Salt Affected Soil

Surface Drainage for Flat Areas
The surface drainage systems applied in flat areas
(maximum slope 2 %) differ from those in
sloping areas. In flat areas the lack of sufficient
slop is a limitation while in steep areas, the main
limitation is the risk of erosion.
Four types drainage systems
1. Bedding system
2. Parallel field drain system
3. Random drain system
4. Parallel open ditch system.

1) Bedding System
• Adoptability :It is one of the oldest surface
drainage practices used on flat poorly
drained soils with low permeability, the land
is ploughed in the course of a number of years
into beds, separated by dead furrows which run
in the direction of the prevailing slope.
• Field operations :Except for ploughing, which
must always be done parallel to the furrows;
all farming operations can be done either
across the beds or parallel to the furrows.

Bedding has proved practicable on land with a
slope up to 1.5%.The bed width depends on
the land use, the slope of the field and that
of the dead furrow, the soil permeability, the
farming operations and the width of the farm
machinery.
In modern farming, bedding is not considered
an acceptable drainage practice for row crops,
because rows adjacent to the dead furrows
will not drain satisfactorily.
It is acceptable for grasslands in some areas,
although there will be some crop loss in and
adjacent to the dead furrows.

• The recommended bed width for land with a very slow
internal drainage (K=0.5cm/day) is 8 to 12 m, slow internal
drainage (K=5 to 10 cm/day)is 15 to 17 m and fair internal
drainage (K=5 to 10 cm/day) is 20 to 10m.
• The length of the beds varies in practice from 100 to 300m.
• The bed height i.e. the difference in height between the
bottom of the furrow and the top of the bed is 40cm at the
most on land used for pastures and 20 cm on arable lands.
• This bed height can be obtained either by repeated
ploughing, with the initial furrows placed in the same location
each time, or by using earth moving machinery.
• Later from the dead furrows discharges into a field drain
constructed at the lower end of the field and normal to the
dead furrows.
• The field drains, in turn discharge into field laterals, which
convey the water to the main drains. The field drains are
shallow (avg.depth 25cm),have flat side sloped (6:1 to 10:1)
and grade of at least 0.1%.

• The bedding system does not provided a
satisfactory solution for surface drainage when
crops are grown in rows parallel to the dead
furrows. The crop ridges prevent overland flow to
the furrows and consequently the rows have to drain
into a field drain or row drains have to be made and
maintained. Therefore, the bedding systems are only
recommended for pasture or hay or any crop,
which allows the surface of the beds to be smoothed.
Even in extremely flat areas, the parallel field drain
system is nowadays preferred.
• Field Drains and Field Laterals
– To prevent ponding in low spots, surface runoff from
field needs to be collected and transported through
field drains and field laterals towards the drainage
outlet of the area.

2) Parallel Field Drain System
• Adoptability :The parallel field drainage system
is the most effective method of surface
drainage. It is particularly appropriate in flat
poorly drained areas with many irregularities.
• The success of the system depends on proper
land forming to assure a proper slope of the rows
(small channels between ridges on which crops
are grown).These rows discharge their water into
parallel field drains constructed at convenient
places in the field. Such field drains consist of
shallow graded channels with side slopes flat
enough to allow farm machinery to cross.

Field drain dimensions are conditioned more by requirements of
installation and maintenance than by those of hydraulic design.
They usually have side slopes of 8:1 to 10:1, minimum depth
of 25cm, minimum cross-sectional area of 0.5m2 and a grade
varying from 0.1 to 0.3%. The following table gives some
recommended field drain dimensions.
Without increasing the drain depth too much, the capacity
can be increased by constructing a bottom width, creating a
shallow trapezoidal shape. Recommended dimensions of V-
shaped and trapezoidal drains are shown in figure. A
distinction is made between single field drains (V-drains),
trapezoidal field drains and double field drains (W-drains).W
drains consist of two V drain parallel and close together, the
spoil in between the drain often being used as a field road.
Double field drains are made when the spoil cannot be
disposed of without blocking drainage and are applied
mainly on flat land with few irregularities.

The drain spacing depends on the hydraulic conductivity
of the soil, the crops to be grown, the topography and
the grade of the land after grading. Spacing varies in
practice from 100 to 200 m on relatively flat land (slope
less than 0.5%), which after grading, slope in one
direction.
The crop rows lead directly into the field drains and should
have a slope of 0.1 to 0.2 %.If the soil is not susceptible
to erosion, the slope of the rows may be as high as
0.5%.The land should be ploughed parallel to the field
drains and all other farming operations done
perpendicular to the field drains and all other
farming operations done perpendicular to the fields
drains.
The system is the most expensive of all systems but
provides good drainage for each part of the field and
does not hamper mechanized farming operations.

• A special adaption of the system is land crowning on very flat
land, where earth is moved to make low ridges or crowns, with
field drains about 30 to 100 m apart.
Field Laterals
The water from the surface field drains is collected in field laterals,
which can be regarded as part of the farm's main drainage
system. The design cross-section of field lateral should meet the
combined requirements of capacities, erosion control, depth,
side slopes, maintenance and, if needed, allowance for
sedimentation. Table gives recommended field lateral side
slopes in combination with their depth. Two types of cross-
sections can be distinguished: the V-type and Trapezoidal type.
The figure gives a cross-section of a trapezoidal field lateral

Special attention should be given to the
transition between field drains and laterals,
because differences in depth might cause
erosion at those places. For discharges below
0.03m3/s, pipes are a suitable means of
protecting those places. For higher
discharges, open drop structures are
recommended.

3) Random Field Drainage System
Adoptability :The random drain system is most
widely used where small-scattered
depressions occur over the area. Where these
depressions are too large, economically
speaking, to be filled by land forming
practices, they can be drained with random
drains or ditches. Where possible, the drains
connect one depression to another in
conveying the water to a suitable outlet.

• The depth of the drains depends on the topography of
the area and on the design discharge and should be at
least 25 cm. The side slopes should be 8:1 or 10:1, if
they are to be crossed by machines.
• If farming operations are carried out parallel to the
drains, side slopes of 4:1are allowed. The spoil from
the drains can be used to fill small depressions not
connected to the system.
• This drainage system is applied where a number of
depressions are distributed at random over a field. The
application of the random drain system is limited by the
number of depression to be connected as too many
drains hamper mechanized farming and increase the
amount and cost of maintenance work.
• Random drains are sometimes used together with the
bedding system, when the land is flat and the soil has
very low permeability. Where the permeability allows
it, the system is sometimes used in conjunction with
sub-surface drainage system.

4) Parallel Open Ditch System
• Adoptability :The method is often applied in
peat and muck soil. Where subsurface
drainage can be used in conjunction with
surface drainage, the field drain spacing
needs to be adjusted to the requirements of
the subsurface drains. The combined system
is referred to as ' parallel open ditch system'. It
is similar to the parallel field drain system
except that now the field drains are replaced by
open ditches.

These ditches are at least 60cm to 1m deep, and the
given steep side slopes less than 4:1,usually 1:1 or
1.5:1, depending on soil conditions.
The maximum spacing applied varies in practice
between 60 to 200m.As these ditches cannot be
crossed by farm machinery, all farming
operations must be done parallel to the ditches.
Discharge of excess surface water from the rows is
made possible by row drains. The method is often
applied in peat and muck soil.
In mineral soils, it will be more convenient to apply
the parallel field drain system for surface drainage
and a tube drainage system for subsurface drainage.

B) Surface Drainage Systems for Slopping
Areas
Surface drainage methods applied in slopping
areas (slopes>2%) are closely related to
problems of erosion control. The methods
comprise the creation of suitable conditions
to regulate or intercept the overland flow
before it become hazardous as an erosion
force. This usually means some form of
terracing.

1) Cross Slope Ditch System
• The cross-slope ditch system is a channel
type graded terrace also called Nichols
terrace and is used on lands with a slope up to
4%, where flat land systems would be
impracticable in view of erosion hazards.
Cross-slope system resembles the parallel field
drainage system. It is effective on soils with
poor drainage characteristics and where the
overall slopes are rather regular but where
many minor depressions occur.

• The ditches should run approximately parallel to
the contours of the land with a uniform or
variable grade of between 0.1 and 1 % (or a
mean of 0.5%), depending on the topography.
The use of a variable grade often permits a
better alignment of the terrace and a better fit
of the terrace to the field. The soil surface
between the ditches must be smoothed and all
farming operations should be done parallel to
the ditches. Spoil from the ditches can be used
to fill up minor depressions or can be spread out
to form a low layer of not more than 7 cm on
the downslope side of the ditch.

• Cross-slope ditches can have either a triangular or a
trapezoidal shape, with side slopes ranging from 1:4 to
1:10. Their cross-sectional area can vary from0.4 to
0.7m2. Depths will be between 15 and 25 cm and the
top width from 5 to 7 m. The maximum length of a
ditch draining to one side only is about 350 to 450m.
The distance between the ditches depends on the
slope, the rainfall intensity, an erodibility of the soil,
and on the crops that will be grown, but are usually
between 30 m on lands with a 4% slope and 45m on
lands with 0.5% slope.
• With the cross-slope ditch system, between 80 and
100% of the water contained the ditch is below the
original land surface, which reduces the harmful effect
of a possible break in the downslope bank.

2) Standard Erosion Control Terrace
• The standard erosion control is a ridge-type
graded terrace also called as Mangum terrace and
is used on lands that slope as much as 10%.
• The difference between the cross-slope ditch and
the erosion control terrace that with the latter the
spoil from the channels is used to build up a
relatively high ridge on the downslope side. In
such channels only 50 % of the water is retained
below the original land surface. Greater storages
would require great amounts of earth moving and
would increase the risk of the ridges rupturing.

• Like the cross-slope ditches, the channels of the erosion
control terraces should run approximately parallel to
the contours of the land with uniform or van grade of
between 0.1 and 0.6%, depending on the topography.
Natural impediments and sharp curves should be
avoided. If there is a sudden break in the slope of the
land, a channel should be located directly above it.
• Terraces should not be so short that they impede
farming operations, not so long that the channels
would require too great a cut. The maximum length of
terrace channel draining to one side only is about 350
to 450m. The flow velocity in the terrace should not
exceed 0.6m/s, although on sandy soils 0.45m/s is more
suitableand0.3 m/s on pure sands.

Diversion or Interceptor Drains
• To protect areas from flooding by surface runoff
from adjacent higher grounds a diversion or
interceptor drain can be constructed at the foot of
these uplands. For areas not larger than 2 to 2.5
ha at the most, the diversion or interceptor drains
can be constructed like terraces; for larger areas
they should be constructed as grasses
waterways.
• To prevent diversion or interceptor drains from
silting up, a filter strip can be constructed on the
upslope side the ditch. A depth of 0.45m for the
drain and a cross-sectional area of about 0.70m2
are considered minimum values.

Reclamation and Management of Salt-
affected Soils
The process and practices involved in bringing saline
and alkali soils into productive conditions are known
reclamation measures. The efficiency of any reclamation
measure depends on the proper diagnosis of the problem
soils.
Hence, before any reclamation procedure is applied, it is
essential to determine
1. The nature of the soil , as saline, alkali or saline-alkali,
2. Degree of salinity or alkalinity in the soil profile,
3. Quality of water available for leaching out the salts and
the reaction products,
4. Drainage characteristics of the soil
5. Topography of the land, and
6. Presence of any hard pan of lime or clay in the soil strata.

Reclamation Procedures
Reclamation of a soil on a temporary basis can be done by
1. Removing the salt crust from the surface of the soil,
2. Ploughing salt- surface crust deep into the soil, and
3. Neutralizing the effects of certain salts by adding other
salts.
However, permanent reclamation can be
obtained by the following procedures:
1. Lowering of water table (if high).
2. Improving infiltration rate of the soil.
3. Leaching of salts in saline soils and providing adequate
sub-surface drainage.
4. Replacing excessive exchangeable Na by Ca salts and
removing the replaced products.
5. Suitable management practices.

Characteristics of Good Tile Drain
Clay or concrete tile should have the following
characteristics
1. Resistance to weathering and deterioration in
the soil;
2. Sufficient strength to support static and impact
loads under conditions for which they are
designed;
3. Low water absorption, that is a high density;
4. Resistance to alternate freezing and dissolving;
5. Relative freedom from defects, such as cracks
and ragged ends;
6. Uniformity in wall thickness and shape,

• Type of Materials of Tile
1) Concrete Tile
Concrete tile should be made with high-
quality materials and be properly cured.
Concrete tile is made of sand and cement, the
usual proportion being 1 part cement to 3 or 4
parts sand. Good-quality concrete tile are
resistant to freezing and dissolve but may be
subject to deterioration in acid alkaline soils,
the tile should be extra-quality and made with
cements having specific chemical
characteristics. Curing methods will also
depend on the degree of acidity or alkalinity of
the soil (Miller and Manson, 1948).

2) Clay Tile
Clay drain tile is classified as either
common or vitrified. Clay tile should be well
burned, with no checks and cracks and should
have a distinct ring when tapped with metal object.
Ordinary drain tile are not burned as hard as
vitrified sewer tile. Clay tile made from shale are
more durable and usually have less absorption
than those made from surface clays. Clay tile are
not generally affected by acid or alkaline soils.
When subjected to frequent alternate freezing and
dissolving conditions, it is safer to use concrete
tile, although most clay tile are resistant to frost
damage. Where clay tile are laid with less than 0.7
m of cover, they should be extra-quality.

3) Corrugated Plastic Tubing (CPT )
The use of plastic pipes for drainage especially
corrugated tubing’s is becoming increasingly popular. CPT
is not damaged by soil chemicals is light in weight and
is shipped in long lengths. Tubing should be uniform in
color and density and free from visible defects. Parallel
plate stiffness when deflected at 127 mm per minute
should not be less than 0.17 N/mm per millimeter of length
at 5 percent deflection and 0.13 N/mm per millimeter of
length at 10 percent deflection for diameter up to
200mm. Standards for PVC tubing (more common in
Europe) are covered in ASTM F800. The CPT are made in
size 4 to 10 cm. diameter for laterals. Larger sizes are
available for collector drains. They are made in black,
white or other colours, depicting on the pigment used.

The most common resin materials are PVC
(polyvinyl chloride) and HDPE (high density
polyethylene). Both are made from
thermoplastics and are subject to damage by
heat and brightness when exposed to sunlight.
Plastic tubing’s can be easily joined together by
means of slight, exposures to about one year.
Plastic tubing’s can be welded. To allow water to
enter, the plastic drainage pipe is perforations
(slits) are 30 to 60 in number per meter and the
usually 0.6cm wide and 2.5 cm long and
represent a total area of 4.5 or 9 sq.cm per
running metre.

Layout of Drainage Systems
The combinations of two or more of these types
are frequently required for the effective drainage of
an area.
1) Random Drainage System
The random or natural system of drain lines is
used where there are scattered wet areas in a field
somewhat isolated from each other. Drain lines are
laid more or less at random to drain these wet areas. In
most cases the drain main follows the largest natural
depression in the field and sub mains and laterals
extend to the individual wet areas. If the individual wet
areas are large, the arrangement of the submain and
lateral for each wet area may utilize the gridiron or
herringbone tile pattern to provide the required
drainage.

2) Herringbone Drainage System
The herringbone system consists of parallel
laterals that enter main at an angle, usually
from both sides. This system is used where
the main or sub main lies in a narrow
depression. In this system, there is
considerable double drainage, where the
laterals and mains join and the system may not
be very economical. However, it is
particularly suitable, where the laterals are
requires thorough drainage.

Fig. (a) Random or natural, (b) Herringbone,
(c) Gridiron and (d) Interceptor or Cutoff

3) Gridiron Drainage System
The gridiron or parallel system is similar to the
herringbone system except that the laterals enter the
main from only one side. It is used on flat regularly
shaped fields and on uniform soil. It is more
economical than the herringbone system because the
number of junctions and the double drained areas are
reduced. Where there is a broad flat depression, which
is frequently a natural water course, a main may be
placed on both sides of the waterway. This system,
known as double main system, is essentially to
separate gridiron patterns. Placing a main on each side
of the depression serves a dual purpose; it intercepts
the seepage water and provides an outlet for the tile
laterals.

4) Interceptor Drainage and Relief Drainage
The intercept or cut off system is used to
intercept seepage water from hillsides; wet
areas are formed by seepage water moving
horizontally through permeable layers, which
lie over an impermeable layer. This condition is
indicated by seepage along horizontal plane
near the foot of the slope or at a break in
grade. The intercept drain should be laid along
the bottom of the permeable layer in order to
intercept the seepage causing the damage.

Drain Envelop (Socks)
An envelope (or socks)is defined as the material
placed around the pipe drains. Envelop/Filter is an
essential component of a subsurface drainage system,
especially in irrigated region and in non-cohesive soils
having clay fraction less than 40%.
Functions of envelope are as follows :
• Filter Function : to prevent to restrict the soil particles
from entering the pipe where they may settle and eventually
clog the pipe;
• Hydraulic Function: to constitute a medium of good
permeability around the pipe and thus reduce entrance
resistance.
• Bedding Function: to provide all-round support to the pipe
in order to prevent damage sue to the soil load. Note that
large-diameter plastic pipe is embedded in gravel especially
for this purpose.

• In view its functions, the envelope should be so designed
that it prevents the entry of soil particles into the pipe,
although a limited flow of clay particles will do little harm,
because they mainly leave the pipe in suspension.
• A wide variety of materials are used as envelopes for
drain pipes, ranging from organic and mineral, to
synthetic and mineral fibers.
• Several types of sheet filters called geotextiles, are
available commercially.
• Filters are made from nylon, polypropylene and other
materials.
• One recommendation is that the 50 percent particle size
of the soil should be greater than or equal to the
average diameter of openings in the filter.
• In humid areas, it is often sufficient to place the topsoil
or permeable material from the sides of the trench
around the tile, which serves as the only filter material.

• The most effective filter material is well-
graded gravel.
• Gravel filters of pit run or graded materials are
extensively used in tile installation in the arid
regions.
• The filter material should be more previous than
the base soil so that hydraulic pressure will not
build up.
• The voids between the filter particles must be
small enough to prevent soil particles from
entering the tile through the filter material.
• Clogging of the filter or excessive settlement due
to soil movement may occur if the voids in the
filter material are too large.
• The minimum thickness of filter material
placed around the tile should be 7.5 cm.

• Fine textured soils with clay content of more than about
0.25 and 0.30 are characterized by a high structural
stability and they mainly do not require the envelope.
• There is a need of a permanent envelope, completely
surrounding the pipe, only as an effective filter, because
there is no high entrance resistance. A thin geotextile
envelope is probably the best solution here.
• In the finer-textures soils of this category (clay content
less than 0.25 to 0.30, but more than 0.10 to 0.15), the
trench backfill remain stable and of good permeability.
• At the coarse-textured side of the intermediate soils
(soils with a clay content below 0.5 and high silt
content), the trench backfill is likely to be unstable, and
also, the trench backfill may become poorly permeable
through a rearrangement of the soil particles. I

2) Synthetic Envelopes
Many of the drawbacks of gravel envelops can
be overcome with the use of synthetic envelopes.
The wide variety in their materials, however and in
their characteristics make it extremely difficult to
develop sound design criteria. Consequently, many
criteria have been developed which most of them
based on the opening size of the envelope
material.

3) Organic Envelopes
Design specifications of organic envelopes
are based on the same principles as those for
synthetic envelopes. The lifetime of organic
envelopes, however, is limited because of their
origin. The lifetime depends on micro-biological
activity in the soil, which is a function of
temperature, soil chemical properties, and the
presence of oxygen. Hence, the rate of
decomposition is slower in temperate climates
under reduced (submerged) conditions.
Consequently, organic envelopes are mainly
used in Western Europe and are not
recommended for arid and semi-arid regions.

Installation of Drainage System
• Prior to making a field survey for drain pipe installation,
preliminary investigation and inspection of field to be
drained are made. The various factors affecting drainage
are carefully investigated and considered.
• Before deciding on a pipe drainage scheme, it should be
established that the soil will respond to pipe drainage and
there are no soil physical conditions prohibiting its
installation. A suitable outlet (an open ditch or stream) is
necessary.
• An accurate contour map of the area is needed to locate
the pipe system, except where the proper layout can be
determined by field inspection.
• A careful study is made of the best way to run the lines of
pipe and of the pipe drainage system to use.
• The pipe outlets are placed at the most advantageous
points and the number of outlets is kept to a minimum.
• Pipe lines are given as much slope as possible. Economy is
obtained by using the longest possible laterals and
reducing the average length of mains per unit area.

The topography and soil conditions will
determine the placement of laterals with
respect to slope. Often, several arrangements of
tile lines will have to be plotted determine
which is the most efficient and economical one.
Each line of tile is given a letter or number in order
to distinguish it from others (e.g. main A or B,
laterals 1,2,3,etc.). This numbering will help in
labeling profiles and making the bill of materials.
After the tile drains have been located on the map,
they are staked out on the field at the places
corresponding to those on the map.
Stakes are driven at every 15m or7.5 m as with
profile leveling.

System Layout
• The goal of drainage system layout and design is to
provide adequate and uniform drainage of field or
area.
• It's best to create a topography map of methods may
be used to create the map, including standard
topography survey, a GPS or a laser system.
• The topography map helps the designer assess overall
grade and identify the high or low spots in a field that
might pose challenges.
• The system outlet, whether an open channel or a closed
pipe, must be large enough to carry the desired drainage
discharge from a field quickly enough to prevent
significant crop damage.
• Drainage outlets are typically located three to five
feet below the soil surface.

• Drainage outlets must be kept clean of weeds,
trash, and rodents.
• These goals include removing water from an
isolated problem area, improving drainage in an
entire field, intercepting a hillside seep and so on.
• Even if a drainage system is installed on an
incremental basis-some this year, more next year
and so on system planning should not be
piecemeal.
• When selecting a layout pattern for a
particular field or topography, lateral drains, or
field laterals, should be oriented with the field's
contours as much as possible.

Fig. Pipe drainage layout adopted to uniform slope of
the land surface

In the areas with a uniform land slope (i.e. with
parallel equidistant contours), the collector is
preferably installed in the direction of the main
slope, while the field drains run approximately
parallel to the contours. To take the advantage
of the slope for the field drains also
herringbone system can be applied.
A major drawback of the latter two alternatives
is that the field drains are only on one side of
the collector. The inherent total collector length
and the consequent higher costs make these
solutions suitable only under special conditions.

Mole Drainage System
• Mole drains are unlined circular or oval
underground earthen channels, formed within
highly cohesive or fibrous soils by a mole
plough.
• The mole plough has a long blade-like shank to
which is attached a cylindrical bullet-nosed
plug, known as a mole. The mole plough is
drawn by a high powered prime mover.
• As the plough is drawn through the soil, the mole
forms the cavity, at a set depth.
• Mole drainage is not effective in those soils that
are so loose, that the channel produced by the
mole will collapse. They are also not suitable in
heavy plastic soils where the mole seals soil to
the movement of water.

• Mole channels usually range in diameter from 7.5 to 10
cm.
• They may empty into open ditches; a short length of
metal tubing may be useful for protecting the outlet.
• Spacing ranges from 1.5 to 9 m and depth from 50 to 75
cm. Mole drains are formed about 40 to 60 cm below the
soil surface, well into the impermeable subsoil.
• The success of mole drainage depends upon the successful
exploitation of the two basic forms of soil failure which
occur when a tine is pulled through a cohesive soil.
• Failure occurs in shear along well defined rapture planes
which radiate from the top of the tine (of the mole
plough) towards the land surface at an angle of about
450 to the horizontal.
• The results in the soil cracking and an increase in the soil
porosity as well as hydraulic conductivity, when the
depth of the mole drain reaches a critical depth.

• The critical depth usually occurs as a depth corresponding to an
aspect ratio (tine depth :tine thickness) of about 5:7.
• The depth of the mole drain should be just below the critical
depth.
• The cracks facilitate direct access of impeded water to the mole
channels.
• Moling is best suited to clay soil with a clay content of over 3 %.
• The ideal time for laying the mole drain is soon after the harvest of
the crops, when the upper part of the soil profile has dried.
• The length of the mole and their effective life time are influenced
by (i) the basic stability of the soil to repeated wetting, (ii) the
uniformity of the soil and (iii) the conditions at the time of
installation.
• Safe lengths vary from 20 to 80 m depending on the soil type.
• It is a good practice to rarely the mole drain every 3 to 7 years.

• Safe gradients usually range from 0.2 % to
3.0%.
• Mole outlet protection comprises of a 1to 2 m
long pipe inserted into the mole channel.
• It is necessary to install the drain trenches first
and then construct the mole drains.
• Clean gravel of size ranging from 3 to 5 mm
are suitable.
• Hence, it is important that the collector pipe sizes
are designed to meet this requirement.
• The main aim of a mole drainage system is to
establish a medium deep drainage base in the
soil.

Tube well (Vertical Drainage)
Tube well drainage is a technique of controlling
the watertable and salinity in agricultural areas. It
consists of pumping, from a series of wells, an amount
of groundwater equal to the drainable surplus.
Advantages:
1. The total length of open surface drains is considerably
less with tube well drainage than with another
subsurface drainage system.
2. On undulating with local depression that has no natural
outlets, the pumped water is generally disposed of
through pipelines connecting the various wells.
Excessive earth moving is thus avoided, because no
deep canals or ditches need to be dug through
topographic ridges. Moreover, the absence of such
canals and ditches allows more efficient farming
operations.
3. Such a pipeline system may cost considerably less to
maintain than open drains and transport canals.

• Tube well drainage enables the watertable to be lowered to
a much greater depth that do the other subsurface drainage
systems. This means that a greater portion of excess water
can be stored before it has to be removed, whilst in arid
and semi-arid regions a deeper watertable reduces
salinization of the soil.
• The deeper layers or substrata may be much more pervious
than the layers near the surface. Pumping from these layers
may reduce the artesian pressure that is often present,
creating instead a vertical downward flow through the
upper layers. If the pervious substrata are found at a depth
of 5 m or more, it is only with tube well drainage that full
benefit can be derived from these favourable
hydrogeological conditions.
• If the water in the pumped aquifer is of good quality, it can
be used for irrigation. The drainage water then has an
economic value, which may contribute considerably to the
economic feasibility of the venture.

Disadvantages :
• A pumped well is more certain disadvantages. To mention a
few.
• The energy required to operate a multiple-well system has to
be purchased as electricity or fuel.
• Legal regulations sometimes forbid the use of pumped wells
for land drainage, pumping from wells can reduce the pressure
in aquifers to such an extent that existing domestic wells cease
to flow.
• Unlike the other subsurface drainage systems, tube well
drainage is not economically feasible in small areas because
too much of the water drained out of the area then consists of
foreign' water (i.e. groundwater flowing in from surrounding
areas).
• Tube well drainage may not be technically and economically
feasible in areas where the artesian pressure in the aquifer is
too high or where seepage is excessive.

• If during the growing season, the watertable rises to the land surface
(because, for instance, of a heavy rainstorm after irrigation), it has to be
lowered rapidly because most crops have only a limited tolerance to
waterlogging. This implies a high drainage rate (i.e. dense network of
wells) of course, the high investment costs of installing a dense network
of wells can be reduced by spacing the wells farther apart and pumping
them continuously, but this in turn will raise the cost of operating and
maintaining the wells.
• Tube well drainage can only be successfully applied if the hydraulic
characteristics are favourable (i.e. if the transmissivity of the aquifer is
fairly high) only then can the wells be widely spaced. If the aquifer is
semi-confined, an additional criterion is the value of the hydraulic
resistance of the upper clay layer (the acquitted). The value must be low
enough to ensure an adequate percolation rate. Hence, a decision in
favour of tube well drainage should only be taken after a careful
hydrogeological investigation has proved that its application is
practicable.
• The salt content of the drainage water can be considerably higher with
tube well drainage because the streamlines towards the well occur
deeper in the aquifer than those towards pipe drains or ditches.

Bio-drainage
• Bio-drainage refers to the drainage effects of
the high rate of withdrawal of groundwater
by certain plants (e.g. eucalyptus,
poplar).However, the quantity of water utilized
is rather limited. The transpiration capacity of
a plant depends upon its species, root depth and
spread, canopy area, leaf area and leaf structure.
When the transpiration is met primarily by
drawing groundwater, the process is called as
bio-drainage.

• This technique is applicable to physically and chemically
degraded lands. It is then an alternate use, rather than reclamation
of such lands for normal crop production.
• The major advantage of bio-drainage is a low-cost measure, does
not require gravity outlet, operation and maintenance are
required only at the plant establishment stage, no energy for
operation and supply of fuel and fodder material.
• The disadvantages of bio-drainage are some area is needed for
growing the plantation, which cannot be available for crop
cultivation and good quality water should be available for plant
establishment.
• The perspective sites for tree plantation for bio-drainage are
government lands and fallow lands with low productivity.
• The difference between vertical drainage and bio-drainage is
that in case of vertical drainage, the area encompassed by the tube
well network is available for normal crop production but in case of
bio-drainage by a cluster of plants, the area within the cluster
cannot be put to use for normal crop production.

IDE 354 ppt final

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IDE 354 ppt final