Drainage systems concept.

1
Drainage systems concept.
are installed to combat the problems of water
logging and salinity associated with the water
table.
2
Choice of a drainage system.Depence on
following factors
        Topographic Factors.
        Soil-related Factors.
        Water-related Factors.
3
  Surface drainage

• remove water from the soil surface but are
  not usually designed to lower the water table in
  the soil profile.

have several advantages. low initial costs,
carry large volumes of water, remove surface
water rapidly, and are easy to construct. But do
not solve problems related to soil saturation
caused by a high water table.
4
Subsurface drainage
Drainage systems are installed to combat the
problems of water logging and salinity
associated with the water table.
5
     Drain Materials
Drainage material may be classified into
drainpipes and their accessories, envelopes and
auxiliary drain structures
Clay tile Cylindrical tiles very durable and
highly resistant to weathering and deterioration
in aggressive soil conditions .
Concrete tiles Pipes made with ordinary cement
are liable to deteriorate in acidic and high
sulphate soils, and by water carrying certain
alkali salts or other chemicals.
Corrugated Plastic Tubing (CPT) made of high
density polyethylene or polyvinyl chloride. are
durable, resistant to soil chemicals, easy to
join and handle.
6
Pipe accessories

• Subsurface drainage systems require accessories
  and special structures such as

End caps End caps prevent the entrance of soil
at the upstream drain-end opening.
7
Couplers They are used to connect two pipes of
the same diameter.
Reducers They are used to connect two pipe
ends of different diameters.
8
   Accessories to Subsurface Drains

• are installed to protect the drainpipe from soil
  particle entry. The porous device designed to do
  this is called envelope or filter.
•  
• These are put in place to surround subsurface
  drains. They are used to
• prevent fine-grained soil particles from entering
  drain
• provide a more permeable zone around drain
• provide a suitable bedding for drain.
• Materials used for filters include
• Sand and gravel - best for tile
• Organic soils or material - will decompose
• Fabrics - used with plastics

9
Drainage design
Typical procedure for designing a drainage system
consist of
1. Selecting a drainage rate or water table
height.
2. Estimating or measuring hydraulic conductivity
and other soil properties.
3. Selecting a suitable depth based on existing
constrains, and Computing spacing.
10
Depth and Spacing

• Depth and spacing are interrelated. Wider spacing
  can be used if drains are placed deeper. The
  objective is to provide an adequate root zone
  depth midway between the tile lines. Depth is
  measured from the soil surface to the bottom of
  the drainage pipe.

11
Installation guidelines

• Care during installation to prevent damage to the
  pipe during the backfilling operation.
• Bedding- Pipe bedded in gravel.Bedding material
  should be placed around the pipe to a depth at
  least 2" over the top of the pipe.
• Depth of Cover- If vehicular traffic is expected
  over pipe, there should be a minimum of 12" of
  cover.
• Proper Selection of Materials- Choose your
  materials according to application.

12
The problem of clogging of pipes and envelopes

• A major problem that is often encountered on
  subsurface drains is mineral clogging of pipes
  and envelopes.

Cause by sedimentation of mineral in drains due
to soil passing through the envelope and the
opening in the pipes.
13
Structure for controlled drainage and sub
irrigation

• There can be some reasons to reduce drainage
  temporarily( e.g. environmental considerations,
  unwarranted and harmful leaching if fertilizers
  ).

14
Drain maintenance

•      Surface drainage
• Drainage ditches can be kept in good working
  condition with proper care and regular
  maintenance. A ditch allowed to become obstructed
  with weed growth, bushes, and sediment will not
  provide good drainage.

15
Drain maintenance

• Sub surface drainage
• Regularly removing sediment deposits at the
  outlet and trees and shrubs from near the drain
  pipes prevents roots and sediment from blocking
  the drain.
• Jet flushingis a technique used to remove
  clogging and precipitating agents (e.g. soil
  particles and microbiological deposits, including
  iron ochre) from drainpipes through the impact of
  water jets.

16
Effects of drainage on the environment

• drainage has many benefits but is also known to
  contribute to environmental change and sometimes
  degradation, including
• poor-quality drainage effluent and contaminated
  receiving waters in some instances
• degradation of riparian zones
• loss of wetlands