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WELCOME
NAMITHA M R
ID. No: 2015664502
M.Tech.
Land and Water
Management Engineering
TNAU
DESIGN OF SUBSURFACE
DRAINAGE SYSTEM
SUBSURFACE DRAINAGE
Drains laid deep in the
ground
and covered
Fig: Subsurface drainage system-sectional view
Placed at suitable depth and grade
below the ground surface
Lowers the capillary surface and
water table
Aerates the ro...
1.Advantages of Subsurface Drains
Provides aeration to root zone
Improves soil structure and
maintains soil temperature
...
Removes undesirable salts from
root zone
Decreases chances of flood hazards
Occupies no surface land
Small capacity dr...
2. Disadvantages of subsurface drains
Require high initial cost
Requires steeper gradient
Repair works are costly and
i...
3. Subsurface drainage methods
Tile drains
Mole drains
Drainage wells
Deep open drains
Combination of tile and
mole d...
4. Investigations for subsurface drainage
Topographic map of the area
Data of soil physiochemical properties
Position o...
Logs of soil and subsurface material
Crops to be grown and their drainage
requirements
Irrigation practices and their
r...
5. Groundwater studies for planning
subsurface drainage
3 parameters:
oDepth and fluctuation of groundwater
table
oQualit...
DESIGN OF TILE DRAINAGE SYSTEM
Consists of :
1. Layout of the system
2. Depth and spacing of the drain
3. Size and grade ...
1. Layout of tile drainage system
Drainage system comprises of laterals,
main drains and an outlet
Laterals
Main drains
O...
Different layouts of tile drainage
system:
a) Natural system
b) Parallel system
c) Herringbone system
d) Grid iron system...
f) Intercepting system
g) Double system
h) Grouping system
i) Composite system
j) Zig zag system
k) Sink hole system
a) Natural system:
b) Parallel system: c) Herringbone system:
d) Grid iron system: e) Random system:
f) Intercepting system:
g) Double system: h) Grouping system:
i) Composite system: j) Zigzag system:
2. Depth and spacing of tile drains
 Depth and spacing are closely inter related
 Depends on:
Texture of soil
Hydrauli...
Outlet conditions
Topography of land
Salt content of soil
Agronomic practices
 Drain depth: From ground surface to th...
 Deeper the drain, wider the spacing, lesser
the number of drains required
 Drain spacing-
’Hooghouts drain spacing form...
H-Height of water in midway between 2
drains
S- Drain spacing
D-Distance from the impermeable layer to the
maximum height ...
3. Size and grade of the tile drains
 Drains are designed based on
Manning's formula
 Drains are laid on longitudinal sl...
Diameter of tile drains,
d = 5.3(Dc)0.375 A0.375 S-0.1875
where,
d- Internal diameter of tile drain, cm
Dc – Drainage coe...
4. Material of tiles
 Clay, Concrete, PVC/Plastic pipes, Bituminous fibre or
steel
 Pipe material should be:
Resistant ...
5. Envelope materials and accessory
structures
a) Envelope materials:
 Materials that cover the drains placed
in less per...
Coarsest material
is placed
immediately
over the tile
Minimum thickness
of envelope: 7.5cm
Recommendations for gravel envelope
(USBR):
For uniform soils,
D50 of envelope/D50 of soil = 5 to 10
For graded soils,
...
b) Manholes and sedimentation basins:
 Vertical structures
 Installed at regular intervals along the
tile lines
 Constr...
A man can enter and
work within it
Placed about 60 cm
below ground surface
Covered by
concrete block
c) Inlet to tile drains:
 Allows water into the drain
 Two types:
 Blind inlet- cheaper but chances of
clogging
 Surfa...
Fig: Blind inlet
Fig: Surface inlet
d) Outlet for drains:
 Water from tile drains are discharged into
big size surface drains
 Either by gravity or pumping
...
e) Installation of tile drains:
 Consists of:
 Excavation of a trench
 Laying the tile at predetermined grade,
depth an...
MULTIPLE WELL SYSTEM
MULTIPLE WELL SYSTEM
Multiple wells are installed in a common
area of influence
Cone of depressions overlap each other
...
Fig: Multiple well system
Wells are arranged in various patterns
Isolated groups or continuous pattern
Suction lines of each well is connected
to...
DESIGN OF SUBSURFACE DRAINAGE SYSTEM
DESIGN OF SUBSURFACE DRAINAGE SYSTEM
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DESIGN OF SUBSURFACE DRAINAGE SYSTEM

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DESIGN OF SUBSURFACE DRAINAGE SYSTEM

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DESIGN OF SUBSURFACE DRAINAGE SYSTEM

  1. 1. WELCOME NAMITHA M R ID. No: 2015664502 M.Tech. Land and Water Management Engineering TNAU
  2. 2. DESIGN OF SUBSURFACE DRAINAGE SYSTEM
  3. 3. SUBSURFACE DRAINAGE Drains laid deep in the ground and covered
  4. 4. Fig: Subsurface drainage system-sectional view
  5. 5. Placed at suitable depth and grade below the ground surface Lowers the capillary surface and water table Aerates the root zone
  6. 6. 1.Advantages of Subsurface Drains Provides aeration to root zone Improves soil structure and maintains soil temperature Avails land for early cultivation Facilitates easy movement of farm machines
  7. 7. Removes undesirable salts from root zone Decreases chances of flood hazards Occupies no surface land Small capacity drains are required Less maintenance cost compared to surface drains
  8. 8. 2. Disadvantages of subsurface drains Require high initial cost Requires steeper gradient Repair works are costly and inconvenient Only seepage water is removed Construction is difficult
  9. 9. 3. Subsurface drainage methods Tile drains Mole drains Drainage wells Deep open drains Combination of tile and mole drains
  10. 10. 4. Investigations for subsurface drainage Topographic map of the area Data of soil physiochemical properties Position of ground water table and its fluctuation Quality of groundwater
  11. 11. Logs of soil and subsurface material Crops to be grown and their drainage requirements Irrigation practices and their requirements
  12. 12. 5. Groundwater studies for planning subsurface drainage 3 parameters: oDepth and fluctuation of groundwater table oQuality of groundwater oHydraulic conductivity of the subsoil material
  13. 13. DESIGN OF TILE DRAINAGE SYSTEM Consists of : 1. Layout of the system 2. Depth and spacing of the drain 3. Size and grade of the tile lines 4. Material of tiles 5. Envelope materials and accessory structures 6. Installation of tile drains
  14. 14. 1. Layout of tile drainage system Drainage system comprises of laterals, main drains and an outlet Laterals Main drains Outlet
  15. 15. Different layouts of tile drainage system: a) Natural system b) Parallel system c) Herringbone system d) Grid iron system e) Random system
  16. 16. f) Intercepting system g) Double system h) Grouping system i) Composite system j) Zig zag system k) Sink hole system
  17. 17. a) Natural system:
  18. 18. b) Parallel system: c) Herringbone system:
  19. 19. d) Grid iron system: e) Random system:
  20. 20. f) Intercepting system:
  21. 21. g) Double system: h) Grouping system:
  22. 22. i) Composite system: j) Zigzag system:
  23. 23. 2. Depth and spacing of tile drains  Depth and spacing are closely inter related  Depends on: Texture of soil Hydraulic conductivity Types of crops grown Extend of surface drainage
  24. 24. Outlet conditions Topography of land Salt content of soil Agronomic practices  Drain depth: From ground surface to the bottom of the tile, usually 1-1.5m  Tiles are placed above impermeable layer, if any
  25. 25.  Deeper the drain, wider the spacing, lesser the number of drains required  Drain spacing- ’Hooghouts drain spacing formula’ S2 = 4K/R [H2-2hd+2Hd-h2] where, d- Depth to the impermeable layer from the drain bottom h- Height of water in the drain
  26. 26. H-Height of water in midway between 2 drains S- Drain spacing D-Distance from the impermeable layer to the maximum height of water between the drains K- Hydraulic conductivity R- Replenishment rate
  27. 27. 3. Size and grade of the tile drains  Drains are designed based on Manning's formula  Drains are laid on longitudinal slope: 0.05-3%  Working grade: 0.2%  Size of tiles pipes: 30-90cm long, 10-15cm diameter
  28. 28. Diameter of tile drains, d = 5.3(Dc)0.375 A0.375 S-0.1875 where, d- Internal diameter of tile drain, cm Dc – Drainage coefficient, cm/day A-Drainage area, ha S- Hydraulic gradient or tile grade, m/m
  29. 29. 4. Material of tiles  Clay, Concrete, PVC/Plastic pipes, Bituminous fibre or steel  Pipe material should be: Resistant to weathering and freezing Have high density Have sufficient strength to withstand static and dynamic loads Have uniformity in shape and wall thickness
  30. 30. 5. Envelope materials and accessory structures a) Envelope materials:  Materials that cover the drains placed in less pervious strata  Gravel, coarse sand etc.  Prevents inflow of soil into the drains  Increases effective drain diameter
  31. 31. Coarsest material is placed immediately over the tile Minimum thickness of envelope: 7.5cm
  32. 32. Recommendations for gravel envelope (USBR): For uniform soils, D50 of envelope/D50 of soil = 5 to 10 For graded soils, D50 of envelope/ D50 of soil = 12 to 58
  33. 33. b) Manholes and sedimentation basins:  Vertical structures  Installed at regular intervals along the tile lines  Constructed by concrete or brick masonry  Helps in cleaning and inspection
  34. 34. A man can enter and work within it Placed about 60 cm below ground surface Covered by concrete block
  35. 35. c) Inlet to tile drains:  Allows water into the drain  Two types:  Blind inlet- cheaper but chances of clogging  Surface inlet- have provisions to prevent the trash entering into the drains but costly
  36. 36. Fig: Blind inlet Fig: Surface inlet
  37. 37. d) Outlet for drains:  Water from tile drains are discharged into big size surface drains  Either by gravity or pumping  Gravity outlet- invert level of tile drain is higher than fully supply level of surface drain  Pump outlet- bed level of the outlet is higher tan the discharging tile drain
  38. 38. e) Installation of tile drains:  Consists of:  Excavation of a trench  Laying the tile at predetermined grade, depth and spacing  Putting the envelope material and backfilling the soil  Installation of tile should start from out let
  39. 39. MULTIPLE WELL SYSTEM
  40. 40. MULTIPLE WELL SYSTEM Multiple wells are installed in a common area of influence Cone of depressions overlap each other Results in increased drawdown in each well Provides more drainage effect
  41. 41. Fig: Multiple well system
  42. 42. Wells are arranged in various patterns Isolated groups or continuous pattern Suction lines of each well is connected to a common pump

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