TERRACES

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TERRACES
Haris Khurshid
2008-ag-1775
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What is Terrace. . ?

• A terrace is an embankment or ridge of earth
  constructed across a slope to control runoff and
  minimize soil erosion

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TERRACING

• It is the practice of making such structures
  like embankments along with flattened portions of
  land on a slope to utilize it precisely, keeping
  in mind the protection and improvement of soil
• Or
• Terracing is the mechanical practice used on
  slopping agricultural land to reduce the length
  and /or the degree of slope

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TERRACE FARMING

• Cultivation of crops on terraces keeping
  suitability of a particular crop and good crop
  husbandry practices in mind to utilize that land
  maximum to get wholesome returns

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Objectives of Terracing

• Land use
• Soil conservation
• To check soil erosion
• To improve soil structure
• To maintain fertility status
• Water conservation
• Increase infiltration rate
• Decrease runoff
• Storage of water by water harvesting
  occasionally

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Types of Terraces

• Ridge Type Terrace
• Which remove or retain water on sloping land
• Level terrace or contour Bunding
• Bench Terrace 
• Which reduce the land slope

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Ridge type Terraces

• Depending on the width of the base, ridge
  type terrace may be classified as
• Narrow Based Terraces
• Medium based Terraces
• Broad Based Terraces

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• Narrow-base terraces
• Where soil movement is limited to about
  three meters
• Medium-base terraces
• Where soil movement is three to six meters
• Wide or broad-based terraces
• Where soil is moved more than six meters, but
  normally less than 12 meters

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Broad based Terraces

• A broad base terrace has a ridge 25 to 50cm
  high with gently slopping sides and a dish
  stopped channel along the upper side constructed
  to control erosion by diverting runoff at a non
  erosive velocity. based on greed it is divided
  or classified as
• Level Terrace
• Graded Terrace

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• Level terrace
• A level terrace follows the contour line, in
  control to a graded terrace and recommended in
  areas having permeable soil.
• Graded terrace
• A grads terrace has a constant or variable
  grade along its lengthened used to convey excess
  runoff at safe velocity into a vegetated waterway
  or channel.

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Bench Terracing

• A bench terrace is shelf like embankment of
  earth with a level or nearly level top and a step
  or vertical downhill face constructed along the
  contour of sloping land.
• In very stable soils, the walls may be held
  by vegetation, and in others some structural
  walls are necessary, as brick, stone or timber.

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Cross section showing benched effect
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. A sketch of a typical bench terrace
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Classification of bench terraces based on slope

• Absorption or Level Terraces
• These are constructed exactly on the contour and
  provided with sufficient freeboard so that they
  can trap all the rain that falls.
• They are principally used in dry areas where
  rainfall is low and moisture for crop production
  is, therefore, at a premium.

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Absorption or Level Terraces
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• Outward-sloping terraces
• Bench terraces sloping outwards are effective
  only in low rainfall areas with a permeable soil
  of medium depth at lower ends graded channels are
  provided for safe disposal of runoff.
• Suitable for orchards
• Better on steep slopes
• Used to mild slope
• Slope up to 15

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• Some terraces have a grassed waterway
  outlet. . .
• While other terraces channel runoff water to
  a storage section where it is released slowly
  through a surface inlet and underground pipe or
  tile. . .

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• 3) Reverse/Inward sloping Terraces
• In heavy rainfall areas, bench terraces of
  sloping inwards type are more effective. It
  prevents in-ponding of water and useful for crops
  susceptible to water logging.
• No super-saturation of
• profile
• Back slope stabilization
• Runoff towards hillside

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• 4) Conservation bench terraces
• Modified form of level terrace
• In limiting soil moisture
• Use moisture of
• Uncropped area by runoff

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Conservation bench terracing
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Pictorial comparison of slope based bench terraces
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Classification of bench terraces based on use

• Depending upon the purpose for which they are
  used, bench terraces are classified as follows
• Hill type Bench Terraces
• Irrigated Bench Terraces
• Orchard Bench Terraces

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• Hill type Bench Terraces
• It is used for hilly areas whit a reverse
  grad towards the hill.

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• Irrigated Bench Terraces
• Level benches are adopted under irrigated
  conditions. The level table top terraces are
  referred to as irrigated bench Terries.

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• Orchard Bench Terraces
• Narrow width terraces for individual trees are
  prepared in this type. These are also referred as
  intermittent terraces and step terraces. The
  conversion of land into bench terraces over a
  period of time is referred as gradual bench
  terracing.

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Designing construction of Bench terraces

• Factors of Site suitability
• Soil depth
• Land slope
• Implement widths
• Back slope stabilization
• Runoff disposal

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• Steps in design of bench Terraces
• Step I-Type of the bench terrace
• Selection of the type of bench terrace
  depends upon the rainfall and soil, condition.
• Step II -Terrace Spacing 
• It is normally expressed in terms of the
  vertical interval between two terraces. It
  depends upon soil, slope, surface condition,
  grade and agriculture use.

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• Considerations for spacing
• Find Out the maximum depth of productive soil,
• maximum admissible cutting depth
• Given land slope
• From this, The width of the terraces can be
  computed for a given slope

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• Step III Terrace cross section
• Design of terrace cross consists of deciding
• 1 The slope2 Dimensions of shoulder bund3
  Inward slope in case of terraces sloping inward,
  and4 Outward slope in case of terraces sloping
  outward.

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• Step IV 
• The cross- section of shoulder bund along outer
  edge of terrace should also be designed suitably
  to make the bund stable against slipping.

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• TERRACING COSTS
• The costs that will be incurred in constructing
  terraces is largely a function of
• Width of terrace,
• Slope of land,
• Type of protection for the back slope
• construction machinery.

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Construction using a disc plough
C LINECUT LINE F LINEFILL LINE
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BENEFITS OF TERRACING

• Avoid soil erosion
• Up to 25 reduction in soil loss

Terraces in China (photo by UN - World Food
Programme)
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• Benefits . . .
• Reduction in Runoff(up to 30-35)
• Soil structure integrity
• Proper land use
• Feasibility of crop production in hilly areas
• Increase in soil moisture level

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• Benefits . . .
• Maintenance of soil fertility
• Water conservation(up to 45-55 saving)
• Enhanced infiltration rate
• Improved water holding capacity

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• TERRACE FARMING WORLDWIDE

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Terraces in northern Luzon Philippines 2000-B.C
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Level terracing in JAPAN
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Tea on bench terraces, BHUTAN
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KOREA
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TERRACES ON ERODED SOILS OF ISRAEL
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TERRACED FIELDS IN SA PA, VETNAAM
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RICE TERRACE PENORAMA IN BALI
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CHINA
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FLAT TERRACES IN HUNZA VALLEY, GILGIT
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SWAT VALLEY, PAKISTAN
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GRASSY TERRACES IN CHITRAL, PAKISTAN
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KASHMIR, PAKISTAN
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• FUTURE OF TERRACE FARMING

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THANKS
Questions ???