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TERRACES Haris Khurshid 2008 -ag-1775
What is Terrace. . ? “A terrace is an embankment or ridge of earth constructed across a slope to control runoff and minimize soil erosion”
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”
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”
Objectives of Terracing q Land use q Soil conservation Ø To check soil erosion Ø To improve soil structure Ø To maintain fertility status q Water conservation ØIncrease infiltration rate ØDecrease runoff ØStorage of water by water harvesting occasionally
Types of Terraces v Ridge Type Terrace: Which remove or retain water on sloping land v Level terrace or contour Bunding v Bench Terrace: Which reduce the land slope
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
ü Narrow-base terraces; Where soil movement is limited to about three meters ü Medium-base terraces; Where soil movement is three to six meters ü Wide or broad-based terraces; Where soil is moved more than six meters, but normally less than 12 meters
Broad based Terraces A broad base terrace has a ridge 25 to 50 cm 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: Ø Level Terrace Ø Graded Terrace
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.
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.
Cross section showing benched effect
. A sketch of a typical bench terrace
Classification of bench terraces based on slope 1) 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. §
Absorption or Level Terraces
2) Outward-sloping terraces Ø 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. Ø Suitable for orchards Ø Better on steep slopes Ø Used to mild slope Ø Slope up to 15%
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. . .
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. Ø No super-saturation of profile Ø Back slope stabilization Ø Runoff towards hillside
4) Conservation bench terraces o Modified form of level terrace o In limiting soil moisture Use moisture of Uncropped area by runoff o
Conservation bench terracing
Pictorial comparison of slope based bench terraces
Classification of bench terraces based on use Depending upon the purpose for which they are used, bench terraces are classified as follows: v Hill type Bench Terraces v Irrigated Bench Terraces v Orchard Bench Terraces
Hill type Bench Terraces: It is used for hilly areas whit a reverse grad towards the hill.
Irrigated Bench Terraces: Level benches are adopted under irrigated conditions. The level table top terraces are referred to as irrigated bench Terries.
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.
Designing & construction of Bench terraces Factors of Site suitability: • Soil depth • Land slope • Implement widths • Back slope stabilization • Runoff disposal
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.
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
Step III: Terrace cross section: Design of terrace cross consists of deciding 1] The slope 2] Dimensions of shoulder bund 3] Inward slope in case of terraces sloping inward, and 4] Outward slope in case of terraces sloping outward.
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.
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.
Construction using a disc plough C LINE=CUT LINE F LINE=FILL LINE
BENEFITS OF TERRACING Ø Avoid soil erosion Up to 25% reduction in soil loss Terraces in China (photo by UN - World Food Programme)
Benefits. . . Ø Ø Ø 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
Benefits. . . Ø Maintenance of soil fertility Ø Water conservation(up to 45 -55% saving) Ø Enhanced infiltration rate Ø Improved water holding capacity
TERRACE FARMING WORLDWIDE
Terraces in northern Luzon Philippines 2000 -B. C
Level terracing in JAPAN
Tea on bench terraces, BHUTAN
TERRACES ON ERODED SOILS OF ISRAEL
TERRACED FIELDS IN SA PA, VETNAAM
RICE TERRACE PENORAMA IN BALI
FLAT TERRACES IN HUNZA VALLEY, GILGIT
SWAT VALLEY, PAKISTAN
GRASSY TERRACES IN CHITRAL, PAKISTAN
FUTURE OF TERRACE FARMING
THANKS Questions ? ? ?