 | Special Public Works Programmes - SPWP - Anti-Erosion Ditches - Training Element and Technical Guide for SPWP Workers, Booklet No. 1 (ILO - UNDP, 84 p.) |
 |  | 3. Different types of anti-erosion ditches |
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3.4 Cropping terraces
These should be built on slopes of less than 15%. The gentleness of the slope they form (flattened cross-section) means that farm machinery has easy access to the land.
There are two main types of cropping terrace:
Channel-type terraces where the ditch is deeper that the hump is high and is used to divert the water.Crest-type terraces where the hump is raised and the ditch shallow so that the water is retained and absorbed.
CHANNEL-TYPE TERRACE
CREST-TYPE TERRACE
ABSORPTION NETWORK
DIVERSION NETWORK
CHOICE OF STRUCTURE
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NATURE OF THE SOIL |
SLOPE | ||
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GENTLE |
MEDIUM |
STEEP |
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SAND |
Crest-type terrace |
Forest tiering |
Silt catchment ditch |
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Normal-type terrace |
Forest tiering |
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CLAY |
Channel-type terrace |
Forest tiering |
Silt catchment ditch |
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Normal-type terrace |
Forest tiering |
SOME RULES FOR THE DESIGN OF DITCHES
Length of terraces: 200-400 m
Longitudinal slope:
2/1000 maximum
Difference in level between two ditches: 0.60-2.00
m
notes
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