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close this bookSpecial Public Works Programmes - SPWP - Anti-Erosion Ditches - Training Element and Technical Guide for SPWP Workers, Booklet No. 1 (ILO - UNDP, 84 p.)
close this folder3. Different types of anti-erosion ditches
View the document(introduction...)
View the document3.1 Silt catchment pits
View the document3.2 Forest tiering
View the document3.3 Forest terracing
View the document3.4 Cropping terraces

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

NATURE OF THE SOIL

SLOPE

GENTLE

MEDIUM

STEEP

SAND

Crest-type terrace

Forest tiering

Silt catchment ditch



Normal-type terrace

Forest tiering

CLAY

Channel-type terrace

Forest tiering

Silt catchment ditch



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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