There is no universal classification or standard terminology for terraces and ditches; the following is based on their sites and major uses.
- On steep slopes (exceeding 7 degrees or 12%)
Continuous type:
- Irrigation or level bench terraces
- Upland bench terraces
Discontinuous type:
- Hillside ditches
- Orchard terraces
- Individual basins
Transitional type:
- Convertible terraces
- Intermittant terraces
- On gentle slopes (less than 7 degrees or 12%)
Drainage type: - Broadbase graded terraces
Absorption type:
- Broadbase level terraces
Soil retarding type:
- Natural terraces
Diversion type:
- Diversions
- Cut-off ditches
Storing type:
- Gradoni
- Infiltration ditches
Terraces are mainly used for erosion control and for growing crops on sloping lands. The selection of suitable types of terraces depends on many factors, including the following:
- Physical conditions of the site such as slope, soils, rainfall, etc.
- Socio-economic conditions of the country such as labour conditions, land use
patterns, cropping and farming systems, population densities, etc.
- Farmers' or land owners' conditions and interests including their age and willingness to
accept innovations, available resources, main crops, tools to be used, etc.
When planning the application of terraces or any soil conservation work it is the farmer who, should make the final decision. However, local government officers or watershed conservationists should assist him by examining the site and explaining what treatment is needed.
- On steep slopes
Fig. 2 shows the relationships between crops and the different types of terraces required on steep slopes for small and medium farms. This can be used as a general guide for the selection of terraces.
- On gentle slopes
On large farms and gentle slopes where machines are used for cultivation, broadbase terraces are the main conservation treatment. In regions with heavy rainfall, and/or heavy soils, the graded or drainage type is used while in regions with light rainfall and/or light soils, the level or absorption type is generally used.
On small farms situated on gentle slopes, natural terraces, which possess the advantage of being labour-saving, can be employed.
The selection of ditches is usually easier than the selection of terraces. There are fewer types of ditches; they are relatively easy to build and they can be used on both steep and gentle slopes. The decision on which ditch to, use depends mostly on plans for handling of run-off water. For intercepting and diverting run-off, diversion or cut-off ditches should be used; for storing and infiltrating run-off, gradoni or infiltration ditches are recommended.
