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close this bookResource Management for Upland Areas in Southeast Asia - An Information Kit (IIRR, 1995, 207 p.)
close this folder3. Soil and water conservation approaches
View the documentIntroduction to soil and water conservation approaches
View the documentBench terraces
View the documentComposting
View the documentContour tillage/planting
View the documentCover crops
View the documentCrop rotation
View the documentDiversion ditches
View the documentDrop structures
View the documentGrass strips
View the documentHedgerows
View the documentMinimum tilIage/zero tillage
View the documentMulching
View the documentRidge terraces
View the documentShifting cultivation
View the documentSoil barriers
View the documentSoil traps
View the documentWater harvesting

Diversion ditches

Diversion ditches are constructed along the contour lines and across slopes for the purpose to intercept surface runoff and divert it to suitable outlets. These ditches are the main soil conservation structures to manage runoff in upland areas. Diversion ditches are dug at varying intervals, depending on the steepness of the slope; the steeper the slope, the closer the interval. Ditches follow the contour, they are 1 meter wide at the top, 0.5 meter wide at the bottom and 0.5 deep.

Another variation is a waterway or drainage canal. A drainage canal is similar to a diversion ditch except that it is larger and deeper. It is normally dug along the boundary of an upland parcel of land, redirecting the runoff around the parcel. In Papua New Guinea, downslope drains also function as sediment traps.

Waterways dispose of the excess flow in diversion drains and surface runoff and channel it to the natural drainage channels.


Diversion ditches (A)


Diversion ditches (B)

Advantages

· Protects cultivated land from hillside runoff.
· Controls gully erosion.
· Slows down the erosive power of runoff.

Limitations

· If not properly designed, the ditches can overflow on to the farms during heavy rain.
· Needs support structures such as check dams and drops to effectively control erosion.
· Needs continuous repair and desilting.

Factors influencing adoption

Biophysical

· To be effective, ditches must be constructed along graded lines. Farmers need to know how to use the A-frame or water-tube level for determining grades.

Socioeconomic

· Part of the cultivable area is lost for constructing a ditch.
· Discharging water into a neighboring farmer's waterway can cause social conflicts.