Get premium membership and access questions with answers, video lessons as well as revision papers.
a) Tied ridges
- This consists of covering the whole surface with closely spaced ridges in two
directions so that the ground is formed into a series of rectangular depressions.
The rainfall is held in place where it falls until it infiltrates into the soil. There will
be no run-off and therefore no overland flow erosion. If the soil becomes saturated
and the depression fill up and then overflow, the ridges will break. If they fail, the
sudden release of run-off is likely to cause more serious damage.
b) Contour cultivation
- Contour tillage is carrying out ploughing, planting and cultivation on the contour.
This can reduce soil loss from sloping land up to 50% compared with cultivated
up-and-down the slope land. The effectiveness of contour farming varies with the
slope steepness. Protection against more extreme storms is improved by
supplementing contour farming with strip-cropping.
c) Grass strip
- This is a method by which strips of row crops and closely growing crops, planted
on the contour, are alternated. Erosion is largely limited to the row-crop strips and
soil removed from these is trapped in the next strip down slope which is generally
planted with a leguminous or grass crop. The grass strips are about 2-4m wide and
the cropped area about 15-45m wide depending on the slope. The size of strip will
be determined by the number of passes one would make - meaning that the size of
strip will be a function of the machinery to be used. The slope will also limit the
strip size e.g., sloppy lands requires a smaller strip width, yet a rather flat land will
necessitate a wider strip.
d) Gulley head dam
- Check-dams are constructed across the gully bed to stop channel bed erosion. By
reducing the original gradient of the gully channel, check-dams reduce the
velocity and erosive power of runoff. Run-off during peak flow is conveyed safely
by check-dams.
e) Gabions
- Gabions are rectangular boxes varying in size and are mostly made of galvanized
steel wire woven in to mesh.
- The boxes are tied together with wire and then field with stone and placed as
building blocks. Gabion boxes are commonly used gully treatment, roadside
protection, dam construction, river training, retaining wall, etc. Gabion check
dams are built by placing the galvanized wire boxes across gullies, “usually not
higher than 1.5 m spillway height”
maurice.mutuku answered the question on July 31, 2019 at 08:02