Soil Erosion by Water/Techniques

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= Techniques in Soil Conservation =

The various conservation techniques can be described under the below headings:

Agronomic measures:
Utilize the role of vegetation to protect the soil against erosion.


 * Crop rotation
 * Limiting longterm erosion rates by eliminating perennial monoculture and reducing the share of erosion promoting crop types, such as row crops, within crop rotation.


 * Cover crops
 * Planting quickly growing crops, which establish an early canopy cover, are aggressive to suppress weeds, and possess a deep root system to improve the macroporosity of the soil as a conservation measure during the off season or as ground protection under trees.


 * Strip-cropping
 * Growing of row crops and protection-effective crops such as leguminous or grass in alternating strips aligned on the contour or perpendicular to the wind in order to limit erosion to the row-crop strips and to trap the soil removed from these within the downslope, or downwind strip.


 * Multiple cropping
 * Increasing the production from the land while providing protection from erosion by sequential cropping, growing two or more crops involving protection-effective ones a year in sequence, or intercropping, growing two or more crops on the same piece of land at the same time.


 * High density planting
 * Increasing plant density of row crops and modifying the plant arrangements effect in a protection soil by an incsreased canopy cover.


 * Mulching
 * Covering of the soil with crop residues such as straw, maize stalks, palm fronds or standing stubble (direct seeding) to protect it from raindrop impact and to reduce the velocity of runoff and wind.


 * Re-vegetation
 * Rapidly reconditioning vegetation plays a major role in the process of erosion control on gullied areas, landslides, sand dunes, road embarkments, construction sites, mine spoils or pipeline corridors, and is also necessary for replanting forest in areas cleared by patch-cutting or for covering land cleared of forest in favour of agriculture.


 * Agroforestry
 * Incorporating trees within a farming system by planting them on land that is not suitable for crop production where trees help to preserve the fertility of the soil through the return of organic matter and the fixation of nitrogen, improve the soil’s structure, and help to maintain high infiltration rates and greater water-holding capacity.

Soil management:
Is concerned with ways of preparing the soil to improve its structure so that it is more resistant to erosion and to promote plant growth.


 * Organic content
 * Applying organic matter as a way of achieving and maintaining soil fertility which effects an improved the cohesiveness of the soil, an increased water retention capacity and a stable aggregate structure.


 * Tillage practices
 * Preventing or reducing soil compaction and increasing the residue cover by reducing intensity and frequency of soil management operations and introducing conservation, contour, strip, mulch, or minimum tillage.


 * Drainage
 * Reducing soil moisture content, runoff and therefore erosion on heavy clay soils by means of subsurface mole or pipe drainage and subsoiling.


 * Soil stabilizers
 * Improving soil structure by applying soil conditioners which may take the form of polyvalent salts such as gypsum, which bring about flocculation of clay particles, organic by-products or synthetic polymers, which both bind the soil particles into aggregates.

Mechanical methods:
Depend on manipulating the surface topography to control the flow of water and air and often involve engineering structures.


 * Contour bunds
 * Building earth banks of 1.5-2 m width, thrown across the slope to act as a barrier to runoff, to form a water storage area on their upslope side and to break up a slope into segments shorter in length than is required to generate overland flow.


 * Terraces
 * Installing earth embankments constructed across the slope to intercept surface runoff (retention terraces), convey it to a stable outlet an a non-erosive velocity and shorten slope length (diversion and bench terraces).


 * Waterways
 * Conveying runoff at a non-erosive velocity to a suitable disposal point by means of a system of diversion channels, terrace channels or grass waterways, which all have to be carefully dimensioned in order to provide sufficient capacity to convey the peak runoff from a storm with at least a ten-year return period.


 * Temporary measures
 * Installing silt fences, burlap rolls, straw bales and sedimentation ponds as temporary measures for erosion control required on construction sites, road banks and pipeline corridors until a soil protecting vegetation cover has been established.


 * Stabilization structures
 * Controlling erosion on steep slopes such as gully sidewalls, embarkments and cuttings using bioengineering techniques like brush layering and wattling, which use live cuttings of quick-rooting plat species, usually willow, to give an immediate reinforcement of the soil and to provide the basis for long-term slope stability as the cuttings take root and vegetation grows.


 * Geotextiles
 * Controlling soil detachment by raindrop inpact with the help of surface-laid mats made of natural fibres which provide effective surface cover, high water absorption, interception of splashed particles from their point of ejection, and ponding water in a rough surface; geotextile products range from open-weave testile meshes made from polypropylene, coir or jute, to blankets, containing natural or synthetic fibres that are woven, glued or structurally bound with nets or meshes.


 * Brush matting
 * Using bush mats as an alternative to geotextiles to provide an immediate cover to the slope and prevent surface erosion and complementarily providing the basis for a long-term vegetation cover, they are only suitable where the used species is appropriate as the final land cover.


 * Gully control
 * Installing stabilization structures such as small dams made from locally available materials such as earth, wooden planks, brushwood or lose rock and built across bullies to trap sediment and thereby reduce channel depth and slope; the structures have a high risk of failure but provide temporary stability and are used in association with agronomic soil conservation treatment of the surrounding land.


 * Footpaths
 * Constructing paths with a camber or a cross-fall and providing them with revetments, surfaced side and cut-off drains where stabilization structures are needed in the construction and maintenance of footpaths, especially in recreational areas on sloping land.

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