Thabakholo Environmental Solutions | Erosion Control

By: Thabakholo  11-11-2011
Keywords: Vegetation, Erosion Control

The purpose of our assessment is to ensure that all essential information is considered, ensuring the process of identifying, evaluating and synthesizing the data before major decisions are taken and commitments made.

We work with all relevant reports e.g.*Environmental Impact Assessments (EIA's), if available, and use all appropriate information to submit a practical, sustainable and cost-effective rehabilitation method statement for specific projects.

*Environmental Impact Assessment (EIA)
An environmental impact assessment is an assessment of the possible positive or negative impact that a proposed project may have on the environment; consisting of the natural, social and economic aspects.

The Need for Site-Specific Information

Our objective is to determine the best solutions for each site based on our assessment of the:

  • Soil quality,
  • Water quality,
  • Topography,
  • Vegetation diversity,
  • Seeding method and
  • Soil erosion.

Soil Quality

A good soil assessment is a critical component for any successful soil analysis in order to ensure appropriate soil amelioration. The soil condition will ultimately determine sustainability of vegetation and which vegetation will merely survive on site.

The best approach is to understand what you already have in place and focus on improving it. Selecting endemic/indigenous species for your site, combined with a focus on improving your soil, will result in low maintenance and successful vegetation cover.

Soil Structure

Generally, soil structure is comprised of topsoil, subsoil, and parent rock. You should be able to see a colour difference between your topsoil and subsoil. The top soil should be dark due to the nutrients and organic matter which it contains. Subsoil should be much lighter because it does not carry the nutrients and organic matter found in the topsoil.

Soil pH

Soil pH is a characteristic most people disregard, despite its significance. pH is the measure of acidity and alkalinity and is an important characteristic of your soil. pH can range from 0 to 14; 7 being neutral. Lower numbers indicate an acidic soil and higher numbers indicate an alkaline soil. Most plants desire a neutral or slightly acidic soil from a range of 5.5 to 7.5. Adjusting soil pH can be a high-maintenance activity, so instead of battling to change the soil pH, rather just select suitable vegetation.

Water quality


(drainage and landform erosion control methods and products)

Erosion rates are controlled primarily by topographic relief or slope, precipitation, climate, vegetation and rock type. Therefore, the terrain of every site assessed is very important in determining the optimum erosion control methods to be used.

Slope factors

The slope or gradient of the land has a direct impact on soil erosion and deposition. The use of , and are especially appropriate for critical slopes adjacent to sensitive areas, such as streams and wetlands, and disturbed soil areas, where planting is likely to be slow in providing adequate protective cover.

Climatic factors

Climatic factors include the amount and intensity of precipitation, the average temperature, seasonality, wind speed and storm frequency. , , ,, and are all effective erosion control techniques that prevent soil loss caused by climatic factors.

Vegetation and rock type factors

Factors include ground cover, vegetation or lack thereof, the type of organisms inhabiting the area, the land use, the sediment and the porosity and permeability of the rock type.

Exotic invasive species control is important to reduce negative impacts on the ecosystem. The active planting of indigenous vegetation is crucial to maintain and preserve the natural biodiversity of any area.

Vegetation Type

Vegetation diversity is a major component of ecosystems. Vegetation is the source of primary production, plays a direct role in water and nutrient cycling, and interacts strongly with other biotic components (insects, game, etc.) being a determinant habitat for many species. Vegetation has also been identified as a specific target for the calculation of critical loads/levels. The composition and structure of vegetation can serve as bio-indicators for environmental changes to ecosystems. Changes in vegetation and in underlying environmental factors can serve as indicators of the status of other organisms based on our current knowledge of the ecological niches of numerous plant species.

The objectives of the vegetation assessment:

  • Characterize the current state of the ecosystems on the basis of the composition of the vegetation;
  • To preserve, maintain and sustain the biodiversity of the indigenous vegetation on the identified sections.

Seeding Method

The seeding method to be used will be determined by the area, associated cost, site access and required seed types.


Manual Seeding/Hand seeding

Tef seeders or gandi dropseeders are typically used to manually seed small and/or inaccessible areas. Sites must first be prepared, levelled and lightly scarified before the spreading of seed can commence. Drop seeders and hand seeders, however, inhibit the application of seed varieties which come in clumps or those that can easily blow away. There are also limitations with regard to the even distribution of seed.

Mechanical Seeding

Mechanical drop seeders,brilliant seeders or agricultural planters are pulled by a tractor to mechanically seed areas that are slightly larger than areas requiring manual or hand seeding. Although this method is faster, it poses the same limitations as manual and hand seeding in regard to the variety of seed that can be applied.

Understanding Soil Erosion

Soil degradation by accelerated water and wind-induced erosion is a threatening predicament and will continue to worsen during the 21st century, especially in developing countries of tropics and subtropics. Erosion is a natural geomorphic process occurring continually over the earth's surface. However, the acceleration of this process through anthropogenic perturbations (degradation of the environment caused by humans) can have severe impacts on soil and environmental quality.

Different energy source agents determine different types of erosion. There are four principal sources of energy: physical, such as wind and water; gravity; chemical reactions and anthropogenic, such as tillage.

Soil erosion is a three stage process: detachment, transport and deposition of soil. It begins with detachment, which is caused by the breakdown of aggregates from raindrop impact, sheering or drag force of water and wind. Detached particles are transported by flowing water (over-land flow and inter-flow) and wind, and deposited when the velocity of water or wind decreases by the effect of slope or ground cover.

Three processes accelerate the natural rate of soil erosion: dispersion, compaction and crusting. These processes decrease structural stability, reduce soil strength, exacerbate erodibility and accentuate susceptibility to transport by over-land flow, interflow, wind or gravity. These processes are accentuated by soil disturbance (tillage, vehicular traffic), lack of ground cover (bare fallow, residue removal or burning) and harsh climate (high rainfall intensity and wind velocity).

Factors of Soil Erosion

The soil erosion process is modified by environmental factors involving soil, climate, terrain and ground cover and interactions between them.

  • Soil erodibility is caused by the susceptibility of soil to the agent of erosion and is determined by inherent soil properties such as; texture, structure, soil organic matter, content, clay minerals, exchangeable cations (atoms that have lost an electron to become positively charged) and water retention and transmission properties.
  • Climatic erosivity includes drop size distribution and intensity of rain, amount and frequency of rainfall, run-off amount and velocity, and wind velocity.
  • Important terrain characteristics for studying soil erosion are slope-gradient, length, aspect and shape.
  • Ground cover exerts a strong moderating impact on dissipating the energy supplied by agents of soil erosion.

The Rate of soil erosion is influenced by the Factors and Causes of Soil Erosion

Keywords: Erosion Control, Vegetation

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