Plants provide protective cover on the land and prevent soil erosion for the following reasons:

• plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;
• plant roots hold the soil in position and prevent soil particles from being washed away;
• plants break the impact of the raindrop before it hits the soil, thus reducing its ability to erode;
• plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion (Enviro Facts, 1999j).

Preventing soil erosion requires political, economical and technical changes. Political and economic changes should address the distribution of land in South Africa, as well as in the north-south devide in Greater Johannesburg, and the possibility of incentives to encourage farmers to manage their land sustainably. Aspects of technical change include:

• the use of contour ploughing and wind breaks;
• leaving unploughed grass strips between ploughed land;
• making sure that there are always plants growing on the soil, and that the soil is rich in humus. This organic matter is the glue that binds the soil particles together and plays an important role in preventing erosion;
• avoiding overgrazing and the over-use of croplands;
• allowing indigenous plants to grow along the river banks instead of ploughing and planting crops right up to the water’s edge;
• encouraging biological diversity by planting several different types of plants together; and
• conservation of wetlands (Enviro Facts, 1999j).

Soil-Sement is a new dust and erosion control agent, developed by Midwest Industries (Midwest Industrial Supply, 1996). It creates a hard, dust-free surface, which is water resistant and very resilient, for use on roads, unpaved roadways or any other surface. It is environmentally safe, non-corrosive, does not pollute groundwater or increase the pH of soil, and will reduce pollutants by reducing the total suspended solids in the runoff and dust pollution. Where the control of PM₁₀ (particulate matter consisting of particles smaller than 10 micrometers in diameter) and PM_2.5 (particulate matter consisting of particles smaller than 2.5 micrometers in diameter) is required by law, this product is ideal to reduce dust emissions by bonding the surface dust to the base.

Soil conservation in agriculture uses various methods to reduce soil erosion, prevent the depletion of nutrients and restore nutrients to their natural levels. The best method is to keep the soil covered by vegetation all the time. Another method is conservation-tillage farming, where special tillers break up the subsurface soil, without turning over the topsoil. Seeds, fertilizers and weed killers are also then injected into the unploughed soil to reduce erosion, compaction and water loss from the soil (Miller, 1993). Soil erosion can be reduced by 30 – 50% on gently sloping land by means of contour farming, plowing in rows across, rather than up and down, the sloped contour of the land. Terracing can be used on steeper slopes to contain some of the water, reduce runoff and erosion and increase infiltration.

Many complaints were received by the Department of Environmental Affairs, as well as the Department of Water Affairs, on mining pollution. In 1993/1994 the City Engineering Governor released a law for the clean up of all mines by 2005. All rock and sand mine dumps have to be detoxified, cleared and the areas rehabilitated. Gold is also then removed from the dumps. Rand Mines have cleaned out all the radon from their mine dumps, and a large Crown City Business Development, is currently underway in the area.

Mining solutions coincide with the wind direction (north, northwest) on the reef in Greater Johannesburg, and it is preferable that mine dumps be recycled from the southeast, to reduce dust and erosion (Weather Bureau, 1999). The Robinson Deep Mine Dump in Booysens/Springfield is being recycled in this way to protect the industries in the Booysens area.

GEOTECHNICAL DEVELOPMENT POTENTIAL

Certain appropriate developments should be considered on certain land zones with certain characteristics. The table in the impact section describes which land characteristics should fall into which development category. According to this the following developments are proposed for the land category (Buttrick & Stapelberg, 1994):

Category 1 = Potentially most suitable for any development type, including semi-formal and formal residential, commercial and industrial development.
Category 2 = Potentially suitable for select development, due to engineering geological constraints. Preferably consider formal residential, commercial and industrial development.
Category 3 = Least favourable to unfavourable for development due to severe geotechnical problems and negative cost consequences.

WHAT CAN YOU DO?

• Reduce demands on soil by not wasting anything that comes from soil;
• If you have a garden, care for the soil by adding compost;
• Avoid pesticides which might kill soil life; and
• Rotate the plants you grow to keep the soil healthy (Enviro Facts, 1999i).

ENVIRONMENTAL LEGISLATION

- National Environmental Management Act 107 of 1998.
- Environmental Conservation Act 73 of 1989.
- Soil Conservation Act 76 of 1969.
- Minerals Act 50 of 1991.
- Conservation of Agricultural Resources Act 43 of 1983.
- White Paper for A Minerals and Mining Policy for South Africa.

ISSUES STILL TO BE CONSIDERED

- The extent of mining and agricultural degradation in Greater Johannesburg.
- The impact of agricultural chemicals on surface and groundwater quality.
- The impact of waste on groundwater quality.
- The impact of erosion and bad management practices on water quality.
- Soil pollution from liquid effluent disposal of sewage sludge (DEAT, 1997).

REFERENCES

Buttrick, D. & F. Stapelberg 1994: A report to the Central Witwatersrand Regional Services Council on an Engineering Geological Study of the Central Witwatersrand Regional Services Council area. The Council for Geoscience.

Department of Environmental Affairs and Tourism & Department of Water Affairs and Forestry 1997: Discussion Document towards a White Paper on Integrated Pollution Control and Waste Management.

Midwest Industrial Supply 1996: Soil-Sement: Dust and Erosion Control. Midwest Industrial Supply: Canton.

Miller, G.T. 1993: Environmental Science – Sustaining the Earth. (4^th ed.) Wadsworth: California.