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in Table J32, where the main groups of environmental effects resulting from project
activities are listed (as per the International Commission on Large Dams - ICOLD). Also
listed are the specific parameters which could be influenced, and certain corrective
measures required to reduce any adverse effects. It should be noted that not all elements
of the matrix are scored and that only the major positive or negative impacts are reflected
in the matrix. Primary environmental impacts can also result in secondary interactions with
other environmental factors, with highly complex situations arising. Table J33 outlines
some environmental effects of water projects according to ICOLD.
The matrix approach of the International Commission on Large Dams has been found to
be too subjective, although the matrix provides a good checklist (Anonymous, 1986). A
more descriptive approach readily understood by a variety of disciplines is generally
preferred by the Department of Water Affairs and Forestry. Overlay techniques which.
superimpose mapped environmental factors are also used. Major environmental
constraints on future water resources development in South Africa include the time
consuming process of undertaking ElAs; the incorporation of relevant findings in the
project; limitations on the development potential of sites suitable for major impoundments
as a result of environmental considerations, and the quantity and quality of water
necessary for environmental management·.
• It is interesting to note that the construction of dams in South Africa is no longer automatically
viewed (by the Department of Water Affairs and Forestry), as "the solution" to a particular water
supply problem. Attention is now being given, for example, to the clearing of dense thickets of exotic
(alien) vegetation which have invaded important catchments and riparian zones. The reduction in area
of exotic species (which generally consume more water than indigenous plants), results in a nett
increase in runoff, and hence a greater availability of water for downstream requirements. It should
be bome in mind however, that adaltional commercial afforestation (where permitted), may negate
the positive effects of alien vegetation removal. The felling of alien species is an integral component
of the RDP Water Conservation Programme, which in tum is part of the Reconstruction and
Development Programme.