Commercial forestry is recognized for both its economic contribution as well as its
environmental impact. Of particular concern, is the soil erosion and sedimentation of
watercourses associated with forestry plantations. Environmental laws regulate many of the
activities of the forestry sector. It is critical that the forestry sector ensure that its
operations are compliant with the legal requirements that govern its use of natural
resources. In pursuing legal compliance it is necessary to ensure that erosion control
strategies are developed so as to ensure the positive effects of any interventions are
optimised. The identification of areas that are particularly at risk to erosion or contribute to
sediment delivery is an essential component in prioritising areas for management
interventions.
Establishing the erosion potential for commercial forestry areas is readily accomplished
through the application of existing models. Process based erosion models generally have
greater data requirements than the empirically derived USLE-based models. Given the
paucity of data available, the latter approach was adopted. Two methods of topographic
sub-factor derivation were investigated, those associated with the RUSLE (Renard, Foster,
Weesies & McCool1991) and the Unit Stream Power method presented by Moore and
Burch (1986). Since no existing methods identifying delivery risk areas existed, a method
was developed based on principles and factors identified in the literature. Additionally,
methods for identifying topographic assets, in terms of sediment attenuation, were
developed. From these models three indices were derived; sediment supply, delivery risk
and sediment attenuation.
Thereafter, the mean Sediment Supply Index was divided by stream length for small
catchments defined within the landscape to derive an index of sediment loading to streams.
This index is used to identify priorities for management intervention across the landscape.
The mean slope and sediment supply is used to develop buffer width recommendations for
the streams draining the catchments, using a method developed by Karssies and Prosser
(2001). Using the three indices in conjunction it is possible to make on-site and off-site
erosion control recommendations as well as identify and exploit any natural features that
can be utilized in erosion control. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4514 |
| Date | January 2002 |
| Creators | Horswell, Michael Wilbur. |
| Contributors | Quinn, Nevil. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
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