Although wetlands were once perceived as wastelands (Maltby 1986), it is now recognised that these ecosystems have particular characteristics which enable them to provide a suite of ecosystem services that is valuable to human society. As wetlands become degraded their capacity to deliver these services is diminished. Wetland rehabilitation interventions typically seek to reinstate driving forces of ecosystem development that were disrupted as a result of degradation, in effect ‘resetting the ecological clock’ (Jordan et al. 1987), and to thereby recover some or the entire suite of ecosystem services associated with a wetland prior to degradation. However, rehabilitation is a costly process (the South African Government spent approximately R60 million on interventions in the last financial year), and care must be taken to ensure that society will accrue an adequate return in ecosystem services from the considerable financial outlay required. It is therefore imperative that interventions selected are appropriate to the particular hydrologic, geologic and geomorphic context in which they are to be applied, given the driving role that hydrology, geology and geomorphology play in ecosystem development in wetland environments (Tooth et al. 2002).

CASE STUDIES

 Hlatikulu Vlei, KwaZulu-Natal Drakensberg

Hlatikulu Vlei (29° 15’ S, 29° 41’ E) is a v-shaped 733 ha wetland system situated 7 km from the source of the Nsonge River in the foothills of the KwaZulu-Natal Drakensberg (Begg 1989). While a variety of wetland hydrogeomorphic types are represented within the wetland system, floodplain and valley-bottom wetlands cover the greatest area. Key threats to the persistence of the wetland include gullying associated with pipe culverts beneath the dirt road network flanking the wetland, ridge and furrow agriculture developed in the mid-1960s to drain areas of wetland for the cultivation of crops and pasture, headward erosion associated with a large furrow that was excavated to prevent flooding of the Kamberg-Giant’s Castle road (28 S), and trampling by livestock grazing in the wetland (Begg 1989). Dam construction, most extensive on the farm Forest Lodge, has replaced approximately 20 % of former palustrine wetland area with permanent open water and lacustrine fringe wetland.

Some areas flanking the wetland were afforested with Pinus patula by Mondi Forests (Pty) Ltd. in 1990 (Guthrie 1996). The same year, following concerns that afforestation would lead to a significant reduction in water supply to the wetland, Mondi, in partnership with the South African Crane Foundation (SACF), established the Hlatikulu Crane and Wetland Sanctuary in the area degraded by ridge and furrow development (Guthrie 1996). In addition to this, the two organisations jointly funded a rehabilitation programme within the Sanctuary. A large earthen weir structure was constructed across the Nsonge River to divert water from the river to a series of permeable dams designed to release subsurface flow to down-slope areas formerly under ridge and furrow. Numerous earthen damlets were constructed to plug furrows within the ridge and furrow network and thereby raise the local water table and encourage the establishment of wetland plant species. More recent rehabilitation effort has focused on the gullies associated with pipe culverts beneath the dirt road network flanking the wetland. The work is being undertaken by Eastern Wetland Rehabilitation with funding provided by SANBI: Working for Wetlands. The funding is intended for poverty relief and thus labour-intensive interventions are favoured. Earthen T-spreaders have been used to plug shallow gullies and spread flood-flows over the adjacent land surface, while concrete weirs have been used to plug deeper gullies to halt further erosion and induce gully-filling through sedimentation.

To date, no interventions have targeted the large gully (Figure 1) eroding headward from the crossing of the 28 S over the wetland. According to Begg (1989), the furrow from which this gully extends starves the northernmost portion of the wetland of water. Furthermore, the gully has captured most of the flow from the former meandering course of the Nsonge River through the floodplain. Flood-flows now appear to be confined within the gully rather than spread across the floodplain, eliminating flood storage in oxbow lakes and meander scar depressions, and flow through the floodplain follows a far less sinuous (more direct) path, thereby decreasing the residence time of water within the wetland.

 Figure 1: A view of the lower floodplain portion of Hlatikulu Vlei. Note the old meandering course of the Nsonge River and meander scars in the foreground, and the gully eroding headward from the furrow excavated to protect the 28 S from flooding in the background.

 References

Begg, GW (1989). The Wetlands of Natal (Part 3): The location, status and function of the priority wetlands of Natal. Natal Town and Regional Planning Report 73, 256pp.

 Guthrie, IA (1996). Aspects of the structure and functioning of the vegetation of the Hlatikulu Vlei. Unpublished Masters thesis, University of Natal, Pietermaritzburg.

 Jordan, WR (III), Gilpin, ME and Aber, JD (1987). Restoration Ecology: ecological restoration as a technique for basic research. In: Jordan, WR (III), Gilpin, ME and Aber, JD (eds.), Restoration Ecology: A synthetic approach to ecological research, Cambridge University Press, Cambridge, 3-21.

Maltby, E (1986). Waterlogged Wealth: why waste the worlds wet places? Earthscan, London, 200pp.

Tooth, S, McCarthy, TS, Hancox, PJ, Brandt, D, Buckley, K, Nortje, E & McQuade, S (2002). The geomorphology of the Nyl River and floodplain in the semi-arid Northern Province. South African Geographical Journal 84, 226-237.