Abstract
This paper presents a synopsis of the findings of a valley bottom wetland monitoring study in which dominant hydrological processes maintaining the system are quantitatively defined. The Craigieburn-Manalana is a wetland subjected to technical rehabilitation, at the headwaters of the Sand River in the lowveld savanna region of South Africa. Findings include the identification of a rapid water delivery mechanism from the surrounding hillslopes to the wetland following a threshold-exceeding precipitation event, when hillslope-toe soil matric potential is close to 0, leading to a raising of the wetland water table by >0.7 m within 3 h. A summary of quantified fluxes and associated water budget of the wetland and its contributing catchment is developed. It is revealed that this wetland does not necessarily conform to the typical assumptions that wetlands augment low flows. Surface layer scintillometry shows actual wetland evapotranspiration to dominate the water budget during the dry season (2.3–3.5 mm/d) compared to its contributing catchment (0.9–2.2 mm/d), whilst stream discharge had ceased. Hydrograph separation, based on stable isotopes (18O), revealed that the wetland does not attenuate peak flows during the summer rains when the wetlands soil moisture deficit is close to 0, since more than 66% of stream discharge comprised event water. These results are discussed within the context of current hydrological understanding of southern African headwater wetlands, such as dambos. Keywords: hillslope processes, hydro-geomorphology, water budget, dambos, rehabilitation, wetlands
Highlights
There is a general dearth of knowledge of the hydrology of wetland systems in Africa, and this has duly been noted for Southern Africa (Grenfell et al, 2005)
Political, social and environmental reasons; the environmental component of this objective may well be undermined by unsatisfactory understanding of the hydro-geomorphic controls and fluxes that would otherwise characterise these wetlands in a natural state, possibly leading to inappropriate rehabilitation measures (Tooth and McCarthy, 2007)
This paper summarises the hydrology of a riparian headwater wetland in the semi-arid north east of South Africa, the degradation of which through significant gully erosion is experienced in other wetlands in the area
Summary
There is a general dearth of knowledge of the hydrology of wetland systems in Africa, and this has duly been noted for Southern Africa (Grenfell et al, 2005). The southern African sub-continent differs vastly from the temperate northern continents in a number of ways: firstly it has an ancient and relatively tectonically stable land-mass which sits at a high mean elevation; second, the region escaped recent glaciation episodes that have shaped the landscapes in other regions; third, southern Africa has significantly lower average rainfall than other continents coupled with a high evapotranspiration demand These factors combine to limit the extent of the majority of wetlands in the region to stream networks. As the systems of southern Africa are studied in more detail, it is hoped that a sphere of overarching principles will emerge by which the sustainable management of their processes and resources may be secured in the future This issue is of tantamount importance given that great emphasis is being placed on wetland rehabilitation, in South Africa, through poverty relief strategies. This is a laudable undertaking for political, social and environmental reasons; the environmental component of this objective may well be undermined by unsatisfactory understanding of the hydro-geomorphic controls and fluxes that would otherwise characterise these wetlands in a natural state, possibly leading to inappropriate rehabilitation measures (Tooth and McCarthy, 2007)
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