Abstract
Abstract. Wetlands are undergoing considerable degradation in South Africa. As interventions are often technical and costly, there is a requirement to develop conceptual process models for these wetland systems so that rehabilitation attempts will be successful. This paper presents an approach using the geophysical methods of Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) to delineate sub-surface hydro-geomorphic controls that maintain equilibrium disconnectivity of wetland-catchment processes, which through gully erosion are increasing the catchments connectivity through loss of water and sediment. The findings presented here give insight into the geomorphic processes that maintain the wetland in an un-degraded state, this allows for the development of a conceptual model outlining the wetland forming processes. The analysis suggests that sub-surface clay-plugs, within an otherwise sandy substrate are created by illuviation of clays from the surrounding hillslopes particularly at zones of valley confinement.
Highlights
Wetlands in southern Africa as in most parts of the world continue to be vulnerable to anthropogenic pressures and climatic shifts which influence the hydrological and geomorphologic processes that otherwise maintain the equilibrium of the wetlands dynamic state
In other words rehabilitation must be sympathetic to and not in conflict with the natural dynamic of the wetland or river system, and seek to maintain those processes that govern the systems water balance (Ellery et al, 2008). It is within this context that a detailed hydrological monitoring of a technical rehabilitation effort was undertaken within a headwater wetland catchment of the Sand River in northeastern South Africa, as part of a river rehabilitation program
This paper presents results of geophysical interpretation of the wetlands hydro-geomorphology using Electrical Resistivity Imaging (ERI) in both 2 dimensional form (2-D) during scoping surveys and a more detailed examination of hydrogeomorphic controls in 3 dimensional form (3-D) using ERI and Induced Polarization (IP) techniques
Summary
Wetlands in southern Africa as in most parts of the world continue to be vulnerable to anthropogenic pressures and climatic shifts which influence the hydrological and geomorphologic processes that otherwise maintain the equilibrium of the wetlands dynamic state. In other words rehabilitation must be sympathetic to and not in conflict with the natural dynamic of the wetland or river system, and seek to maintain those processes that govern the systems water balance (Ellery et al, 2008) It is within this context that a detailed hydrological monitoring of a technical rehabilitation effort was undertaken within a headwater wetland catchment of the Sand River in northeastern South Africa, as part of a river rehabilitation program. It was postulated that zones of finer sediment within this matrix controlled the lateral movement of water within these wetlands prior to their degradation, and these fine sediment zones are being removed through extensive gully erosion (Pollard et al, 2005) It is the stabilization of these gullies that are the focus of technical rehabilitation efforts. Descriptions of the hydrodynamic behaviours of the wetland phreatic surfaces prior to rehabilitation interventions revealed stark differences in event driven responses
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