Topographic thresholds in gully development on the hillslopes of communal areas in Ngqushwa Local Municipality, Eastern Cape, South Africa

Kakembo, Vincent and Xanga, W.W. and Rowntree, Kate (2009) Topographic thresholds in gully development on the hillslopes of communal areas in Ngqushwa Local Municipality, Eastern Cape, South Africa. Geomorphology, 110 (3-4). pp. 188-194. ISSN 0169-555X

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Official URL: http://dx.doi.org/10.1016/j.geomorph.2009.04.006

Abstract

The relationships between the spatial distribution of gully erosion and topographic thresholds in the form of slope angle, position and configuration, as well as land use change in the form of abandoned lands were examined in several affected catchments of the Eastern Cape Province, South Africa. Land use and permanent gullies were mapped, digitized from orthophoto maps in Arc/info 3.5.2 GIS and converted to shapefiles using ArcView 3.2 GIS. Relationships between the mapped phenomena and topographic variables were sought using a Digital Elevation Model (DEM) in Idrisi Kilimanjaro GIS. A comparison between areas with a high potential for gullying and actual gully erosion was made using the Stream Power Index (SPI) as a surrogate for critical flow shear stress. Field surveys were also conducted to assess the present condition of the gullied sites as well as to validate DEM derivations. Seventy five percent of the gullied area was noted to lie on abandoned lands. A predominance of gullying in concave bottom lands was also identified. The SPI values highlighted a distinct preferential topographic zone for gully location. A conceptual model depicting the interaction between land use and topographic parameters to induce gully erosion was developed. This should assist local authorities to develop a policy regarding management of abandoned lands.

Item Type:Article
Uncontrolled Keywords:Gully erosion; Abandoned lands; Slope configuration; Stream power index; Topographic threshold; ArcView; conceptual framework; digital elevation model; hillslope; land use; slope angle; spatial distribution; stream; topography; Eastern Cape; South Africa
Subjects:Y Unknown > Subjects to be assigned
Divisions:Faculty > Faculty of Science > Geography
ID Code:1462
Deposited By:INVALID USER
Deposited On:04 Sep 2009
Last Modified:01 Aug 2012 09:37
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