NFEPA Atlas 5.3_20111025_FINAL.indd - Biodiversity GIS - SANBI

4.5 LandformsLandforms describe the topography of a land surface in the context within which it occurs, identifyinga range of landform classes such as valley floors, slopes and benches. Landforms provide a frameworkfor the role the landscape plays in processes related to geology, hydrology and ecology. Landformswere developed by NFEPA for classifying wetlands according to the landscape setting within which theyfall, and provided one of the primary determinants for classifying wetland ecosystem types (Section4.3). Four landform classes recommended by the national wetland classification system (SANBI 2009)were identified: benches, plains, slopes and valley floors (Figure 4.10).Valley floorsSlopesPlainsBenchesThese landform classes are useful to a wide range of planning and management applications beyondbiodiversity planning, such as assessments of soil, geology, hydrology, fire and flood risk, hazardprediction, forestry, agricultural and forestry potential, climate change as well as numerous engineeringand military applications.50 kmBENCHseepSLOPEdepressionBENCHVALLEY FLOORchannelledvalley-bottom wetlandunchannelledvalley-bottom wetlandWilma StrydomPLAINriver channelfloodplain wetlandflatdepression500 kmFigure 4.10: Schematic showing the different landscape settings of each landform class (afterSANBI 2009), which inform classification of the different wetland ecosystemtypes. Landform classes are shown in upper case, and the wetland ecosystemtypes that they potentially contain are shown in lower case.Landforms for the country were generated using a 50 m resolution digital elevation model generatedfrom contours at 20 m intervals and spot height data per 1:50 000 data sheets. The ArcGIS 9.3Landform Tool was used, which calculates the standard deviation from the average elevation ina specified search area to identify landform classes. This tool offers the option of using a smallneighbourhood to consider the landform within a local context, and a large neighbourhood toreflect the regional context within which the landform occurs. The maximum valley widths pergeomorphic province (as calculated by Partridge et al. 2010) were used to inform selection of the smallneighbourhood across the country, and the maximum width tertiary catchments (Midgley et al. 1994)informed selection of the large neighbourhood (van Deventer et al. in review). The results (Figure 4.11)were compared to 260 random points that were classified manually using Google Earth imagery andtopographical maps, and showed a 50-60% overall accuracy. The Landform Tool tended to overestimatebenches and valleys, and underestimate slopes. This level of congruency suggests that this landformlayer may be suitable for coarse-scale national application, but will have to be further refined for useat the local scale.Figure 4.11: Landforms of wetland vegetation groups (Section 4.6) to classify wetland ecosystem types.Input data layers- 54 -