cgvhbjnkl middelburg comprises undulating topography in the southern part at an approximate height of 1600 m above sea level. numerous hills and steep inclines are found towards the northwestern part of the middelburg at a height of 1400 m figure 4.2.4.1 the olifants river system is the largest drainage system in mpumalanga and is found in the southern part of the area where middelburg resides. the drainage network of the study area is typical of the dendritic pattern. figure 4.2.4.2 stlm 2008 the following datasets have been used in the study area; digital elevation model dem was acquired from global land cover facility glcf for generation of slope drainage and geomorphology maps.
the geology map was acquired from diva-gis in vector format on a 1:250 000 scale. the lineaments were extracted automatically from the pci geomatica software and the lineament density was calculated using the line density under the spatial analyst tool in arcgis software figure 4.3 groundwater recharge potential map was correlated and validated with the field groundwater data obtained from the article written by meulenbeld and hattingh 1999 and from the department of water affairs. the following proposed methodology figure 5 was used to generate groundwater recharge potential zones map. different datasets comprising remote sensing data and conventional maps were used. all the acquired data have been geo-referenced into universal transverse mercator utm spheroid and datum wgs-1984.
five different factor maps including; geomorphology geology slope lineament density and drainage density were prepared and processed using arcgis 10.4 software. the geology map is used to deduce possible groundwater aquifers through the evaluation of the physical description of the rocks and it was prepared by using existing geological map of south africa. for characterization of rock type unique values corresponding to each unit were used under categories in layer properties arcgis singh et al. 2013 the major groundwater storage units observed are sandstone shale diamictite and diabase where the intrusive rocks are found to be good groundwater prospecting units due to the presence of fractures and cracks figure 5.1 a geomorphological map depicts land forms and associated features that may have direct influence on groundwater recharge occurrence singh et al.
2013 based on interpretation of satellite images and a dem of the study area different geomorphological units have been delineated. each unit was identified on satellite images of the study area then traced to create polygons representing each unit. the major geomorphic units observed are steep inclines valleys and hills and figure 5.2 hills and steep inclines are characterised by high drainage densities thus make poor groundwater recharge potential zones since runoff exceeds infiltration and the valleys make good groundwater recharge potential zones since they have low drainage densities and are characterised by gentle slopes where infiltration exceeds runoff singh et al. 2013 the rate of groundwater recharge is influenced by the drainage system characteristics. drainage density is the ratio of the total length of stream network in a given basin to the total basin area. higher drainage density results in lower recharge rate since runoff exceeds infiltration.
however lower drainage density favours groundwater recharge since infiltration exceeds runoff singh et al. 2013 hence areas of low drainage density make good groundwater recharge potential zones. the stream networks were extracted from the dem of the study area using the hydrology tool under the spatial analyst tool in arcgis software. the following simple steps were followed to generate stream networks from the dem; firstly the imperfections were removed from dem using the fill tool under hydrology.
direction of water flow was determined using the flow direction tool; basin tool was used to create a raster delineating drainage basin. the output drainage basin raster was then converted to vector polygon using the raster to polygon tool under conversion tools; flow accumulation tool was used to create stream networks and the output flow direction raster was used as an input. threshold was specified using the raster calculator under map algebra tool and lastly the output steam networks raster was converted to polyline using the raster to polyline tool under conversion tools. the drainage density was then calculated using the line density also found under the spatial analyst tool figure 5.3
