Gully Features Extraction Using Remote Sensing Techniques

Gullies are large and deep erosion depressions or channels normally occurring in drainage ways. They are spectrally heterogeneous, making them difficult to map using pixel based classification technique. The advancement of remote sensing in terms of Geographic Object Based Image Analysis (GEOBIA) provides new possibilities to extract gullies with relative ease. This study investigates and tests a GEOBIA technique called Imagine Objective for gully features extraction in the Capricorn District Municipality of Limpopo Province. IO extracts gullies by firstly group the pixel information and then subjects them to raster and vector conversion and refinement algorithms. For the purpose of assessing the accuracy of the IO created gullies, reference data were created by manual digitising gullies from SPOT 5 satellite imagery on the background. The error matrix was computed and the results indicated a user's accuracy of 98.67% and 54% for non-gully and gully class respectively; a producer's accuracy of 68.20% and 97.59% for non-gully and gully class respectively; a overall classification accuracy of 76.33% and a kappa statistic of 0.95, 0.36 and 0.52 for non-gully class, gully class and total kappa statistic respectively. Although the accuracy levels are considered moderately acceptable, it is recommended that much higher spatial resolution imagery such as Quickbird be used in future and other functionalities of IO be tested

Characterizing variable renewable energy generation uncertainty towards improved forecasting and operational decision making

Electrical and Electronic Engineerin

Developments in the remote sensing of soil erosion in the perspective of sub-Saharan Africa. Implications on future food security and biodiversity

The remote sensing of soil erosion has gained substantial consideration, with considerable scientific research work having been conducted in the past, due to technological improvements that have resulted in the release of robust, cheap and high resolution datasets with a global foot-print. This paper reviews developments in the application of remote sensing technologies in sub-Saharan Africa with a explicit emphasis on soil erosion monitoring. Soil loss due to soil erosion by water has been identified by African geomorphologists, environmentalists and governments, as the primary threat to agriculture, biodiversity and food security across the continent. The article offers a detailed review of the progress in the remote sensing as it summarises research work that have been conducted, using various remote sensing sensors and platforms and further evaluates the significance of variations in sensor resolutions and data availability for sub-Saharan Africa. Explicit application examples are used to highlight and outline this progress. Although some progress has been made, this review has revealed the necessity for further remote sensing work to provide time-series soil erosion modelling and its implications on future food security and biodiversity in the face of changing climate and food insecurity. Overall, this review have shown the immediate need for a drastical move towards the use of new generation sensors with a plausible spatial, temporal characteristics and more importantly a global foot-print

A comparative study of gully erosion contributing factors in two tertiary catchments in Mpumalanga South Africa

Gully erosion is one of the most important forms of soil erosion due to the loss of agricultural production land, sediment generation that leads to siltation of reservoirs, and damage to infrastructure such as roads, bridges, buildings and water pipes. Gully erosion has attracted the interest of many scientists worldwide, but some key priority research areas have not yet been widely reported on. A review of gully erosion research in South Africa presented in this study shows that contributing factors have not been addressed sufficiently and that most of the previous research has been confined to the Eastern Cape and KwaZulu Natal regions. This study quantifies, compares and contrasts the influence of various biophysical and land use factors controlling gully erosion, including land use history, from the two tertiary catchments (X12 and W55) of the Komati and Usutu Rivers in the Mpumalanga province. A desktop-based research approach was followed, which includes the extraction of topographic variables, including the slope, upslope contributing area, planform curvature, Topographic Wetness Index and Stream Power Index from contours derived Digital Elevation Models. The study used existing contributing factor datasets including soil, geology, rainfall erosivity and vegetation cover and type. Gullies were digitised manually from a background 0.5m spatial resolution aerial photographs. Land use history and gully dynamics were studied from historical aerial photographs within two selected gully systems. The influence of a contributing factor class on gullies was assessed based on the proportion of gullies in each class, calculated using a zonal approach in ArcGIS®. Zonal results were analysed further using Information Value statistic to assign the weight for each class. Numerous gully erosion features were observed in tertiary catchment X12 (n = 5 397) compared to W55 (n = 1 654). An Information Value statistic in tertiary catchment X12 shows that gullies are influenced by soils with varied depths belonging to oxidic, vertic, duplex, lithic and melanic soil groups. These soil groups overlie ultramafic rocks, colluvium and alluvium deposits and granite rock of Swazian age. Topographic variables influencing gully location include low to moderately steep slopes, concave curvature, higher upslope contributing area, high Topographic Wetness Index and both low and high Stream Power Index. Other contributing factor classes influencing gullies include lower erosivity values, Swaziland sour bushveld, Barberton serpentine sourveld, moderate Normalised Difference Vegetation Index, moderate to high Normalised Difference Vegetation Index and cultivation. In tertiary catchment W55, gullying significantly affects the very deep Hutton dominated soil form with texture varying from loamy sand, sand and very sandy, underlain by granitic rock of Randian age. A topographic influence was observed on moderate to steep slopes on an area where flow accumulates and is characterised by concave and convex planform curvatures, low and high Topographic Wetness Index and high Stream Power Index. Both moderate and moderate to high Normalised Difference Vegetation Index classes have a significant influence on gully location, as does indigenous forest and thicket/ bushland. An historical land use analysis showed that cultivation was responsible for the initiation and expansion of gullies at two selected sites. The findings confirm that factors important in one area are not necessarily important in the other due to factors spatial variability. However, results can be improved by applying and comparing further statistics, deriving new datasets for the study and detailed historical land use and gully dynamics analyses.Dissertation (MSc)--University of Pretoria, 2015.Geography, Geoinformatics and MeteorologyMScUnrestricte

Gully erosion : a comparison of contributing factors in two catchments in South Africa

Gully erosion is an environmental, agricultural and social problem requiring extensive research and mitigation actions to control. This study assesses the influence of factors contributing to gully erosion using Geographic Information System (GIS) and Information Value (InfVal) statistics from two catchments coded X12 and W55 in the Mpumalanga province of South Africa. Existing spatial data representing contributing factors; soil, geology, vegetation and land use were analyzed. Topographic variables were extracted from a 10 m Digital Elevation Model (DEM) interpolated from map contours, and gullies were mapped from aerial photos with 0.5 m spatial resolution. A zonal approach was used to extract the proportion of gullies in each of the contributing factor classes using GIS software packages, and InfVal weighting was performed to determine the influence of each class. Comparison of the results shows the variation in the level of influence of factors contributing to gully erosion. The findings in catchment X12 support a commonly held assumption that gully formation is influenced by duplex soils underlain by colluvium and alluvial deposits on a lower slope position where overland flow converges and accumulates, resulting in high soil moisture. Gullies were also influenced by soils developed over weathered granite, gneiss and ultramafic rocks. The influence of a granite rock was further highlighted in catchment W55 where there is a variable thickness of very deep Hutton dominant soil form and shallow Lithosols with sandy texture, on an area of moderate to steep slopes where overland flow converges and accumulates, with high stream power in overgrazed grassland. An understanding of these factors will assist future modelling of the vulnerability to gully erosion over a wider geographical area.The University of Pretoria and the Department of Agriculture, Forestry and Fisheries.http://www.elsevier.com/locate/geomorph2018-07-01hj2017Geography, Geoinformatics and Meteorolog

Evaluation of Nguni cattle performance from communal property associations and private ownership types across three ecological zones of Mpumalanga province, South Africa

Nguni cattle in South Africa are diminishing at the expense of exotic breeds and crossbreeds. Therefore, the Industrial Development Corporation and Mpumalanga Province Department of Agriculture adopted the Nguni cattle conservation project. Herds of 30 heifers and a bull were allocated to 34 communal property associations (CPAs) and 40 private farms. This study aimed to evaluate growth and reproductive performance across three ecological zones and two ownership patterns. Nine CPAs and nine private farms were sampled. Age at first calving, conception, calving, and weaning rates were determined from production records, while calf birth and weaning weights were digitally measured. Data was analyzed using two-way analysis of variance (ANOVA) with Tukey’s honestly significant difference (HSD) used for mean separation. Significant differences were observed across ecological zones for age at first calving, weaning rate, and birth and weaning weights (p < 0.05). Concerning age at first calving, the Midveld ecological zone performed best (24 months) for both ownership types compared to the Highveld (28.09 months private, 26.00 CPA) and Lowveld (28.35 months for both ownership types). Highveld performed higher on birth weight (25.35 kg) and weaning rate for private (93%) and CPA (80%). Lower birth weights were observed in both ownership types in Midveld (22.17 kg). The Lowveld zone had a higher birth weight (26.80 kg) in CPA. Higher weaning weights were observed in private ownership of Highveld (190.16 kg) and the lowest (160.39 kg) in the Midveld zone. CPAs in Highveld had higher weaning weights (187.55kg) than in Midveld (167.50 kg). The results suggest that Nguni cattle respond differently in the various ecological zones of Mpumalanga Province

Evaluation of Nguni cattle performance from communal property associations and private ownership types across three ecological zones of Mpumalanga province, South Africa

Nguni cattle in South Africa are diminishing at the expense of exotic breeds and crossbreeds. Therefore, the Industrial Development Corporation and Mpumalanga Province Department of Agriculture adopted the Nguni cattle conservation project. Herds of 30 heifers and a bull were allocated to 34 communal property associations (CPAs) and 40 private farms. This study aimed to evaluate growth and reproductive performance across three ecological zones and two ownership patterns. Nine CPAs and nine private farms were sampled. Age at first calving, conception, calving, and weaning rates were determined from production records, while calf birth and weaning weights were digitally measured. Data was analyzed using two-way analysis of variance (ANOVA) with Tukey’s honestly significant difference (HSD) used for mean separation. Significant differences were observed across ecological zones for age at first calving, weaning rate, and birth and weaning weights (p < 0.05). Concerning age at first calving, the Midveld ecological zone performed best (24 months) for both ownership types compared to the Highveld (28.09 months private, 26.00 CPA) and Lowveld (28.35 months for both ownership types). Highveld performed higher on birth weight (25.35 kg) and weaning rate for private (93%) and CPA (80%). Lower birth weights were observed in both ownership types in Midveld (22.17 kg). The Lowveld zone had a higher birth weight (26.80 kg) in CPA. Higher weaning weights were observed in private ownership of Highveld (190.16 kg) and the lowest (160.39 kg) in the Midveld zone. CPAs in Highveld had higher weaning weights (187.55kg) than in Midveld (167.50 kg). The results suggest that Nguni cattle respond differently in the various ecological zones of Mpumalanga Province

International procurement policies influencing renewable energy siting – implications for South Africa

The South African Renewable Independent Power Producer Procurement Programme selects bid winners based on bid tariff (70% weighting) and various economic development criteria (30% weighting). Locating renewable energy (RE) projects in areas with better resources increases their cost competitiveness. As a result, most successful bids for wind and solar photovoltaic (PV) systems to date have been concentrated in the Eastern Cape and Northern Cape provinces, respectively. Studies have shown that a wider geographic distribution of wind and solar PV projects mitigates the impacts of the variability of wind and solar PV resources, eases grid congestion and generally improves the power system’s operation. This paper conducts a literature review to investigate the procurement methods used in different regions of the world to influence the placement of RE plants, the results of which then inform proposals on adjustments to the current REI4P. The study finds that, after congestion incidents due to concentration of RE plants, some regions implement location-based tariff, where high-resource areas receive the lowest tariff and vice versa. Other regions prioritise on building transmission infrastructure in high-resource areas, while others limit the size of RE installations in one area. Given the current generation and transmission constraints in South Africa, it is important to encourage geographical dispersion of RE plants and avoid RE curtailment, since this can escalate the cost of RE integration significantly

Railway side mapping of alien plant distributions in Mpumalanga, South Africa

Background: Alien plant invasions are among the major threats to natural and semi-natural ecosystems in South Africa on approximately 18 million hectares of land. Much of the available data are not suitable for planning of local scale management because it is presented at a quarter degree grid square scale, which makes accurate location and estimates of invaded areas difficult. Objectives: The aim was to identify the dominant alien plant species and quantify their areal extent along a 479 km railway corridor in the Mpumalanga province. Method: The extent of the invaded area was obtained by manual digitising of alien plant distribution and density from Satellite Pour l’Observation de la Terre 5 imagery and by further applying an Iterative Self-Organising Data Analysis technique of the unsupervised classification method. Species’ occurrences were located and identified in the field using a Global Positioning System. Results: The most dominant invaders in terms of the number of individual polygons and the infested area were Eucalyptus spp., Acacia spp., Populus alba L., Pinus patula Schltdl & Cham., Salix babylonica L. and Caesalpinia decapetala (Roth) Alston. These species have also been previously classified as major invaders, although the Conservation of Agricultural Resources Act regulations permit their planting provided spreading to adjacent areas is avoided except for C. decapetala, which must be cleared under all circumstances. Conclusion: Knowledge of the species’ occurrence and their extent will assist landowners and relevant authorities to control the spread of alien plants, which impact rail safety, agricultural production, water availability and biodiversity