No description available.

At present one of the challenges of soil erosion research in South Africa is the limited information on the location of gullies. This is because traditional techniques for mapping erosion which consists of the manual digitization of gullies from air photos or satellite imagery, is limited to expert knowledge and is very time consuming and costly at a regional scale (50-10000km²). Developing a robust, reliable and accurate means of mapping gullies is a current focus for the Institute for Soil, Climate and Water Conservation (ISCW) of the Agricultural Research Council (ARC) of South Africa. The following thesis attempted to answer the question whether “medium resolution multi-spectral satellite observations, such as Landsat TM, combined with information extraction techniques, such as Vegetation Indices and multispectral classification algorithms, can provide a semi-automatic method of mapping gullies and to what level of accuracy?”. More specifically, this thesis investigated the utility of three Landsat TM-derived Vegetation Index (VI) techniques and three classification techniques based on their level of accuracy compared to traditional gully mapping methods applied to SPOT 5 panchromatic imagery at selected scales. The chosen study area was located in the province of KwaZulu-Natal (KZN) South Africa, which is considered to be the province most vulnerable to considerable levels of water erosion, mainly gully erosion. Analysis of the vegetation indices found that Normalized Difference Vegetation Index (NDVI) produced the highest accuracy for mapping gullies at the sub-catchment level while Transformed Soil Adjusted Vegetation Index (TSAVI) was successful at mapping gullies at the continuous gully level. Mapping of gullies using classification algorithms highlighted the spectral complexity of gullies and the challenges faced when trying to identify them from the surrounding areas. The Support Vector Machine (SVM) classification algorithm produced the highest accuracy for mapping gullies in all the tested scales and was the recommended approach to gully mapping using remote sensing

At present one of the challenges of soil erosion research in South Africa is the limited information on the location of gullies. This is because traditional techniques for mapping erosion which consists of the manual digitization of gullies from air photos or satellite imagery, is limited to expert knowledge and is very time consuming and costly at a regional scale (50-10000km²). Developing a robust, reliable and accurate means of mapping gullies is a current focus for the Institute for Soil, Climate and Water Conservation (ISCW) of the Agricultural Research Council (ARC) of South Africa. The following thesis attempted to answer the question whether “medium resolution multi-spectral satellite observations, such as Landsat TM, combined with information extraction techniques, such as Vegetation Indices and multispectral classification algorithms, can provide a semi-automatic method of mapping gullies and to what level of accuracy?”. More specifically, this thesis investigated the utility of three Landsat TM-derived Vegetation Index (VI) techniques and three classification techniques based on their level of accuracy compared to traditional gully mapping methods applied to SPOT 5 panchromatic imagery at selected scales. The chosen study area was located in the province of KwaZulu-Natal (KZN) South Africa, which is considered to be the province most vulnerable to considerable levels of water erosion, mainly gully erosion. Analysis of the vegetation indices found that Normalized Difference Vegetation Index (NDVI) produced the highest accuracy for mapping gullies at the sub-catchment level while Transformed Soil Adjusted Vegetation Index (TSAVI) was successful at mapping gullies at the continuous gully level. Mapping of gullies using classification algorithms highlighted the spectral complexity of gullies and the challenges faced when trying to identify them from the surrounding areas. The Support Vector Machine (SVM) classification algorithm produced the highest accuracy for mapping gullies in all the tested scales and was the recommended approach to gully mapping using remote sensing

>Magister Scientiae - MSc / Gully erosion and headcut migration has been at the crux of wetland degradation in South Africa. The resulting erosion and draining effect has seen more than 50% of wetlands in the country degraded. This study investigated the degradation of indigenous Palmiet, peat forming, wetlands through headcut erosion. This was done by exploring the relationship between headcut migration rate and morphodynamic characteristics through the use of multiple regression analysis. Wetlands investigated in this study occurred in the Kromme River catchment and Nuwejaars River catchment, in the Eastern Cape and Western Cape respectively. Morphodynamic characteristics assessed include headcut dimensions, gully characteristics, soil characteristics and drainage basin characteristics. These parameters were determined either through infield assessment, image analysis or laboratory analysis. Three headcut migration rate types were calculated through a combination of infield measurements and image analysis techniques executed within ArcGIS. These migration rate types include apex advancement (m/a), gully expansion (m2/a) and volume erosion (m3/a). Statistical analysis revealed significant relationships between morphodynamic characteristics and both volume erosion and gully expansion. Morphodynamic characteristics such as drop height, apex width, gully width, drainage rate and sand content were found to have a direct relationship with migration rates, whereas characteristics such as average drainage basin slope, clay content, silt content, SOM content and soil saturation were found to have an indirect relationship with headcut migration rates. Results provide insight into the headcut migration process, its influencing factors and the potential for headcut migration rate prediction. An evaluation of these results using WET-Health found that the wetland management tool captures wetland geomorphic controls to an accuracy of 68% and 70%. Furthermore, the influence of morphodynamic characteristics on migration rates contributes to the wetland rehabilitation process as it allows for the identification of headcut sites most susceptible to erosion. This will then allow for timely wetland rehabilitation, decreasing the rate of net wetland degradation and improving the management and efficiency of wetland restoration.

No description available.

Master of Science / Department of Biological & Agricultural Engineering / Stacy L. Hutchinson / Gully erosion is a serious problem on military training lands resulting in not only soil erosion and environmental degradation, but also increased soldier injuries and equipment damage. Assessment of gully erosion occurring on Fort Riley was conducted in order to evaluate different gully location methods and to develop a gully prediction model based on logistic regression. Of the 360 sites visited, fifty two gullies were identified with the majority found using LiDAR based data. Logistic regression model was developed using topographic, landuse/landcover, and soil variables. Tests for multicollinearity were used to reduce the input variables such that each model input had a unique effect on the model output. The logistic regression determined that available water content was one of the most important factors affecting the formation of gullies. Additional important factors included particle size classification, runoff class, erosion class, and drainage class. Of the 1577 watersheds evaluated for the Fort Riley area, 192 watersheds were predicted to have gullies. Model accuracy was approximately 79% with an error of omission or false positive value of 10% and an error of commission or false negative value of 11%; which is a large improvement compared to previous methods used to locate gully erosion.

Master of Science / Department of Biological and Agricultural Engineering / Stacy Hutchinson / Military maneuvers result in significant physical and environmental impacts to the landscape. These impacts generally result in a loss of vegetative cover and increased watershed runoff and rate depending on vehicle speed, turning radius, and soil moisture content. Unless adequately monitored or mitigated, this increased runoff can lead to excessive soil erosion and gully formation. Past studies have revealed that these gullies can impact water quality from excessive erosion and create concerns regarding soldier safety. In order to better understand how gullies form and evolve overtime on military installations, a study is being conducted at Fort Riley, KS. In 2010, approximately forty gullies were identified, assessed, and measured using common erosion monitoring and surveying techniques. These gully locations, and any newly formed gullies, were remeasured using these same methods in 2012 to determine the rate of growth for each site with respect to width, depth, and headcut. Of fifty-nine gullies total, twenty one were initially included in this study. Upon further analysis including the utilization of watershed characteristics and land management techniques, eleven of the 21 utilized gullies were deemed appropriate to include in predictive assessment, as these eleven systems exhibited singular headcut migration. Multiple Regression Analysis was utilized to produce predictive equations for Headcut Growth. This equation [Headcut Growth = 0.666 + 0.137(Watershed Slope) – 0.478(Training Intensity) + 0.757(log[Watershed Area]) – 0.278(Drainage Density) – 0.0138(Above Ground Biomass Change) + 0.187(Burning Frequency] resulted in a model relationship of approximately 90%, with Watershed Slope being the most significant variable when an output Headcut Growth was reached.

Environmental degradation is a serious problem in Lesotho, Africa. The majority of studies dealing with soil loss and gully erosion have mainly focused on the mechanics of the erosion. However, mountain watersheds are sensitive and vulnerable to degradation and in so being, have large inherent environmental implications. Gully erosion diversifies the micro-topographical and hydrological environment. The severe changes and eventual system degradation incurred as a result of gullying has rarely been quantified. This paper specifically highlights mire phytogeographic responses to valley head degradation at selected sites in eastern Lesotho by comparing patterns observed in gullied mires to those seen in other non-gullied mires. Soil and vegetation belt transects are set up across five mires (2 gullied) in the highlands of eastern Lesotho. The response of many of the plant species to the overall environmental gradient was asymmetrical and unimodal in pattern. The spatial distribution of the soil’s physical properties, topography and vegetation community patterns were found to reflect the spatial mosaic of the soil moisture gradient. The negative impact that gullying has on the ecohydrological regime of the valley heads is evident and is allowing for shrub encroachment. Both the wetland and dryland vegetation communities correlate strongly with the changes in the surface soil moisture gradient. Gully erosion is clearly a threshold phenomenon. Continued grassland degradation, accelerated soil erosion and subsequent gullying of the wetlands will lead to plant and animal diversity loss, decreased livestock productivity, sediment-laden water and shortened dam life-span.

Devido a dificuldade em se modelar a contribuição de aporte de sedimentos provenientes de erosões lineares em uma bacia hidrográfica, muitas vezes estes são desconsiderados nos estudos hidrossedimentológicos, contudo, podem corresponder a parcela significativa do assoreamento. O presente projeto analisou como a contribuição de uma voçoroca no município de Santo Antônio do Aracanguá (SP), para o assoreamento do Ribeirão das Cruzes, tributário do reservatório da UHE Três Irmãos (Rio Tietê). O estudo foi conduzido por meio de pesquisa teórica (levantamento bibliográfico), coletas de dados na área de estudo e por meio de simulação computacional. Com auxílio de ferramentas de geoprocessamento foram quantificados o volume assoreado no tributário determinado por levantamento batimétrico (12,31 hm³) e o volume de solo erodido na voçoroca por meio de levantamento topográfico (0,22 hm³). Comparando estes resultados obtivemos a contribuição de 1,80% da erosão linear para o assoreamento do tributário nos 21,12 anos anteriores a pesquisa. No entanto, devido a estimativa do surgimento e desenvolvimento da voçoroca estar associado aos últimos 7,11 anos, a contribuição no assoreamento para este período foi de 5,17%. O estudo ainda apontou o depósito destes sedimentos nos primeiros 2 km à jusante da interface erosão-represa. Erosões lineares podem contribuir significativamente no processo de assoreamento como demonstrado no estudo de caso, sendo necessário se considerar este tipo de contribuição nos estudos de aporte de sedimento em corpos d\'água. / Due the difficulty of modeling the contribution of sediment delivery from linear erosions in a watershed, these are often overlooked in hydrosedimentological studies, however, may represent a significant portion of siltation. This project analyzes the contribution of a gully erosion in Santo Antonio do Aracanguá (SP) for the sedimentation of Ribeirão das Cruzes, a tributary of the UHE Three Brothers reservoir (Tietê River). The study was conducted from theoretical research (bibliographic research), data collection in the study area and through computer simulation. With the aid of GIS tools were quantified the silted volume in the tributary, determined by bathymetric survey (12.31 hm³) and the volume of eroded soil in the gully erosion by topography surveying (0.22 hm³). Comparing these results, we have obtained the contribution of 1.80% from linear erosion to the sedimentation in the tributary during the 21.12 years preceding the survey. However, due to estimative of the beginning and development of the gully erosion being associated with the last 7.11 years, the contribution to sedimentation in this period was 5.17%. The study also accused the deposit of sediment in the first 2 km downstream interface \"erosion-dam\". Linear erosions can contribute significantly in the process of sedimentation as shown in the study case, being necessary to consider this type of contribution in studies of sediment input into water bodies.

Devido a dificuldade em se modelar a contribuição de aporte de sedimentos provenientes de erosões lineares em uma bacia hidrográfica, muitas vezes estes são desconsiderados nos estudos hidrossedimentológicos, contudo, podem corresponder a parcela significativa do assoreamento. O presente projeto analisou como a contribuição de uma voçoroca no município de Santo Antônio do Aracanguá (SP), para o assoreamento do Ribeirão das Cruzes, tributário do reservatório da UHE Três Irmãos (Rio Tietê). O estudo foi conduzido por meio de pesquisa teórica (levantamento bibliográfico), coletas de dados na área de estudo e por meio de simulação computacional. Com auxílio de ferramentas de geoprocessamento foram quantificados o volume assoreado no tributário determinado por levantamento batimétrico (12,31 hm³) e o volume de solo erodido na voçoroca por meio de levantamento topográfico (0,22 hm³). Comparando estes resultados obtivemos a contribuição de 1,80% da erosão linear para o assoreamento do tributário nos 21,12 anos anteriores a pesquisa. No entanto, devido a estimativa do surgimento e desenvolvimento da voçoroca estar associado aos últimos 7,11 anos, a contribuição no assoreamento para este período foi de 5,17%. O estudo ainda apontou o depósito destes sedimentos nos primeiros 2 km à jusante da interface erosão-represa. Erosões lineares podem contribuir significativamente no processo de assoreamento como demonstrado no estudo de caso, sendo necessário se considerar este tipo de contribuição nos estudos de aporte de sedimento em corpos d\'água. / Due the difficulty of modeling the contribution of sediment delivery from linear erosions in a watershed, these are often overlooked in hydrosedimentological studies, however, may represent a significant portion of siltation. This project analyzes the contribution of a gully erosion in Santo Antonio do Aracanguá (SP) for the sedimentation of Ribeirão das Cruzes, a tributary of the UHE Three Brothers reservoir (Tietê River). The study was conducted from theoretical research (bibliographic research), data collection in the study area and through computer simulation. With the aid of GIS tools were quantified the silted volume in the tributary, determined by bathymetric survey (12.31 hm³) and the volume of eroded soil in the gully erosion by topography surveying (0.22 hm³). Comparing these results, we have obtained the contribution of 1.80% from linear erosion to the sedimentation in the tributary during the 21.12 years preceding the survey. However, due to estimative of the beginning and development of the gully erosion being associated with the last 7.11 years, the contribution to sedimentation in this period was 5.17%. The study also accused the deposit of sediment in the first 2 km downstream interface \"erosion-dam\". Linear erosions can contribute significantly in the process of sedimentation as shown in the study case, being necessary to consider this type of contribution in studies of sediment input into water bodies.