Gullies are significant contributors of sediment to streams in the southeastern USA. This study investigated gully erosion in the clay-rich soils of east Tennessee under a humid subtropical climate. The aims of this study were to (1) estimate long-term erosion rates for different gully geomorphic settings, (2) compare patterns of erosion for the different settings, and (3) model the response of gully erosion to freeze-thaw events. Erosion was measured weekly from June 2012 to August 2018 using 105 erosion pins distributed in gully channels, interfluves, and sidewalls. Erosion rates were estimated from average slopes of lines of best fit of pin lengths versus time. Maximum and minimum temperature was calculated daily using an on-site weather station and freeze-thaw events were identified. Gully erosion was modeled using antecedent freeze-thaw activity for the three geomorphic settings. Long-term erosion rates in channels, interfluves, and sidewalls were 2.5 mm/year, 20 mm/year, and 21 mm/year, respectively; however, week-by-week erosion was statistically different between the three settings, indicating different erosive drivers. Models of erosion with lagged freeze-thaw variables explained up to 34.8% of the variability in erosion variables; sidewall erosion was most highly related to freeze-thaw activity. Freeze-thaw in prior weeks was an important variable in all erosion models.

Gully erosion is a global problem that degrades land and reduces its utility for agriculture, development, and water quality. Quantification of sediment yield and control of sediment sources is essential for environmental protection. Five methods to evaluate erosion rates and sediment yield on an east Tennessee, USA, hillslope were compared: (1) physical measurement by removal of accumulated sediment using 10 L buckets; (2) repeated measurement of erosion pins in gully (erosional) and delta (depositional) areas; (3) geometric model using a combination trapezoidal prism-cylinder segment; (4) geometric model using a series of trapezoidal pyramids; and (5) 3D solid computer modeling. The 3D solid model created in SolidWorks was selected as the reference model and all other methods overestimated sediment yield to varying degrees. Erosion pin methods overestimated sediment yield by 368% in deltas and 123% in gullies. Volumetric measurement of sediment using buckets overestimated sediment yield by 160% due to void space in the buckets. The trapezoidal prism-cylinder segment model overestimated sediment yield by 66% and the trapezoidal pyramids method overestimated sediment yield by 5.7%. For estimation of sediment trapped behind an elliptical or circular silt fence dam, use of the trapezoidal pyramid method provides a good approximation comparable to 3D solid computer modeling.

Le bassin supérieur de l’oued Djemaa qui fait partie de la montagne du Djurdjura est affecté par une importante morphogenèse. Les mouvements de terrain présentent une grande variété dans le secteur d’étude et jouent un rôle prépondérant dans l’évolution des versants. L’étude géomophologique détaillée, une enquête auprès des populations locales, des analyses géotechniques et l’analyse sédimentologique des formations déplacées nous ont permis de faire une typologie des mouvements de terrain et de dégager les facteurs de leur développement et de leur localisation. Les fortes précipitations d’hiver et de printemps sont à l’origine de tous les mouvements de terrain et des ravinements, mais l’exposition et la lithologie permettent de comprendre les formes différentes rencontrées sur les adrets et sur les ubacs. Les activités humaines jouent un rôle croissant dans l’accélération de la morphogenèse. Dans cette étude, un système d’Information Géographique a été utilisé pour produire les cartes des risques de dégradation du milieu qui sont des outils pour la planification et la gestion de l’utilisation du sol dans le bassin supérieur de l’oued Djemaa. Il permet de croiser la vulnérabilité avec l’aléa. Le résultat de ces croisements que nous avons codifiés débouche sur une carte globale de niveaux de risque / The upper basin of the oued Djemaa which includes to the mountain of Djurdjura is affected by an important morphogenesis. The ground movements introduces a large variety in the study area and play a preponderant role in the evolution of mountainsides. The geomorphology detailed study an investigation into the local populations, geotechtonic and analyses it sedimentology of displaced trainings allows us to do ground typology movement and to chow theire development factors and their location. The big rainfalls of winter and sprinter are the origin of these ground movements and gully erosions, but exposition and lithology allow to understand different forms on northern and southern slope. Human activities play more and more an important role in morphogenesis acceleration. In this study, a geographical information system has been used to provide degradation maps of risks of which are tools for planning and management of soil using in the upper basin of the oued Djemaa. He allows to cross vulnerability witch vagary. The result of these crossroads which we codified results in a total map of risk levels

Considerando a importância de se definir as condições críticas para a deflagração, desenvolvimento e estabilização das voçorocas e outras feições erosivas lineares, e tendo em conta as poucas abordagens nesse sentido realizadas no Brasil, o objetivo geral desta pesquisa é avaliar os limites críticos topográficos para o desenvolvimento das formas resultantes da erosão linear em Piratininga (SP). Os procedimentos metodológicos envolveram a identificação e caracterização das feições erosivas por meio de fotografias aéreas e in situ; a mensuração da declividade (S) em campo e com diversas resoluções de Modelo Digital de Terreno (MDT) e da Área de Contribuição (A) também a partir do MDT; e, a definição dos limites críticos topográficos na forma da seguinte Função Potência: S = a × . A linha do limite crítico foi ajustada no limite inferior dos dados, paralelamente à inclinação linha ortogonal de regressão de S e A. As feições erosivas foram categorizadas em 4 classes e 13 subclasses de acordo com seus aspectos morfométricos e indicadores dos processos atuantes. A mensuração de S e A por diferentes métodos resultou em algumas variações significativas nos dados gerados, sobretudo na comparação entre os valores obtidos em campo e pelo MDT. Foi obtido o seguinte limite crítico topográfico: S = 0,064 × ,, que tem coeficientes semelhantes a outras pesquisas que analisaram feições erosivas resultantes do escoamento subsuperficial. A distinção entre as feições erosivas onde ainda há indícios de recuo das cabeceiras e feições erosivas que já atingiram o equilíbrio, assim como a análise dos pontos de início dos processos erosivos em relação ao limite crítico, forneceu bases empíricas para a discussão da evolução das feições erosivas lineares em relação ao limite crítico topográfico e também para ao entendimento dos estados estável e instável dos voçorocamentos, permitindo a construção de um modelo teórico de previsão da estabilidade e instabilidade das feições erosivas baseado na relação entre a declividade e a área de contribuição em diferentes perfis de encosta. / Considering the importance of defining the critical conditions for the generation, development and stabilization of gullies and other erosional features, and taking into account the few approaches accordingly held in Brazil, the aim of this research is to evaluate the topographical critical limits for developing of gully erosion in Piratininga (SP). The methodological procedures involved: the identification and characterization of the gullies using aerial photographs and in situ; measurement of the slope (S) in the field and with various resolutions of Digital Terrain Model (DTM) and drainage area (A) also from DTM, and the definition of topographical thresholds in the form of following Power Function: S = a × . The topographical threshold line has been set at the lower limit of data, parallel to the slope of orthogonal regression line of S and A. The erosional features were categorized into 4 classes and 13 subclasses according to their morphometric aspects and indicators of active processes. The measurement of S and A by different methods resulted in some significant changes in the data generated, particularly when comparing the values obtained in the field and the DTM. We obtained the following topographic threshold: S = 0,064 × , which has coefficients similar to other studies that analyzed erosional features resulting from subsurface flow. The distinction between active and stabilized gullies, as well as analysis of the starting points of erosion in relation to threshold line, provide an empirical basis for the discussion of the evolution of gullies in relation to the topographic threshold line and also for the understanding of stable and active states of gullies, allowing the construction of a theoretical model for predicting the stability and instability of the gullies based on the relationship between slope and drainage area in different slope profiles.

Gully erosion has been established as a major source of sediment pollution in the upper Trinity River watershed in north-central Texas. This fact, along with a lack of models appropriate for a large-area gully erosion analysis established a need for a gully erosion study in the upper Trinity basin. This thesis project attempted to address this need by deriving an index indicative of gully erosion risk using remote sensing and geographic information systems (GIS) methodology. In context of previous field studies, the coarse spatial resolution of the input GIS data layers presented a challenge to prediction of gully prone areas. However, the remote sensing/GIS approach was found to provide useful reconnaissance information on gully risk over large areas.

O presente trabalho propõe índices que indicam o limiar topográfico para predição do desencadeamento de canais de erosão linear em uma região de clima tropical. A área escolhida para a realização do estudo localiza-se no município de São Pedro/SP e apresenta uma área de aproximadamente 7 \'KM POT.2\'. Nesta área foi realizado um inventário detalhado das feições erosivas pré-existentes para obtenção dos valores das áreas das bacias de contribuição, considerando as cabeceiras de algumas erosões e as declividades médias dessas áreas, por meio de ferramentas de SIG e também por fotografias aéreas ortorretificadas. Trabalhos de campo, com o auxílio de GPS de precisão, permitiram definir a situação atual das erosões e com o uso de fotografias aéreas de anos anteriores foi possível observar a sua evolução. Com isso, através dos mapas em SIG, como MDT, declividade, direção de fluxo e etc. foram obtidos os valores de área de contribuição (A) e declividade média (S). Os valores de A x S foram apresentados em gráficos que permitiram identificar o ponto mínimo para a ocorrência de um evento erosivo e estabelecer de forma empírica os limiares topográficos que definem as condições para o início do processo erosivo. Para o Índice I foram feitas duas equações (uma para canais menos profundos que 1 metro e outra para canais mais profundos que 1 metro) e para o Índice II foi obtida apenas uma equação, pois em fotografias aéreas nas escalas disponíveis (1:25.000 e 1:30.000) foram possíveis serem observados apenas os canais profundos. Os índices obtidos neste trabalho foram para o Índice I: S = 0,0219A(-0,376) (canais profundos) e S = 0,0128A(-0,443) (canais rasos); enquanto que para o Índice II o valor obtido é: S = 0,0588A(-0,377). Para a validação destes índices propostos, foram realizados os mesmos procedimentos para obtenção das áreas de contribuição (A) e declividade média (S), porém em outra área. A área escolhida para se fazer a validação dos índices foi a Bacia do Ribeirão do Meio, que apresenta 48 \'KM POT.2\' aproximados de área e apresenta características físicas semelhantes da área utilizada neste presente estudo, ou seja, apresenta semelhança em geologia, geomorfologia, clima, uso e ocupação. Foi observado com esta validação, que todos os pontos com problemas de erosão da área usada para validação localizam-se dentro da área prevista pelos índices para ocorrência de problemas de erosão, o que significa dizer que os índices exprimem o limiar topográfico para erosões lineares nas condições encontradas na área de estudo e em áreas semelhantes. / This paper proposes indexes indicating the topographic threshold for predicting the trigger of gully erosion in a tropical climate region. The area chosen for the study is located in São Pedro/SP and presents an area of approximately 7 \'KM POT.2\' . In this area was carried out a detailed inventory of pre-existing erosion to obtain the values of watershed areas of contribution, considering the headwaters of some erosions and the mean slope of these areas, using GIS tools and also orthorectified aerial photographs. Fieldwork, with the assistance of GPS accuracy, allowed defining the current condition of erosion and with the use of aerial photographs from previous years was possible to observe its evolution. Thus, through the maps in GIS, as DEM, Slope, Flow Direct ion among others, were obtained values from contribution area (A) and mean slope (S). The values of A x S were represented in charts al lowing to identify the lower point for the occurrence of an erosion event and establish empirical ly the topographic thresholds that def ine the conditions for initiating the erosion process. For the index I were made two equations (one for channels less than 1 meter deep and one for channels deeperthan 1 meter) and Index II was obtained only one equation, because in aerial photographs available (scales1:25,000 and 1:30,000) were possible only be observed the deep channels. The indexes obtained in this paper were for the Index I: S = 0,0219A(-0,376) (deep channels) and S = 0,0128A(-0,443) (shallow channels), while the index II the value obtained is: S = 0,0588A(-0,377). To validate these proposed indexes, the same procedures were performed to obtain the contribution area (A) and mean slope (S), but in another area. The area chosen to perform the validation of the indexes was the Basin Ribeirão do Meio, which is 48 \'KM POT.2\' extents and shows similarity in geology, geomorphology, climate, use and occupation. The results have been showed that the selected points with erosion problem of the area used for validation are located wi thin the area specified by the indexes for the occurrence of erosion problems, which means that the indexes reflect the topographic threshold for gully erosions in conditions found in the study area and similar areas.

Made available in DSpace on 2017-07-21T18:13:39Z (GMT). No. of bitstreams: 1 Carla Correa Prieto.pdf: 8419682 bytes, checksum: 9829b418de394d33b2eb17754ec8a160 (MD5) Previous issue date: 2010-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The urban area of Ponta Grossa city, located in Parana state, South of Brazil, has different kinds of erosion process, as landslides, river erosion, hillslopes, piping and gully erosion. These processes occur even in authorized as much as in unauthorized areas. The present research intends to comprehend the relations connecting the urban planning and the erosion process occurrences. As a base for the research, it was studied a gully erosion located near Jardim Santa Edwirges and Vila Romana. As well, the aims of this study it to comprehend which were the factors that influenced the occurrence and the evolution of this gully erosion. Therefore, the present research intends to investigate the relation between the rock base and its fragility to accelerated erosion, besides, it has been done an analysis of the rain data from 1946 to 2009, as the water is known as a relevant factor in the erosion process. Finally, it has been made chronological analysis, aiming to comprehend the influence of the street shapes, especially without a drainage system, as an influence in the development and evolution of the gully channels. Although, to elaborate the chronological analysis, it was used aerial photographs and a satellite image. The dates chosen were 1980, 1995 and 2009, because those were the available images with appropriated scale/resolution, according to the size of the studied area. It was also made a comparison of photographs and information acquired in loco, during the research time, as they made possible to observe the recent changes and the fast environmental degradation. / A área urbana do município de Ponta Grossa, Paraná, possui diferentes tipos de processos erosivos como escorregamentos, solapamentos de margens e desmoronamentos, além de erosão subterrânea remontante com colapsos associados e voçorocas. Estes processos ocorrem tanto em área de ocupação regular como irregular. Com isso, realizou-se o presente trabalho com o intuito de compreender quais são as relações entre o planejamento urbano e a ocorrência de processos erosivos. Foi utilizada como base para o estudo a voçoroca que se localiza nas proximidades do Jardim Santa Edwirges e da Vila Romana. Assim, o objetivo do trabalho é compreender quais são os fatores que possibilitaram a ocorrência e o contínuo aumento da voçoroca em questão. Para tanto, o presente trabalho visou investigar a relação entre o substrato geológico e sua fragilidade para ocorrência de erosão acelerada, realizou-se uma análise dos índices pluviométricos de Ponta Grossa entre 1946 e 2009, visto que a água é um fator relevante na ocorrência de processos erosivos. E finalmente, foram realizadas análises temporais para compreender a influência do traçado das ruas, mesmo que sem pavimentação, porém sem sistemas de captação de água pluvial completos, como influencia na formação e no crescimento dos canais da voçoroca. Desse modo, para a elaboração do estudo temporal, foram utilizadas fotografias aéreas e imagem de satélite. As datas escolhidas para a análise da evolução foram 1980, 1995 e 2006 em decorrência da disponibilidade de material com escala/resolução espacial compatíveis com o tamanho da área estudada. Realizou-se a comparação de fotografia e informações obtidas em campo, ao longo do período da pesquisa, visando observar as alterações recentes, e a rapidez da degradação do ambiente.

O presente trabalho propõe índices que indicam o limiar topográfico para predição do desencadeamento de canais de erosão linear em uma região de clima tropical. A área escolhida para a realização do estudo localiza-se no município de São Pedro/SP e apresenta uma área de aproximadamente 7 \'KM POT.2\'. Nesta área foi realizado um inventário detalhado das feições erosivas pré-existentes para obtenção dos valores das áreas das bacias de contribuição, considerando as cabeceiras de algumas erosões e as declividades médias dessas áreas, por meio de ferramentas de SIG e também por fotografias aéreas ortorretificadas. Trabalhos de campo, com o auxílio de GPS de precisão, permitiram definir a situação atual das erosões e com o uso de fotografias aéreas de anos anteriores foi possível observar a sua evolução. Com isso, através dos mapas em SIG, como MDT, declividade, direção de fluxo e etc. foram obtidos os valores de área de contribuição (A) e declividade média (S). Os valores de A x S foram apresentados em gráficos que permitiram identificar o ponto mínimo para a ocorrência de um evento erosivo e estabelecer de forma empírica os limiares topográficos que definem as condições para o início do processo erosivo. Para o Índice I foram feitas duas equações (uma para canais menos profundos que 1 metro e outra para canais mais profundos que 1 metro) e para o Índice II foi obtida apenas uma equação, pois em fotografias aéreas nas escalas disponíveis (1:25.000 e 1:30.000) foram possíveis serem observados apenas os canais profundos. Os índices obtidos neste trabalho foram para o Índice I: S = 0,0219A(-0,376) (canais profundos) e S = 0,0128A(-0,443) (canais rasos); enquanto que para o Índice II o valor obtido é: S = 0,0588A(-0,377). Para a validação destes índices propostos, foram realizados os mesmos procedimentos para obtenção das áreas de contribuição (A) e declividade média (S), porém em outra área. A área escolhida para se fazer a validação dos índices foi a Bacia do Ribeirão do Meio, que apresenta 48 \'KM POT.2\' aproximados de área e apresenta características físicas semelhantes da área utilizada neste presente estudo, ou seja, apresenta semelhança em geologia, geomorfologia, clima, uso e ocupação. Foi observado com esta validação, que todos os pontos com problemas de erosão da área usada para validação localizam-se dentro da área prevista pelos índices para ocorrência de problemas de erosão, o que significa dizer que os índices exprimem o limiar topográfico para erosões lineares nas condições encontradas na área de estudo e em áreas semelhantes. / This paper proposes indexes indicating the topographic threshold for predicting the trigger of gully erosion in a tropical climate region. The area chosen for the study is located in São Pedro/SP and presents an area of approximately 7 \'KM POT.2\' . In this area was carried out a detailed inventory of pre-existing erosion to obtain the values of watershed areas of contribution, considering the headwaters of some erosions and the mean slope of these areas, using GIS tools and also orthorectified aerial photographs. Fieldwork, with the assistance of GPS accuracy, allowed defining the current condition of erosion and with the use of aerial photographs from previous years was possible to observe its evolution. Thus, through the maps in GIS, as DEM, Slope, Flow Direct ion among others, were obtained values from contribution area (A) and mean slope (S). The values of A x S were represented in charts al lowing to identify the lower point for the occurrence of an erosion event and establish empirical ly the topographic thresholds that def ine the conditions for initiating the erosion process. For the index I were made two equations (one for channels less than 1 meter deep and one for channels deeperthan 1 meter) and Index II was obtained only one equation, because in aerial photographs available (scales1:25,000 and 1:30,000) were possible only be observed the deep channels. The indexes obtained in this paper were for the Index I: S = 0,0219A(-0,376) (deep channels) and S = 0,0128A(-0,443) (shallow channels), while the index II the value obtained is: S = 0,0588A(-0,377). To validate these proposed indexes, the same procedures were performed to obtain the contribution area (A) and mean slope (S), but in another area. The area chosen to perform the validation of the indexes was the Basin Ribeirão do Meio, which is 48 \'KM POT.2\' extents and shows similarity in geology, geomorphology, climate, use and occupation. The results have been showed that the selected points with erosion problem of the area used for validation are located wi thin the area specified by the indexes for the occurrence of erosion problems, which means that the indexes reflect the topographic threshold for gully erosions in conditions found in the study area and similar areas.

Considerando a importância de se definir as condições críticas para a deflagração, desenvolvimento e estabilização das voçorocas e outras feições erosivas lineares, e tendo em conta as poucas abordagens nesse sentido realizadas no Brasil, o objetivo geral desta pesquisa é avaliar os limites críticos topográficos para o desenvolvimento das formas resultantes da erosão linear em Piratininga (SP). Os procedimentos metodológicos envolveram a identificação e caracterização das feições erosivas por meio de fotografias aéreas e in situ; a mensuração da declividade (S) em campo e com diversas resoluções de Modelo Digital de Terreno (MDT) e da Área de Contribuição (A) também a partir do MDT; e, a definição dos limites críticos topográficos na forma da seguinte Função Potência: S = a × . A linha do limite crítico foi ajustada no limite inferior dos dados, paralelamente à inclinação linha ortogonal de regressão de S e A. As feições erosivas foram categorizadas em 4 classes e 13 subclasses de acordo com seus aspectos morfométricos e indicadores dos processos atuantes. A mensuração de S e A por diferentes métodos resultou em algumas variações significativas nos dados gerados, sobretudo na comparação entre os valores obtidos em campo e pelo MDT. Foi obtido o seguinte limite crítico topográfico: S = 0,064 × ,, que tem coeficientes semelhantes a outras pesquisas que analisaram feições erosivas resultantes do escoamento subsuperficial. A distinção entre as feições erosivas onde ainda há indícios de recuo das cabeceiras e feições erosivas que já atingiram o equilíbrio, assim como a análise dos pontos de início dos processos erosivos em relação ao limite crítico, forneceu bases empíricas para a discussão da evolução das feições erosivas lineares em relação ao limite crítico topográfico e também para ao entendimento dos estados estável e instável dos voçorocamentos, permitindo a construção de um modelo teórico de previsão da estabilidade e instabilidade das feições erosivas baseado na relação entre a declividade e a área de contribuição em diferentes perfis de encosta. / Considering the importance of defining the critical conditions for the generation, development and stabilization of gullies and other erosional features, and taking into account the few approaches accordingly held in Brazil, the aim of this research is to evaluate the topographical critical limits for developing of gully erosion in Piratininga (SP). The methodological procedures involved: the identification and characterization of the gullies using aerial photographs and in situ; measurement of the slope (S) in the field and with various resolutions of Digital Terrain Model (DTM) and drainage area (A) also from DTM, and the definition of topographical thresholds in the form of following Power Function: S = a × . The topographical threshold line has been set at the lower limit of data, parallel to the slope of orthogonal regression line of S and A. The erosional features were categorized into 4 classes and 13 subclasses according to their morphometric aspects and indicators of active processes. The measurement of S and A by different methods resulted in some significant changes in the data generated, particularly when comparing the values obtained in the field and the DTM. We obtained the following topographic threshold: S = 0,064 × , which has coefficients similar to other studies that analyzed erosional features resulting from subsurface flow. The distinction between active and stabilized gullies, as well as analysis of the starting points of erosion in relation to threshold line, provide an empirical basis for the discussion of the evolution of gullies in relation to the topographic threshold line and also for the understanding of stable and active states of gullies, allowing the construction of a theoretical model for predicting the stability and instability of the gullies based on the relationship between slope and drainage area in different slope profiles.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Gully erosion is a major environmental problem not only having direct influences on site but also indirect influences felt further down the catchment. Combating gully erosion has proven to be elusive due to the difficulty in finding the causal factors and developing mechanisms involved. Soil is the medium in which gully erosion occurs yet few research have investigated it as a driving factor behind gully development and those that have has done it in a very elementary way. The first aim of this project was to physically and chemically characterise and classify the discontinuous gully system at Malansdam to establish the relationship between landscape hydrology and geomorphologic gully development with a focus on control factors. This was done by field observations, physical measurements and spatial and hydrological analyses with a Geographical Information System (GIS). The Malansdam gully system was the first ever recorded Strahler stream order (SSO) 5 classical gully system with the most active region being in the upper reaches where a steeper slope is experienced. Although piping was observed the V-shape channels and SAR data from traditional wet analysis indicated runoff to be the dominant formation process. A duo of factors, consisting of one anthropogenic and one natural factor respectively, was found that the major control factors behind the gully formation. A unique anthropogenic factor that has never been published beforehand was found to be the anthropogenic driving factor namely the ploughed contour cultivation technique employed by the farmers in the Sandspruit catchment. The ploughed contours act as channels firstly collecting and secondly moving water that would have drained naturally downwards in the valley to one exit point in the gully system. This allows increased erosive energy because of the larger volumes of water entering one single point in the upper reaches of the gully system where a steeper slope is experienced. The driving factor in the natural group was determined to be weak soil structure due to an abundant amount of exchangeable Mg2+ cations occupying the exchange sites on the clay fraction. This would cause soil to disperse in the presence of water even with a low amount of exchangeable Na+. Combat methods would accordingly exist in the form of rectifying the soil structure and finding an alternative to the ploughed contour system currently employed, but also planting vegetation especially grass or wheat in the gully channels. The second aim of this project was to determine the capability of Near Infrared (NIR) spectrometry, with wavenumbers 12 500 – 4 000 cm-1, to predict indicators used in soil science to establish the dispersive nature of a soil. These indices included the Exchangeable Sodium Percentage (ESP), Sodium Absorption Ratio (SAR), Magnesium Saturation Percentage (MS%), Electrical Conductivity (EC), Potential Hydrogen (pH) as well as the four main exchangeable cations namely calcium (Ca2+), potassium (K+), sodium (Na+) and magnesium (Mg2+). Surface and subsurface soil samples were collected from active gully heads. These samples were minimally pre-processed thus only dried, milled and sieved. Thereafter it was subject to NIR analysis making use of the Bruker multi-purpose FT-NIR Analyser (MPA; Bruker Optik GmbH, Germany) with a spectral range of 12 500cm-1 to 4000cm-1 which is. Partial Least Square Regression (PLSR) models were built for each index and the exchangeable cations making use of QUANT 2 utility of OPUS 6.5 (MPA; Bruker Optik GmbH, Germany) software. Five different regrssion statistics namely the coefficient of determination (r2), Root Mean Square Error of Cross Validation (RMSECV), Ratio of Performance to Deviation (RPD), Bias and the Ratio of Performance of Quartiles (RPIQ) were used to assess the legitimacy of each PLSR model. Upon validation all the PLSR models performed in line with previously published work and in certain cases better. The only exception was MS% which would require further investigation. NIR thus possess the capability to predict a soil’s dispersive nature in a fast, reliable, inexpensive and non- destructive way, thus implying whether or not it contributes to gully erosion at a significant level or only minimally. / AFRIKAANSE OPSOMMING: Donga erosie is 'n groot omgewingsprobleem. Dit het nie net ‘n direkte invloed op die area waar dit geleë is nie, maar het ook ‘n indirekte invloed wat elders in die opvangsgebied ervaar word. Bekamping van donga erosie is moeisaam aangesien die faktore wat aanleiding gee tot die vorming en dryf daarvan moeilik is om te bepaal. Grond is die medium waarin erosie plaasvind, maar daar is nogtans steeds min navorsing wat grond ondersoek het as ‘n moontlike faktor aanleiding gee tot donga erosie. Die wat dit al wel ingesluit het, het dit slegs op n baie elemntêre manier ondersoek. Die eerste doel van hierdie projek was om die diskontinue donga stelsel fisies en chemise te karakteriseer en klassifiseer om soedoende die verhouding tussen die landskap hidrologie en geomorfologiese donga ontwikkeling te bepaal met n fokus op die faktore wat dit dryf. Dit was gedoen deur middel van observasies gedoen terwyl veldwerk uitgerig was, fisiese metings asook ruimtelike en hidrologiese analises deur gebruik te maak van n Geografiese Inligting Stelsel (GIS). Die klassieke Malansdam donga stelsel is ‘n Strahler stroomorde (SSO) van 5 toegeken en is die eerste een ooit wat dit behaal het. Die mees aktiefste area was in die bolope waar die steilste helling ervaar was. Alhoewel ondergrondse pyp formasie waargeneem was het die V-vormige donga kanale en SAR data van die tradisionele nat analise aangedui dat afloop die dominante vorming proses was. Daar was gevind dat 'n duo van faktore, wat bestaan uit een menslike en een natuurlike faktor onderskeidelik, die faktore was wat donga ontwikkeling in die area dryf. 'n Unieke menslike faktor wat nog nie vantevore gepubliseer is, was bevind as die menslike faktor wat aanleiding gee tot donga erosie. Hierdie faktor is die bewerkiingsmetode wat in die Sandspruit opvangsgebied gebruik word naamlik geploegde kontoerbewerking. Die geploegde kontoere tree op as kanale om eerstens water te versamel en tweedens om die vloeirigting daarvan te wysig. Water wat onder natuurlike toestande afwaarts sou dreineer tot in die vallei word vasgevang deur die kontoere en gekanaliseer na een invloei punt in die donga. Hierdie proses verhoog die erosiekrag van die water aangesien groter volumes by 'n enkele punt in die steiler bolope van die donga stelsel invloei. Die dryf faktor in die natuurlike groep was swak grond struktuur. Die oorsaak hiervan was die besetting van ‘n grootmaat uitruilbare Mg2+ katione op die uitruil plekke van die kleifraksie. Dit sou veroorsaak dat grond in die teenwoordigheid van water maklik sou dispergeer, selfs in die teenwoordigheid van 'n lae hoeveelheid uitruilbare Na+ katione. Metodes om donga erosie te bekamp sal dienooreenkomstig bestaan uit die herstel van die grondstruktuur en die toepassing van 'n alternatiewe gondbewerkings stelsel. Die aanplanting van plantegroei, veral gras en koring binne die donga kanale sal verder help met die veg tot bekamping Die tweede doel van hierdie projek was om te bepaal indien naby infrarooi (NIR) spektrometrie (met golfnommer van 12 500 – 4 000cm-1) oor die vermoë beskik om aanwysers wat traditioneel in grondkunde gebruik word om die dispergering van grond te meet te voorspel. Hierdie aanwysers sluit vyf indekse in naamlik die Veranderlike Natrium Persentasie (ESP), Natrium Absorpsie Verhouding (SAR), Magnesium Versadiging Persentasie (MS%), Elektriese Geleidingsvermoë (EC) en die Potensiële Waterstof (pH) sowel as die vier hoof uitruilbare katione naamlik kalsium (Ca2+) , kalium (K+), natrium (Na+) en magnesium (Mg2+). Oppervlak en ondergrondse grondmonsters is ingesamel by die punt van oorsprong by aktiewe dongas. Hierdie monsters is minimaal voorberei, dus slegs gedroog, gemaal en gesif. Daarna was dit onderworpe aan die NIR analise. Die Bruker meerdoelige FT-NIR Analiseerder (MPA; Bruker Optik GmbH, Duitsland) met 'n spektrale omvang van 12 500cm 1 4000cm-1 is hiervoor gebruik. Parsiële kleinste kwadraat regressie (PLSR) modelle is gebou vir elke indeks asook die uitruilbare katione deur gebruik te maak van die nutsprogram Quant 2 van die OPUS 6.5 (MPA; Bruker Optik GmbH, Duitsland) sagteware. Vyf verskillende regressie statistieke naamlik die bepalingskoëffisiënt (r2), vierkantswortel fout tydens kruis validasie (RMSECV), verhouding van prestasie teenoor voorspellingsafwyking (RPD), sydigheid en die verhouding van prestasie van kwartiele (RPIQ) was gebruik om die geldighied van elke PLSR model te asseseer. Alle PLSR modelle het goed presteer, behalwe vir MS% wat verdere navorsing vereis. NIR beskik dus oor die vermoë om die aard van dispergering van grond te bepaal op 'n vinnige, betroubare, goedkoop en nie afbrekende manier. Dit kan dus effektief aangewend word as ‘n substitusie vir die traditionele metodes om te bepaal as grond a beduidende faktor is of nie.