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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Mapping rill soil erosion in agricultural fields with UAV-borne remote sensing data

Malinowski, Radek, Heckrath, Goswin, Rybicki, Marcin, Eltner, Anette 27 February 2024 (has links)
Soil erosion by water is a main form of land degradation worldwide. The problem has been addressed, among others, in the United Nations Sustainability Goals. However, for mitigation of erosion consequences and adequate management of affected areas, reliable information on the magnitude and spatial patterns of erosion is needed. Although such need is often addressed by erosion modelling, precise erosion monitoring is necessary for the calibration and validation of erosion models and to study erosion patterns in landscapes. Conventional methods for quantification of rill erosion are based on labour-intensive field measurements. In contrast, remote sensing techniques promise fast, non-invasive, systematic and larger-scale surveying. Thus, the main objective of this study was to develop and evaluate automated and transferable methodologies for mapping the spatial extent of erosion rills from a single acquisition of remote sensing data. Data collected by an uncrewed aerial vehicle was used to deliver a highly detailed digital elevation model (DEM) of the analysed area. Rills were classified by two methods with different settings. One approach was based on a series of decision rules applied on DEM-derived geomorphological terrain attributes. The second approach utilized the random forest machine learning algorithm. The methods were tested on three agricultural fields representing different erosion patterns and vegetation covers. Our study showed that the proposed methods can ensure recognition of rills with accuracies between 80 and 90% depending on rill characteristics. In some cases, however, the methods were sensitive to very small rill incisions and to similar geometry of rills to other features. Additionally, their performance was influenced by the vegetation structure and cover. Besides these challenges, the introduced approach was capable of mapping rills fully automatically at the field scale and can, therefore, support a fast and flexible assessment of erosion magnitudes.
412

Smallholder Farmers, Environmental Change and Adaptation in a Human-Dominated Landscape in the Northern Highlands of Rwanda

William, Apollinaire 24 May 2018 (has links)
No description available.
413

An Erodibility Assessment of Central Ohio Cropland Soils

Tomashefski, David J. 26 September 2016 (has links)
No description available.
414

Application of Data Mining and Big Data Analytics in the Construction Industry

Abounia Omran, Behzad January 2016 (has links)
No description available.
415

Erhaltung der Bodenfruchtbarkeit unter Anwendung angepasster Anbausysteme in Bergregionen Vietnams / Soil Fertility Conservation for Sustainable Agriculture in Sloping Lands by applying appropriate Crop Systems and Green Manure Crops in Mountainous Area of Northern Vietnam

Do, Thi Lan 19 January 2004 (has links)
No description available.
416

Measurement of 222Rn Exhalation Rates and 210Pb Deposition Rates in a Tropical Environment

Lawrence, Cameron Eoin January 2006 (has links)
This thesis provides the measurements of 222Rn exhalation rates, 210Pb deposition rates and excess 210Pb inventories for locations in and around Ranger Uranium Mine and Jabiru located within Kakadu National Park, Australia. Radon-222 is part of the natural 238U series decay chain and the only gas to be found in the series under normal conditions. Part of the natural redistribution of 222Rn in the environment is a portion exhales from the ground and disperses into the atmosphere. Here it decays via a series of short-lived progeny, that attach themselves to aerosol particles, to the long lived isotope 210Pb (T1/2 = 22.3 y). Attached and unattached 210Pb is removed from the atmosphere through wet and dry deposition and deposited on the surface of the earth, the fraction deposited on soils is gradually transported through the soil and can create a depth profile of 210Pb. Here it decays to the stable isotope 206Pb completing the 238U series. Measurements of 222Rn exhalation rates and 210Pb deposition rates were performed over complete seasonal cycles, August 2002 - July 2003 and May 2003 - May 2004 respectively. The area is categorised as wet and dry tropics and it experiences two distinct seasonal patterns, a dry season (May-October) with little or no precipitation events and a wet season (December-March) with almost daily precipitation and monsoonal troughs. November and April are regarded as transitional months. As the natural processes of 222Rn exhalation and 210Pb deposition are heavily influenced by soil moisture and precipitation respectively, seasonal variations in the exhalation and deposition rates were expected. It was observed that 222Rn exhalation rates decreased throughout the wet season when the increase in soil moisture retarded exhalation. Lead-210 deposition peaked throughout the wet season as precipitation is the major scavenging process of this isotope from the atmosphere. Radon-222 is influenced by other parameters such as 226Ra activity concentration and distribution, soil porosity and grain size. With the removal of the influence of soil moisture during the dry season it was possible to examine the effect of these other variables in a more comprehensive manner. This resulted in categorisation of geomorphic landscapes from which the 222Rn exhalation rate to 226Ra activity concentration ratios were similar during the dry season. These results can be extended to estimate dry season 222Rn exhalation rates from tropical locations from a measurement of 226Ra activity concentration. Through modelling the 210Pb budget on local and regional scales it was observed that there is a net loss of 210Pb from the region, the majority of which occurs during the dry season. This has been attributed to the fact that 210Pb attached to aerosols is transported great distance with the prevailing trade winds created by a Hadley Circulation cell predominant during the dry season (winter) months. By including the influence of factors such as water inundation and natural 210Pb redistribution in the soil wet season budgeting of 210Pb on local and regional scales gave very good results.
417

Land degradation in Mhondoro (Zimbabwe) : an environmental assessment of communal land uses and resource management practice

Tichagwa, Cornelius Gibson 04 1900 (has links)
Thesis (MA)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: When land loses its intrinsic qualities or suffers a decline in its capabilities it is said to be degraded. Land degradation manifests itself in various forms such as deforestation, soil erosion, land, air and water pollution. In the context of sustainable development land degradation has become one of the world's major concerns. Now, more than ever before, it has become urgent to carry out empirical studies on the nature and extent of land degradation and to come up with appropriate responses to the problem. In much of the developing world communal natural resource management practices are common. It is often assumed that communal exploitation of common property resources such as woodlands, pastures, water sources and wildlife inevitably leads to land degradation. This is due to the belief that humankind would seek to derive maximum benefit from common pool resources without incurring any costs towards the conservation of those resources. This study was an environmental assessment of the impacts of communal land-use systems and common property resources management practices in the Mhondoro communal lands of Zimbabwe. The area has been subject to human settlement for over a century and is regarded as a typical representation of a well-established communal land management system. Several methods were used to make the assessment. These included the following: a questionnaire survey; interviews with key informants; soil and vegetation traverses and field measurements; tree density counts in demarcated plots; calculation of the population density and livestock density for the study area; completion of an environmental evaluation matrix and a communal projects sustainability index checklist; and analysis of geo-referenced time-lapse aerial photography covering a fifteen year period (1982-1997). It was established that serious land degradation had occurred in Chief Mashayamombe's ward in Mhondoro. Degradation manifested itself in the form of soil erosion and stream sedimentation, woodland depletion, pasture degradation and wildlife habitat destruction. Communal land-use and natural resource management practices are only partially to blame for this state of affairs. The fragile nature of the sandy soils of the uplands, the sadie soils of the vlei areas, combined with the fairly high rainfall amounts (annual average 750mm) make the area prone to soil erosion. Rainfall intensity tends to be high in the area and when the rain falls on the poorly vegetated, and highly erodible soils erosion occurs. The land has become severely stressed due to over-utilisation; a population density of 93 people per km2 and livestock density of 110 cattle per km2 were recorded. The land available for communal settlement in the area has been limited in extent. Due to the general poverty of the communal farmers the replacement of nutrients into the cultivated soil has not kept pace with the deteriorating condition of the land. Contrary to popular misconceptions, communal area residents have shown concern for environmental conservation through fallowing their fields, gully reclamation efforts, grazing schemes, woodland preservation and tree growing practices. Remedial and/or mitigatory measures for the environmental recovery of the area could adopt some of these well-established practices and incorporate them in a whole-catchment management strategy. Key words Land degradation, environmental degradation, pollution, environmental assessment, common property resources, communal land uses, sustainable resources management, sustainability indicators, soil erodibility, soil erosivity / AFRIKAANSE OPSOMMING: Wanneer grond sy intrinsieke waarde verloor of 'n afname in sy vermoë toon, kan gesê word dat die grond gedegradeer is. Gronddegradasie manifesteer in verskeie vorme, soos ontbossing, gronderosie, grond, lug en water besoedeling. Gronddegradasie het binne die konteks van volhoubare ontwikkeling wêreldwyd van besondere belang geword. Nou, meer as ooit vantevore, is dit noodsaaklik om empiriese studies uit te voer aangaande die aard en omvang van gronddegradasie, en om vorendag te kom met toepaslike reaksies tot die probleem. Gemeenskaps natuurlike hulpbron bestuur praktyke is algemeen in die ontwikkelende wêreld. Daar word dikwels veronderstel dat uitbuiting van gemeenskaplike eiendoms hulpbronne deur die gemeenskap, soos woude, weivelde, waterbronne en wild, onvermeidelik lei na gronddegradasie. Hierdie aanname het ontwikkel as gevolg van die oortuiging dat die mensdom daarna sal streef om maksimum voordeel te trek uit gemeenskaplike hulpbronne, sonder om enige koste aan te gaan ten opsigte van die bewaring daarvan. Hierdie studie behels 'n omgewings evaluering van die impakte van gemeenskaps grondgebruik sisteme en gemeenskaplike eiendoms hulpbron bestuur praktyke in die Mhondoro gemeenskaplike grond van Zimbabwe. Die area word al vir meer as 'n eeu deur mense bewoon, en word beskou as 'n tipiese voorbeeld van 'n gevestigde gemeenskaps grondbestuur sisteem. Verskeie metodes is toegepas met die evaluering, en sluit in: 'n vraelys opname; onderhoude met sleutel segspersone; grond en plantegroei opnames en veldopnames; boom digtheidstelling in afgebakende persele; berekening van bevolkingsen veedigtheid vir die studiegebied; opstelling van 'n omgewing evaluerings matriks en 'n gemeenskap projek volhoubaarheids indeks kontroleerlys; en 'n analise van geo-referenced time-lapse lugfoto's wat strek oor 'n tydperk van 15 jaar (1982-1997). Daar is vasgestel dat ernstige gronddegradasie voorkom in Hoofman Mashayamombe se wyk in Mhondoro. Degradasie word gemanifesteer in die vorm van gronderosie en stroom sedimentasie, uitputting van woude, weiveld degradasie en die verwoesting van wild habitatte. Gemeenskaps grondgebruik en natuurlike hulpbron bestuurspraktyke is net gedeeltelik verantwoordelik vir die stand van sake. Gronderosie vind plaas ook as gevolg van die sensitiewe aard van die sanderige grond van die hoogland, die sodic grond van die vlei areas, in kombinasie met redelike hoë reënval (gemiddeld 750mm per jaar). Reënval intensiteit in die area is geneig om hoog te wees, en erosie vind plaas wanneer reën val op die hoogs erodeerbare grond wat met yl plantegroei bedek is. Die grond verkeer onder geweldige druk as gevolg van oorbenutting; 'n bevolkingsdigtheid van 93 mense per km2 en veedigtheid van 110beeste per km2 is aangeteken. Die grond beskikbaar vir vestiging van gemeenskappe word in omvang beperk. Die vervanging van grondvoedingstowwe in bewerkte grond hou nie tred met die agteruitgang in die kondisie van die grond nie, as gevolg van die algemene armoede van die gemeenskapsboere. Inwoners van die gemeenskapsarea , teenstrydig met algemene wanopvattings, toon besorgdheid ten opsigte van omgewingsbewaring deur die grond braak te lê, donga herwinnings pogings, wei velds planne, bewaring van woude en praktyke ten opsigte van die groei van bome. Remediërende en/of versagtende maatstawwe vir die herstel van die omgewing kan van hierdie gevestigde praktyke inkorporeer in 'n bestuursstrategie wat die hele opvangsgebied insluit. Sleutelwoorde Gronddegradasi e, omgewingsde gradasi e, besoedeling, omgewingsassessering, gemeenskaplike eiendoms hulpbronne, gemeenskaplike grondgebruik, volhoubare hulpbron bestuur, volhoubaarheids aanwysers, grond erodeerbaarheid, grond verwering.
418

The influence of Acacia Mearnsii invasion on soil properties in the Kouga Mountains, Eastern Cape, South Africa

Van der Waal, Benjamin Wentsel January 2010 (has links)
The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes
419

Modélisation multi-échelle et simulation numérique de l’érosion des sols de la parcelle au bassin versant / Multiscale modelling and numerical simulation of soil erosion by water from the plot scale to the catchment scale

Le, Minh Hoang 26 November 2012 (has links)
L’objectif global de ce travail est d’étudier une modélisation multi échelle et de développer une méthode adaptée pour la simulation numérique du processus d’érosion à l’échelle du bassin versant. Après avoir passé en revue les différents modèles existants, nous dérivons une solution analytique non triviale pour le système couplé modélisant le transport de sédiments par charriage. Ensuite, nous étudions l’hyperbolicité de ce système avec diverses lois de sédimentation proposées dans la littérature. Concernant le schéma numérique, nous présentons le domaine de validité de la méthode de splitting, pour les équations modélisant l’écoulement et celle décrivant l’évolution du fond. Pour la modélisation du transport en suspension à l’échelle de la parcelle, nous présentons un système d’équations couplant les mécanismes d’infiltration, de ruissellement et le transport de plusieurs classes de sédiments. L’implémentation et des tests de validation d’un schéma d’ordre élevé et de volumes finis bien équilibré sont également présentés. Ensuite, nous discutons sur l’application et la calibration du modèle avec des données expérimentales sur dix parcelles au Niger. Dans le but d’aboutir la simulation à l’échelle du bassin versant, nous développons une modélisation multi échelle dans laquelle nous intégrons le taux d’inondation dans les équations d’évolution afin de prendre en compte l’effet à petite échelle de la microtopographie. Au niveau numérique, nous étudions deux schémas bien équilibrés : le schéma de Roe basé sur un chemin conservatif, et le schéma avec reconstruction hydrostatique généralisée. Enfin, nous présentons une première application du modèle avec les données expérimentales du bassin versant de Ganspoel qui nécessite la parallélisation du code. / The overall objective of this thesis is to study a multiscale modelling and to develop a suitable method for the numerical simulation of soil erosion on catchment scale. After reviewing the various existing models, we derive an analytical solution for the non-trivial coupled system modelling the bedload transport. Next, we study the hyperbolicity of the system with different sedimentation laws found in the literature. Relating to the numerical method, we present the validity domain of the time splitting method, consisting in solving separately the Shallow-Water system (modelling the flow routing) during a first time step for a fixed bed and updating afterward the topography on a second step using the Exner equation. On the modelling of transport in suspension at the plot scale, we present a system coupling the mechanisms of infiltration, runoff and transport of several classes of sediment. Numerical implementation and validation tests of a high order wellbalanced finite volume scheme are also presented. Then, we discuss on the model application and calibration using experimental data on ten 1 m2 plots of crusted soil in Niger. In order to achieve the simulation at the catchment scale, we develop a multiscale modelling in which we integrate the inundation ratio in the evolution equations to take into account the small-scale effect of the microtopography. On the numerical method, we study two well-balanced schemes : the first one is the Roe scheme based on a path conservative, and the second one is the scheme using a generalized hydrostatic reconstruction. Finally, we present a first model application with experimental data of the Ganspoel catchment where the parallel computing is also motived.
420

Role of Composition, Structure and Physico-Chemical Environment on Stabilisation of Kuttanad Soil

Suganya, K January 2013 (has links) (PDF)
Soft soil deposits of coastal regions and lowland areas pose many geotechnical problems but it is indispensable to utilize these grounds to meet the growing demand for infrastructure with ever increasing urbanization and industrial development. Soft soils are generally associated with high compressibility and low strength characteristics which augment the risk of huge settlements and foundation failure. It is essential to understand the complex behaviour of the ground consisting of soft clays as construction and maintenance of infrastructure in these areas is challenging. Marine sediments mostly possess open microstructure irrespective of the differences in their mineral composition and sedimentation environment. Also this particular microstructure in marine sediments is generally accompanied by the presence of a great amount of organic residues and fragments of marine organisms. Formation of pyrite is also possible because of the presence of decomposable organic matter, dissolved sulfate and reactive iron minerals. These soils due to their inherent mineralogy and microstructure have high void ratios and consequently high water holding capacity which explains the reason for their low shear strength and high compressibility characteristics. And often the formation environment is conducive for incorporation of organic content in the soft clay deposits which further aggravates the problem. A complete characterization of the soil can enhance the understanding of soil behavior and therefore can play a crucial role in suggesting suitable and sustainable ground improvement method. Soft clay deposits of Kuttanad area in Kerala, India extending to varying depths below the ground level, present a challenge as a foundation soil due to low bearing capacity and high settlement. Geologically Kuttanad is considered as a recent sedimentary formation. In the geological past, the entire area was a part of the Arabian Sea. Presently Kuttanad area covers an area of about 1,100 km2. Many intriguing reports of distresses to structures founded on this soil are available. An over view of specific characteristics of soft clays along with the comprehensive description of soft clays from various parts of the world is presented in the introductory Chapter. Deep soil mixing and mass stabilization methods are found to be relatively advantageous in reducing differential settlements and in achieving expeditious construction. A more detailed review of literature on Kuttanad soil problems and various ground improvement methods adopted are presented. The different ground improvement techniques attempted are soil reinforcement, stone columns, preloading etc. Soil mixing can be relatively advantageous over the other conventional ground improvement methods. Laboratory studies carried out earlier with different binders such as cement, lime and lime fly ash combinations did not exhibit appreciable improvement in soil strength. It is reasoned that the lack of understanding of the soil characteristics is responsible for the limited success of these attempts. Based on the review of literature the detailed scope of the work is presented at the end of Chapter 1. The method of collection of the soil from Kuttanad region, methods adopted for characterization of soil, characteristics of various binders used and testing procedures adopted for assessing the geotechnical behavior with and without binders are described in Chapter 2. In order to characterize the soil for understanding its behaviour under different conditions as well as to gauge its response to different stabilizers, a detailed physico¬chemical, mineralogical, morphological and fabric studies are carried out and presented in Chapter 3. An attempt has been made to explain the role of components of soils such as organic substances, pyrite and sesquioxides for variations in its properties with change in water content. The high water holding capacity of the soil reflected in its Liquid limit along with relatively low plasticity characteristics of the soil has been explained as due to the presence of minerals such as metahalloysite and gibbsite, the flocculated fabric, porous organic matter and water filled diatom frustules (amorphous silica). Based on the study conducted on the plasticity characteristics of Kuttanad soil under different conditions of drying and treatment, it was brought about that the organic content plays a dominant role in particle cementation and aggregation causing a substantial reduction in plasticity upon drying. Further, the presence of minerals such as pyrite and iron oxides also account for the plasticity changes. The significant changes in soil properties upon drying have also been successfully explained in Chapter 4. Attempts made to stabilize the soil using conventional chemical stabilizers are described in Chapter 5. The effect of binders on the strength improvement of soil has been explained based on the changes occurring in the composition, fabric and physico-chemical characteristics of soil upon addition of the binders. Lack of strength development in soil with lime has been attributed to the inherent composition of the soil hindering the formation of pozzolanic compounds and unfavourable modification of the fabric. On the other hand the soil responded well to cement stabilisation. The influence of various parameters such as Water/Cement (W/C) ratio, Initial water content, curing period and additive dosage on the strength development of cement treated soil has been examined. Cement improved the strength of the soil by binding the soil particles without depending on the interaction with the soil. It was observed that the role of initial water content is insignificant and the strength improved with reducing W/C ratio. The dependence of strength development with cement addition on the fabric at different W/C ratios has been assessed. Also the role of other additives such as Lime, Sand, Fly Ash, Ground granulated blast furnace slag, Silica fume and Sodium silicate to enhance the strength of cement treated soil has been analysed in Chapter 5. It was shown that only Sodium Silicate (NS) along with cement meets with good success. The studies on the undrained shear strength and compressibility characteristics of cemented soil carried out to understand the strength and deformation behaviour of the cemented soil are presented in Chapter 6. It is clear from the compressibility characteristics of the cemented soil that there is a well defined yield stress demarcating the least compressible pre-yield zone and more compressible post yield zone. Generally the yield stress increases with reducing water cement ratio. It is interesting to note that the post yield compressibility of the cemented soil is controlled more by the fabric of soil than by cementation effect. The study on the undrained shear behavior of cemented soil revealed that the cohesion intercept and angle of internal friction increases with addition of cement. However the impact of cementation is reflected more as increase in cohesion intercept with increasing cement content. The uniqueness of failure envelope observed for the cemented soil irrespective of whether the confining stress is above or below the yield stress has been explained in detail. A case study on the performance of embankment founded on Kuttand soil improved with Deep mixed cement columns (DMCC) has been evaluated through numerical simulations using FLAC 2D and this forms the subject matter of Chapter 7. For this work the soil properties of the Kuttanad soil determined by experimental investigations have been used. The simulation results showed that the introduction of DMCC columns improved the factor of safety against failure and reduced settlements. This study clearly endorses the analysis and the results of the test carried out on Kuttanad soil. The final chapter summarizes the details of the work carried out which brings out the importance of characterization of the soil in terms of soil components, physico-chemical environment as well as the micro structure of the soil in predicting the behaviour of the soil in changing environment and to understand the stabilization response of the soil with different binders which intern helps to select appropriate binder and or binder combinations.

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