Soil erosion is a persistent problem that requires continued control efforts as agricultural land loses productivity and communities dependent on the land become increasingly vulnerable to decreased food security. The negative effects of soil erosion in Khamopele River catchment, in the Mount Fletcher southern Drakensberg region of South Africa, are manifest in extensive gullying and wetland loss. Soil erosion has resulted in siltation in a recently constructed dam and the alteration of aquatic habitats. This research was undertaken to identify the sources of eroded sediment in the small upper catchments of the Mzimvubu River catchment to inform broader catchment management strategies. The scale of erosion was quantified using field surveys of gully extent and form. Environmental magnetic tracing techniques were used to determine the sources of eroded sediment in Khamopele River and upper Tina River catchments. The radionuclide ¹³⁷Cs was used to determine soil loss over a 55 year period in Khamopele River catchment. The Landscape Connectivity framework was used to describe the sediment source, pathway and sink interactions at sample area level. Results indicated that historical and contemporary land management practices such as uncontrolled grazing, grassland burning and furrows promoted soil erosion in the catchment. Soil erosion was most pronounced in the Taung sample area where there was extensive gullying, tunnelling and subsurface erosion. Environmental magnetic tracing results indicated that there were clear differences in source areas. Despite its prevalence in the area, gully erosion was not shown to be a major source of sediment to downstream sinks. Topsoil and hillslope derived sediment were shown to be mobile in the catchment, suggesting that sheet erosion processes were dominant in the catchment. Radionuclide tracing studies showed that at least 20 cm of soil had been eroded from the Khamopele River catchment surface since 1956. This research has shown that it is possible to distinguish source areas of erosion in the catchment by matching catchment mineral magnetic signatures to those in sink areas. This means that rehabilitation projects can use resources efficiently as the areas needing the most attention can be identified.

[Portion of abstract]: Sediment dynamics are influenced by transformed landscape connectivity in catchments worldwide. The upper Thina catchment, an important high rainfall resource in the northern Eastern Cape, South Africa, is an example of where ongoing subsistence farming on communal land has led to overgrazing and trampling that has initiated large erosive features (e.g. gullies) and river incision. The formation of gullies led to increased hillslope-channel connectivity and the resultant river incision decreased the channel-valley fill connectivity. These two changes in connectivity led to increased sediment export from the catchment that has various down-stream ecological and socio-economic impacts. This study investigates how the change in hillslope-channel and channel-valley fill connectivity has altered the sediment dynamics in the Vuvu catchment, a headwater tributary of the Thina River. A combination of methods were used to assess the changes in hillslope-channel and channel-valley fill connectivity. High resolution aerial images were used to map source features, such as fields, gullies, sheet erosion, landslides, roads and livestock tracks. Topographic and geological characteristics of the source features were extracted using a Geographic Information System. Furthermore, hillslope-channel pathways, such as the natural drainage network, continuous gullies, discontinuous gullies, roads and livestock tracks were mapped and analysed in terms of topographic and geological characteristics. Historic aerial images were assessed to calculate the date the larger gullies began forming. Recent aerial photos and cross sectional surveys of the valley fill were combined to map the various sediment sinks. Particle size and organic content were analysed for flood bench cores and terrace samples. The chronology of the flood benches was determined using unsupported Pb-210 and Cs-137 dating, and determined for the terraces using Optically Stimulated Luminescence dating. Quantitative and qualitative sediment tracing approaches, using mineral magnetic properties, were used to trace the origin of suspended sediment (collected during flood events), sediment stored in the flood benches and sediment stored in the terraces. Hydrological monitoring was used to assess the potential to store sediment on flood benches along the valley fill through flood bench inundation frequency. Hydrological and hydraulic modelling extended the measured inundation frequencies to a 73 year period and other cross sections along the valley fill. Furthermore, a future scenario of an increased vegetation cover and reduced hillslope-channel connectivity was assessed in terms of channel-valley fill inundation frequency.

Most soil particles loses cohesion and split up the soil mass into individual soil grains when they come in contact with water and get saturated. In dispersive soils the particles detach more spontaneously from each other and go into suspension even in quiet water. Thus the phenomenon of dispersion is common to most soils, the degree varying from soil to soil. Dispersive soils are abundantly found in various parts of the world such as Thailand, United States, Australia, Mexico, Brazil, South Africa and Vietnam. Several geotechnical failures such as piping due to internal erosion, erosion and gullying in relatively flat areas, collapse of sidewalls and topsoil removal have been reported worldwide due to the construction in dispersive soil. Failures as reported could be prevented if such soils are identified before-hand or if the quantification of dispersivity in the soil is done accurately. There are several methods of measuring dispersivity in soils which include several physical tests, chemical tests and some common laboratory tests. It is reported in literature that no method could be completely relied upon to identify dispersive soils with absolute confidence. In addition, when these methods were studied in detail, several flaws surfaced needing a better estimation of dispersivity. In order to develop a new method of estimation of dispersivity, the mechanism of dispersion in soils was studied in depth, which revealed that the existing concepts regarding dispersivity are incomplete in many aspects. An exhaustive philosophy of dispersion which addresses every detail is non-existing. To solve these problems, the concept of dispersivity was investigated in detail. It was found out that the observed dispersivity is a result of repulsion in the soil overcoming the attractive force. Thus a list of factors that could possibly affect the repulsion and attraction (and hence the dispersivity) in soils were found out. Even though literature focuses on exchangeable sodium as the principal reason for dispersivity, from fundamental theoretical considerations several other factors such as Cation exchange capacity (CEC), pH, structure of the soil, electrolyte concentration in the pore fluid, presence of organic matter, clay minerals involved in the soil and dissolved salts in the soil could possibly have an influence on dispersivity. Several studies have reported soils of high dispersivity to possess a high pH, high CEC, high amounts of sodium. The influence of these factors on dispersivity of other soils (or generally in any soil) is not well explored. Research on understanding their mechanism of action led to the conclusion that these parameters could be generalized for any soil. Through the analysis of these parameters, it was found that the fundamental parameter governing the dispersivity of soils is the number of charges on clay particles and that the repulsion in the soils is mainly contributed by the electrostatic repulsion. The attractive force in a soil/clay mass is primarily contributed by the van der Waal’s attraction and dispersion occurs when the electrostatic repulsion (resulting due to permanent and pH dependent charges) dominates over the van der Waal’s attraction. A practical estimation of charge with least effort could be possibly carried out through the measurement of zeta potential of soils. In order to verify whether the effect of all the factors is completely and sufficiently reflected in the zeta potential values, experiments were conducted on various soils. Three soils namely Suddha soil (a locally available dispersive soil), Black cotton soil and Red soil were selected for the study. These soils were chosen as the soil samples as they could display wide ranges of dispersivity values. In order to perform dispersivity tests, soil fraction finer than 75µ (75 micron meter sieve size) was fixed as the sample size as dispersivity pertaining to the finer fractions play a greater role than that of the coarser particles. All the three soil samples were treated with sodium hydroxide and urea solutions to alter the dispersivity so that the influence of all parameters could be studied. The dispersivity of the treated and untreated soils was found out through the various conventional tests and it was found that there exists a good correlation between the dispersivity and the zeta potential of soils. It was also observed that the increase in the dispersivity is higher when treated with salts of monovalent cations. Increase in the organic content also increased zeta potential, but not as significantly. One of the popularized theories on colloidal dispersions is the classical DLVO theory which has formulated the total interaction energy of colloidal particles by estimating the electrostatic repulsion and van der Waal’s attraction energy between two particles. The total interaction energy is then expressed as the difference between them. A similar approach as taken by the DLVO is adopted in this study. The total attractive energy existing in a soil mass is mathematically derived from the expression for van der Waal’s energy between two particles and the total repulsive energy from the zeta potential values. Two different approaches namely an infinitesimal particle approach and a finite particle approach is taken for finding the energy in a soil mass. In the infinitesimal particle approach, a clay particle is assumed to be infinitely small such that any soil particle of a finite radius could be conceived to be formed by a combination of infinite number of these infinitesimal particles. With this setting, the total energy in a soil mass is computed without really bothering about what exact particles constitute the mass. The increase in energy due to the increase in radius is then integrated to obtain the final expression. The dispersivity of the soil is then estimated under defined physical conditions of the soil. In the finite particle approach, each particle is considered to be of finite radius and to estimate the total energy, the total number of particle ombinations is then taken and the total energy is expressed as a sum of all the possible combinations. The dispersivity of a soil in both approaches is expressed as a release of energy when the repulsion rules over the attraction. In order to validate the derived propositions and expressions, experiments were conducted again on soils. The soils were treated with hydroxide salt of monovalent cations such as lithium, sodium and potassium. The dispersivity of the various treated and untreated soils was measured with the conventional methods and with the derived expressions of dispersivity through zeta potential. The similarity in the trend of the dispersivity values confirmed the validity of the derived expression. It was also concluded that the infinitesimal particle approach could be adopted when information about the physical properties are available and when they are not, the finite approach could be used. An accurate determination of zeta potential is critical for representation of dispersivity with zeta potential. Thus the procedure for measurement of zeta potential was standardized. The standardization was primarily focused on establishing the ideal conditions for zeta potential measurement. The role of Brownian motion, in electrophoretic mobility measurements were studied by employing the usage of zeta deviations. Untreated, potassium hydroxide treated, sodium hydroxide treated and lithium hydroxide treated samples of Suddha soil, Black Cotton soil and Red soil (finer than 75µ) were used for the study. Zeta potential measurements on unfiltered soil water suspensions, suspensions passing 2.5µ and suspensions passing 0.45µ were conducted along with recording their zeta deviations. It was observed that soil suspensions finer than 0.45µ show acceptable values of zeta deviations and thus could be used as a standard procedure for estimating zeta potentials. It was also concluded that the presence of Brownian motion makes the assessment of zeta potential through electrophoretic measurements easier and accurate. In an alternate perspective it as deduced that the amount of total monovalent ion concentration in the soil (dissolved and adsorbed) could adequately serves as an ideal parameter that could be used to quantify dispersion in soils. In order to verify the speculation, the variation of repulsive pressure with monovalent cation concentration was studied for the above mentioned treated and untreated soils. Within the monovalent cations, the role of ionic size in repulsion along with physical factors was also studied with the help of Atterberg limits, compaction characteristics, and dispersivity measurements. It could be concluded that even though there are several chemical factors such as CEC, pH, electrolyte concentration, type of clay minerals, dissolved salts etc. and physical factors such as plasticity, water holding capacity, density and structure which influence dispersion in soils, these factors affect either directly forces between the particles or the surface charge of clays which again affect the forces. The two phenomena can be combined through the hydration behaviour of the adsorbed cations on the clay surface in view of dispersivity. It is that force due to hydration which acts as the principal reason to separate the clay particles apart. As the radius of the inner hydration shell is higher for monovalent cations than those of higher valency ions, more force would be offered by the monovalent ions. Higher the charge and higher is the number of monovalent cations, higher will be the repulsion and thus the dispersivity. The repulsive force offered by the monovalent cations in soil was calculated through osmotic pressure differences and the dispersivity was expressed as the release of energy as earlier. In order to validate the proposal, the dispersivity of the samples as measured with the conventional methods was compared and studied with the derived expression. The similarity in the trend of the dispersity values confirmed the validity of the derived expressions. Thus, it can be seen that there are primarily two different methods of quantifying dispersivity of soils. When one method estimates dispersivity by calculating the electrostatic repulsion through zeta potential, the other method gives a dispersivity value based on the repulsive pressure offered by the monovalent cations in the soil. Two methods could be regarded as two different measurements of the electrical double layer. Any method could be used based on the property that could be easily quantified. The applicability of the new approaches – calculation of monovalent cations and zeta potential- for estimating the dispersivity in soils through a complete development of philosophy of dispersion and is presented, in this thesis, in nine chapters as follows: In Chapter 1 the background of the study and review of literature connected with the present study is presented. The mechanism of dispersion and the geotechnical problems associated with dispersion is elaborately presented in this section. As the dispersive soils cannot be identified through conventional tests, a description about the various tests designed to identify dispersive soils is presented. Earlier works relevant to the topic and the shortcomings of those studies are discussed. Finally, the objectives of the current research along with the scope of the work are explained in the concluding part of this chapter. Various factors that could have influence on the dispersivity of soils and their mechanism of action are presented in Chapter 2. The relationship of the factors with zeta potential is discussed. Theories dealing with dispersivity, conventional methods of measurement, role of geotechnical characteristics in assessing dispersivity are being presented. Chapter 3 deals with the various materials and methods used for the study. A locally available dispersive soil called Suddha soil along with Black Cotton soil and Red soil were chosen as the soils for the study of dispersion. The basic material properties and testing programs adopted for the study are presented in this chapter. The codal procedures followed to determine the physical, chemical, index and engineering properties are described in detail. The experimental investigations carried to bring out the role of zeta potential in dispersivity of soils are described in Chapter 4. Detailed analysis of the results showed estimation of zeta potential is possible and can sufficient quantify dispersivity of soils. The formulation of the equation for estimating dispersivity from zeta potential is described in Chapter 5. The estimation dispersivity based on attraction and repulsion energies in a soil mass is presented here. The adoption of the approach and methodologies used based on classical DLVO theory for the current work is explained in detail. The values of dispersivity obtained from the derived equation are compared with those obtained from the conventional tests. The validity of the expression is confirmed with the results of the experiments. Chapter 6 deals with the standardization of the measurement procedure of zeta potential. Role of Brownian motion in the accurate measurement of electrophoretic mobilities are brought out here. Chapter 7 brings out an alternate perspective of quantifying dispersivity through monovalent cations. The role of monovalent cations and the mechanism in which they contribute to the repulsive pressures (hence the dispersivity) are discussed. Experimental research design adopted has brought that the effect of monovalent and ionic size on repulsive pressures leading to dispersivity is described. The results of the experiments added with the inferences drawn are explained at the end. The estimation of repulsive pressures for measuring dispersivity from monovalent cations is discussed in Chapter 8. The dispersivity of a soil mass is derived from monovalent ion concentration and experiments were carried out for verification purposes. The experimental investigation procedure adopted followed by the results are presented in this chapter. It was observed that a good co-relation exists with the dispersivity obtained from the monovalent ion concentration and that obtained from conventional methods. Chapter 9 compares the dispersivity obtained through the various methods proposed in this thesis. The comparison is made in light of the classical electrical double layer theory. The major conclusions of the study are brought out at the end of this chapter.

The vadose zone is the unsaturated zone between the ground surface and water table. This zone is of much importance as it acts as a link between surface water and ground water. Knowledge of soil moisture in this zone is very much essential to understand the meteorologic, hydrologic and agronomic process. Flow and transport in the unsaturated zone are more complex compared to saturated medium, as the pores in unsaturated zone are partly filled by air and partly by water. Most of vadose zone studies are done on agricultural plots where anthropogenic activities govern the vadose zone flows. Vadose zone studies in natural pristine conditions such as in forested areas where no anthropogenic activities are present are very limited that too in Indian conditions are rare. The present research work deals with understanding of the flow behavior in the vadose zone in a small experimental forested watershed called Mule Hole. Mule Hole watershed is 4.5 km2 and located in Bandipur National Park in Chamrajnagar District of Karnataka state, in the southern part of India. The forest is of deciduous type with 3 to 4 months of leafless dry period. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The rainfall pattern is bimodal i.e. it receives rainfall during South West Monsoon (June -September) and North East Monsoon (October – December) with dominant rainfall occurring during South West Monsoon. Human activity is minimal as watershed is a part of Bandipur National Park, dedicated to wildlife and biodiversity preservation. The watershed consists of around 80 % of red soils, and black soil and saprolite covering the rest. The first part of the study involves soil moisture measurements by neutron probe and electrical resistivity measurements by geophysical method and their linking, i.e. developing volumetric soil moisture vs electrical resistivity relationship. The second part of the study involves application of neutron probe soil moisture measurement in identifying relationship between soil and erosion in the watershed. The third part involves development of two dimensional (2D) vadose zone model for watershed and validating it with measured data. The last part involves development of three dimensional model of watershed and validating it with observed data. Vadose zone is briefly described in chapter 1 along with its governing equations. Different soil moisture measurement techniques including invasive and non – invasive ones are also discussed. Different vadose zone modeling software which are public domain as well as commercial ones are also discussed. The chapter ends with organization of this thesis. Chapter 2 reviews relevant literature related to this study with focus on soil moisture measurement techniques and vadose zone flow modeling. Different soil moisture measurement techniques, their applications and limitations are reviewed. In the soil moisture measurement techniques, invasive and non – invasive types are reviewed. In the modeling part, different vadose zone models for 2D and 3D flow along with its applications and limitations are reviewed. Also a brief review about application of HYDRUS 2D/3D model is done which is used for the vadose zone modeling in this thesis. Chapter 3 introduces study area Mule Hole watershed, which is a forested watershed located in Bandipur National Park, Karnataka. India. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The watershed has average regolith thickness or vadose zone of 17 m with roots of the trees able to penetrate up to groundwater. A toposequence T1 is identified in the watershed which has red soil – black soil confluence where soil moisture measurements and electrical resistivity measurements are carried out. The toposequence consists of 8 layers with organic layer forming the top layer followed by 3 red soil layer with 2 black soil layers intruding from stream into red soil layers and sandy weathered horizon at base of red and black soil. Also a sandy horizon at the top of black soil. Soil moisture measurements with neutron probe and electrical resistivity measurements with electrical logging tool which are done on toposequence periodically for two years are explained and the data are presented in this chapter. These data are used for validation of vadose zone models. Chapter 4 discusses in detail about comparison of electrical resistivity by geophysical method and neutron probe logging for soil moisture monitoring in a forested watershed. The electrical resistivity data and soil moisture data are compared for different soils and existence of relationship between them are studied and discussed in this chapter. For the red soil, existence of relationship between volumetric soil moisture content and electrical resistivity is found. Chapter 5 discusses soil moisture measurements as a tool to study erosion processes in forested watershed. Hydrodynamic behavior of the red soil – black soil system at toposequence T1 is studied using neutron probe soil moisture measurements. Two distinctive types of erosional landforms have been identified at T1 viz, rotational slips (Type 1); seepage erosion (Type 2),which are highlighted by neutron probe soil moisture measurements. Based on the observations relative chronology of formulation of different soil horizons are studied, which guided in developing four-stage model showing the relative chronology in the recent formation of the soil cover at downslope. Chapter 6 discusses application of 2D vadose zone modeling using HYDRUS – 2D model at two experimental sites in forested watershed where soil moisture monitoring and groundwater monitoring have been conducted. At the first site, which is toposequence T1 in the forested watershed, where soil moisture measurements are done, three case studies for comparison of daily scale data with hourly scale data and effects of internal layering by clubbing red soil layers and black soil layers to equivalent red soil and black soil layers respectively are performed. The model is run for two years. In that, first year results are used for calibrating the model where measured soil moisture content data are used to get soil hydraulic parameters for all the three cases by inverse modeling using Marquardt – Levenberg algorithm which is a part of HYDRUS 2D. The parameters thus obtained fall under particular soil range and performed efficiently in predicting soil moisture content. The second year results of model run is used for validation of the model in all the three cases where simulated soil moisture content is compared with measured soil moisture content. It is found that model is performing well and match between measured and simulated soil moisture contents is good in all the three cases. It can be said that having hourly scale data with detailed layering information is always advantageous in modeling soil moisture content. But, in absence of hourly scale data or finer scale data and absence of detailed layering information, the soil moisture model can also perform well. The scale of data and detailed layering information has minimal effect on soil moisture modeling. At the second site ERT profile near the watershed outlet has five monitoring wells are available and all layering information regarding regolith and hard rock layer distribution profiles. The soil hydraulic parameters obtained at toposequence T1 for soil and sandy weathered horizon are used and tested at this site to simulate the groundwater levels. The parameter for rock layer is estimated by testing different hydraulic parameters from HYDRUS database. The results are validated using observed groundwater levels at the site. The results show significant match between observed and simulated groundwater levels. Chapter 7 discusses 3D modeling of Mule Hole forested watershed using HYDRUS – 3D model. A three layer model of Mule Hole along with its topographic details is modeled. The layering information is derived from geophysical study done at 12 Electrical Resistivity Tomography (ERT) profiles distributed in the watershed. The three layers considered are top soil layer followed by sandy weathered layer and bottom rock layer. Anisotropy in hydraulic conductivity, root water uptake and sloping water table are introduced to make the model more realistic. Soil hydraulic parameters obtained during 2D vadose zone modeling of toposequence T1 are used initially for soil and sandy weathered layers and are subsequently tuned to make model more efficient. Different scenarios are considered to test flux as well as constant head boundary conditions and effect of different porosities for rock layer. The model is run for 7 years and model simulations are validated with observed groundwater levels from monitoring wells across the watershed. The result shows good fit between simulated and observed groundwater levels especially for monitoring well which has shallow groundwater level. It is found that porosity in the rock layer is not uniform and there exist different porosities for the rock layer across the watershed. Also the distribution of sandy weathered zone requires improvement. The model is also able to predict ET closer to ET predicted by COMFORT model which was developed earlier. Also the model shows rise in groundwater fluxes as groundwater starts replenishing. Over all, the 3D model of Mule Hole watershed in HYDRUS – 3D worked well with satisfactory results and HYDRUS – 3D can be used for modeling small forested watersheds. Chapter 8 concludes the study and discusses the further scope of the work.

La rupture des barrages et des digues en terre est susceptible d’avoir des conséquences importantes en aval et dans les zones protégées. Nous avons mené une analyse hydro-mécanique de la formation et du développement de brèche destinée à améliorer la précision des approches actuelles. Dans le cas de l’érosion interne, un modèle d’agrandissement de conduit a été proposé pour modéliser la rupture des digues et barrages en terre par écoulement concentré. Ce modèle tient compte de l’érosion du sol par un écoulement de conduit turbulent. En ce qui concerne l’élargissement de la brèche, un modèle simple d’estimation de la longueur critique d’afouillement par “headcut” est proposé, fonction de la résistance du sol à la traction. Ce modèle est en bon accord avec les résultats numériques obtenus par équilibre limite. Un modèle simplifé pour la contrainte latérale sur les parois de la brèche a ensuite été proposé. Ce modèle tient compte des écoulements secondaires. Il montre que la contrainte latérale peut être plus grande que la contrainte de fond, suivant la situation. Finalement, une expérimentation de grande dimension de rupture de barrage par erosion de conduit a été modélisée avec le modèle d’érosion de conduit proposé, et quelques composantes des modèles d’élargissement de brèche proposés. L’élargissement de la brèche par paliers a été reproduite au début du processus. Les perspectives de validation et d'application des modèles proposés sont discutées. / The failure of embankment dams and levees can have serious consequence in floodplains. Hydro-mechanical analyses of the breach processes were conducted to develop the accurate estimation of the failure of embankment dams and levees. Considering the internal erosion process, a pipe enlargement model was proposed to simulate the failure of embankment dams and levees by concentrated leak erosion. In this model, the turbulent pipe flow with erosion mechanism was employed as well as the soil erosion law. Considering the breach enlargement process, a simple headcut migration model based on the soil tensile strength was presented to simulate the critical length of the headcut. Good agreements were obtained by comparing with the limit equilibrium numerical model. A simple model was eventually proposed to simulate the lateral shear stress on the breach sides, accounting for the secondary flow. The lateral shear stress can be greater than the bottom shear stress, depending on the situation. . Finally, a large-scale test of dam failure was simulated by using the pipe enlargement and some components of the breach widening models proposed. The simulation of the pipe enlargement process had good agreement with the measured data. Both of the pipe diameter and the discharge flow were well simulated. The stepwise enlargement of the breach width was also well simulated at the beginning of the breach widening process. Validation and application prospects of the proposed models are discussed.

This dissertation is focused to modeling of the rainfall in laboratory conditions by the rainfall simulator invented in VUT Brno. Results of the measuring are compared with measured values of the original rainfall simulator located in VVU VSH VUT in Brno by the Kninicky village in 1976-1980. Dissertation verifies rightness of substituting the natural rain with the rainfall simulator on bare soil in the original location, kinetic energy of the rain drops is substituted with the energy gained from the weight of the drops - the flow. Generally the dissertation determines the possibilities of the rainfall simulator's current location.

Below vegetation, throughfall kinetic energy (TKE) is an important factor to express the potential of rainfall to detach soil particles and thus for predicting soil erosion rates. TKE is affected by many biotic (e.g. tree height, leaf area index) and abiotic (e.g. throughfall amount) factors because of changes in rain drop size and velocity. However, studies modelling TKE with a high number of those factors are lacking. This study presents a new approach to model TKE. We used 20 biotic and abiotic factors to evaluate thresholds of those factors that can mitigate TKE and thus decrease soil erosion. Using these thresholds, an optimal set of biotic and abiotic factors was identified to minimize TKE. The model approach combined recursive feature elimination, random forest (RF) variable importance and classification and regression trees (CARTs). TKE was determined using 1405 splash cup measurements during five rainfall events in a subtropical Chinese tree plantation with five-year-old trees in 2013. Our results showed that leaf area, tree height, leaf area index and crown area are the most prominent vegetation traits to model TKE. To reduce TKE, the optimal set of biotic and abiotic factors was a leaf area lower than 6700mm2, a tree height lower than 290 cm combined with a crown base height lower than 60 cm, a leaf area index smaller than 1, more than 47 branches per tree and using single tree species neighbourhoods. Rainfall characteristics, such as amount and duration, further classified high or low TKE. These findings are important for the establishment of forest plantations that aim to minimize soil erosion in young succession stages using TKE modelling.

In der vorliegenden Arbeit wurden Doppelringinfiltrationsexperimente an teilweise gefro­renen Böden durchgeführt. Diese Experimente wurden anschließend mit den zwei computer­ge­stützten Modellen, Erosion 3D / Winter und COUP, nachgestellt, um die Frage zu beantworten, ob es möglich ist, die Infiltration in teilweise gefrorene Böden vorherzusagen. Die Doppelringinfiltrationsexperimente wurden auf einem ackerbaulich genutzten Lehm­boden mit geringer Lagerungsdichte und Bodenfeuchten im Bereich der Feld­kapa­zität, an der nördlichen Grenze des hydrologischen Untersuchungsgebietes „Schäfertal“ durch­ge­führt. Drei Experimente erfolgten bei teilweise gefrorenen und ein Experiment bei unge­frorenem Boden. Bei diesen Experimenten wurde herausgefunden, dass die Endinfiltrationsrate des gefro­renen Bodens mit 7·10-5 m/s gleich der Endinfiltrationsrate des ungefrorenen Bodens war. Während bei dem Infiltrationsexperiment mit ungefrorenem Boden die Endinfiltrations­rate bereits nach 10 bis 20 min erreicht war, wurden bei den Experimenten mit gefrorenen Böden aufgrund der zusätzlichen Sättigung des kryoturbativen Sekundärporenvolumens mehr Zeit benötigt. Zu den im Boden ablaufenden Prozessen bei Zugabe von Infiltrationswasser (Tem­pe­ratur­veränderung, Gefrier- und Auftauprozesse, Veränderung der Porosität) besteht noch Klärungsbedarf. Der für die Modellierung wichtige Eingabeparameter der Anfangsbodenfeuchte konnte bei winterlichen Bedingungen nicht genau bestimmt werden. Gravimetrische Boden­feuchtebestimmungen liefern aufgrund des Eintrags von zusätzlichen Eis- und Schnee-Wasser zu hohe Werte. TDR- und Watermark-Messungen unterschätzen hingegen die Bodenfeuchten, weil sie nur den Anteil des flüssigen Wassers berücksichtigen. Mit Erosion 3D / Winter konnten die Ergebnisse der Infiltrationsexperimente, unter der Voraussetzung, dass die effektive gesättigte hydraulische Leitfähigkeit des ungefrorenen Bodens exakt bekannt war, sehr gut nachgestellt werden. Eine Modellierung der Infiltration in einen teilweise gefrorenen Boden ist damit, zumindest für den untersuchten Boden und die betrachteten meteorologischen Bedingungen, möglich. Das COUP - Modell lieferte dagegen völlig andere Ergebnisse, weil von einem Ein­frieren des infiltrierten Wassers bei negativen Temperaturen ausgegangen wird. Eine Verbesserung der Infiltrationsbeschreibungen könnte hier wahrscheinlich durch die Vorgabe einer größeren Anzahl von Eingabeparametern, die die natürliche Situation besser repräsentieren als die für die Modellierung verwendeten Daten, erfolgen.

This thesis deals with the projection of water management and erosion control measures in the Javornický stream floodplain to improve water quality in the Rosnička pond near the town of Svitavy. In the teoretical part, the author summarized current practices in the areas of small river restorations and protection against soil erosion in the Czech Republic. In the practical part, the analasis of the area was first made, including the analysis of natural conditions, hydroecological monitoring of watercourses according to the HEM 2014 method and quantification of soil loss conditions according to the USLE method. Then, revitalization measures on the Javornický stream were designed to improve the self-purification of water and the restoration of ground water in the floodplain, as well as two variants of erosion control measures on agricultural areas to reduce the input of sediments into the hydrographic network. Finally, conceptual and technical recommendations for the implementation of these measures were formulated, as a basis for planning and decision-making of the political leadership of the town of Svitavy.

Ziel dieser Arbeit ist die Verbesserung der Vorhersagekraft des Bodenerosionsmodelierungs-werkzeugs EROSION-3D, welche oftmals durch die Identifizierung der werkzeugspezifischen Parameter Skinfaktor und Erosionswiderstand limitiert ist. Als drei Betrachtungsebenen der Arbeit werden 1. Beobachtungsdaten, 2. die Fähigkeit von EROSION-3D zur Beschreibung der Beobachtungsdaten und 3. die Vorhersagekraft des Werkzeugs untersucht. Aufzeichnungen verschiedener Beregnungsversuche wurden maschinenlesbar zusammengefasst. Daran wurde EROSION-3D mit den bisher üblichen sowie Monte-Carlo Methoden kalibriert. Anhand beschreibender Daten der Beregnungsversuche wurden Vorhersagemethoden zur Schätzung der modellspezifischen Parameter entwickelt und hinsichtlich der Parameterwerte und damit modellierter Abfluss-/Abtragswerte validiert. Die Ergebnisse zeigen, dass verbesserte Vorhersagen mit den neuen Schätzmethoden möglich sind, aber auch Möglichkeiten zur Verbesserung der Modellstruktur bestehen.