Fluvial sediment transport is controlled by hydraulics, sediment properties and arrangement, and flow history across a range of time scales. This physical complexity has led to ambiguous definition of the reference frame (Lagrangian or Eulerian) in which sediment transport is anal- ysed. A general Eulerian-Lagrangian approach accounts for inertial characteristics of particles in a Lagrangian (particle fixed) frame, and for the hydrodynamics in an independent Eulerian frame. The necessary Eulerian-Lagrangian transformations are simplified under the assumption of an ideal Inertial Measurement Unit (IMU), rigidly attached at the centre of the mass of a sediment particle. Real, commercially available IMU sensors can provide high frequency data on accelerations and angular velocities (hence forces and energy) experienced by grains during entrainment and motion, if adequately customized. IMUs are subjected to significant error accu- mulation but they can be used for statistical parametrisation of an Eulerian-Lagrangian model, for coarse sediment particles and over the temporal scale of individual entrainment events. In this thesis an Eulerian-Lagrangian model is introduced and evaluated experimentally. Absolute inertial accelerations were recorded at a 4 Hz frequency from a spherical instrumented particle (111 mm diameter and 2383 kg/m3 density) in a series of entrainment threshold experiments on a fixed idealised bed. The grain-top inertial acceleration entrainment threshold was approxi- mated at 44 and 51 mg for slopes 0.026 and 0.037 respectively. The saddle inertial acceleration entrainment threshold was at 32 and 25 mg for slopes 0.044 and 0.057 respectively. For the evaluation of the complete Eulerian-Lagrangian model two prototype sensors are presented: an idealised (spherical) with a diameter of 90 mm and an ellipsoidal with axes 100, 70 and 30 mm. Both are instrumented with a complete IMU, capable of sampling 3D inertial accelerations and 3D angular velocities at 50 Hz. After signal analysis, the results can be used to parametrize sediment movement but they do not contain positional information. The two sensors (spherical and ellipsoidal) were tested in a series of entrainment experiments, similar to the evaluation of the 111 mm prototype, for a slope of 0.02. The spherical sensor entrained at discharges of 24.8 ± 1.8 l/s while the same threshold for the ellipsoidal sensor was 45.2 ± 2.2 l/s. Kinetic energy calculations were used to quantify the particle-bed energy exchange under fluvial (discharge at 30 l/s) and non-fluvial conditions. All the experiments suggest that the effect of the inertial characteristics of coarse sediments on their motion is comparable to the effect hydrodynamic forces. The coupling of IMU sensors with advanced telemetric systems can lead to the tracking of Lagrangian particle trajectories, at a frequency and accuracy that will permit the testing of diffusion/dispersion models across the range of particle diameters.

No description available.

The Landsat programme, which started in 1972, initiated an era of space-based Earth observation relevant to the study of large river systems through the provision of spatially continuous, synoptic and temporally repetitive multi-spectral data. Free access to the Landsat archive from mid-2008 has enabled the scientific community to reconstruct the Earth’s changing surface and, in particular, to reconstruct the planform dynamics of the world’s largest rivers. The present research reconstructs the planform dynamics in the lower reaches of one of the Asian mega-rivers, the River Ganga-Padma (Ganges), from 1972-2010 using the Landsat archive. The research based on sequential river planform maps generated from the time series revealed a periodic pattern of evolution of the river system over the study period which began by means of meandering at four locations. The meander bends increased in sinuosity until chute cut-offs were triggered, returning the river to a state similar to that at the beginning of the sequence. This periodic pattern is constrained by natural and artificial hard points, and by the Farakka Barrage, meaning that the observed cyclic pulsing is likely to continue into the future. The characteristics and dynamics of meandering rivers have been the subject of extensive research, though the mechanisms involved are still not completely understood. Presently, availability of archival satellite sensor data at regular and frequent intervals for almost four decades presents a great potential for increasing our understanding of the natural processes of meander growth. Though early research indicates that meander growth can be explained by instability of alternate bars in a straight channel, but research based on field data and simulation models have shown that instability of river meanders is an inherent property and the meanders reach a critical value of sinuosity when cut-offs occur and then the complex system undergoes an self-adjusting process. The meander dynamics of the lower reaches of the Ganga-Padma system has been studied in the context of threshold response of a complex system. A conceptual model was developed based on spatial information from the sensor data and quantitative information on river metrics to explain the behaviour of the river system including evidence for self-organising criticality and the attempts of the river to reach dynamic equilibrium. The meandering channel pattern with a tendency of braiding of the river Ganga-Padma were explained based on existing empirical models as well as models based on mobility number and channel stabilization criterion. The threshold for chute cut-off was explored and subsequently the conditions for soft avulsion / branching were studied which showed that the condition for chute cut-off in the Ganga-Padma system is not due to bankfull flow velocity and the super elevation of flow at the centreline of channel but may be due to lack of vegetation stabilization on the Ganga-Padma floodplain. The effect of tectonics and meandering in the moderately paced avulsion of the Ganga-Bhagirathi system to the present Ganga-Padma system was modelled in the present research. It was found that gradient advantage and bend upstream of bifurcation does not result in modelled avulsion as observed in small and medium rivers and large rivers in tectonically inactive regions. A tectonic uplift results in a modelled avulsion period consistent with historical observations. It was found that backwater effect and high sediment mobility keep both bifurcated channels active to attain an anabranching pattern. The backwater effect was found to play an important role for sustaining the anabranch planform of many of the largest rivers of the world.

No description available.

This thesis firstly reviews the current literature available on antidune bedforms and their hydrodynamic environment, alongside recent studies of the turbulence environments associated with bedforms in unidirectional flow. Based on this understanding, three suites of experiments were designed and conducted to elucidate turbulent flow structure within the standing waves above antidunes and to record the sedimentary response of a loose mobile bed that constituted the antidunes. The first suite of experiments used Acoustic Doppler Velocimetry (ADV) to quantify and characterise the flow structure above fixed bedforms and this was supported by a second suite of experiments that used high-speed video to visualise flow structure. Finally, in the third suite of experiments a loose bed of sediment was allowed to deform into antidunes beneath standing waves and the resultant sedimentary structures were recorded and related to the growth and decay of both standing waves and antidune form. Taken together these data have been interpreted in order to identify and elucidate the bulk-flow, turbulent environment of the flow field above antidunes and the sedimentary structures that characterise the preserved antidune bedding. The ADV experiments have shown that a coherent and organised spatial pattern of turbulence exists above antidune bedforms. Initially, when antidune amplitude is small, turbulent stresses are relatively equally distributed along the entire bed boundary layer, however as antidune amplitude increases there is a progressive concentration of turbulent stresses. Turbulence becomes increasingly concentrated in the near-bed region within the trough between upstream and downstream contiguous antidunes and on the upstream flank of the antidune immediately downstream. Velocities in the trough region drop significantly below the mean velocity elsewhere over antidune bedforms. A clear distinction can be drawn between sand and gravel antidunes, with gravel antidunes having comparatively much lower velocities in the trough region, and turbulence stresses (ejections, sweeps, turbulence Intensity, TKE and Reynolds Stress) an order of magnitude higher than for sand bedforms. Further, experiments over a porous gravel bed indicate levels of near bed turbulence higher than over a gravel-surfaced concrete bedform without interstitial flow. High-speed photography and interpretation of streak images further supports this ADV data. It is proposed that antidunes break when turbulence reaches an ‘intensity’ that constitutes a threshold above which rapid erosion occurs in the trough causing a pronounced increase in turbulent ejections laden with sediment and consequent rapid deposition on the downstream antidune flank. Flow then stalls over the downstream antidune; the standing wave collapses and erodes much of the bed. In terms of distinctive sedimentary structure, three types of bedding were observed in sediment sections taken after mobile bed runs where antidunes had been active. Type I bedding is formed by the erosion of the bed and marks the lowest surface formed by antidune downcutting during active migration or collapse. Type II bedding is formed by turbulent sweeps during antidune growth and migration. However the contrasts in sediment size and type that mark bedding are dependent on the heterogeneity of bed sediment. A third type of downstream dipping, bipartite planar bedding was observed to form under an upstream migrating standing wave. The preservation of a suite of sedimentologic features produced by a period of antidune activity is however dependent on the degree of downcutting and erosion during standing wave collapse.

Model equifinality is the property by which very similar model outputs can be generated by many different combinations of model inputs. It is known in numerical models used in other disciplines, and is thought to be likely in landscape evolution models (“LEMs”) also, as they incorporate many process parameters of uncertain value. LEM equifinality, if pervasive, would be a serious obstacle to falsifying working hypotheses and would frustrate landscape evolution research, but to date it has not been quantified. This is attempted here, by sampling a LEM’s response in its parameter space. A well known LEM (‘GOLEM’, Tucker & Slingerland, 1994), used here as an exemplar, is applied to evolution of a c. 38 km2, 4th order catchment in the Oregon Coast Range. Ten of GOLEM’s parameters are selected for variation, covering mass movement, channel formation, fluvial erosion and weathering processes, and value ranges appropriate for the catchment are established from published data and calibration. Parameter space sampling is then carried out using a response surface methodology approach which reduces by c. 3 orders of magnitude the simulation run size needed to explore the 10-D parameter space. Initial simulations are run sampling the space according to a central composite design of 149 targeted parameter value combinations, which afford estimation of all parameter main and two-way interaction effects. Model outputs at 100,000 years are summarised by four metrics (sediment yield, drainage density, sediment delivery ratio, and a topographic metric), which serve as landscape descriptors. Equations, or “metamodels”, are derived by regression to describe each metric as a function of the GOLEM parameters, and further simulations allow testing and improvement of model fits (R2 of c. 98% for the sediment yield, drainage density and sediment delivery ratio, and c. 92% for the topographic metric). The parameter space is then sampled rapidly and densely (>>106 times), using each metamodel to predict GOLEM’s output at each sample point. Results are compared with a reference value for each metric, to obtain equifinal proportions in a range of permitted tolerance bands around the reference, and using a bootstrap to aid calculation of confidence intervals. The likelihood of obtaining an equifinal result is found to depend on the tolerance band and the metric e.g. the equifinal probabilities for drainage density are estimated to be c. 26% and 58% respectively in the 2% and 5% tolerance bands, compared with c. 68% and 99% for the sediment delivery ratio in the same bands. Where combinations of metrics are used, the polymetric equifinal probability is often lower (and never higher) than it would be for any of the component metrics used singly. Also, the equifinal probability for any metric and tolerance band usually decreases as the number of parameters employed in the model increases. More generally, equifinal probabilities are seen to result from the combinations of parameter main effects and interactions driving each metric, thus allowing equifinality to be explored through the use of metamodel archetypes. Further research using other LEMs is needed, and the response surface methodology is recommended for both its computational efficiency and clarity in this respect.

Management of lake-catchment systems is a long-term challenge for prevention of hazard risk and further sustainable development. Climate change and human activities are two important factors that concurrently affect the hydrology and sediment regimes within systems. Many soil conservation and sediment control techniques are known and widely studied based on experimental field plots. Catchments are complex dynamic systems. Spatially-distributed and process-based models provide powerful tools to simulate the complex behaviour of hydro-geomorphological processes in response to climate change and human impact on fluvial systems. Accordingly, this study addresses the principles, testing and application of an established cellular automata landscape evolution model (CAESAR) to study the dynamic non-linear behaviour of complex systems, past and present interactions among landscape elements and environmental controls, and potential future impacts. The results from a series of simulations of different systems (simple catchment, Old Alresford Pond, UK and Holzmaar, Germany) over different timescales (50 years to 5000 years), demonstrate a rapid catchment response to climatic drivers. This is characterised by variations, particularly peaks of modelled sediment discharge controlled by the magnitude and frequency of floods and droughts happened in a single year or a period of time. The effect of vegetation cover also plays an important role in accelerating the delivery of sediment or protecting the catchment from soil erosion. This erosional response is validated by comparing modelled sediment discharge and system evolution to magnetic susceptibility and accumulation rates of lake sediments, as well as documented data. The non-linear properties of complex systems, such as thresholds, feedback mechanisms and self-organised capability, are shown to exist in these simulations. This study also provides the probabilistic results of potential erosion risks in terms of future natural and human pressures. The modelling application permits a better understanding of the relationship between environmental forcings and complex dynamic system evolution processes. In addition, it allows investigations of the extent to which past and present human-environmental interactions generate subsequent impacts for the purpose of effective landscape management.

Published, well-described examples of multiple mixed bedrock-alluvial character systems largely pertain to small to medium systems. No descriptions exist for large river systems such as the Mekong River in Cambodia (South East Asia). The published literature concerning the 120km long and up to 5km wide multichannel study reach are outdated and do not provide sufficient levels of detail. Therefore the first part of the thesis offers an amplified portrait of the modern and palaeo-Mekong based upon limited published literature, updated by ground survey data and complemented by analyses of remote sensing data. The second part of the thesis is devoted to applying quantitative channel network characteristics in order to describe the Mekong River but importantly to separate mixed bedrock-alluvial from alluvial multichannel rivers. The key question in this respect is whether the planform characteristics of the river networks reflect whether they are within alluvial settings or are influenced by bedrock controls. The channel metrics comparison is accompanied by a specially designed methodology based upon standard GIS tools so that the results obtained in this study could be later incorporated into subsequent channel network metrics research using a larger dataset for these or other rivers. Geomorphological findings reveal that the multichannel pattern of the Mekong is comprised by primary channels, secondary channels, cross-channels and blind channels, divided by two classes of islands: major and seasonally-inundated islands. The riverbed is represented by outcrops of Mesozoic bedrock and temporally and spatially fixed sand bars whereas the planview variations in the disposition of sand bodies versus bedrock define the extent of longitudinal geomorphological zones. Structurally and qualitatively diverse geological units are dissected by regional and local faults which partially control channel alignments. Topographic and dating control of river terraces and palaeochannel deposits show that the river incised during the Last Glacial Maximum but was essentially within the same course as seen today for at least last 70ka. Distinctive floristic associations emphasise an important role that vegetation plays in channel dynamics in this mixed bedrock-alluvial system. Comparative study of channel network metrics shows that reach-scale standard planform indices (e.g., braiding intensity, channel sinuosity) are less effective than non-standard indices developed at scales less than the reach-scale (e.g., channel network bifurcation angles asymmetry, island convexity) in successfully separating channel patterns. In addition, DEM trend surfaces reveal variable topographic trends generic for the mixed bedrock-alluvial patterns only. Ultimately, it shows that the mixed bedrock-alluvial pattern classification might be more effectively based on channel cross-section properties, e.g. variations between bedrock/alluvium as a part of a channel continuum.

Inledning: Uppgiften, som den presenterades för mig i juni 1976, var att göra en allmän morfologisk beskrivning av några olika typer av sluttningsdepositioner samt deras partikelorientering. Huvudlokal har varit Skansbukta på Spetsbergen, där välutbildade talusbranter och svämkäglor finnes. Speciellt intresse har ägnats åt studiet av dessa depositionsformer. Vidare har även depositioner i anslutning till de talrika mudflows studerats. Jämförande studier beträffande ovanstående former har gjorts vid två andra lokaler, nämligen Longyeardalen och en lokal, som av handledaren tilldelats arbetsnamnet Timglaset. Arbetet har främst omfattat en beskrivning av sluttningsdepositionerna som gjorts på basis av profildragningar, grävda skärningar, partikelorientering samt okulär besiktning. Först i andra hand har processernas förlopp diskuterats.

The production and consumption of food, throughout the whole supply chain, have negative and large impacts on the environment (Tukker et al., 2006). Environmental impacts could be reduced using sustainable diets, such as the vegetarian or the vegan diets (Baroni et al., 2006). In Sweden, in addition to these two diets, the New Nordic Diet and the Nordic Nutritional Recommendation are diets for Nordic countries that can be considered as sustainable (Saxe et al., 2012). Sustainable diets are seldom adopted by the Swedish population, even if they could considerably reduce negative impacts on the environment (Stehfest et al., 2009; Marlow et al., 2009). Depending on diets composition and type of products eaten, each diet might not reduce to the same degree environmental impacts compared to the others. The research will try to answer the question: How much environmental impacts can be reduced by different sustainable diets in Sweden?