On-orbit targeting, guidance, and navigation relies on state vector propagation algorithms that must strike a balance between accuracy and computational efficiency. To better understand this balance, the relative position accuracy and computational requirements of numerical and analytical propagation methods are analyzed for a variety of orbits. For numerical propagation, several differential equation formulations (Cowell, Encke-time, Encke-beta, and Equinoctial Elements) are compared over a range of integration step sizes for a given set of perturbations and numerical integration methods. This comparison is repeated for two numerical integrators: a Runge-Kutta 4th order and a NLZD4/4. For analytical propagation, SGP4, which relies on mean orbital elements, is compared for element sets averaged with different amounts of orbit data.

Introduction Choice and access to health care are important determinants of health outcomes. Various issues influence choice and determine the degree of, and differences in access to health care. Choice of health care facilities by individuals is often determined by the interplay between patient and provider characteristics. The influence of factors that determine choice of a health care facility or a provider varies depending on individual patient's socio-ecological factors, type and severity of illness (including the presence or absence of co-morbidities), cost of healthcare (including travel costs), and the presence or absence of a third party such as a health insurance plan. On the other hand, provider or facility factors, which include spatial and non-spatial factors such as technical and functional dimensions of quality of care, are the supply–side factors that influence choice of provider and facility. In order to achieve universal health coverage and attain the Sustainable Development Goals, Nigeria adopted a prepayment health care financing method through the National Health Insurance Scheme (NHIS) in 2005. However, population coverage of the scheme remains very low, while it also has a reputation of less than optimal performance. Evidence showed that while some accredited NHIS facilities were burdened with a high volume of enrolees, others had registered low volume (of enrolees). This study explored the influence and magnitude of the various factors responsible for the poor performance of the scheme as well as the lopsided/uneven distribution of enrolees across these health care facilities. Findings will assist in repositioning the scheme for better performance as well as serve as a guide for other countries planning to design and implement similar schemes. This will enable such schemes to learn from and avoid mistakes made under the present scheme. Methods This study was cross-sectional in design, with descriptive and analytical components. Data were collected using a mixed-method approach (geo-spatial, quantitative and qualitative). The geo-spatial component was achieved using three data layers of x and y coordinates: the enrolees' locations, locations of NHIS facilities and locations of health care facilities typically used by enrolees, were used in the spatial analysis to identify the closest NHIS accredited health care facility to each enrolee's residence and also estimate the distance between enrolee's location and NHIS facility being utilised. The Distance to the Nearest Hub (points) function in Quantum GIS 3.10 was used to automatically assign enrolees to the nearest NHIS facility while the Join by lines (Hub Lines) function was used to assign enrolees to the NHIS facility they used. Spider web diagrams that depict geo-spatial relationship between enrolees' residence, patronised health care facilities and health care facilities closest to the residences were constructed. Quantitative data were collected from 432 NHIS enrolees using an adapted questionnaire. A checklist was also used to collect data on structural components of health facilities such as the number and cadre of the health workforce, availability and functionality of medical equipment and facility infrastructure. Quantitative data were analysed using STATA and frequency tables were generated. Qualitative data were collected through in-depth interviews conducted among 29 participants of the NHIS, HMOs, enrolees, head of facilities and an academic. Qualitative data analysis was done using an inductive thematic approach. Audio-taped interviews were transcribed and codes were generated. Themes were thereafter searched for and generated from the codes. Emerging themes were named, documented and analysed accordingly. A conceptual framework that illustrated the Nigeria contextual environment, the health system and the current governance of the NHIS with a highlight on the relationships, factors and patterns of interaction among stakeholders was designed. Results The majority of the enrolees received care across a small proportion of the accredited facilities and bypassed nearby health facilities to receive care. Almost all the study respondents, 405 (93.9%) bypassed, however, only 147 (34.0%) reported to have done so. In this study, predictors of bypass of healthcare facilities were younger age (OR 0.67, CI 0.46 – 0.99, p = 0.046) and employment in the civil service (OR 0.49, CI 0.31-0.79, p = 0.003). Older age (1.66, CI 1.07-2.58, p = 0.024), attainment of tertiary level of education (OR 1.57, CI 1.02-2.44, p = 0.043), high socioeconomic status (OR 1.94, CI 1.24 -3.02, p = 0.003) and presence of multiple morbidities (OR 1.66, CI 0.99-2.78, p = 0.053) were predictors of personal choice of health facility. Physical infrastructure was poor in all the facilities; most of the facilities depended on more than one source of power supply and water supply was mainly from other sources apart from pipe-borne. Identified predictors of satisfaction with care were age, occupation and seeking information about quality of care. Knowledge of the NHIS and patronage of faith-based health facilities were also predictors of satisfaction with care. Respondents who were younger than 35 years of age were more likely to be satisfied with care than those who were older (OR 1.85, CI = 1.05 – 3.25, p< 0.05). Private sector workers under the scheme (OR 1.84, CI 1.03 – 3.28, p< 0.05) were more likely to be satisfied with care than those employed in the civil service. Likewise, compared with those who did not seek information, those who did (OR 1.63, CI = 1.04 – 2. 53, p< 0.05) were more likely to report satisfaction with care. Respondents who claimed not to have a knowledge of the NHIS were more likely to be satisfied with care (OR 1.65, CI = 1.06 – 2.55, p< 0.05). Likewise, patronage of faith–based facilities was identified to be a predictor of satisfaction with care (OR 1.84, CI = 1.09 – 3.08, p< 0.05). Qualitative data revealed that there was a very low level of trust among the stakeholders. The design and operations of the scheme indicated that the NHIS managers lacked the technical and managerial skills required to manage the scheme and other stakeholders. Both the NHIS officials and the health care providers were of the opinion that the HMOs had more political influence than other stakeholders in the scheme, and were using this to take advantage of others. Enrolees and health care providers were reluctant to collaborate with the scheme at inception, because of the low level of trust in government policies generally. In addition, at inception of the scheme, the majority of the enrolees were arbitrarily allocated to the few available health care providers. For some of the enrolees, choice of health care facilities was based on perceived quality of care and occasionally, as a result of proximity to places of residence. Instances of corrupt and unethical practices were reported across the board among the scheme stakeholders. Discussion There was a high level of facility bypassing among study respondents, though only a few of them claimed to be aware of this. This finding is because of the allocation or assignment of majority of the enrolees to the few facilities that were available to participants in the scheme at its inception. The study also revealed that younger age enrolees and civil servants bypassed more than their respective counterparts did. Studies have shown that younger people are more likely to explore and become more adventurous than older individuals. The apparent bypassing among civil servants was largely because of the arbitrary allocation of reluctant enrolees to the available few health care providers at the inception of the scheme. This also explained the skewed distribution of the enrolees in these few facilities under the scheme. Findings also support the observation that most of the facilities with fewer enrolees were those that stayed away from the scheme at inception. However, the observed lopsided/uneven pattern was difficult to reverse despite the complaints of the facilities with fewer enrolees and the efforts of the scheme to address the skewness. It should also be noted that high social economic class is a strong factor of personal choice of healthcare facilities. The only plausible explanation was the fact that this group of enrolees were not civil servants and who had the financial capacity to pay the premiums, which enabled them buy into the scheme voluntarily and personally chose facilities where to receive care. The state of physical infrastructure in all the facilities that were involved in the study is illustrative of the weak health system in Nigeria. Poor facility infrastructure is a known recipe for the failure of social health insurance. Ability to search for healthcare facilities and in the process, the phenomenon of bypass as seen in this study appeared to play a major role in satisfaction with care amongst younger people, and among those from the private sector, the economic ability to search for and receive care in healthcare facilities of choice, and that meets their expectations. Similarly, enrolees who had the opportunity and sought information about the quality of care in the facilities before enrolment were more likely to be satisfied with care than those who did not seek information. Enrolees who claimed they had no knowledge of the scheme were more likely to be satisfied than those who had knowledge of it and may have had a higher expectation of the quality of care than they received. Satisfaction with care that was attributed to patronage of faith-based facilities in this study has similarities with findings in previous studies. Compared with other types of facilities, it has been reported that the likelihood of higher levels of satisfaction with care among those who patronise faith-based facilities, may have been as a result of higher levels of functional quality, (including spiritual care, that is more valued in this setting) in addition to the technical quality of care. The fundamental finding from the qualitative component of the study was a high level of mistrust of government by almost all the stakeholders involved in the scheme. This manifested itself in the reluctance of the majority of the private health facilities to collaborate with the government in providing health care services to enrolees on the scheme at inception. The same explanation goes for the then potential enrolees' outright refusal to take up the opportunity to access health care services through the scheme. Previous failed government policies both in the health and in the non-health sectors were cited as reasons for the low interest in the scheme. Because of this, except for the government health facilities that were instructed to do so, majority of the private facilities stayed away from providing care to enrolees on the scheme until some years later. Thus, the majority of these enrolees at inception were assigned to the few health facilities that were available. This is what was primarily responsible for the lopsided/uneven distribution of enrolees across the NHIS accredited facilities, whereby some had a high volume of enrolees, while the majority, especially those that showed interest in the scheme much later had very low volumes. Unfortunately, this pattern of enrolees' distribution may be irreversible. In addition, mistrust also exists between the NHIS and the HMOs, between the HMOs and providers, and to some extent between the enrolees and providers. It is important to note that the design of the scheme put the HMOs in a powerful position, which they used to influence the political class to their advantage. To compound the situation, NHIS officials had poor technical and managerial skills to administer the scheme. These are indications of an inefficiently managed health intervention. Under these circumstances, it is highly unlikely that universal health coverage could be achieved unless the observed challenges are appropriately addressed. In addressing these issues, a reform should be considered in the design of the scheme and appropriate training given to the NHIS officials saddled with its day-to-day operation. Conclusion This study has elucidated the reasons for the poor uptake and skewed distribution of enrolees across accredited NHIS facilities in the study area. In addition to poor structure and inefficient management, the high level of mistrust among the stakeholders has played a major role in the lopsided/uneven geo-spatial pattern of enrolees' distribution across the NHIS accredited health facilities. As it is presently structured and managed, the NHIS is highly unlikely to achieve its set objectives. It is advocated that a reform that addresses the observed anomalies be instituted to enable the scheme achieve its goals. This is a lesson for other countries planning to design and implement similar schemes.

Miniature air vehicles (MAVs) have attracted a large amount of interest recently both from the research community and from the public. New battery technologies as well as rapid developments in embedded processing and MEMS sensor technologies have greatly increased the potential of these vehicles. MAVs have been envisioned playing significant roles in both civil and military applications. Examples include: fire monitoring, search and rescue, traffic monitoring, crop monitoring, convoy protection, border surveillance, troop support, law enforcement, natural disaster relief, and aerial photography. The application of MAVs tends to center on the ability of the MAV to collect and deliver visual information to the user. In many applications it is important to be able to accurately geolocate items of interest in the visual data. However, the inaccuracies associated with MAV platforms have led to relatively large errors in previous attempts at geolocation. The first half of this thesis focuses on increasing the accuracy of geolocation estimates achievable using a hand-launchable MAV. To accomplish this, methods are presented for bias estimation, wind estimation, recursive least squares filtering, and optimal flight path generation. Hardware results are presented which demonstrate the ability to consistently localize targets to within 5 m regardless of wind conditions. The second half of this thesis focuses on using the high accuracy geolocation estimates to complete a search and engage mission. This is a mission in which the MAV not only locates the target, but also accurately delivers a payload to the target site. The focus is on delivering an attached payload via accurate landing at the target site. A vision-based landing approach is presented which is robust to both wind and moving targets. Simulation results are presented which demonstrate the effectiveness of the control.

<p> Gypsum karst areas in British Columbia and Wood Buffalo National Park, Alta.-N.W.T. are described. Investigation of the geo-hydrology of these areas, particularly specifically the saturation states of rising waters, is demonstrated to be a valuable tool in defining the major geomorphic processes acting. The combination of thermo-dynamic equilibrium studies of the gypsum and limestone processes serves to define zones within which the dominant controls of rock solution can be inferred.</p> <p> The commonly accepted parameters of limestone solution equilibria (Picknett's curves) are examined and shown to be incorrect. Use of the parameters and indices presented in this thesis gives much better accordance with observed characteristics of karst waters. </p> / Thesis / Master of Science (MSc)

La representación del entorno juega un papel crucial en la navegación autónoma. A esta representación, se le suele denominar en la literatura como mapa, y su construcción suele realizarse mediante vehículos de mapeado dedicados. Sin embargo, aunque este tipo de mapas son muy precisos a nivel local, presentan el inconveniente de ser globalmente inconsistentes debido a la acumulación de pequeños errores que se hacen relevantes cuando los mapas crecen en tamaño. En la presente tesis doctoral, se propone como alternativa, la navegación autónoma basada en mapas públicos geo-referenciados. Este tipo de mapas, a diferencia de los construidos mediante vehículos de mapeado, son por naturaleza globalmente consistentes debido a que proceden de imágenes aéreas que se encuentran geo-referenciadas. Esto, además de ser una ventaja en sí misma, conlleva otro tipo de beneficios, como la no dependencia de un proceso de mapeado, o la posibilidad de navegar sin restricciones en el tamaño del entorno. No obstante, la integración de los mapas públicos geo-referenciados introduce algunas particularidades en la implementación de los algoritmos de navegación autónoma. Durante la investigación que se expone en esta memoria, se han desarrollado diferentes métodos para abordar dichas particularidades. En el módulo de localización, la representación de mapas geo-referenciados introduce la dependencia de un tipo de marcas que deben ser observables, tanto desde imágenes por satélite, como desde los sensores locales del vehículo. Esta restricción genera representaciones escasas que, a menudo, resultan en zonas ambiguas para la asociación de datos (efecto aliasing). Para abordar estos temas, se han desarrollado diferentes métodos robustos, como Delta-Angle Lane Markings Representation, una estrategia de representación para el proceso de asociación de datos, y Distance-Compatible SAmple Consensus, un método de asociación de datos. Para mitigar el efecto del aliasing en el módulo de localización, también se han empleado capacidades de autoajuste, que modifican de manera dinámica la configuración del método de asociación de datos en función de la pseudo-entropía medida en las observaciones. Por otra parte, para el módulo de planificación de rutas, se ha desarrollado un método llamado Naive-Valley-Path que corrige las imprecisiones locales intrínsecas en los mapas públicos. Todos estos métodos han sido comparados con sus homólogos en el estado del arte, demostrando en todos los casos mejoras que han resultado en contribuciones de gran impacto para la comunidad científica. / La presente tesis doctoral ha sido financiada por la Conselleria d’Innovació, Universitats, Ciència i Societat Digital de la Generalitat Valenciana y el Fondo Social Europeo de la Unión Europea a través de las subvenciones ACIF/2019/088 y BEFPI/2021/069.

This report is a case study about geothermal energy system and its application forthe hospital in the city of Gävle. Today the hospital uses district heating and -coolingas their main energy source.There is a report about the hospital in the city of Umeå where geothermal energyhas been installed. Both hospitals have the same need when it comes to using heatand cooling all year round. The hospital in Umeå installed geothermal energy sothat they got a less vulnerable energy system. The emissions of CO2 were also lowereddue to this installation.This report aims to answer the following research question.How geothermal energy can be a option of choice for the hospital I the city ofGävle?The report presents a literature study on subject close to this research question. Focusfor the report is to find out if increased electricity consumption is better than usinglocal district heating- and cooling. The report from the geothermal installation inUmeå has on big difference and that is from which fuels the district heating is produced.In Gävle the energy comes from biomass which gives that the emission factoris almost zero.The calculations and modelling are performed in Excel and the results presented ingraphs.The results are positive both from an economical view and environmental perspective.If the total electricity price doesn’t increase more than 36% per year then geothermalenergy is more cost effective. Looking at the emissions of CO2 equivalentswith an emission factor of 90.4 kg per MWh electricity the COP-factor should notbe lower than 7.5. If that can be reached, then geothermal energy performs betterthan district heating- and cooling.

Driftwood is widely recognized as a relevant component of riverine systems due to its complex interactions with flow, sediment transport and vegetation dynamics. In-channel large wood has a relevant geomorphic and ecological role as it enhances morphological diversity and creates a variety of physical habitats that sustain high biodiversity. Its presence can also increase flood risk and therefore wood is often removed from streams especially in densely populated areas. Recent river restoration policies aim to maximise the environmental benefits of driftwood and minimise risks. The study of wood dynamics can provide useful information to define guidelines for sustainable wood management. Multi-thread systems represent a particularly interesting and challenging context for the investigation of wood dynamics because of their complex geometry, the presence of vegetated islands and the frequent, intense changes in channel pattern observed even for moderate discharge fluctuations. However, comparatively few studies focus on driftwood in large braided rivers and limited quantitative information is available on wood transport, deposition and remobilisation in these systems. The goals of the present work are: a) characterising the spatial organisation of wood deposits and identifying typical retention sites and styles; b) analysing the influence of flow regime, channel morphology, wood supply and log properties (size and shape) on dispersal patterns; c) investigating wood remobilisation induced by discharge fluctuations and bed reworking; and d) analysing long-term wood storage volume and budget. A combination of field-scale direct observations, remote sensing techniques and physical modelling was used to investigate wood and channel dynamics. Field-scale monitoring carried out on the Tagliamento River (Italy) allowed the observation of complex interactions and feedbacks between channel, vegetation and wood dynamics. Laboratory simulations – carried out in two large flumes at the University of Trento (Italy) and at the University of Hull (UK) – were employed to investigate individual wood dispersal mechanisms under controlled conditions and to explore the role of governing parameters. In large rivers, floods are the primary driver of wood recruitment through the erosion of vegetated banks and islands; field-scale observations showed that these localised wood inputs control wood storage at sub-reach scale because a large proportion of eroded trees is retained close to the input point in sparse, small jams. Physical modelling highlighted a complex relationships between flow stage and the longitudinal and vertical distribution of wood; high discharge increases the ability of the system to transfer wood, but at the same time generates complex inundation patterns where a larger number of sites are available for wood retention. No clear link between flow stage and the vertical distribution of wood is observed, probably because water surface elevation exhibits small changes with discharge in flat braided river cross-sections. Driftwood element properties also influence deposition patterns; log diameter controls travel distance as it governs flotation and therefore the likeliness of deposition. High element length and complex piece shape sustain the formation of large jams. The presence of a root bole is also associated to short travel distance and low relative elevation. At reach-scale, the spatial distribution of wood is the product of local inputs during major floods and reorganisation of deposits induced by minor events. Wood pattern exhibits a threshold behaviour with supply. High input rates determine very high spatial density and the formation of large, stable jams. Two processes govern wood reorganisation over different time scales, namely network inundation – inducing rapid changes in flow field – and bed reworking. In the first case, the persistence of deposits depends on the magnitude of discharge fluctuations as wood dispersed by small floods is easily removed by larger events. High relative elevation and large jam size enhance wood stability, while the presence of a root wad has a dual effect as it determines large accumulations at low elevation. Channel pattern reworking determines intense turnover of driftwood deposits regardless of supply rate, piece properties and jam size, save for very large accumulations. As a consequence, wood deposition occurs mostly on empty braidplain areas as opposed to pre-existing sites. These results suggests that wood (alone) has little direct effect on reach-scale bed geometry in a large braided river; however, deposited wood significantly influences local hydraulics and morphology, enhancing physical habitat diversity. Moreover, deposited wood favours the accumulation of fine sediment, nutrients and seeds and often exhibits vegetative regeneration. These processes lead to the transformation of instable driftwood pieces into vegetated islands, which in turn can trap more wood. Therefore, wood has a relevant, indirect effect on braided river morphodynamics through the establishment of vegetation, whose presence influences network complexity and evolution.

This thesis develops and tests a classification of ‘near-natural’ European single-thread rivers, which are free to adjust to fluvial processes. The research involves subdividing rivers along a continuum of geomorphological characteristics to assign river reaches to geomorphologically-meaningful classes according to their channel dimensions and forms, and floodplain characteristics. The classification was developed and tested through three research components. First, a preliminary classification was developed using information entirely derived from a new information system containing remotely-sensed imagery and digital terrain data: Google Earth. This research stage required the development of rules for identifying, extracting and standardising information from this source for a large sample of river reaches. 221 single-thread river reaches distributed across 75 European rivers were investigated. Analysis of the derived information resulted in the development of a classification comprising six classes of European single thread river. Second, the robustness of the classification was explored including assessments of (i) the degree to which the classes were interpretable in relation to the geomorphic features they displayed; (ii) the degree to which sub-divisions of the six classes could be identified and justified; (iii) the accuracy of some specific types of information extracted from Google Earth; and (iv) the degree to which the six classes corresponded to expected gradients in two controlling variables: stream power and bed sediment calibre. Thirdly, bar theory was applied to a sample of rivers representative of the six classes. Since bars are an important contributor to river channel form and dynamics, the correspondence of the bars in the six river classes to their expected distribution as indicated by bar theory, provided further confirmation of the robustness of the classification. The outputs of the research are (i) a fully-tested classification of European single-thread rivers; and (ii) a demonstration of how Google Earth can provide valuable information for research in fluvial geomorphology. Some additional future research stages are proposed that could turn the classification into an operational tool in the context of river assessment and management.

Understanding and predicting the effects of width variability and the controls on width adjustment in rivers has a key role in developing management approaches able to account for the physical, ecological and socio-economical dimensions of a river system. Width adaptation in a river occurs due to erosion and accretion of banks, within various geomorphic, environmental and anthropogenic contexts, which set the most relevant factors controlling the morphological dynamics of the river corridor. In turn, changes in channel width imply alterations of the river channel morphodynamics at a variety of space and time scales, implying, for instance, modifications of important controlling parameters, like the width-to-depth ratio, which is closely related to the planform morphology of alluvial rivers. Width adaptation bears crucial implications for river management: on one hand, channel widening may result in loss of valuable land and in the increase of the damage risk of infrastructures in surrounding areas, which are often subjected to increasing pressures related to human settlements and economic activities. On the other hand, several approaches to river restoration are based on the concept of “giving more room to the river”, and thus allow the banks to erode and widen, to increase morphological and physical habitat diversity. In view of these implications, the prediction of width adaptation, understanding of its main causes and controlling factors, and quantification of the riverbed morphodynamic response to width variability is of crucial importance to support effective river management. The practical and engineering interest on stable cross-sections of alluvial channels has attracted a considerable amount of scientific research since late 19th century. Much of the research has focused in developing width prediction tools mostly based on empirical approaches and methods based on extremal hypothesis and to lesser extent on mechanistic methods. In the past two decades, research has advanced in developing numerical models including geotechnical as well as fluvial processes to simulate bank failure mechanism more accurately. Despite significant development on the width predictors, research in controls on width evolution of river channels cannot still be considered a fully settled issue. The study of the morphodynamic response of the riverbed to width variability in space and time is somehow more recent, and has focussed on the dynamics of large-scale bedforms (river bars) that produce a variety of riverbed configurations and planform morphologies. The effect of spatial width variability on river bars has mainly been based on assessing the role of such planform forcing effects to the bed topography, both in case of straight and meandering river channels. The amplitude of width variability has been related to fundamental questions as those behind the transition between single- and multi-thread river morphologies, and most studies consider regular spatial variations of the channel width. Research on the response of channel bed to spatial width variability has mostly consisted of modelling and theoretical approaches, which point out the limit cases of a purely “free” system response, associated with morphodynamic instability, an of purely “forced” bedform pattern by spatial planform non-homogeneity. The large spectrum of mixed configurations between those two theoretical limits has been so far seldom investigated, despite its strong relevance for real river systems. The limits of what can actually be considered a “planform forcing” effect, or has instead a too small variability have never been clarified, a well as its role on the resulting channel morphodynamics. For instance, the effects of small amplitude width variations on straight channels, which may be due to imperfect bank lines or protrusion due to vegetations, on morphodynamics of river bed has been neglected so far. This study has two main scientific goals. The first goal is to quantitatively investigate the role of potentially controlling factors on the width evolution of bedload-dominated straight river channels, including the initial channel width, the flow regime and the sediment supply regime. The major question driving the research is whether a river would attain the same width independently of the initial conditions and whether this would be true for all types of discharge regimes of water and sediment supply. The study is carried out using both laboratory experiments (Chapter 3), analytical model (Chapter 4) and numerical model (Chapter 5) tested with reference to real river data. Integrating the results of the experiments with those of analytical and numerical models allows deriving a more robust and complete understanding of the processes involved, including transient width evolution, time scales to morphodynamic equilibrium, equilibrium conditions and role of each controlling factor. In Chapter 3 a set of controlled laboratory experiments have been performed to study channel adjustments in a movable-bed, erodible-bank channel under different flow and sediment regimes and different initial widths. The long-term width evolution is observed to be independent of initial channel width under uniform formative discharge without upstream sediment supply. Width evolution rate is observed to depend on the initial channel width when the sediment is supplied from upstream with the narrowest initial channel evolving at the highest widening rate and resulting into the widest channel. A physics based analytical model of channel adjustment (Chapter 4) has been applied to some of the experiments described in Chapter 3. Furthermore, in Chapter 5 a field scale numerical model was setup using the flow and topographic data of gravel bed reach of Upper Severn River near Abermule (UK). The trend of width evolution computed by analytical model is also qualitatively in agreement with the observations in the experiments. The results of numerical modeling have further supported the observations in the experiments which reinforce the findings in agreement with laws of physics. The second goal of the present PhD research is to analyze the morphodynamic response of the riverbed to small-scale spatial variability of the channel width, focusing on alternate bars. The main question driving the investigation (Chapter 6) is to which extent small-amplitude, irregular width variations in space affect the morphodynamics of river bars, the fundamental riverbed patterns at the scale of the channel width. The key theoretical question behind this investigation is to which extent “small amplitude” width variations can be considered as a planform forcing, for the channel bed morphodynamic response, and whether it is possible to establish a threshold amplitude below which they may act as a near bank-roughness element. The study is based on hydraulic conditions typical of bedload-dominated piedmont streams, often having flows with Froude numbers around 1 or higher at bar-forming or channel-forming conditions. The study is developed through a numerical modeling approach. Because of the considered hydraulic conditions (close to critical-Froude number) first, a comparison is made between one semi-coupled numerical morphodynamic model, expected to be most suitable for sub critical flows, and one fully-coupled numerical morphodynamic model which can handle Froude-critical flows to assess the potential shortcomings of applying a semi-coupled model under close-to-critial Froude conditions. Such test, (Appendix B) supports the use of both models, and the semi-coupled model is eventually preferred for the advantages in computational speed. Such model is used for the numerical investigations performed in Chapter 6 and to some extent also in Chapter 5. The comparison is based on the reproduction of alternate bars morphodynamics observed in existing sets of flume experiments with fixed banks and super-critical flow conditions. The results of numerical modeling have shown that the small width variations have accelerated the development of the steady bars suppressing the free bar instability. Further investigations reveal that the effects of small width variations to a certain extent can be captured by parameterizing them in the form of increased roughness close to the banks or as small obstructions along the banks.

Increasing energy demand driven by rapid population and economic growth, the need for climate change mitigation, and the depletion of fossil fuels is stimulating the search for renewable, climate neutral energy sources. Hydropower provides an efficient, low maintenance and flexible form of energy, which can provide ancillary benefits such as flood control, water storage and job creation. Yet, the construction of dams for hydropower production has been recognised by scientists as one of the major threats to the ecological integrity of river systems. For instance, the fragmentation of river systems alters the flow, thermal, and sediment regimes of rivers, and restricts the free movement of aquatic organisms. Disruption to the natural flow regime results in the degradation of physical habitat features which generate acoustic stimuli that are relevant to organisms. In addition, initial flooding of terrestrial habitats results in the rapid decay of organic matter, which releases greenhouse gases (GHG) into the atmosphere. Conservation and management of river systems therefore requires a greater understanding of the processes and mechanisms which underpin the ecohydrological impacts of hydropower. In this context, this doctoral thesis aims to investigate: (i), the ramifications of a global boom in hydropower construction, (ii) the prediction of GHG emissions from hydropower reservoirs, and (iii) the temporal and spatial changes in underwater river soundscapes affected by hydropower. Researchers have investigated the social, economic and ecological consequences of reservoir construction for decades. However, the lack of coordinated, georeferenced databases has hindered catchment decision making, and limited the development of regional and global research in particular. In Chapter 1, the primary objectives were to create a high resolution, georeferenced database of hydropower dams under construction or planned to assess the dimension and spatial distribution of hydropower developments, their density relative to available catchment water resources and the future impact on river fragmentation. Data were collected on hydropower schemes under construction or planned with a capacity of 1 MW or above, from government and non-government databases, grey literature and news reports. Spatial analyses were conducted in a geographical information system (GIS) on the extent of global development, impact per water availability and potential consequences for existing status of river fragmentation. The relative contribution of hydropower reservoirs to the global GHG budget, particularly in sub-tropical and tropical regions, remains the subject of intense critical debate. The initial objective of the second study was therefore, to identify principal parameters and underlying processes that drive GHG emissions from reservoirs. The second step was to review global reservoir emission measurements and their source pathways in hydropower systems. Meteorological and landscape derived parameters were then correlated with the GHG measurements in order to assess if and which selected parameters might explain variations in GHG emission data. Similarly, existing empirical models were applied to the measured data to assess their suitability in predictive modelling. Finally, a newly developed process based model (FAQ-DNDC v1.0) was used to simulate ‘net’ CO2 emissions from a newly flooded tropical reservoir and compared to the measured results. The final study (Chapter 3) examined the influence of hydropower systems on the underwater acoustic properties of river habitats. Using recently developed acoustic sensors in addition to traditional hydrophones, the study characterised the temporal and spatial changes in river soundscapes affected by hydropeaking, compared their frequency composition to unaffected river soundscapes, and critically appraised the ecological implications. The results of Chapter 1 indicate that we are now experiencing an unprecedented growth in global hydropower construction. Over 3,700 dams are planned or under construction, primarily in Africa, South America and East Asia. The expansion in dam building will reduce the number of free flowing rivers on a global scale by approximately 21%. The results of Chapter 2 show that variation in measured emissions due to the inherent heterogeneity of the underlying processes, in addition to methodological limitations, impede the prediction of GHG emissions. Source pathways of CO2 are similar for the majority of systems, however, pathways of CH4 emissions are highly variable and dependent on local operating conditions and the configuration of the given hydropower system. A newly developed process based model (FAQ-DNDC v1.0) shows that a mechanistic approach may provide the basis for the ‘net’ assessment of future hydropower reservoirs. Chapter 3 reveals that distinct river soundscapes undergo changes which are highly correlated to hydropower operations, and thus rapid sub-daily changes occur at timescales not often found in natural systems. These changes occur mostly in low frequency bands, which are within the range of highest acoustic sensitivity for fish. In pool habitats affected by hydropeaking, sound pressure levels in the lower frequencies (~0.0315 kHz) may increase by up to 30 decibels. Similarly, sound pressure levels of riffles increase by up to 16 decibels in the low to mid frequencies (~0.250 kHz). Overall, the findings of this thesis have a number of implications for river catchment management. Hydropower construction is taking place in some of the most ecologically sensitive areas of the globe, thus, this research provides a timely contribution to: (i) Provide a foundation for future research at catchment, regional and global scales. For instance, systematic conservation based planning is required to designate ‘no go’ areas to promote the long-term survival of biodiversity. Strategic positioning of future dams or reconfiguration of existing hydropower systems may reduce the combined impacts on biodiversity and GHG emissions without losing power capacity. (ii) Assess driving parameters of GHG emissions, critically appraise current predictive GHG emission models and use a process based approach to simulate ‘net’ emissions from a sub-tropical reservoir. Future reservoirs will sequester, mineralise and emit an increasing quantity of carbon to the atmosphere, and subsequently, will take a greater role in the global GHG budget. This research concludes that, in some cases empirical models may not be suitable for making robust estimations of future GHG’s from hydropower reservoirs. Combining the underlying carbon cycling processes within a process-based model allows the estimation of ‘net’ CO2 emissions from hydropower reservoirs. This approach may be integrated by catchment planners into the future lifecycle assessment of hydropower reservoirs. (iii) Characterise acoustic changes in underwater sound in rivers affected by hydropeaking. The findings emphasise that flow regulation by hydropower results in rapid changes to the amplitude and frequency spectrum of the riverine acoustic environment. These changes persist for longer periods than other forms of anthropogenic sound and may have implications for the whole biota. Thus, future studies should focus on measuring the behavioural and physiological impact on riverine organisms in order to develop guidelines for hydropower licensing.