Ce travail porte sur la morphodynamique des bancs de galets alternés dans une rivière de montagne aménagée. Le site expérimental est un tronçon long de 8 km de la rivière Arc située dans les Alpes françaises. Une analyse des cartes historiques, des photos aériennes et des relevés topographiques montre que le lit de la rivière a évolué d’un style en tresse vers un lit rectiligne avec des bancs alternés contraints entre deux digues. Au milieu des années 1990, le lit de la rivière a été aplani pour former des profils trapézoïdaux. Cependant, les bancs alternés ont réapparu en moins de dixans. Une analyse des facteurs contrôlant leur formation est fournie. Les observations de terrain et l’analyse numérique 1D suggèrent que le motif de bancs alternés représente un état de quasi équilibre du tronçon. D’autre part, la topographie d’un sous-tronçon incluant un banc de galets aété mesurée 18 fois entre 2006 et 2012. Une méthodologie de construction des MNT basée sur leslignes directrices et incluant une estimation de l’erreur a été proposée pour une application aux litsde rivières. La technique de différenciation des MNT a été utilisée pour détecter les changements morphologiques du banc. Ainsi, la morphodynamique du sous-tronçon a été étudiée en la reliant aux principaux processus qui la contrôlent tels que l’hydrologie, les formes des hydrogrammes, la répartition des contraintes de cisaillement, les apports amont en sédiments et l’énergie du coursd’eau. La forme des hydrogrammes de crue ainsi que les apports en sédiments semblent être lesprincipaux facteurs influençant le bilan sédimentaire sur le site étudié. En outre, des modélisationsnumériques 2D hydro-sédimentaires ont été utilisées pour appréhender la dynamique du banc. Lessimulations ont révélé l’importance de l’interaction entre les sédiments fins et les galets sur ladynamique globale du banc. / The current research investigates the morphodynamics of gravel alternate bars in an engineeredmountainous river. The experimental site corresponds to an 8 km long reach of the Arc River, in the French Alps. An analysis of historical maps and recent aerial photographs and topographic campaigns shows that the original braided river bed has evolved to a straight bed with alternate bar system constrained within two embankments following two centuries of man-made engineeringprojects. In the mid 1990s the river bed was flattened to fit a trapezoidal cross-sectional design. However, alternate bars re-appeared in less than ten years. An analysis of the controlling factors of bar formation and evolution is provided. Field observation and 1D numerical analysis suggest that the alternate-bar pattern represents a quasi-equilibrium state of the river bed. A singlegravel bar within the reach was monitored 18 times from 2006 to 2012. A methodology of DTM construction based on breaklines is proposed for river beds and an error estimation is presented. DTM differencing technique was used to detect morphologic changes of the gravel bar. Therefore, the gravel bar and main channel dynamics were analyzed relative to main controlling processes suchas extreme hydrologic events, sediment supply, hydrograph shape, bed shear stress distribution andriver energy. Sediment supply and hydrograph shape appeared to be the main factors influencing the study site sediment budget. Moreover, 2D numerical modelling of water flow and sediment transport was performed. Sensitivity analysis was conducted to yield results in agreement with observations. Simulations revealed the relevance of the interaction between fine sediments and gravels on the bar dynamics.

I Sverige finns i dagsläget närmare 10 000 dammar i våra vattendrag. Dammar som har varit en viktig del i den svenska historien men som nu utgör ett hot mot att uppsatta miljömål nås. Dammarna fragmenterar effektivt vattendragen då de utgör vandringshinder för fisk och andra vattenlevande organismer.  På senare tid har problemen som dessa dammar skapat blivit högre prioriterat av myndigheter och beslutsfattare. För att uppnå EU:s miljökvalitetsnormer krävs åtgärder vid i stort sett samtliga av Sveriges dammar. Vid vissa av dessa får naturen kompromissa och fiskvägar av olika slag tas i anspråk. Total utrivning av dammar är i Sverige fortfarande en ovanlig åtgärd men som börjar få spridning. Utrivning har visat sig vara det mest ekonomiska alternativet samtidigt som det bästa för miljön då det återställer inte bara konnektiviteten utan även vattendragets naturliga geomorfologiska processer och flödesdynamik.  I denna studie har konsekvenserna av en avsänkning av Dragby kvarndamm i Björklingeån undersökts. Studien har genomförts genom att sammanväga data från biotopkartering, elfiske samt en hydraulisk modellering i HEC-RAS. Den hydrauliska modelleringen visade hur flödesförhållanden och fallhöjd kommer fördela sig vid en potentiell avsänkning av Dragby kvarndamm. Tillsammans med övriga undersökningar kunde en sammanvävd bild av konsekvenserna av en avsänkning formas. Vid en avsänkning kommer vattenytan sänkas med 1-1,7 m och inga nya strömsträckor kommer att bildas. Trots detta tyder elfisket och biotopkarteringen på att en avsänkning kommer att gynna arter som till exempel lake. En avsänkning kan därav bidra till ökad ekologisk status i Björklingeån. / Sweden is a country revolved around different types of water. With a coastline stretching around a big part of the country. The Baltic Sea which is fed with so much fresh water that it classifies as a brackish sea. The fresh water from Sweden originates from almost 100 000 lakes and nearly 30 000 rivers and streams. However, these different waterways are heavily impacted by approximately 10 000 artificial dams. Dams that for example block fish from migrating to their spawning grounds.  In the last couple of years, the problems revolving around dams have been put higher up on the agenda of politicians and authorities. Significant efforts need to be made to be able to reach the goals of the European Water Framework Directive. Those efforts include building different kinds of fish passage solutions around dams, but also removing dams that no longer have a purpose. Dam removal is often the most cost-effective solution and at the same time the one with most ecological benefits.    In this study, the consequences of a removal of the Dragby mill dam have been investigated. The study have been done by collecting and combining data from habitat assessment, electrofishing and hydraulic modeling in HEC-RAS. The hydraulic modelling showed that the water level upstream of the dam will decrease with approximately 1-1.5 m if the dam is removed.  Simulated water velocities indicate that no rapids and stream habitat suitable for trout will immerse if the dam is to be removed. Nonetheless, the combined information suggests that a dam removal would most likely benefit other species such as the threatened burbot. Therefore, a removal of Dragby mill dam could result in a ecological boost for river Björklingeån.

MEnv.Sc / Department of Geography and Geo-Information Sciences

The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites. A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin. A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake. An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique. / Det ökande intresset för att producera elektricitet från förnybara energikällor har lett till en satsning på forskning inom området marin strömkraft, främst när det gäller tidvattenströmmar och tidvattenturbiner för fritt strömmande vatten. Tidvatten har fördelen att vara förutsägbar årtionden i förväg. Dock så är tidvattenresursen periodisk och varierar lokalt vilket påverkar effektuttaget från ett kraftverk. Variationerna beror till största delen på fyra aspekter: antal hög- och lågvatten per dag, tidvattencykeln, djupförhållanden på platsen (batymetri) och vädereffekter. Varje potentiell plats är unik, vattnets hastighetsfält påverkas i hög grad av lokal batymetri och turbulens. Därför krävs noggranna undersökningar för att karakterisera resursen. Att tillhandahålla hastighetsdata av hög kvalitet från mätningar är därför av stor betydelse. I denna avhandling har mätningar av flödeshastigheter utförts på tre typer av platser. En plats med tidvattenströmmar, belägen i en av alla fjordar längs Norges kust, har undersökts för sin resurspotential. Mätningar har utförts för att kartlägga resursens variation i både tid och rum. Resultaten visar att strömmar i storleksordningen 2 m/s återfinns i mitten av kanalen. Dessutom uppvisar flödet liten variation från huvudriktningen för både inkommande (flod) och utgående (ebb) flöden. Platsen har således potential för energiomvandling av fritt strömmande vatten. En modell föreslås som förutsäger strömmarnas maxhastighet från information om höjdskillnaden mellan ebb och flod och vice versa. En motsvarande modell kan ställas upp och användas på andra platser med liknande förhållanden som berörs av tidvatten, dvs. fjordinlopp som förbinder havet med en fjord eller en bassäng. En älv fungerar som en plats för experiment för ett marint strömkraftverk som har utvecklats vid Uppsala universitet och sjösatts i Dalälven, Söderfors. Flödeshastigheten på platsen regleras uppströms av ett närliggande vattenkraftverk, vilket gör platsen bra för att utföra experiment på prestandan av den vertikalaxlade turbinen i dess naturliga miljö. Turbinen har körts i jämnt flöde och mätningar har utförts för att karaktärisera vakens utbredning. En plats med havsströmmar var mål för en utredning av dess potential för att ge användbar förnybar energi. En mätningskampanj genomfördes för att kartlägga flödets variation både rumsligt och tidsmässigt. Emellertid visade sig platsen inte vara lämplig för energiomvandling utifrån användning av nuvarande teknik.

The effects of climate and environmental change are likely to exacerbate water stress in Africa over the next five decades. It appears obvious, therefore, that large river basins with considerable total renewable water resources will play a prominent role in regional cooperation to alleviate the pressure of water scarcity within Africa. However, managing water resources in the large river basins of Africa involves problems of data paucity, lack of technical resources and the sheer scale of the problem. These river basins are located in regions that are characterized by poverty, low levels of economic development and little food security. The rivers provide multiple goods and services that include hydro-power, water supply, fisheries, agriculture, transportation, and maintenance of aquatic ecosystems. Sustainable water resources management is a critical issue, but there is almost always insufficient data available to formulate adequate management strategies. These basins therefore represent some of the best test cases for the practical application of the science associated with the Predictions in Ungauged Basins (PUB). The thesis presents the results of a process-based hydrological modelling study in the Congo Basin. One of the primary objectives of this study was to establish a hydrological model for the whole Congo Basin, using available historical data. The secondary objective of the study was to use the model and assess the impacts of future environmental change on water resources of the Congo Basin. Given the lack of adequate data on the basin physical characteristics, the preliminary work consisted of assessing available global datasets and building a database of the basin physical characteristics. The database was used for both assessing relationships of similarities between features of physiographic settings in the basin (Chapters 3 and 4), and establishing models that adequately represent the basin hydrology (Chapters 5, 6, and 7). The representative model of the Congo Basin hydrology was then used to assess the impacts of future environmental changes on water resources availability of the Congo Basin (Chapter 8). Through assessment of the physical characteristics of the basin, relationships of similarities were used to determine homogenous regions with regard to rainfall variability, physiographic settings, and hydrological responses. The first observation that comes from this study is that these three categories of regional groups of homogenous characteristics are sensible with regards to their geographical settings, but the overlap and apparent relationships between them are weak. An explanation of this observation is that there are insufficient data, particularly associated with defining sub-surface processes, and it is possible that additional data would have assisted in the discrimination of more homogenous groups and better links between the different datasets. The model application in this study consisted of two phases: model calibration, using a manual approach, and the application of a physically-based a priori parameter estimation approach. While the first approach was designed to assess the general applicability of the model and identify major errors with regard to input data and model structure, the second approach aimed to establish an understanding of the processes and identify useful relationships between the model parameters and the variations in real hydrological processes. The second approach was also designed to quantify the sensitivity of the model outputs to the parameters of the model and to encompass information sharing between the basin physical characteristics and quantifying the parameters of the model. Collectively, the study’s findings show that these two approaches work well and are appropriate to represent the real hydrological processes of Congo Basin. The secondary objective of this study was achieved by forcing the hydrological model developed for the Congo Basin with downscaled Global Climate Model (GCMs) data in order to assess scenarios of change and future possible impacts on water resources availability within the basin. The results provide useful lessons in terms of basin-wide adaptation measures to future climates. The lessons suggest that there is a risk of developing inappropriate adaptation measures to future climate change based on large scale hydrological response, as the response at small scales shows a completely different picture from that which is based on large scale predictions. While the study has concluded that the application of the hydrological model has been successful and can be used with some degree of confidence for enhanced decision making, there remain a number of uncertainties and opportunities to improve the methods used for water resources assessment within the basin. The focus of future activities from the perspective of practical application should be on improved access to data collection to increase confidence in model predictions, on dissemination of the knowledge generated by this study, and on training in the use of the developed water resources assessment techniques.

I Sverige finns cirka 2000 vattenkraftverk men endast 10 procent har någon form av omlöp eller annan lösning (Risinger, 2012). Nya, strängare regler håller nu på att införas. Sedan 2014 finns en gemensam strategi från Energimyndigheten och Havs- och vattenmyndigheten för åtgärder i svensk vattenkraft (Risinger, 2014). En godkänd fiskväg är ett av kraven.Särskilt den småskaliga vattenkraften (energitillförsel under 10 MWh enligt Risinger (2012)) drabbas. Deras intäkter står många gånger i proportion till energiproduktionen och därmed saknas ofta de ekonomiska förutsättningarna för en fiskväg. Vidare kommer en del av vattnet, och därmed potentiella inkomster, att gå förlorade. Den här undersökningen syftar till att utröna vad ett omlöp får för konsekvenser i form av effektförluster. Det är naturligtvis omöjligt att komma fram till ett universellt svar. Istället mäts förlusterna hos ett specifikt mindre verk som redan har ett omlöp: Åby vattenkraftverk som ägs och drivs av Växjö kommun. Metoden som används är traversering i kombination med hydroskopisk flygel. Sedan tidigare finns beräknade värden från kommunen för flödet i omlöpet. Dessa jämförs med undersökningens uppmätta värden. Undersökningen visar att vid normalt vattenstånd (165,13 MÖH) flödar 167 ± 10 l/s vatten genom omlöpet. Detta är ett 70 l/s större flöde i jämförelse med kommunens beräknade värde. Förklaringar till den skillnaden ges av mätfel då djupet mättes och att inloppet hade byggts om mellan kommunens beräkningar och utförda mätningar. Även den formel som användes då de beräknade värdena togs fram föreslås som en tänkbar felkälla. 167 ± 10 l/s innebär ett bortfall om 4,2 ± 0,3 kW potentiell effekt. / There are around 2000 hydropower plants in Sweden, but only 10 percent of them has a bio channel, fishway or equivalent solution (Risinger 2012). New, more strict rules are now about to be introduced. Since 2014 there is a mutual strategy from the two Swedish authorities ”Energimyndigheten” and ”Havs- och vattenmyndigheten”, which demands multiple actions from Swedish hydropower. (Risinger, 2014). An approved fishway is one of these.The small-scale hydropower plants (plants who produce less than 10 MWh according to Risinger (2012)) are especially affected from this. Their income is proportional to their production and therefore they’ll usually lack the economical ability to build a fishway. Furthermore, a part of the streaming water (which otherwise would equal income) will get lost. This study aims to decide the loss of effect a fishway causes. Of course, it is impossible to derive a universal answer. Instead the losses are measured at a specific smaller plant that already has a fishway: Åby hydropower plant that is owned and operated by Växjö municipality. Method being used is traversing in combination with a turbine flow meter. There are already calculated flows made by the municipality. These values will be compared with the measured values. The study shows that at a normal water level (165,13 m.a.sl) 167 ± 10 l/s of water is streaming through the fishway. This is a 70 l/s bigger flow in comparison with the municipality’s calculations. An explanation to this difference is given by measurement errors when the depth was measured, that the intake had been modified between when the calculations was being made and when the study’s measurements took place. Also, the formula being used for the calculated values is proposed as a possible source of error. 167 ± 10 l/s will result in a loss of 4,2 ± 0,3 kW potential effect.

För att uppskatta influensområdet till följd av skyddsinfiltartion finns ett antal analytiska modeller att tillämpa. Dessa modeller tar hänsyn till parametrar så som hydraulisk konduktivitet och magasinkoefficient, men de följer också med en rad antaganden som i praktiken inte kan uppfyllas. En alternativ tillvägagång för att bestämma influensområdet är därför med hjälp av numeriska modeller, som i större grad kan göras platsspecifika. Numeriska modeller är till följd av detta mer tidskrävande och behöver mer indata. I denna studie undersöktes vilken metod som är bäst lämpad för att bestämma skyddsinfiltrationens influensområden för en fallstudie i Bromstens industriområde, belägen cirka 15 km nordväst om Stockholm centrum. Två numeriska modeller med varierande underlag av platsspecifika data utvecklades över områdets geologi och grundvattenmagasin för att kunna simulera grundvattennivåer med och utan infiltration. Utöver detta beräknades influensområdet med fyra analytiska modeller. Modellerna testades sedan utifrån olika scenarion, där såväl dataupplösning som den platsspecifika kännedomen över området stegvis ökades. Platsspecifika data tillkom till följd av geotekniska undersökningar och hydrogeologiska tester. Studien ämnar även att besvara vilken data som är av störst vikt för att bestämma influensområdet med de analytiska respektive numeriska modellerna samt vilka skillnader som uppstår mellan analytiskt beräknade influensområden och numeriskt simulerade influensområden. Resultaten visar att de numeriska modellerna i huvudsak är känsligast med avseende på den hydrauliska konduktiviteten, samt att den enklare numeriska modellen är känslig för magasinkoefficienten, något som indikerar att denna modell inte uppnår jämvikt i enlighet med vad som observerats i fält. Utöver detta stod det klart att vattenavgivningstalet inte hade någon nämnvärd inverkan på resultaten. Bland de analytiska modellerna råder den största känsligheten i magasinkoefficienten, följt av konduktiviteten. För Sichardts formel, som inte tar hänsyn till magasinkoefficienten var konduktiviteten den känsligaste parametern. Akvifärens mäktighet, vilken reviderades mellan scenario 2 och 3, hade ingen betydande inverkan på de analytiska modellerna. Vidare visade infiltrationstestet på stora skillnader i skyddsinfiltrationens influensområde med avseende på de olika modellerna och dataunderlaget. Den minsta avvikelsen mätt i residualer observerades för den komplexa numeriska modellen under scenario 4, vilket motsvarar det scenario då dataunderlaget var som störst. Trots att detta scenario tillsammans med modell anses vara det dyraste fallet, anses detta vara det bästa och samtidigt mest tillförlitligt metoden för att uppskatta skyddsinfiltrationens influensområde. / To evaluate the area of influence due to artificial infiltration several analytical models are available. Some of the parameters taken into account by these models are the hydraulic conductivity and storage coefficient, but with these models some assumptions, which in reality cannot be fulfilled, are made. An alternative approach to evaluate the area of influence is therefore with numerical models, which in a greater extent account for the site-specific conditions. Due to this, numerical models are more time consuming and require more input data. This project aims to investigate the most effective approaches to evaluate the area of influence due to artificial infiltration for a case study in Bromsten, located 15 kilometers northwest of Stockholm. Two numerical models, with different background data due to the extent of site knowledge, were developed to represent the site's geological settings and groundwater properties to simulate the groundwaterlevels with and without infiltration. Moreover the area of influence were calculated with four analytical models. All of the models were then applied on four different scenarios, in which the data resolution and the site knowledge increased. Site-specific data was added as a result of geological surveys and hydrogeological tests. The study also aims to answer which data is most important in order to determine the area of influence with analytical and numerical models and what differences there are between the analytical solutions compared with the numerical solutions. Among the methods investigated, constructing a more complex model with data from scenario 4, the scenario with the greatest data supply, resulted in the most reliable results and was therefore the best method and the method to choose for this case-study. Other results indicated that the numerical models first of all are sensitive to the conductivity and that the more simpel numerical model is sensitive to the storage coefficient as well. The last result shows that this model does not reach the steady state conditions as observed in field, which highlights the importance of goetechnical investigation for the numerical models. Moreover none of the numerical models were sensitive to the specific yield. Among the analytical models the storage coefficient was the most important followed by the conductivity. For one of the analytical models (Sichardts formula) the conductivity was the most sensitive parameter. The thickness of the aquifer had no significant impact on the analytical models.

In the pursuit of low-carbon, renewable energy sources one option with great potential in the UK is tidal energy. Specifically the proposed construction of the Swansea Bay Tidal Lagoon (SBTL) in South Wales has become one such discussed option. With a potential net annual output of 400 GWh and a 120-year lifetime the scheme represents a long-term and large-scale electricity production option. An assessment of carbon emissions and embodied energy (EE) of the lagoon’s life cycle was carried out. Total lifetime carbon emissions for the SBTL are in the region of 470,000 tCO2e and EE was found to be around 7,800 TJ. The assessment shows that the SBTL has significantly lower emissions per year than the existing National Grid mix and with emissions of around 0.01 kgCO2e/KWh is significantly lower than the UK emissions target of 0.07 kgCO2e/KWh. Energy payback of the SBTL was found to be in the region of 5.5 years. The use of dredged ballast infill sourced from within the area of the lagoon plays an important role in keeping emissions and energy use low; and is a key consideration when planning future tidal lagoon structures.

The main objective of wave energy converters (WECs) is to ensure reliable electricity production at a competitive cost. Two challenges to achieving this are ensuring an efficient energy conversion and offshore survivability.         This thesis work is structured in three different sections: Control and maximum power optimization, forces and dynamics analysis in extreme wave conditions, and statistical modeling of extreme loads in reliability analysis.        The need for prediction and future knowledge of waves and wave forces is essential due to the non-causality of the optimal velocity relation for wave energy converters. Using generic concepts and modes of motion, the sensitivity of the prediction horizon to various parameters encountered in a real system is elaborated. The results show that through a realistic assumption of the dissipative losses, only a few seconds to about half a wave cycle is sufficient to predict the required future knowledge for the aim of maximizing the power absorption.          The results of a 1:30 scaled wave tank experiment are used to assess the line force and dynamic behaviour of a WEC during extreme wave events. Within the comparison of different wave type representations, i.e. irregular, regular and focused waves, of the same sea state, the results show that not all the wave types deliver the same maximum line forces. As a strategy of mitigating the line forces during extreme wave events, changing the power take-off (PTO) damping may be employed. With consideration of the whole PTO range, the results indicate an optimum damping value for each sea state in which the smallest maximum line force is obtained. Although wave breaking slamming and end-stop spring compression lead to high peak line forces, it is possible that they level out due to the overtopping effect. Waves with a long wavelength result in large surge motion and consequently higher and more damaging forces.         On the investigation of reliability assessment of the wave energy converter systems, computing the return period of the extreme forces is crucial. Using force measurement force data gathered at the west coast of Sweden, the extreme forces are statistically modelled with the peak-over-threshold method. Then, the return level of the extreme forces over 20 years for the calm season of the year is computed.