[pt] A construção de Barragens de Enrocamento no Brasil tem se desenvolvido nas últimas décadas, por ser uma solução adequada para regiões onde há falta de solos finos e grande volume de escavações obrigatórias em rocha. Este desenvolvimento está relacionado tanto à quantidade de barragens construídas quanto ao incremento da altura das mesmas. A construção de protótipos de instrumentos para medição de deslocamentos neste tipo de barragem é de fundamental importância. Com a simulação das leituras em laboratório, torna-se possível implementar modificações no projeto, na construção, na instalação e na operação destes instrumentos, disponibilizando-se leituras mais acuradas e precisas, obtendo-se maior confiabilidade nos dados e, assim, informações mais consistentes sobre o comportamento das barragens. Além da elaboração de uma abrangente revisão bibliográfica sobre instrumentação geotécnica, foram estudados dois protótipos de instrumentos de medidas de deslocamento, Medidor Hidrostático de Recalques e Extensômetro Horizontal de Hastes Múltiplas. Ambos desenvolvidos no Laboratório de Engenharia Civil de Furnas, em Aparecida de Goiânia, estado de Goiás. Os resultados obtidos permitirão modificações na construção e instalação destes instrumentos. / [en] The number and height of rockfill dams in Brazil has been steadily growing, because rockfills constitute an adequate solution when the project requires a large volume of rock excavation and there is a lack of fine grained soils in the region. The development of new equipment for measuring displacements in these dams is of fundamental importance. Testing prototypes in the laboratory, under simulated field conditions, allows the researcher to implement modifications in the design characteristics and installation procedures for the instrument. As a result, measurements with higher accuracy and reliability are obtained and, consequently, higher safety for the dams. A comprehensive review of the literature on geotechnical instrumentation is presented. Two prototypes of displacement measuring devices have been studied and tested: a hydrostatic displacement cell and a multiple rods horizontal extensometer. Both were constructed and tested in the Civil Engineering Laboratory of Furnas, in Goiás, Brazil. The results and conclusions obtained will result in important modifications in the design and installation details of these instruments.

Cette thèse présente des travaux de deux natures différentes ; (1) l'étude approfondie des travaux de James Reason (Swiss cheese model) et (2) l'activité d'ingénierie d'un modèle (ECHO) pour l'étude des facteurs organisationnels et humains dans l'exploitation des barrages d'EDF. Ces travaux sont articulés autour de la question du rôle, de la valeur et de la place des modèles d'erreur humaine dans la gestion de la sécurité industrielle.Une revue de littérature montre que les dispositions de sécurité dans les barrages sont essentiellement techniques. Les considérations relatives au facteur humain, bien que prégnantes dans l'accidentologie, semblent faire défaut dans les pratiques. Constatant sa très large utilisation, nous présentons en détail le modèle de Reason. Nous mettons en lumière une « double » collaboration (peu documentée) entre recherche et industrie d'une part, sciences humaines et sciences de l'ingénieur d'autre part. Partant de cette double collaboration comme une condition de réussite à des évolutions culturelles de sécurité, nous présentons le processus d'ingénierie qui a permis la conception puis la mise en place d'un modèle facteur humain dans les études de dangers de barrages d'EDF. Nous tentons enfin de mesurer et de présenter les effets produits par ECHO sur les représentations et les pratiques. La discussion porte sur l'intérêt et les modalités de double collaboration dans la sécurité industrielle et espère contribuer à un recadrage du débat sur la nature et la valeur des modèles. / This thesis presents two different works: (1) an in-depth study of James Reason's work (Swiss cheese model) and (2) the engineering activity of a model (ECHO) of organizational and human factors in operation of EDF's dams. These works are articulated regarding the role, value and place of human error models in industrial safety management.A literature review shows that dams' safety is mainly based on technical issues. The considerations relating to human factors, although pervasively present in the accidents, seem to be lacking in practice. After its wide use, we present in detail the Reason's model. We highlight a double collaboration (poorly documented) between research and industry on the one hand, Humanities and engineering Sciences on the second hand. Based on this dual partnership as a success condition for efficient safety culture developments, we present the engineering process associated with the design and the implementation of a human factor model in EDF dams' hazards study. Finally, we try to measure and report the effects produced by ECHO on the representations and practices.The discussion focuses on the interest and modalities for double collaboration in industrial safety and, therefore hopes to contribute to reframe the debate on model's nature and value.

Hydrological modeling, like runoff modelling for flood prevention, is based on digital elevation models (DEMs). The fact that the DEMs do not represent existing road culverts can lead to considerable hydrological misinterpretations. In order to overcome this limitation, a GIS method was developed to automatically adjust the elevation model, hydrologically enforcing the DEM, so that the results of hydrological modeling accounts for flow through culverts. The hydro-enforced DEM showed to better represent the drainage network than the former DEM when compared with the river map. The topographic wetness index is the most commonly applied topographic index and a good indicator of soil moisture distribution. It has been integrated into many hydrological models and pollution risk indices as well as into the prediction of wetland distribution. Using the hydro-DEM from the previous step and the soil map in conjunction with the TWI, an improved TWI was achieved, namely a soil-topographic wetness index (STI). The linkages between specific soil types and TWI or STI values were analyzed. They revealed a clear linkage between STI values and soil type based on the soil transmissivity (R2=0.77). However, the TWI values showed low correlations to the soil types (R2=0.02). As a specific application, both TWI and STI were tested for the detection of wetlands. Wetlands are important ecosystems which act as buffer zones by filtering pollutants and slowing floodwater. Being able to identify their distribution is important in landscape planning and ecology. A wetland threshold value was determined for each index and their results where compared with the wetland map from the property map (assumed as ground truth) and with the potential wetland area. Finally, a visual validation was performed with the use of an aerial photography. The results showed that the STI performed slightly better than the TWI for the detection of wetlands, detecting 3% more wetlands. The impact of the soil map on the topographic wetness index was therefore determined as positive.

Expanding anthropogenic development within the tropical forest biome is driving the loss of an irreplaceable global resource. Mega-diverse tropical forests are vital for regulating the global carbon cycle, and are essential for climate change mitigation. Today, over half of the world’s remaining tropical forest is degraded or regenerating secondary forest. Tropical forests are becoming increasingly fragmented through the expansion of agriculture and roads. Landscape-scale flooding of terrestrial habitats caused by dam construction is an emerging driver of habitat loss and fragmentation. Much attention has been paid to the long-term impacts of tropical forest fragmentation for biodiversity, ecosystem functioning, and carbon emissions. Most of our understanding of the impacts associated with habitat fragmentation originates from systems in which the habitat matrix surrounding remnant forest patches is another, albeit low quality, terrestrial habitat. However, dam-induced habitat fragmentation results in remnant terrestrial biological communities becoming isolated on islands within a water matrix. A water matrix presents the worst-case scenario for remnant habitat fragments. In Chapter 2 I synthesise the results of numerous studies reporting the responses of taxonomic groups to isolation on reservoir land-bridge islands, and uncover a globally-applicable pattern of extinction debt acting upon remnant biological communities on reservoir islands. All islands, regardless of taxonomic group, habitat type, or island area lose species as island isolation time increases. Moreover, I show that contrary to existing ecological theory, once terrestrial habitat becomes isolated within a water matrix, it is effectively too isolated for species losses to be buffered by metapopulation dynamics. Dam development is rapidly expanding in the largest remaining tract of intact tropical forest, the Amazon Basin. In Chapters 3 and 4 I study the Balbina mega-dam system in the central Brazilian Amazon. Here, I use detailed field inventories of trees and lianas on islands and in continuous mainland habitat to determine the impact of landscape-scale habitat fragmentation caused by reservoir creation on these taxonomic groups. I find that islands maintain tree communities at significantly lower densities, richness and diversity compared to continuous forest. Furthermore, tree communities on islands exhibit compositional divergence from those found in mainland continuous forest. Island tree assemblages are dominated by low-wood density species, and may be on a trajectory towards communities characteristic of early successional forests with reduced carbon storage capacity. In contrast, liana assemblages remain compositionally intact and are becoming increasingly dominant relative to trees. Thus, lianas appear robust to many of the negative impacts associated with landscape-scale habitat fragmentation. As insular tree communities continue to degrade through area- and edge-effects, lianas may become a key feature of this archipelagic landscape due to their competitive advantage over trees in disturbed forest habitats. Lianas significantly inhibit tree recruitment and carbon storage. Thus, findings from Chapters 3 and 4 provide strong evidence for additional, and currently unaccounted-for biodiversity and carbon impacts associated with tropical dams. As development of tropical forest regions increases, there is an urgent need to reconcile the need for resources with the need for ecosystem service provision, such as carbon storage, particularly as we attempt to mitigate the impacts of rising atmospheric carbon. Recent studies have shown that secondary tropical forests have the potential to rapidly uptake atmospheric carbon, and act as a powerful tool in climate change mitigation policy. Broad-scale estimates of secondary forest carbon uptake are currently based on above-ground biomass alone. In Chapter 5 I present carbon stock estimates of additional tropical forest carbon pools - soil and dead woody biomass - in secondary forests ranging from 40-120 years. I find that soil fertility (nitrogen concentration) is key in determining carbon storage in secondary forests, and that the stability of carbon stocks held in dead woody biomass increases with secondary forest stand age. I highlight the need to integrate detailed site-specific information into broad-scale predictive models of secondary tropical forest carbon sequestration. This thesis links ecological theory and landscape-scale field inventories, to provide new understanding of the long-term costs of tropical forest fragmentation for biodiversity conservation and carbon storage, and provides further evidence of the important role secondary tropical forests may play in carbon sequestration and climate change mitigation.

Les ouvrages hydrauliques – barrages et digues – sont des ouvrages de génie civil à risque. Leur rupture engendre des conséquences humaines et matérielles souvent dramatiques. Parmi eux, les barrages en remblai représentent une part importante du parc de barrages au niveau national comme mondial, auxquels s’ajoutent d’importants linéaires de digues en remblai fluviales et maritimes. La sécurité structurale de ces ouvrages est traditionnellement évaluée par des méthodes déterministes ou semi-probabilistes aux états-limites. Cependant, la réglementation française en matière d’ouvrages hydrauliques a récemment évolué en préconisant pour les grands barrages la réalisation d’études de dangers (EDD) basées sur les méthodes d’analyse de risques et impliquant l’utilisation de démarches probabilistes. Dans ce cadre, l’objectif principal de la thèse est de développer une démarche probabiliste pour l’évaluation de la fiabilité structurale des ouvrages hydrauliques en remblai vis-à-vis du mécanisme de glissement, qui constitue l’état-limite conditionnant la géométrie de ces ouvrages. Le développement d’une telle démarche nécessite de traiter trois questions scientifiques principales : · l’élaboration d’un modèle hydromécanique pour l’évaluation déterministe de la stabilité de l’ouvrage vis-à-vis du mécanisme de glissement ; · la modélisation probabiliste de la variabilité spatiale des propriétés mécaniques et hydrauliques des matériaux constituant le remblai ; · le couplage mécano-fiabiliste intégrant les modèles de variabilité spatiale au modèle hydromécanique. De nombreux travaux de recherche ont été réalisés sur ces questions et sont disponibles dans la littérature scientifique. Cependant, ils ne traitent qu’une partie des aspects de la problématique globale d’évaluation de la fiabilité et l’absence de recherches intégratrices est à déplorer. Notre travail, propose une démarche méthodologique complète intégrant l’ensemble des questions scientifiques, en mettant en oeuvre des démarches de modélisation hydraulique et mécanique s’appuyant sur des données réelles disponibles sur un barrage en remblai. La démarche générale développée est appliquée à un barrage bien documenté servant de cas d’étude. Le modèle hydromécanique utilise la méthode des éléments finis et est développé avec le code élément finis Cast3M ouvert et compatible avec un usage en recherche scientifique. Le modèle développé permet le calcul du facteur de sécurité de l’ouvrage par la méthode de réduction de paramètres en intégrant un champ de pressions interstitielles calculé en régime transitoire. La variabilité spatiale des paramètres des matériaux du remblai est modélisée à partir d’une analyse géostatistique des mesures de contrôle de compactage sous forme de champs aléatoires qui sont intégrés au modèle éléments finis. Un couplage mécano-fiabiliste entre le code de calcul Cast3M et le logiciel de fiabilité OpenTURNS permet au final de propager les incertitudes et d’évaluer la fiabilité de l’ouvrage. / Hydraulic works – dams and dikes – are risky civil engineering structures. Dramatic consequences in terms of human and material losses may be induced by their failure. Embankment dams represent an important part of the whole dams in France and the majority of dams worldwide, without considering the important lengths of fluvial and coastal dikes. The structural safety of such structures is traditionally evaluated with limit-state deterministic or semi-probabilistic methods. Nevertheless, French regulations regarding hydraulic works has recently evolved and now impose for all large dams the realization of risk assessment studies based on probabilistic approach. In this purpose, the principal objective of this thesis work is to develop a probabilistic approach to evaluate earth dam reliability concerning the sliding mechanism, which is one of the designing limit-state of such structures. Three scientific issues have to be treated for developing such approach: · elaboration of an hydro-mechanical model for the dam deterministic evaluation towards sliding mechanism; · probabilistic modeling of hydraulic and mechanical soil properties spatial variability; · mechanical-reliability coupling with integration of the spatial variability representations in the hydro-mechanical model. Some research studies already exist on these issues. However these works concern generally only a part of the general issue: the lack of global work is to be deplored. Our work proposes a global methodologic approach taking into account the whole scientific issues and applying hydraulic and mechanical modeling approaches based on real data available in the earth dam. The developed approach is then applied on a dam case study. Hydro-mechanical model uses finite element method and is developed with the user-free code Cast3M which is compatible for a research use. This code allows the safety factor calculation through the strength reduction technique with integration of the pore pressures field estimated in transient condition. The spatial variability of embankment properties is represented with random fields based on a geostatistical analysis of construction controls data. These random fields are then integrated into the finite element model. A coupling between the physical finite element code Cast3M and the reliability software OpenTURNS finally allows assessing the uncertainties propagation and the reliability evaluation of the studied dam.

Numerical analyses are presented in this thesis to address potential stability problems that may occur during gradual raisings and under seismic loading conditions of Aitik tailings dam in northern Sweden. The dam is mainly raised using upstream construction method. It is planned to raise the dam gradually in several stages. Two dam parts were studied. The first dam part is a straight dam portion, and the second dam part is a corner. The main concerns associated with future raisings of the straight dam part were: (i) the stability of the dam could be affected by an increase in excess pore pressures during sequential raisings, (ii) how to gradually strengthen the dam by using rockfill berms as supports in such a way that required slope stability can be achieved with a minimum volume of rockfill berms, and (iii) if the dam is subjected to seismic loading, whether or not an increase in excess pore pressures could lead to extensive liquefaction which may cause a failure. The problems related to the dam corner were that tension zones and/or low compression zones could develop because of the horizontal pressure of the stored tailings on the inside of the curvature of the dam corner.Numerical analyses were conducted on both the dam parts using finite element method. Two dimensional (2D) plane strain finite element model was utilized to analyse the straight dam. The dam corner was analysed with both the three dimensional (3D) finite element model, and the 2D axisymmetric finite element model. Coupled deformation and consolidation analyses, and slope stability analyses were performed on both the dam parts to simulate gradual raisings, and to compute safety factors. In addition to this, dynamic analyses were carried out on the straight dam part to evaluate the potential for liquefaction, and seismic stability of the dam. The seismic behaviour of the dam was analysed for two cases: (i) a normal case (earthquake of 3.6 Swedish local magnitude), and (ii) an extreme case (earthquake of 5.8 moment magnitude).The results of the straight dam part, with only previously existing rockfill berms, indicate that stability of the dam was reduced due to an increase in excess pore pressures during raisings. Rockfill berms were utilized as supports to raise the dam with enough safety. An optimization technique was utilized to minimize the volume of rockfill berms. This technique could result in significant saving of cost of rockfill berms.The results of the dam corner show that tension zones and/or low compression zones were located on the surface of the dam corner, mainly above the phreatic level. It is interpreted that there is no risk of internal erosion through the embankments because no seepage path occurs above the phreatic level, and a filter zone exists along the slope of the dam. It is suggested to gradually strengthen the dam corner with rockfill berms. The results of the 2D axisymmetric analyses of the dam corner were in a fairly good agreement with those of the 3D analyses. This implies that the 2D axisymmetric analyses are valid for this dam corner. This is an important finding as 2D axisymmetric analyses require much less computational time compared to 3D analyses.The results of the dynamic analyses performed on the straight dam (including additional rockfill berms) suggest that, for the extreme case, liquefaction could occur in a limited zone that is located below the surface near the embankments. For both the normal and the extreme case, (i) seismically induced displacements seem to be tolerable, and (ii) the post seismic stability of the dam is considered to be sufficient.The findings of this study have been practically applied to the Aitik tailings dam. In general, the modelling procedure and the optimization technique to minimize volume of rockfill berms, presented in this study, could be applied to other tailings dams. / Godkänd; 2013; 20130513 (muhauc); Tillkännagivande disputation 2013-05-20 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Muhammad Auchar Zardari Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Avhandling: Numerical Analyses of Stability of a Gradually Raised Tailings Dam Opponent: Professor Daichao Sheng, School of Engineering, The University of Newcastle, New South Wales, Australia Ordförande: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Torsdag den 13 juni 2013, kl 10.00 Plats: F1031, Luleå tekniska universitet

The main purpose of this study is to determine the difference in water quality of the rivers between the Katse and Vaal Dams (Wilge River and Vaal Dam reservoir sub-catchments) after the construction of the Lesotho Highlands Water Project. These rivers include the Ash, Liebenbergsvlei and Wilge Rivers. The temporal changes in water constituents, namely: electrical conductivity, chemical oxygen demand, pH, turbidity, ammonia, calcium, manganese and chlorophyll a, at selected water sampling points were analysed to clarify if Katse Dam water has had any impact on the water quality of the Ash, Liebenbergsvlei and Wilge Rivers and the Vaal Dam. The water quality was studied over an eleven-year period from November 1994 until December 2005. This includes a five-year period prior to, and a six-year period following the completion of the Katse Dam. The Ash, Liebenbergsvlei and Wilge Rivers fall within the Wilge sub-catchment, and the Vaal Dam falls within the Vaal Dam reservoir sub-catchment. Both the aforementioned sub-catchments form part of the Vaal River catchment. Physical, chemical and microbiological sampling results were obtained from Rand Water. The results were compared with the in-stream water quality guidelines as set by the Vaal Barrage Catchment Executive Committee. The results of the selected constituents were depicted visually in the form of graphs. Trends in the constituents over the period were then determined. The graphs were divided into two sections namely, pre-Katse Dam (before 1999) and post-Katse Dam (1999 to 2005). Differences in water quality before and after the construction of the Katse Dam were determined from sampling and chemical analysis at six locations, and hence evaluations were made whether the release of Katse Dam water has had a significant effect on the water quality results in the Vaal River System. The water quality results with respect to the different water constituents illustrated a distinct change in water quality over the period. Northwards, towards the Vaal Dam, the difference in water quality became less apparent. Sampling points throughout the study area experienced decreases in: electrical conductivity, chemical oxygen demand, turbidity, ammonia, and manganese. Hence, the release of Katse Dam water into the Vaal River system has had a ii positive influence on the water quality and thus changed the riverine environments in the Vaal River system. The high quality water from the Katse Dam that enters the Vaal River system thus initially increases the quality of the water in the recipient system with a lesser effect downstream. The result is an improvement of water quality in the upper reaches of the Vaal River system and no significant influence on the Vaal Dam itself. However, the change in water quality may have a detrimental effect on the river environment as a result of the increased volume of water entering the system and the resultant soil erosion, which serves for further studies. Consequently, the advantageous high quality water from the Lesotho Highlands is not being optimally utilised, hence the proposed recommendation by Rand Water to alternatively transfer Katse Dam water via a gravity-fed pipeline to the Vaal Dam thereby receiving the full benefit of high quality water, leaving river environments unaltered and possibly lowering purification costs. / Prof. J. T. Harmse Prof. H. J. Annegarn

A represa das Antas e represa Bortolan fazem parte da Sub-Bacia Hidrográfica do Ribeirão das Antas, sendo que a primeira sofre impacto de uma mineradora de urânio (UTM/INB), uma vez que recebe despejos de efluentes radioativos tratados procedentes de DAM, já a represa Bortolan recebe maior influência da malha urbana de Poços de Caldas. O objetivo do presente estudo foi analisar a diversidade da comunidade zooplanctônica, bem como realizar a caracterização física e química da UTM/INB e represas das Antas e Bortolan. Diferenças em relação às condições físicas, químicas e a comunidade foram verificadas entre os ambientes. Na UTM/INB as condições químicas da água apresentaram-se não favoráveis ao desenvolvimento do zooplâncton. A represa das Antas apresentou condições ambientais intermediárias entre a UTM/INB e represa Bortolan, devido provavelmente ao lançamento de efluentes em condições inadequadas pela UTM/INB. Na represa Bortolan as concentrações de nutrientes e clorofila a explicaram a maior densidade e, portanto, a maior diversidade das espécies zooplanctônicas. / The Antas and Bortolan Dams are part of the Ribeirão das Antas Hydrographical Sub-Basin, being that the Antas Dam suffers impact from a uranium mining (UTM/INB), once it receives discharges of treated radioactive effluents derived from DAM, while Bortolan Dam suffers greater influence from the urban area of Poços de Caldas. The objective of the current study was to analyze the zooplanktonic community\'s diversity, as well as to perform the physical and chemical characterizations of UTM/INB and Antas and Bortolan Dams. Differences related to the physical and chemical conditions and the community were verified among the environments. In UTM/INB, the water\'s chemical conditions were not favorable to zooplankton development. The Antas Dam presented intermediate environmental conditions between UTM/INB and Bortolan Dam, probably due to the release of effluents in inadequate conditions, done by UTM/INB. In Bortolan Dam, the concentrations of nutrients and chlorophyll a have justified the higher density and thus, the greater diversity of zooplanktonic species.

Evaluating the safety of unreinforced concrete structures, such as concrete dams, requires an accurate prediction of cracking. Developing a suitable constitutive material model and a reliable computational procedure for analysing cracking processes in concrete has been a challenging and demanding task. Although many analytical methods based on fracture mechanics have been proposed for concrete dams in the last few decades, they have not yet become part of standard design procedures. Few of the current research findings are being implemented by practising engineers when evaluating dam safety. This research is focused on the development of a suitable crack modelling and analysis method for the prediction and study of fracturing in concrete gravity dams, and consequently, for the evaluation of dam safety against cracking. The research aims to contribute to the continuing research efforts into mastering the mechanics of cracking in concrete dams. An analytical method for the purpose of establishing a crack constitutive model and implementing the model for the fracture analysis of concrete structures, in particular massive concrete gravity dams under static loading conditions, has been developed, verified and applied in the safety evaluation of a concrete gravity dam. The constitutive material model is based on non-linear fracture mechanics and assumes a bilinear softening response. The crack model has various improved features: (1) an enhanced mode I bilinear strain-softening approach has been put forward; (2) a new formula for bilinear softening parameters has been developed and their relation with linear softening has been outlined; (3) the influence of bilinear softening parameters on the cracking response has been studied; and (4) an enhanced modification to the shear retention factor which depends on the crack normal strain is included. The material model has been incorporated into a finite element analysis using a smeared crack approach. A sub-program was specially coded for this research. The validity of the proposed cracking model and the computational procedure developed for the purpose of analyzing the tensile fracture behaviour of concrete structures has been confirmed by verification on various concrete structures, including beams, a dam model and actual gravity dams. The crack modelling technique developed was successfully used in evaluating the safety of an existing concrete gravity dam in South Africa and adequately predicted the cracking response of the dam structure under static loadings. The main conclusions drawn are as follows: <ul><li>Both mode I and mode II fracture have been modelled successfully.</li> <li>The proposed bilinear softening model remains relatively simple to implement but significantly improves on predicting the softening response of “small-scale” concrete structures.</li> <li>Both plane stress and plane strain crack analyses have been considered and can be confidently adopted in two-dimensional applications.</li> <li>The proposed method is mesh objective.</li> <li>The crack modelling method developed can correctly predict the crack propagation trajectory and the structural behaviour with regard to fracturing in concrete structures.</li> <li>If not considering shear stress concentration near the tip of a crack, constitutive crack analysis normally indicates a higher safety factor and a higher Imminent Failure Flood (IFF) than the classical methods in the analysis of concrete gravity dams for safety evaluation.</li></ul> / Thesis (PhD(Civil Engineering))--University of Pretoria, 2007. / Civil Engineering / PhD / unrestricted

There is a concern that the ecosystems around the world are suffering from fragmentation. Ecosystems such as rivers have lost their connectivity to a large extent due to hydroelectric dams with no or insufficient passways for the natural flow of organisms, matter and energy. The Atlantic salmon, Salmo salar, is anadromous, migrating up rivers to spawn as adults and downstream to the sea as juveniles to feed. Before entering the sea, juveniles go through a parr-smolt transformation which alters their behavior, morphology, and physiology. Using radio telemetry, we assessed how the degree of smoltification, in combination with migrational timing and the juvenile’s size, affected their migration. Overall migratory success was found to differ significantly across the range of smoltification, with more fully smoltified juveniles having the highest probability (94%) of reaching the sea. No relationship was found between smoltification status and average migrational speed or delays when passing a dam. Migrational timing was also correlated to migrational success, with earlier juveniles being 50 % more likely to reach the sea than those leaving 2-3 weeks later. All of the tagged juveniles (28) that passed the dam were delayed by an average of 1,32 km/h relative to their median speed in the river, and 18 of the juveniles made it down to the sea. No effect of migrational timing was found with average migrational speed or with dam delays however. Unexpectedly, larger lengths were correlated with slower average migration speeds and greater delays when encountering a dam. This new knowledge about the degree of smoltification and its relation to migration success can help river management to direct their efforts in the right direction to strengthen salmon populations. / Ekosystem som älvar och åar har i stor utsträckning förlorat konnektiviteten till följd av vattenkraftverk med otillräckliga passager för det naturliga flödet av organismer, materia och energi. Atlantlax Salmo salar är en anadrom fisk vars livscykel kräver att den vandrar mellan olika habitat. Den vandrar upp i vattendrag som vuxna för att leka och ut till havet som unga för att äta. De unga laxarna går igenom en utvecklingsprocess (smoltifiering) innan de simmar ut i havet vilket förändrar deras beteende, morfologi och fysiologi. Med hjälp av radiotelemetri bedömde vi hur graden av smoltifiering i kombination med timing och storlek påverkade deras nedströmsvandring. Vi såg en avsevärd skillnad inom dem olika smoltifierings graderna och en lyckad nedströmsvandring, de fullständigt smoltifierade fiskarna var mest sannolika att klara nedströmsvandringen (94%). Inget samband hittades mellan smoltifieringsgrad och genomsnittliga vandringshastigheten genom ån eller förbi ett vattenkraftverk. En lyckad nedströmsvandring var relaterad till tid och vi fann att de som vandrade tidigt hade 50% större chans att nå ut till havet än de som lämnade 2–3 veckor senare. Alla radiomärkta fiskar (28) som passerade vattenkraftverket vart försenade med -1,32 km/h jämfört med deras genomsnittliga hastighet, av 48 märkta fiskar klarade sig 18 ut till havet. Oväntat nog var längre längd relaterat till större förseningar både i medianhastighet och vid passage av en damm. Den här kunskapen om sambandet mellan smoltifieringsgrad och lyckad nedströmsvandring kan förbättra insatser som görs i åar och älvar för att optimera för djur och natur.