Cette thèse présente une étude de la dynamique des plages sableuses ouvertes dominées par la houle, au travers d’une base de données originale, couvrant une période de 29 mois, et composée de 150 levés DGPS couvrant 750m de linéaire côtier, donnant accès à la morphodynamique du site de Biscarrosse à différentes échelles de temps. Dans un premier temps, l’analyse du jeu de données à l’échelle des événements (tempêtes et successions de tempêtes appelées clusters) nous a permis de montrer que la réponse des plages sableuses aux clusters ne résulte pas de la somme des impacts induits par chaque tempête d’un cluster. Ainsi, l’effet cumulé des clusters, rapporté sur d'autres sites dans la littérature, n’est ici pas vérifié. L'impact de l’enchainement des tempêtes a également été étudié et il en résulte que lors d’un cluster, un changement des conditions hydrodynamique, à savoir, une augmentation des hauteurs de vagues et/ou du niveau d’eau, est nécessaire pour que la tempête suivante ait un impact érosif significatif sur le système. Dans un second temps, nous avons étudié la dynamique saisonnière du système plage/dune, que ce soit la saison hivernale ou estivale, dans le but de mettre en relief les principaux processus impliqués à cette échelle. Nos travaux montrent que la réponse hivernale de la plage ne dépend pas uniquement des conditions énergétiques et du profil pré-hivernal de la plage, mais également du séquençage des événements, comme lors d'un cluster. Mes travaux confirment également la nécessité de prendre en compte de nombreux paramètres dans l’étude de la dynamique hivernale des littoraux sableux : les conditions hydrodynamiques, le séquençage des évènements érosifs mais également reconstructifs, en particulier le ré-engraissement post-évènement, les transports sédimentaires cross-shore et longshore, ainsi que la position de la barre interne et des courants d’arrachements. La saison estivale est, quant-à-elle, marquée par la reconstruction de berme. Elle semble être liée à la fois aux conditions hydrodynamiques et aux caractéristiques des barres sableuses. L’étude de deux étés et deux hivers successifs a ainsi permis d’identifier les interactions entre les saisons et l’impact de la saison hivernale sur l’estivale, et l’influence de la dynamique événementielle sur la dynamique saisonnière. Elle a aussi permis de mettre en relief l’impact de l’urbanisme et des stratégies d’aménagement dans la réponse du système, à différentes échelles de temps. / This thesis presents a study of an open sandy beach wave-dominated, based on an original dataset, covering 29 months and composed by 150 DGPS surveys recorded along 750m of sandy shore, giving an access to the morphodynamic of Biscarrosse beach at different timescales. In a first time, event scale analysis showed that sandy beach response to clusters is not the result of the sum of the impact generated by each storm of a cluster on the system. Thus, the cumulated effect of clusters, described in the literature is not verified here. The storm sequencing has also been studied: during a cluster, changes in hydrodynamics conditions (rising of the water level and/or wave height) are necessary to provoke a significant erosion of the system by the second storm. In a second time, we studied the seasonal scale dynamic of the beach/dune system (winter and summer seasons) with the purpose to highlight dominant processes involved at this timescale. Beach response to winter seasons not only depends on hydrodynamic conditions and previous beach profile, but also on erosion/recovery event sequencing, post-storm recovery, cross-shore and longshore sediment transport, the barline characteristics and RIP current positions. Summer seasons are here defined by the berm reconstruction. Recovery periods are both linked to hydrodynamic conditions and barline characteristics (e.g. position and shape).The study of successive winters and summers allowed us to identify interactions between seasons, and the influence of short-scale dynamics on the seasonal one. It also emphasizes the impact of urbanism and coastal management strategies on the system’s response, at different timescales.

<p>Erozija predstavlja vrlo složen fizički proces u kome pod dejstvom atmosferskih sila nastaju&nbsp;destruktivne promene na povr&scaron;inskom sloju zemlji&scaron;ta. Kada je osnovni agens pokretanja&nbsp;čestica zemlji&scaron;ta vetar, govori se o eroziji vetrom ili eolskoj eroziji. Eolska erozija je&nbsp;specifičan proces koji se odvija u izrazito složenim okolnostima uzajamnog delovanja&nbsp;brojnih prirodnih i antropogenih faktora uglavnom stohastičkog karaktera, zbog čega je&nbsp;njeno istraživanje kompleksan naučno-istraživački problem.</p><p>Osnovni cilj sprovedenih istraživanja je bio da se na izabranim lokalitetima Deliblatske&nbsp;pe&scaron;čare, najvećeg i najznačajnijeg područja takve vrste u Evropi, uspostavi praćenje stanja&nbsp;procesa eolske erozije, odnosno neposrednim, sistematskim merenjima u terenskim&nbsp;uslovima ustanove količine eolskog nanosa &ndash; pronos nanosa, odrede dominantni pravci&nbsp;njegovog kretanja, defini&scaron;e njegova unutargodi&scaron;nja raspodela i utvrdi efekat vegetacije na&nbsp;smanjenje intenziteta eolske erozije. U toku četvorogodi&scaron;njeg perioda su po prvi put na&nbsp;ovim prostorima, na istom lokalitetu, sprovedena uporedna istraživanja eolske erozije&nbsp;primenom mehaničkih hvatača nanosa i metoda zasnovanih na praćenju aktivnosti&nbsp;radionuklida ve&scaron;tačkog porekla 137Cs u zemlji&scaron;tu, čije količine služe da se posebnim&nbsp;teorijskim modelima pretvore u gubitke zemlji&scaron;ta.</p><p>Praćenje procesa eolske erozije je vr&scaron;eno od 2006. do 2009. godine na lokalitetu Cvjićev vis,&nbsp;koji je izabran kao karakterističan, jer je pored centralne pozicije na Deliblatskoj pe&scaron;čari,&nbsp;obrađivani povr&scaron;inski sloj zemlji&scaron;ta bio bez za&scaron;tite od vetra. Paralelno sa ovim merenjima,&nbsp;na lokalitetu Dragićev hat &ndash; rasadnik, praćenje procesa eolske erozije vr&scaron;eno je na dva&nbsp;merna mesta u periodu od maja 2006. godine do aprila 2007. godine u uslovima postojanja&nbsp;za&scaron;titne uloge vegetacionog pokrivača i/ili vegetacionog pojasa. Merenje intenziteta eolske&nbsp;erozije je realizovano statičnim hvatačima nanosa tipa deflametar (dimanzija ulaznog&nbsp;otvora 10 x 10 cm) orijentisanih prema određenim pravacima (N, NE, E, SE, S, SW, W, NW) da bi potpuno definisali procese eolske erozije u vektorskom smislu. Kvantifikacija eolskog nanosa statičnim hvatačima stalno usmerenim prema određenim pravcima duvanja vetrova, omogućila je da se posebno evidentiraju i razlikuju &bdquo;sumarna&rdquo; produkcija eolskog nanosa (aritmetički zbir zahvaćenih količina nanosa iz svih hvatača) i &bdquo;rezultujuća&rdquo; količina eolskog nanosa (vektorski zbir), jer te veličine određuju pored ukupno pokrenute količine eolskog nanosa (produkcija nanosa) i delove nanosa koji se transportuju van granica&nbsp;erozionog polja (gubitak zemlji&scaron;ta), generalni pravac i smer njegovog kretanja.</p><p>Merenja eolske erozije na lokalitetu Cvijićev vis za period 2006-2009. godine su ukazala na&nbsp;značajne procese eolske erozije koji su definisani srednjim godi&scaron;njim pronosom nanosa od&nbsp;4,48 kg m-1. Ustanovljeno je da su ukupno zahvaćene količine nanosa na 8 hvatača bile &Sigma; =&nbsp;25,94, 20,92, 52,98 i 43,47 kg m-1 god-1, a pronosi nanosa &Sigma;&#39; (&Sigma;/8) = 3,24, 2,61, 6,62 i 5,43 kg&nbsp;m-1 god-1 u 2006., 2007., 2008. i 2009. godini respektivno.</p><p>Pronosi nanosa za period od maja 2006. do aprila 2007. godine su pokazali da je na<br />lokalitetu Cvijićev vis koga karakteri&scaron;u neobraslost i otvorenost povr&scaron;ine zabeležen najveći&nbsp;intenzitet eolske erozije na godi&scaron;njem nivou koji je 4 puta veći u odnosu na lokalitet&nbsp;Dragićev hat &ndash; rasadnik I koga karakteri&scaron;u neobraslost i za&scaron;tićenost povr&scaron;ine i 30,2 puta veći&nbsp;u odnosu na Dragićev hat &ndash; rasadnik II koga karakteri&scaron;u obraslost i za&scaron;tićenost zemlji&scaron;ta. Na&nbsp;lokalitetu Dragićev hat &ndash; rasadnik I intenzitet eolske erozije na godi&scaron;njem nivou je 7,5 puta&nbsp;veći od onog na lokalitetu Dragićev hat &ndash; rasadnik II.</p><p>Gubici zemlji&scaron;ta izraženi preko rezultujućih mesečnih pronosa nanosa (vektorski zbir)<br />iznosili su 5,13, 2,04, 4,31 i 11,94 kg m-1 u 2006., 2007., 2008. i 2009. godini respektivno, a&nbsp;procentualni udeo godi&scaron;njih gubitaka zemlji&scaron;ta u odnosu na ukupnu produkciju nanosa&nbsp;(aritmetički zbir) se kretao od 8,1% do 27,5. Rezultujući pravac kretanja eolskog nanosa u&nbsp;toku perioda istraživanja bio je jugoistok - severozapad (SE-NW) pod uticajem dominantnog&nbsp;jugoistočng vetra &bdquo;Ko&scaron;ava&rdquo;.</p><p>Iako se najpouzdanije determinisanje eolske erozije i njenih efekata postiže na osnovu&nbsp;neposrednih sistematskih merenja u realnim terenskim uslovima, počev od kraja pro&scaron;log&nbsp;veka se sve vi&scaron;e primenuju i metode praćenja radionuklida iz radioaktivnih padavina,&nbsp;posebno 137Cs, u cilju procene gubitaka zemlji&scaron;ta i prostornog rasporeda eolskog nanosa.</p><p>Ukupan broj uzetih uzoraka za metodu praćenja količina 137Cs je iznosio 149, od kojih je bilo&nbsp;9 inicijalnih uzoraka (3 profila po 3 uzorka), 14 osnovnih uzoraka (2 profila po 7 uzoraka), 32&nbsp;ostala uzorka (8 profila po 4 uzorka), 36 referentnih uzoraka (9 profila po 4 uzorka) i 58&nbsp;uzoraka uzetih zrakasto po određenim pravcima (N, NE, E, SE, S, SW, W, NW).</p><p>Osnovni uzorak na neobrađenom zemlji&scaron;tu sa detektovanom količinom 137Cs od 10.603,57&nbsp;Bq m-2 predstavlja uporednu vrednost, tj. lokalni padavinski ulaz 137Cs za modele&nbsp;pretvaranja količina 137Cs u količine izgubljenog zemlji&scaron;ta. Ovaj uzorak odslikava sredinu na&nbsp;kojoj su sprovedena istraživanja i predstavlja uporednu vrednost koja može korektno da&nbsp;defini&scaron;e procese eolske erozije.</p><p>Za pretvaranje izmerenih količina 137Cs u količine izgubljenog zemlji&scaron;ta po modelima&nbsp;Walling-a kori&scaron;ćen je najjednostavniji proporcionalni model (PM) za obrađena zemlji&scaron;ta, a&nbsp;najprimenjeniji model profilne distribucije (PDM) za neobrađena zemlji&scaron;ta u okviru najnovije verzije PC-kompatibilnog softverskog paketa u Microsoft Excel Add-Ins varijanti. Modelom profilne distribucije (PDM) za sve uzorake uzete na eksperimentalnom području dobijeni su prosečni gubici zemlji&scaron;ta od 207,06 t ha-1 god-1 i 2,10 cm. Model Basher &amp; Webb je dao prosečne gubitke zemlji&scaron;ta od 212,18 t ha-1 god-1 i 2,09 cm. Gubici zemlji&scaron;ta dobijeni modelima pretvaranja količina 137Cs u količine izgubljenog zemlji&scaron;ta ukazuju na značajne procese eolske erozije definisane jakom i ekscesivnom eolskom erozijom.</p><p>Za 58 uzoraka zemlji&scaron;ta uzetih na tačkama raspoređenih zrakasto po određenim pravcima&nbsp;(N, NE, E, SE, S, SW, W, NW), pored koncentracija i količina 137Cs i 210Pbex, određene su&nbsp;prostorne koordinate X i Y i nadmorske visine uzetih uzoraka. Prostorne distribucije&nbsp;koncentracija 137Cs i 210Pbex izražene su izolinijama, a kreiranani su i 3D prikazi u procentima&nbsp;odstupanja 137Cs i 210Pbex od lokalnog padavinskog ulaza 137Cs i 210Pbex. U oba slučaja je&nbsp;primetan dominantan uticaj pravca jugoistok - severozapad (SE-NW), odnosno jugoistočnog&nbsp;vetra &bdquo;Ko&scaron;ava&rdquo;.</p><p>Komparativna analiza ovih metoda je ukazala na validnost u kvantifikaciji procesa eolske&nbsp;erozije i mogućnost njihove primene u budućnosti, a dobijeni rezultati produkcije eolskog&nbsp;nanosa i gubitaka zemlji&scaron;ta su dali doprinos oceni stanja degradacije zemlji&scaron;ta i ugroženosti Deliblatske pe&scaron;čare.&nbsp;</p><p>&nbsp;</p> / <p>Erosion is a very complex physical process which, under the impact of atmospheric forces,&nbsp;creates destructive changes on the soil surface layer. In case the primary agent of particle&nbsp;movement is wind, we talk about wind or aeolian erosion. Aeolian erosion is a specific&nbsp;process which occurs in extremely complex situations of mutual interaction of numerous&nbsp;natural and anthropogenic factors of mainly stochastic properties making its research a&nbsp;complex scientific-research problem.</p><p>The main goal of conducted research was to monitor the process of aeolian erosion at the&nbsp;chosen localities of Deliblato Sands, the largest and the most important area of the kind in&nbsp;Europe. In other words, the goal is to determine the quantities of aeolian sediment &ndash;&nbsp;sediment transport by direct systematic measurements in field conditions, determine&nbsp;dominant direction of sediment transport, define its annual distribution and determine the&nbsp;effect of vegetation on reducing the intensity of aeolian erosion. During a four-year period,&nbsp;for the first time in this area, i.e. at the same locality, a comparative research of aeolian&nbsp;erosion have been conducted using the mechanical sediment trap and activities based on&nbsp;137Cs radioisotope tracing technique for estimating soil losses using special theoretical&nbsp;models.</p><p>The monitoring of aeolian erosion processes was conducted during the period 2006 &ndash; 2009&nbsp;at Cvijićev vis which was chosen as a typical locality since it was, apart from the central&nbsp;position on Deliblato Sands, a cultivated surface without any wind protection. Alongside&nbsp;with these measurements, at Dragićev hat &ndash; nursery garden, the monitoring of aeolian&nbsp;erosion was conducted on two measurement points during the period May 2006 &ndash; April&nbsp;2007 in areas with the protective vegetative covers and/or vegetative belts. Aeolian erosion&nbsp;intensity measurement was performed by static sediment traps of the type &ldquo;deflametre&rdquo;&nbsp;(dimension of entry opening 10 x 10 cm) oriented on certain directions (N, NE, E, SE, S, SW,&nbsp;W, NW) in order to define the aeolian erosion processes in vector terms. The quantification&nbsp;of aeolian sediment using static traps constantly facing certain wind blowing directions enabled to log and differentiate &ldquo;summary&rdquo; yield of aeolian sediment (arithmetic sum of all sediment quantities from all traps) and &ldquo;resulting&rdquo; quantity of aeolian sediment (vector sum), since those quantities determine not only the entire amount of transported aeolian sediment (sediment yield) but also the sediment transported outside the areas of erosion field (soil loss), bur also the general direction of its transport.</p><p>Aeolian erosion measurement on Cvijićev vis for the period 2006 &ndash; 2009 indicated the<br />significant aeolian erosion processes which were defined by medium annual ediment<br />transport of 4.48 kg m-1. It has been determined that the total quantities of moved<br />sediment were 25.94, 20.92, 52.98 and 43.47 kg m-1 year-1, and sediment transport 3.24,&nbsp;2.61, 6.62 and 5.43 kg m-1 year-1 in 2006, 2007, 2008 and 2009 respectively.</p><p>Sediment transport for the period May 2006 &ndash; April 2007 showed that on Cvijićev vis which&nbsp;is characterized by bareness and openness there was the biggest aeolian erosion &ndash; four&nbsp;times bigger compared to Dragićev hat &ndash; nursery garden I characterized by bareness and&nbsp;protectiveness and 30.2 times bigger compared to Dragićev hat &ndash; nursery garden II&nbsp;characterized by overgrown condition and protectiveness of erosive field. At the locality&nbsp;Dragićev hat &ndash; nursery garden I the aeolian erosion was recorded 7.5 times bigger&nbsp;compared to the one recorded on Dragićev hat &ndash; nursery garden II.</p><p>Soil loses expressed through the resulting monthly sediment transport (vector sum)<br />equalled 5.13, 2.04, 4.31 and 11.94 kg m-1 in 2006, 2007, 2008 and 2009 respectively, and&nbsp;the percentage share of annual soil losses compared to total sediment yield (arithmetical&nbsp;sum) varied between 8.1% and 27.5%. The resulting aeolian sediment movement direction&nbsp;was SE-NW under the influence of the dominant southeast wind &ldquo;Koshava&rdquo;.</p><p>Even though the most reliable determination of aeolian erosion and its effects is based on&nbsp;direct systematic measurements in real time conditions in the field, starting from the end&nbsp;of the last century the methods of tracking radionuclide from radioactive precipitation,&nbsp;especially 137Cs, for the purposes of estimating the soil loss and spatial distribution of&nbsp;aeolian sediment, have been used increasingly.</p><p>The total number of samples taken for the method of monitoring the quantity of 137Cs was&nbsp;149, 9 of which were initial samples (3 profiles with 3 samples each), 14 main samples (2&nbsp;profiles with 7 samples each), 32 remaining samples (8 profiles with 4 samples each), 36&nbsp;reference samples (9 profiles with 4 samples each) and 58 samples taken radially on certain&nbsp;directions (N, NE, E, SE, S, SW, W, NW).</p><p>The main sample taken from the uncultivated land with the detected quantity of 137Cs of&nbsp;10,603.57 Bq m-2 represents the comparative value, i.e. local precipitation input of 137Cs for&nbsp;the models of 137Cs quantities conversion into the quantities of lost soil. This sample depicts&nbsp;the area where the research was conducted and represents the comparative value which&nbsp;can properly define the aeolian erosion processes.</p><p>For converting the measured quantities of 137Cs into the quantities of lost soil using Walling&nbsp;model the simplest proportional model (PM) for cultivated land was used and the most&nbsp;appropriate profile distribution model (PDM) for uncultivated soil with the newest version&nbsp;of PC compatible software package in Microsoft Excel Add-Ins. Using the profile distribution model (PDM) on all samples taken from the experimental area the quantities of average soil loss obtained were 207.06 t ha-1 year-1 and 2.10 cm. Basher &amp; Webb model gave the average soil loss of 212.18 t ha-1 year-1 and 2.09 cm. Soil loss calculated using the conversion of 137Cs quantities into the soil loss quantities indicate the significant aeolian processes defined by strong and excessive aeolian erosion.</p><p>For 58 soil samples taken from areas radially distributed on certain directions (N, NE, E, SE,&nbsp;S, SW, W, NW), apart from 137Cs and 210Pbex concentrations and quantities, spatial&nbsp;coordinates X and Y were determined as well as the altitude of taken samples. Spatial&nbsp;distribution of 137Cs and 210Pbex quantities are represented by isolines, and also 3D&nbsp;demonstrations were created showing the percentage of deviation of 137Cs and 210Pbex from&nbsp;the local precipitation input of 137Cs and 210Pbex. In both cases, the dominant direction SENW&nbsp;was noticeable, i.e. the southeast wind &ldquo;Koshava&rdquo;.</p><p>The comparative analysis of these methods indicated the validity in the quantification of&nbsp;aeolian erosion process and the possibility of its application in the future and the obtained&nbsp;results of aeolian sediment yield and soil loss contributed to determining the state of soil&nbsp;degradation and vulnerability of Deliblato Sands.</p>

Le transport de sédiments en rivières et torrents reste un phénomène mal compris en raison de la polydispersité des particules et de la ségrégation résultante. Il a été mené une étude expérimentale sur un canal permettant d’étudier la ségrégation en charriage d’un mélange de deux classes de billes. Le déplacement collectif des billes est enregistré sous la forme de séquences vidéos. Cette thèse traite des méthodes de traitement d’images développées pour analyser les données obtenues. Premièrement, nous avons développé une méthode de segmentation d’images pour étudier l’influence de l’infiltration de particules fines sur l’évolution d’un lit mobile. Avec cette méthode d’analyse, une étude expérimentale a permis de montrer que l’évolution de la pente du lit présente une décroissance exponentielle. Deuxièmement, nous avons optimisé les algorithmes déterministes de suivi de particules pour permettre l’étude des trajectoires sur l’intégralité du phénomène de ségrégation, ce qui n’était pas possible dans les travaux précédemment effectués à Irstea. Nous avons de plus mis en place des mesures d’évaluation et conçu des vérités terrains afin d’apprécier la qualité des résultats. Des gains de temps, cohérence, précision et mémoire ont été quantifiés. Troisièmement, nous avons développé un nouvel algorithme basé sur le filtrage particulaire à modèles multiples pour mieux gérer les dynamiques complexes des particules et gagner en robustesse. Cette approche permet de prendre en compte les erreurs du détecteur, les corriger et ainsi éviter des difficultés lors du suivi de trajectoires que nous rencontrons notamment avec l’algorithme déterministe / Sediment transport in rivers and mountain streams remains poorly understood partly due to the polydispersity of particles and resulting segregation. Experiments in a channel were carried out to study bedload transport of bimodal bead mixtures. The behavior of the beads is recorded through video sequences. This work is about the development of image processing methods to analyse the obtained data. Firstly, we developed a method of image segmentation to study the infiltration of fine particles and its influence on the evolution of bed mobility. Thanks to this method, an experimental study shows that the bed slope evolution follows an exponential decay. Secondly, we optimised deterministic tracking algorithms to enable the study of trajectories on long-duration phenomena of segregation, which was not possible with previous work done at Irstea. Moreover we set up relevant evaluation measures and elaborated ground truth sequences to quantify the results. We observed benefits in execution time, consistency, precision and memory. Thirdly, we developed a new algorithm based on multiple model particle filtering to better deal with complex dynamics of particles and to gain robustness. This approach allows taking unreliable detections into account, correcting them and thus avoiding difficulties in the target tracking as encountered with the deterministic algorithm

Les rivières présentent généralement un lit ondulé dû à la présence de bancs, qui correspondent à des larges dépôts sédimentaires alternant avec des zones profondes (mouilles). Des travaux d'ingénierie importants et répétés modifiant la géométrie du cours d'eau, le régime hydraulique et l'apport sédimentaire peuvent à terme modifier la dynamique des bancs à l'échelle de la rivière. Une meilleure compréhension des processus liés aux bancs est importante pour les gestionnaires des rivières, car les bancs contrôlent activement la morphologie du lit et érodent les berges, impactant la navigation, les prises d'eaux, les ouvrages et la qualité des habitats. Même si les mécanismes régissant la formation et le développement des bancs sont bien compris, la compréhension de la morphodynamique des bancs en milieu fluvial reste limitée, en raison de la non-linéarité induite par la combinaison de facteurs naturels en atrophiques. La non-uniformité des sédiments est une caractéristique inhérente des rivières, mais son impact sur la propriété des bancs, même dans des cas simplifiés, reste obscure. Ce travail de thèse vise à étudier l'impact de l'hétérogénéité granulométrique sur des bancs dans des chenaux endigués, via l'utilisation d'un modèle morphodynamique bi-dimensionnel implémenté dans le système Telemac-Mascaret. Les développements numériques nécessaires sont apportés afin d'être en accord avec l'état de l'art sur la modélisation de bancs avec un sédiment-non-uniforme. Par la suite, ce modèle est utilisé pour l'étude de la morphodynamique des bancs dans un chenal rectiligne sur la base d'expériences réalisées en laboratoire. Finalement, l'analyse est transférée sur un tronçon de 1 km de la Loire, caractérisé par sa géométrie relativement complexe. Les résultats permettent de valider l'approche de modélisation et démontrent la portabilité pour d'autres études, apportent plus d'éléments sur la relation entre sédiment non-uniforme et les bancs, et pourront être utilisés pour préconiser les gestionnaires des rivières / Rivers often present a wavy bed topography due to the presence of bars, corresponding to large sediment deposits alternating with deeper areas (pools). Intense and continual river engineering works altering the river geometry, flow regime and sediment supply can impact bar morphodynamics at the reach scale. A deep knowledge of bar processes is important for river managers, because bars actively control the river bed topography and influence bank erosion, with consequences for navigation, water intakes, infrastructure and the quality of their habitats. Although the origin of bar formation and propagation is well understood, the understanding of bar morphodynamics in rivers remains limited due to the non-linearity of combined natural and anthropogenic effects. Sediment non-uniformity is an inherent characteristic of rivers, but its impact on bar properties, even considering simple configurations, is still unclear. This Ph.D. thesis aims at investigating the impact of sediment size heterogeneity on bars in rivers with non-erodible banks, using a two-dimensional morphodynamic model implemented in the Telemac-Mascaret system. The necessary model developments are brought to comply with the state of the art on the modelling of heterogeneous sediment with bars. Then, the model is used to study bar morphodynamics in a straight channel on the basis of laboratory experiments. Eventually, the analysis is transferred in a 1 km reach of the Loire river characterized by a relatively complex geometry. General outcomes validate the modelling approach and demonstrate the application portability for other study cases, shed more light on the relationship between non-uniform sediment and bars, and can be later used as recommendations for river managers.

Eskilstuna har sedan länge varit en industristad vilket har inneburit utsläpp av främst metallföroreningar men även organiska ämnen till Eskilstunaån. Provtagningar har vid upprepade tillfällen gjorts och det har visats att sedimentet i ån innehåller höga halter av förorenande ämnen. Sediment förorenat av miljögifter utgör en risk för både miljön och människors hälsa. Beroende på vilka förhållanden som råder i vattendraget skiljer sig sedimentationshastigheten åt, dels mellan olika vattendrag men den kan också variera inom recipienten vilket gör att det kan finnas särskilda områden där sediment och föroreningar ackumuleras. Det kan vara av vikt att identifiera dessa platser för att minska risken för återsuspension av sedimentet, som sedan kan transporteras vidare nedströms, samt för eventuella framtida åtgärder.  I examensarbetet undersöktes föroreningsspridningen i Eskilstunaån och var ackumulationsbottnar kan förväntas ligga. En sedimenttransportmodell byggdes upp i programmet HEC-RAS med åns batymetri som utgångspunkt. Resultaten från modelleringar analyserades och tolkades med det geografiska informationssystemet ArcGIS och jämfördes med bottens hårdhet samt tidigare utförda sedimentprovtagningar. Sedimenttransportmodelleringen tyder på att området med mest ackumulation finns i Eskilstunaån där den passerar centrum och där åns botten är relativt mjuk. De högsta halterna för majoriteten av de undersökta metallföroreningarna påträffades trots detta längre nedströms där botten, sett till hela ån, inte var utmärkande mjuk men i jämförelse med närliggande platser var den däremot mjuk och relativt djup. En slutsats som kan dras ur detta är att vid lokalisering av ackumulationsbottnar bör vattendragets batymetri analyseras i kombination med bottens hårdhet och det bör göras på kortare sträckor. / Eskilstuna has been an industrial town for a long time which has caused emissions of mostly metal contaminants but also organic substances in to the Eskilstuna river. Samples from the sediment shows high content of some pollutants. Contaminated sediments can cause environmental and health hazards. Therefore, it is of importance to locate accumulation areas in the riverbed to avoid resuspension of the sediment, for preventing further transport downstream, and it may be of use if remediation measures becomes necessary.  In this thesis the distribution of metal contaminants in the Eskilstuna river were investigated and accumulation areas located. A sediment transport model, based on the bathymetry, was implemented in the river analysis system HEC-RAS. The results from the model were later analyzed in the geographical information system ArcGIS and compared to the riverbeds hardness and the sediment samples. The sediment transport model showed an accumulation area in the river where it flows through the city center and the riverbed is relatively soft. The highest concentrations of most pollutants were found further downstream where the riverbed has a higher relative hardness. However, if only the neighbouring areas are compared to this locations the accumulation area is soft with a relative large depth. As a conclusion, one may have to take both bathymetry and the riverbeds hardness into account when locating accumulation areas.

[Truncated abstract] With rapidly increasing population densities along coastlines and rising global sea levels, coastal protection has become a major concern for coastal communities. Predicting sediment transport in nearshore regions, however, is one of the most challenging tasks faced by coastal researchers in designing coastal structures or beach nourishment schemes. Although nearshore sediment transport mainly occurs in the longshore direction, cross-shore sediment transport is crucial in determining the shoreline evolution and beach morphology . . . This study investigated the factors influencing sediment re-suspension and cross-shore suspended sediment flux in the frequency domain through a series of field measurements conducted at several different locations and a numerical model. Only oscillatory flow components were examined and the mean flow components were not considered. Although many different factors such as cross-shore location with respect to breaker line, significant wave height to water depth ratio (Hs/h), normalised horizontal velocity skewness (<u³>/‹u²›³/²), median grain size (d50), breaker type, and wave groupiness appeared to influence the magnitude of cross-shore suspended sediment flux, bed ripples was identified as the major contributing factor in changing the direction of suspended sediment flux due to incident swell waves. Moreover, the direction changed significantly with ripple type. High frequency measurements, obtained to examine the influence of turbulent kinetic energy (TKE) on higher sediment suspension events observed under wave groups indicated that higher TKE was generated at the seabed by approaching wave groups, which in turn resulted in higher suspension events.°1

Graduation date: 2006 / Dam removal is increasingly viewed as a river restoration tool because dams affect so many aspects of river hydrology, geomorphology, and ecology; but removal also has impacts. When a dam is removed, sediment accumulated over a dam’s lifetime may be transported downstream; and the timing, fate and consequences of this sediment remain some of the greatest unknowns associated with dam removal. In this thesis, I develop a conceptual model for erosion and deposition following removal of sediment-filled dams in mountain streams, and use field studies to document actual change. The data show that reservoir erosion in mountain rivers is likely to occur by knickpoint migration, with 85% of stored sediment being released during a single storm event in two field studies, at shear stresses less than that required for mobilization of the median surface particle size. Coarse sediment is predicted to deposit close to the dam with channel aggradation decreasing exponentially with increasing distance downstream, although some channel features are shown to have a greater propensity for aggradation than others. Field studies show that turbidity associated with dam removal and reservoir erosion may decrease hyporheic exchange, but gravel deposition (e.g., 470 m3 of gravel from Dinner Creek Dam) has the potential to more than offset that decrease, and increased hyporheic exchange is shown to reduce diurnal temperature change. Macroinvertebrate density and taxa richness did not respond to dam removal itself, but rather with time-lagged reservoir erosion. Following reservoir erosion, macroinvertebrate density recovered quickly, although longterm taxa community composition appears to be altered. On the Sandy River, field measurements of shear stress and patterns of sediment deposition following cold lahars were used as an analog to predict the fate of fine sediment, which is likely to deposit far from the dam. Results show that the Sandy River has little capacity for fine sediment storage in pools above RK 6.4 (~ 42 kilometers below Marmot Dam) at discharges associated with reservoir sediment releases. Taken as a whole, this paper illustrates a complex suite of process that may accompany removal of sediment-filled dams in mountain rivers.

The advective motion of seawater governs the transport of almost everything, animate or inanimate, present in the ocean and those lacking the ability to outswim the currents have to follow the flow. This makes modelling of advective ocean transports a powerful tool in various fields of science where a displacement of something over time is studied. The present thesis comprises four different applications of ocean-transport modelling, ranging from large-scale heat transports to the dispersion of juvenile marine organisms. The aim has been to adapt the method not only to the object of study, but also to the available model-data sets and in situ-observations. The first application in the thesis is a study of the oceanic heat transport. It illustrates the importance of wind forcing for not only the heat transport from the Indian to the Atlantic Ocean, but also for the net northward transport of heat in the Atlantic. In the next study focus is on the particle-transport differences between an open and a semi-enclosed coastal area on the Swedish coast of the Baltic Sea. The modelled patterns of sedimentation and residence times in the two basins are examined after particles having been released from a number of prescribed point sources. In the two final studies the transport-modelling framework is applied within a marine-ecology context and the transported entities are larvae of some Scandinavian sessile and sedentary species and non-commercial fishes (e.g. the bay barnacle, the blue mussel, the shore crab and the gobies). The effects of depth distribution of dispersing larvae on the efficiency of the Marine Protected Areas in the Baltic Sea are examined. Further, the diversity in dispersal and connectivity depending on vertical behaviour is modelled for regions with different tidal regimes in the North Sea, the Skagerrak and the Kattegat. The spatial scales dealt with in the studies varied from global to a highly resolved 182-metres grid. The model results, excepting those from the global study, are based on or compared with in situ-data. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. 4: Manuscript.</p>

Shoreline sand waves are shoreline undulations with a length scale of several kilometres and a time scale of years to decades. They occur on many coasts, migrating in the direction of the dominant littoral drift and they introduce a variability into the shoreline position that can be greater than the long term coastal trend. The objective of this thesis is to provide more insight into the formation and dynamics of shoreline sand waves and, in particular, to explore the role of the so called high angle wave instability. Previous studies showed that the shoreline can be unstable under very oblique wave incidence. This high angle wave instability develops due to the feedback of shoreline changes and the associated changes in the bathymetry into the wave field. Wave propagation over this perturbed bathymetry leads to specific gradients in the alongshore transport that can cause the growth and migration of shoreline sand waves. In this thesis a quasi 2D non-linear morphodynamical model is improved and used to explore high angle wave instability and predict the formation and evolution of shoreline sand waves. The model assumes that the large scale and long term shoreline dynamics is controlled by the wave driven alongshore transport so that the details of the surfzone morphodynamics are not resolved. It overcomes some of the limitations of previous modelling studies on high angle wave instability. The wave field is computed with a simple wave module over the evolving bathymetry and an empirical formula is used to compute the alongshore transport. Cross-shore dynamics is described in a parameterized way and the model is capable of describing shoreline perturbations with a finite and dynamic cross-shore extent. The conditions under which shoreline instability can lead to the formation of shoreline sand waves are refined. Generic simulations with constant wave conditions and random initial perturbations show that the shoreline becomes unstable when the wave incidence angle at the depth of closure (i.e., the most offshore extent of the shoreline perturbations) is larger than a critical angle of about 42 degrees and shoreline sand waves develop in unison. The cross-shore dynamics plays an essential role because it determines the offshore extent of the shoreline perturbations. Using default model parameters, wave conditions and cross-shore profile, the sand waves develop with wavelengths between 2 and 5 km, the time scale for their formation is between 5 and 10 years and they migrate downdrift at about 0.5 km/yr. Simulations with a localized large scale perturbation trigger the formation of a downdrift sand wave train. Larger wave obliquity, higher waves and shorter wave periods strengthen the shoreline instability. A more realistic wave climate, with alternating high and low angle wave incidence reduces the potential for shoreline instability. A percentage of about 80% of high angle waves is required for sand wave formation. It is demonstrated that the range of low wave angles that can occur on a coast is larger than the range of high wave angles, and that the stabilizing effect produced by low angle waves (causing diffusion) is bigger than the destabilizing effect produced by high angle waves (causing growth and migration). Even if high angle waves are not dominant, the instability mechanism might still play a role in the persistence and downdrift migration of large scale shoreline perturbations. The model results are in qualitative agreement with observations of shoreline sand waves. The quasi 2D approach provides new insight into the physical mechanisms behind high angle wave instability and the occurrence of a minimal and optimal length scale for sand wave formation. Essential physical processes are wave energy dispersion due to wave refraction, wave energy focusing near the crest of a sand wave and the monotonic decrease of the gradients in alongshore transport for increasing length scales. / Les ones de sorra a la línia de costa són ondulacions de la línia de costa amb una escala espacial de kilòmetres i una escala temporal d’anys a dècades. Ocorren a moltes costes, migren en la direcció del transport litoral i introdueixen una variabilitat a la línia de costa que pot ser major que la seva tendència a llarg termini. L’objectiu d’aquesta tesi és estudiar amb més profunditat la formació i la dinàmica de les ones de sorra i, més concretament, explorar el rol de l’anomenada inestabilitat d’angle gran. Estudis previs van demostrar que la línia de costa pot ser inestable en cas d’onades obliqües que incideixen amb un angle gran. Aquesta inestabilitat d’angle gran es produeix degut a la retroalimentació entre els canvis a la línia de costa (i els que conseqüentment ocorren a la batimetria) i els canvis al camp d’onades. La propagació de les onades sobre la batimetria pertorbada crea gradients del transport de sediment longitudinal que causen el creixement i la migració de les ones de sorra. En aquesta tesi s’ha millorat un model morfodinàmic quasi 2D i no lineal per usar-lo per explorar la inestabilitat d’angle gran i predir la formació i evolució de les ones de sorra. El model assumeix que la dinàmica a gran escala i llarg termini està dominada pel transport de sediment longitudinal produït per les onades de manera que la morfodinàmica de la zona de rompents no es detalla. S’han superat algunes de les limitacions dels estudis anteriors de modelat de la inestabilitat d’angle gran. El camp d’onades es calcula amb un mòdul senzill de propagació sobre la batimetria canviant i el transport longitudinal s’estima usant una fórmula empírica. La dinàmica transversal es parametritza per descriure pertorbacions de la línia de costa amb una extensió transversal finita i dinàmica. S’han refinat les condicions sota les quals la inestabilitat d’angle gran produeix la formació d’ones de sorra. Les simulacions amb condicions constants d’onades i pertorbacions inicials aleatòries mostren que la línia de costa esdevé inestable quan l’angle d’incidència a la profunditat de tancament és major que un angle de 42 graus i les ones de sorra es desenvolupen a l’uníson. La dinàmica transversal té un rol essencial al determinar l’extensió transversal de les pertorbacions. Usant els valors per defecte dels paràmetres del model, les ones de sorra tenen espaiats d’entre 2 i 5 km i temps de creixement d’entre 5 i 10 anys, i migren en la direcció del transport a uns 0.5 km/any. Les simulacions també mostren que una pertorbació inicial localitzada desencadena la formació d’un tren d’ones de sorra. Com més obliqües i grans són les onades i com menor és el seu període major és la inestabilitat. Un clima d’onatge més realista, alternant onades d’angle d’incidència gran i petit, redueix el potencial de la inestabilitat d’angle gran. Calen almenys un 80% d’onades d’angle gran perquè es formin ones de sorra. El rang d’onades d’angle petit que poden succeir en una costa és major que el d’onades d’angle gran, i l’efecte estabilitzador de les onades d’angle petit (que produeix difusió) és més important que l’efecte desestabilitzador de les onades d’angle gran (que produeix creixement i migració). Fins i tot si les onades d’angle gran no dominen, el mecanisme d’inestabilitat pot tenir un paper important en la persistència i migració de pertorbacions de la línia de costa a gran escala. Els resultats s’assemblen qualitativament a les observacions d’ones de sorra. L’enfocament quasi 2D permet estudiar més detalls del mecanisme físic que hi ha darrere de la inestabilitat d’angle gran i del fet que existeixin longituds d’ona mínima i òptima per la formació d’ones de sorra. Els processos físics essencials són la dispersió de l’energia de l’onatge degut a la refracció, la concentració d’energia de les onades a les crestes de les ones de sorra i el decreixement monòton del transport litoral quan augmenta l’escala espacial.

Nutrient limitation in aquatic ecosystems results from a deficiency in nitrogen or phosphorus levels relative to cellular growth needs. Nutrient limitation of freshwater systems is a function of biotic and abiotic factors. Biotic factors include vascular and nonvascular plant community composition. Abiotic factors include underlying bedrock and land-use activities (e.g. agriculture, septic systems). Nutrient availability directly affects growth, productivity, and community structure of primary producers. The purpose of this study was two-fold: (1) to assess the relationship between ambient algal biomass. and in-stream nutrient levels along the longitudinal course of a river through a transition from weak to well-developed underlying karst bedrock, and (2) experimentally assess if periphyton was nitrogen or phosphorous limited between weak and well-developed karst sites. Sestonic and filamentous biomass (= chlorophyll-a) levels increased monthly along the longitudinal gradient. In contrast, periphyton biomass levels increased minimally monthly and displayed no longitudinal pattern. Nitrate and soluble reactive phosphorus levels exhibited distinct longitudinal increases, whereas total phosphorous displayed minimal change and ammonia levels decreased in the downstream direction. Total nitrogen (TN) levels increased upstream but decreased sharply in the well-developed downstream karst sites. The nutrient limitation assays revealed that the highest periphyton levels were with N + P treatments at the most upstream sites. Overall, in Kentucky's Green River algal biomass accrual appears to be mainly P-limited but likely also by TN availability during late summer.