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To improve human-robot collaborations, more and more researches focus on the study of human behaviour. It is in this context of growing relationships between robotics and biomechanics that theCollaBorative roBot (CoBot) project has emerged. Funded by the French Agence Nationale de la Recherche (ANR), this project (ANR-CoBot) targets a human-humanoid robot collaboration in the context of a load-carriage task. During this collaboration, the robot is aimed to safely and pro-actively assist its human partner to handle a load. The idea of the ANR-CoBot project is, first, to understand the mechanisms at stake during a human-human collaboration and, then, to model and simulate them to finally implement them on a humanoid robot TALOS from PAL Robotics to perform the same task with a human partner.As part of this project, my PhD deals with the transition from the modelling of the human behaviourto the integration of this model in a humanoid robot. The final goal of this thesis is to perform a pro-active human-robot interaction to carry a table. From a biomechanics point of view, my thesis aims to better understand human locomotion in order to enable the robot to anticipate its partner’s behaviour. To achieve this goal, experiments were performed to measure Center of Mass (CoM) human trajectories, first during simple locomotion and then during carriage task. Then, models based on optimal control problems were designed to generate human-like trajectories or even predict them. This prediction may improve the human-robot interactions making the robot acting pro-actively. Then, from a robotics point of view, to achieve a collaborative carriage task, five matters need to be handled:• Localization: the robot needs to locate the table and its human partner in order to interactwith them.• Walk generation: the robot needs to walk toward the table at the beginning of theexperiment and also needs to walk with the table towards an unknown location chosenby its human partner.• Whole-body control: the robot needs to lift the table and handle it while walking.• Balance: the robot should not fall during the experiment.• Safety: the robot should not harm its human partner.Among those matters, my thesis mainly focuses on the walk generation. The other topics are handled by other members of the Gepetto team in LAAS-CNRS. One major contribution of my thesis is to embed the prediction trajectory model into the robot walking pattern generator. This aims to improve the human-robot interaction for two main reasons. First, it may allow the robot to be more reactive by anticipating its partner motions and, then, it may make the interaction less disturbing and more natural for the human as the robot may act in a human-like manner., Ma thèse est financée par l’Agence Nationale de la Recherche (ANR) à travers le projet intitulé ANR-CoBot. Ce projet pluri-disciplinaire a pour but d’étudier les interactions entre 2 individus lors d’un transport de charges collaboratif et de réaliser une collaboration homme-robot pour transporter une charge. Dans le cadre de ce projet, ma thèse s’intéresse spécifiquement à la réalisation d’un transport de table en collaboration entre un humain et un robot de type TALOS produit par l’entreprise PAL Robotics.Lorsqu’on s’intéresse à une telle interaction homme-robot, les deux principaux enjeux à relever sont les suivants : comprendre le comportement de l’humain, d’une part, et contrôler le robot pour qu’il puisse adapter ses actions à celles de son partenaire humain d’autre part. Le premier enjeu est d’ordre biomécanique, tandis que le second est d’ordre robotique. Ma thèse allie donc ces deux disciplines. En biomécanique, mon travail s’est focalisé sur l’étude des trajectoires de Centre de Masse (CdM) d’individus marchant seuls sans contraintes puis marchant en transportant une table en binôme. Le but de cette étude est de modéliser ces trajectoires de marche avec un problème de contrôle optimal afin de pouvoir prédire où va un individu à partir de sa trajectoire passée. Cette information est nécessaire pour réaliser une interaction homme-robot fluide où le robot arrive à anticiper le comportement de son partenaire lors du transport, comme le ferait un être humain. En robotique, cinq aspects sont à maîtriser afin de réaliser un transport de charge :• La localisation: le robot doit pouvoir « voir » la table et son partenaire pour pouvoir interagir avec eux.• La génération de la marche : le robot doit pouvoir marcher jusqu’à l’endroit où l’humain veut amener la table, endroit qui est a priori inconnu au robot.• Le contrôle corps-complet : le robot doit pouvoir soulever la table et marcher en la tenant.• La stabilisation : le robot doit pouvoir réaliser tous ces mouvements sans perdre l’équilibre.• La sécurité : le robot ne doit pas mettre en danger l’intégrité physique de son partenaire humain.Parmi ces différents aspects, ma thèse se focalise sur la génération de la marche tandis que les autres points font l’objet de travail d’autres gens au sein de l’équipe Gepetto du LAAS-CNRS. Lors d’une interaction homme-robot, la génération des trajectoires du CdM du robot et de ses pieds doit être rapide et doit prend en compte les mouvements de l’humain en temps réel. Ainsi, ma principale contribution au générateur de marche du robot, lors de ma thèse, a été de le coupler au modèle de prédiction des trajectoires humaines.

Prevoz tovora se v logistiki in proizvodnji ponavadi opravlja z večjimi mobilnimi roboti, ki pa za infrastrukturo niso vedno najbolj primerni. So tudi težki, neokre- tni in zahtevajo veliko prostora, tudi ko ničesar ne prevažajo. V tem magistrskem delu je predstavljen algoritem za prevoz tovora z več manjšimi mobilnimi roboti, ki si tovor delijo. Manjši mobilni roboti so lahko lažji, hitrejši in bolj okretni, če je potrebno lahko učinkovito prevažajo tudi manjše tovore. V primeru večjega tovora pa se roboti s posebnim prijemalom pritrdijo na kolesa tovornega vozička, nase prevzamejo del teže tovora in voziček s tovorom odpeljejo na želeno mesto. Za prevoz tovora med točkami je bil razvit centraliziran algoritem, ki omogoča vodenje poljubnega števila robotov z diferencialnim pogonom. Algoritem je se- stavljen iz treh delov: sistema za izračun kinematike vožnje tovora, sistema za določanje orientacije robotov glede na tovor in dela, ki skrbi za vodenje robotov. Orientacija robotov glede na tovor se izračuna na podlagi treh metod, ki temeljijo na globalni legi robotov, odometriji robotov in kinematičnem modelu ter vizu- alnih markerjih. Za iskanje poti se uporablja algoritem A*, za sledenje poti pa prediktivni algoritem načrtovanja in sledenja trajektorije (Trajectory Rollout). Algoritem pretvori kontrolne ukaze za premik tovora iz algoritma za sledenje poti v kontrolne ukaze za posamezne mobilne robote. Implementacija algoritma temelji na okolju ROS (Robot Operating System). Algoritem je bil razvit in ovrednoten v simulacijskem okolju Gazebo. Nato se je prenesel in ovrednotil še na realnem sistemu – mobilnem robotu podjetja Epilog d.o.o. V simulaciji in na realnem sistemu so bili opravljeni eksperimenti z odprto- in zaprtozančnim vodenjem. Ustrezno delovanje algoritma se je določilo s tremi pokazatelji. Prvi pokazatelj je primerjava hitrostnega ukaza z dejansko hitrostjo tovora. Drugi pokazatelj so sile med roboti in tovorom, tretji pa bočno drsenje robotov. Algoritem je v vseh simuliranih in realnih eksperimentih deloval kar je pomenilo, da se je tovor premikal v skladu z želenimi ukazi brez bočnih drsenj robotov in brez prevelikih sil. Transport of load in production and logistics is usually done with bigger mobile robots that are not always the most suited for infrastructure. They are heavy, slow, and require lots of space even when not transporting anything. This mas- ter’s thesis presents the algorithm for transportation of load with multiple smaller mobile robots that share the load. Smaller robots are lighter, faster, and require less space. If needed they can more effectively transport smaller loads. In the case of bigger load robots use special gripper to attach themselves to the wheels of the transport cart and transfer some weight to themselves. A centralized algorithm was developed that is capable of controlling any num- ber of differential drive robots with the aim of transporting a load between points. The algorithm consists of three parts: a system for calculating kinematics of load transport, a system for determining the orientation of the robots with respect to load and robots control system. The orientation of robots with respect to load is calculated based on three methods that use the global pose of the robots, odom- etry of the robots and kinematic model, and visual markers. For path searching A* algorithm is used and for path following Trajectory Rollout algorithm is used. The algorithm is used to transform control orders for the load to controls for individual robots. The implementation of the algorithm is based on ROS (Robot Operating System) environment. The algorithm was developed and evaluated in Gazebo simulation environ- ment. It was then transferred and evaluated on a real system - on the mobile robot from company Epilog d.o.o. Open and closed-loop control experiments were done in simulation and on the real system. The proper working of the algorithm was determined using three indicators. First indicator in comparison of desired versus real velocity of the load. The second one is the forces between robots and the load. The third is sideways sliding of the robots. The algorithm worked in all simulated and real experiments which meant that the load was moving according to the commands without sideways sliding and without too big forces.

Load transport is rarely observed in animals. In this respect, ants probably display the most outstanding performances: they are indeed able to carry loads weighing up to ten times their own mass over dozens of meters. During this thesis, we studied ant locomotion and how it was affected by load transport. We investigated three aspects of locomotion: leg kinematics, center of mass dynamics and energetic expenditure associated with locomotion. We especially looked into the effect of ant mass on load transport. Indeed, the polymorphism of the worker caste of the ant species we studied, Messor barbarus, is characterized by allometric relationships, which implies that locomotion and/or load transport could be different for workers of different sizes. We also examined the effect of different relative mass of the loads carried. We found that big ants have a different locomotor pattern than small ants, probably because they have to compensate for the imbalance caused by their relatively bigger head. During load transport, the locomotor pattern does not change much for ants of different sizes and loaded ants often have to cling to the substrate in order to avoid falling off. For unloaded ants, the dynamics of the ant center of mass is similar to what has already been reported for other insects in the literature: the ant locomotion is well described by a bouncing gait with no aerial phases. This gait is hardly altered for small items. For bigger items however, the locomotion becomes erratic and does not follow a periodic pattern across consecutive strides. Finally, we measured the metabolic rates of ants of different sizes when unloaded and when loaded with loads of varying mass. The changes of the metabolic rate with temperature, ant mass, activity and load transport is coherent with previous experiments on other ant species. From these experiments, we computed the rate of food intake for which ants increase the energetic content of the colony. The function maximizing this rate predicts that optimal foraging would occur if small ants carry small seeds and big ants, big seeds. The results of this work will help to better understand the division of labor and the foraging ecology of Messor barbarus and could give new insights for the design of biomimetic hexapodal robots., Lors de cette thèse, nous avons étudié la locomotion chez la fourmi Messor barbarus et la manière dont celle-ci est affectée par la charge transportée. Ce travail recouvre trois aspects de la locomotion : la cinématique des pattes, la dynamique du centre de masse de la fourmi et la dépense énergétique associée à la locomotion. Nous avons porté une attention particulière à l'effet de la taille de la fourmi sur la locomotion ainsi qu'à l'effet de la masse relative de la charge transportée. Ce travail a montré que, lors de la locomotion non chargée, les petites et grosses fourmis n'ont pas le même patron locomoteur, les grosses fourmis s'ajustant au déséquilibre induit par leur tête proportionnellement plus grosse. Pour les fourmis chargées, le patron locomoteur varie peu avec la taille de la fourmi et celles-ci doivent régulièrement s'agripper au substrat avec leurs pattes arrières afin de ne pas basculer vers l'avant. Pour les fourmis non chargées, ou chargées avec de petites charges, la trajectoire du centre de masse lors de la locomotion correspond aux démarches observées chez d'autres insectes. Cependant, une charge de masse relative trop importante rend la locomotion erratique. Enfin, nous avons mesuré le taux métabolique pour différentes fourmis non chargées et chargées avec des charges de masses variables. Les variations du taux métabolique sont cohérentes avec les résultats de la littérature sur d'autres espèces de fourmis. Grâce à ces expériences, nous avons pu calculer le taux auquel les fourmis ramènent de l'énergie à la colonie en fonction de leur masse et de la masse de la graine transportée. Afin de maximiser ce taux, les petites fourmis ont intérêt à récolter de petites graines, alors que les plus grosses fourmis devraient transporter des graines plus lourdes. Les résultats obtenus durant cette thèse permettront de contribuer à une meilleure compréhension de la division du travail, de l'écologie et du comportement d'approvisionnement chez l'espèce Messor barbarus.

Submitted by Nadir Basilio (nadirsb@uninove.br) on 2019-07-10T19:31:14Z No. of bitstreams: 1 Laira Augusta Freitas Castro.pdf: 2243367 bytes, checksum: 309522ecaf2421300268fed2c29ba41b (MD5) Made available in DSpace on 2019-07-10T19:31:14Z (GMT). No. of bitstreams: 1 Laira Augusta Freitas Castro.pdf: 2243367 bytes, checksum: 309522ecaf2421300268fed2c29ba41b (MD5) Previous issue date: 2019-02-25 The increase in population growth in addition to the increasing of the urbanization rate and the intense use of the road transport lead to several problems in urban centers, such as trafic congestion, acustic pollution, air pollution and vibrations, thus reducing the living quality from people. Freight transportation in urban centers represents a significant part of these impacts. With the worldwide trend of reduction in greenhouse gas emissions and Brazil's commitment to COP 21 to reduce their emissions rates in the next few years, the issue of emissions from freight transport will have a major influencer and so be targeted, and strategies for mitigation of impacts and optimization of technologies. Some actions can be taken, including among them the adoption of cleaner technologies, such as the use of electric vehicles, which show a worldwide trend and, in addition to the benefits of lower greenhouse gas and carbon dioxide emissions in urban centers, emission of other pollutants such as aldehydes nitrous oxides that are responsible for numerous diseases. However, the use of electric vehicles still has a low adhesion, mainly in Brazil and even less when it comes to electric vehicles for freight transportation in the logistics sector. Considering this context, this reserch is aimed to identify ways to accelerate the adoption of electric vehicles in the logistics sector in urban centers with a special focus on the city of Sao Paulo. A field survey was carried out joined by a research of barriers and measures of adoption of electric vehicles of load in the literature through a structured bibliographical research, an interview was made with representatives of a company that already uses electric vehicles of load in the city of Sao Paulo and a questionnaire was sent to logistics operators operating in the city. The data obtained in the structured review served as the basis for the construction of the questionnaire and the interview and the responses of the questionnaire were evaluated by a qualitative approach with the purpose of discovering the main barriers and what the most efficient measures for the context of the city of Sao Paulo. It was concluded that economic barriers such as the initial cost of the vehicle and batteries are the main barrier followed by lack of recharging infrastructure, and that measures that can accelerate the adoption of these vehicles include fiscal and financial measures and operational measures such as supply of subsidies for the purchase of the vehicle and for the installation of private recharging stations and an increase in investments of public recharge infrastructure. O aumento crescente na popula????o em adi????o a crescente taxa de urbaniza????o e intenso uso do modal rodovi??rio de transporte geram diversos problemas nos centros urbanos como congestionamentos, polui????o sonora, polui????o do ar e vibra????es, reduzindo a qualidade de vida das pessoas. O transporte de cargas nos centros urbanos representa uma significativa taxa nestes impactos. Com a tend??ncia mundial a minimizar as emiss??es de gases do efeito estufa e o comprometimento do Brasil frente a COP 21 a reduzir suas taxas de emiss??es nos pr??ximos anos, a quest??o das emiss??es por transporte de carga passam a ter uma influ??ncia importante e a ser alvos de estudo e estrat??gias para mitiga????o de impactos e otimiza????o de tecnologias. Algumas a????es podem ser tomadas, dentre elas a ado????o de tecnologias mais limpas, como o uso de ve??culos el??tricos, que se mostram uma tend??ncia mundial e apresentam, al??m dos benef??cios de menores emiss??es de gases do efeito estufa e g??s carb??nico nos centros urbanos a menor emiss??o de outros poluentes como alde??dos e ??xidos nitrosos que s??o respons??veis por in??meras doen??as. Entretanto o uso de ve??culos el??tricos ainda possui uma baixa ades??o, principalmente no Brasil e menor ainda quando se trata de ve??culos el??tricos de transporte de carga no setor de log??stica. Considerando este contexto este estudo objetivou identificar as principais barreiras ado????o de ve??culos el??tricos no setor de log??stica em centros urbanos com um enfoque especial para a cidade de S??o Paulo. Foi realizada uma pesquisa de campo com o levantamento de barreiras e medidas de ado????o de ve??culos el??tricos de carga na literatura por meio de uma pesquisa bibliogr??fica sistem??tica, foi realizada uma entrevista com representantes de uma empresa que j?? utiliza ve??culos el??tricos de carga na cidade de S??o Paulo e foi veiculado um question??rio a operadores log??sticos que atuam na cidade. Os dados obtidos na revis??o sistem??tica da literatura serviram de base para a constru????o do question??rio e a entrevista e as respostas do question??rio foram avaliadas por uma abordagem qualitativa com a finalidade de descobrir quais as principais barreiras e quais as medidas mais eficientes para o contexto da cidade de S??o Paulo. Concluiu-se que as barreiras econ??micas como o custo inicial do ve??culo e das baterias s??o a principal barreira, seguida da aus??ncia de infraestrutura de recarga e que as medidas que podem acelerar a ado????o destes ve??culos compreendem medidas fiscais e financeiras e medidas operacionais como o fornecimento de subs??dios para compra do ve??culo e para instala????o de postos de recarga particulares e aumento em investimentos de infraestrutura p??blica de recarga.

Self‐similar downstream grain‐size fining trends in fluvial deposits are being increasingly used to simplify equilibrium sediment transport dynamics in numerical models. Their ability to collapse time‐averaged behavior of a depositional system into a simple mass‐balance framework makes them ideal for exploring the sensitivity of sediment routing systems to their climatic and tectonic boundary conditions. This is important if we want to better understand the sensitivity of landscapes to environmental change over timescales > 102 years. However, the extent to which self‐similarity is detectable in the deposits of natural rivers is not fully constrained. In transport‐limited rivers, stored sediment can be remobilized or ‘recycled’ and this behavior has been highlighted as a mechanism by which externally forced grain‐size fining trends are distorted. Here, we evaluate evidence of self‐similarity in surface gravel‐size distributions on three geomorphically diverse alluvial fans in the Iglesia basin, south Central Argentine Andes. We determine the statistical similarity between size distributions and demonstrate that a deviation from similarity occurs with significant variability in the coarse tails. Our analysis indicates a strong correlation between the degree of sediment recycling and the proportion of coarse clasts present on the bed surface. However, by fitting a relative mobility transfer function, we demonstrate that size‐selectivity alone can explain the bulk size distributions observed. This strengthens the application of self‐similar grain size fining models to solving problems of mass‐balance in a range of geomorphic settings, with an aim for reconstructing environmental boundary conditions from stratigraphy.

Made available in DSpace on 2018-12-11T17:22:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 Leaf cutting ants of the genus Atta build long lasting physical trails to exploit the vegetation around their nest. In this paper we investigated the dynamics of physical trail construction and usage in the leaf-cutting ant Atta laevigata. We assessed the average duration of physical trail construction in a pasture environment and estimated the impact of the change in the physiognomy of the terrain on ant speed, individual gross transport rate and rate of resource collection by taking into account the effects of confounding variables for each of these parameters. We also examined whether ants are able to adjust their foraging behaviour at the individual or collective level in order to maintain the same rate of vegetation return to their nest along the construction process. We found that a colony of A. laevigata needs between 4½ and 6½ days to complete a physical trail. The construction proceeded in a fairly uniform manner along the trail, suggesting that it is not the result of the coordinated action of a small group of specialized individuals progressing along the trail but rather of the sum of uncoordinated actions of individual workers. Ant speed increased by a 2.6 factor on a cleared trail compared to an uncleared trail and individual gross transport rate nearly doubled. However, there was no significant change along the construction process in traffic intensity, the proportion of ants returning to the nest with a piece of vegetation or the rate of resource delivery to the nest. The main benefit of trail construction is thus to mobilize less foragers on the trail to collect the same amount of food, leaving the possibility for the remaining workers to forage on other trails or to accomplish other tasks. Centre de Recherches sur la Cognition Animale Centre de Biologie Intégrative Université de Toulouse CNRS UPS Laboratorio de Insetos Sociais Pragas UNESP Faculdade de Ciências Agrònomica de Botucatu Departamento de Produção Vegetal Fazenda Experimental Lageado, P.O. Box 237 Laboratorio de Insetos Sociais Pragas UNESP Faculdade de Ciências Agrònomica de Botucatu Departamento de Produção Vegetal Fazenda Experimental Lageado, P.O. Box 237

Razvijen je algoritam koji koristi dva Pioneer robota s diferencijalnim pogonom za autonomni prijevoz tereta. Algoritam za koordinirani prijevoz tereta sa dva robota lako je moguće primijeniti u suvremenim samoupravnim skladištima uz male preinake i prilagodbu algoritma za druge tipove vozila. Algoritam koji upravlja robotima koristi A* kao algoritam traženja optimalnog puta, a algoritam čistog slijeđenja za slijeđenje pronađenog puta. Testiranje algoritma provedeno je u simulaciji i na fizičkim robotima. An algorithm which is using two Pioneer robots with differential-drive for autonomous load transport had been developed. An algorithm for coordinated two-robot load transport can easily be implemented in modern warehouses with small changes and adjustments for other types of vehicles. For finding an optimal path of robots, algorithm is using A*, and for following that path, it uses pure pursuit algorithm. An algorithm was tested in simulation and on physical robots.

[1] We characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat-mounted acoustic Doppler current profiler (ADCP), to survey transects at bifurcating branches during a semidiurnal tidal cycle. The ADCP collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge, adopting a recently introduced calibration procedure. Measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity, the roughness length and the Rouse number. Spatiotemporal distributions of the settling velocity were obtained by combining the Rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer. Bed-load transport rates were inferred from shear stress estimates. The concentration field shows a direct response to bed shear stress, stressing the alluvial context of the system. The flow in the bifurcation regions is characterized by counter rotating secondary-flow cells, which stretch over the full width and depth of the cross sections in the downstream branches, and persist throughout the entire tidal cycle. The pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads. A two-cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width. The division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration, which is in turn dependent on geometrical factors such as upstream curvature.

U okviru ovoga diplomskog rada analiziraju se svojstva upravljanja formacijom pokretnih objekata korištenjem Gaussove funkcije potencijala . Bitno svojstvo korištenog pristupa su elementarne funkcije potencijala ovisne o parametru $\sigma$ koji je različit za svaki agent. Posljedica tog svojstva je jednak oblik privlačnih i odbojnih sila između agenata i meta, te između samih agenata. Takvo svojstvo na kraju daje željenu formaciju kao singularnu točku neovisnu o parametrima. Za razliku od centraliziranog modela upravljanja u kojem su agenti identični, u decentraliziranom sustavu upravljanja agenti nisu identični, pa struktura potencijala formacije nije invarijantna s obzirom na zamjene konfiguracija pojedinih agenata. Nadalje je pokazano da se položaj neželjenih stabilnih ravnotežnih stanja može mijenjati oblikom elementarne funkcije potencijala, odnosno načinom na koji agenti i mete međusobno djeluju. Da bi se potrebne vrijednosti kontrolnog parametra tokom rada sustava ispravno odredile, uveden je adaptivni algoritam koji, ovisno o zaposjednutom ravnotežnom stanju, skokovito mijenja vrijednost kontrolnog parametra za pojedine agente. Simulacija, izvedene u simulatoru razvijenom u Matlab programskom okruženju u laboratoriju LARICS, pokazuje ispravnost predloženog pristupa upravljanja formacija pokretnih objekata. This Master thesis uses the Gaussian potential function to analyse control characteristics of a formation of mobile objects. The analysis uses elementary potential functions dependent on a control parameter that is different for each agent. The consequence is that the attractive and repulsive forces among agents and targets, as well as among agents themselves, have the same characteristics. This approach results in a desired formation expressed as a singular point independent of these parameters. As opposed to a centralized control model for which the agents are identical, in a decentralized control system, the agents are not identical resulting in a dependence of the formation's potential structure on the swapping of agents' configurations. It is further shown that the position of the undesired stable equilibrium states can be changed by the characteristics of the elementary potential functions, i.e. by a mutual interaction of the agents and targets. An adaptive algorithm is introduced in order to determine the required values of the control parameters during the operation of the system. It step-wise changes the control parameters depending on the acquired equilibrium state. The simulation, implemented as a GUI in Matlab in the LARICS lab, confirmed the correctness of the proposed control of a formation of mobile objects.

[1] We characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat-mounted acoustic Doppler current profiler (ADCP), to survey transects at bifurcating branches during a semidiurnal tidal cycle. The ADCP collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge, adopting a recently introduced calibration procedure. Measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity, the roughness length and the Rouse number. Spatiotemporal distributions of the settling velocity were obtained by combining the Rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer. Bed-load transport rates were inferred from shear stress estimates. The concentration field shows a direct response to bed shear stress, stressing the alluvial context of the system. The flow in the bifurcation regions is characterized by counter rotating secondary-flow cells, which stretch over the full width and depth of the cross sections in the downstream branches, and persist throughout the entire tidal cycle. The pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads. A two-cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width. The division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration, which is in turn dependent on geometrical factors such as upstream curvature.

This study presents the comparison of experimental results with assumptions used in numerical models. The aim of the field experiments is to test the linear relationship between different hydraulic parameters and soil detachment. For example correlations between shear stress, unit length shear force, stream power, unit stream power and effective stream power and the detachment rate does not reveal a single parameter which consistently displays the best correlation. More importantly, the best fit does not only vary from one experiment to another, but even between distinct measurement points. Different processes in rill erosion are responsible for the changing correlations. However, not all these procedures are considered in soil erosion models. Hence, hydraulic parameters alone are not sufficient to predict detachment rates. They predict the fluvial incising in the rill's bottom, but the main sediment sources are not considered sufficiently in its equations. The results of this study show that there is still a lack of understanding of the physical processes underlying soil erosion. Exerted forces, soil stability and its expression, the abstraction of the detachment and transport processes in shallow flowing water remain still subject of unclear description and dependence.

Riverbed erosion and bottom deepening are part of natural fluvial processes in the upper stream. The increasing gradient of these changes is interconnected with the level of human influence in the river basin and riverbed as well. In time the consequences of riverbed erosion will become serious as well as dangerous, i.e. they may have an impact on the lowering of the underground water levels in the river basin or threaten the stability of hydro technical structures. This process in not usually visible to the naked eye, it is lengthy and slow, but can be easily detected by analysis of specific types of measurements. The article will show the section of the Sava River from the Croatian-Slovenian border down to the rkm 670+000, where the Drenje hydropower plant is planned. Regular measurements of water levels, discharge, amount of load transport and cross section profiles along this section of the Sava River prove that significant changes in the riverbed have occurred in the last 20 years. Because of the deepening of the riverbed, at some locations by more than 3.5 m, the stability of bridges in Zagreb and the surrounding area are especially at risk. As a result of unpredictable bottom erosion, the railway bridge Sava Jakuševac was damaged on March 30, 2009. This incident showed that erosion may lead to the wearing away of bridge foundations which in turn is very likely to lead to serious damage to other bridges.

The upper Columbia River, British Columbia, Canada, shows typical anastomosing morphology — multiple interconnected channels that enclose floodbasins — and lateral channel stability. We analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper Columbia River is caused by sediment (bedload) transport inefficiency, in combination with very limited potential for lateral bank erosion because of very low specific stream power (≤ 2.3 W/m 2 ) and cohesive silty banks. In a diagram of channel type in relation to flow energy and median grain size of the bed material, data points for the straight upper Columbia River channels cluster separately from the data points for braided and meandering channels. Measurements and calculations indicate that bedload transport in the anastomosing reach of the upper Columbia River decreases downstream. Because of lateral channel stability no lateral storage capacity for bedload is created. Therefore, the surplus of bedload leads to channel bed aggradation, which outpaces levee accretion and causes avulsions because of loss of channel flow capacity. This avulsion mechanism applies only to the main channel of the system, which transports 87% of the water and > 90% of the sediment in the cross-valley transect studied. Because of very low sediment transport capacity, the morphological evolution of most secondary channels is slow. Measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper Columbia River than in the relatively gentle lower anastomosing reach. With anastomosing morphology and related processes (e.g., crevassing) being best developed in the upper reach, this confirms the notion of upstream rather than downstream control of upper Columbia River anastomosis.

A laboratory study was undertaken to investigate how changes in flow regime and hydrograph shape (number of cycled hydrographs and duration of each hydrograph) together impact bedload transport and resulting bed morphology. Three hydrologic conditions (experiments) representing different levels of urbanization, or analogously different flow regimes, were derived from measured hydrometric field data. Each experiment consisted of a series of hydrographs with equal peak discharge and varying frequency, duration and flashiness. Bedload transport was measured throughout each hydrograph and measurements of bed topography and surface texture were recorded after each hydrograph. The results revealed hysteresis loops in both the total and fractional transport, with more pronounced loops for longer duration hydrographs, corresponding to lower rate of unsteadiness until reaching the peak discharge (pre-urbanization conditions). Shorter duration hydrographs (urban conditions) displayed more time above critical shear stress thresholds leading to higher bedload transport rates and ultimately to more variable hysteresis patterns. Surface textures from photographic methods revealed surface armoring in all experiments, with larger armor ratios for longer duration hydrographs, speculated to be due to vertical sorting and more time for bed rearrangements to occur. The direction of bed surface adjustment was linked to bedload hysteresis, more precisely with clockwise hysteresis (longer hydrographs) typically resulting in bed coarsening. More frequent and shorter duration hydrographs result in greater relative channel adjustments in slope, topographic variability and surface texture. (c) 2019 John Wiley & Sons, Ltd.