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River widening is commonly used as a solution for the rehabilitation of rivers with the main purposes of allowing the river to adjust to its natural dynamics and to improve riparian and instream habitat for flora and fauna, by increasing the heterogeneity in substrate, flow and morphology. Local widening may also be used for confluences rehabilitation as, for many of them, the heterogeneity and fragmentation of the river system were severely affected by previous human interventions. Local tributary widening amplifies the morphodynamic processes, enhancing the diversity in sediment substrate, flow velocities and flow depths. In addition, widening should neither affect aspects such as water level in the tributary nor in the main channel, which is an important consideration for flood safety. The aim of this paper is to analyze the differences in terms of bed morphology and flow dynamics induced by different confluence angles in widen channel confluences.

Most sediment transport equations overestimate the bedload transport rate by several times when applied to mountain rivers. This is due to the fact that the presence of large relatively immobile boulders, which disrupt the flow, is generally not taken into account. Sediment transport in steep channels with boulders was herein investigated using 41 laboratory experiments carried out on a tilting flume for three slopes (S = 6.7%, 9.9%, and 13%). Sediment transport, mean flow velocities and morphology-describing variables were measured regularly during the experiments. The sediment transport capacity is clearly decreasing with dimensionless boulder distance and is better estimated in terms of critical discharge for incipient motion of mobile sediments than in terms of bed shear stress. A sediment transport formula based on excess discharge relative to a critical value, which depends not only on the channel slope but also on the boulder spatial density, is herein developed.

A role of the difference in bed elevations in the main-river (ΔzMR) at its entrance to a 90º straight-channels' confluence is studied numerically using a 3D finite-volume model. Three characteristic hydrological scenarios with DR = {0.250, 0.583, 0.750} are analysed in four confluence layouts having ΔzMR / hd [0.0, 0.50] (where hd stands for the flow depth in the deeper canal at the confluence). It is found that: 1) a portion of the tribu-tary flow in the bottom layers is entrained by the bed-step, 2) the w- velocity has the same order of magnitude as Vxy for ΔzMR ≥ 0.25hd and DR > 0.5, 3) the opposite bank is endangered by erosion due to strong upward motion along this bank, 4) additional shear layer develops on the outer side of the distorted umax-core and 5) the presence of bed-step favours bed-load transport both in and far downstream of the confluence.

Former studies on combining flows resulted in an efficient layout of sewer junctions operated under supercritical approach flow conditions. Straight extensions allowed a reduction in the shock wave heights generated by the merging flows, so that the global discharge capacity was significantly increased. Herein, an extensive experimental campaign is presented on a physical model with the aforementioned layout, although with generalized geometrical conditions now including various conduit diameters. The effects of the main parameters governing the energy losses for combining flows were ascertained to enhance the information available from the literature. The results and their analysis provide a basis for the prediction of energy losses at junction manholes with different upstream and lateral conduit diameters and various flow conditions.

The Klingnau reservoir, situated in north Switzerland, suffers from sedimentation in its left enlargement. The dam is placed in the Aare River about 1 km upstream of its confluence with the Rhine. Due to natural conservation and flood protection reasons, it has been sought for decades to slowdown the sedimentation process in the reservoir. For this purpose, 20’000 m3 of deposited material will be excavated by suction dredge and injected downstream into the Rhine. The objective of the present study is firstly to spot the best place for the material injection downstream. It is then aimed to assure that this injected material will not deposit along the Rhine River down to the Birsfelden dam. The latter is situated 60 km downstream of Klingnau and is the last reservoir on the Rhine River in Swiss territory. To accurately simulate the sedimentation process, one and two-dimensional numerical models are applied. It is confirmed that the majority of injected material stays in suspension and can be transported through the Rhine River down to Birsfelden.

Flow field in shallow waters, which is characterized by its complex mixing process and inherent dynamic nature, is interesting mainly due to its practical importance (e. g. in free flushing operation and sedimentation in large reservoirs). 3D numerical models make it possible to track two-dimensional large turbulence coherent structures, which are the dominant phenomenon in shallow reservoirs flow field. In the present study a fully three-dimensional numerical model SSIIM that employs the Finite Volume Approach (FVM) was utilized to reproduce the 3D flow field. Various shallow reservoir geometries with fixed and deformed equilibrium bed were considered. The measurements by Large-Scale Particle Image Velocimetry techniques (LSPIV) and Ultrasonic Doppler Velocity Profiler (UVP) over the flow depth were used for model validation. Outcomes revealed reasonable agreement between the simulated and measured flow velocity field even when an asymmetric flow pattern exists in the reservoir.

In this paper, we present an experimental study about the motion of bed load particles in water. Recent developments in the stochastic theory of bed load transport call for precise experimental data to validate the models. We set up the experiment in a tilted narrow flume, where we could control water discharge. The erodible bed was made of natural rounded particles of mean diameter 8 mm. Two high speed cameras, disposed next two each other, recorded the transport process at 200 frames per seconds over an observation window of approximatively 1 meter and during periods of 150 seconds. Contrasting with previous experimental study that aimed to track moving particles, we imposed ourselves three constraints: (i) all moving particles have to be tracked, (ii) tracking should be fully automatic, (iii) bed load transport rates have to be measured independently. The former constraint is mandatory to correctly compare to theoretical predictions while the second is a condition to be able to get large samples of trajectories in relatively short time periods. The latter is obviously needed to validate the algorithm. After briefly introducing the numerical treatment that allow the particle tracking, we present some interesting results about the bed load particles dynamics.

River confluences are known for their marked 3D patterns and, due to the complexity of local flow features and bed morphology, they require particular consideration. Although there are studies on the flow structure in junctions of two streams, amore detailed description of the flow patterns is still required. The objective of this work is to contribute to such description at river confluence for concordant bed, where both main and tributary channel beds have the same elevation. For that purpose, a set of experiments with fixed bed under quasi-uniform approach flow conditions was carried out. The experimental facility included a 12 m long and 1 m wide main channel, and a 4.5 m long and 0.15 m wide tributary channel. The confluence angle was 70° so as to represent common natural conditions and the discharge ratio between discharges in the tributary and in the main channel was kept constant. An Acoustic Doppler Velocimeter (ADV) with a side-looking configuration was used to measure the three components of flow velocity on a dense grid of measuring points, providing the accurate characterization of the mean flow and second-order velocity moments. The acquired data set constitutes the most refined characterization of river confluence flow structures known to date, due to the adopted temporal and spatial discretization, and may serve for the validation of 3D numerical models of complex confluent flows. Flow dynamics zones typical of confluent beds are present in the studied case. The separation zone limits the effective lateral flow cross-section, and, hence, results in the added acceleration of the mainstream flow near the downstream junction corner. The upward orientated vertical velocities of high magnitude were observed all along the separation zone.

Dam failures, impulse waves, tsunamis and storm surges are disasters that challenge humanity, often leading to massive casualties and important economic losses. These events generate highly unsteady flow conditions in the form of surges or turbulent bores, associated with extreme loading on infrastructure. In the past, the impact on these flows on buildings was considered too rare and wave induced forces neglected in the design process. However, recent events showed that some measures can guarantee human safety and reduce reconstruction costs. As such, vertical shelters able to withstand extreme loading are fundamental and an estimation of induced forces necessary. Field studies showed that buildings with openings perform better during wave impact and the objective of this research is to evaluate and analyse damage potential of resilient buildings hit by both surges and bores. In particular, the influence of openings as a mitigation measure on the loading process is addressed and quantified. The research is based on an experimental approach. Wave formation is achieved through the vertical release of a water volume from an upper reservoir, generating dry bed surges and wet bed bores in the downstream horizontal channel. A variation of the released discharge results into waves with different hydrodynamic properties. A detailed methodology to hydraulically characterize the generated waves in terms of their water depths and flow velocities is presented and good agreement with the classical dam-break case for both dry surges and wet bed bores is demonstrated. Particular attention is given to wave front celerity and velocity profiles measured behind the wave front, showing some features typical of open channel flows. Buildings were reproduced using aluminium structures installed on a force plate, providing a detailed time history of impact forces and moments. The impact was characterised by high splashes, followed by a quasi-steady flow around the building. For the impervious structures, dry bed surges resulted into horizontal forces proportional to the momentum flux. For wet bed bores, an attenuation of the peak force was constantly observed and the introduction of a reduction coefficient was necessary to achieve a realistic force estimation. In this study the effect of openings and overflow were tested. Four building configurations with seven opening values ranging from 0 to 84\% were investigated using 12 standard waves. The flow through the structure reduced the upstream water depths, providing safer vertical shelters. In terms of loading, the openings produced a linear reduction of the maximum horizontal force, if compared to the impervious case. The configuration with an impervious back wall showed similar results to the impervious building. Openings on the side walls had no influence on the resulting maximum load. Analysis in terms of peak time, wave height at maximum force and impulse pointed out some key differences between forces exerted by surges and bores. The time occurrence of the maximum tilting moment corresponded to the maximum horizontal force and the resulting cantilever arm was constant for all opening configurations. In case of overflow, milder loading conditions were constantly measured. Finally, new formulae to estimate the hydrodynamic load are introduced, taking into account the effect of openings within an adapted resistance coefficient, providing relevant information for the design of safer infrastructures.

One of the common measures for river bank protection is the installation of riprap. There are several methods to design riprap appropriately, which are however generally limited to dumped medium size blocks. Nevertheless, an additional resistance against erosion can be achieved by individually placing blocks in one or several layers instead of dumping them arbitrarily. An experimental investigation has thus been performed to study the stability of large blocks which are compressed as a river bank protection. Tests were carried out including one layer of stones as well as two layers, to evaluate the influence of the riprap layering (e.g. riprap thickness) on the bank stability. The effect of the thickness on the stability of ripraps is investigated in a 10 m long and 1.2 m wide tilting flume, with a rough fixed bed. Riprap median particle size was D50 = 37 mm. Testing was conducted for channel longitudinal slopes 0.015 and 0.030 and riprap bank inclinations of 27, 31 and 35 degrees. The riprap was installed on the top of a wide grain size distribution filter. Supercritical flow conditions were considered, given the steep channel slope. The complete removal of the riprap in a section under a constant discharge was defined as the failure criterion. The riprap failure threshold discharge was determined based on the series of tests with duration of maximum 180 minutes. In each test, riprap transport rate was measured every minute while the stones were tracked by a video camera and collected in a sediment trap at the channel end. The time of total failure was defined by standard video-image processing techniques. A time based analysis of failure was performed and first results revealed that, for similar conditions, the second layer stabilizes the riprap significantly and delays the time for total failure. Nonetheless, transport rate was found to be increased in this latter situation.

Les réseaux d’assainissement font partie des infrastructures clés des pays industrialisés. Selon l’Office fédéral de l’environnement, environ 50'000 km de canalisations publiques sont installés en Suisse, avec une valeur de remplacement supérieure à 50 milliards de francs. Dans un contexte d’urbanisation dynamique, les réseaux de canalisations sont soumis à des modifications et à une extension constantes, qui doivent respecter un cadre légal très strict. Cela nécessite des connaissances approfondies des ingénieures dans la tâche du renouvellement et de l’extension. Le séminaire a comme objectif le renforcement des connaissances hydrauliques dans le domaine des canalisations et la transmission de nouveaux résultats de recherche aux ingénieurs impliqués dans la planification des réseaux. Des exemples de réalisation permettent d’établir le lien entre la planification, l’exécution et le fonctionnement d’ouvrages particuliers. C’est avec grand plaisir que ce séminaire intitulé « Hydraulique des canalisations » est organisé à l’EPFL avec la participation et avec le support du Groupe Romand du VSA et du VSA Suisse

Tsunamis, dam-break waves and impulse waves are catastrophic phenomena that leave thousands of victims and cause severe infrastructural damage. Understanding the impact that these waves have on structures is therefore necessary to properly dimension buildings in wave hazard zones. Previous studies have analyzed the impact of waves on structures, and the effects of building orientation and porosity have been separately investigated, however both factors have not been considered simultaneously. In addition many discrepancies are found in the literature regarding expressions to calculate wave-induced forces. In this study, waves are generated in a laboratory environment, and their impact on buildings with openings is analyzed for different orientations. Results show that rotating the structure does not have an effect on the recorded forces per unit with, but rather delays the time at which forces peak. At the first stages of the wave impact, the influence of streamlining appears to be more important than that of the porosity, and this behavior is then inverted. An expression to predict force maxima is given, with excellent agreement for tsunami-like waves, and conservative estimates for more impulsive waves.

The trap efficiency of a shallow reservoir depends on the characteristics of the inflowing sediments and the retention time of the water in the reservoir, which in turn are controlled by the reservoir geometry. With the purpose of controlling the trapped and flushed sediments in shallow reservoirs, the effects of the geometry on sediment deposition and removal were investigated with systematic physical experiments. The geometry shape factor is an important factor to predict the flow and sediment deposition in the reservoir. The evolution of trap efficiency has an increasing or decreasing effect according to the geometry shape factor and flow patterns. The channel formed during flushing attracts the jet and stabilizes the flow structures over the entire reservoir. Empirical formulas to describe the relationship between the geometry shape factor and sediment trap efficiency as well as flushing efficiency were developed.

Numerical modeling of sediment transport in reservoirs, especially for sudden events such as flushing, is still a challenging research topic. In the present study, sediment transport and sediment flushing are simulated for a Peruvian reservoir. Situated in the Peruvian Andes, the watershed is affected by high erosion rates and the river carries high amounts of suspended sediment whose estimated annual volume is about 5 Million m3. This study aims to investigate the reservoir sedimentation using different numerical models. A one-dimensional (1D) sediment transport model, a horizontal two-dimensional (2D) hydraulic model and a vertical 2D model are used for this purpose. Annual sedimentation, full drawdown flushing, and sediment concentration in power intakes are particularly investigated.

Despite the mechanisms of reservoir sedimentation being well known for a long time, sustainable and preventive measures are rarely taken into consideration in the design of new reservoirs. To avoid operational problems of powerhouses, sedimentation is often treated for existing reservoirs with measures which are efficient only for a limited time. Since most of the measures will lose their effect, the sustainable operation of the reservoir and thus the water supply, as well as production of valuable peak energy is endangered. Today’s worldwide yearly mean loss of reservoir storage capacity due to sedimentation is already higher than the increase of capacity by the addition of new reservoirs for irrigation, drinking water, and hydropower. Depending on the region, it is commonly accepted that about 1–2% of the worldwide capacity is lost annually. In Asia, for example, 80% of the useful storage capacity for hydropower production will be lost by 2035. The main sedimentation process in narrow and long reservoirs is the formation of turbidity currents, transporting fine sediments near to the dam every flood season, increasing sediment levels up to 1 m per year. The outlet devices including intakes and bottom outlets are often affected after only 40 to 50 years of operation, even in catchments with moderate surface erosion rates. The effects of climate change will considerably increase the sediment yield of reservoirs in the future, mainly in Alpine regions due to glacier retreat and melting of permafrost grounds. The today’s challenge of dam owners and engineers is to guarantee with adequate mitigation measures, the future sustainable use of the vital reservoirs supplying water for drinking, food and energy production. Research and development is still urgently needed to identify efficient mitigation measures adapted to the main sedimentation processes involved in reservoirs.

Despite the mechanisms of reservoir sedimentation being well known for a long time, sustainable and preventive measures are rarely taken into consideration in the design of new reservoirs. To avoid operational problems of powerhouses, sedimentation is often treated for existing reservoirs with measures which are efficient only for a limited time. Since most of the measures will lose their effect, the sustainable operation of the reservoir and thus the water supply, as well as production of valuable peak energy is endangered. Today’s worldwide yearly mean loss of reservoir storage capacity due to sedimentation is already higher than the increase of capacity by the addition of new reservoirs for irrigation, drinking water, and hydropower. Depending on the region, it is commonly accepted that about 1–2% of the worldwide capacity is lost annually. In Asia, for example, 80% of the useful storage capacity for hydropower production will be lost by 2035. The main sedimentation process in narrow and long reservoirs is the formation of turbidity currents, transporting fine sediments near to the dam every flood season, increasing sediment levels up to 1 m per year. The outlet devices including intakes and bottom outlets are often affected after only 40 to 50 years of operation, even in catchments with moderate surface erosion rates. The effects of climate change will considerably increase the sediment yield of reservoirs in the future, mainly in Alpine regions due to glacier retreat and melting of permafrost grounds. The today’s challenge of dam owners and engineers is to guarantee with adequate mitigation measures, the future sustainable use of the vital reservoirs supplying water for drinking, food and energy production. Research and development is still urgently needed to identify efficient mitigation measures adapted to the main sedimentation processes involved in reservoirs. A traditional distinctive feature of River Flow conferences has been the organisation of Master Classes the day before the formal opening of the conference. Master Classes present a unique opportunity for PhD and MSc students and young researchers to address their research with renowned senior scientists, meet peers working on similar topics and identify possible collaborations for the continuation of their work. At River Flow 2014 six Master Classes were conducted by 13 masters, enrolling 65 students from 15 countries. This confirms the vitality of the fluvial hydraulics community contributing to ensure the sustainability of IAHR.

To protect spillways against cavitation damage, adding a small air concentration to the flow close to the invert is efficient. Aerator performance on smooth chutes was therefore well studied in terms of air entrainment and downstream air concentration development. Since bottom aerators are built upstream of regions exposed to cavitation, no damages have been observed on spillways. The introduction of roller compacted concrete (RCC) dams in the 1980s promoted the use of stepped spillways rarely used until then. Compared to conventional smooth spillways, they have the advantage of a higher energy dissipation rate, and of a self-aeration point located higher upstream. However, the non-aerated flow upstream of the inception point is exposed to an increased cavitation risk due to flow separation on the steps. Until recently, the uncertainty about the conditions required for cavitation inception motivated conservative unit discharges. Today, the cavitation potential on stepped spillways is better known and is significant, so that techniques are necessary to safely use stepped spillways under increased unit discharges. This research includes a physical model investigation of a deflector aerator on a stepped spillway. The key parameters influencing aerator performance and stepped spillway flow are systematically varied. The air concentration downstream of the aerator is measured at regularly spaced profiles by means of a fiber optical probe. The flow field downstream of the stepped spillway aerator can be described in three main zones: (i) thejet zone where air is entrained on the lower and upper surfaces, (ii) the spray and reattachment zone where spray is produced by the jet impact and where there are rapid variations of the average and bottom air concentrations, and (iii) the far-field zone where the flow depth as well as the average and bottom air concentrations gradually tend towards quasi-uniform conditions. The lower and upper surfaces of the jet issued by the deflector were considered to derive the effective takeoff angles. With the takeoff velocity, it allows to describe the lower and upper jet surfaces with projectile motion trajectories. The maximum jet elevation, the jet length, and the jet impact angle on the pseudo-bottom can then be determined. Similarly to smooth spillways, the air entrainment coefficient of the aerator is described as a function of the relative jet length. Besides, a relation for the air entrainment coefficient in function of the Froude number and the deflector geometry is presented. The average and bottom air concentration developments show a minimum shortly after the jet impact, followed by a maximum in the spray zone. These extrema are quantified and are related to the relative jet length. In the far-field zone, unlike smooth chutes, no continuous detrainment is observed for the bottom air concentration. Both the average and the bottom air concentrations gradually converge to quasi-uniform flow values. Tests with an increased approach flow bottom roughness showed a large increase of air entrainment due to the higher flow turbulence, but only small average and bottom air concentration differences downstream of the jet impact result. A pre-aerated approach flow leads to slightly higher average and bottom air concentrations downstream of the aerator. The design of a stepped spillway aerator is presented in the end to summarize the results obtained and their practical application.