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Advances of roller compacted concrete (RCC) in the construction of concrete dams has significantly influenced the development of stepped spillways. The latter are now more frequently implemented in the rocky abutments of embankment dams. The energy dissipation downstream of stepped chutes is mostly ensured by stilling basins. Such stilling basins are typi-cally designed according to guidelines developed for basins below smooth chutes. A systematic experimental research study revealed that these design guidelines are not applicable for stilling basins with stepped chute approach flows. The aim of this paper is thus to present a practical design guide-line for stilling basins downstream of stepped chutes based on two design examples that highlight the significant differences with smooth approach flows.

Recent studies showed that a specific design can reduce the impact of water waves on structures, thus limiting the damages. Herein the impact of waves on buildings is addressed, pointing out the influence of orientation on the hydrodynamic process.

Chute aerators protect spillways from cavitation damage. Several parameters affect their efficiency, which were intensively discussed in literature. One implicit parameter is the cavity jet impact angle at the re-attachment point of the flow on the chute bottom, which may however not be defined a priori by the designer. The herein conducted experimental research derived this angle and a related general prediction of it, and shows its effect on the aerator performance. The experiments indicate that no distinctive effect occurs if considering the air entrainment coefficient, but that the relative air detrainment rate downstream of the re-attachment point significantly augments with increasing impact angle.

Spillways are designed to evacuate floods in a safe way. They should safely release water in order to avoid dam overtopping with its related damages. Nevertheless, it may be dangerous to assume that a flood is only carrying “clear” water. Large woody debris (LWD) and sediments are often transported by rivers into reservoirs during heavy rainfall events. There is still a lack of knowledge regarding the behaviour of LWD at spillway inlets equipped with piers and gates. The accumulation and blockage of LWD at spillway inlets are a significant problem as they can reduce the discharge capacity of the spillway and consequently, an uncontrolled increase of the water level in the reservoir may occur. Literature provides mainly knowledge on the effect of LWD at bridges in rivers with relatively high flow velocities. However, the latter is hardly applicable for reservoir approach flow conditions. Knowledge of the LWD blockage processes at spillways is important regarding the safety assessment of a dam. The present paper summarizes a series of preliminary laboratory experiments, where the influences of different LWD characteristics are linked to blocking probabilities at an ogee crest spillway equipped with piers. The results highlight the influence of repeatability of events and density of LWD on blocking probabilities under different hydraulic conditions.

Hydrodynamic waves are characterised by unsteady, highly turbulent and irregular behaviours. In nature, such phenomena can be observed in dam breaks, impulse waves and tsunamis. Both wet bed bores and dry bed surges were experimentally reproduced on smooth and rough surfaces. For all tested scenarios a front propagating in the channel was observed, with secondary waves with various frequencies occurring behind the propagating front. Such phenomena are probably a consequence of the non-hydrostatic pressure distribution around the bore front. The present study investigates in both time and frequency domains, the distribution of the frequencies observed on top of the bore. The latter represent the surface fluctuations of a bore behind the front. Measurements allowed to characterise the eddy-size distribution for all configurations. Results also showed that the most recurring frequencies are between 0.5 and 2 Hz. Furthermore, it was shown that the first part of the wave was characterised by high-amplitude oscillations associated with greater energy content.

The blockage of weirs or bridges by in-stream wood can reduce the flood discharge capacity, leading to hazardous situations. To assess the related risk, blocking probabilities quantifications are needed. However, large wood has a random behaviour and it is challenging to accurately evaluate the blockage process and the influence of different large wood or hydraulic parameters properly. Investigations of large wood processes with physical models have been performed in the past but some contradictions regarding the coherence of the results has been found. Herein, a compromise between statistical accuracy and experimental repetitions is presented. The influence of a different number of experimental repetitions on the accuracy of blocking probabilities estimations of groups of stems in an ogee crested weir equipped with piers was systematically evaluated. Statistically justified numbers of repetitions for achieving maximum standard errors of 0.20 are presented for different semi-congested LW transport regimes. The bootstrap re-sampling technique was applied to generalize the results obtained experimentally. It was found that an increasing number of stems may decrease the randomness of the blockage process. This observation allowed to decrease the number of experimental repetitions needed to achieve equal levels of statistical accuracy compared to individual stem experiments.

Piano Key weirs (PKWs) are a hydraulically attractive alternative to linear overflow weirs, increasing the unit discharge at the unregulated spillway inlet for similar heads and spillway widths. This advantage, allowing for operation of dam reservoirs on elevated supply levels thus providing an increased retention volume, is a result of the non-linear nature of PKWs being folded back and forth to make repeating cycles or keys. As PKWs are relatively novel structures, few practical design criteria are available, so that often physical model tests of prototypes are conducted. Nevertheless, first comprehensive and systematic model test series were performed, which provided general design equations. They include the relevant and frequent geometrical dimensions and hydraulic parameters. The paper summarizes recently published design equations relating to the head-discharge ratio of PKWs, and compares the latter with the rating curve of a standard crest profile.

In recent decades, stepped chutes followed by a stilling basin became a standard for spillways of dams. The comprehensive knowledge of stepped chute approach flows on internal air-water flow properties of the hydraulic jump is still too limited for an appropriate design of stilling basins. Therefore, an experimental campaign was performed on a large-scale physical model of a plain stilling basin preceded by a 30 degrees sloping smooth or stepped chute. Stepped chute approach flows induce lower deaeration rates along the jump roller as compared to smooth chute approach flows, indicating longer dimensionless jump lengths, normalized by the tailwater depth. Pronounced bottom air concentrations were observed within the first 40% of the jump length in the stilling basin downstream of the stepped chute. Thus, despite the significantly higher pressure fluctuations, this zone seems better protected against cavitation damage than in stilling basins following a smooth chute.

La combinaison d’écoulements représente un des phénomènes hydrauliques des plus fascinants, en particulier pour les écoulements torrentiels. L’efficacité des réseaux d’écoulement à surface libre, comme les systèmes d’évacuation des eaux en milieu urbain, dépend fortement du bon fonctionnement des regards de jonctions. Récemment, des études poussées sur modèles physiques ont permis une meilleure connaissance des caractéristiques hydrauliques principales des jonctions, fournissant ainsi de critères pour le dimensionnement de cette structure hydraulique.

A diversion tunnel is planned for flood protection in the City of Lyss, Switzerland. This tunnel includes a junction, from which water from a side creek is added to the tunnel flow. The latter is sensitive to choking, so that the junction had to be optimized in a hydraulic laboratory investigation. Its setup finally consists of a drop shaft and an injector generating annular flow in the tunnel. Free surface tunnel flow then occurred for all relevant discharges. This setup is also of interest in sewer systems as well as in spillway and diversion tunnels, where similar problems may occur. The concept was optimized for a specific prototype. General recommendations may be derived for similar situations

Le comportement hydraulique des réseaux d’égouts est généralement de type gravitaire et par essence non-stationnaire, car tributaire des cycles de consommation et du caractère aléatoire des apports naturels. Toutefois, les conditions rencontrées, liées en particulier à des sections prismatiques à rugosité constante ainsi qu’à une variation lente du débit, sont favorables à un dimensionnement stationnaire. Cette approche simplifiée offre l’avantage d’imposer un contrôle systématique du réseau en tenant compte des particularités locales sur l’écoulement. Le dimensionnement des canalisations vise à garantir un écoulement à surface libre, avec une circulation d’air suffisante pour éviter leur mise en charge. Les débits à considérer sont préalablement définis par le Plan Général d’Evacuation des Eaux (PGEE). Ils concernent la capacité maximale requise d’une part et le débit de temps sec pour lequel la formation de dépôts doit être évitée. Le présent article passe en revue les méthodes classiques du dimensionnement hydraulique, dans le respect des consignes de la Norme SIA 190 (2000). Il se concentre ensuite sur les conditions particulières d’écoulement susceptibles de réduire la capacité théorique d’une canalisation. Les effets liés à la turbulence de l’écoulement et à l’entrainement d’air sont considérés et des méthodes sont proposées pour les prendre en compte dans le calcul. Finalement deux exemples de dimensionnement préliminaire sont présentés pour illustrer la démarche. Le premier concerne une canalisation à faible pente, le second traite le cas d’une forte pente.

A comparative analysis of a wide range of air-water flow properties was conducted for two types of phase-detection intrusive probes including fiber-optical and conductivity probes. Experiments were conducted on a stepped spillway model for a skimming flow discharge q = 0.478 m(2)/s and for Re = 4.7 105 in a flow region just downstream of the inception point of free-surface aeration and in the fully developed flow region. The comparison of a large number of key air-water flow properties showed a very close agreement for the two sensor types including void fraction, interfacial velocity and equivalent clear water flow depth enabling a direct comparison of past and future data collected with either phase-detection probe type. Minor differences were observed in terms of chord sizes, clustered properties and interparticle arrival times linked with the slightly smaller sensor size of the fiber-optical probe. The in-line positioning of the leading and trailing tips of the fiber-optical probe affected the trailing tip properties resulting in elevated turbulence intensities. An optimum dual-tip phase-detection probe design should consist of small probe tips positioned side-by-side. (C) 2017 Elsevier Ltd. All rights reserved.

Nach erfolgreichem Abschluss der interdisziplinären Vorgängerprojekte «Rhone-Thur» und «Integrales Flussgebietsmanagement » wurde im Rahmen des durch das Bundesamt für Umwelt (BAFU) unterstützten Forschungsprogramms «Wasserbau und Ökologie» ein neues Projekt gestartet, welches sich auf die Geschiebe- und Habitatsdynamik in Fliessgewässern konzentriert. Im Projekt werden die zwei Themenschwerpunkte Geschiebereaktivierung und Gewässerdynamisierung sowie Revitalisierung von Auenlandschaften bearbeitet. Im vorliegenden Beitrag werden die Zielsetzung sowie die Projektschwerpunkte mit den daraus resultierenden einzelnen Teilprojekten vorgestellt.

Aufgrund des Fortschritts im Talsperrenbau mit Walzbeton (RCC) werden weltweit häufig Treppenschussrinnen erstellt. Nach jeder Schussrinne ist ein hydraulisches Bauwerk zur Energiedissipation vorzusehen, beispielsweise ein Tosbecken. Obwohl die Hydraulik von Treppenschussrinnen in den letzten Jahrzehnten eingehend untersucht wurde, sind aktuell nur wenige Ansätze zur Bemessung von Tosbecken nach einer Treppenschussrinne verfügbar. Die hier vorgestellten umfangreichen Modellversuche sollen diese Lücke für klassische Tosbecken mit ebener Sohle ohne Einbauten schliessen. Die Experimente zeigen, dass solche Tosbecken unterhalb von Treppenschussrinnen nicht mit den gleichen Ansätzen dimensioniert werden können, wie sie nach glatten Schussrinnen verwendet werden. Ziel dieses Artikels ist es, neue Bemessungsansätze für solche Tosbecken bereitzustellen.

New design information regarding the hydraulic behaviour of classical stilling basins downstream of stepped chutes is presented and discussed. An extensive experimental campaign revealed that classical stilling basins preceded by stepped chutes cannot be adequately designed using the principles developed for smooth chute approach flow, as is done in common engineering practice. As such, new practical design recommendations are proposed. The detailed design procedure is illustrated with examples of stilling basins downstream of smooth and stepped chutes.

The Authors made an interesting contribution to the assessment of the discharge coefficient of Piano Key Weirs (PKW). The Discussers were impressed to read that the Authors conducted some 600 tests thereby producing nearly 3000 data points.

Spillways are safety elements of dams that allow to release floods. They spill water to avoid overtopping with its potential structural damages at the dam and the downstream environment. Nevertheless it may be unsafe to assume that a flood only carries clear water. Large woody debris (LWD) are often transported by rivers into reservoirs during heavy rainfall events. There is still a lack of knowledge regarding the behaviour of LWD at spillway inlets. The accumulation and blockage of LWD at spillway inlets is a significant problem as it can change the load on the structure and also the functioning of the spillway by reducing the discharge capacity and increasing the reservoir water level. Once this point is reached, new conditions upstream are developed for the reservoir as head increase or enlargement of inundated areas. Literature provides mainly knowledge on the effect of LWD at bridges in rivers with relatively high flow velocities. However, information of the effects and consequences for reservoir approach flow conditions is generally unknown. Knowledge of the LWD blockage processes at a reservoir spillway may be vital regarding the safety evaluation of a dam. The present paper summarizes a series of laboratory experiments, where different LWD characteristics were related to blocking probabilities at an ogee crest spillway equipped with piers.

The Karahnjukar dam spillway is the spillway for the Halslon reservoir, the main reservoir for the 690 MW Karahnjukar Hydroelectric Project in East Iceland. The spillway consist of a 140 m long overflowing weir with a capacity of 2250 m3/s which discharges into a side channel, followed by a 450 m long chute. The chute terminates at a canyon edge where the jet drops some 100 m into a narrow gorge downstream of the Karahnjukar dam. During the design phase of the project, the flow conditions in the spillway were modelled in the hydraulic model tests in 1:45 scale model at the Laboratory for Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich. The power plant went into operation in 2008 and since then considerable experience has been obtained from operation of the spillway. In particular, flow depths and air discharge measurements have been obtained during spilling periods. In this paper, these measurements are presented and compared with results from the hydraulic model tests. In particular, flow depths are discussed as well as aeration effectiveness.

The weir is a fundamental structure in hydraulic engineering, serving to retain a water body, to control a water level, facilitate flow diversion, or to measure discharge. Under particular site conditions, the cross-sectional width at the weir location is limited so that either higher overflow depths or a compressed weir expansion are set. A form of the latter arrangement is the so-called labyrinth weir, which is composed of rectangular, trapezoidal or triangular plan shaped weirs, so that the geometrical crest length is increased. Along with the recently developed Piano Key Weir, labyrinth weirs represent economically and hydraulically sound alternative for increasing spillway discharge capacity. The present paper describes their historical development, reviews the main advances until the 1980s, summarizes current design guidelines, and presents the main individuals having participating in their development.

Hydrodynamic waves are an unsteady flow motion generated by rapid water level rise. In nature, such events can be found in dam-break waves, impulse waves and tsunamis. These phenomena are rare, but highly destructive. The present study is based on an experimental approach and it investigates the hydrodynamic behavior of bores propagating on wet bed in terms of height and velocity profiles. The waves are investigated using Ultrasonic distance Sensors (US) to measure the wave height and average front velocity; the instantaneous velocity profiles were obtained through an Ultrasonic Velocity Profiler (UVP), installed in the bottom of the channel, with an emitting frequency of 2 MHz and inclined with an angle of 20° in the upstream direction. The acoustic scattering was increased using a hydrogen bubble technique with an anode and a cathode installed in the upstream part of the channel. The probe was sampled with a frequency varying from 13.5 to 55 Hz depending on the maximum wave height. A sensitivity analysis of the main influential factors was carried out, pointing out the need for a compromise between quality and quantity for these highly unsteady flows. Results showed some interesting logarithmic profiles typically associated with open channel flows for all wave configurations.

Side-channels are a typical element of earth or rockfill dams to discharge floods sideways instead frontally, such as normally adopted for concrete dams. The side channel received attention from the hydraulics community from the 1920s, once the first large mentioned dams were erected, and its use culminated at Hoover Dam in the mid 1930s, based on a large test program. This paper highlights the major advancement of this basic element of hydraulic structures up to the late 1950s,both describing key installations over the world, and the actors who have furnished the governing design equations for water flow with spatially-increasing discharge. Short summaries on the biographical background are also provided, along with a discussion of the main literature that allowed for the current knowledge in this fascinating field of open channel flow.

Inland navigable waterways are significant in cargo transport and leisure activities. In parallel, these channels and rivers often suffer from the ship traffic, as the generated waves may damage waterway banks, along with their riparian fauna. As a consequence, speed limits have commonly been introduced. In some cases, adaptations on the vessel might be more appropriate as an alternative. This paper describes a flap that is mounted at the stern of a barge and is operated by a pusher tug. The barge is used to transport around 170 tons of waste per course from the City of Geneva (Switzerland) to an incineration plant. The optimum shape of the flap was derived from numerical and physical modeling, and its effect tested in situ. The latter indicated that, on site, the wave energy at 20 m distance to the convoy was reduced by half with the use of the flap.

Existing riverbank riprap could face the risk of failure if the flood regime changes in future. Additionally, changed sediment transport in rivers, as a possible result of climate change, impacts the failure risk of flood protection measures. Evaluation of this potential failure is the primary issue of riprap stability and safety assessment. The consequences of the bank failure are probably uncontrolled erosion and flooding with disastrous consequences in residential areas or damage to infrastructures. Thus, a probabilistic analysis of riprap failure considering different mechanisms due to the flood and sediment transport uncertainties is required to assess embankment stability. In this article, the concept of a probabilistic assessment model based on Monte Carlo simulation method, moment analysis methods, and Rosenblueth point estimation method are presented to define the failure risk of riprap as the river bank protection. The probability of failure in different modes, namely direct block erosion, toe scouring and overtopping, has been defined by taking into account the river bed level variation based on bedload transport described with a probabilistic function of the peak discharge. The result of three models comparison revealed a good agreement (the average deviation of less than 2%) in estimation of riprap failure probability. This model is a strategical tool to search the critical river reaches and helps to evaluate the risk maps. So that, the model could cover the engineering aspect of environmental stability in the rivers with riprap as the bank protections.

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger.

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.

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