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In the context of a comprehensive research project investigating the hydrodynamic loading on structures with openings, this paper focuses on the wave generation techniques currently used and the test results associated with it, proposing a particular tsunami-like wave using a vertical water volume release mechanism. The latter allowed a certain volume of water to flow gravitationally from an upper reservoir into a lower basin through a set of pipes. The propagation of the resulting wave took place in a horizontal channel where wave height and velocities were measured. Both dry bed surges and wet bed bores were investigated, however the present paper mostly focuses on dry bed surges. The study indicated that the surges generated with this mechanism had similar behavior to those resulting from a Dam-Break technique and a good agreement between the experimental points and the theoretical solutions of Ritter (1892) and Whitham (1955) was found. Lastly some differences between wet bed bores and dry bed surges are presented and briefly discussed herein.

Beside analytical approaches, physical modelling represents probably the oldest design tool in hydraulic engineering. For free surface flows, the similitude according to a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. In parallel, fluid constants such as the surface tension and the viscosity might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Consequently, small physical models operated under the Froude similitude systematically underestimate the air entrainment rate and air-water interfacial properties. To limit this deficit, minimal values of the Reynolds or Weber number have to be respected. The paper summarises the physical background of these limitations and their combination in terms of the Morton number. Based upon a literature review, these limits are listed and discussed, resulting in a series of more conservative recommendations in terms of air concentration scaling.

The Kühtai reservoir is planned as an addition to the existing Sellrain-Silz group of HPPs. Two natural hazards relevant in terms of potential impulse wave impact on the dam were identified: a snow avalanche near the dam axis and a possible landslide further upstream. A preliminary analytical evaluation of impulse wave heights and wave run-up based on empirical equations showed that dam overtopping could not be excluded. However, several limitations of this evaluation were not satisfied, resulting in a reduced validity of the prediction. Thus, impulse wave generation was investigated in a 1:130 hydraulic scale model. Beside tests related to the relevant events, an additional systematic parameter variation validated the quality of the results. However, as no overtopping occurred even for the parameter variation, no measures such as breakwater or increase of the freeboard were required. The model test results are compared to a further analytical evaluation based on the recently published VAW-manual on landslide generat-ed impulse waves.

Riprap is a common measure for protecting river banks against lateral erosion and several methods exist to design them. However, they are generally limited to dumped medium size rocks. If large rock blocks are required for stability reasons, they cannot be dumped anymore but they have to be placed individually. This gives additional resistance against flow erosion. The behavior of large rock blocks for alpine river embankments was so far rarely studied. Thus, an experimental investigation was conducted to investigate the stability of such compressed large blocks as river bank protection. Experiments were conducted in a 10 m long, 1 m wide flume with a rough fixed bed. Riprap was reproduced with uniform crushed stones having three different median block sizes of D50=0.037, 0.042 and 0.047m. Testing was undertaken for a Stream-Wise slope of 0.03 in supercritical flow conditions. Transversal slope of the riprap was 3.5V-5H: One layer of blocks as well as two layers was studied in order to investigate the influence of the riprap thickness. They were compressed and placed on the filter with a wide grain size distribution. The riprap failure threshold discharge was determined based on series of tests with duration of 3 hours. Riprap erosion rate was measured with a one minute frequency, by means of block tracking with three cameras and standard video-image processing techniques. Furthermore, the eroded rocks were collected and weighed in a sediment trap at the downstream end of the channel. The time of first total failure was recorded and a time based analysis of failure was performed. Total collapse of the blocks in a reach over the whole bank was defined as full failure. First results revealed that for similar unit discharge the rate of block erosion is significantly decreased by increasing the size of the riprap. The time of failure dépends also on the size of blocks. It could be observed that under the same conditions, the upper layer stabilized the protection system and delayed the time of total failure. Nevertheless, erosion rate of the upper layer of rock blocks increased.

Kariba Dam is a 128 m high arch dam located on the border between Zambia and Zimbabwe. The dam has been constructed in the late 1950s and formed at that time the largest man-made lake worldwide. The dam is equipped with 6 flood gates, each about 9 m high by 9 m wide, allowing for a total outflow of about 9000 m3/s. The plunge pool downstream of the dam consists of sound and relatively hard gneiss bedrock and is basically unlined. Nevertheless, frequent outflows generated between 1962 and 1981 have formed an 80 m deep scour hole in the bedrock, which is unprecedented in dam history. As the flood gates are located in the upper part of the dam wall, they operate under relatively low velocities and thus generate plunging jets that impact quite close to the dam foundations. As such, potential regression during further scour formation might approach the dam foundations and should be avoided This paper presents a combined physical-numerical study investigating scour potential at Kariba Dam, performed by a consortium consisting of the Laboratory of Hydraulic Constructions of the Swiss Federal Institute of Technology in Lausanne (EPFL) for the physical modelling and the consulting company AquaVision engineering Ltd. In Ecublens, Switzerland (AVE) for the numerical modelling and for future scour predictions. The paper focuses on the hybrid methodology that has been proposed to assess past and future scour formation in the plunge pool.

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.

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.

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.

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.

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.