Frederic M. Evers

Last Name

Evers

First Name

Frederic M.

ORCID

0000-0001-5181-8978

Organisational unit

03820 - Boes, Robert / Boes, Robert

Show all metadata

Search Results

Publications 1 - 10 of 56

Landslide-generated Impulse Waves in Reservoirs
Evers, Frederic M.; Heller, Valentin; Fuchs, Helge; et al. (2019)
VAW-Mitteilungen
Landslide-generated impulse waves are typically caused by landslides, rockfalls, shore instabilities, snow avalanches or glacier calvings in oceans, bays, lakes or reservoirs. They are particularly relevant for the Alpine environment because of steep valley sides, possible large slide masses and impact velocities and the great number of reservoirs. In this manual, a state-of-the-art on the impulse wave generation and its effects on dams are presented including a computational procedure. Based on this method, engineers or natural scientists may predict the hazards originating from impulse waves efficiently and economically. The 1st edition of this manual was published in 2009. This 2nd edition includes both updates of existing and new computational approaches for additional hydraulic processes. The introduction in Chapter 1 contains background information on the topic and compares the available methods dealing with landslide-generated impulse waves. The method presented in this manual is based on generally applicable equations derived from hydraulic model tests. Chapter 2 introduces basic principles of the water wave theory. The computational procedure is presented in Chapter 3 and shown in Figure 3-1. It is based on the findings of impulse wave generation and its effects on dams. The computational procedure (Figure 3-1) includes two steps: in Step 1 the generally applicable equations are applied according to Chapter 3, whereas in Step 2 the effects not contained in Step 1 such as the effective instead of the idealised reservoir geometry are considered according to Chapter 4. In Step 1, the mass movement is modelled as a granular slide. To analyse the effect of impulse waves on dams, the wave height, amplitude, period and length are important. These are computed with the equations of Heller and Hager (2010) and Evers et al. (2019) as a function of the slide parameters. Two extreme cases for estimating the wave parameters are considered: (a) laterally constricted (2D) and (b) free radial propagation of the impulse waves (3D). The wave generation in both (a) and (b) depend on the identical parameters, whereas these for the wave propagation are not identical. Once the necessary wave parameters in front of the dam are determined, the run-up height and the overtopping volume may be computed according to Evers and Boes (2019) and Kobel et al. (2017), respectively. Potential overland flow on horizontal shorelines is covered by the equations of Fuchs and Hager (2015). The force effects on dams are computed using the method of Ramsden (1996). This method is first applied as if the dam would be vertical since the horizontal force component is independent from the dam inclination. The additional vertical force component for inclined dams is then computed assuming static wave pressure. If an impulse wave partially overtops a dam, only a partial water pressure has to be considered resulting in a reduction method. Once the results from Step 1 are available, the effects of the geometrical differences to the idealised extreme cases (a) and (b) have to be quantified in Step 2 according to Chapter 4. These differences may result from the prototype reservoir geometry differing from the idealised 2D or 3D geometries, or by the non-granular mass characteristics. The impulse wave parameters may considerably differ due to these effects. The presented method of Ruffini et al. (2019) allows for impulse wave height estimation in intermediate reservoir geometries between 2D and 3D. Approaches for the assessment of edge wave propagation along the shoreline perpendicular to the slide impact direction include equations of Heller and Spinneken (2015) and McFall and Fritz (2017). Moreover, the extent of underwater landslide deposits is covered by the equations of Fuchs et al. (2013). Step 2 is also required if the computational tool is applied, because these include only the generally applicable equations from Step 1. Finally, Sections 4.6 and 4.7 contain a sensitivity analysis and some reservoir safety aspects. Chapter 5 includes four computation examples and the application instructions for the computational tool. In Chapter 6 the conclusions are presented. Although the computational results, such as the run-up height, seem to be exact, it should be kept in mind that the present method results in estimations. Safety allowances for all planned actions have to be considered. Predictions that are more exact may emerge from a prototype-specific model test or numerical simulations.
Tsunamis ausgelöst durch Unterwasserrutschungen in Seen
Fuchs, Helge; Evers, Frederic M.; Razmi, Amir; et al. (2018)
Wasserbausymposium Graz 2018: Wasserwirtschaft - Innovation aus Tradition. Tagungsband
Forces on a Vertical Dam due to Solitary Impulse Wave Run-up and Overtopping
Hess, Fabian; Boes, Robert; Evers, Frederic M. (2023)
Journal of Hydraulic Engineering
Impulse waves feature tsunami-like characteristics and are generated by very rapid mass wasting, including landslides and avalanches, into water bodies. In engineered reservoirs, these waves may run up and overtop the dam, thereby exerting hydrostatic and dynamic forces on its structure. For this work, solitary waves were applied as a proxy for impulse waves and the forces acting on vertical structures during wave run-up and overtopping were investigated with hydraulic laboratory experiments. The solitary waves were generated in a wave channel with a piston-type wave generator and the horizontal pressure forces at a vertical wall as well as a vertical dam-like structure were measured with multiple pressure sensors. The discrete pressure data were used to interpolate pressure distributions and the resulting horizontal forces. Empirical equations were derived, approximating the measured maximum forces and their respective centers of pressure within ±7% for both cases with and without wave overtopping. For small freeboards, already small relative wave amplitudes may exert forces similar to those induced by an earthquake as estimated with a pseudo-static approach.
Run-Up of Impulse Wave Trains on Steep to Vertical Slopes
Kastinger, Maximilian; Evers, Frederic M.; Boes, Robert (2020)
Journal of Hydraulic Engineering
Impulse wave trains are generated by subaerial landslides, rockfalls, or avalanches impacting a water body. Especially in engineered reservoirs, the run-up of waves with small relative heights is critical due to the small freeboard between the still water level and the dam crest. To prevent overtopping, an accurate prediction of the maximum run-up height is important for dam safety and hazard mitigation. The run-up behavior of impulse wave trains on a plane and impermeable barrier with slope angles between 18.4° and 90° was investigated in a two-dimensional wave channel. New breaker-type criteria and a run-up prediction equation for the first five waves were developed. The main findings are that (1) wave crest celerity decreases monotonically from leading to following waves; (2) for nonbreaking and surging-breaking waves of the same wave crest amplitude, the leading wave does not induce the maximum run-up height; and (3) the proposed run-up equation predicts the run-up height of nonbreaking waves and surging breakers with a maximum underestimation of 25% and 40%, respectively. For plunging breakers, it may serve as an upper limit.
Fish downstream passage over weirs at low-head hydropower plants: Field study of total dissolved gas concentrations
Süss, Gabor; Albayrak, Ismail; Evers, Frederic M.; et al. (2024)
Proceedings of the 10th International Symposium on Hydraulic Structures (ISHS 2024)
Hydropower plants (HPPs) and other barriers interrupt the longitudinal connectivity in river networks, which hinders or delays fish migration. One potential solution for downstream fish passage is to use conventional spillways and weirs, e.g., in periods of pronounced fish downstream migration. However, the knowledge of fish injury and mortality during weir/spillway passage as well as on the hydraulic conditions in the associated stilling basins is limited. In particular, it has been rarely studied for European fish species. Weir overflow leads to the entrainment of air, which dissolves in water under pressure. Excessive Total Dissolved Gas (TDG) saturations can lead to gas bubble disease in fish, which can potentially cause fish injuries and mortality. Therefore, in this study we investigate the safety of fish passage over weirs in terms of characteristic hydraulic parameters at the case study low-head HPP Bannwil on the Aare River in Switzerland. To this end, TDG saturations and flow velocities were measured and mapped in the flow reach upstream of the weir and powerhouse and from the stilling basin to 500 m downstream of the power plant. The measurements were conducted using a remote-controlled Teledyne Marine Q-Boat equipped with a River Pro 1200 kHz Acoustic Doppler Current Profiler (ADCP), a Tal-Tech Barotrauma Detection System (BDS) with multiple pressure sensors and a Pro-Oceanus Solu-Blu TDG probe. Compared to the upstream flow reach, the TDG saturation was higher both at the end of the stilling basin and in the turbine outlets. At the downstream end of the study area, 500 m downstream of the weir, the water was still supersaturated. However, compared to thresholds reported in literature, the measured uncompensated TDG saturations were non-critical for juvenile Atlantic salmon (Salmo salar), a target fish species in the Aare River. More measurements at higher discharges and at weirs/spillways with different heads are recommended for follow-up studies because Atlantic Salmon, which are expected to come back to Swiss rivers in the future following considerable fish passage restoration efforts, are sensitive to TDG supersaturation.
Sedimentation in a narrow reservoir under climate change and sediment bypass tunnel operation scenarios
Dahal, Sudesh; Evers, Frederic M.; Boes, Robert; et al. (2024)
Proceedings of the 10th International Symposium on Hydraulic Structures (ISHS 2024)
Reservoir sedimentation is one of the main issues interfering with the sustainable operation of many hydropower reservoirs as it causes a reduction of storage capacity and may also affect dam safety. The rate of sedimentation is anticipated to change due to changes in flow following climate change. Although quantifying the variation of sedimentation is subject to high uncertainty, sediment yield is mainly expected to increase for Alpine catchments due to retreating glaciers and thawing permafrost. Sediment Bypass Tunnels (SBTs) are hydraulic structures to counteract sedimentation problems as they allow for bypassing incoming sediment (bedload and parts of the suspended load) around the dam into the tailwater reach. This study deals with the SBT in Solis reservoir (Switzerland) where an SBT has been operating for more than a decade to counteract sedimentation. The aim is to evaluate the performance of the Solis SBT under climate scenarios by conducting 1D numerical simulations. The HydroCH2018-Runoff ensemble is referred for the future projection of river inflows into the Solis reservoir. In absence of quantified impact on the sediment input, it is computed from calibrated sediment transport equations based on monitored data. The model is found useful to simulate future sedimentation and to compare scenarios of SBT operation during flood events. Considering the impact of SBT operation on energy generation due to water losses, SBT operation during two different floods is more effective than its operation in a single flood for a given total duration of operation.
Composite Modeling to Detect Scale Effects in Embankment Dam Breaching due to Overtopping
Halso, Matthew Christopher; Knüsel, C.L.; Vetsch, David F.; et al. (2024)
Proceedings of the 10th International Symposium on Hydraulic Structures (ISHS 2024)
The failure of a dam can have catastrophic consequences for populations and infrastructure downstream. The processes of dam failure are typically studied with small to medium scale laboratory physical model investigations. Findings from laboratory scale studies should inform decision making for prototype scale dams, but upscaling introduces uncertainties and complexity. Detailed numerical models can simulate complex breach processes and depict larger dams, allowing for investigations at larger scale. But with increasing detail and numerical refinement comes increasing computational cost, making modeling of prototype systems potentially prohibitive. Parametric numerical models allow for efficient simulation at prototype scale, but with simplified geometries and limited erosion processes. These numerical options could connect findings from smaller scale studies to prototype scale, if the effect of scale in each method is accounted for. In this study, the effect of scale is investigated with medium laboratory scale (dam height = 0.5 m) and large laboratory scale (dam height = 1.0 m) breach modeling. Laboratory experiments, detailed numerical modeling, and parametric numerical modeling (with the Macchione and Peter methods) are performed at both scales. During initial breach formation (while reservoir head was constant), the laboratory experiments showed no effect of scale. Later, as the reservoir head fell, a faster increase in breach discharge occurred at large scale, leading to an earlier peak discharge. Detailed numerical modeling showed the effect of scale on breach growth, but with limited reproduction of the effect on breach discharge. Both parametric methods replicated the discharge hydrographs well, but only the Peter model adequately reproduced the effect of scale on timing of peak discharge.
Photovoltaik und Wasserkraftspeicher in der Schweiz-Synergien und Potenzial
Maddalena, Gioele; Hohermuth, Benjamin; Evers, Frederic M.; et al. (2022)
Wasser Energie Luft
In dieser Arbeit wurde das Potenzial von schwimmenden Photovoltaikanlagen (floating PV, FPV) und von an Talsperren montierten Photovoltaikanlagen (dam mounted PV, DMPV) an 23 Schweizer Speicherseen respektive Talsperren untersucht. Jeder Standort wurde mit einer Bewertungsmatrix anhand der Hauptkriterien «Akzeptanz», «Energie und Potenzial» sowie «Wirtschaftlichkeit» bewertet. Für den Bereich «Energie und Potenzial» wurde eine GIS-Analyse zur Bestimmung der geeigneten Fläche unter Berücksichtigung von Beschattung durchgeführt und die erwartete Energieproduktion wurde mithilfe des Tools SUNWELL berechnet. Die Anwendung der Bewertungsmatrizen führte zu separaten Ranglisten der Standorte für FPV und DMPV. Nach Ausschluss der am wenigsten geeigneten Standorte beträgt die geschätzte mögliche Gesamtstromproduktion 350 bis 450GWh/a für FPV und 11,5 bis 14,5GWh/a für DMPV. Ein Vergleich mit bereits realisierten oder geplanten Anlagen in der Schweiz zeigt eine gute Übereinstimmung mit den Ergebnissen gemäss der entwickelten Bewertungsmethodik. Die Ermittlung der möglichen Flächen ist zuverlässig, die Stromproduktion wird jedoch tendenziell leicht unterschätzt. Das erwartete Produktionspotenzial für die untersuchten 23 Standorte ist verglichen mit der gemäss Energieperspektiven 2050+ angestrebten Photovoltaikproduktion von 34TWh/a eher gering, im Vergleich zur aktuellen Produktion von 2TWh/a jedoch erheblich. Zudem liefern PV-Anlagen im Gebirge bis zu 50 Prozent der Jahresproduktion im Winter und die Installation an bestehender Infrastruktur schont natürliche Ressourcen. Eine weitere Abklärung der Machbarkeit für die in dieser Studie identifizierten Standorte sowie die Abschätzung des gesamtschweizerischen Potenzials scheint darum lohnenswert.
1D numerical modelling of Sediment-Bypass-Tunnel operation in a narrow reservoir.
Dahal, Sudesh; Evers, Frederic M.; Boes, Robert; et al. (2023)
Proceedings of the 40th IAHR World Congress
Sustainable operation of many hydropower reservoirs is impacted by reservoir sedimentation which is not only causing a reduction of storage capacity but may also impair the functionality of dam outlets thereby implicating dam safety issues. Sediment Bypass Tunnels (SBTs) represent an effective countermeasure to mitigate sedimentation problems as they allow for bypassing incoming sediment (bedload and parts of the suspended load) around the dam into the tailwater reach. This study considers the Solis reservoir (Switzerland) which has effectively implemented an SBT with intake within the reservoir (type-B SBT) for managing high sediment inflow. The aim is to evaluate the performance of the Solis SBT by conducting 1D numerical simulations. The results show that a 1D model can closely reproduce the processes of sedimentation and SBT operation. Furthermore, the effect of the reservoir water level on SBT efficiency is assessed by conducting a scenario simulation. We found that the reservoir water level has a major impact on the SBT efficiency. For type-B SBTs, synchronous lowering of water level is recommended during SBT operation to ensure effective sediment bypassing.
Efficiency evaluation and simulation of sediment bypass tunnel operation: Case study Solis reservoir
Dahal, Sudesh; Maddahi, Modammad Reza; Albayrak, Ismail; et al. (2023)
Role of Dams and Reservoirs in a Successful Energy Transition
Hydropower is the major source of electricity in Switzerland contributing about 57% (36 TWh/yr) of the total annual generation. Therefore, water storage in hydropower reservoirs is crucial to balance the electricity demand over variable river flow. With the increase in storage demand and climate-related stress it becomes important to sustain the existing reservoir storage capacities. Sedimentation impairs the sustainable operation of reservoirs by reducing the storage volume and may also cause dam safety related issues by the interference of sediment deposits with dam outlets. Sediment Bypass Tunnels (SBTs) are an effective countermeasure to reduce or even stop sedimentation and contribute to a sustainable use of reservoir storage capacity. This study investigates the performance of an SBT constructed at Solis reservoir in the Swiss Alps, operated by ewz. The SBT was commissioned in 2012 to mitigate continuous propagation of sediment aggradation towards the dam since its construction in 1986. As the inlet of the SBT is located within the reservoir and therefore typically submerged, optimized reservoir operation is required during the intended period of sediment bypassing. Annual field measurements were conducted to measure the reservoir bathymetry, sediment concentrations, transport rate and sediment particle sizes on the bed to derive the reservoir’s sediment balance. The measurements between October 2018 and August 2019 are analyzed to investigate bypass efficiencies of the SBT. The results indicate that the efficiency of the SBT was 80%, and thus considerably higher than the previous efficiency rate of 17%, due to adaptation of the reservoir operation to a lower water level during SBT operation. This implies that with proper synchronization of SBT and reservoir operation, this type of SBT can be highly efficient. Furthermore, a 1D numerical model is applied to investigate the processes of sedimentation and sediment management for the Solis reservoir. The data from the field measurements is used to set-up, calibrate and validate the model aiming at investigating the performance of the SBT. The model can reproduce the sedimentation as well as SBT operation in terms of longitudinal bed profile evolution and deposition volume. Moreover, the model also allows for simulating additional scenarios, including e.g. no SBT operation, to compare the effects of different operation modes.

Publications 1 - 10 of 56

Frederic M. Evers

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results