Spatially continuous hydrodynamic pressure measurements remain a key challenge in coastal and offshore engineering, where conventional discrete point sensors offer limited spatial coverage and high installation costs. This study presents the first application of a distributed fiber-optic pressure sensor (DPS) cable and Distributed Acoustic Sensing (DAS), deployed in the Large Wave Current Flume (GWK+), providing 500 Hz pressure measurements over a 25 m section. Nine regular wave conditions combining three wave heights (0.4, 0.6 and 0.8 m) and three periods (3, 5 and 7 s) were generated at 3.0 m still water depth and benchmarked against wave gauges. DAS-derived surface wave elevations reproduced the expected wave shape and phase, with wave height errors of -13.8% to +11.7% (MAE 2.8-8.8%) and no systematic period/height dependence. Wave celerity and wavelength, derived from the DAS measurements, deviated from theory by -0.3% to +1.8% and -9.8% to +1.2%. The spatially resolved reflection coefficient, estimated from the DAS record, ranged from 0.031 to 0.414, following surf similarity theory.The DPS-DAS combination delivers spatially continuous measurements of wave elevation, wave celerity, wavelength, and reflection coefficient from a single acquisition, representing a scalable alternative to discrete sensor arrays for coastal structures assessment.

Reliable real-time measurement of suspended sediment mass concentration (SSC) is essential for effective environmental monitoring and management. It is also important for the operation and maintenance of hydropower schemes, particularly in managing reservoir sedimentation and mitigating turbine abrasion. However, sensor readings are strongly influenced by variable sediment properties, particularly size and shape, hindering reliable monitoring. This study systematically investigates the effects of particle size (median particle diameter d50 and Sauter Mean Diameter SMD) and shape (sphericity Ψ) on the responses of several turbidimeters and acoustic sensors (single- and multi-frequency), and develops methods for practical application. A customized recirculating cylindrical tank with a volume of 246 L and a maximum upward flow velocity of 0.2 ms-1 enabled testing various natural and artificial particles (up to 2 mm) across SSCs from 0.5 to 25 gl-1. We analyzed the specific outputs of the instruments, defined as the outputs divided by SSC, representing the calibration factors for each particle type. We found that for turbidimeters, the specific output scaled with inverse power-law relations of d50 as well as SMD, and decreased nearly linearly with Ψ. SMD and Ψ proved effective for combining size/shape effects and representing shape-related output, offering a basis for generalized field calibration. We developed three generic models to predict sensor output conversion factors for improved real-time SSC monitoring and calibration. The best-performing data-driven model, applied to a natural sediment sample, showed good agreement for turbidimeters but overestimated acoustic sensor response, highlighting refinement needs. The findings advance the understanding of sensor responses and support the feasibility of generic prediction models across diverse sediment types and sensor technologies. This study contributes to better informed sensor selection and calibration, directly enabling more effective and sustainable monitoring and management of water and sediment resources.

The breaching of earthen embankment dams can result in uncontrolled release of immense volumes of water, which can be catastrophic to downstream settlements, infrastructure, and ecosystems. The spatial dam breach process depends on the embankment sediment grain size distribution (GSD), a dependence that is investigated here with an experimental hydraulic model in combination with a numerical model. Experimental results indicate that breach development is faster, and therefore a larger flood discharge is expected, for dams made of sediment with wider GSDs. The numerical model was set up to reproduce the experiments, by applying a single-grain morphodynamic solver that was systematically calibrated to the two dominant morphodynamic processes. The model reproduced the rates of breach growth, breach discharge, and sediment erosion for the uniform-sediment dam, as well as the faster breach growth in dams made of wider-GSD sediment. However, the breach growth rate was overestimated for dams with wider sediment GSDs.

The failure of embankment dams due to overtopping can produce floods that inundate vast downstream regions. Flooding extents are related to the breach formation process, which depends on numerous properties of the dam-reservoir system, including the embankment material grain size distribution (GSD). The effect of GSD on spatial breaching in non-cohesive homogeneous dams is studied here through composite modelling. A numerical model that applies a multi-grain morphodynamic solver was systematically calibrated using a previous laboratory hydraulic model parameter investigation of constant-head overtopping with mixed-size sediment dams with varying GSDs. The numerical model is applied to extend the parameter investigation by simulating longer dams with larger reservoirs, and two additional dams with different GSDs. Dimensionless equations for breach evolution, and a proposed empirical-analytical model for estimating breach discharge and sediment erosion, show good agreement with experimental results. Relations are proposed for determining the hydraulic roughness coefficient and the number of grain classes needed for multi-grain morphodynamic numerical modelling, as a function of GSD.

Sediment Bypass Tunnels (SBTs) are hydraulic structures designed to mitigate reservoir sedimentation, mainly used in Switzerland, Japan, and Taiwan. The SBT efficiency depends on multiple factors including the incoming sediment yield, SBT inlet location, reservoir water level, and the timing of SBT operation relative to a flood event. To evaluate bypassing efficiency and optimize SBT operation, a methodology is developed to integrate sediment bypassing processes in a 1D numerical model for simulating the sedimentation dynamics under varying hydraulic conditions. The well-monitored case of the Solis reservoir in Switzerland with SBT operation serves as a good basis for this study. After calibrating and validating the model with the field data, three different categories of SBT operation scenarios are studied for a 5-year flood event: i) no SBT operation, ii) the effect of reservoir water level during SBT operation, and iii) the optimum duration of SBT operation. The simulations reveal that SBT operation is highly effective in reducing the amount of sedimentation by 89% compared to no SBT operation. This equals to the prevention of a 9% loss in active storage volume. However, the SBT efficiency is highly sensitive to reservoir operation. A maximum efficiency is achieved at a lower reservoir water level below the minimum operating level for energy generation, while it also releases higher sediment concentrations to the downstream reach. Furthermore, a longer duration of SBT operation increases the bypassing efficiency and minimizes the loss of active storage volume but goes along with a reduction in hydropower generation. Thus, a comparison of net benefits for different scenarios is suggested to derive an optimal SBT operation mode for similar situations. Overall, the applied methodology serves as a useful basis for evaluating and optimising the sediment management efficiency of SBTs and can thus contribute to improving the sustainable operation of reservoirs.

Storage hydropower has the ability of flexibly generating electricity to match fluctuating power demand. However, rapid changes of water discharge in river reaches downstream of storage hydropower plants, referred to as hydropeaking, result from this intermittent production mode and may have potentially damaging effects on a river’s ecosystem. The construction of compensation basins usually embedded along the waterway between the powerhouse and the receiving water represents the state-of-the-art for hydropeaking mitigation. In recent studies, the application of battery energy storage systems (BESS) as an alternative mitigation option has been proposed. Instead of buffering the turbine discharge in a basin, electrical energy is stored in and retrieved from a BESS to meet short-term demand requirements, while the hydraulic machinery is ramping up and down according to environmental discharge constraints. The technical and economic feasibility of BESS compared to compensation basins is evaluated based on a newly introduced first-order assessment approach. If environmental discharge constraints are to be strictly followed, the exclusive application of BESS is deemed not feasible, due to the limited operation range of Francis and – to a lesser extent – Pelton turbines, especially for low partial loads. Therefore, hybrid systems combining a BESS with a smaller compensation basin are investigated as existing research focused either on a basin- or a BESS-only approach. Based on production time series of three case study hydropower plants, the sizes of basins and BESS are estimated. Basin sizes can be reduced with a hybrid system by 51% to 96% compared to a basin-only approach, with BESS energy capacities ranging approximately from 10 to 100 MWh. The cost efficiency of hybrid systems is strongly influenced by two factors, namely the future battery costs as well as the overall unit costs for the compensating basin. While the former are subject to considerable uncertainty especially as BESS reach their end-of-life much earlier compared to hydraulic structures and therefore require regular replacements after 10 to 15 years, the latter are highly site-specific as they include land availability and acquisition costs. The case studies show that a hybrid system of basin and BESS may represent a cost-competitive alternative to a basin-only approach when the latter’s investment costs are high or space is limited, even if additional revenue streams including ancillary services and energy arbitrage are not considered.

Wave assessment is essential for the design and monitoring of coastal structures, assisting engineers to ensure infrastructure integrity. Common methods for wave monitoring involve measuring water surface height or hydrostatic pressure, with pressure-based systems offering significant advantages, especially in the detection of small wave heights such as tsunamis in open ocean conditions. Distributed fiber optic (DFO) technology has played a key role in addressing complex engineering challenges by providing spatially high and accurate temperature and strain measurements. Recently, a distributed fiber optic pressure sensor (DPS) has been developed that can measure hydrostatic pressure with high spatial resolution and over long distances. This study assesses the dynamic wave measurement capability of the DPS by testing its ability to measure the hydrostatic pressure of a propagating solitary wave under controlled laboratory conditions. The DPS was tested with different relative wave heights and validated by two independent conventional measurement systems: 1) ultrasonic distance sensors (UDS) and 2) piezoresistive pressure sensors (PPS). The free water surface profile wave was reconstructed from the DPS and PPS pressure measurements using the Bonneton water surface reconstruction method. Comparison of the three measurement systems shows good agreement in detecting the target wave crests, with deviations of less than 3%. The proposed measuring system has great potential to be adopted as monitoring tool for wave-related field applications, such as coastal/surf zone monitoring or tsunami early warning systems, where high-resolution pressure measurements are required. However, additional field validations are needed to further assess its effectiveness under real-world conditions.

Anthropogenic plastic waste heavily pollutes global water systems. In particular, micron-sized plastic debris can have severe repercussions for the ocean flora and fauna. Microplastics may also affect physical processes such as wave breaking, which are critical for air–sea interaction and albedo. Nevertheless, the effects of micron-sized plastic debris on geophysical processes are widely unexplored. Herein, we investigate the effect of microplastic collected from the North Pacific and a surfactant mimicking surface active materials present in the ocean on the stability of foam generated by breaking wave experiments. We found that microplastic particles increase foam stability. In particular, an increased foam height was found in a column foaming setup, while an increased foam area was observed in a laboratory-scale breaking wave channel. We propose that microplastic particles assemble at the air–water interface of foam bubbles, form aggregates, presumably decrease the liquid drainage in the liquid film, and thus change the lifetime of the liquid film and the bubble. The effect of surfactants is generally larger due to their higher surface activity but still in a range where synergistic effects can be observed. Our results suggest that microplastic could influence oceanic processes essential for air–sea interaction, sea spray formation, and albedo.

Sedimentation challenges water reservoir operations globally, particularly for storage hydropower plants (HPPs), necessitating effective management strategies. One such strategy, fine sediment venting through turbines, though effective in managing sediment continuity, increases hydro-abrasive erosion on turbines due to the additional sediment load. Hence, there is a need for precise real-time monitoring of suspended sediments. Existing systems, however, often lack the capability to measure suspended sediment mass concentration (SSC) and particle size distribution (PSD) with low uncertainty, particularly for coarser particles, such as sand. To maintain particles with sizes up to 2 mm in suspension, which is the size of particles vented through the power waterways of the turbines, this study developed a customized laboratory setup with an upward flow column and a closed pump circuit. To foster a homogeneous SSC distribution, the setup was hydraulically optimized by different diffusor designs at the inlet of the upward flow column. We tested particles ranging from 1500 - 2000 mu m at SSCs up to 20 gl(-1) with optical and acoustic sensors to prove our concept. First results yielded as expected mostly linear relationships between instrument outputs and nominal SSC, particularly for larger particles. This indicates that the setup allows keeping particles up to 2 mm in suspension, enabling further measurement series to better understand the impacts of sand particles in combination with silt on sensor performance. This is crucial for enhancing suspended sediment monitoring capabilities for fine sediment venting at HPPs.

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.

Abstract Mass movements constitute major natural hazards in the Alpine realm. When triggered on slopes adjacent to lakes, these mass movements can generate tsunami-like waves that may cause additional damage along the shore. For hazard assessment, knowledge about the occurrence, the trigger and the geomechanical and hydrogeological mechanisms of these mass movements is necessary. For reconstructing mass movements that occurred in or adjacent to lakes, the lakes’s sedimentary record can be used as an archive. Here, we present a prehistorical mass-movement event, of which the traces were found in an alpine lake, Lake Thun, in central Switzerland. The mass movement is identified by large blocks on the bathymetric map, a chaotic to transparent facies on the reflection seismic profiles, and by a mixture of deformed lake sediments and sandy organic-rich layers in the sediment-core record. The event is dated at 2642–2407 cal year BP. With an estimated volume of ~ 20 × 106 m3 it might have generated a wave with an initial amplitude of > 30 m. In addition to this prehistorical event, two younger deposits were identified in the sedimentary record. One could be dated at 1523–1361 cal year BP and thus can be potentially related to an event in 598/599 AD documented in historical reports. The youngest deposit is dated at 304–151 cal year BP (1646–1799 AD) and is interpreted to be related to the artificial Kander river deviation into Lake Thun (1714 AD).

The overtopping of embankment dams and levees often causes erosion of embankment material, and can result in failure of the structure by breaching. The breaching process is affected by numerous characteristics of the embankment and reservoir system, including embankment geometry, material composition, and hydraulic conditions. The effects of these parameters are generally investigated by physical model experiments. The extent to which a parameter is investigated is often limited by the amount of time required for physical model setup, experimentation, and data post-processing. This study proposes a composite modeling strategy for more efficient modeling of embankment dam breaching due to overtopping. First, an embankment dam breach is modeled with physical experiments. Second, a corresponding numerical model is set up, with the same geometry, material composition, and hydraulic inputs as the physical model. Next, important findings from the physical modeling are implemented in the numerical model. Lastly, the numerical model is validated with results from the physical modeling. The composite modeling strategy was applied to an investigation of the effect of material grain size on dam breaching. The composite modeling strategy showed the ability to represent numerous effects of material grain size, including erosion rates and timing of peak outflow, as confirmed by separate physical modeling of the same system. Preliminary results indicate that the composite modeling strategy is a viable option for modeling dam breaching to investigate effects of various parameters on the breach process, allowing for greater efficiency and larger test series than with physical modeling by itself.

In freshwater systems (rivers and lakes), historical and recent tsunamis have been documented and their traces have been found in the geological record, but studies of paleotsunamis (prehistorical tsunamis) in such environments are still underrepresented. This contribution reviews paleotsunami studies with a focus on the post 2011 period and uses historical events to highlight some areas of research that have received little attention. In the past decade, the number of paleotsunami studies has increased and this includes those carried out over freshwater settings. However, studies of lacustrine paleotsunamis compared to studies on marine paleotsunamis are still rare and those for rivers are to our knowledge non-existent. Similarly, studies of historical tsunamis generated by meteorological disturbances have been carried out but there have been none for their paleotsunami counterpart. Thus, within this review, to cover all different aspects of tsunami generation processes in freshwater systems, we have used several historical examples, although there is a notable focus on lacustrine paleotsunamis. This review shows that future studies of freshwater paleotsunamis are necessary in order to better understand their causes, frequencies and hazard potential.

Landslides along river, lake, reservoir and ocean shorelines may trigger impulse waves when they slide into the water body with a high velocity. This secondary process can extremely expand the area threatened by the landslide beyond its primary impact zone. Since the impoundment of the Three Gorges Reservoir in 2003, several landslides have caused huge property damage and several casualties due to an insufficient understanding of and reaction to impulse waves as a secondary process in landslide disaster risk management. This contribution aims to provide an integrative approach for risk perception and mitigation of a local landslide considering impulse waves as a secondary disaster risk. Jiuxianping landslide is located in the middle part of the Three Gorges Reservoir in China. Featuring a large thick layer of rock slope, the elevation of the landslide ranges from 95 to 385 m a.s.l., and the volume is approximately 5.7×107 m3. The trailing edge of the landslide appeared as a more than 100 meters transverse tensile crack with an opening width of at least 25 cm in 2008, leading to damaged housing. The landslide stability is strongly influenced by rainfall and the reservoir water level. More than 300 people still live at the landslide site and there is a shipyard in operation at its toe. As a new perspective to detect secondary disasters, the areas with the highest risk and probability of damage under different conditions were estimated using an auto search function in GeoStudio and the Morgenstern-Price method. Then, we simulated the landslide runout as well as wave generation and propagation using Tsunami Squares to predict the risk intensity and impact area of the generated impulse waves. Lastly, we evaluated the warning levels for different scenarios and proposed the area restricted for navigation at corresponding warning levels. Our case study demonstrates the necessity and the importance of considering secondary disaster risks such as impulse waves in landslide early warning system.

Landslide tsunamis generated by extremely rapid subaerial mass wasting are also referred to as impulse waves and may occur both along coastal areas and in inland waters including engineered reservoirs. The hydraulic process chain comprising wave generation, propagation, and run-up needs to be comprehensively assessed to predict whether these waves represent a threat to the shore and adjacent infrastructure. Hazard assessment studies based on site-specific hydraulic laboratory models and numerical simulations may generally yield quite accurate predictions of the expected wave and run-up heights. While the former involves the availability of specialized lab infrastructure and instrumentation, the latter requires in-depth knowledge of suitable numerical methods as well as experience in their application to scenarios at prototype-scale. Therefore, both approaches are time-consuming, involve high costs, and pose substantial entry thresholds for practitioners. Especially in emergency situations, when first-order estimations need to be quickly at hand, the ad-hoc applicability of these approaches may therefore be limited. Motivated by an imminent landslide hazard at Carmena reservoir, Switzerland, in 2002, the national supervisory authority for dam safety, the Swiss Federal Office of Energy, commissioned the development of a fast and readily applicable computational procedure. As a result, the first edition of the so-called ‘impulse wave manual’ was published in 2009 and provides an extensive literature review of generally applicable equations derived from lab experiments. It combines selected equations into a coherent computational framework covering all stages of an impulse wave event’s hydraulic process chain. Based on the estimation of e.g. wave and run-up heights, this manual allows to rapidly implement mitigation measures including reservoir drawdown or precautionary evacuation. In addition to an improved emergency planning, the manual proved to be an inexpensive tool to obtain an estimation of an impulse wave event’s magnitude during the preliminary design phase of new reservoirs. Back in 2009, the manual’s literature analysis already identified specific research gaps, leading to the initiation of further experimental investigations. Following these research efforts over the past ten years, a second edition of the manual was published in 2019 featuring an updated computational procedure. This contribution provides a brief introduction to the updated computational procedure and applies it to prototype events with available survey data, e.g. Chehalis Lake, Canada, in 2007. The comparison to prototype data allows to highlight the procedure’s capabilities as well as its limitations for future ad-hoc estimations of landslide-generated impulse waves.

Historical reports and recent studies have shown that tsunamis can also occur in lakes where they may cause large damages and casualties. Among the historical reports are many tsunamis in Swiss lakes that have been triggered both by subaerial and subaqueous mass movements (SAEMM and SAQMM). In this study, we present a simplified classification of lakes with respect to their relative tsunami potential. The classification uses basic topographic, bathymetric, and seismologic input parameters to assess the relative tsunami potential on the 28 Swiss alpine and perialpine lakes with a surface area >1 km2. The investigated lakes are located in the three main regions “Alps,” “Swiss Plateau,” and “Jura Mountains.” The input parameters are normalized by their range and a k-means algorithm is used to classify the lakes according to their main expected tsunami source. Results indicate that lakes located within the Alps show generally a higher potential for SAEMM and SAQMM, due to the often steep surrounding rock-walls, and the fjord-type topography of the lake basins with a high amount of lateral slopes with inclinations favoring instabilities. In contrast, the missing steep walls surrounding lakeshores of the “Swiss Plateau” and “Jura Mountains” lakes result in a lower potential for SAEMM but favor inundation caused by potential tsunamis in these lakes. The results of this study may serve as a starting point for more detailed investigations, considering field data.

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 degrees and 90 degrees 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.

Tsunamis can occur in lacustrine environments, similar to marine settings. In lake settings, these tsunamis are mainly generated by mass-movement processes displacing large volumes of water, and triggered by seismic or aseismic phenomena. In Swiss lakes, several historical tsunamis are reported. Some of the most prominent examples are: the 563 AD Lake Geneva tsunami presumably caused by a rockfall-induced delta failure, the 1601 AD Lake Lucerne tsunami caused by earthquake-triggered sublacustrine mass movements, and the 1687 AD Lake Lucerne tsunami that was caused by a delta failure. Nowadays, the shorelines of many Swiss lakes are densely populated and host important infrastructures. The occurrence of lake tsunamis in Switzerland is known, however, we still miss a workflow to assess the hazard related to tsunamis. Within the framework of a multidisciplinary project (Lake Tsunamis: Causes, Consequences and Hazard), funded by the Swiss National Science Foundation and the Federal Office for the Environment, we aim towards better understanding lake-tsunami processes using Swiss lakes as laboratories. The major objectives of this project are to investigate a) the diverse causes of lake tsunamis, b) the geotechnical and sedimentological properties of unstable slope sediment, c) the potentially unstable sediment volumes on charged slopes, d) the wave generation, propagation and shore run-up, e) the onshore and shallow offshore tsunami deposits and d) their related hazard. Since 2018, extensive field work using ocean bottom seismometers and cone penetration tests, as well as laboratory tests on sediment sample have been performed to assess the slope stability during seismic shaking on Lake Lucerne. Tsunami waves have been reproduced at laboratory scale to benchmark the numerical simulations of generation, propagation and run-up of tsunamis in lakes. To characterize and date historical and prehistorical tsunami deposits, on and off-shore sediment cores have been retrieved at Lake Lucerne, Geneva, Zurich and Sils. A first work-flow to assess the tsunami hazard related to earthquake-triggered sublacustrine mass movements is proposed. In this contribution, we will summarise the current status of this project.