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1
Mares-Nasarre, Patricia, Gloria Argente, M. Esther Gómez-Martín und Josep R. Medina. „Overtopping layer thickness and overtopping flow velocity on mound breakwaters“. Coastal Engineering 154 (Dezember 2019): 103561. http://dx.doi.org/10.1016/j.coastaleng.2019.103561.
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2
Suzuki, Tomohiro, Corrado Altomare, Tomohiro Yasuda und Toon Verwaest. „Characterization of Overtopping Waves on Sea Dikes with Gentle and Shallow Foreshores“. Journal of Marine Science and Engineering 8, Nr. 10 (27.09.2020): 752. http://dx.doi.org/10.3390/jmse8100752.
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Due to ongoing climate change, overtopping risk is increasing. In order to have effective countermeasures, it is useful to understand overtopping processes in details. In this study overtopping flow on a dike with gentle and shallow foreshores are investigated using a non-hydrostatic wave-flow model, SWASH (an acronym of Simulating WAves till SHore). The SWASH model in 2DV (i.e., flume like configuration) is first validated using the data of long crested wave cases with second order wave generation in the physical model test conducted. After that it is used to produce overtopping flow in different wave conditions and bathymetries. The results indicated that the overtopping risk is better characterized by the time dependent h (overtopping flow depth) and u (overtopping flow velocity) instead of hmax (maximum overtopping flow depth) and umax (maximum overtopping flow velocity), which led to overestimation of the risk. The time dependent u and h are strongly influenced by the dike configuration, namely by the promenade width and the existence of a vertical wall on the promenade: the simulation shows that the vertical wall induces seaward velocity on the dike which might be an extra risk during extreme events.
3
Van der Meer, Jentsje Wouter, Bianca Hardeman, Gosse Jan Steendam, Holger Schuttrumpf und Henk Verheij. „FLOW DEPTHS AND VELOCITIES AT CREST AND LANDWARD SLOPE OF A DIKE, IN THEORY AND WITH THE WAVE OVERTOPPING SIMULATOR“. Coastal Engineering Proceedings 1, Nr. 32 (31.01.2011): 10. http://dx.doi.org/10.9753/icce.v32.structures.10.
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Wave overtopping discharges at coastal structures are well described in the EurOtop Manual (2007), including the distribution of overtopping wave volumes. Each volume that overtops a dike or levee will have a certain flow velocity and depth record in time, often given by the maximum velocity and flow depth. This paper describes some further development of the theory on flow depth and velocities on the crest, but will also show an inconsistency with respect to the mass balance. The second part of the paper gives an analysis of measured values on real dikes, simulated by the Wave Overtopping Simulator. It gives also the method of "cumulative hydraulic load" to compare overtopping discharges for different wave conditions. A large wave height with less overtopping waves, but larger overtopping wave volumes, is more damaging than a small wave height with more, but smaller overtopping volumes, even if the overtopping discharge is similar. The reasons to develop the cumulative hydraulic load have been compared with the recently in the US developed method of erosional equivalence.
4
Llana, Alberto, Rafael Molina, Alberto Camarero, Alvaro Campos, Ana Francisca Alises und José Damián López. „OVERTOPPING FLOW PROPERTIES CHARACTERIZATION IN LABORATORY AND PROTOTYPE THROUGH THE COMBINATION OF NON INTRUSIVE INSTRUMENTAL TECHNIQUES“. Coastal Engineering Proceedings 1, Nr. 33 (15.12.2012): 46. http://dx.doi.org/10.9753/icce.v33.currents.46.
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Overtopping events may cause different failure modes depending on overtopped flow characteristics. Most of the studies about overtopping hazard analysis link the damages caused by the overtopping event to its mean overtopping discharge (q), which provides no information about overtopped flow characteristics or its spatial distribution. In this paper it is presented a non intrusive measurement system based on video imagery techniques and optical level sensors (OLS), which aim is to obtain overtopped highly aerated flows´ principal characteristics: velocity, volume, and density, in order to deep in the knowledge of this phenomenon, and minimizing the damages that it may cause to port´s infrastructures and exploitation
5
Altomare, Corrado, Xavi Gironella, Tomohiro Suzuki, Giacomo Viccione und Alessandra Saponieri. „Overtopping Metrics and Coastal Safety: A Case of Study from the Catalan Coast“. Journal of Marine Science and Engineering 8, Nr. 8 (24.07.2020): 556. http://dx.doi.org/10.3390/jmse8080556.
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Design criteria for coastal defenses exposed to wave overtopping are usually assessed by mean overtopping discharges and maximum individual overtopping volumes. However, it is often difficult to give clear and precise limits of tolerable overtopping for all kinds of layouts. A few studies analyzed the relationship between wave overtopping flows and hazard levels for people on sea dikes, confirming that one single value of admissible mean discharge or individual overtopping volume is not a sufficient indicator of the hazard, but detailed characterization of flow velocities and depths is required. This work presents the results of an experimental campaign aiming at analyzing the validity of the safety limits and design criteria for overtopping discharge applied to an urbanized stretch of the Catalan coast, exposed to significant overtopping events every stormy season. The work compares different safety criteria for pedestrians. The results prove that the safety of pedestrians on a sea dike can be still guaranteed, even for overtopping volumes larger than 1,000 L/m. Sea storms characterized by deep-water wave height between 3.6 and 4.5 m lead to overtopping flow depth values larger than 1 m and flow velocities up to 20 m/s. However, pedestrian hazard is proved to be linked to the combination of overtopping flow velocity and flow depth rather than to single maximum values of one of these parameters. The use of stability curves to assess people’s stability under overtopping waves is therefore advised.
6
van Bergeijk, Vera M., Jord J. Warmink und Suzanne J. M. H. Hulscher. „Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences“. Journal of Marine Science and Engineering 8, Nr. 7 (02.07.2020): 489. http://dx.doi.org/10.3390/jmse8070489.
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The wave overtopping flow can exert high hydraulic loads on the grass cover of dikes leading to failure of the cover layer on the crest and the landward slope. Hydraulic variables such as the near bed velocity, pressure, shear stress and normal stress are important to describe the forces that may lead to cover erosion. This paper presents a numerical model in the open source software OpenFOAM® to simulate the overtopping flow on the grass-covered crest and slope of individual overtopping waves for a range of landward slope angles. The model provides insights on how the hydraulic forces change along the profile and how irregularities in the profile affect these forces. The effect of irregularities in the grass cover on the overtopping flow are captured in the Nikuradse roughness height calibrated in this study. The model was validated with two datasets of overtopping tests on existing grass-covered dikes in the Netherlands. The model results show good agreement with measurements of the flow velocity in the top layer of the wave, as well as the near bed velocity. The model application shows that the pressure, shear stress and normal stress are maximal at the wave front. High pressures occur at geometrical transitions such as the start and end of the dike crest and at the inner toe. The shear stress is maximal on the lower slope, and the normal stress is maximal halfway of the slope, making these locations vulnerable to cover failure due to high loads. The exact location of the maximum forces depends on the overtopping volume. Furthermore, the model shows that the maximum pressure and maximum normal stress are largely affected by the steepness of the landward slope, but the slope steepness only has a small effect on the maximum flow velocity and maximum shear stress compared to the overtopping volume. This new numerical model is a useful tool to determine the hydraulic forces along the profile to find vulnerable points for cover failure and improve the design of grass-covered flood defences.
7
Hughes, Steven A., Christopher I. Thornton, Jentsje W. Van der Meer und Bryan N. Scholl. „IMPROVEMENTS IN DESCRIBING WAVE OVERTOPPING PROCESSES“. Coastal Engineering Proceedings 1, Nr. 33 (25.10.2012): 35. http://dx.doi.org/10.9753/icce.v33.waves.35.
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This paper presents a new empirical relation for the shape factor in the Weibull distribution that describes the distribution of overtopping wave volumes. This improvement increases the applicable range of the Weibull distribution from very low average overtopping discharges to large discharges resulting from combined wave overtopping and steady surge overflow at negative freeboards. The effect this improvement has on wave overtopping simulation is also discussed. Measured maximum flow thicknesses, velocities, and discharges from experiments of combined wave and surge overtopping are examined to learn more about the variability of these key parameters as a function of individual overtopping wave volumes. A key finding is that wave volumes containing the 2%-exceedance value of maximum velocity typically have maximum flow thicknesses well below the 2%-exceedance level, and vice-versa. Furthermore, the 2%-exceedance hydrodynamic parameters do not occur in the 2%-exceedance wave volumes. Finally, empirical relationships are developed for several parameters that showed strong trends.
8
Brito, Moisés, Rui M. L. Ferreira, Luis Teixeira, Maria G. Neves und Luís Gil. „Experimental Investigation of the Flow Field in the Vicinity of an Oscillating Wave Surge Converter“. Journal of Marine Science and Engineering 8, Nr. 12 (01.12.2020): 976. http://dx.doi.org/10.3390/jmse8120976.
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The main objective of this paper is to characterize the flow field on the front face of an oscillating wave surge converter (OWSC) under a regular wave. For this purpose, the longitudinal and vertical velocity components were measured using an Ultrasonic Velocity Profiler (UVP). In order to explain the main trends of the OWSC’s dynamics, the experimental data were firstly compared with the analytical results of potential theory. A large discrepancy was observed between experimental and analytical results, caused by the nonlinear behavior of wave-OWSC interaction that determine the turbulent field and the boundary layer. The experimental velocity field shows a strong ascendant flow generated by the mass transfer over the flap (overtopping) and flow rotation generated by the beginning of the flap deceleration and acceleration. These features (overtopping and flow rotation) have an important role on the power capture of OWSC and, therefore, analytical results are not accurate to describe the complex hydrodynamics of OWSC.
9
Pu, Jaan Hui, und Songdong Shao. „Smoothed Particle Hydrodynamics Simulation of Wave Overtopping Characteristics for Different Coastal Structures“. Scientific World Journal 2012 (2012): 1–10. http://dx.doi.org/10.1100/2012/163613.
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This research paper presents an incompressible smoothed particle hydrodynamics (ISPH) technique to investigate a regular wave overtopping on the coastal structure of different types. The SPH method is a mesh-free particle modeling approach that can efficiently treat the large deformation of free surface. The incompressible SPH approach employs a true hydrodynamic formulation to solve the fluid pressure that has less pressure fluctuations. The generation of flow turbulence during the wave breaking and overtopping is modeled by a subparticle scale (SPS) turbulence model. Here the ISPH model is used to investigate the wave overtopping over a coastal structure with and without the porous material. The computations disclosed the features of flow velocity, turbulence, and pressure distributions for different structure types and indicated that the existence of a layer of porous material can effectively reduce the wave impact pressure and overtopping rate. The proposed numerical model is expected to provide a promising practical tool to investigate the complicated wave-structure interactions.
10
Warmink, Jord J., Vera M. Van Bergeijk, Weiqui Chen, Marcel R. A. Van Gent und Suzanne J. M. H. Hulscher. „MODELLING WAVE OVERTOPPING FOR GRASS COVERS AND TRANSITIONS IN DIKE REVETMENTS“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 53. http://dx.doi.org/10.9753/icce.v36.papers.53.
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Transitions in the dike revetment or in the grass cover can significantly affect the wave overtopping discharge and the dike cover erosion. At the University of Twente, two PhD students recently started on the challenge of quantifying the effect of (1) waterside transition on the wave overtopping discharge and (2) transitions in grass covered dikes on dike erosion. In this paper we present their preliminary results and outline their future plans. Firstly, new laboratory experiments show that the existing wave overtopping formulas are not able to accurately predict the overtopping discharge in case of transitions on the waterside slope. Secondly, the analytical dike cover erosion model shows that transitions in grass covers significantly affect the location of maximum flow velocity and potential dike cover erosion. In future work, detailed numerical models will be developed for both the waterside slope and the landward slope to further increase our understanding of the effects of transitions on the wave overtopping discharge and the dike cover erosion.
11
De Rouck, Julien, Koen Van Doorslaer, Tom Versluys, Karunya Ramachandran, Stefan Schimmels, Matthias Kudella und Koen Trouw. „FULL SCALE IMPACT TESTS OF AN OVERTOPPING BORE ON A VERTICAL WALL IN THE LARGE WAVE FLUME (GWK) IN HANNOVER“. Coastal Engineering Proceedings 1, Nr. 33 (14.12.2012): 62. http://dx.doi.org/10.9753/icce.v33.structures.62.
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To meet up with the requirements of the Flemish Government, the Belgian coastline needs a protection to a storm with a return period of 1000 years. At well-chosen locations, storm walls will be built, and for the structural design of these walls the impact loadings need to be known. Tests have been carried out at full scale in the Grosser Wellen Kanal, to determine the impact loads by overtopping bores. Wave overtopping over the crest of the dike occurs, and the overtopping bore progresses along the horizontal crest of the dike before impacting the storm wall. It is of major importance that such a wall can withstand the impacts. This paper describes the hydraulic process on the crest of the dike, expressed with parameters such as flow depth and flow velocity, and links them to the impact measured on the storm wall. Both pressures and forces are measured, and compared to each other.
12
Ryu, Yong-Uk, Jong-In Lee und Young-Taek Kim. „Analyses of Overtopping Velocity using Analytical Solution(Ritter's Solution) of Dam-Break Flow“. Journal of Korea Water Resources Association 41, Nr. 7 (31.07.2008): 669–79. http://dx.doi.org/10.3741/jkwra.2008.41.7.669.
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13
Barbosa, D. V. E., J. A. Souza, E. D. dos Santos, L. A. Isoldi und J. C. Martins. „NUMERICAL ANALYSES OF OPENFOAM'S OVERTOPPING DEVICE SOLUTION“. Revista de Engenharia Térmica 16, Nr. 1 (30.06.2017): 96. http://dx.doi.org/10.5380/reterm.v16i1.62198.
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Studies related to ocean energy are getting more important lately, once world claims for renewable energy usage. The Overtopping Device is a kind of Ocean Waves Energy Converter (OWEC), which main concept is storing water provided by incident waves above sea level to feed a set of low head turbines. In order to obtain the desired effect, this device contains a ramp which elevates the incident waves toward the reservoir. Present study aims to perform a numerical model of a 2D Overtopping Device by means of OpenFOAM simulations. OpenFOAM is a free open source code which has shown applicability in many areas of engineering. The adopted solver (InterFOAM) is Volume of Fluid based (VOF) according to Finite Volume Method (FVM), these methodologies has been largely used among researchers in propagating waves field. FLUENT (commercial code) is used to verify OpenFOAM's results. Once, the main point of this paper is to present OpenFOAM as a considerable tool for propagating waves studies, it firstly presents a numerical wave verification with analytical solutions (second order Stokes theory). The second section of results presents overtopping time series peaks in 100 s of simulation. Also, by mass flow rate integration, it presents total mas of water climbed to the reservoir. The integration of mass flow rate takes 94 s of simulation (not 100 s) because it is noticeable a pause between two peaks of overtopping at that time. Results show agreement between wave elevation and wave velocity profiles with straight convergence of periods between analytical and numerical waves. Most important differences are found near air/water interface, owed to faster air flow at that region. Generally OpenFOAM and FLUENT results are similar, with converged overtopping time series peaks and their magnitudes too. Similarly, the amount of water marked by both software are close with very similar trend lines.
14
Formentin, Sara Mizar, und Barbara Zanuttigh. „A NEW FULLY-AUTOMATIC PROCEDURE FOR THE IDENTIFICATION AND THE COUPLING OF THE OVERTOPPING WAVES“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 36. http://dx.doi.org/10.9753/icce.v36.papers.36.
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This contribution presents a new procedure for the automatic identification of the individual overtopping events. The procedure is based on a zero-down-crossing analysis of the water-surface-elevation signals and, based on two threshold values, can be applied to any structure crest level, i.e. to emerged, zero-freeboard, over-washed and submerged conditions. The results of the procedure are characterized by a level of accuracy comparable to the human-supervised analysis of the wave signals. The procedure includes a second algorithm for the coupling of the overtopping events registered at two consecutive gauges. This coupling algorithm offers a series of original applications of practical relevance, a.o. the possibility to estimate the wave celerities, i.e. the velocities of propagation of the single waves, which could be used as an approximation of the flow velocity in shallow water and broken flow conditions.
15
Mares-Nasarre, Patricia, M. Esther Gómez-Martín und Josep R. Medina. „Influence of Mild Bottom Slopes on the Overtopping Flow over Mound Breakwaters under Depth-Limited Breaking Wave Conditions“. Journal of Marine Science and Engineering 8, Nr. 1 (19.12.2019): 3. http://dx.doi.org/10.3390/jmse8010003.
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The crest elevation of mound breakwaters is usually designed considering a tolerable mean wave overtopping discharge. However, pedestrian safety, characterized by the overtopping layer thickness (OLT) and the overtopping flow velocity (OFV), is becoming more relevant due to the reduction of the crest freeboards of coastal structures. Studies in the literature focusing on OLT and OFV do not consider the bottom slope effect, even if it has a remarkable impact on mound breakwater design under depth-limited breaking wave conditions. Therefore, this research focuses on the influence of the bottom slope on OLT and OFV exceeded by 2% of incoming waves, hc,2% and uc,2%. A total of 235 2D physical tests were conducted on conventional mound breakwaters with a single-layer Cubipod® and double-layer rock and cube armors with 2% and 4% bottom slopes. Neural networks were used to determine the optimum point to estimate wave characteristics for hc,2% and uc,2% calculation; that point was located at a distance from the model toe of three times the water depth at the toe (hs) of the structure. The influence of the bottom slope is studied using trained neural networks with fixed wave conditions in the wave generation zone; hc,2% slightly decreases and uc,2% increases as the gradient of the bottom slope increases.
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Chanson, H., und L. Toombes. „Experimental investigations of air entrainment in transition and skimming flows down a stepped chute“. Canadian Journal of Civil Engineering 29, Nr. 1 (01.02.2002): 145–56. http://dx.doi.org/10.1139/l01-084.
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Stepped spillways have been used for about 3500 years. The last few decades have seen the development of new construction materials, design techniques, and applications, for example, embankment overtopping protection systems. Although it is commonly acknowledged that free-surface aeration is significant in stepped chutes, experimental data are scarce, often limited to very steep slopes (α ~ 50°). This paper presents an experimental study conducted in a large-size stepped chute (α = 22°, h = 0.1 m, W = 1 m). Observations demonstrate the existence of a transition flow pattern for intermediate flow rates between nappe and skimming flows. Detailed airwater flow measurements were conducted in both transition and skimming flows, immediately downstream of the inception point of free-surface aeration where uniform equilibrium flow conditions were not achieved. In skimming flows, a complete characterization is developed for the distributions of void fraction, bubble count rate, and velocity, and flow resistance data are compared with other studies. Transition flows exhibit significantly different airwater flow properties. They are highly aerated, requiring the design of comparatively high chute sidewalls.Key words: stepped spillway, air entrainment, two-phase flow properties, skimming flow, transition flow.
17
Yoon, Kwang, Seung Lee und Seung Hong. „Time-Averaged Turbulent Velocity Flow Field through the Various Bridge Contractions during Large Flooding“. Water 11, Nr. 1 (15.01.2019): 143. http://dx.doi.org/10.3390/w11010143.
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Extreme rainfall events, larger than 500-year floods, have produced a large number of flooding events in the land and also close to the shore, and have resulted in massive destruction of hydraulic infrastructures because of scour. In light of climate change, this trend is likely to continue in the future and thus, resilience, security and sustainability of hydraulic infrastructures has become an interesting topic for hydraulic engineering stakeholders. In this study, a physical model experiment with a geometric similarity of the bridge embankments, abutments, and bridge deck as well as river bathymetry was conducted in a laboratory flume. Flow conditions were utilized to get submerged orifice flow and overtopping flow in the bridge section in order to simulate extreme hydrologic flow conditions. Point velocities of the bridge section were measured in sufficient details and the time-averaged velocity flow field were plotted to obtain better understandings of scour and sediment transport under high flow conditions. The laboratory study concluded that existing lateral flow contraction as well as vertical flow contraction resulted in a unique flow field through the bridge and the shape of velocity profile being “fuller”, thereby increasing the velocity gradients close to the bed and subsequently resulting in a higher rate of bed sediment transport. The relationships between the velocity gradients measured close to the bed and the degree of flow contraction through the bridge are suggested. Furthermore, based on the location of maximum scour corresponding to the measured velocity flow field, the classification of scour conditions, long setback abutment scour and short setback abutment scour, are also suggested.
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Karim, Ibtisam R., Zahraa F. Hassan, Hassan Hussein Abdullah und Imzahim A. Alwan. „2D-HEC-RAS Modeling of Flood Wave Propagation in a Semi-Arid Area Due to Dam Overtopping Failure“. Civil Engineering Journal 7, Nr. 9 (01.09.2021): 1501–14. http://dx.doi.org/10.28991/cej-2021-03091739.
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Dam overtopping failure and the resulting floods are hazardous events that highly impact the inundated areas and are less predictable. The simulation of the dam breach failure and the flood wave propagation is necessary for assessing flood hazards to provide precautions. In the present study, a two-dimensional HEC-RAS model was used to simulate the flood wave resulting from the hypothetical failure of Al-Udhaim Dam on Al-Udhaim River, Iraq, and the propagation of the resulting dam-break wave along 100 km downstream the dam site for the overtopping scenario. The main objective is to analyze the propagation of the flood wave so that the failure risk on dam downstream areas can be assessed and emergency plans may be provided. The methodology consisted of two sub-models: the first is the dam breach failure model for deriving the breach hydrograph, and the second is the hydrodynamic model for propagating the flood wave downstream of the dam. The breach hydrograph is used as an upstream boundary condition to derive the flood impact in the downstream reach of Al- Udhaim River. The flood inundation maps were visualized in RAS-Mapper in terms of water surface elevation, water depth, flow velocity, and flood arrival time. The maximum recorded values were: 105 m (a.m.s.l.), 18 m, 5.5 m/s, and, respectively. The flow velocity decreased from upstream to downstream of the terrain, which means less risk of erosion in the far reaches downstream of the study area. The inundation maps indicated that the water depth and flow velocity were categorized as Catastrophic limits on the terrain's area. The results offer a way to predict flood extent and showed that the impact of a potential dam break at Al-Udhiam Dam will be serious, therefore, suitable management is needed to overcome this risk. Moreover, the maps produced by this study are useful for developing plans for sustainable flood management. Doi: 10.28991/cej-2021-03091739 Full Text: PDF
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Bijlard, Roel, Gosse Steendam, Henk Verhagen und Jentsje Van der Meer. „DETERMINING THE CRITICAL VELOCITY OF GRASS SODS FOR WAVE OVERTOPPING BY A GRASS PULLING DEVICE“. Coastal Engineering Proceedings, Nr. 35 (23.06.2017): 20. http://dx.doi.org/10.9753/icce.v35.structures.20.
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DETERMINING THE CRITICAL VELOCITY OF GRASS SODS FOR
WAVE OVERTOPPING BY A GRASS PULLING DEVICE
Roel Bijlard, Delft University of Technology, roelbijlard@gmail.com
Gosse Jan Steendam, INFRAM International, gosse.jan.steendam@infram.nl
Henk Jan Verhagen, Delft University of Technology, h.j.verhagen@tudelft.nl
Jentsje van der Meer, Van der Meer Consulting bv, jm@vandermeerconsulting.nl
INTRODUCTION
There is a shift in the approach for designing coastal
structures in the Netherlands, such as dikes or levees.
In the past dikes were designed on the probability of
exceedance of the water level during specific incoming
(wave) storm conditions. In the near future the design
criterion will be the probability of flooding of the
hinterland. In order to determine this flood probability,
the strength of the dike has to be known at which
failure occurs. During extreme storm conditions waves
will overtop the crest which can lead to erosion of the
grass sod on the landward slope. This can finally result
in instability of the dike and flooding of the hinterland.
Past research focused on the erosion of the grass sod
during different wave overtopping conditions, see
Steendam 2014. The last few years many tests have
been performed with the Wave Overtopping Simulator.
During these tests the Cumulative Hydraulic Overload
Method has been developed, see Van der Meer 2010
and Steendam 2014. With this method an estimation
of the critical velocity of the grass sod has to be made.
The critical velocity is a strength parameter for a grass
sod on a dike during loads induced by overtopping
wave volumes.
SOD PULLING TESTS
For safety assessments it would be beneficial if there
is also an easier way to determine the critical velocity
of the grass sod. However, it is important to measure
the actual strength of the grass cover, so a visual
inspection cannot be satisfactory. The sod pulling
test is developed in order to investigate the
resistance of the grass cover. It lifts the grass sod
perpendicular to the slope out of the sod and
measures the force as a function of the deformation.
In order to lift the sod, a pull frame is anchored into
the top layer with pins. This frame then is lifted out of
the grass sod by a hydraulic cylinder.
In order to insert the pins into the sod, the soil has to
be excavated on two sides (condition 2 test) or on all
4 sides (condition 4 test). This has the disadvantage
that the strength of an intact sod cannot be
measured directly. So a methodology is developed to
estimate the strength of an intact grass sod from the
measured data. A further introduction on the sod
pulling tests is given in Steendam 2014. The goal is
to rewrite the measured forces from the sod pulling
test into a critical velocity so that the Cumulative
Hydraulic Overload Method can be used for
determining the flooding probability of a dike.
Some of the locations tested with the wave
overtopping simulator have also been tested for the
strength of the grass cover with the sod pulling tests.
The two methods use the same failure mechanism of
the grass, erosion of the grass sod.
The top layer of a dike consists of soil and roots
growing in multiple directions. The roots anchor the
grass into the soil and can deform centimeters
without tearing. Pressures acting on the grass cover
will first break the weakest roots, but the forces will
be redistributed to other roots. Only when a critical
amount of roots are broken, the redistribution stops
and the grass cover will fail.
CONCLUSION
It is possible to rewrite the measured forces with the
sod pulling tests into a critical grass normal stress
(σgrass.c), which is one of the input parameters for
determining the critical velocity of a grass sod, see
Hoffmans 2012.
The equation also uses the pore water pressure (pw),
the relative turbulence intensity (r0) and the density of
the water (Ï). When the critical velocity resulting from
this equation is compared with the determined critical
velocity during the wave overtopping simulations,
there is good correspondence between the values for
the five tested locations. So the sod
pulling test could provide results that are reliable
enough to determine the critical velocity of a dike
section. Further elaboration and scientific background
will follow in the paper after the conference.
REFERENCES
Hoffmans (2012): The influence of turbulence on soil
erosion. Eburon, Delft.
Steendam, van Hoven, van der Meer, Hoffmans
(2014): Wave Overtopping Simulator tests on
transitions and obstacles at grass covered slopes of
dikes, proc. ICCE 2014 Seoul.
Van der Meer, Hardeman, Steendam, Schüttrumpf,
Verheij (2010): Flow depths and velocities at crest
and inner slope of a dike, in theory and with the Wave
Overtopping Simulator, Proc. ICCE 2010, Shanghai.
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Castillo, Luis G., José M. Carrillo und Fabián A. Bombardelli. „Distribution of mean flow and turbulence statistics in plunge pools“. Journal of Hydroinformatics 19, Nr. 2 (19.12.2016): 173–90. http://dx.doi.org/10.2166/hydro.2016.044.
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When the capacity of the spillway of a dam is exceeded for a given flood, overtopping occurs; in such cases potentially dangerous hydrodynamic actions and scour downstream of the dam need to be foreseen. Detailed studies of jets impinging in plunge pools from overflow nappe flows are scarce. This work addresses plunge pool flows, and compares numerical results against our own experiments. The energy dissipation is larger than 75% of the impingement jet energy. Instantaneous velocities and air entrainment were obtained with the use of an Acoustic Doppler Velocimeter and optical fibre probe, respectively. Mean velocity field and turbulence kinetic energy profiles were determined. To identify the level of reliability of models, numerical simulations were carried out by using the ‘homogeneous’ model of ANSYS CFX, together with different turbulence closures. The numerical results fall fairly close to the values measured in the laboratory, and with expressions for submerged hydraulic jumps and horizontal wall jets. The observations can be well predicted for characterized profiles at a minimum distance of 0.40 m downstream from the stagnation point, horizontal velocities greater than 40% of the maximum velocity in each profile, and when the ratio of the water cushion depth to the jet thickness is lower than 20.
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van Bergeijk, Vera M., Vincent A. Verdonk, Jord J. Warmink und Suzanne J. M. H. Hulscher. „The Cross-Dike Failure Probability by Wave Overtopping over Grass-Covered and Damaged Dikes“. Water 13, Nr. 5 (03.03.2021): 690. http://dx.doi.org/10.3390/w13050690.
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A probabilistic framework is developed to calculate the cross-dike failure probability by overtopping waves on grass-covered dikes. The cross-dike failure probability of dike profiles including transitions and damages can be computed to find the most likely location of failure and quantify the decrease in the failure probability when this location is strengthened. The erosion depth along the dike profile is calculated using probability distributions for the water level, wind speed and dike cover strength. Failure is defined as the exceedance of 20 cm erosion depth when the topsoil of the grass cover is eroded. The cross-dike failure probability shows that the landward toe is the most vulnerable location for wave overtopping. Herein, the quality of the grass cover significantly affects the failure probability up to a factor 1000. Next, the failure probability for different types of damages on the landward slope are calculated. In case of a damage where the grass cover is still intact and strong, the dike is most likely to fail at the landward toe due to high flow velocity and additional load due to the slope change. However, when the grass cover is also damaged, the probability of failure at the damage is between 4 and 125 times higher than for a regular dike profile.
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Devolder, Brecht, Peter Troch und Pieter Rauwoens. „VALIDATION OF A BUOYANCY-MODIFIED TURBULENCE MODEL BY NUMERICAL SIMULATIONS OF BREAKING WAVES OVER A FIXED BAR“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 71. http://dx.doi.org/10.9753/icce.v36.waves.71.
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The surf zone dynamics are governed by important processes such as turbulence generation , nearshore sediment transport , wave run-up and wave overtopping at a coastal structure. During field observations , it is very challenging to measure and quantify wave breaking turbulence . Complementary to experimental laboratory studies in a more controlled environment , numerical simulations are highly suitable to understand and quantify surf zone processes more accurately.
In this study, wave propagation and wave breaking over a fixed barred beach profile is investigated using a two phase Navier-Stokes flow solver. We show that accurate predictions of the turbulent two-phase flow field require special attention regarding turbulence modelling. The numerical wave flume is implemented in the open source OpenFOAM library. The computed results (surface elevations , velocity profiles and turbulence levels) are compared against experimental measurements in a wave flume (van der A et al., 2017) .
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Briganti, Riccardo, Rosaria Ester Musumeci, Jentsje Van der Meer, Alessandro Romano, Laura Maria Stancanelli, Matthias Kudella, Rizki Akbar et al. „LARGE SCALE TESTS ON FORESHORE EVOLUTION DURING STORM SEQUENCES AND THE PERFORMANCE OF A NEARLY VERTICAL STRUCTURE“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 13. http://dx.doi.org/10.9753/icce.v36.papers.13.
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This work presents the results of an experimental investigation on the effects of a sequence of storms on wave overtopping at a nearly vertical battered seawall at the back of a sandy foreshore. The experiments were carried out in the Large Wave Flume (GWK) at Leibniz Universität Hannover (Germany), as part of the research project ICODEP (Impact of Changing fOreshore on flood DEfence Performance), within the European Union programme Hydralab+. The layout consisted of a 10/1 battered seawall and a natural sandy foreshore with an initial 1:15 slope. The beach sand had a nominal diameter of 0.30 mm. Three storm sequences were simulated, where each consisted of three individual storms. Each storm was divided into six steps in which the wave conditions and still water level were varied to represent the peak of an actual storm. The six sea states were based on a JONSWAP spectral shape, with wave heights roughly between 0.6 m and 0.8 m. Two still water levels were tested. For the central two steps the level was such that the freeboard was only 0.14 m and almost all waves were overtopping. In the remaining steps low still water levels were employed, leaving a narrow swash zone. Two storm profiles were considered, the first one with a lower level of energy and the second one with a higher one. These were combined in the three different sequences. All the tested wave conditions were designed to be erosive for the beach, with no recovery in between. Each sequence started from a plain beach configuration and the beach was not restored in between storms. The measurements included waves, pressure and forces, sediment concentrations and flow velocity together with overtopping. The profile of the beach was measured after each sea state tested.
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Sujono, Joko. „Hydrological Analysis of the Situ Gintung Dam Failure“. Journal of Disaster Research 7, Nr. 5 (01.10.2012): 590–94. http://dx.doi.org/10.20965/jdr.2012.p0590.
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Early on the morning ofMarch 27, 2009, the Situ Gintung dam, located near Jakarta, Indonesia, and with an catchment area of 3.1 km2, failed and flooded the area below it. This disaster has awakened most of the Indonesian people, especially those who are concerned about hydraulic structures, natural disasters and sustainable water resources management. During the disaster, about 100 people died and a number of people went missing. There are hundreds of dams like the Situ Gintung dam and other big dams have been built in Indonesia. Most of these dams pose a high potential hazard to life and property if a failure or levee breach occurs. Dam failures may occur at different locations such as spillway, embankments and foundations. The failure may occur as a result of a number of problems such as overtopping, surface erosion, and piping. Dam failures due to spillway problems may occur, for instance, as a result of inadequate spillway capacity (overtopping) or spillway loss by erosion (surface erosion). In this study, the Situ Gintung dam failure has been analyzed based on hydrology analysis. Results show that heavy monsoon rainfall was not the main cause of the situ Gintung dam failure. The daily rainfall on March 26, 2009, was 113 mm that equal to a 10 year return period. Reservoir routing shows that there was no overtopping during March 27, 2009, flood, the maximum water depth on the spillway is 0.63 m. Assuming that maintenance was done well, the spillway was still safe under a 100 year return period with the maximum water level is +98.95 m. It means that the embankment was still safe with 1.05 m freeboard. Due to high water flow velocity, however, surface erosion may occur at the end of a chute spillway that consists of silt, clay and sand. Continuous scoring/erosion happened throughout the spill over the spillway, which started at around 06:00 pm and lasted until 03.00 am, resulting in a big pond at the chute spillways and surrounding areas. This phenomenon adversely affected the instability of the spillway structure. As a result, the spillway failure occurring resulted high flow discharge that reached more than 425 m3/s.
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Carré, David M., Pascale M. Biron und Susan J. Gaskin. „Flow dynamics and bedload sediment transport around paired deflectors for fish habitat enhancement: a field study in the Nicolet River“. Canadian Journal of Civil Engineering 34, Nr. 6 (01.06.2007): 761–69. http://dx.doi.org/10.1139/l06-083.
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Schemes to restore fish habitat in rivers often involve installing instream structures such as current deflectors to create and maintain riffle-pool sequences. However, there is a lack of field studies on the impact of these structures on flow dynamics and bed topography. The objective of this research is to characterize flow dynamics and sediment transport around paired deflectors used to enhance fish habitat in the Nicolet River, Quebec. Bed and bank topography surveys were taken with a total station, and velocity and bed shear stress estimates were obtained from an acoustic doppler velocimeter. Bedload sediment transport was assessed by two methods: tracer rocks (painted "particles" and passive integrated transponder tags) and sediment traps. Results show marked differences in bedload sediment transport patterns between the left bank and the right bank downstream of the deflectors. This is surprising considering that paired deflectors should produce a relatively symmetrical disruption to the flow field on each side. More high-flow dynamics data during overtopping conditions are required to understand the complex interactions between these instream structures and bedload transport. Key words: stream restoration, pool, bedload transport, radio frequency identification (RFID), passive integrated transponder (PIT) tags, fieldwork, deflectors, fish habitat.
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Wang, Shuangling, Wanshun Zhang und Fajin Chen. „Simulation of Drainage Capacity in a Coastal Nuclear Power Plant under Extreme Rainfall and Tropical Storm“. Sustainability 11, Nr. 3 (26.01.2019): 642. http://dx.doi.org/10.3390/su11030642.
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To ensure the safety of coastal nuclear power plants, accurately simulating water depth due to flooding resulting from heavy rainfall and tropical storms is important. In this paper, a combined model is developed to analyze and simulate the drainage capacity in a coastal nuclear power plant under the combined action of extreme rainfall and wave overtopping. The combined model consist of a surface two-dimensional flood-routing model, a pipe network model, and an offshore wave model. The method of predictive correction calculation is adopted to calculate the node return flow. The inundated water depth varying with time for different design rainstorm return periods (p = 0.1 and 1%) was simulated and analyzed by the combined model. The maximum inundated water depth is calculated for the important entrances of the workshop. The model was validated and calibrated with the data of the rainfall, outflow discharge, and flow velocity measured on 23 June 2016 in plant. Modeling indicates that the simulated depths are consistent with the observed depths. The results show that the water depths in the left and right of the nuclear power plant are 0.2–0.4 m and 0.3–0.8 m, respectively. The water depth increases of Monitoring Point 22 are the largest in different design rainstorm return periods (p = 0.1 and 1%), which increase by 16% for a rainstorm once every thousand years compared to events occurring once in one hundred years. The main factor influencing water accumulation is wave overtopping, and the seawall, revetments, and pipe system play an important role in decreasing the inundated water depth. Through scientific analysis, a certain decision-making basis has been provided for flood disaster management and a certain security guarantee has also been provided for regional sustainable development.
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Khoolosi, Vafa, und Sedat Kabdaşli. „Numerical Simulation of Impulsive Water Waves Generated by Subaerial and Submerged Landslides Incidents in Dam Reservoirs“. Civil Engineering Journal 2, Nr. 10 (30.10.2016): 497–519. http://dx.doi.org/10.28991/cej-2016-00000053.
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The water wave generation by a freely falling rigid body is examined in this paper. Landslides on the margins of dam reservoirs may generate large waves that can produce flooding over the banks or overtopping the dam crest. In the present investigation, landslide generated waves are studied using a numerical model based on Navier-Stokes equations. Impulse wave amplitude, period, energy is studied in this work. The effects of bed slope angle on energy conversion from slide into wave are also investigated, and the numerical model we used in this study is the full three dimensional commercial code Flow-3D. Results of the Navier-Stokes model show that waves generated are highly dependent upon the details of slide mechanism and kinematics. Numerical solutions for the velocity fields, pressure distributions, and turbulence intensities in the vicinity of the falling rigid body are also presented. Results show that the general pattern of wave in all cases is the same but the amplitude and period are different. Data analysis shows that the maximum wave crest amplitude in subaerial induced waves is strongly affected by bed slope angle, landslide impact velocity, thickness, kinematics and deformation and by landslide shape.
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Omira, R., M. A. Baptista, F. Leone, L. Matias, S. Mellas, B. Zourarah, J. M. Miranda, F. Carrilho und J. P. Cherel. „Performance of coastal sea-defense infrastructure at El Jadida (Morocco) against tsunami threat: lessons learned from the Japanese 11 March 2011 tsunami“. Natural Hazards and Earth System Sciences 13, Nr. 7 (12.07.2013): 1779–94. http://dx.doi.org/10.5194/nhess-13-1779-2013.
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Abstract. This paper seeks to investigate the effectiveness of sea-defense structures in preventing/reducing the tsunami overtopping as well as evaluating the resulting tsunami impact at El Jadida, Morocco. Different tsunami wave conditions are generated by considering various earthquake scenarios of magnitudes ranging from Mw = 8.0 to Mw = 8.6. These scenarios represent the main active earthquake faults in the SW Iberia margin and are consistent with two past events that generated tsunamis along the Atlantic coast of Morocco. The behaviour of incident tsunami waves when interacting with coastal infrastructures is analysed on the basis of numerical simulations of near-shore tsunami waves' propagation. Tsunami impact at the affected site is assessed through computing inundation and current velocity using a high-resolution digital terrain model that incorporates bathymetric, topographic and coastal structures data. Results, in terms of near-shore tsunami propagation snapshots, waves' interaction with coastal barriers, and spatial distributions of flow depths and speeds, are presented and discussed in light of what was observed during the 2011 Tohoku-oki tsunami. Predicted results show different levels of impact that different tsunami wave conditions could generate in the region. Existing coastal barriers around the El Jadida harbour succeeded in reflecting relatively small waves generated by some scenarios, but failed in preventing the overtopping caused by waves from others. Considering the scenario highly impacting the El Jadida coast, significant inundations are computed at the sandy beach and unprotected areas. The modelled dramatic tsunami impact in the region shows the need for additional tsunami standards not only for sea-defense structures but also for the coastal dwellings and houses to provide potential in-place evacuation.
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Verbrugghe, Tim, José Manuel Dominguez, Corrado Altomare, Angelantonio Tafuni, Peter Troch und Andreas Kortenhaus. „APPLICATION OF OPEN BOUNDARIES WITHIN A TWO-WAY COUPLED SPH MODEL TO SIMULATE NON-LINEAR WAVE-STRUCTURE INTERACTIONS“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 14. http://dx.doi.org/10.9753/icce.v36.papers.14.
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A two-way coupling between the fully non-linear potential flow (FNPF) solver OceanWave3D and the Smoothed Particle Hydrodynamics (SPH) solver DualSPHysics is presented. At the coupling interfaces within the SPH domain, an open boundary formulation is applied. An inlet and outlet zone are filled with bu er particles. At the inlet, horizontal orbital velocities and surface elevations calculated with OceanWave3D are imposed on the bu er particles. At the outlet, horizontal orbital velocities are imposed, but the surface elevation is extrapolated from the fluid domain. Velocity corrections are applied to avoid unwanted reflections in the fluid domain. The SPH surface elevation can be coupled back to OceanWave3D, where the original solution is overwritten. The coupling methodology is validated using a 2-D test case of a floating box. Additionally, a 3-D proof of concept is shown where overtopping waves are acting on a heaving cylinder. The 2-way coupled model proofs to be capable of simulating wave propagation and wave-structure interaction problems with an acceptable accuracy with RMSE values remaining below the smoothing length h.
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Jiang, Changbo, Xiaojian Liu, Yu Yao, Bin Deng und Jie Chen. „Numerical Investigation of Tsunami-Like Solitary Wave Interaction with a Seawall“. Journal of Earthquake and Tsunami 11, Nr. 01 (März 2017): 1740006. http://dx.doi.org/10.1142/s1793431117400061.
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Seawall is a most commonly used structure in coastal areas to protect the landscape and coastal facilities. The studies of interactions between the tsunami-like solitary waves and the seawalls are relatively rare in the literature. In this study, a three-dimensional numerical model based on OpenFOAM® was developed to investigate the tsunami-like solitary waves propagating over a rectangular seawall. The Navier–Stokes equations for two-phase incompressible flow, combining with methods of [Formula: see text] for turbulence closure and Volume of Fluid (VOF) for tracking the free surface, were solved. Laboratory experiments were performed to measure some of the hydrodynamic feature associated with solitary waves. The model was then validated by the laboratory data, and good agreements were found for free surface, velocity and dynamic pressure around the seawall. Finally, a series of numerical experiments were conducted to analyze the evolution of both wave and flow fields, the overtopping discharge as well as wave pressure (force) around the seawall, special attention is given to the effects of seawall crest width. Our findings will help to improve the understanding in the occurrences of tsunami-induced damages in the vicinity of seawall such as wave impact and local scouring.
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Verbrugghe, Tim, Vasiliki Stratigaki, Corrado Altomare, J. Domínguez, Peter Troch und Andreas Kortenhaus. „Implementation of Open Boundaries within a Two-Way Coupled SPH Model to Simulate Nonlinear Wave–Structure Interactions“. Energies 12, Nr. 4 (21.02.2019): 697. http://dx.doi.org/10.3390/en12040697.
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A two-way coupling between the Smoothed Particle Hydrodynamics (SPH) solver DualSPHysics and the Fully Nonlinear Potential Flow solver OceanWave3D is presented. At the coupling interfaces within the SPH numerical domain, an open boundary formulation is applied. An inlet and outlet zone are filled with buffer particles. At the inlet, horizontal orbital velocities and surface elevations calculated using OceanWave3D are imposed on the buffer particles. At the outlet, horizontal orbital velocities are imposed, but the surface elevation is extrapolated from the fluid domain. Velocity corrections are applied to avoid unwanted reflections in the SPH fluid domain. The SPH surface elevation is coupled back to OceanWave3D, where the originally calculated free surface is overwritten. The coupling methodology is validated using a 2D test case of a floating box. Additionally, a 3D proof of concept is shown where overtopping waves are acting on a heaving cylinder. The two-way coupled model (exchange of information in two directions between the coupled models) has proven to be capable of simulating wave propagation and wave–structure interaction problems with an acceptable accuracy with error values remaining below the smoothing length h S P H .
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Hassan, Marwan Adil, und Mohd Ashraf Mohamad Ismail. „Effect of Soil Types on the Development of Water Levels and Erosion Processes during Overtopping Test“. Civil Engineering Journal 4, Nr. 10 (30.10.2018): 2315. http://dx.doi.org/10.28991/cej-03091161.
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The construction of dike materials is an essential parameters in controlling the safety of hydraulic engineering. The dike material is an earthfill material constructed from non-cohesive materials or mixed from cohesive and non-cohesive materials. Overtopping failure can affect the dike stability during water cross above dike crest and could threat people lives and property. It is reduced the matric suctions binds soil particles due to the increasing volumetric water content during the transition of water level from the upstream into downstream slopes. In this paper, two spatial overtopping tests are conducted in Hydraulic Geotechnical laboratories at the Universiti Sains of Malaysia to observe the evolution of horizontal and vertical water levels as well as the development of lateral and vertical erosion processes under constant inflow discharge of 30 L/min. The vertical and horizontal water levels as well as the vertical erosion process are measured using one digital camera installed in front of dike embankment, while the horizontal erosion process was measured using another digital camera installed in front of downstream slope. Two types of coarse sand and very silty sand soils are used to construct dike embankment in small flume channel. The small flume is constructed from transparent PVC material to observe the development of water distributions and erosion processes with sediment box to collect the eroded materials. A pilot channel is cut in dike crest along the side wall of small flume channel to initiate breach channel in the dike crest. The initiation of breach channel is crucial for the evolution breach channel failure in the downstream and upstream slopes. The results show that the vertical and horizontal water levels are distributed faster in coarse sand soil compared with those in the very silty sand soil while the horizontal water levels are distributed faster than vertical water levels for both soils. The permeability of coarse sand increases the velocity of water flow for occupation soil particles and beginning failure in dike crest faster. The presence of fine particles in the very silty sand has reduced the rate of erosion processes inside dike particles in horizontal and vertical directions. The fine particles absorb a large amount of water content and, thus reduce the easiest water infiltration into particles with higher matric suctions. The analyzing of the distributions of water levels and erosion process help to understand the behavior of dike embankment during overtopping failure and increase the maintenance for dikes parts to reduce the potential danger.
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Othman, Ilya Khairanis, Tom E. Baldock und David P. Callaghan. „MEASUREMENT AND MODELING OF THE INFLUENCE OF GRAIN SIZE AND PRESSURE GRADIENTS ON SWASH ZONE SEDIMENT TRANSPORT“. Coastal Engineering Proceedings 1, Nr. 33 (15.12.2012): 58. http://dx.doi.org/10.9753/icce.v33.sediment.58.
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The paper examines the dependency between sediment transport rate, q, and grain size, D, (i.e. q∝Dp) in the swash zone. Experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach. The magnitude and nature of the dependency (i.e. p value) is inferred for different flow parameters; the initial dam depth (or initial bore height), do, the integrated depth averaged velocity, ∫u3 dt, and against the predicted transport, qp using the Meyer-Peter Muller (MPM) transport model. Experiments were performed over both upward sloping beds and a horizontal bed. The data show that negative dependencies (p0) are obtained for ∫u3 dt. This indicates that a given do and qp transport less sediment as grain size increases, whereas transport increases with grain size for a given ∫u3 dt. The p value is expected to be narrow ranged, 0.5≤ p≤-0.5. A discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport. The incorporation of a pressure gradient correction, dp/dx, using the surface water slope (i.e. piezometric head), in the transport calculation greatly improved the transport predictions on the horizontal bed, where dp/dx is positive. On average, the incorporation of a pressure gradient term into the MPM formulation reduces qp in the uprush by 4% (fine sand) to 18% (coarse sand) and increases qp over a horizontal bed by 1% (fine sand) to two orders of magnitude (coarse sand). The measured transport for fine and coarse sand are better predicted using MPM and MPM+dp/dx respectively. Poor predictions are obtained using Nielsen (2002) because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper. It is suggested that future swash sediment transport models should incorporate the grain size effect, partly through the pressure gradient, although the dp/dx influence is small for fine sands because of the grain size scaling contained in the stress term.
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Galani, Konstantina A., und Athanassios A. Dimas. „EXPERIMENTAL STUDY OF THE FLOW INDUCED BY WAVES IN THE VICINITY OF A DETACHED LOW-CRESTED (ZERO FREEBOARD) BREAKWATER“. Coastal Engineering Proceedings, Nr. 36 (30.12.2018): 14. http://dx.doi.org/10.9753/icce.v36.waves.14.
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The combined action of environmental forcing (waves, coastal currents, sediment transport, e.t.c.), the continuously decreasing supply of coastal areas with sediment from rivers, as well as the intense anthropogenic activity, results in the appearance of severe erosion problems in coastal areas and constantly decreasing beach width. A frequently used coastal protection measure is the construction of detached breakwaters parallel to the coastline. Detached breakwaters have a direct effect on the incoming waves, which contributes to the control of coastal sediment transport, hence the morphodynamics of the coastal bed. There are many examples of such structures, the majority of which are emerged breakwaters. Recently, interest has been directed towards the construction of low-crested (LC) and submerged breakwaters due to the reduced construction cost and a more effective harmonization with the natural environment. These structures are characterized by wave overtopping and breaking over their crest in addition to all other coastal processes that are involved with emerged breakwaters. For the proper design of such structures, one critical aspect is the behavior of the induced flow in their vicinity due to their presence. To this purpose, several studies have been carried out in recent years. In particular, Petti et al. (1994) studied experimentally the large scale vortices developed by waves breaking above a submerged breakwater. Mory and Hamm (1997) performed measurements of wave height, surface elevation and wave generated currents around a detached breakwater for incoming regular and irregular waves. Kramer et al. (2005) performed a series of experimental measurements in order to study the waves - LC structure interaction, in terms of flow velocity and turbulence developing around such structures within the European Project DE.LO.S. Garcia et al. (2004), Losada et al. (2005), Johnson et al. (2005) e.t.c. used the database created within the DE.LO.S. project to develop and validate numerical codes for the simulation of wave-induced flow around LC breakwaters. The aim of the present study was the experimental study of the flow developed by waves in the vicinity of an LC rubble mound breakwater with crest level at the water line (zero freeboard). The geometrical scale of the physical model was 1/30. The breakwater was placed on a beach of constant slope 1/15, which is typical of steep beaches in Greece.
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Flatley, Alissa, Ian Rutherfurd und Ross Hardie. „River Channel Relocation: Problems and Prospects“. Water 10, Nr. 10 (29.09.2018): 1360. http://dx.doi.org/10.3390/w10101360.
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River relocation is the diversion of a river into an entirely new channel for part of their length (often called river diversions). Relocations have been common through history and have been carried out for a wide range of purposes, but most commonly to construct infrastructure and for mining. However, they have not been considered as a specific category of anthropogenic channel change. Relocated channels present a consistent set of physical and ecological challenges, often related to accelerated erosion and deposition. We present a new classification of river relocation, and present a series of case studies that highlight some of the key issues with river relocation construction and performance. Primary changes to the channel dimensions and materials, alongside changes to flow velocity or channel capacity, can lead to a consistent set of problems, and lead to further secondary and tertiary issues, such as heightened erosion or deposition, hanging tributaries, vegetation loss, water quality issues, and associated ecological impacts. Occasionally, relocated channels can suffer engineering failure, such as overtopping or complete channel collapse during floods. Older river relocation channels were constructed to minimise cost and carry large floods, and were straight and trapezoidal. In some countries, modern relocated channels represent an exciting new challenge in that they are now designed to replicate natural rivers, the success of which depends on understanding the characteristics, heterogeneity, and mechanisms at work within the natural channel. We discuss shortcomings in current practice for river relocation and highlight areas for future research for successful rehabilitation of relocated rivers.
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Guthrie, R. H., P. Friele, K. Allstadt, N. Roberts, S. G. Evans, K. B. Delaney, D. Roche, J. J. Clague und M. Jakob. „The 6 August 2010 Mount Meager rock slide-debris flow, Coast Mountains, British Columbia: characteristics, dynamics, and implications for hazard and risk assessment“. Natural Hazards and Earth System Sciences 12, Nr. 5 (04.05.2012): 1277–94. http://dx.doi.org/10.5194/nhess-12-1277-2012.
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Abstract. A large rock avalanche occurred at 03:27:30 PDT, 6 August 2010, in the Mount Meager Volcanic Complex southwest British Columbia. The landslide initiated as a rock slide in Pleistocene rhyodacitic volcanic rock with the collapse of the secondary peak of Mount Meager. The detached rock mass impacted the volcano's weathered and saturated flanks, creating a visible seismic signature on nearby seismographs. Undrained loading of the sloping flank caused the immediate and extremely rapid evacuation of the entire flank with a strong horizontal force, as the rock slide transformed into a debris flow. The disintegrating mass travelled down Capricorn Creek at an average velocity of 64 m s−1, exhibiting dramatic super-elevation in bends to the intersection of Meager Creek, 7.8 km from the source. At Meager Creek the debris impacted the south side of Meager valley, causing a runup of 270 m above the valley floor and the deflection of the landslide debris both upstream (for 3.7 km) and downstream into the Lillooet River valley (for 4.9 km), where it blocked the Lillooet River river for a couple of hours, approximately 10 km from the landslide source. Deposition at the Capricorn–Meager confluence also dammed Meager Creek for about 19 h creating a lake 1.5 km long. The overtopping of the dam and the predicted outburst flood was the basis for a night time evacuation of 1500 residents in the town of Pemberton, 65 km downstream. High-resolution GeoEye satellite imagery obtained on 16 October 2010 was used to create a post-event digital elevation model. Comparing pre- and post-event topography we estimate the volume of the initial displaced mass from the flank of Mount Meager to be 48.5 × 106 m3, the height of the path (H) to be 2183 m and the total length of the path (L) to be 12.7 km. This yields H/L = 0.172 and a fahrböschung (travel angle) of 9.75°. The movement was recorded on seismographs in British Columbia and Washington State with the initial impact, the debris flow travelling through bends in Capricorn Creek, and the impact with Meager Creek are all evident on a number of seismograms. The landslide had a seismic trace equivalent to a M = 2.6 earthquake. Velocities and dynamics of the movement were simulated using DAN-W. The 2010 event is the third major landslide in the Capricorn Creek watershed since 1998 and the fifth large-scale mass flow in the Meager Creek watershed since 1930. No lives were lost in the event, but despite its relatively remote location direct costs of the 2010 landslide are estimated to be in the order of $10 M CAD.
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Sakai, Yuji, Yosimasa Takahasi, Tomoyuki Mitani, Toshihiko Yamashita und Hiroshi Saeki. „Overtopping Velocity of Ice Floe on the Breakwater due to Wave Action“. PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN 10 (1994): 247–52. http://dx.doi.org/10.2208/prooe.10.247.
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Bereta, Getachew, Peng Hui, Han Kai, Liwen Guang, Pan Kefan und Yu Zhen Zhao. „Experimental Study of Cohesive Embankment Dam Breach Formation due to Overtopping“. Periodica Polytechnica Civil Engineering, 03.02.2020. http://dx.doi.org/10.3311/ppci.14565.
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The recurrent floods in recent decades have imposed a challenge of embankment dam breaching, which needs great attention through improved design methods that are based on risk approach, the evacuation plans for people at risk, etc. In this study, based on the small-scale model tests a series of experiments were conducted to determine the breaching process of cohesive embankment dam using a simplified physical based breach model due to overtopping; the breach process observed during tests in the laboratory and the results from analyzed parameters are described. Five dam models, three of which were constructed with homogenous clay soil while two were sandy-clay mixture tested. The heights of the embankments dam were 0.45 m, and the widths at the crest were 0.20 m. The data from these examinations indicated that headcut erosion played an important role in the process of breach development. Initiation of erosion, flow shear erosion, sidewall bottom erosion, and distinct soil mechanical slope mass failure from the headcut vertically and laterally were all observed during these tests. In this physical based experimental model, the initial scouring position calculated by applying a hydraulic method, the broad crested weir formula used for breaching flow discharge and flow velocity computed based on breach flow discharge. The stability of the side slope failures was estimated by comparing the resisting and deriving force. Further, using data from laboratory experiments, the calculated peak breach discharge, breach characteristics times, breach widths, and breach flow velocity generally agreed well with the measured data and also the knowledge acquired from observed breach process at several stages. Finally, the accuracy of model was checked by root-mean-square-error.
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Freitas, Mario, Etienne Favre, Pierre Léger und Lineu José Pedroso. „Stability Evaluation of Overtopped Concrete Hydraulic Structures Using Computational Fluid Dynamics“. Canadian Journal of Civil Engineering, 13.02.2020. http://dx.doi.org/10.1139/cjce-2019-0287.
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A particularly challenging aspect in gravity dam stability assessment is the estimation of the induced hydrodynamic water pressure when water with significant velocity is overtopping gravity dams and flowing in or over spillway components. The water flow conditions, including the related pressure fields and resultant forces, are difficult to quantify accurately. Herein, existing dam safety guidelines to estimate the weight of the overflowing water nappe on gravity dams with rectangular crests are first reviewed. Then, a CFD methodology is developed to improve the simplified estimation of hydrodynamic pressure fields acting on the rectangular crests of submerged gravity dams. The CFD pressures are used as input data to classical structural stability analyses based on the gravity method to more adequately quantify the dam stability during overtopping. A back analysis is also performed on the stability of an existing gated spillway that was overtopped during the 1996 Saguenay flood in Québec.
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Boyden, Patrick, Elisa Casella, Christopher Daly und Alessio Rovere. „Hurricane Matthew in 2100: effects of extreme sea level rise scenarios on a highly valued coastal area (Palm Beach, FL, USA)“. Geo-Marine Letters 41, Nr. 4 (08.09.2021). http://dx.doi.org/10.1007/s00367-021-00715-6.
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AbstractSea-level rise represents a severe hazard for populations living within low-elevation coastal zones and is already largely affecting coastal communities worldwide. As sea level continues to rise following unabated greenhouse gas emissions, the exposure of coastal communities to inundation and erosion will increase exponentially. These impacts will be further magnified under extreme storm conditions. In this paper, we focus on one of the most valuable coastal real estate markets globally (Palm Beach, FL). We use XBeach, an open-source hydro and morphodynamic model, to assess the impact of a major tropical cyclone (Hurricane Matthew, 2016) under three different sea-level scenarios. The first scenario (modern sea level) serves as a baseline against which other model runs are evaluated. The other two runs use different 2100 sea-level projections, localized to the study site: (i) IPCC RCP 8.5 (0.83 m by 2100) and (ii) same as (i), but including enhanced Antarctic ice loss (1.62 m by 2100). Our results show that the effective doubling of future sea level under heightened Antarctic ice loss amplifies flow velocity and wave height, leading to a 46% increase in eroded beach volume and the overtopping of coastal protection structures. This further exacerbates the vulnerability of coastal properties on the island, leading to significant increases in parcel inundation.