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1.
《Coastal Engineering》2005,52(10-11):931-947
This paper deals with wave overtopping associated to low emergent detached breakwaters. It starts presenting the various mechanisms which define the functional behaviour of detached breakwaters which are frequently overtopped. The emphasis is on the role played by overtopping and how this contributes to the wave pumping in the area around the structure. The paper then reviews the available formulations for predicting overtopping, considering the sensitivity of various equations to climatic drivers and their suitability for low crested coastal structures. The paper then analyzes nearshore circulation models and how overtopping discharges can be included. This is illustrated with a sample Q-3D model by analyzing the differences obtained with/without overtopping. The emphasis is on the implications for the functional design of the structure and its morpho-hydrodynamic impact. The main conclusion is the sensitivity of the functional design of such structures to the underlying hydrodynamics processes and the importance to explicitly include overtopping for numerical simulations of the morpho-hydrodynamic behaviour of low crested breakwaters. 相似文献
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Leopoldo Franco Jimmy Geeraerts Riccardo Briganti Marc Willems Giorgio Bellotti Julien De Rouck 《Coastal Engineering》2009
The paper presents the comparison between the results of small-scale model tests and prototype measurements of wave overtopping at a rubble-mound breakwater. The specific structure investigated is the west breakwater of the yacht harbour of Rome at Ostia (Italy) and is characterized by a gentle seaward slope (1/4) and by a long, shallow foreshore. The laboratory tests firstly aimed at carefully reproducing two measured storms in which overtopping occurred and was measured. The tests have been carried out in two independent laboratories, in a wave flume and in a wave basin, hence using a two-dimensional (2-D) and a three-dimensional (3-D) setup. In the 2-D laboratory tests no overtopping occurred during the storm reproductions; in the 3-D case discharges five to ten times smaller than those observed in prototype have been measured. This indicates the existence of model and scale effects. These effects have been discussed on the basis of the results of several parametric tests, which have been carried out in both laboratories, in addition to the storm reproductions, varying wave and water level characteristics. Final comparison of all the performed tests with 86 prototype measurements still suggests the existence of scale and model effects that induce strong underestimation of overtopping discharge at small scale. The scale reproduction of wave breaking on the foreshore, together with the 3-D features of the prototype conditions and the absence of wind stress in the laboratory measurements, have been individuated as the main sources of scale and model effects. The paper also provides a comparison between the data and a largely used formula for wave overtopping discharges in the presence of structures similar to the one at hand. The suitable value of a roughness factor that appears in that formula is investigated and good agreement is found with other recent researches on rubble-mound breakwaters. 相似文献
4.
The performance of the new wave diffraction feature of the shallow-water spectral model SWAN, particularly its ability to predict the multidirectional wave transformation around shore-parallel emerged breakwaters is examined using laboratory and field data. Comparison between model predictions and field measurements of directional spectra was used to identify the importance of various wave transformation processes in the evolution of the directional wave field. First, the model was evaluated against laboratory measurements of diffracted multidirectional waves around a breakwater shoulder. Excellent agreement between the model predictions and measurements was found for broad frequency and directional spectra. The performance of the model worsened with decreasing frequency and directional spread. Next, the performance of the model with regard to diffraction–refraction was assessed for directional wave spectra around detached breakwaters. Seven different field cases were considered: three wind–sea spectra with broad frequency and directional distributions, each coming from a different direction; two swell–sea bimodal spectra; and two swell spectra with narrow frequency and directional distributions. The new diffraction functionality in SWAN improved the prediction of wave heights around shore-parallel breakwaters. Processes such as beach reflection and wave transmission through breakwaters seem to have a significant role on transformation of swell waves behind the breakwaters. Bottom friction and wave–current interactions were less important, while the difference in frequency and directional distribution might be associated with seiching. 相似文献
5.
《Coastal Engineering》1999,38(3):143-166
Two different concepts are applicable to model the nearshore morphodynamics. The first one takes into account only final consequences of acting mechanisms and is aimed at the prediction of long-term trends in beach development. Another approach implies the modelling of the whole suite of elementary processes responsible for changes in nearshore bottom topography during a given storm, and it is the approach used in the present work. A coastal area model complex is proposed that allows to reproduce the local morphological changes due to both the natural processes and the influence of coastal structures, such as a groin, a detached breakwater and a navigable channel (underwater trough). Consisting of a traditional series of basic components, the model differs from other ones in essential aspects concerning the treatment of transport mechanisms. In particular, the determination of wave-induced near-bed mean flow is based on the hypothesis that the direction and magnitude of bottom drift depend on difference between the actual rate of energy dissipation and its threshold value marking the flow reversal point. This hypothesis is shown to explain a general trend of cross-shore mean flow distributions observed in the nearshore region. Besides, the influence of the wave breaking process on sediment suspension is taken into account and the contribution of the swash zone to total sediment transport is included. Examples of computed morphological response are represented to demonstrate the model capability. A satisfactory agreement of computations with available data is pointed out. 相似文献
6.
南渡江三角洲海岸泥沙纵向运移与岸滩演变的响应 总被引：7，自引：0，他引：7
南渡三角洲沿岸在盛行ＮＮＥ向波浪等动力条件的作用下,泥沙产生纵向运移,岸滩遭受侵蚀或堆积,岸滩演变剧烈。本文利用基于网格的波注折射绕射模型,分析南渡江三角洲海岸波浪动力过程、破波带波能与辐射应力分布及其引起的沿岸泥沙纵向运称。浴海岸动力学地貌的角度,通过三角洲沿岸波浪动力特征、泥沙运动的分析,探讨沙质岸滩的动态与地貌演变。 相似文献
7.
Field measurements of beach morphology and sedimentology were made along the Monterey Peninsula and Carmel Bay, California, in the spring and summer of 1997. These data were combined with low-altitude aerial imagery, high-resolution bathymetry, and local geology to understand how coastal geomorphology, lithology, and tectonics influence the distribution and transport of littoral sediment in the nearshore and inner shelf along a rocky shoreline over the course of decades. Three primary modes of sediment distribution in the nearshore and on the inner shelf off the Monterey Peninsula and in Carmel Bay were observed. Along stretches of the study area that were exposed to the dominant wave direction, sediment has accumulated in shore-normal bathymetric lows interpreted to be paleo-stream channels. Where the coastline is oriented parallel to the dominant wave direction and streams channels trend perpendicular to the coast, sediment-filled paleo-stream channels occur in the nearshore as well, but here they are connected to one another by shore-parallel ribbons of sediment at depths between 2 and 6 m. Where the coastline is oriented parallel to the dominant wave direction and onshore stream channels are not present, only shore-parallel patches of sediment at depths greater than 15 m are present. We interpret the distribution and interaction or transport of littoral sediment between pocket beaches along this coastline to be primarily controlled by the northwest-trending structure of the region and the dominant oceanographic regime. Because of the structural barriers to littoral transport, peaks in wave energy appear to be the dominant factor controlling the timing and magnitude of sediment transport between pocket beaches, more so than along long linear coasts. Accordingly, the magnitude and timing of sediment transport is dictated by the episodic nature of storm activity. 相似文献
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I~crIOWIn the coastal area, especially at the sandy seashore, wave and nearshore current are the major factors which affect sediment transPOrt and the motyhChdynamics.The numerical models of predicting the beach evolution can be classified intO the medi~term and long-term models according to their space and time scales (De Briend et al., 1993;Watanabe, 1990; Watanabe et al., 1986; Tao, 1996). In the medium-term model the effects ofwave, nearshore current and sediment transport are conside… 相似文献
9.
J. Nicholson I. Broker J. A. Roelvink D. Price J. M. Tanguy L. Moreno 《Coastal Engineering》1997,31(1-4)
Five different coastal area morphodynamic models have been set up to run on the same offshore breakwater layout and an intercomparison carried out on the hydrodynamic and morphodynamic output produced by each scheme. In addition, the predicted morphodynamics was checked against available laboratory and field data.It is concluded that the models are capable of producing realistic estimates for the dominant morphodynamic features associated with offshore breakwaters. Coupling of the wave, current and sediment transport components of each scheme is shown to yield bathymetry which attains a state of equilibrium, unlike models which are based on the initial transport field only. 相似文献
10.
A numerical model of beach morphological evolution due to waves and currents in the vicinity of coastal structures 总被引：2，自引：0，他引：2
A numerical model was developed of beach morphological evolution in the vicinity of coastal structures. The model includes five sub-models for random wave transformation, surface roller development, nearshore wave-induced currents, sediment transport, and morphological evolution. The model was validated using high-quality data sets obtained during experiments with a T-head groin and a detached breakwater in the basin of the Large-scale Sediment Transport Facility at the Coastal and Hydraulics Laboratory in Vicksburg, Miss, USA. The simulations showed that the model reproduced well the wave conditions, wave-induced currents, and beach morphological evolution in the vicinity of coastal structures. Both salient and tombolo formation behind a T-head groin and a detached breakwater were simulated with good agreement compared to the measurements. 相似文献
11.
《Marine Geology》2003,193(3-4):171-176
Megaripples in the combined flow environment of the nearshore are proposed to behave like dunes or large ripples in rivers, tidal estuaries, and deserts. Their profile basically is symmetric and thus significantly different from the traditional asymmetric triangular features observed in steady flows. Similarly their planform often exhibits little directionality, unlike crescentic or lunate steady flow dunes that point in the downstream direction. These characteristics are the result of complex combined flows in the nearshore, including oscillatory flows, wave skewness, and steady currents (undertow, rips and alongshore flows). Recent observations of megaripples in the nearshore suggest that they occur frequently. However, they are rarely considered in studies of flow resistance or sediment transport. In addition, megaripples are thought to be the source of hummocky cross-stratification in sedimentary sequences and are generally attributed to storm waves on inner continental shelves. However, observations show that they also exist inside the surf zone and under lower-energy conditions. A better understanding of their dynamics and thus their occurrence and characteristics would improve the understanding of nearshore wave and circulation dynamics, sediment transport, large-scale morphodynamics, and the resulting sedimentary sequences. It is hypothesized that megaripples in the nearshore are dynamically similar to steady flow features, which are observed in rivers, estuaries and deserts and have been studied in much more detail. 相似文献
12.
Significant effort has been made to generate a homogeneous database on wave overtopping consisting of more than 10,000 irregular wave overtopping tests from more than 160 independent projects or test series, each described by means of 31 parameters. Many coastal structures, including dikes, rubble mound breakwaters, berm breakwaters, caisson structures and combinations have been considered and have been schematised for inclusion in the database. All these overtopping tests are represented by over 300,000 numbers in the database. 相似文献
13.
近岸波、流作用下结构物附近海岸演变的数值模拟 总被引：5，自引：0，他引：5
针对与砂质海岸在波浪作用下的演变有关的波浪、近岸流及输沙问题进行了系统的研究,并对结构物附近海岸演变进行了数值模拟。考虑了波浪折射-绕射及波浪破碎的综合作用,在近岸流场的模拟中用沿水深积分形成的K方程模型确定涡粘系数。计算岸滩地形变化时,综合波浪、近岸流作用的底沙和悬沙输沙率,并考虑波浪对泥沙作用的影响。模型对防波堤和近岸沉船附近地形变化进行了模拟,效果良好。 相似文献
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The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference finite-volume TVD-type scheme, is coupled with the wave model SWAN in the Nearshore Community Model (NearCoM) system. The new modeling system is named NearCoM-TVD and the purpose of this study is to report the capability and limitation of NearCoM-TVD for several coastal applications. For tidal inlet applications, the model is verified with the semi-analytical solution of Keulegan (1967) for an idealized inlet-bay system. To further evaluate the model performance in predicting nearshore circulation under intense wave–current interaction over complex bathymetry, modeled circulation patterns are validated with measured data during RCEX field experiment (MacMahan et al., 2010). For sediment transport applications, two sediment transport models are applied to predict three sandbar migration events at Duck, NC, during August to October 1994 (Gallagher et al., 1998). The model of Kobayashi et al. (2008) incorporates wave-induced onshore sediment transport rate as a function of the standard deviation of wave-induced horizontal velocities. The modeled beach profile evolution for two offshore events and one onshore event agrees well with the measured data. The second model investigated here combines two published sediment transport models, namely, the total load model driven by currents under the effect of wave stirring (Soulsby, 1997) and the wave-driven sediment transport model due to wave asymmetry/skewness (van Rijn et al., 2011). The model study with limited field data suggests that the parameterization of wave stirring is appropriate during energetic wave conditions. However, during low energy wave conditions, the effect of wave stirring needs to be re-calibrated. 相似文献
16.
A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant. 相似文献
17.
The accuracy of predicting wave transformation in the nearshore is very important to wave hydrodynamics, sediment transport and design of coastal structures. An efficient numerical model based on the time-dependent mild-slope equation is presented in this paper for the estimation of wave deformation across the surf zone. This model incorporates an approximate nonlinear shoaling formula and an energy dissipation factor due to wave breaking to improve the accuracy of the calculation of wave height deformation prior to wave breaking and also in the surf zone. The model also computes the location of first wave breaking, wave recovery and second wave breaking, if physical condition permits. Good agreement is found upon comparison with experimental data over several one-dimensional beach profiles, including uniform slope, bar and step profiles. 相似文献
18.
Li Yan-ting Zeng Cheng-jie Yi-han Zhao Hu Po Sun Tian-ting Hou Yi-jun Mo Dong-xue Wang Deng-ting 《中国海洋工程》2022,36(3):413-426
Storm surges are cataclysmic natural disasters that occur along the coasts and are usually accompanied by large waves. The effects of coupled storm surges and waves can pose a significant threat to coastal security. Previous laboratory studies on the effects of storm surges and waves on coastal structures have typically utilized steady water levels and constant wave elements. An indoor simulation of the coupled processes of tides and waves is developed by adding a tide generation system to an existing laboratory wave basin to model continuous dynamic tide levels so that tide generation and wave-making occur synchronously in the pool. Specific experimental methods are given, which are applied to further study waves overtopping on artificial sea dikes and coastal flooding evolution under the coupled actions of tides and waves. The results of the overtopping discharge obtained by the test with a dynamic water level are compared with those obtained from steady water level tests and the existing empirical formula. In addition, the impacts of ecological coastal shelterbelts and structures on coastal flood processes and distributions are also investigated. The proposed simulation methods provide a new approach for studying the effects of storm surges and waves on coastal areas. The study also aims to provide a reference for coastal protective engineering.
相似文献19.
Understanding the sediment transport and the resulting scour around coastal structures such as pile breakwaters under local extreme wave conditions is important for the foundation safety of various coastal structures. This study reports a wave-flume experiment investigating the scour induced by solitary waves at a pile breakwater, which consists of a row of closely spaced large piles. A wave blacking gate with a simple operation procedure in the experiment was designed to eliminate possible multiple reflections of the solitary wave inside the flume. An underwater laser scanner and a point probe were used in combination to provide high-resolution data of the bed profile around the pile breakwater. Effects of incident wave height and local water depth on the maximum scour depth, the maximum deposition height and the total scour and deposition volumes were examined. An existing empirical formula describing the evolution of the scour at a single pile in current or waves was extended to describe the scour at the pile breakwater under the action of multiple solitary waves, and new empirical coefficients were obtained by fitting the formula to the new experimental data to estimate the equilibrium scour depth. It appears that the maximum scour depth and the total scour volume are two reliable quantities for validation of numerical models developed for the scour around pile breakwaters under highly nonlinear wave conditions. 相似文献
20.
In this paper we present a process-based numerical model for the prediction of storm hydrodynamics and hydrology on gravel beaches. The model comprises an extension of an existing open-source storm-impact model for sandy coasts (XBeach), through the application of (1) a non-hydrostatic pressure correction term that allows wave-by-wave modelling of the surface elevation and depth-averaged flow, and (2) a groundwater model that allows infiltration and exfiltration through the permeable gravel bed to be simulated, and is referred to as XBeach-G. Although the model contains validated sediment transport relations for sandy environments, transport relations for gravel in the model are currently under development and unvalidated. Consequently, all simulations in this paper are carried out without morphodynamic feedback. Modelled hydrodynamics are validated using data collected during a large-scale physical model experiment and detailed in-situ field data collected at Loe Bar, Cornwall, UK, as well as remote-sensed data collected at four gravel beach locations along the UK coast during the 2012–2013 storm season. Validation results show that the model has good skill in predicting wave transformation (overall SCI 0.14–0.21), run-up levels (SCI < 0.12; median error < 10%) and initial wave overtopping (85–90% prediction rate at barrier crest), indicating that the model can be applied to estimate potential storm impact on gravel beaches. The inclusion of the non-hydrostatic pressure correction term and groundwater model is shown to significantly improve the prediction and evolution of overtopping events. 相似文献