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1.
This paper is focussed on the derivation of a set of general scaling laws valid for both beach and dune erosion volumes based on scaling law analysis, existing and new experimental results. This latter experiments concern beach profile changes in three different laboratory flumes using identical wave conditions based on Froude scaling. The experiments with planar sloping beaches have been done at three scales: large-scale Hannover wave flume experiment (beach slope of 1 to 15), medium scale Barcelona wave flume experiment (beach slope of 1 to 15) and small-scale Delft wave flume experiments (beach slopes of 1 to 10, 15 and 20) using an identical wave train of irregular waves (single topped spectrum). 相似文献
2.
Torrey Pines State Beach, a site with large seasonal fluctuations in sand level, received a small shoreface beach fill (about 160,000 m3) in April 2001. The 600 m-long, flat-topped nourishment pad extended from a highway riprap revetment seaward about 60 m, terminating in a 2 m-tall vertical scarp. A 2.7 km alongshore span, centered on the nourishment region, was monitored prior to the nourishment and biweekly to monthly for the following 2 years. For the first 7 months after the nourishment, through fall 2001, significant wave heights were small, and the elevated beach fill remained in place, with little change near and above Mean Sea Level (MSL). In contrast, the shoreline accreted on nearby control beaches following a seasonal pattern common in southern California, reducing the elevation difference between the nourished and adjacent beaches. During the first winter storm (3 m significant wave height), the shoreline retreated rapidly over the entire 2.7 km survey reach, forming an alongshore-oriented sandbar in 3 to 4 m water depth [Seymour, R.J., Guza, R.T., O'Reilly, W., Elgar, S., 2004. Rapid erosion of a Southern California beach fill. Coastal Engineering 52 (2), 151–158.]. We show that the winter sandbar, most pronounced offshore of the nourishment, moved back onto the beach face during summer 2002 (following the usual seasonal pattern) and formed a wider beach above MSL at the site of the original nourishment than on the control beaches. Thus, the April 2001 shoreline nourishment was detectable until late fall 2002, persisting locally over a full seasonal cycle. In an extended 7-year time series, total sand volumes (summed between the back beach and 8 m water depth, over the entire 2.7 km reach) exhibit multi-year fluctuations of unknown origin that are twice as large as the nourishment volume. 相似文献
3.
In the light of global warming and sea level rise there are many coastal beaches that suffer from erosion. Beach nourishment has become a common practice to maintain the sediment balance on a shore-face. In this paper, a three-dimensional numerical model for evaluating long-term impact of beach nourishment projects has been developed. The model addresses the longstanding complex issue of coastal morphology and sediment grain size distribution from an unconventional angle, which exploits the strong links between grain size distribution and the prevailing transport direction of each sediment constituent under ‘average’ wave and storm action. The present model predicts the redistribution of nourished sediment according to the subtle clues implied by equilibrium distribution curves and latest coastal wave transformation theories. After verification against recent field observations in Terschelling, The Netherlands, the model was used to predict long-term effects of different beach nourishment strategies. It was found that: (a) given the source sediment available in Terschelling the tactics of large volume and less frequent implementation are better than otherwise; and (b) from a pure engineering point of view, waterline nourishment outperforms offshore trough nourishment.The model offers an additional tool for coastal engineers to evaluate the feasibility, effectiveness and the optimization of dumping locations for beach nourishment projects. It is also a useful tool for stratigraphic modelling of shallow-marine sedimentation in conjunction with sea level changes. 相似文献
4.
This study focuses on barred beach shoreface nourishments physically simulated in a wave flume. The attack of a schematic storm on three different nourishments is analysed. The apex and waning storm phases lead respectively to offshore and onshore sediment transports. Nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore. The bar acts as a wave filter and reduces shore erosion (lee effect). In contrast, nourishment on the beach face leads mostly to shore feeding and reconstruction (feeder effect). With successive nourishments, the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates. The surface grain size analysis reveals marked variations. Coarser sediments are sorted on the bar and the upper beach face. These locations correspond to large wave dissipation zones during the storm apex. 相似文献
5.
Sediment transport and beach morphodynamics induced by free long waves,bound long waves and wave groups 总被引：1，自引：0，他引：1
New laboratory data are presented on the influence of free long waves, bound long waves and wave groups on sediment transport in the surf and swash zones. As a result of the very significant difficulties in isolating and identifying the morphodynamic influences of long waves and wave groups in field conditions, a laboratory study was designed specifically to enable measurements of sediment transport that resolve these influences. The evolution of model sand beaches, each with the same initial plane slope, was measured for a range of wave conditions, firstly using monochromatic short waves. Subsequently, the monochromatic conditions were perturbed with free long waves and then substituted with bichromatic wave groups with the same mean energy flux. The beach profile changes and net cross-shore transport rates were extracted and compared for the different wave conditions, with and without long waves and wave groups. The experiments include a range of wave conditions, e.g. high-energy, moderate-energy, low-energy waves, which induce both spilling and plunging breakers and different turbulent intensities, and the beaches evolve to form classical accretive, erosive, and intermediate beach states. The data clearly demonstrate that free long waves influence surf zone morphodynamics and promote increased onshore sediment transport during accretive conditions and decreased offshore transport under erosive conditions. In contrast, wave groups, which can generate both forced and free long waves, generally reduce onshore transport during accretive conditions and increase offshore transport under erosive conditions. The influence of the free long waves and wave groups is consistent with the concept of the relative fall velocity, H/wsT, as a dominant parameter controlling net beach erosion or accretion. Free long waves tend to reduce H/wsT, promoting accretion, while wave groups tend to increase the effective H/wsT, promoting erosion. 相似文献
6.
This paper illustrates the results of an experimental investigation (model-to-prototype length ratio equal to 12) carried out to reproduce the cross-shore evolution of nourished sandy beaches. New two-dimensional experiments were performed to study the short-term response of the cross-shore profile for both “soft” (unprotected) and “mixed” (protected by submerged breakwaters) beach fill projects. Due to the simplified reproduction of prototype conditions in a two-dimensional geometry, only cross-shore sediment transport is considered. The results are related to the immediate post-nourishment evolution and far from beach fill boundaries where long-shore gradients of long-shore sediment transport are likely to be negligible. Three different pseudo-random wave trains were generated in order to simulate both accretive and erosive conditions. A fourth wave train, characterised by time-varying incident wave spectrum was generated for the investigation of the beach response to simplified storm time evolution. Dimensionless experimental results are given in terms of wave parameters, key features of cross-shore profile evolution and sediment transport rates. Furthermore, being highly resolved in both time and space, experimental data are suitable for mathematical model validation. It was observed that submerged breakwater switches erosive conditions to slightly accretive, at least within the tested experimental range. 相似文献
7.
This study presents sand activation depth (SAD) measurements recently obtained on two contrasting beaches located along the Atlantic coast of France: the gently sloping, high-energy St Trojan beach where wave incidence is usually weak, and the steep, low-energy Arçay Sandspit beach where waves break at highly oblique angles. Comparisons between field measurements and predictions from existing formulae show good agreement for St Trojan beach but underestimate the SAD on the Arçay Sandspit beach by 40–60%. Such differences suggest a strong influence of wave obliquity on SAD. To verify this hypothesis, the relative influence of wave parameters was investigated by means of numerical modelling. A quasi-linear increase of SAD with wave height was confirmed for shore-normal and slightly oblique wave conditions, and a quasi-linear increase in SAD with wave obliquity was also revealed. Combining the numerical results with previously published relations, both a new semi-empirical and an empirical formula for the prediction of SAD were developed which showed good SAD predictions under conditions of oblique wave breaking. The new empirical formula for the prediction of SAD (Z 0) takes into account the significant wave height (H s), the beach face slope (β) and the wave angle at breaking (α), and is of the form $ Z_{0} = 1.6\tan {\left( \beta \right)}H^{{0.5}}_{{\text{s}}} {\sqrt {1 + \sin {\left( {2\alpha } \right)}} } This study presents sand activation depth (SAD) measurements recently obtained on two contrasting beaches located along the
Atlantic coast of France: the gently sloping, high-energy St Trojan beach where wave incidence is usually weak, and the steep,
low-energy Ar?ay Sandspit beach where waves break at highly oblique angles. Comparisons between field measurements and predictions
from existing formulae show good agreement for St Trojan beach but underestimate the SAD on the Ar?ay Sandspit beach by 40–60%.
Such differences suggest a strong influence of wave obliquity on SAD. To verify this hypothesis, the relative influence of
wave parameters was investigated by means of numerical modelling. A quasi-linear increase of SAD with wave height was confirmed
for shore-normal and slightly oblique wave conditions, and a quasi-linear increase in SAD with wave obliquity was also revealed.
Combining the numerical results with previously published relations, both a new semi-empirical and an empirical formula for
the prediction of SAD were developed which showed good SAD predictions under conditions of oblique wave breaking. The new
empirical formula for the prediction of SAD (Z
0) takes into account the significant wave height (H
s), the beach face slope (β) and the wave angle at breaking (α), and is of the form . The use of a dataset from the literature demonstrates the predictive skill of these new formulae for a wide range of wave
heights, wave incidence and beach gradients. 相似文献
8.
Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity. 相似文献
9.
Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion. 相似文献
10.
Longshore Currents of Random Waves on Different Plane Beaches 总被引：8，自引：0，他引：8
1 .IntroductionWhenwavespropagateobliquelytotheshorelineandbreak ,ameancurrentisgeneratedflowingparalleltothecoast.Thegenerationoflongshorecurrentscanbeexplainedasfollows .Withbreakingwaveheightdecreasing ,themomentumofwavemotionwillchangecorrespondingly .Accordingtothemomentumconservationtheory ,thechangesofthemomentumwillbeaccompaniedwithadditionalforcesactingonfluid .Longuet Higgins ( 1 970 )usedtheconceptofradiationstresstodescribetheaboveadditionalforceactingonfluidduetothechangeofwavemo… 相似文献
11.
This work presents a frequency-domain method for estimating incident and reflected waves when normally incident waves’ propagating over a sloping beach in a wave flume is considered. Linear wave shoaling is applied to determine changes of the wave amplitude and phase due to variations of the bathymetry. The wave reflection coefficient is estimated using wave heights measured at two fixed wave gauges with a distance. The present model demonstrates a high capacity of estimating reflection and shoaling coefficients from synthetic wave-amplitude data. Sensitivity tests for the present model due to measurement errors of wave amplitudes and distance of two probes can more accurately predict the reflection coefficients. The measurement error of wave amplitude affects more significantly than measurement error of distance of two probes on calculating reflection coefficient of waves over a sloping bed. 相似文献
12.
Charles W. Finkl 《Geo-Marine Letters》1981,1(2):155-161
Artificial beach nourishment, the placing of sand onto eroded beaches, is increasingly employed by coastal engineers as an
alternative to structural control of shoreline erosion. Man-made beaches approximating natural forms and processes offer greater
protection against storms than eroded beaches and provide increased recreational opportunities. It is hoped that maintenance
nourishment will keep pace with subsidence and eustatic rise in sea level, primary causes of beach erosion. Even though negative
impacts of beach restoration may be short-lived and limited in scope, sound ecological engineering practices require careful
monitoring of dredging operations. 相似文献
13.
准确确定越浪量对于斜坡堤设计有重要意义。利用格子Boltzmann方法(LBM),并采用主动吸收式速度入口造波、出流边界消波、VOF方法追踪自由表面以及静态Smagorinsky模型模拟紊流运动,建立二维数值波浪水槽,对光滑斜坡堤上规则波与不规则波越浪进行数值模拟。模拟结果与试验值及其他数值模型结果比较表明,二维LBM数值波浪水槽具有模拟斜坡堤越浪的能力,但对于破碎较为剧烈的越浪过程模拟,该模型还存在一定的不足,未来可从提高自由表面模型精度等方面进一步改善其性能。 相似文献
14.
Wave-induced currents may drive nearshore mixing and transport processes, including coastal pollutant dispersion, littoral drift, and long-term morphological changes through beach erosion and accretion. In this study, a numerical model is newly developed to simulate wave climate and localized currents in complicated coastal environments. The model developed is based on a quadtree grid system. The two-dimensional hydrodynamic governing equations are solved by using an explicit Adams-Bashforth finite difference scheme. Effects of wave breaking, shoaling, refraction, diffraction, wave-current interaction, set-up and set-down, turbulent mixing, bed friction, and shoreline movement are incorporated in the model. Results are presented for set-up at a beach in a flume due to normally incident waves, and longshore currents generated by oblique waves on a plane beach. 相似文献
15.
海岸波浪多次破碎波能耗散模型 总被引：1，自引：0，他引：1
在坡度很缓(接近或小于1∶100)的海岸,波浪在向海岸传播的过程中,可能经历多次破碎,而在两次波浪破碎之间将伴随着波浪恢复(波浪恢复到不破碎状态)。在现有海岸波高计算模型中,波浪破碎是通过波能耗散来模拟的,但所采用的波能耗散模型都不能自动考虑波浪出现多次破碎的过程,特别精确模拟这一过程中出现的波浪恢复。本文提出了解决这一问题的新的波能耗散模型,模型的建立是通过在Dally模型中重新建立稳定波能、饱和波高水深比和波能耗散系数,并引入了波浪恢复的判断条件实现的。该模型的波能耗散在波浪恢复区的值很小故能描述波浪恢复区的波浪运动。与实验结果的对比表明,新模型可以适合缓坡情况波浪多次破碎的波高模拟,而且对不同坡度的平坡和沙坝海岸(1∶100～1∶10)的破碎波模拟都可以给出与实验结果符合的结果,并且可以自动识别多次波浪破碎的存在和波浪恢复的发生。 相似文献
16.
《Coastal Engineering》2006,53(4):349-362
This paper provides information on the experimental set-up, data collection methods and results to date for the project “Large scale modelling of coarse grained beaches”, undertaken at the Large Wave Channel (GWK) of FZK in Hannover by an international group of researchers in Spring 2002. The main objective of the experiments was to provide full scale measurements of cross-shore processes on gravel and mixed beaches for the verification and further development of cross-shore numerical models of gravel and mixed sediment beaches. Identical random and regular wave tests were undertaken for a gravel beach and a mixed sand/gravel beach set up in the flume. Measurements included profile development, water surface elevation along the flume, internal pressures in the swash zone, piezometric head levels within the beach, run-up, flow velocities in the surf-zone and sediment size distributions.The purpose of the paper is to present to the scientific community the experimental procedure, a summary of the data collected, some initial results, as well as a brief outline of the on-going research being carried out with the data by different research groups. The experimental data is available to all the scientific community following submission of a statement of objectives, specification of data requirements and an agreement to abide with the GWK and EU protocols. 相似文献
17.
M.J.F. Stive 《Coastal Engineering》1985,9(2):151-158
A measurement programme, conducted in a small-scale wave flume, which comprised the breaking of periodic and random waves on a gently sloping beach, was partly repeated in a large-scale wave flume. The results are used here to make a scale comparison. The quantities considered in the comparison are wave heights, set-up and vertical profiles of maximum seaward, maximum shoreward and time-mean horizontal velocities. It appears that, both qualitatively and quantitatively, scale effects in these quantities are virtually absent in the wave height range of 0.1 m to 1.5 m. 相似文献
18.
由于自然因素和人类活动的影响等原因,世界很多海滩经受着侵蚀和破坏。而利用人工养护工程来保护和恢复海滩具有养护效果较明显、干滩面积明显增加以及不破坏环境景观的优点,目前得到越来越多国家的认可。国外由于养滩历史较久,养滩工程后的监测和质量评价不仅开展得早,而且已经成为工程的一个重要部分。评价指标已经比较完善,甚至有些国家已经将养滩效果评价列入法规框架之中。我国的海滩养护工程在十几年前才开始,虽然工程量逐年增长,但是对海滩养护工程施工后的工程监测和工程评价却较少涉及。本文对美国、荷兰、英国、丹麦以及我国等国家的海滩养护工程的工程评价工作进行总结,从而提出适用于我国工程特点的养滩工程质量评价因子和方法。 相似文献
19.
《Coastal Engineering》2001,42(2):143-153
Beach erosion problems have been solved by adding sand to the beaches along the Gulf of Cadiz. The Gulf is located in SW Spain between the Portuguese border and the Strait of Gibraltar. During the last decade, more than 12×106 m3 of sand have been nourished in 38 restoration operations carried out on 28 beaches. The main characteristics of the nourishment campaigns (year, volume, budget, transport method, sand data, etc.) are presented. Location of sand borrow sites and distance to the beaches are also shown. Monitoring programs have been performed in order to calculate sediment loss rates. These results have been related to the beach length, the berm width and the budget in order to obtain a variety of relationships for maintenance cost as, for example, the total annual cost for each beach. This information is very useful when developing a strategy in coastal zone management. Furthermore, at least in reef-protected beaches, small yearly renourishments similar to the yearly losses, instead of greater nourishments performed with a periodicity of many years, lead to an economical saving, as well as to a better use of the natural resources. 相似文献
20.
研究养护海滩对风暴潮的响应过程在人工养滩工程设计与施工中具有重要意义。老龙头养护海滩在竣工半个月后遭遇“803”风暴潮,导致岸滩滩肩最大蚀退 6.5 m,沙坝坝顶最大下蚀 1.2 m。在现场测量的基础上,利用 XBeach 建立风暴潮过程
的老龙头海滩海床演变模型,研究结果表明： （1） XBeach 模拟结果与实际地形变化侵淤趋势一致,风暴潮期间人工沙坝均向岸移动,但模拟结果的侵蚀程度更大,海滩响应更加剧烈; （2） 强浪条件下人工沙坝的透射系数为 0.29~0.42,常浪条件下透射系数为 0.45~0.95,因而人工沙坝在大浪条件下掩护作用更佳; （3） 风暴潮期间人工沙坝附近破波显著,坝顶流速明显增大,最大可达 1.21 m/s,是无人工沙坝情况下的 2.3 倍,而在人工沙坝向岸侧,因波能提前耗散,流速减为 0.28 m/s,是无人工沙坝时的 0.4 倍,且没有产生离岸流。老龙头养护工程整体泥沙损失较少,易于恢复. 相似文献