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1.
Beach profiles characteristics along Giao Thuy and Hai Hau coasts, Vietnam: A field study 总被引：1，自引：0，他引：1
Giao Thuy and Hai Hau coasts are located in Nam Dinh province, Vietnam, with a total coastline of 54.42 km in length. The sea-dike system has been seriously damaged and there have been many dike breaches which caused floods and losses. This situation is considered of a general representative for coastal area in the northern part of Vietnam. A variety of studies have shown that the gradient in the longshore sediment transport rate and the offshore ?ne sediment lost are the main mechanisms causing the beach erosion. This study presents a field investigation of the beach profiles at Giao Thuy and Hai Hau beaches. Three types of empirical functions for the equilibrium beach profile are applied and compared with the observations. Results show that all observed beach pro?les can be described by a single function. However, one specific equilibrium pro?le equation is not sufficient to assess all beach pro?les. In Section 1 of Giao Thuy and Section 3 of Hai Thinh beaches, beach profiles are consistent with the logarithmic function, while the exponential function fits well in Section 2. This difference is explained with respect to coastal morphology, sediment characteristics and hydrodynamic conditions which vary in site. An analysis of the validity of the beach profile functions is recommended for the numerical modeling and engineering designs in this area. 相似文献
2.
Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper. 相似文献
3.
This study introduces three typical models on equilibrium beach profile, and discusses the application limitations of these models. Then this study examines the selections for applying these models on different coastal segments of a headland-bay beach in west Guangdong, South China, and explores the physical significances of those parameters in the models. The results indicate that: (1) Bodge’s model is more in line with the equilibrium beach profile of the tangential or transitional segment, whereas Lee’s model is more consistent with the shadow profile; (2) most of the parameters in three models have clear physical significances in accordance with the actual characteristics of this headland-bay beach; and (3) both the selections for the equilibrium beach profile from different segments and significances of most of the parameters in three models are in essence correlated with the morphodynamic states at various coastal locations. 相似文献
4.
An engineering application tool for prediction of the static equilibrium bay(Beach Mod)is established to describe two bay shape formulas by use of the programming software "MATLAB" with a graphic user interface(GUI).The tool is user-friendly for engineering students for the design of beach shapes.This tool was tested through application on three types of beaches in Taiwan and Australia.By implementing the concept of Headland Control,the Beach Mod program allows users to draw a structure and create an artificial headland.The results indicate that Beach Mod can efficiently forecast beach changes as well as MEPBAY,a competing software package,while boasting a better user interface. 相似文献
5.
The abandoned Yellow River Delta coast is a typical erodible silty and muddy coast in China. The paper analyses the marine dynamic characteristics and the mechanism of beach erosion of this area. Analysis and calculation show that in this sea area wave and tidal current action should be considered. Based on the above analysis, an equilibrium beach profile calculation model is developed, in which the wave-current interaction is considered while sediment supply and sediment re-deposition are neglected. The model consists of four parts: (1) calculation of wave parameters, (2) calculation of velocity due to wave-current interaction at different water depth, (3) calculation of friction velocity and shear stress at different water depths, and (4) calculation of the amount of sediment erosion, erosion intensity and variation of beach profile. Calculated results are in good agreement with observed data. Finally, the evolution tendency is discussed and the equilibrium beach profile of this coast is calculated. B 相似文献
6.
Joevivek Vincent Jayaraj Chandrasekar Nainarpandian Jayangondaperumal Ramakrishnan Thakur Vikram Chandr Shree Purniema Krishnan 《海洋学报(英文版)》2019,38(5):151-160
To analyze the grain size and depositional environment of the foreshore sediments, a study was undertaken on wave refraction along the wide sandy beaches of central Tamil Nadu coast. The nearshore waves approach the coast at 45° during the northeast(NE) monsoon, at 135° during the southwest(SW) monsoon and at 90° during the non-monsoon or fair-weather period with a predominant wave period of 8 and 10 s. A computer based wave refraction pattern is constructed to evaluate the trajectories of shoreward propagating waves along the coast in different seasons. The convergent wave rays during NE monsoon, leads to high energy wave condition which conveys a continuous erosion at foreshore region while divergent and inept condition of rays during the SW and non-monsoon, leads to moderate and less energy waves that clearly demarcates the rebuilt beach sediments through littoral sediment transport. The role of wave refraction in foreshore deposits was understood by grain size and depositional environment analysis. The presence of fine grains with the mixed population, during the NE monsoon reveals that the high energy wave condition and sediments were derived from beach and river environment. Conversely, the presence of medium grains with uniform population, during SW and non-monsoon attested less turbulence and sediments were derived from prolong propagation of onshore-offshore wave process.These upshots are apparently correlated with the in situ beach condition. On the whole, from this study it is understood that beaches underwent erosion during the NE monsoon and restored its original condition during the SW and non-monsoon seasons that exposed the stability of the beach and nearshore condition. 相似文献
7.
薛春汀 《海洋通报(英文版)》2004,6(2):45-50
Excavating sands and gravel on land in combination with constructing reservoirs for storing fresh water is an ideal approach in atolls. Appropriate mining of gravel from the prograding gravel beach is acceptable. Digging reef rock close to the edge of the wide ocean reef flat without surface loose sediments on it or sand beach can be accepted. Excavating sand from some depths in lagoon is a scientific approach particularly important for urbanized atolls. However, selecting appropriate sites for mining sand other than at some depths in lagoon is suitable to rural islands without dense populations. These sites include up drift side of long groin on the reef flat,partly filled access channel-port, outlet of artificial channel and lagoon margin on the prograding coast. 相似文献
8.
An edge wave is a kind of surface gravity wave basically travelling along a shoaling beach. Based on the periodic assumption in the longshore direction, a second order ordinary differential equation is obtained for numerical simulation of the cross-shore surface elevation. Given parameters at the shoreline, a cross-shore elevation profile is obtained through integration with fourth-order Runge-Kutta technique. For a compound slope, a longshore wavenumber is obtained by following a geometrical approach and solving a transcendental equation with an asymptotic method. Numerical results on uniform and compound sloping beaches with different wave periods, slope angles, modes and turning point positions are presented. Some special scenarios, which cannot be predicted by analytical models are also discussed. 相似文献
9.
Tao Jianhua Tian Zhenfu
Professor Dept. of Mechanics Tianjin University Tianjin
Assistant Dept. of Mathematics Ningxia University Yinchuan Ningxia Hui Autonomous Region 《中国海洋工程》1991,(1)
Based on the singleline theory, a numerical simulation is presented to predict the shoreline evolution on sand beach. A parabolic equation of longshore sediment transport and boundary conditions are proposed. The combined effect of wave diffraction and refraction on the shoreline evolution on the downdrift side of the breakwater is taken into account and is calculated using the theory of regular waves and irregular waves. The present model is verified by the field observation data of erosion for half a year on the downdrift side of a harbor, and compared with some experimental results. The numerical results are in good agreement with the field measured and experimental data. 相似文献
10.
An investigation on the formation of submerged bar under surges in sandy coastal region 总被引：1，自引：0，他引：1
Cross-shore sediment transport rate exposed to waves is very important for coastal morphology,the design of marine structures such as seawalls,jetties,breakwaters etc,and the prevention of coastal erosion and accretion due to on-off shore sediment transportation.In the present study,the experiments on cross-shore sediment transport are carried out in a laboratory wave channel with initial beach slopes of 1/8,1/10 and 1/15.By using the regular waves with different deep-water wave steepnesses generated by a pedal-type wave generator,the geometrical characteristics of beach profiles under storm conditions and the parameters affecting on-off shore sediment transport are investigated for the beach materials with medium diameters of d50=0.25,0.32,0.45,0.62 and 0.80 mm.The offshore bar geometric characteristics are the horizontal distances from the shoreline to the bar beginning(Xb),crest(Xt),and ending(Xs) points,the depth from the bar crest to the still water level(ht),and the bar volume(Vbar).The experimental results have indicated that when the deep-water steepness(H0/L0) increased,the net movement to seaside increased.With the increasing wave steepness,the bars moved to widen herewith the vertical distances from still water level to the bar beginning(Xb),crest(Xt) and ending(Xs) points and the horizontal distances from the coast line to the bar beginning,crest and ending points increased.It was also shown from experimental results that the horizontal distances from the bar beginning and ending points to the coast line increased with the decrease of the beach slope.The experimental results obtained from this study are compared with previous experimental work and found to be of the same magnitude as the experimental measurements and followed the expected basic trend. 相似文献
11.
海南万宁岬湾海岸海滩稳定性研究 总被引：1，自引：0，他引：1
岬湾海岸海滩的稳定性及其演变是砂质海岸研究的重要内容。基于多期遥感影像、海滩沉积物粒度分布,并采用岬湾海滩平衡形态模型(MEPBAY),分析探讨了海南岛东部万宁4个典型岬湾海岸海滩的稳定性及其模型的应用。研究表明,除东澳湾凸角处于不稳定状态,其余海岸处于静态或准静态平衡状态;岬湾海滩沉积物粒度在遮蔽段和开敞段有明显的差异,相邻海滩之间没有明显的泥沙交换,每个岬湾海滩都是相对独立的地貌单元;模型中上岬角控制点选取应考虑岛礁及水下礁坪;抛物线模型可以拓展应用于有离岸岛情况下的海湾。研究成果可为岬湾海滩的稳定性评估和管理提供科学依据。 相似文献
12.
Charles W. Finkl Jr. Syed M. Khalil Jeffrey L. Andrews 《Marine Georesources & Geotechnology》2013,31(2):155-173
Erosion of sandy beaches is a worldwide problem that elicits innovative geoengineer‐ing techniques to reduce adverse impacts of shoreline retreat. Beach replenishment has emerged as the “soft”; shore‐stabilization technique of choice for mitigating beach erosion. This method of shore protection involves the addition of sand to the littoral sediment budget for sacrificial purposes. Because inland sand sources are often uneconomical or impractical to use, and known nearshore sources are limited, finding adequate quantities of suitable sand on the inner continental shelf is often vital to beach replenishment projects. The technical studies of survey and materials analysis that identify and delineate usable sand sources are sometimes almost as expensive as small‐project dredging, pumping, and placing the sand on the beach as fill. Inadequate quantity or substandard quality of shelf sand, as well as often‐prohibitive overhead expenses, thus compel shoreline managers to seek suitable sand sources offshore. In the study area off the central‐west coast of Florida, offshore potential borrow areas (PBAs) were identified on the basis of studies conducted in reconnoitory and detailed phases. Sophisticated state‐of‐the‐art equipment used in this investigation provided more detailed subbottom mapping information than is normally obtained with conventional seismic equipment. An example of sand exploration studies was incorporated in a 215‐km2 survey of offshore areas by conducting bathymetric surveys and subbottom seismic profiling, collecting jet probes, grab samples, and vibrocores, and analyzing sediment grading in subsamples from vibrocores. These combined analyses indicated that at least 8.8 ×106 m3 of sand is available in potential borrow areas from 7.0 to 12 km offshore in water depths of 8.0 to 11.5 m. In the PBAs, mean grain size of sand falls into the range 0.13–0.53 mm, sorting averages 0.65–1.31ø, and the overall silt content varies from 3.9–8.5%. High silt contents (13–19%) mapped in some areas make these sedimentary deposits unsuitable as fill for artificial beach renourishment. 相似文献
13.
我国硬式护岸、渔港工程和人工岛等3类典型海岸工程对相邻海滩有显著影响.本研究以泉州青山湾护岸、泉州崇武中心渔港、海口南海明珠人工岛等建设前后海滩变化为例,开展对海滩岸线形态及部分典型剖面形态的对比分析.结果表明,临海硬式护岸岸前海滩发生明显下蚀,护岸下游海滩岸线侵蚀后退,发育侵蚀热点,剖面伴有下蚀;渔港工程拦沙堤附近岸线局部淤涨,下游海滩岸线大范围侵蚀后退,出现侵蚀热点,侵蚀热点处剖面明显下蚀;人工岛后波影区内海滩淤积,形成沙岬或连岛沙坝突出体,突出体两侧岸线均发生不同程度侵蚀后退.通过分析典型工程案例,探讨了3类海岸工程对相邻海滩的影响方式、影响尺度和原因,对比分析不同类型海岸工程对相邻海滩的负面影响,可为海岸工程建设管理和海滩保护提供参考. 相似文献
14.
依据地质钻探和海滩观测资料，分析了后江湾海岸在海进作用下，海岸形成海进地层层序。滨面遭受侵蚀并正在后退和变陡。晚更新统陆相杂色粘土层和砾砂层直接暴露于海底。在海域供沙不足的情况下，整个海湾的海滩被侵蚀后退，而海滩各岸段侵蚀程度存在差异。 相似文献
15.
海滩是砂质海岸重要的沉积地貌单元,其沉积特征和稳定性对于海滩的开发利用与保护具有重要意义。本文根据海口湾西海岸海滩表层沉积物粒度数据,阐述了该区域海滩沉积物的时空分布规律,并通过对比滩面高程数据和水下地形数据分析了该区域的岸滩稳定性。结果表明：海口湾西海岸海滩处于滩面微蚀的轻度不稳定态,其岸外浅滩处于边坡侵蚀的轻度不稳定态。另外,根据波浪作用和泥沙来源进一步探讨了海口湾西海岸海滩沉积物动力机制及其海滩侵蚀的原因。 相似文献
16.
The empirical bay shape model proposed by Hsu and Evans in 1989 for predicting the static planform of a pocket beach is expanded to enable the calculation of three-dimensional beach changes on a pocket beach with a seawall. The original formulation was developed on the basis of a second-order regression analysis. Unlike the one-line model of shoreline changes, the model of Hsu and Evans does not require repeated calculations of the wave field and shoreline position, because it was derived on the assumption of null sediment movement within a pocket beach in static equilibrium, hence without the need of applying the continuity condition of total sand volume in the calculation. The expanded model proposed by the present authors satisfies the total sand budget on a pocket beach, by taking into account the concept of depth change due to longshore sand transport. Model tests were carried out and the new model was further applied to the beach changes at Kemigawa on the northeast of Tokyo Bay in Chiba Prefecture, as well as at Oarai in Ibaraki Prefecture, Japan. On both locations, seawall has been installed as countermeasures against beach erosion, where wave sheltering effect of the main breakwater and beach changes in front of the seawall has also been observed. With this expansion, the present model can be applied to predict the three-dimensional beach changes on a coast with seawall on a pocket beach. 相似文献
17.
Three models were applied to analyse the planform of bay-shaped Portuguese beaches. They are based on empirical mathematical functions: the logarithmic spiral bay equation, the hyperbolic-tangent bay equation, and the parabolic bay equation. These models were applied to analyse the fitting to the beach planform of 42 beaches on the Portuguese Atlantic coast which was calculated through the validation against the waterline extracted from rectified aerial photographs. The logarithmic spiral model fits well the curved zone of the beaches, in particular small beaches with two headlands. Despite the good fitting of the hyperbolic-tangent model for one headland beach, its process of approximation to the solution was less intuitive than the processes of the other two models, therefore its application was more exhaustive. A comparative analysis between the logarithmic spiral model and the hyperbolic-tangent model revealed the best fit of the first. The application of the parabolic model allowed to conclude that despite the majority of the beaches analysed being in dynamic equilibrium condition due to the high energy wave regime of the Portuguese Atlantic coast, their planform was very close to the planform in static equilibrium condition due to the high dynamics of the coastal environment. 相似文献
18.
Antonio H.F. Klein Óscar Ferreira Joao M.A. Dias Moyses G. Tessler Lucas F. Silveira Lindino Benedet Joao T. de Menezes Jose G.N. de Abreu 《Coastal Engineering》2010
This paper presents a comprehensive review on the interaction between hydrodynamic processes, beach morphology and sedimentology at large scale coastal behaviour along the coastline of Santa Catarina, between Laguna and São Francisco Island, a microtidal east coast swell environment with headland and bay geomorphologies. The parabolic bay shape equation has proven to be a convenient and practical tool for studying the stability of the headland-bay beaches, tombolos, and salients in Santa Catarina. The beaches exhibit different patterns of sediment removal as a function of the degree of beach curvature. In highly curved beaches, there is a well-developed shadow zone and a range of morphodynamic conditions, from a sheltered low-energy beach adjacent to the downdrift headland to a high-energy exposed beach on the straight end of the headland-bay beach. The less curved beaches instead, tend to show more uniform behaviour since they are directly exposed to incident waves. There is no obvious relationship between average wave height and mean grain size, showing the importance of sediment source to characterize the sedimentary distribution patterns in the study area. The analysis of beaches showed that beach morphodynamics and sequence profiles for a bay–headland coast in a microtidal east coast environment is a function of geological inheritance (e.g., distance between headlands and orientation, nearshore and inner shelf morphology, coastal plain morphology, and sediment source), and hydrodynamic factors (wave conditions, oceanic wave exposure and relative tidal range). 相似文献
19.
Headland-bay beach equilibrium planform has been a crucial problem abroad to long-term sandy beach evolution and stabilization,extensively applied to forecast long-term coastal erosion evolvement and the influences of coastal engineering as well as long-term coastal management and protection.However,little concern focuses on this in China.The parabolic relationship is the most widely used empirical relationship for determining the static equilibrium shape of headland-bay beaches.This paper utilizes the relation to predict and classify 31 headland-bay beaches and concludes that these bays cannot achieve the ultimate static equilibrium planform in South China.The empirical bay equation can morphologically estimate beach stabilization state,but it is just a referential predictable means and is difficult to evaluate headland-bay shoreline movements in years and decades.By using Digital Shoreline Analysis System suggested by USGS,the rates of shoreline recession and accretion of these different headland-bay beaches are quantitatively calculated from 1990 to 2000.The conclusions of this paper include that (a) most of these 31 bays maintain relatively stable and the rates of erosion and accretion are relatively large with the impact of man-made constructions on estuarine within these bays from 1990 to 2000;(b) two bays,Haimen Bay and Hailingshan Bay,originally in the quasi-static equilibrium planform determined by the parabolic bay shape equation,have been unstable by the influence of coastal engineering;and (c) these 31 bays have different recession and accretion characters occurring in some bays and some segments.On the one hand,some bays totally exhibit accretion,but some bays show erosion on the whole.Shanwei Bay,Houmen Bay,Pinghai Bay and Yazhou Bay have the similar planforms,characterized by less accretion on the sheltering segment and bigger accretion on the transitional and tangential segments.On the other hand,different segments of some bays have two dissimilar evolvement characters.Dacheng Bay,Shenquan Bay,Hudong Bay,Wukan Bay,Fengjia Bay,Wuchang Bay,Lingshui Bay and Tufu Bay produce accretion on the tangential segment,erosion on the transitional segment and accretion on the sheltering segment.However,Guang’ao Bay,Haimen Bay,Jinghai Bay,Sanya Bay(a),Dajiao Bay,Hailingshan Bay,Hebei Bay,Fuhu Bay,Shuidong Bay,Wangcun Bay and Bomao Bay generate erosion on the tangential part,accretion on the transitional part and accretion on the sheltering part.It seems to imply some relations between headland-bay beach evolvement and controls on headland-bay beaches,which may possibly to classify headland-bay beach types and should be further studied. 相似文献
20.
The paper concerns beach growth by trapping longshore drift to form a protective beach seaward of the principal “weather” breakwater at the Port of Timaru, east coast, South Island. This “spending beach” concept was aproached by evaluating downdrift extension and considerable progradation of an existing accumulation at South Beach which is a product of harbour development since 1879 and which was held in quasi-stability by ongoing extractions of the net surplus littoral drift of coarse sands and gravels (averaging 60,000 m3 yr−1).A one-line model was adapted from sand beach conditions and scaled to the morphology and processes of the mixed sand and gravel beaches at Timaru. Calibration of the model was performed from related research into the rates and temporal pattern of longshore drift on South Beach. A hundred year history of shoreline progradation against the harbour structures was utilised to verify the model.The concept offered a high benefit: cost ratio for a small engineering intervention provided shoreline forms and behaviour could be specified sufficiently for planning, statutory consent, engineering, economic and environmental impact assessment purposes. A 150 m long spur groin near the harbour entrance would trap about 12 ha of sand and gravel in about 8 years. The new shore would be better aligned to the dominant swell and storm waves than the present shore, so reducing long term net drift rates.Construction of the scheme commenced in May 1987 and progress to date is detailed. 相似文献