Budget of sediments and forecast of long-term coastal changes

A method for predicting the coast evolution based on the calculated estimates of the components of the sediment budget is discussed. The approaches outlined in a series of previous publications of the author [9, 10, 11] are further developed. The prerequisites and concepts used as the basis of the suggested method for forecasting are characterized. The sediment budget parameters under typical conditions are presented. The contributions of natural processes and the anthropogenic impact are compared. Different approaches for calculating the principal sediment budget components, including the cross-shore flux through the lower boundary of the coastal zone, the eolian flux of sand material through the upper limit of the coastal zone, and the alongshore sediment flux gradients, are considered. The examples of forecasting the development of coasts in the Baltic and Kara seas and the Sea of Okhotsk are given for the period from 100 to 500 years. The results obtained show that, in the case of a balanced budget of the sediments, the future behavior of the coast would be mainly governed by the variations in the sea level. This factor is capable of determining the changes in the coastline, whose recession and advancing would depend on the rate of the sea level rise. Under specific conditions, an enhanced sea level rise can trigger destructive processes (for example, the erosion of a coastal bar or the thermal abrasion of a cliff). In the case of a strong imbalance in the sediment budget, sea-level changes play a subordinate role.     

布容法则及其在中国海岸上的应用

布容（Ｂｒｕｕｎ）法则是预测海平面上升引起海岸侵蚀最早的方法也是最简单的方法。根据中国砂质和淤泥质海岸的情况,布容法则可定性地解释海平面上升与海岸侵蚀的关系,在满足它要求条件的海岸地段和发育时期,用它预测海岸侵蚀或许是可能的。但是,若不严格审查海岸环境和条件,把它作为海平面上升情况预测海岸侵蚀的普遍模式,有待更多的研究加以证明。     

Wave driven alongshore sediment transport and stability of the Dutch coastline

The wave-driven alongshore sediment transport is commonly supposed to smooth out the irregularities on the coastline. However, it has been shown that waves approaching the coast with a high angle with respect the shore-normal can reverse that tendency and cause the rectilinear coast to be unstable [Ashton, A., Murray, A.B., Arnault, O., 2001. Formation of coastline features by large-scale instabilities induced by high-angle waves. Nature 414, 296–300; Falqués, A., Calvete, D., 2005. Large scale dynamics of sandy coastlines. Diffusivity and instability. J. Geophys. Res. 110, doi:10.1029/2004JC002587]. The extended one-line coastline model presented in the latter paper is here applied to investigate the stability of the Dutch coast. The main aim is testing the hypothesis that the shoreline sand waves observed along this coast could be generated by such an instability. It is found that the Dutch coast has potential for instability. This is most prominent on the Holland coast, followed by the Delta coast and is very weak on the Wadden coast. Whether the instability actually occurs or not depends on the cross-shore bathymetric profile of the shoreline waves. Under the sensible assumption that the bathymetric perturbation is just a shift of the equilibrium beach profile, the Dutch coast is stable. In this case, the mean annual coastline diffusivity is evaluated and it is found to be typically about 0.010–0.015 m² s^− 1, that is, roughly smaller by a factor 2 than that predicted by the traditional one-line model. However, the Dutch coast may be unstable with respect to coastline waves with a maximum bathymetric signal at a few hundred meters from the coast. This is shown in one case where the shoals associated with the sand wave are inside the surf zone during moderate storm waves. Thus the sand waves could result from the cross-shore redistribution of the sand associated with an alongshore series of shoals and bed depressions generated by the alongshore transport in the surf zone. While the generation or not of such shoreline waves by this instability strongly depends on their profile, its propagation once they have been created is less sensitive and is well reproduced by the present model. It is explained why the propagation is to the NE along the Delta and Wadden coasts, why it is faster on the latter and why on the Holland coast there is no clear propagation direction.     

Modeling erosion of sedimentary coasts in the western Russian Arctic

Morphodynamic modeling is employed in the present work to predict the long-term evolution (over the next 100 years) of typical sedimentary coasts in the western Russian Arctic. The studied objects are the coasts of Varandey (the Barents Sea), Baydaratskaya Bay and Harasavey (the Kara Sea). The model developed takes into account both the short-term processes (storm events) and long-term factors (for example, changes in sea level, inter-annual variations in gross sediment flux, lack or excess of sediment supply). Predicted and observed morphological changes in coastal profiles are shown to agree well for time scales ranging from weeks to decades. It is revealed that under given environmental conditions, the morphological evolution is strongly influenced by storm surges and associated wind-driven circulation. The water level gradient created by a surge generates a seaward flow at the bed. This outflow is shown to be an important destructive mechanism contributing to the erosion and recession of Arctic coasts. The rate of change is found to depend on both the exposure of the coast (relative to the direction of dominant winds) and its height above the sea. The open coast of Varandey is expected to retreat as much as 300–500 m over 100 years, while recession of the less exposed coasts of Baydaratskaya Bay would not exceed about 100 m/century. If long-term sediment losses are insignificant, the rate of erosion decays with time and the morphodynamic system may tend toward equilibrium. It is concluded that the expected relative sea-level rise (up to 1 m over the nearest 100 years) is non-crucial to the future coastal evolution if an erosion activity is already high enough.     

6000年来我国低平海岸线的冲淤变化及其对海岸带开发的影响

自约 6ka前我国海岸轮廓形成以来 ,海岸线主要呈淤进状态。在距今 6～ 3ka前 ,因黄河等河流泥沙主要填淤平原洼地 ,岸线稳定微涨 ;在距今约 3ka至 2 0世纪 60年代 ,河流以巨量泥沙使海岸线 ,尤其是低平的平原海岸线迅速外移 ;最近 30 a来 ,因为黄河等河流入海水沙大量减少 ,造成目前除行水河口处淤涨外 ,多数岸段转为侵蚀或稳定 ,且被侵蚀岸线有逐渐扩大的趋势。这种变化导致了新淤土地的减少 ,也破坏了原有的沙滩、湿地资源 ,需要采取一些措施以减少海岸侵蚀带来的损失     

冰后期最大海侵以来长江,钱塘江河口湾发育过程的沉积动力学研究

利用二进流数学模型对冰后期最大海侵以来５期古岸线与现在岸线条件下古长江河口湾、古钱塘江河口湾及其邻近海域的主要水动力Ｍ２潮流场进行了数值模拟;在此基础上,分别计算了进入不同时期潮流场的７种粒径泥沙的潮平均单宽悬移输沙率与扒移输沙率及其相应的输沙率散度,据此得出不同粒径泥沙在当时潮流场中的悬移与推移输过趋势,划分了海 淤积区与冲刷区 同时期的潮流场作用下,长江入海泥沙除最大限度地沉积在古长江河口湾（     

闽粤交界的大埕湾岸滩稳定分析及岸滩防护对策

本文在实地调查的基础上，通过对大埕湾沿岸输沙率变化和岸线形态的分析，综合探讨了该海湾的泥沙来源，沿岸泥沙迁移特征，岸滩冲淤动态以及海岸的演变趋势．结果表明：该湾沿岸带形成了一股朝W向迁移的波生泥沙流，泥沙主要来自诏安湾和宫口湾；该湾海岸除东部沙坝泻湖岸段略有淤伸外，其余岸段均处于侵蚀状态：随着泥沙来源的减少，海岸内凹蚀退是今后岸线调整的自然过程．文中还对大埕湾岸滩的防侵蚀提出了相应的对策建议。     

Recent changes of Shandong sandy coast and in fluence of human activities

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An application of a Markov-chain model of shore erosion for describing the dynamics of sediment flux

Acquisition of coastline retreat rate time sequences (RRTS) is an important component of Arctic coastal monitoring. These data can be used not only to estimate sediment input into the sea during a fixed time period, but also to dynamically simulate sediment flux intensity. The RRTS were investigated at the Marre-Sale (Kara Sea) and Malii Chukochii Cape (East Siberian Sea) key sites. Statistical analysis demonstrated that the RRTS possess Markov characteristic. This allowed coastline dynamics to be described using a Markov-chain model. A model is discussed that combines Markov characteristic and information about the composition and structure of the permafrost sediments to describe sediment flux dynamics.     

水动力在江苏北部岸外辐射沙洲形成和演变中的作用

江苏北部(下称苏北)岸外辐射沙洲形态特殊,面积广大,是我国唯一、世界罕见的沉积动力地貌特征类型区。开展该区的调査和研究对苏北海岸带开发和海洋沉积动力学理论研究都具有非常重要的意义。近年来我国学者通过大量海洋水文、泥沙、海底地形和地貌调查研究,对苏北海岸的成因和岸外沙洲的演变提出了许多新的看法(王文清等,1982)。本文通过对历史资料和1958-1993年苏北海岸带调査资料、卫星照片等的对比分析,以及利用数值模拟方法的诊断,指出水动力是苏北海岸和岸外沙洲形成和演变的主要作用力。     

Estimation of Longshore Sediment Transport Rate for a Typical Pocket Beach Along West Coast of India

Estimation of Longshore Sediment Transport Rate (LSTR) in the littoral zone is essential for managing and developing any coastal zone. Numerical models are powerful tool to understand and investigate various processes responsible for LSTR in a systematic manner since direct measurement of LSTR is a difficult task. A one dimensional LITDRIFT model was implemented along the Vengurla coast for estimation of LSTR and to analyze the sensitivity of each input parameters towards the computation of LSTR. Major input parameters required for the estimation of LSTR are nearshore wave climate, bathymetry, and sediment characteristics. The nearshore wave data at a depth of 15 m were collected using wave rider buoy in 2015 is used in the present study. Field observations were carried out to survey the regional bathymetry and sediment characteristics. Annual net LSTR along Vengurala coast is relatively less and varies from ?7778 to ?9015 m³ with an average of ?8511 m³. The net direction of LSTR is towards south and gross LSTR is 1.18 × 10⁵ m³/year. The LSTR reveals more sensitivity to coastline orientation and wave direction. A 1° changes in coastline angle and wave direction causes approximately 3000 m³/month difference in LSTR. Moreover, wave height, wave period, and bed roughness has an important role for controlling LSTR. The model results help to identify the role of each parameter contributing towards LSTR estimation and a similar model approach can be applied to other coasts for estimating LSTR in an accurate way.     

Shape Classification of AltiKa 40-Hz Waveforms using Linear Discriminant Analysis and Bayes Decision Rule in the Gujarat Coastal Region

Shape classification of the 40-Hz waveforms obtained by the recently launched AltiKa satellite has been attempted in the paper. Since retracking algorithms suitable for altimeter return echoes based on Brown model are not applicable for the echoes from coastal ocean, specific algorithms are to be devised for such echoes. In the coastal ocean, waveforms display a wide variety of shapes due to varying coastline geometry, and topography. Hence, a proper classification strategy is required for classifying the waveforms into various categories so that suitable retracker could be applied to each category for retrieving the oceanic parameters. The algorithm consists of three steps: feature selection, linear discriminant analysis, and Bayesian classifier. The classification algorithm has been applied to the waveforms in the close proximity of Gujarat coast. Independent validation has been done near the eastern coast of India. Confusion matrices obtained for both the coasts are quite encouraging. Individual examples of classification have been provided for the purpose of illustration.     

Sediment distribution and transport along a rocky, embayed coast: Monterey Peninsula and Carmel Bay, California

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.     

海南岛南渡江三角洲海岸演变的波浪作用分析

本文应用白沙门1984年波浪统计资料,通过对南渡江三角洲北部近岸海底泥沙活动特性与东部废弃海岸泥沙沿岸输移方式及其岸外沙坝、堡岛响应波浪动力而具有的形状进行分析,揭示了波浪在南渡江三角洲北部沿岸演变中的重要作用。     

渤海湾连片开发对湾内水沙通量的影响研究

渤海湾内海岸的连续开发导致岸线 、海床发生较大变化, 同时影响着湾内的水沙通量。根据不同时期的遥感影像、 实测地形和水文泥沙资料, 统计分析了渤海湾岸线 、面积和海床冲淤变化, 构建了渤海潮流泥沙数学模型, 模拟了 1984 年、 2006 年和 2015 年三个时期的水沙分布, 探究了海岸连续开发对水沙分布和通量引起的累积效应。结果表明： 渤海湾岸线和 海湾面积变化主要发生于 2005 年后, 与 1984 年相比, 2020 年的岸线长度增长超过 185%,海湾面积减少近 19%;曹妃甸港 区南侧海域冲刷基本在 2 m 等深线以内, 而近岸和港池水域基本呈现淤积状态, 淤积幅度在 2 m 以内; 海湾的连续开发利用 使得湾内分潮波振幅增大 、传播速度减缓, 近岸海域的余流变化较为明显,南部较北部海域更甚;西北湾顶 0.2 kg/m3 悬沙 分布区域不断缩小, 西南近岸 0. 15 kg/m3 悬沙分布区域向中部海域推进; 悬沙通量变化与潮流通量并不完全一致, 呈外海增 加、近岸整体降低的变化特征, 湾内向外海输移泥沙的能力减弱。     

Integrated Assessment of Shoreline Change along the Calypsostranda (Svalbard) from Remote Sensing,Field Survey and GIS

Abstract

Arctic coasts are sensitive indicators of polar environment change. Here we present the results of a study that examines the coastal morphodynamics of the Calypsostranda coastline in Svalbard (High Arctic) between 2007 to 2017 and compare these short-term changes to previous studies for the period 1936–2007. During the 2007–2017 study period, the study area lost ca. 10,710 m², at a mean Net Shoreline Movement (NSM) of ?1.86 m and End Point Rate (EPR) ?0.19 m/yr. Erosion also dominated between 1936–2007, ?28,800 m², at a mean NSM of ?4.99 m and EPR ?0.07 m/yr. Using EPR and Linear Regression Rate (LRR) parameters, we divide the Calypsostranda coastline into eroding and aggrading zones. The overall pattern of coastline change during the two study periods is similar, but the rate of erosion is higher in the recent interval, reflecting stronger climate-driven processes. Recent climate warming in the study area has been accompanied by an intensification of extreme events such as storms (e.g. ocean swell). The situation is becoming more pronounced due to the progressively reduced period of winter shore ice. Depending on the anemometric conditions, the Calypsostranda coast is modified by wind waves, and consequently longshore currents and associated sediment movement.     

Short-term shoreline changes due to cross-shore structures: a one-line numerical model

The proposed numerical model simulates the short-term temporal changes in shoreline position due to a structure interrupting the longshore sediment flux. The impacts of both the groin-type construction and underwater trench of arbitrary orientation relative to the shore are discussed. In order to estimate the sediment mass trapped by the structure, a submodel of the longshore sediment transport induced by a random wave field is developed. The contribution of the surface roller in momentum balance as well as in sediment suspension is included. The shoreline changes are computed from the equation deduced from the mass conservation. The perturbations in the longshore sediment discharge caused by a structure are assumed to concentrate within some boundary area of which the spatial scale is proportional to the structure's length until the latter is exceeded by the width of the sediment flux. It is shown in particular that the total effect of a long trench (channel) and a pier in its nearshore part results in general shoreline recession except for the vicinity of a pier. The model is tested against the laboratory data of Baidei et al. (1994) and applied to the Baidara Bay coast (Kara Sea) where a pipeline would be designed.     

Holocene sea level changes and coastline snitts in Zhejiang Province, China

In the present paper, the Holocene sea level changes and coastline shifts in Zhejiang, China are discussed, based on the ancient coastline evidence related with sea level changes and 21 14C dat-ings of shell, peat or mud and wood samples along the Zhejiang coast. The development of Zhejiang coastline during the Holocene period can be divided into four stages. A lot of data of historical period and modern times have shown that tracing coastline shifts back to its source, we have to consider tremendous effects of man's activities besides natural factors, such as elevation and subsidence of the earth crust, sea level changes, supply of sediment, and littoral hydrodynamics.     

基于规则的多种类型海岸线TM/ETM+影像智能检测方法

A coastline is defined as the average spring tide line. Different types of seacoast, such as sandy, silty, and bio- logical coast, have different indicators of interpretation. It is very difficult to develop a universal method for interpreting all shorelines. Therefore, the sandy, the silty, and the biological coast are regarded as research objects, and with data mining technolog,found the rules of interpretation of those three types of coastlines. Then, an intelligent coastline interpretation method based on rules was proposed. Firstly, the rules for ex- tracting the waterline in Landsat TM/ETM＋ （Thematic Mapper/Enhanced Thematic Mapper Plus） imagery were discovered. Then, through analyzing the features of sandy, silty and biological coast, the indicators of interpreting different types of shoreline were determined. According to the indicators, the waterline could be corrected to the real coastline. In order to verify the validity of the proposed algorithms, three Landsat TM/ETM＋ imageries were selected for case studies. The experimental results showed that the proposed methods could interpret the coastlines of sandy; silty, and biological coasts with high precision and without human intervention, which exceeded three pixels.