Determination and control of longshore sediment transport: A case study

The fishery harbor of Karaburun coastal village is located at the south west coast of the Black Sea. The significant waves coming from north eastern direction cause considerable rate of sediment transport along 4 km sandy beach towards the fishery harbor in the region. The resulting sediment deposition near and inside the harbor entrance prevents the boat traffic and cause a vital problem for the harbor operations. In order to determine the level and reasons of the sediment transport, the long-term observations of shoreline changes, the long-term statistical analysis of wind and wave characteristics in the region, and sediment properties have been performed. The data obtained from observations, measurements and analysis were discussed. The long-term statistics of deep water significant wave heights for each direction was discussed by comparing the results obtained from different data sources and methods. For shoreline evolution, the numerical study using one-line model was applied to describe the shoreline changes with respect to probable wave conditions. Initial shoreline was obtained from the digitized image in 1996 since there was no previous shoreline measurement of the site. The results were compared using the techniques of remote sensing obtained from sequent images using IKONOS and IRS1C/D satellites.     

A new formula for the total longshore sediment transport rate

A new predictive formula for the total longshore sediment transport (LST) rate was developed from principles of sediment transport physics assuming that breaking waves mobilize the sediment, which is subsequently moved by a mean current. Six high-quality data sets on hydrodynamics and sediment transport collected during both field and laboratory conditions were employed to evaluate the predictive capability of the new formula. The main parameter of the formula (a transport coefficient), which represents the efficiency of the waves in keeping sand grains in suspension, was expressed through a Dean number based on dimensional analysis. The new formula yields predictions that lie within a factor of 0.5 to 2 of the measured values for 62% of the data points, which is higher than other commonly employed formulas for the LST rate such as the CERC equation or the formulas developed by Inman–Bagnold and Kamphuis, respectively. The new formula is well suited for practical applications in coastal areas, as well as for numerical modeling of sediment transport and shoreline change in the nearshore.     

Modeling beach profile evolution at centennial to millennial scales

The proposed model allows the satisfactory reproduction of the changes in the profile geometry in each time step depending on the sediment budgets in a given morphodynamic system. The applied modification to the general Bruun rule governing the conservation of mass must account for the effect of the sediment transport, which is described in terms of the erosion and accretion rates (Er and and Ac, respectively). The scale of the erosion is a function of the total annual wave energy flux reaching the beach. The accretion is governed by the Er, on the one hand, and by the sediment budget in the morphodynamic system, on the other hand. The equilibrium profile obtained for the case of a balanced sediment budget (Er = Ac) shows good agreement with the observed profiles. A deficit or surplus in the sediment budget results in the shoreline??s retreat or advance accompanied by either a decrease or increase in the slope of the bottom profile. The model accounts for different types of shoreline responses to changes in the sea level (the Bruun rule, the development of a coastal barrier, and abrasion). Sediment budget imbalances can be a factor in the profile??s evolution due to changes in the sea level, while the combination of both factors will produce a variety of behaviors of the shoreline, as was shown by our calculations. The model was verified using historical data on the behavior of the Central Holland coast and the Abkhazian coast during the Late Holocene. It was shown that the model satisfactory reproduces the progradation of coastal barriers. An example of a relatively short-term forecast (over a 100-year period) is given.     

Sea-level, sediment supply and coastal changes: Examples from the coast of Ireland

Sediment supply and pre-existing shoreline morphology are crucial factors in controlling coastal changes due to sea-level rise. Using examples from both southeast and northeast Ireland, it can be shown that sea-level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium. Cliff erosion and longshore sediment movement in east Co. Wexford has led to injection of sediment onto the shelf, and the growth, under both wave and tide regimes, of linear offshore shoals. These shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea-level rise. In contrast, the nearby coast of south Co. Wexford comprises a series of coarse clastic barriers moving monotonously onshore, via overwash processes. Here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms. Finally, the rock platform coast of Co. Antrim presents a far more resistant shoreline to incident marine processes, yet even here there is strong evidence of present process control over so-called ‘raised’ platforms and embayments. It is concluded that coastal sediment supply and dynamics, together with coastal morphology and its interaction with waves, present a far more complex variety of sea-level indicators than is normally acknowledged.     

河口海岸泥沙输移的分组数学模型研究

根据河口海岸水沙输移的特点,建立了一个新的二维分组数学模型,用来预测该区域的水沙输移过程。该模型耦合了水动力模块、泥沙输移模块和床面演变模块。其中水动力模块基于浅水方程组,综合考虑了柯氏力、床面切应力以及表面风应力的影响,引入干湿判断法处理动边界。泥沙输移模块首先将泥沙按照粒径分组,针对不同泥砂性质,对各组泥沙分别进行建模求解。床面演变模块基于质量守恒方程,实时更新床面高程以及床沙级配变化,并传递给水动力模块,更新底部边界。该模型被应用在了英国塞汶(Severn)河口,其预测的泥沙浓度和实测数据以及不分组的模型的预测结果进行了比较,结果显示,文中建立的分组模型预测的结果要明显好于不分组模型。     

Predicting shoreline evolution on a centennial scale using the example of the vistula (Baltic) spit

The proposed algorithm comprises three main steps. The first step is the evaluation of the sediment transport and budget. It was shown that the root segment of the Vistula Spit is dominated by eastward longshore sediment transport (up to 50 thousand m³/year). Over the rest of the spit, the shoreline??s orientation causes westward sediment transport (more than 100 thousand m³/year). The gradients of the longshore and cross shore sediment transport become the major contributors to the overall sediment balance. The only exception is the northeastern tip of the spit due to the appreciable imbalance of the sediment budget (13 m³m^?1 yr^?1). The second step in the prediction modeling is the estimation of the potential sea-level changes during the 21st century. The third step involves modeling of the shoreline??s behavior using the SPELT model [6, 7, 8]. In the most likely scenario, the rate of the recession is predicted to be about 0.3 m/year in 2010?C2050 and will increase to 0.4 m/year in 2050?C2100. The sand deficit, other than the sea-level rise, will be a key factor in the control of the shoreline??s evolution at the northeastern tip of the spit, and the amount of recession will range from 160 to 200 m in 2010?C2100.     

Numerical Simulation of Sand Shoreline Evolution Under Action of Regular Waves and Irregular Waves

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.     

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.     

Sediment characteristics and water circulation of Big Jemsa Bay,Red Sea,Egypt

Big Jemsa Bay is one of the indentations dissecting the continuity of the Red Sea north-western shoreline. The data was collected from bathymetric survey, current meters and sediment samples. Analyses have been undertaken of coastal processes, seabed morphology, grain size characteristics and the effect of current circulation on the distribution of sediment characteristics. The sediment pattern varies from coarse sand in the southern part to silt and fine sand in the northern part. The central part of the study area is mainly composed of terrigenous isometric-medium sand facies. The sorting distribution of sediments varies from moderately well sorted to poorly sort. The significant factors that control the sediment transport process are downslope gravity and wave-induced currents that are affected by the seafloor configuration and the shoreline orientation. According to the circulation effect on the sediment transport of the study area where deposition of fine sand and silt was observed in the northern part. Because sediment transport mitigates the occurrence of pollutant deposition in this part of the bay, we recommend that future constructions along the bay should be in the southern part.     

Shoreline changes and beach-sand sorting along the northern Sinai coast of Egypt

 Changing shoreline positions along the Sinai coast of Egypt were determined by comparing aerial photographs and historical charts with present-day conditions. The analyses identify longshore patterns wherein erosion along a protruding stretch of the coast gives way to accretion in an adjacent major embayment. This pattern defines two coastal subcells consisting of source/sink couplets. There is a general correspondence between the mineral variation, grain sizes of beach sand, and the patterns of shoreline changes. Associated with erosion/ accretion shoreline change is a selective transport of different minerals according to their densities and grain sizes. Two heavy-mineral groups were obtained by applying Q-mode factor analysis on the heavy-mineral data. These two groups are influenced by transport processes, including sediment provenance from different sources: eroded Nile delta west of Sinai, relict sediments from the former Nile distributaries, and sediment supply by land valleys and from wind-blown sand. Received: 2 June 1995 / Revision received: 29 May 1996     

基于数字化海岸分析系统(DSAS)的海岸线变迁速率研究:以黄河三角洲和莱州湾海岸线为例

海岸线变化对海岸带生态环境改变、滨海土地侵蚀有着极其重要的影响,海岸线的提取和监测对海岸带生态系统的保护和管理具有重要意义。本研究基于数字化海岸线分析系统(DSAS,Digital Shoreline Analysis System),研究了黄河三角洲和莱州湾的海岸线时空变化规律。研究结果表明:通过提取1985-2015年6期的Landsat影像,发现近30年来黄河三角洲和莱州湾地区海岸线均呈现显著的向海方向扩张的趋势,且增长速率逐渐加快。黄河三角洲的终点变化速率(EPR,End Point Rate)约为73.0 m/a、线性回归速率(LRR,Linear Regression Rate)约为75.5 m/a,黄河港-大咀沟增长速度最快(129.2 m/a),受黄河泥沙输送的影响,黄河口和老黄河口岸线的几何形态呈现平滑的变化趋势;莱州湾岸线的EPR和LRR约为139.5 m/a和144.3 m/a,淄脉河河口-白浪河河口段增长速度最快(197.6 m/a),岸线变化较为显著的区域主要集中在港口、圈海堤坝、海水养殖等的地方。DSAS模型在海岸线定量化分析中具有显著优势,利用EPR和LRR指标能够科学有效地模拟岸线在时间和空间上的变化速率。     

厦门湾海域表层沉积物分布特征及其动力响应

沉积物分布对河口海岸地区的地貌演变和岸线变化非常重要。本文收集了2008年9月厦门湾海域的230个表层沉积物样品的数据,研究其表层沉积物空间分布和运输特征。厦门湾海域表沉积物的粒度分布特征非常明显。同时在应用GSTA模型对沉积物进行输运趋势分析的基础上探讨该区域泥沙运移趋势。结果表明,该海域有八种沉积物类型,粘土质粉砂占有比例最高,为65.22%;而且在不同的分区,由于不同的沉积物源和水动力条件,粒度参数特征也有所不同。径流、潮汐和波浪是海床表层沉积物、滩涂变化的主要控制动力,泥沙运动趋势与水动力条件密切相关。     

Prediction of shoreline behaviour for Madras, India-a numerical approach

A satellite port has been proposed about 14.8 km north of Madras port on the east coast of India. As the interference of a satellite port with the existing pattern of longshore sediment transport will generate coastal imbalance in the region, a numerical model study involving sediment transport and combined wave refraction-diffraction was conducted to predict the shoreline behaviour. A realistic approach to the study was made to meet the objectives by considering wave height-wave period distributions in the region and duration and sequence of their occurrence during major monsoon seasons. This method of analysis enabled us to predict: (i) the extent of general shoreline advancement, particularly in front of a tidal inlet—a source of the cooling water requirement for an existing thermal power plant; (ii) the extent of the coastal region that will be affected owing to recession of shoreline and its impact on: (a) the fishing community living along the coastal stretch; (b) the national highway running along the coast; and (c) the changes in nearshore bathymetry. Based on the studies, management plans were drawn to safeguard the coastal region from imbalances that will arise out of construction of the satellite port. This paper highlights the effects of a satellite port on the coastal region and the need for proper management.     

Numerical modeling of crenulate bay shapes

A numerical model is developed to compute the shoreline planform in a crenulate bay beach. The new model combines polar and Cartesian coordinates and can be used effectively to compute a hooked zone shoreline in the lee of upcoast headland. The model is calibrated using laboratory data with an incident wave angle ranging from 25° to 60°. The results of calibration and verification suggest that the ratio of the sediment transport parameters by wave and longshore current in this model is close to unity, and the computed shoreline planforms for the hooked and unhooked zones are in good agreement with the ones measured, especially when a bay is close to static equilibrium. In addition, the bay shape calculated by the present model is similar to that given by the well-known empirical parabolic equation for a bay in static equilibrium. The process of bay shape development from a straight beach to a static equilibrium bay is studied using laboratory experiments and the present numerical model. The temporal variations in the computed longshore sediment transport at different locations within a bay beach are analyzed. From this the decrease in the sediment transport becomes apparent while a bay beach changes its shape from straight toward a state of equilibrium. Based on this experience, it may be concluded that the present numerical model can produce a temporal change in the shoreline planform of a crenulate bay beach from a transition state to static equilibrium subject to seasonal wave action.     

Using mangroves as a geological indicator of coastal changes in the Bragança macrotidal flat,Brazilian Amazon: A remote sensing data approach

A mangrove ecosystem shows close links between geomorphology and vegetation assemblage. In addition, the vegetation can change over time as landforms can accrete or erode, which is a direct response to coastal sedimentary processes. This demonstrates that significant changes can occur on short time scales and mangroves provide an excellent register of these modifications. Therefore, mangrove morphology and sedimentation are good indicators of interactions between relative sea level changes, coastal processes and sediment supply. These interactions are responsible for landward migration of the shoreline (erosion) and seaward migration of the shoreline (accretion), which is possible to detect from multi-date satellite data and field observations. Mangroves are one of the best geo-indicators in global coastal change research and they are an excellent procedure to detect and quantify coastal modifications.     

珊瑚礁海岸侵蚀的研究方法

珊瑚礁海岸海滩和礁坪是海岸作用是活跃的部分，也是近几十年来与海岸发育，海岸侵蚀联系最密切的部分，这一部分高潮时被淹没，低潮时完全出露或大部分出露，使得在此进行地质填图成为可能，这样的地质图可以提供许多信息，如沉积物粒度分布规律，沉积物来源和搬运方向，海滩岩所指示的古海岸线位置，人类活动特别是海岸工程对沉积物分布的影响以及海岸线的变化过程和趋势，在礁坪上开挖的人工水道内测流，能够了解水流的性质以及是否有足够的速度搬运沉积物，从而了解人工水道对海岸的影响和预测海岸的状态，这些方法也可以用于大陆泥质和砂质第岸侵蚀的研究。     

Simulation of the Fate of Faecal Bacteria in Estuarine and Coastal Waters Based on A Fractionated Sediment Transport Model

A two-dimensional depth-integrated numerical model is refined in this paper to simulate the hydrodynamics, graded sediment transport process and the fate of faecal bacteria in estuarine and coastal waters. The sediment mixture is divided into several fractions according to the grain size. A bed evolution model is adopted to simulate the processes of the bed elevation change and sediment grain size sorting. The faecal bacteria transport equation includes enhanced source and sink terms to represent bacterial kinetic transformation and disappearance or reappearance due to sediment deposition or re-suspension. A novel partition ratio and dynamic decay rates of faecal bacteria are adopted in the numerical model. The model has been applied to the turbid water environment in the Bristol Channel and Severn estuary, UK. The predictions by the present model are compared with field data and those by non-fractionated model.     

Longshore sediment transport via littoral drift rose

The littoral drift rose (LDR) concept is presented herein for improvement in understanding of longshore sediment transport and consequent shoreline processes in areas with smooth (gradually varying) offshore bathymetry extending over a coastal region where the deep water wave climate is reasonably uniform. The concept of the littoral drift rose (LDR) is presented and LDRs are shown to provide insight into coastal evolution and shoreline stability (or instability) for a given region having uniform wave climate. This paper reviews earlier documented applications and work using LDRs and provides an interpretation of earlier findings of shoreline stability using LDRs. Previously known but undocumented findings are also discussed herein which show that the wave climate and hence the LDR can be synthesized into an equivalent LDR developed from one wave component of given magnitude and direction. Practical applications using LDRs are presented, which show that the magnitude and direction of littoral drift throughout a region can be interpreted from limited measured, calculated, or observed data on littoral drift at two locations in the region.