近岸过程与海岸侵蚀机制研究进展

首先简单介绍了砂质海岸近岸地形动力过程的时空多尺度特征及其复杂性,海岸系统相互依存的3个方面和近岸带地形动力基本特征;进而从5个方面论述了国内外对砂质海岸侵蚀地形动力过程与机制研究的进展:1)长重力波运动与海岸侵蚀;2)近岸环流、波增水、底流运动与岸滩侵蚀;3)海滩-碎波带地形动力状态与岸滩侵蚀方式;4)波生沿岸流、沿岸输沙与海岸长期变化;5)海岸侵蚀终极平衡形态规律。最后概括了未来需优先探索的地形动力学问题和研究策略。     

常波况下前滨剖面地形动力过程分析

利用在粤东后江湾多日逐时连续观测的近岸波浪、流、海滩潜水位和海滩前滨剖面地形数据,通过典型相关分析方法提取了占总方差90%以上的4个显著的典型相关变量,进而分别论述了常波况下海滩前滨剖面不同部位的地形动力过程。     

华南水东湾波控、中等潮差岬湾海滩地形动力分类

海滩地形动力分类在国外的海岸地貌研究中已经被广泛接受。本文使用了华南粤西水东湾切线带、过渡带和遮蔽带海滩连续16个月32次大潮期间同步获取的波浪、潮汐、泥沙和海滩地形数据,分别按照无量纲沉降参数、相对潮差参数和无量纲海湾尺度参数对这一岬湾海滩不同岸段的海滩类型进行了研究,研究发现：（1）水东湾切线带海滩的主要状态为有裂流的低潮台地状态和沙坝型海滩状态,过渡带海滩主要状态是低潮沙坝/裂流海滩和沙坝消散型状态,遮蔽带海滩主要状态是有或无沙坝的消散型状态;（2）海湾不同岸段海滩状态的顺序变化与差异体现了岬湾海滩状态的时空变化性,与现场观测的海滩地形的变化基本一致,说明了对波控中到强潮海滩进行研究时,需要考虑潮汐的影响。同时,本文主要给出了海滩状态研究的一个框架体系,由于海滩不同的状态伴随不同的侵蚀模式,要求我国今后需加强在这一方面研究,以进一步丰富我国海滩地形演变、海滩地形动力过程和海滩防侵蚀的理论基础。     

基于自组织机制理论的滩角地形数值模拟

一般认为滩角是近岸带泥沙、水动力和地形耦合作用的产物,对近岸带特别是碎波带和冲流带的动力变化响应迅速,还可以反映海滩状态,但具体的成因一直得不到很好的解释.首先详细介绍了关于滩角成因的争论以及自组织机制理论,其中驻立边缘波假说和自组织机制假说是最为认同的两种滩角成因假说.基于WERNER(1993)提出的滩角形成的自组织机制假说,建立包含冲流动力、泥沙输运和地形演变的滩角形成和发育的元胞自动机模型.模型中修正了以前研究中的坡度参数表达式和水动力输入方式.经过200个冲流循环的数值模拟,原来平直的滩面上形成了明显的滩角形态,滩角间距约为5.5～6.0 m,520个循环周期后,滩角形态基本上达到稳定状态.对模拟过程进行分析,结果表明:(1)模拟得到的滩角形态比先前的研究结果更接近天然状态下的滩角;(2)随机的水质点冲流运动使海滩地形呈无规律变化,但通过动力、泥沙、地形之间的反馈过程逐渐形成了滩角地形;(3)滩角形成过程中,海滩基本上处于堆积过程中.开始堆积速度较快,当滩角形态达到准平衡状态时(大约300个循环后),海滩体积增速变慢,并逐渐地达到稳定状态,海滩体积变化呈现小的波动调整;(4)模拟得到的有效冲流距离(S)和滩角间距(λ),满足滩角自组织机制假说的基本关系.因此,可以认为滩角是在海滩泥沙、地形与波、流的自组织过程中形成的,是一种堆积地形.自组织理论为从不同的侧面认识和研究海岸带现象与过程提供一扇窗口,是一个值得研究的方向.     

华南海岸岬间海滩地形动力状态类型研究

海滩地形动力状态分类对于理解近岸带动形动力过程、海滩浴场风险评估等方面有重要的意义。收集了华南51个岬间海滩波高、波周期、潮差和泥沙粒径等地形动力要素特征值,利用分层聚类分析方法,同时结合海滩相对潮差分类模型,对华南岬间海滩的类型进行了探讨,结果表明:(1)华南岬间海滩可以聚类成7个类型。通过与相关的现场观测比较,各类型在地形组合上具有各自的显著特征;(2)聚类分析结果能很好的区分中到大潮差海岸与小潮差海滩之间的差异,与相对潮差模型结果一致。对于小潮差海滩,聚类结果与相对潮差模型有一定的差异,表明华南小潮差海滩的分类还需要进一步深入研究。     

海滩冲流带高频振动及碎波带波浪作用的模态分析

一般来说,研究者对海滩中长尺度变化的研究比较多,通过时间间隔为数小时、1d,1周、1个月甚至1a一次的重复测量来分析海滩的变化特征,但海滩冲流带是动力和地形发生高频率变化的一个区域,每次波浪引起的上冲和回流过程均要引起滩面泥沙的运动,造成滩面的局部堆积和侵蚀,而滩面地形的改变又反过来影响到下一次的冲流过程。这些现象对研究海滩碎波带动力和滩面地形相互作用机理、认识近岸泥沙的运动规律以及探讨岸滩的长期冲淤演变是十分有意义的。     

不同受损情况下珊瑚礁海岸动力地貌差异性分析

探索珊瑚礁与海滩地貌之间动力地貌联系是认识珊瑚礁海岸变化的重要一环.本文以雷州半岛徐闻西落港珊瑚礁海岸为研究对象,应用RTK-GPS和无人船开展岸滩剖面和近岸水下地形的测量、结合海滩沉积物分析,基于FUNWAVE-TVD数值模型模拟并分析不同珊瑚礁地形地貌条件下波浪动力传播过程.结果显示,研究区珊瑚礁水下地形是影响礁后...     

珠江口外伶仃岛海滩修复研究

海滩养护是当前全球广泛流行的具有生态环境保护意义的软式海岸工程手段。文章以广东珠海外伶仃岛小石嘴沙滩为例,首次选取珠江口海岛沙滩,开展近岸动力、近岸地形、海岸动力地貌、沉积特征等多方面的研究,最终通过补沙方法修复了一个适应于该研究区近岸动力条件的人工海滩,不仅极大地增强了海滩抗蚀能力,而且较好地改良了海岸景观。     

海口湾中间岸段海滩剖面短期时空变化及沉积动态分析 *

海滩的演变特征是海岸地形动力学研究的一个重要内容。基于在海口湾假日海滩连续33d的地形剖面观测数据和台风前后表层沉积物粒度参数数据, 分析了海口湾中间岸段海滩剖面及沉积物变化特征。利用经验正交函数分析, 得出观测期间海口湾海滩有4个主要模态, 分别对应于涌浪对海滩的建设过程、当地风浪对海滩的侵蚀过程、台风对海滩的侵蚀过程和海滩特征地形的调整过程。研究结果表明: 涌浪和风浪对海滩剖面的作用受到了潮位调制的影响; 海口湾海滩显示出遮蔽型海滩变化特征; 沉积物粒度参数对海滩变化反应敏感, 可以提供丰富的海滩演变信息。     

砂质海岸演变的地貌动力学研究进展

７０年代以来,海岸演变的地貌动力学研究成果引人注目。本文着重论述了在砂质海岸演变研究中,海滩状态,海滩地下水动力,砂坝动力学,海岸沙岸,近岸带过程等方面研究进展。     

Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil

This study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Paraná (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and summer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sediment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO₃, chlorophyll a , omega indexes, temperature and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon's diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that polychaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P < 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal variability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes.     

粤东靖海湾海岸地貌动力演变及其工程影响

受人为工程的影响,相对稳定的岬湾海岸地貌常经历显著的动态调整。本文以粤东靖海湾典型岬湾海岸为例,运用Mc Laren模型、波浪动力场数值模拟、等深线对比、冲淤计算等多种方法,从海岸地貌动力学角度,对人为岬角工程前后岬湾海岸地貌动力过程和冲淤演变进行综合分析。结果表明:1)海岸地貌动力系统内常存在负反馈机制以维持系统的稳定。岬角工程后上岬角防波堤沿SSW延伸,ESE和E向浪经过防波堤时发生绕射,波能削减,湾顶动力减弱,海滩沉积物从下岬角向湾顶反向运移;2)海滩的蚀积状态在工程前后发生了转换,工程前遮蔽段侵蚀、开敞段堆积;工程后遮蔽段堆积、开敞段侵蚀;3)海湾水下地形对岬角工程的响应敏感,工程后海湾水下地形冲淤剧烈。     

Physical determinants of intertidal communities on dissipative beaches: Implications of sea-level rise

Sea-level rise is likely to cause significant changes in the morphodynamic state of beaches in the higher latitudes, resulting in steeper beaches with larger particle sizes. These physical changes have implications for beach invertebrate communities, which are determined largely by sediment particle size, and hence for ecosystem function. Previous studies have explored the relationships between invertebrate communities and environmental variables such as particle size, beach slope and exposure to wave action, and often these physical variables can be integrated in various indices of morphodynamic state. Most of these studies incorporated a full range of beach types that included wave-dominated surf beaches, where the wave action is harsh enough to enable reliable estimates of breaker height, a parameter included in several of the indices, and concluded that more dissipative beaches with gentler slopes and finer particle sizes often support a higher number of species and greater abundance than more reflective beaches. Whether these predictions remain valid for less wave-dominated beaches, where breaker height is more difficult to determine, is uncertain. In the present study, the abundance of meio- and macrofauna was quantified across a range of beaches in the UK, which are generally towards the lower energy end of the morphodynamic gradient, and their relationships with beach physical properties explored. No significant relationships were found between abundance and the standard morphodynamic indices, but significant relationships were found for both macro- and meiofaunal abundance when these indices were combined with an exposure index (derived from velocity, direction, duration and the effective fetch). All the relationships identified between abundance and combined morphodynamic indices indicated a higher abundance of both macro- and meiofauna on the more dissipative beaches. The reverse was however found for species richness. If predictions that accelerated sea-level rise will move beaches towards a more reflective morphodynamic state are correct, this could lead to declines in the abundance of meio- and macrofauna, with potential adverse consequences for ecosystem functioning.     

Morphodynamics of intertidal bars on a megatidal beach, Merlimont, Northern France

The morphology, bedforms and hydrodynamics of Merlimont beach, in northern France, characterised by intertidal bars and a spring tidal range of 8.3 m, were surveyed over a 10-day experiment with variable wave conditions that included a 2-day storm with significant wave heights of up to 2.8 m. The beach exhibited two pronounced bar-trough systems located between the mean sea level and low neap tide level. Waves showed a cross-shore depth modulation, attaining maximum heights at high tide. The mean current was characterised dominantly by strong tide-induced longshore flows significantly reinforced by wind forcing during the storm, and by weaker, dominantly offshore, wave-induced flows. Vertical tidal water-level variations (tidal excursion rates) showed a bimodal distribution with a peak towards the mid-tide position and low rates near low and high water. The two bar-trough systems in the mid-tide zone remained stable in position during the experiment but showed significant local change. The absence of bar migration in spite of the relatively energetic context of this beach reflects high macro-scale bar morphological lag due to a combination of the large vertical tidal excursion rates in the mid-tide zone, the cross-shore wave structure, and the pronounced dual bar-trough system. The profile exhibited a highly variable pattern of local morphological change that showed poor correlation with wave energy levels and tidal excursion rates. Profile change reflected marked local morphodynamic feedback effects due mainly to breaks in slope associated with the bar-trough topography and with trough activity. Change was as important during low wave-energy conditions as during the storm. Strong flows in the entrenched troughs hindered cross-shore bar mobility while inducing longshore migration of medium-sized bedforms that contributed in generating short-term profile change. The large size and location of the two pronounced bars in the mid-tide zone of the beach are tentatively attributed respectively to the relatively high wave-energy levels affecting Merlimont beach, and to the cross-shore increase in wave height hinged on tidal modulation of water depths. These two large quasi-permanent bars probably originated as essentially breakpoint bars and are different from a small bar formed by swash and surf processes in the course of the experiment at the mean high water neap tide level, which is characterised by a certain degree of tidal stationarity and larger high-tide waves.     

Development of a medium–long term beach evolution model

A new medium–long term beach evolution model is proposed. This model is based on an analytically integrated sediment conservation equation and on a beach profile evolution model. The sediment conservation equation provides the sediment supplies or losses. The beach profile evolution model redistributes the sediment supplies or losses along the beach profile. In the beach profile evolution model, the definition of the complete profile is incorporated (breaking zone, transition zone, exterior zone and geological zone). The proposed model has been applied to several theoretical cases and to field data, showing the advantages of this model compared to classical “one-line models”.     

乡村海滩旅游资源质量评价的建立——以雷州半岛为例

我国海滩旅游资源开发程度不高,还存在大量的优质乡村海滩资源未被利用,具有巨大的潜在经济价值和社会效益,是未来海滨旅游开发的重点。对旅游海滩质量进行科学评价是海滩开发的重要基础工作之一。国内外成熟的海滩质量评价体系侧重于滨海旅游的舒适性和服务完善性,比较适合于开发完善的城市旅游海滩,目前没有针对乡村旅游海滩资源的质量评价体系。本文结合了国内外海滩资源质量评价的研究方法,根据乡村海滩旅游海滩的独特性,从资源开发潜力、资源自然条件、海滩沉积动力特征及安全性3类评价因素19个评价因子,建立了乡村海滩旅游资源质量评价指标体系和乡村海滩旅游资源质量分类体系。结合现场调查数据,利用该评价体系对雷州半岛沿岸18个乡村海滩进行了质量评价和分类。结果表明该海滩质量评价体系可为乡村海滩资源的综合利用、保护和开发提供理论和技术支持。最后,分析指出在海滩质量评价体系中引入地形动力理论,对海滩裂流安全性因子进行评价的重要性。     

北海银滩响应台风作用的动力地貌过程

极端高能事件影响下的海滩动力地貌过程直接关乎岸滩稳定及海堤安全。本文基于2020年16号台风“浪卡”前后北海银滩顺直岸段的剖面高程及表层沉积物等资料, 探究了中等潮差的顺直响应台风作用的地貌变化机制。结果表明: 1) 台风后海滩地貌表现为冲流带的大型沙坝消失, 后滨沙丘-滩槽体系被削平, 滩面坡度趋于平缓。2) 银滩沉积物均以中砂、细砂和极细砂为主, 三者占比超过95%; 台风后, 高潮位带沉积物变细, 低潮位带沉积物变粗, 沙坝附近则出现粗细交错式变化; 银滩中高潮位带滩面响应台风过程的特征与强潮型海滩相似, 呈现消散型海滩的特征, 而低潮位带滩面则因大型沙坝的作用而呈现弱潮型海滩特征。3) 台风期间波浪是影响海滩的主要动力因素, 海滩地形影响了近岸水动力的表现形式, 从而改变了沉积物的粒径分布。     

Mapping beach morphodynamics remotely: A novel application tested on South African sandy shores

Sandy beaches have been identified as threatened ecosystems but despite the need to conserve them, they have been generally overlooked. Systematic conservation planning (SCP) has emerged as an efficient method of selecting areas for conservation priority. However, SCP analyses require digital shapefiles of habitat and species diversity. Mapping these attributes for beaches from field data can take years and requires exhaustive resources. This study thus sought to derive a methodology to classify and map beach morphodynamic types from satellite imagery. Since beach morphodynamics is a strong predictor of macrofauna diversity, they could be considered a good surrogate for mapping beach biodiversity. A dataset was generated for 45 microtidal beaches (of known morphodynamic type) by measuring or coding for several physical characteristics from imagery acquired from Google Earth. Conditional inference trees revealed beach width to be the only factor that significantly predicted beach morphodynamic type, giving four categories: dissipative, dissipative-intermediate, intermediate and reflective. The derived model was tested by using it to predict the morphodynamic type of 28 other beaches of known classification. Model performance was good (75% prediction accuracy) but misclassifications occurred at the three breaks between the four categories. For beaches around these breaks, consideration of surf zone characteristics in addition to beach width ameliorated the misclassifications. The final methodology yielded a 93% prediction accuracy of beach morphodynamic type. Overlaying other considerations on this classification scheme could provide additional value to the layer, such that it also describes species’ spatial patterns. These could include: biogeographic regions, estuarine versus sandy beaches and short versus long beaches. The classification scheme was applied to the South African shoreline as a case study. The distribution of the beach morphodynamic types was partly influenced by geography. Most of the long, dissipative beaches are found along the west coast of the country, the south coast beaches are mostly dissipative-intermediate, and the east coast beaches range from short, estuarine pocket and embayed beaches in the former Transkei (south east), to longer intermediate and reflective beaches in KwaZulu-Natal (in the north east). Once combined with the three biogeographic regions, and distinguishing between estuarine and sandy shores, the South African coast comprised 24 different beach types. Representing shorelines in this form opens up potential for numerous spatial analyses that can not only further our understanding of sandy beach ecology at large spatial scales but also aid in deriving conservation strategies for this threatened ecosystem.