浙江朱家尖岛东沙海滩对热带风暴“娜基莉”的响应及风暴后的恢复

海滩对风暴的响应及风暴后海滩的恢复过程一直以来都是国内外海滩研究的热点。本文通过对浙江舟山市朱家尖岛东沙海滩地形地貌的现场调查,对比分析了热带风暴"娜基莉"影响下东沙海滩剖面的蚀积变化,探讨了海滩在热带风暴发生后的恢复情况。结果表明,在"娜基莉"影响期间,因风暴浪为向岸浪,东沙海滩几乎遭受全线侵蚀,12个剖面单宽侵蚀总量为73.46 m3/m,其中海滩直线段较两个遮蔽段侵蚀显著。由于海滩在风暴前进方向的左侧,且"娜基莉"距东沙较远,使得东沙海滩普遍侵蚀但强度较小。东沙海滩在热带风暴后的恢复过程中,不同部位的地貌调整和冲淤变化不同,下岬角遮蔽段基本趋于稳定,直线段和上岬角遮蔽段在恢复过程中因受海滩季节性调整的影响呈现持续侵蚀。     

热带气旋前进方向两侧海滩风暴效应差异研究--以海滩对0307号台风"伊布都"的响应为例

在0307号台风“伊布都”(Imbudo)袭击华南沿海前后,对相距约300km的高栏岛飞沙湾(位于气旋前进方向右侧)和水东港下大海(位于气旋前进方向左侧)的固定海滩剖面地形及滩面沉积物进行了对比调查。调查结果表明,右侧海滩地形受台风暴浪冲击发生剧烈变化：后滨陆侧堆积,后滨向海侧及前滨滩面侵蚀(单宽侵蚀量达55m^3／m,平均海面(MSL)位置蚀退13m,岸线位置蚀退5m),以致剖面类型由滩肩式断面向沙坝式断面转变,表现出了海滩对台风做出快速响应;而左侧海滩剖面地形基本保持原状,虽也略呈侵蚀,但冲淤变化不大,表现为对台风做出迟缓响应。同时,从动力、滨海输沙、滩面沉积物变化和海岸地貌等方面对两侧海滩明显差异的风暴效应的机制进行了探讨。     

海南岛东北部海滩侵蚀与恢复对连续台风的复杂响应

在连续台风作用下海滩的侵蚀与恢复是一个复杂的过程。基于海南岛东北部木兰-抱虎湾海滩的现场调查,对比分析台风"威马逊"和"海鸥"登陆前后海滩剖面和后滨沉积物的动态响应。结果表明,超强台风"威马逊"引起海滩的严重侵蚀和强烈的泥沙输移,在木兰湾海滩主要表现出由北向南沿岸海滩的差异性变化,在抱虎湾各海滩变化较为相近;后继登陆台风"海鸥"引起海滩显著堆积,对海滩主要起恢复作用,木兰湾海滩恢复效果明显,海滩后滨沉积物趋于恢复至台风前的状态,由于抱虎湾水下珊瑚礁及近岸岩礁地貌减缓了台风对该处海滩的侵蚀和堆积作用,抱虎湾海滩表现出与台风前较大差异性。两处海湾海滩的不同走向及台风的风向变化也是造成海滩不同响应的重要原因。研究将有助于更好地理解海滩对连续台风作用的复杂响应。     

海滩-珊瑚礁系统风暴响应特征研究——以1409号台风“威马逊”对清澜港海岸影响为例

珊瑚礁海岸在我国热带地区广泛发育,海滩-珊瑚礁海岸的动力地貌过程是认识该类海岸的关键。本文基于对海南铜鼓岭-高隆湾岸段的台风"威马逊"前后跟踪观测,讨论了海滩风暴响应特征及其与珊瑚礁发育之间的联系。结果表明该岸段海滩在"威马逊"风暴作用下响应最为剧烈的区带位于平均海平面(MSL)以上,表现为后滨冲越,以及岸线蚀退、滩肩变窄、滩面侵蚀等响应特征。海滩风暴响应特征与近岸珊瑚礁发育密切相关,在无珊瑚或珊瑚受损的岸段海滩响应剧烈,剖面平均变化率(MPC)为其他岸段的3~6倍,珊瑚礁通过消耗波能对相邻海滩提供良好保护。海滩-珊瑚礁系统对风暴的响应特征受控于珊瑚礁对海岸波浪的消耗能力和海滩固有的缓冲能力。基于本文研究结果,归纳出风暴极端动力条件下海滩-珊瑚礁海岸的4种风暴响应模式。     

岬湾海滩剖面中长期变化特征及其控制因素——以青岛石老人海滩为例

了解海滩剖面变化可以更好地理解海滩动态过程。利用2007年5月~2014年12月近8 a青岛石老人海滩剖面的实测资料,计算剖面各段单宽体积变化量及后滨宽度,结合交叉小波和小波相干分析方法,探讨海滩剖面中长期淤蚀变化特征及其控制因素。结果表明,近8 a来海滩剖面表现为侵蚀状态,不同岸段侵蚀程度不同。剖面1岸段侵蚀明显,剖面2和剖面3岸段轻微侵蚀。剖面的变化过程可划分为平稳期、剧变期和微调期3个时期。各时期剖面的季节性变化较复杂,平稳期具冬蚀夏淤的交替变化特征,整体淤蚀量较小;剧变期剖面呈阶段性蚀退,变化幅度相对较大,微调期剖面可能仍处于剧变期的恢复阶段,季节性变化不明显。剧变期和微调期的小波交叉谱和相干谱分析显示,波浪和前滨单宽体积相干性较好,尤其当大于2 m的波高达到10%以上,海滩地形可以和波高变化产生同周期的变化。因此波高变化基本控制了剖面的季节变化。而海滩长周期变化主要受控于风暴潮作用及其漫长的恢复期,沿岸输沙和海平面变化则一定程度上导致了剖面长期侵蚀格局的形成。     

预测随时间演化的长期滨线侵蚀的概率方法

本文主要介绍了一个预测长期滨线侵蚀的概率分布的方法。它把一段时间内滨线的动力响应作为随时间变化的随机体系。系统输入的是长期的波候和滨线特征 ,输出的是在任何时间内滨线后退最远的概率分布情况。这一方法考虑了沉积物的沿岸输送和垂岸输送对滨线侵蚀的共同作用 ,因为这两个过程都与最大滨线侵蚀有关。对理想化的长期波浪分布进行模拟来评价方法的可行性。通过模拟发现波浪的分布和波候变化对预测岸线的侵蚀有重要影响 ,而年代的作用不明显 ,尤其在较长的时间内。对垂岸输送使用简单的海滩后退模型 ,对沿岸输送使用标准的单线模型来…     

海滩风暴效应若干问题思考与我国研究前景

热带风暴是一种频发的灾害性事件,其诱发的大浪及其伴生的风暴潮会在短时间内搬运大量沉积物,对海岸地貌、海底地形和海洋沉积的影响极为严重.总结了未来风暴变化趋势和风暴动力方面的研究进展,概述了近几十年来海滩风暴效应领域几个重要方向的进展,内容包括岸滩风暴灾害调查和研究、海滩风暴效应差异性研究、风暴作用下的泥沙运动和岸滩风暴响应沉积学特征等方面.从国内外的研究现状来看,我国在风暴作用下泥沙运动实测与定量分析、多因素耦合控制下海滩风暴效应差异和海滩风暴地貌过程等方面存在着明显的不足.作为我国海岸科学研究中必需又薄弱的环节,今后该领域的研究应该在强化野外现场实验和监测的基础上,深入探讨极端条件下的海滩过程,发展海滩风暴响应预测模型,并积极开展海滩风暴潮防护技术开发与应用.     

1211号台风对浙江象山皇城海滩剖面的影响分析

通过对浙江象山皇城海滩地形地貌的现场调查,对比分析了1211号台风"海葵"登陆象山前后海滩剖面的蚀积变化,探讨了该处海滩对1211号台风"海葵"的响应特征。研究结果表明,在2012年8月台风"海葵"过境期间,皇城海滩从总体上看,剖面表现为上冲下淤,平面表现为北冲南淤,其后滨沙丘蚀积变化剧烈,海滩沉积物总收支变化不大。皇城海滩不同岸段剖面对台风"海葵"的响应特征不同,切线段以淤积为主,过渡段、遮蔽段以侵蚀为主,且遮蔽段在三个岸段中变化最小,台风响应强度最弱。台风路径走向、岬湾海滩相对台风的走向和岬角突出程度是其对台风响应强度的重要影响因素。     

基于高频观测数据的徐闻青安湾海滩对台风“贝碧嘉”的响应研究

风暴是造成海滩剧烈变化的重要因子。由于观测环境的恶劣,目前极少有风暴过程中海滩响应的现场高频观测工作。本研究在2018年台风“贝碧嘉”期间对徐闻青安湾海滩开展了历时6天半的高频观测,获得了全时水动力要素和164组逐时海滩滩面高程变化数据。通过分析表明:(1)青安湾海域风暴增水及波浪受控于海南岛?雷州半岛特有的地形地貌和台风“贝碧嘉”的多变路径,增水稳定在0.38～0.5 m之间,而波高先由0.78 m衰减至0.43 m,再增加至0.56 m;(2)海滩剖面地形变化总体表现为滩肩侵蚀,形成水下沙坝,滩肩响应过程分为快速向下侵蚀、缓慢侵蚀至最大值、振荡回淤恢复3个阶段,台风期间滩肩振荡恢复幅度可达最大侵蚀深度的1/4;(3)海滩的风暴响应过程主要由4个模态耦合而成:第一模态体现大潮滩肩侵蚀生成水下沙坝过程;第二模态体现风暴滩肩侵蚀,补偿大潮滩肩侵蚀位置和进一步促进沙坝形成过程;第三模态揭示了波浪二次破碎位置的上冲流和离岸底流使泥沙发生双向输移过程;第四模态表明台风大浪使得碎波带内泥沙大量悬浮,在沿岸流和离岸流作用下部分悬沙进入深水区,可能造成海滩泥沙的永久亏损。     

雷州半岛南部海滩对1720号台风(卡努)的响应研究

海滩风暴响应的观测和研究有助于加深对海滩过程的认识。2017年10月16日台风“卡努”在广东徐闻县沿海登陆, 对雷州半岛南部海滩造成了显著影响。文章通过海滩剖面观测和沉积物采样, 探讨了该区域海滩对台风“卡努”的响应特征, 得出以下主要结论。1) 台风浪作用下, 海滩表层沉积物变粗, 分选性变差。海滩状态朝着更加消散的状态转化, 以缓冲和适应高强度波浪的能量。2) 受到岬角和湾口朝向、大小等因素影响, 各海滩及同一海滩的不同岸段剖面变化表现出差异性。台风作用后海滩可能形成水下沙坝, 或者在海滩上部形成滩肩等特征地形。因此, 研究海滩风暴响应时, 要注意到区域地质地貌的影响。3) 水下礁坪、巨型砂质岬角等因素影响了台风过程灯楼角海滩的变化。对这种海滩–珊瑚礁坪系统的风暴效应, 还需要进行进一步探讨和更详细的观测和研究。     

Applications of EMD to analyses of high-frequency beachface responses to Storm Bebinca in the Qing'an Bay,Guangdong Province,China

On average, five to six storms occur in the Qiongzhou Strait every year, causing significant damage to coastal geomorphology and several property losses. Tropical Storm Bebinca is the most unusual and complex storm event that has occurred in this region over the last 10 years. To detect the high-frequency beachface responses to the storm, a pressure sensor was deployed in the surf zone to record the free sea surface height, and the heights of grid pile points on the beachface were measured manua...     

Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland

Large sections of the western Irish coast are characterised by a highly compartmentalised series of headland-embayment cells in which sand and gravel beaches are backed by large vegetated dune systems. Exposure to modally high-energy swell renders most of these beaches dissipative in character. A mesotidal range (c. 3.5–4.5 m) exists along much of the coast. Analysis of instrumental wind records from three locations permitted the identification of a variety of storm types and the construction of storm catalogues. Few individual storms were recorded at all three stations indicating a lack of regional consistency in storm record. Of the total storms recorded, only a small percentage are potentially damaging (onshore directed) and even fewer span a high tide and thus potentially induce a measurable morphological response at the coast.

Through a combination of historical records, meteorological records, field observations and wave modelling we attempt to assess the impact of storms. Quantifiable records of coastal morphology (maps, air photos and beach profiles) are few in number and do not generally record responses that may be definitely attributed to specific storms. Numerical wave simulations and observations at a variety of sites on the west Irish coast, however, provide insights into instantaneous and medium term (decadal) storm responses in such systems.

We argue that beaches and dunes that are attuned to modally high-energy regimes require extreme storms to cause significant morphological impact. The varying orientation of beaches, a spatially nonuniform storm catalogue and the need for a storm to occur at high water to produce measurable change, impart site-specific storm susceptibility to these embayments. Furthermore, we argue that long-period wave energy attenuation across dissipative shorefaces and beaches reduces coastal response to distant storms whereas short-period, locally generated wind waves are more likely to cause major dune and beach erosion as they arrive at the shoreline unrefracted.

This apparently variable response of beach and dune systems to storm forcing at a decadal scale over a coastline length of 200 km urges caution in generalising regarding regional-scale coastal responses to climatic change.     

Drones as tools for monitoring beach topography changes in the Ligurian Sea (NW Mediterranean)

The aim of this study was to evaluate topographic changes along a stretch of coastline in the Municipality of Borghetto Santo Spirito (Region of Liguria, Italy, north-western Mediterranean) by means of a remotely piloted aircraft system coupled with structure from motion and multi-view stereo techniques. This sector was surveyed three times over 5 months in the fall–winter of 2013–2014 (1 November 2013, 4 December 2013, 17 March 2014) to obtain digital elevation models and orthophotos of the beach. Changes in beach topography associated with storm action and human activities were assessed in terms of gain/loss of sediments and shifting of the wet–dry boundary defining the shoreline. Between the first and second surveys, the study area was hit by two storms (10–11 November 2013 and 21–22 November 2013) with waves approaching from the E–NNE, causing a shoreline retreat which, in some sectors, reached 7 m. Between the second and third surveys, by contrast, four storms (25–27 December 2013, 5–6 January 2014, 17–18 January 2014 and 6–10 February 2014) with waves propagating from the SE produced a general advancement of the shoreline (up to ~5 m) by deposition of sediments along some parts of the beach. The data also reflect changes in beach topography due to human activity during the 2013 fall season, when private beach managers quarried ~178 m³ of sediments on the emerged beach near the shoreline to accumulate them landwards. The results show that drones can be used for regular beach monitoring activities, and that they can provide new insights into the processes related to natural and/or human-related topographic beach changes.     

The effects of storms and storm-generated currents on sand beaches in Southern Maine, USA

Storms are one of the most important controls on the cycle of erosion and accretion on beaches. Current meters placed in shoreface locations of Saco Bay and Wells Embayment, ME, recorded bottom currents during the winter months of 2000 and 2001, while teams of volunteers profiled the topography of nearby beaches. Coupling offshore meteorological and beach profile data made it possible to determine the response of nine beaches in southern Maine to various oceanographic and meteorological conditions. The beaches selected for profiling ranged from pristine to completely developed and permitted further examination of the role of seawalls on the response of beaches to storms.

Current meters documented three unique types of storms: frontal passages, southwest storms, and northeast storms. In general, the current meter results indicate that frontal passages and southwest storms were responsible for bringing sediment towards the shore, while northeast storms resulted in a net movement of sediment away from the beach. During the 1999–2000 winter, there were a greater percentage of frontal passages and southwest storms, while during the 2000–2001 winter, there were more northeast storms. The sediment that was transported landward during the 1999–2000 winter was reworked into the berm along moderately and highly developed beaches during the next summer.

A northeast storm on March 5–6, 2001, resulted in currents in excess of 1 m s⁻¹ and wave heights that reached six meters. The storm persisted over 10 high tides and caused coastal flooding and property damage. Topographic profiles made before and after the storm demonstrate that developed beaches experienced a loss of sediment volume during the storm, while sediment was redistributed along the profile on moderately developed and undeveloped beaches. Two months after the storm, the profiles along the developed beaches had not reached their pre-storm elevation. In comparison, the moderately developed and undeveloped beaches reached and exceeded their pre-storm elevation and began to show berm buildup characteristic of the summer months.     

Storm-induced readjustment of an embayed beach after modification by protection works

This paper examines storm-induced morphological and hydrodynamic changes after a submerged and a detached breakwater were constructed at La Barceloneta beach (Barcelona, NW Mediterranean) in 2006–2007. The shoreline configurations before and after beach nourishment and the construction of the protective structures were compared using a video dataset comprising 29 storm events spanning the pre- (2001 to 2005, n?=?17) and the post-breakwater situation (2006 to 2011, n?=?12), and hydrodynamic modelling based on the SMC coastal modelling system. As a result of the protection works, La Barceloneta was subdivided into two beaches separated by an artificial salient. The analysis of shoreline response to storms has been improved by using the shoreline hyperbolic tangent fit to represent the beach planform. Comparing the pre- and post-breakwater situations on the basis of these shoreline fits facilitated the identification of beach rotation processes because interference by smaller-scale morphological features was eliminated (e.g. the formation, changes in shape or migration of mega-cusps). In the current post-breakwater situation, there is evidence for a change in the behaviour of the north-eastern beach triggered by the submerged breakwater built in 2007. Furthermore, a counter-clockwise beach rotation has occurred at the north-eastern beach, whereas the south-western beach has experienced a clockwise beach rotation. This morphodynamic behaviour is caused by a new, complex wave-induced circulation system comprising two dominant alongshore currents flowing in opposite directions. In contrast to the pre-breakwater situation, the alongshore component of the radiation stress does not accomplish beach rotation in the post-breakwater situation.     

Monitoring and comparison to predictive models of the Perdido Key beach nourishment project, Florida, USA

This paper summarizes the results of over 8 years of data describing the performance of a large beach nourishment project on Perdido Key, immediately adjacent to Pensacola Pass in Escambia County, FL, USA. As a result of a major excavation of the entrance channel to Pensacola Bay, over 7 million m³ of beach-quality sand were placed along the easternmost 7.5 km of Perdido Key, adjoining the entrance channel at Pensacola Pass. The project included the placement of 4.1 million m³ of sand directly upon the shoreline in 1989–1990, followed by the placement of an additional 3 million m³ as an underwater berm just offshore of the beach nourishment project in water depths of roughly 6 m. Monitoring of the performance of the beach nourishment project and the offshore berm has been conducted since 1989, beginning with a pre-construction survey of the project area. Monitoring surveys have been conducted on an annual or biennial basis since that time, with the most recent survey occurring in July/August, 1998. Over 8 years of monitoring data indicate that the beach nourishment project has retained approximately 56% of the original volume placed within the 7.5-km project length. In addition, according to the latest monitoring survey, the dry beach width of the project, initially constructed as 135 m on average, is still 53 m wider than pre-project conditions. Approximately 41% of the originally placed dry planform area remains as of July 1998. The most recent monitoring surveys in 1995, 1997, and 1998 encompass the effects of two major storm systems, Hurricanes Erin (August 1995) and Opal (October 1995). Monitoring of the offshore berm area indicates only a slight landward migration of the berm, accompanied by a minor decrease in volume, over the entire monitoring period. The performance of both the beach nourishment project and the offshore berm appear to be significantly related to the two storm events, particularly Hurricane Opal, and the proximity of the project to the tidal entrance at Pensacola Pass. Comparison of the documented performance of the beach nourishment project to simple existing analytical models of beach-fill evolution have yielded encouraging results in terms of preliminary design aids for future beach nourishment projects in the vicinity of deep tidal entrances.     

The influence of seawalls on subaerial beach volumes with receding shorelines

The results summarized herein are based on subaerial beach profiles taken on the Atlantic Ocean at Sandbridge, Virginia (USA). The shoreline has experienced an average, historic recession rate of about 2 m/yr for more than 120 years before seawall construction began in 1978. The purpose of this study is to determine whether or not the 16 walled sections increase the existing erosional trend at adjacent, non-walled beaches. Fifteen years of survey data are employed with 8–9 years of data taken before wall construction peaked in 1989. The main focus of these results is on five full wave years of monthly and post-storm survey data taken at 28 locations (16 walled, 4720 m, 62% and 12 non-walled, 2950 m, 38%) since October 1990. Three time scales (historic, seasonal, storms) and three analysis methods were used to address three questions concerning the effects of seawalls on adjacent beaches.It has been determined that volume erosion rates are not higher in front of seawalls (Question No. 1). However, the seasonal variability of the sand volume in front of walls is generally greater than at non-walled locations. Winter season waves drag more sand offshore in front of walls but also summer swell waves pile more sand up against walls in beach rebuilding.Walled beaches were found to recover about the same time as non-walled beaches for both seasonal transitions (winter to summer) and following erosional storm events (Question No. 2).At a few non-walled locations, the sand volume landward of adjacent walls was found to be eroding at a faster rate after wall construction. At some other non-walled locations, the sand volume landward remained constant or increased in time after nearby walled construction. The evidence for Sandbridge beach as a whole was considered inconclusive for Question No. 3.After wall construction, sand trapped behind the wall is not available for transport to adjacent beaches during and after storm events. The loss of this sand volume is felt to be in the initial stage of detection at Sandbridge. More full years of profile data are needed to confirm and quantify the effect. Sand is also trapped beneath the road (baseline) at non-walled locations. The study is continuing.