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1.
陈杰  管喆  蒋昌波 《水科学进展》2016,27(2):206-213
近年来频发的海啸灾害造成巨大损失,而红树林具有很好的减小海啸灾害的作用。实验采用PVC圆管来概化模拟红树林,以无黏性沙堆砌而成1/10~1/20组合坡概化岸滩,选取孤立波模拟海啸波。实验结果表明,红树林的存在对岸滩剖面变化产生了较大影响,适当增加植物分布密度,并优化植物的分布方式,可有效减小海啸波对岸滩的冲刷危害。在本次实验条件下,得到了岸滩冲刷坑尺度、淤积沙坝尺度、最大冲刷深度、最大淤积高度与红树林的分布方式和密度、海啸波波高、泥沙比重和岸滩坡度之间的关系式,揭示了沙质岸滩剖面变化与红树林、海啸波水动力特性、泥沙颗粒、岸滩坡度之间的内在联系,为减小海啸灾害提供科学依据。  相似文献   

2.
Handling and visualizing of beach profile data using visual programming provides better and more user-friendly effects to geologists, environmentalists, and policy makers. Several computer programs are available to visualize beach profile data. But in all programs, the raw field data cannot be used to calculate the sediment erosion and accretion. In this report, we describe the development of a simple piece of software BEACH using Visual Basic 6.0 that can store and analyze large volumes of profile survey data obtained from graduated pole or level surveys. The program precisely calculates the beach width, slope, and sediment volume above any user-specified datum. It also estimates the erosion and accretion made in a beach. This program is very useful for coastal zone management and environmental impact assessment studies.  相似文献   

3.
在波浪水槽实验的基础上,对海啸波作用下的床沙组成变化规律开展研究。实验采用1/10~1/20的组合坡度,选取N波作为入射波。实验对波高进行采集,对波浪的上爬、回落和水跃过程进行拍摄记录,对每个波作用后的地形进行测量,并对初始和最终的床面顶层泥沙进行采样筛分。实验结果表明,N波作用下泥沙在离岸区水跃发生区域堆积,淤积沙坝泥沙粒径呈粗化趋势。同时采用规则波和非规则波进行对比,波浪作用后形成岸滩也为沙坝剖面,淤积沙坝泥沙粒径呈细化趋势,结果均遵循Çelikoğlu提出的泥沙运动的基本规律,细颗粒泥沙会在强烈的紊动作用下从床面中被筛选出来,并被搬运到低紊动地区,此过程造成了剧烈紊动区泥沙的粗化。  相似文献   

4.
The morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions. Two years of seasonal surveys were carried out on Charf el Akab, a gently sloped beach in the North Atlantic coast of Morocco. The method of survey consisted of a 3D study of the beach morphological changes and provided 2 cm vertical accuracy. During the surveyed period, Charf el Akab beach underwent very energetic wave conditions, and the breaking wave height was of H b ≥ 1.5 m. The beach is characterized by a nonpermanent swash bar and composed of well-sorted medium sand. The application of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over the studied period. Morphological changes consist of beach erosion and bar decay under high-energy waves, whereas the intertidal bar re-established and the beach recorded an accentuated accretion due to relatively fair weather conditions. The beach volume reveals a seasonal behavior; the sand accumulated during summer is dramatically removed during winter season. The range in beach sand volume from the most accreted to the most eroded conditions observed is about −5,493 m3. The average sand volume flux between surveys reaches −1 and 0.4 m2/day during peak erosion and accretion periods. The relationships between the wave forcing and the sand volume adjustments were examined. The sand volume change was found to be highly correlated (0.91) with the wave energy flux. The highest correspondence (0.95) was found between the sand flux rate and the wave energy flux. The wave forcing is expected to be the main factor governing beach morphodynamics at Charf el Akab site.  相似文献   

5.
海啸波作用下泥沙运动——Ⅰ.岸滩剖面变化分析   总被引：1，自引：0，他引：1  
在波浪水槽实验的基础上,对海啸波作用下的岸滩剖面演变规律开展研究。实验采用1/10~1/20的组合坡度,考虑3种不同的水深,选取N波作为入射波,同时采用规则波和非规则波进行对比研究。实验对波高、波浪的上爬、回落和水跃过程、每个波作用后的地形进行了测量和记录。研究结果表明,水动力特性的不同造成了N波与规则波和不规则波作用下不同的岸滩剖面演变特点。N波作用下发生了明显的岸滩冲刷和淤积,水流回落时滩肩发生冲刷,高速薄层回流和出渗水流作用是滩肩冲刷的主要原因,离岸区水跃发生水流挟沙力降低,泥沙淤积呈沙坝剖面。  相似文献   

6.
通过三维地震资料海底平面成像和浅层地震剖面解释、分析,识别和描述了西非科特迪瓦盆地深水底形类型。研究区发育下切水道、侵蚀冲坑、周期阶坎、小型沉积物波、大型沉积物波多种深水底形。下切水道表现为直线型,地形坡度从上斜坡5°过渡到下斜坡1.9°,水道历经多次合并,合并后水道内部起伏地貌指示侵蚀—沉积交互作用;识别出孤立状、串珠状和猫爪状三种类型侵蚀冲坑;在斜坡限制性水道内部地形坡度1.9°～3.1°之间识别出8个不同波长和波高的“周期阶坎”底形,周期阶坎具有剖面上向上游方向迁移、平面上呈新月形态的特征,从上游到下游波长有逐渐变短的趋势。小型沉积物波发育于水道内和水道外两种环境,其中限定性环境小型沉积物波发育在周期阶坎上游方向,非限定环境小型沉积物波发育地形坡度为1°左右,具有加积或轻微向下迁移的内部反射结构。大型沉积物波发育在非限定环境中,显示为长波长、低幅度浅层构造特征,分析认为早期滑塌地貌对晚期大型沉积物波的形成具有重要的控制作用。在现象描述基础上,对不同底形的成因、形成过程、控制因素和其发育的深水动力学背景与环境展开探讨,加深了对西非赤道段科特迪瓦盆地深水底形成因的认识,可对未来深水区...  相似文献   

7.
Man-made coastal structures directly affect sediment balance and sediment dynamics on the surrounding beaches. The Colombo Harbor Expansion Project has created about 5-km-long breakwater nearly perpendicular to the beach. The present study is focused on quantitatively and qualitatively analyzing the effect of the Colombo Harbor Expansion Project on economically important beaches in and around Colombo city area. In this study, the authors measured monthly variations of beach width, beach profile and the mean grain-size of the sediments at mean sea level for complete annual monsoon cycle. Data were analyzed to establish site-specific erosion vulnerability. Monitoring results show that cumulative beach erosion has increased after the construction of the breakwater (rate = 0.7 m/year from May 2000 to April 2011 and rate = 28.2 m/year from April 2011 to June 2012). In addition, the cumulative and site-specific sand accretion and erosion patterns have a clear relationship with the monsoon seasonality. Beaches were narrower during the stormy southwestern monsoon, whereas beaches were wider during fair weather of northeast monsoon and inter-monsoon periods. In contrast, the constructed breakwater obstructs natural longshore sediment dynamics. For example, a significant amount of sediments from the Kelani-Ganga River were buried in the Colombo Harbor due to alteration of prominent longshore sediments transportation on the western coast of Sri Lanka. Therefore, this study shows enhancement of coastal erosion in the studied southern beaches due to a lack of sediment deposition.  相似文献   

8.
Aerial photographs taken in the 1963 and 2001 and bathymetric charts, in conjunction with coastal processes are analyzed to assess changes in rate of shoreline position, seabed level, and seabed grain sizes along the Tabarka–Berkoukech beach at the north-western Tunisian coastline. The littoral cell of this beach, 12-km-long, is bounded by pronounced embayments and rocky headlands separated by sandy stretches. Although not yet very much undeveloped, this littoral is still experienced degradation and modification, especially along its shoreline, with significant coastal erosion at some places. Results obtained from analysis of shoreline position indicate that El Morjene Beach is experienced a landward retreat of more than −62 m, at a maximum rate of −1.64 m/year, whereas the El corniche beach is advanced about 16–144 m, at an average rate of 0.42 m–3.78 m/year. This beach accretion has been formed on the updrift side of the Tabarka port constructed between 1966 and 1970. Comparison of bottom contours deduced from bathymetric charts surveyed in 1881 and 1996 off the coastline between Tabarka Port and El Morjene Beach identifies erosional areas (sediment source) and accretionary zones (sediment sink). Erosion (0.87–4.35 cm/year) occurs between El kebir River Mouth and El Morjene beach, whereas accretion exists in the zone down wind of the port ranges between 0.87 and 5.21 cm/year. Morphological analyses of the shoreline and the seabed of the study nearshore area indicate that shoreline retreat corresponds to areas of seabed scour (sediment source) while shoreline accretion is associated with areas of seabed deposition (sediment sink). Furthermore, simulation of wave propagation using STWAVE model combined with grain size distributions of the seabed shows that fine sands are much dominated in depositional areas with low wave energy, whereas coarser sands in erosive zones with high wave energy. The results obtained suggest that the change of seabed morphology, wave height pattern and grain size sediment have a great influence on the modification of shoreline morphology and dynamics.  相似文献   

9.
This study evaluates the impacts resulting from the construction of two large-scale detached breakwater systems on the Nile delta coast of Egypt at Baltim and Ras El Bar beaches (~18.3 km shoreline length). The two protective systems were installed in a water depth of between 3 and 4 m and consist of 17 units in total (each ~250 m long). A comprehensive monitoring program spanning the years 1990 to 2002 was implemented and included beach-nearshore profiles, grain size distribution of seabed sand and information related to the background coastal processes. Evaluation of these systems concentrates on the physical impacts on coastal morphodynamics, mitigation and their design implications. The beach and nearshore sedimentation (erosion/accretion patterns) and grain texture of seabed sediment in the study areas have been substantially disrupted due to the interruption of longshore transport by the shore-parallel detached breakwaters. Rate of shoreline and seabed changes as well as alongshore sediment volume have been substantially affected, resulting in accretion in the breakwater landward sides (tombolo or salient) followed by downdrift erosion. The preconstruction beach erosion at Baltim (–5 m/year) and at Ras El Bar (–6 m/year) has been replaced, respectively, by the formation of sand tombolo (35 m/year) and salient (9 m/year). On the other hand, beach erosion has been substantially increased in the downdrift sides of these protective systems, being –20 m/year at Baltim and –9 m/year at Ras El Bar. Further seaward, the two protective systems at Baltim and Ras El Bar have accumulated seabed sand at maximum rates of 30 and 20 cm/year and associated with downdrift erosion of –45 and –20 cm/year, respectively. Strong gyres and eddies formed in the breakwater gabs have drastically affected swimmers and subsequently caused a significant number of drownings each summer, averaging 35 and 67 victims/year at Baltim and Ras El Bar beaches, respectively. This study provides baseline information needed to help implement mitigation measures for these breakwater systems.  相似文献   

10.
在热带砂质海岸,生物碎屑是海滩沉积物的重要组成部分,其分布和变化影响海滩沉积物的粒度特征。采用添加过量盐酸和双氧水的方法对海南高隆湾海滩表层沉积物进行了去生物碎屑前后粒径分布的对比,并结合海滩高程测量分析,结果表明:（1）海滩剖面上沉积物中生物碎屑的含量主要受到海水动力的影响,且生物碎屑颗粒较粗、重量较大,在高潮时由波浪流推上海滩并滞留。（2）海滩沉积物中生物碎屑的分布主要受三方面影响:一是地形及常涌浪向;二是区域中养殖业产生的生物碎屑;三是岸外发育的珊瑚礁坪。（3）海滩沉积物中生物碎屑的含量随季节变化,冬季至春季由海水供给的生物碎屑减少、进一步分解,使得北部海滩生物碎屑含量减少;而珊瑚碎屑的稳定供给和春季较强的波浪动力条件又使研究区南部断面的生物碎屑含量增加。（4）海滩沉积物中粗颗粒所含生物碎屑多于细颗粒中的生物碎屑,生物碎屑粒径主要为-1~2,即粗砂至细砾。沉积物中生物碎屑含量愈大,对粒径参数的影响也愈大。  相似文献   

11.
三亚海岸演变与人工海滩设计研究*   总被引：12，自引：0，他引：12  
三亚海岸位于海南岛南部,属弱潮海区,以来自开阔外海的偏南向风浪为海岸优势动力。三亚海岸经历了从基岩港湾海岸到岬角与港湾相间的海蚀-海积海岸的发育演化过程,沙坝(沙咀)发育始于中更新世初期,珊瑚礁发育始于8kaB.P. ,目前海岸总体处于相对平衡发展阶段。对三亚地区海岸地貌、动力及泥沙运动的调查研究,总结三亚湾及其周边不同类型海滩的特点,提取其海滩参数。依据处于不同发展时期的自然海滩形成演变的条件和规律,设计建构三亚白排人工海滩的关键参数。设计海滩总长度约400m,宽度\{40~\}50m,坡度4.5°~5.0°,相对高度约2m,填砂M为0.5,以粒径1.0~\}0.5mm的粗砂为主,总填砂量48000m3。从滩面物质和滩面坡度两个关键方面,利用代表性的数学模型,检验了设计海滩的稳定性。本项研究旨在服务白排人工海滩建设,研究方法对海滩侵蚀防护与同类海岸工程建设等具有参考价值。  相似文献   

12.
Beach profile data, covering the coast of Ras El Bar, northeast Nile Delta, collected during the years from 1990 to 2002 combined with landsat images for the area and sedimentological investigation have been used to identify beach and nearshore seafloor sediment changes. Along the coast of Ras El Bar, two accretion sectors and one of erosion have been recognized. The first accretion sector is located west of Damietta harbour, where the harbour jetties have halted the littoral transport, while the second one is behind a system of detached breakwaters protecting Ras El Bar resort. Both the two sectors are characterized by growing shoreline with maximum rates ∼15 and 10 m/year, respectively. Also, they have maximum nearshore seafloor accretion rates of ∼18 and 22 cm/year, respectively. The erosion sector is located east of Damietta port and has a maximum rate of shoreline retreat ∼−10 m/year. Erosion of its nearshore seafloor is indicated recording a maximum rate of ∼−20 cm/year. The rate of net sediment volume change in the area indicates shifting of the accretion sector (II) westward, responding to installation of the new breakwaters unit. The two accretion sectors are characterized by dominance of moderately sorted fine sands in their shore area which change seaward into less sorting very fine sands. Beach sands of the eroded sector are poorly sorted medium grain size. The dominant constituents of heavy mineral species in beach and sea-bottom sands are the characteristic assemblages of the Nile deposits. The sands of the eroded zone are relatively enriched in monazite, zircon, tourmaline, garnet, and rutile.  相似文献   

13.
The variation during 15 years in the shoreline along the North Sinai coast has been determined by analysing TM and ETM true colour Landsat images from 1986 to 2001. The analyses identified erosion and accretion patterns along the coast. The shoreline has advanced west of El Bardawil inlet1, El Bardawil inlet2, and El Arish Harbour, where the wave-induced littoral transport has been halted by jetty construction and beach growth rates are 20,681, 69,855 and 20,160 m2/year, respectively. On the downdrift side of the constructed jetties to the east, the shoreline is retreating and beaches erode at rates of −71,710, −69,968, and −11,760 m2/year, respectively. Sedimentological analyses of beach sediment samples have indicated selective transport of heavy minerals according to their densities and grain sizes. A general correspondence has been found between variation in grain size, sorting and heavy-mineral content of beach sand and the patterns of shoreline changes.  相似文献   

14.
Field research of wave generated bed forms within complex sediment size distributions near the inlet of a tidal lagoon at the northern coast of Brittany has stimulated an experimental study in a laboratory wave tank. Several sediment mixtures, most of them with bimodal grain size distributions, were exposed to different monochromatic shallow water waves. The observations and measurements included the dynamics of the water waves and the generation, shape, and size of oscillatory bed forms. The experiments confirm the known relationship between grain size and ripple size. In addition it is shown that coarse sand, added to a preexisting fine bed material leads to an increasing asymmetry of ripples. There is some suggestion that the variability of ripple heights is reduced by higher contents of coarse sand. Bimodal sediment size distributions obviously do not cause unusual geometry of ripples — at least within the range of the experimental tests. The different sand size modes move together in one phase, forming structures with more or less homogeniously distributed bed material. Differentiation of sediment sorting does of course occur, but this is in the range of the whole test section. Finally the experiments allowed to test the validity of some wave formulas. The own experiments are compared with some results from field and laboratory studies of other authors.  相似文献   

15.
A laboratory experiment was conducted to determine whether retention of waterborne sand by salt marsh cordgrass, Spartina alterniflora Loisel, is directly related to the number of stems per unit area. Waves generated in a trough washed over a sloping beach planted with S. alterniflora sprigs: a range of stem densities (0–108 stems/m2) was examined in separate trials. The amount of sand accumulated after 60 waves is a positive nonlinear function of stem density. The greatest accretion coincided with the highest stem density tested. Shape of the beach profile was also strongly influenced by the number of stems per m2.  相似文献   

16.
The effects of wave action and horseshoe crab spawning on the topography and grain-size characteristics on the foreshore of an estuarine sand beach in Delaware Bay, New Jersey, USA were evaluated using data collected over six consecutive high tides. Data were gathered inside and outside a 25 m long exclosure constructed to create a control area free of disturbance by crabs. The density of crabs in the swash zone outside the exclosure was 8·1 organisms m−2. The maximum depth of sediment activation on the upper foreshore where spawning occurred was 0·103 m during periods characterized by low significant wave heights: < 0·08 m. This depth is greater than the depth of activation by waves alone during moderate significant wave heights of 0·16–0·18 m but less than the maximum depth (0·127 m) recorded when spawning occurred during periods of moderate wave heights. Spawning, combined with moderate wave heights, creates a concave upper foreshore that is similar to the type of profile change that occurs during storms, thus lowering the wave-energy threshold for morphological response. Spawning during low wave heights increases the mean grain size and sorting of surface sediments caused by the addition of gravel to the swash. Sedimentological differences are most pronounced on the upper foreshore, and data from this location may be most useful when using grain-size characteristics to interpret the effect of spawning in the sedimentary record. Depths of sediment reworking by horseshoe crabs can be greater than those by subsequent storm waves, so evidence of spawning can be preserved on non-eroding beaches. Greater depth of activation by horseshoe crab spawning than by waves alone, even during moderate-energy conditions, reveals the importance of crab burrowing in releasing eggs to the water column and making them available for shore birds.  相似文献   

17.
A 97-day-long record on waves and currents was obtained using wave rider buoy and current meter moored at 2.5 km off Gopalpur from 19 May to 23 August 2008 representing southwest monsoon months. A Valeport tide gauge was used to record water level at Gopalpur port. Simultaneously, beach profiles at 4 transects were monitored using real-time kinematic (RTK) global positioning system (GPS). A total of 636,167 waves were analyzed for the period; a range of 3,200–9,700 waves approach the coast in an individual day. During the study, unusual characteristics of wave were observed on July 29, 2008, with a magnitude of significant wave height, Hs = 2.85 m, maximum wave height, Hmax = 5.22 m, and peak wave period, Tp = 10.2 s, and on August 11, 2008, with Hs = 2.28 m, Hmax = 5.37 m, and Tp = 11.1 s. Significant beach loss was noticed during these periods, and severe erosion was recorded on August 1, 2008. Beach profile data indicates that 18–58 cu. m/m sediment was lost during the study period. The paper provides an overview of the statistical analysis of wave heights, periods, direction, and spectral energy density and explains the cause of coastal erosion and loss of sediment.  相似文献   

18.
Shoreline changes are largely dependent on coastal morphology. South-west coast of India is a high energy coast characterised by monsoon high waves, steep beach face and medium-sized beach sand. Waves are generally from west and west south-west during rough monsoon season and from south-west during fair weather season. Shoreline change along this coast is studied with reference to coastal morphological features. Various morphological features, modifications and chronological positions of shoreline are analysed with the information derived from multidated satellite imageries, toposheets and GPS shoreline mapping along with extended field survey. Image processing and GIS techniques have been used for the analysis of data and presentation of results. Sediment accumulation on the leeward side of artificial structures such as harbour breakwaters and groynes is used as a sediment transport indicator. Artificial structures such as seawalls, groynes and harbour breakwaters modify morphology. Shoreline south of headlands/promontories and breakwaters are stable or accreting due to net northerly longshore sediment transport while erosion tendency is observed on the north side. Lateritic cliffs fronting the sea or with seasonal beach undergo slumping and cliff edge retreat as episodic events. Spits adjoining tidal inlets are prone to shoreline variations due to oscillations of inlet mouth. Interventions in the form of inlet stabilization and construction of coastal protection structures trigger erosion along adjoining coasts. Seawalls constructed along highly eroding coasts get damaged, whereas those constructed along monsoon berm crest with frontal beaches for protection against monsoon wave attack are retained. Fishing gaps within seawalls are areas of severe temporary erosion during rough monsoon season. Accretion or erosion accompanies construction of harbour breakwaters in a stable coastal plain. Close dependence of shoreline changes on morphology necessitates detailed understanding of impacts on morphology prior to introducing any intervention in the coastal zone.  相似文献   

19.
Devastating tsunami waves can change the coastal morphology considerably. The effects of vegetation to coastal morphodynamics have been of primary interest for decades, because of their role in coastal protection and ecological environment. The damping of wave and impact of beach evolution are the two significant contributions on emerged vegetation. However, the laboratory study of tsunami erosion and deposition under protection of coastal vegetation was less understood compared to tsunami run-up and tsunami inundation. A set of laboratory experiments were reported in this study on changes of size-selective sandy beach profile under the protection of rigid emergent vegetation. The total of fifteen experiments was carried out in a wave flume including two initial profiles (with vegetation and none vegetation), three different wave conditions and four forest densities. The experiments show that rigid emergent vegetation changes the depth and location of tsunami deposition and erosion in sandy beach. The dimensionless numbers were derived to characterize the cross-shore beach profile response under the protection of rigid emergent vegetation. These parameters were written as a dimensionless group, and based upon this present experimental datum, the empirical equations were developed. The study reveals the internal connection among tsunami deposition and erosion, wave height and forest density. The findings of this study have the potential to assist the tsunami hazards prevention and mitigation.  相似文献   

20.
The responses of a sandy beach to the southwest monsoonal waves are studied based on biweekly observations. The onslaught of the first spell of monsoonal breakers causes maximum erosion in the sub-aerial section of the beach. However, further spells of high breakers do not affect this zone significantly. The erosion in the sub-aerial zone is followed by accretion in the nearshore zone and vice versa. Whereas the sub-aerial zone has a net erosion the total section of the beach including the nearshore zone shows near equilibrium condition. It is concluded that in spite of erosion or accretion of the sub-aerial zone, equilibrium conditions may be found in the total section of the beach.  相似文献   

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