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1.
盐沼的侵蚀、堆积和沉积动力 总被引：16，自引：0，他引：16
最近国外对盐沼侵蚀、堆积过程进行了较深入细致的研究,取得了很大进展,主要包括野外短尺度详细的沉积过程观测,室内物理模拟的尝试和数学模拟的不断应用,本文对此作了综述。这将加深人们对盐沼如何响应海平面、潮型、泥沙供给和波浪气候变化的认识。 相似文献
2.
Theoretical constraints and chronological evidence of Holocene coastal development in central and southern New South Wales, Australia 总被引：3，自引：0，他引：3
Holocene coastal evolution in New South Wales has been interpreted essentially as the unfolding of the impact of marine transgression. Sea level on this coast supposedly reached its present height at 6–6.5 ka, and varied < 1 m since then. The early Holocene rise of the sea has been considered the key factor (“forcing function”) in dune migration, coastal sand barrier development, and the evolution of estuaries. Episodic storminess during the late Holocene has been seen as an important, though secondary, factor in beach erosion and dune mobilisation. An alternate interpretation presented here challenges the concept of the marine transgression as the primary “forcing function”. It (a) attributes early Holocene dune mobilisation to climate rather than the rising sea; (b) shows that the sea reached its present level by 7 ka and rose to at least + 2 m until 1.5 ka; (c) links late Holocene dune activity to local disruption of vegetation rather than to regional episodic storminess; (d) demonstrates a fall of 2°C in sea surface temperature after 3 ka that coincides with the onset of barrier erosion; (e) recognises the imprint of at least three tsunamis in the coastal sedimentary record. 相似文献
3.
After ~ 11,000 years of glacio-isostatically induced forced regression, geomorphological evidence indicates that the coastline of eastern Melville Island, western Canadian Arctic Archipelago, is now being transgressed. Recently developed coastal features associated with this transgression include: drowned gullies and small estuaries, barriers and lagoons, barrier islands, erosional notches, backstepping beaches, and drowned tundra vegetation and vehicle tracks dating from the 1970s. We mainly attribute this relative sea-level rise to the eastward migration of a peripheral crustal forebulge. Furthermore, the reported transgression also includes a component from recent eustatic sea-level rise during the 20th century. Recent earthquakes recorded in the Gustav-Lougheed Arch Seismic Zone located in Byam Martin Channel, 70 km east of Melville Island, suggest that neotectonics could also be involved in local relative sea-level adjustments. Other factors associated with global warming, especially the formation of an earlier shore-ice lead coupled with increased storm activity might also be responsible for some of the coastal changes. Our study indicates that the current zero isobase, separating areas of net transgression from those of net regression, is now located off the east coast of the island. Our field observations support recent glacio-isostatic modelling that shows the island is presently undergoing a transgression. 相似文献
4.
Monitoring of frontal dune erosion and accretion on the Sefton coast in northwest England over the past 50 years has revealed significant spatial and temporal variations. Previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology, energy regime and sediment budget, but the causes of temporal variations have not previously been studied in detail. This paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms, surges and resulting high tides. Dune toe erosion/accretion records dating from 1958 have been compared with tide gauge records at Liverpool and Heysham. Relatively high dune erosion rates at Formby Point 1958–1968 were associated with a relatively large number of storm tides. Slower erosion at Formby, and relatively rapid accretion in areas to the north and south, occurred during the 1970's and 1980's when there were relatively few major storm tides. After 1990 rates of dune erosion at Formby increased again, and dunes to the north and south experienced slower accretion. During this period high storm tides have been more frequent, and the annual number of hours with water levels above the critical level for dune erosion has increased significantly. An increase in the rate of mean sea-level rise at both Liverpool and Heysham is evident since 1990, but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms. The incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle, but the evidence indicates that meteorological forcing has also had a significant effect. Storms and surges in the eastern Irish Sea are associated with Atlantic depressions whose direction and rate of movement have a strong influence on wind speeds, wave energy and the height of surge tides. However, preliminary analysis has indicated only a modest relationship between dune erosion/accretion rates and the North Atlantic Oscillation index. 相似文献
5.
海平面上升与海滩侵蚀 总被引：27，自引：1，他引：27
世纪性的海平面持续上升，加大了海岸水下斜坡深度，逐渐减小波浪对沉溺古海岸的扰动作用而形成海底的横向供沙减少，却加强激浪对上部海滩的冲刷。逐渐上升的海平面，降低了河流坡降而减少了入海沙量。因此世界海滩普遍出现沙量补给匮乏。海平面上升伴随着厄尔尼诺现象与风暴潮频率的增加，水动力加大。这两者的综合效应，使海滩遭受冲刷，沙坝向陆移动。如按ＩＰＣＣ估计，至２１００年海面上升５０ｃｍ时，中国主要旅游海滨的沙滩将损失现有面积的１３％─６６％。主要对策是海岸防护与海滩人工喂养。 相似文献
6.
Sediment-rich estuaries typically exhibit considerable dynamicity, with channel shifts and shoreline erosion/deposition occurring over timescales of years to decades. Contemporary behaviour is usually attributed to the immediate effect of short-term events (such as storms), longer-term forcing (such as sea-level change) or anthropogenic modifications to system controls (such as wave–tidal–fluvial regime and sediment supply). In this context, geological control is understood to provide an inherited framework within which an estuary will evolve. This paper examines the morphodynamics of two sand-filled, but sediment-limited, mixed-energy estuaries of Loughros Bay in northwest Ireland. Analysis of ebb channel morphometry shows that estuaries can be divided into upper and lower estuary components, which appear to represent a down-valley increasing energy gradient. Examination of historical ebb channel migration reveals three morphodynamic zones delimited by a significant spatial variability in channel mobility that reflects the distribution of specific structural controls along the estuary and their influence on the changing energy gradient. Based upon analysis of low tide channel migration over the last 172 years, three phases of geomorphic response are identified. In Loughros More, the behaviour is characterised by a 19th century phase of steady-state equilibrium; a subsequent period of dynamic response to extrinsic (storm) forcing; and, most recently, adjustment to intrinsically forced changes in structural control. In Loughros Beg, the phases are comparable, but contrast specifically in inlet and ebb-tidal behaviour. This analysis illustrates discontinuities in decadal- to century-scale forcing and morphological response, identified here as complex response. It suggests that the sedimentary evolution of coastal systems that have no appreciable external sediment supply is potentially more strongly determined by local variability in system character than climate or sea-level driven mechanisms. 相似文献
7.
We established sediment geochronologies for cores from eight deltaic areas in Lake Tanganyika (the Lubulungu, Kabesi, Halembe, Malagarasi, Nyasanga/Kahama, Mwamgongo, Nyamusenyi, and Karonge/Kirasa River deltas), recording a range of watershed disturbance histories from the eastern margin of this African rift valley lake. Cores from currently disturbed sites on the central Tanzanian coast display remarkably uniform and low rates of sediment accumulation from the 18th century until the early 1960s, when a synchronous and dramatic rise in rates occurs. Through this same time interval sedimentation rates offshore from undisturbed Tanzanian watersheds either remain unchanged or decline. Further north, at disturbed sites along the northern Tanzania and Burundi coasts, the pattern of sedimentation rate increase is more complex. Although a mid-late 20th century increase is also evident in these sites, indications of earlier periods of increasing sediment erosion, dating from the mid-late 19th century, are also evident. Synchronous changes in sediment accumulation rates dating from the early 1960s may be the result of exceptionally wet years triggering an increase in the discharge of previously eroded and unconsolidated alluvium and stream/beach terrace deposits, previously accumulated in the deltas and stream valleys of impacted watersheds. Sedimentation rate impacts of deforestation on lake ecosystems are likely modulated by short-term climatic forcing events, which can impact the specific timing and location of sediment discharge to lakes. 相似文献
8.
海平面上升的灾害效应研究--以江苏沿海低地为例 总被引：8，自引：6，他引：8
海平面上升是全球变暖和沿海地区人类活动加剧的必然结果,其灾害效应直接影响沿海地区社会经济的持续发展。文章运用地面沉降与绝对海面变化叠加法和潮位记录法,预测未来30年,50年和100年江苏沿海海平面将分别上升0.30 m,0.53 m和1.37 m。在此基础上,对不同海平面上升量引起的风暴潮灾害、海岸侵蚀、潮滩盐沼损失、涵闸破坏、洪涝灾害加剧和海堤工程受损等方面的灾害效应进行了定量分析,并对江苏沿海低地进行分区灾害预警,认为海平面上升后的灾害效应在江苏中部海积平原表现得最为严重,废黄河三角洲平原和长江三角洲平原中等,而海州湾海积平原最轻。 相似文献
9.
近百年广东沿海海平面变化趋势 总被引：5，自引：3，他引：2
为预估本世纪末广东海平面的可能上升量,从探讨近百年来广东海平面上升率的阶段性变化入手,通过对广东沿海验潮站潮位观测资料的统计分析,得出广东沿海海平面近86年(1925-2010年)、近40年(1970-2010年)和近20年(1993-2010年)的上升率分别为2.1 mm/a、2.5 mm/a和3.2 mm/a,存在加速上升的趋势,并与全球大体呈准同步变化.20世纪90年代以来,广东沿海海平面上升和热带西太平洋的海平面出现突变上升有密切关系. 相似文献
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11.
Coastal defence and the Habitats Directive: predictions of habitat change in England and Wales 总被引：2，自引：0，他引：2
Mark Lee 《The Geographical journal》2001,167(1):39-56
Future coastal defence policies and 'natural' processes will have an impact on habitats within Special Areas of Conservation (SAC), Special Protection Areas (SPA) and Ramsar sites. An overview of the potential nature and extent of these changes (losses or gains over the next 50 years) around the coast of England and Wales was carried out to inform policy decisions on the legal and funding aspects of coastal defence options and possible habitat replacement. It is predicted that there could be a net loss of freshwater and brackish habitat of around 4000 hectares, together with a net gain of intertidal (saltmarsh and mudflat/sandflat) habitats of around 770 hectares, with the gains associated with managed retreat ( c .12 500 ha) balancing the expected losses due to coastal squeeze and erosion on the unprotected coast. The likely costs of freshwater and brackish habitat replacement, on a hectare-for-hectare basis, is estimated to be in the order of £50–60 million, including site purchase, set-up and on-going management costs. 相似文献
12.
海平面上升对长江三角洲和苏北滨海平原海岸侵蚀的可能影响 总被引：33，自引：5，他引：33
本区海岸现有30％的岸段为侵蚀海岸,海平面上升将使海岸侵蚀加剧。海平面上升因素在海岸侵蚀诸因素中的比重较国外同类研究结论偏小,这与本区海岸的特殊演变原因有关。海平面上升通过潮流、波浪和风暴潮作用增强,海岸潮滩和湿地损失,岸滩消浪和抗冲能力减小等途径引起海岸侵蚀加剧。其结果是,侵蚀岸段扩大,淤涨岸段减少甚至转为侵蚀,潮间带宽度变窄,坡度加大,从而使沿岸海堤等挡潮工程的标准要相应提高。 相似文献
13.
江苏海岸侵蚀过程及其趋势 总被引：51，自引：2，他引：51
江苏省侵蚀海岸的总长度为 30 1 7km ,分为 4段 :废黄河三角洲海岸、港海岸、吕四海岸以及海州湾的沙质海岸。各段海岸侵蚀原因不同。废黄河三角洲海岸是因黄河改道失去泥沙来源 ;吕四与港海岸则因辐射沙洲调整过程中滨岸水道的向岸移动造成的 ;而北部沙岸则是因人类活动 (上游建设水库及开挖海滩沙 )的干扰。江苏海岸是一个沉积物准封闭系统 ,全球性海平面上升将加剧这一侵蚀过程 ,预计未来侵蚀海岸的长度将增加 ,辐射沙洲区的外围沙洲将因侵蚀而向中心区退缩。一些目前是隐型侵蚀的岸段将向显性侵蚀的阶段发展。由于连云港到长江口北支的岸段是软性海岸 ,缺乏硬质节点 ,在没有建造大型人工设施的前提下 ,估计江苏海岸动态及制定开发规划时必须考虑平直化的大趋势。 相似文献
14.
基于模糊数学的广东沿海陆地地质环境区划 总被引：5，自引：0，他引：5
针对广东沿海地震、水土流失、崩塌、滑坡、地裂缝、地面沉降、岩溶塌陷、软土地基形变等地质灾害发育历史与现状 ,从土地开发利用的风险与费用出发 ,构建了一套地质环境评价的指标体系 ,包括活动断裂、历史地震、地形起伏度、地形坡度、沟谷密度、水土流失程度、崩滑密度、地裂缝密度、土体承载力等。通过指标量化分级、指标赋权和构造隶属函数 ,构建了模糊数学综合评价模型 ,对广东沿海 190单元进行了运算 ,将广东沿海陆地地质环境划分五级 17个亚区 ,为广东沿海2 1世纪土地开发利用和防灾减灾等提供了决策依据。 相似文献
15.
Where Have All the Beaches Gone? Coastal Erosion In The Tropics 总被引：1，自引：0，他引：1
P.P. Wong 《Singapore journal of tropical geography》2003,24(1):111-132
From a physical geography perspective, tropical coasts are characterised by coral reefs, mangroves and carbonate beaches on atolls and low reef islands. They face threats not only from sea level rise, but also from human activities that destroy mangroves, degrade coral reefs and accelerate beach erosion. Physical conditions in the tropics are suitable for the ideal tourist beach. Conceptually, the tourist coast can be considered as the integration of a physical system (the coast) and a human system (tourism). Studies have been carried out on various types of tourist coasts in Southeast Asia. For many atoll island states, sea level rise is more than just a threat to their tourism; it also determines their survival. In recent years, assessments of their vulnerability and adaptation have favoured a more integrative approach of physical and human sciences. Hopefully, this should result in a better analytical tropical geography that could play an important role in reducing coastal erosion and assist the small island states. 相似文献
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17.
Over the past century the cultural and physical landscape of the Shire of Denmark on the south coast of Western Australia has been transformed by successive waves of in-migrants. The paper examines the period since the early 1970s when alternative lifestylers and early retirees, attracted by the district's natural beauty and low land prices, began moving in and acquiring former Group Settlement holdings. The activities of these and subsequent 'alternatives' and 'cashed out' early retirees settling in the district have raised the marketability of the Shire's cultural capital. These changes have occurred in association with broader processes of rural restructuring and changing notions of 'rurality'. Increasingly, Denmark's cultural and physical landscape has become a highly marketable product for consumption by Perth's affluent middle classes. In recent years land prices have risen rapidly as speculators and financiers seek to 'cash in' on the 'cashed out' society. The paper explores these issues and relates them to broader processes of economic and social change occurring at the national and international levels. 相似文献
18.
Vance T. Holliday 《Geomorphology》1990,3(3-4)
Sheets of eolian sediment cover many areas of the earth's surface, sand seas, dune fields, and loess sheets being the best known examples of such features. Less well known are deposits of sandy, eolian sediment forming extensive plains. An excellent example of such a region is the semi-arid Southern High Plains (northwest Texas and eastern New Mexico). The level landscape of the area was created by deposition of multiple, extensive (≈ 80,000 km2) sheets of eolian sediment (Blackwater Draw Formation) over the past 1.4+ Ma. This deposit grades from sandy (southwest) to silty and clayey (northeast) and is up to 27 m thick. Surface soils (at least 30,000 and possibly 120,000 years old) are well developed (5YR hues, agrillic horizons, 1–2m thick with prismatic structure, Stage II–III calcic horizons) and are generally Paleustolls and Paleustalfs, with some Paleargids and Haplargids. Morphologic variation is due mainly to textural variation of the eolian parent material, although locally thickness of the parent material and wind erosion and cumulization are important factors, and locally slight variation in effective precipitation may be significant. The Blackwater Draw Formation contains as many as six well-developed buried soils, each formed in individual layers of eolian sediment, similar to or more strongly expressed (2.5YR hues, higher illuvial clay content) than the regional surface soils. The presence of the buried soils indicates that sedimentation was episodic and separated by long periods of relative landscape stability. Eolian processes also appear to have been important during the periods of stability and pedoenesis by providing clayey, calcareous dust that was added to the soil, promoting formation of the argillic and calcic horizons. The sedimentologic and pedologic uniformity of the deposit suggests that the regional environment has not varied significantly during the Quaternary except for periods of increased sedimentation or wind deflation. Underlying the Blackwater Draw Formation is an Upper Tertiary deposit (up to 36 m thick) of eolian sand, silt, and clay (Ogallala Formation). This deposit contains buried soils very similar to those in the Blackwater Draw Formation, suggesting that the geomorphic processes that created the Quaternary landscape of the Southern High Plains began to operate in the late Tertiary, perhaps as much as 11 million years ago. 相似文献
19.
Are assemblages of black bream (Acanthopagrus butcheri) in different estuaries genetically distinct?
J.A. Chaplin G.A. Baudains H.S. Gill R. Mcculloch I.C. Potter 《International Journal of Salt Lake Research》1997,6(4):303-321
Samples of the estuarine-spawning teleostAcanthopagrus butcheri were collected from nine estuaries and a coastal lake, located in the Pilbara and South-western drainage divisions of Western
Australia and distributed along a coastline covering a distance of nearly 2,000 km. The patterns of allozyme variation in
these samples were used to explore the extent to which there was variation in the genetic compositions of black bream assemblages
in geographically-isolated estuarine systems, and whether or not any such variation could be related to the geographical location
or type of estuary. Although only three of 36 scorable loci (Gpi-1, Ldh andMdh-2) exhibited variation that could be used for analysis, there was considerable variation in allele frequencies at these loci
among the different samples (mean FST=0.166). Much of the detected variation was attributable to differences between the samples collected from the two drainage
divisions, which are located in very different climatic regions. Furthermore, the genetic compositions of samples from neighbouring
estuaries were typically more similar to each other than to those of samples collected from more distantly-located systems.
However, the assemblages in one west coast and two south coast estuaries, that are closed to the ocean for extensive periods
of time during the year, all showed very similar genetic compositions. Nevertheless, it is crucial to recognise that, pairwise
comparisons of samples collected from the different estuaries, both within and between the two drainage divisions, almost
invariably showed statistically significant differences in allele frequencies at one or more loci. Thus, our results indicate
that the local populations of black bream in individual estuaries are genetically distinct, which is probably a consequence
of both a limited movement by individuals between estuaries and the effects of differences in regional and local environmental
conditions. 相似文献
20.
《Geomorphology》2006,73(1-2):64-77
Retreat of the clay and sandstone cliffs of the northern Boulonnais (France) has been quantified using stereophotogrammetry. The low retreat rate of this coastal strip — 0.08 m/yr between 1939 and 2003 — is far less than that encountered on chalk and clay-chalk cliffs of either side of the Channel, and even less than a previous estimate of 0.17 m/yr regularly quoted in management studies. The retreat rate is closely related to shore platform morphology and dynamics. The shore platform presents 1) a steeply sloping ramp due to the accumulation of flat calcareous megaclasts that reduce marine erosion; 2) upstanding bare platform surfaces, related to tectonic deformation; and 3) thick platform-beaches trapped in troughs. In all three cases, the reflective behaviour of the nearshore protects the cliff foot from the incoming waves. Two critical eroding segments are the result of changes in the platform sedimentary budget. Around Cran Poulet, and between Plage de la Sirène and Pointe de la Courte Dune, the retreat rate is up to 0.25 and 0.15 m/yr, respectively. At Cran Poulet, recession has been facilitated by the extraction of pebble for more than half a century, whereas erosion of the beach at la Sirène is probably linked to severe erosion of the coastline in the adjacent Wissant Bay. Mass movements on the cliff face are essentially shallow-seated translational slides along with small debris falls and mudflows. The instability of the Argiles de Châtillon is greatly diminished by their sandy and silty texture and by the presence of interstratified solid shelly limestone beds that allow steep slopes to develop in rather weak material. The ‘vertical erosion antecedent’ is the erosional mode of the cliff, and its reduced efficiency explains the slow recession of the cliff. This study will help to determine the long term evolution of the Boulonnais coast. 相似文献