杭州湾南岸庵东潮坪现代沉积特征     

徐建卿  邵虚生 《上海国土资源》1988,(2)

在进行庵东潮坪水文要素定点测量的基础上,对地貌特征,沉积粒度,沉积构造及重向剖面作了全面分析与研究。结果表明,滩地位于杭州湾进、退潮流的交会点,控制其发育的主动力为潮汐作用,具明显的不规则半日潮特性,涨潮流强度远大于落潮流,造就了宽达十余公里的潮滩地貌。滩地水动力深受湾内水流影响,高潮期服从其总体潮流流向,导致潮坪上发育众多与杭州湾深槽系统相连的潮沟,破坏了沉积物正常分布规律,高潮坪存在一定向平行岸线的大型潮沟,受强劲水流影响,沉积粒度粗化,并因快冲快淤而产生变形构造;中潮坪接受退潮期潮沟漫岸物质,粒度相对较小,分选性变差,沉积构造以直脊流水波痕及板状交错层理为主;低潮坪潮流作用大、沉积粒度粗,分选性最佳,发育小型流水波痕,内部构造以槽状交错层理,“青鱼刺”层理及再作用构造为特征。潮坪近岸处潮沟迁移层序及浪成波痕层理的发现反映水动力异常强大,威胁人工海塘的安全,建议停止进一步围垦滩涂,采取促淤方法,抑制潮沟的发育,以维持滩地稳定。  相似文献   

A morphodynamic model for beach gradients     

J. Hardisty 《地球表面变化过程与地形》1986,11(3):327-333

This paper outlines a general framework for analysis of the problem of beach gradients which divides the system into: (1) the independent controls, (2) the hydrodynamics, (3) the sediment dynamics, and (4) the morphodynamics. A model is derived from the combination of these stages which shows close agreement with field data for wave steepnesses of less than about 0.06, but predicts lower beach gradients than arc observed for steeper waves. The use of ‘analytical feedback’ in the present model rather than the ‘iterative feedback’ which is used in computer simulations demonstrates that differential sediment transport may be responsible for stabilizing the beach gradient.  相似文献   

Municipal initiatives for managing dunes in coastal residential areas: a case study of Avalon, New Jersey, USA     

Karl F. Nordstrom  Nancy L. Jackson  Michael S. Bruno  Harry A. de Butts 《Geomorphology》2002,47(2-4)

The characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values. Shoreline management zones include a naturally evolving, undeveloped segment; a noneroding, developed segment; eroding and noneroding segments of an “improved beach” where dunes have been built by artificial nourishment; and a privately built, artificially nourished dune on the shoreline of an inlet.A disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences, vegetation plantings, purchase of undeveloped lots, and sediment backpassing to maintain beach widths and dune elevations. The present nourished and shaped foredune in the improved beach is higher, wider, and closer to the berm crest than the natural dune. Restricted inputs of aeolian sand keep the surface flat and poorly vegetated. A stable section of this engineered shore has a wider beach, and sand fences have created a higher foredune with greater topographic diversity. The cross shore zonation of vegetation here is more typical of natural dunes, but the environmental gradient is much narrower. The privately built dune is low, narrow, and located where it could not be created naturally. Foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size (0.16–0.21 mm) and sorting (0.31–0.39φ), but sediment on the surface of the nourished dune is coarser (28.1% gravel) with a more poorly sorted sand fraction (1.30φ) representing lag elements on the deflation surface.Willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the Federal Emergency Management Agency (FEMA) to replace lost sediment, thus placing an economic value on dunes. Success of the management program is attributed to: (i) timing property-purchase and dune-building programs to periods immediately after storms (causing residents to accept high dunes that restrict access or views); (ii) instituting a vigorous education program (reminding residents of hazards during nonstorm periods); (iii) maintaining control over local sediment supplies (to keep pace with erosion and create new shoreline environments); (iv) investing private and municipal economic resources in landforms (qualifying them for external funds for replacement); and (v) maintaining, augmenting, or simply tolerating biodiversity and natural processes (retaining a natural heritage).  相似文献   

Distribution and sources of surfzone bacteria at Huntington Beach before and after disinfection on an ocean outfall-- a frequency-domain analysis     

Noble MA  Xu JP  Robertson GL  Rosenfeld LK 《Marine environmental research》2006,61(5):494-510

Fecal indicator bacteria (FIB) were measured approximately 5 days a week in ankle-depth water at 19 surfzone stations along Huntington Beach and Newport Beach, California, from 1998 to the end of 2003. These sampling periods span the time before and after treated sewage effluent, discharged into the coastal ocean from the local outfall, was disinfected. Bacterial samples were also taken in the vicinity of the outfall during the pre- and post-disinfection periods. Our analysis of the results from both data sets suggest that land-based sources, rather than the local outfall, were the source of the FIB responsible for the frequent closures and postings of local beaches in the summers of 2001 and 2002. Because the annual cycle is the dominant frequency in the fecal and total coliform data sets at most sampling stations, we infer that sources associated with local runoff were responsible for the majority of coliform contamination along wide stretches of the beach. The dominant fortnightly cycle in enterococci at many surfzone sampling stations suggests that the source for these relatively frequent bacteria contamination events in summer is related to the wetting and draining of the land due to the large tidal excursions found during spring tides. Along the most frequently closed section of the beach at stations 3N-15N, the fortnightly cycle is dominant in all FIBs. The strikingly different spatial and spectral patterns found in coliform and in enterococci suggest the presence of different sources, at least for large sections of beach. The presence of a relatively large enterococci fortnightly cycle along the beaches near Newport Harbor indicates that contamination sources similar to those found off Huntington Beach are present, though not at high enough levels to close the Newport beaches.  相似文献   

半遮蔽型海滩剖面长期时空演化过程的经验正交函数分析     

梁伟强  王永红 《海洋与湖沼》2021,52(4):834-845

半遮蔽型海滩由于一侧海岬的差异作用而影响海滩的演变过程。本文以青岛石老人海水浴场海滩为例,基于对3条典型剖面连续11年现场监测的高程数据,利用经验正交函数(empirical orthogonalfunction,EOF)分析方法将该海滩各剖面高程数据组成的原始距平矩阵依次分解为相应的空间和时间特征函数,分析了石老人海滩的形态演化特征、蚀淤趋势及驱动因素,并采用方差总占比超过77%的前3个经验正交函数来反映此类海滩的基本演化情况,分别为:表征长时间尺度砂质海滩滩面最主要蚀淤变化趋势的第一模态、表征季节性蚀淤变化及其引起的滩肩剖面形成增长或削弱消亡的第二模态和表征人类活动、偶发因素或海岸地形等引起的具有随机性的不规律蚀淤变化的第三模态。结果表明:11年来石老人海滩经历了三个阶段,第一阶段为平稳期(2009年1月—2011年7月),第二阶段为突变期(2011年7月—2012年9月),该阶段之后至今,是第三阶段的平稳期(2012年9月—2019年12月)。海滩剖面在自然和人类活动影响下的高程变化范围在0.1—2.0m范围内。波浪是影响该海滩形态演化的最主要水动力因素,岬角对半遮蔽型海滩的差异庇护作用导致不同位置的剖面演化存在差异。高频率台风的影响、海平面阶段性升高并长期保持较高水平导致了远离岬角的开放岸段存在明显阶段性调整,剖面滩肩宽度减少约30m,岬湾内部剖面则相对稳定,目前海滩剖面形态在第二阶段突变期后达到了新的稳定状态。  相似文献   

Coastal landscape evolution tracked from late Holocene wave-cut benches in the Sinan Archipelago,Southwest Korea     

Sung-Ja Choi  Bokchul Kim  Yong Sik Gihm  Sanghoon Kwon 《地学前缘(英文版)》2020,11(1):293-301

Glacio-isostatic adjustment(GIA)and tectonic activity are important factors in the formation of marine terraces.Late Holocene wave-cut benches in the eastern part of the West Sea of Korea,also called the Yellow Sea,can be divided into two steps:531 cm above sea level(ASL)for the upper bench(T2)and 464-481 cm ASL for the lower bench(T1).Sediments on the benches a re classified into four units,and are interpreted to be beach deposits acco rding to gravel shape,textu re,and seaward inclination.The ove rlying sediment indicates that T2 was formed at approximately 530 cm ASL before 2900 yr BP,and T1 at approximately 460-480 cm ASL before 1520 yr BP.Late Holocene(4000-2000 yr BP)relative sea level(RSL)curves based on GIA models are inconsistent with the wave-cut bench elevations.Comparing T1 and T2 benches to the RSL curves of the West Sea,the upper and the lower benches were uplifted by approximately 5-8 m and 4-7 m,respectively.Although the area is several hundred kilometers away from plate boundaries,the high frequency of earthquakes in the West Sea may have induced the uplift of wave-cut benches during the last 2000 years.These indicate that the west coast of the Korean Peninsula(KP)should no longer be considered an area of subsidence,but be assigned to a regime of uplift during the late Holocene.  相似文献   

Statistical simulation of wave climate and extreme beach erosion     

D.P. Callaghan  P. Nielsen  A. Short  R. Ranasinghe 《Coastal Engineering》2008

Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.  相似文献   

Evaluation of the physical process controlling beach changes adjacent to nearshore dredge pits     

L. Benedet  J.H. List   《Coastal Engineering》2008,55(12):1224-1236

Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion.  相似文献   

Coastal morphodynamics and Chenier-Plain evolution in southwestern Louisiana, USA: A geomorphic model   总被引：1，自引：0，他引：1  

Randolph A. McBride  Matthew J. Taylor  Mark R. Byrnes 《Geomorphology》2007,88(3-4):367-422

Using 28 topographic profiles, air-photo interpretation, and historical shoreline-change data, coastal processes were evaluated along the Chenier Plain to explain the occurrence, distribution, and geomorphic hierarchy of primary landforms, and existing hypotheses regarding Chenier-Plain evolution were reconsidered. The Chenier Plain of SW Louisiana, classified as a low-profile, microtidal, storm-dominated coast, is located west and downdrift of the Mississippi River deltaic plain. This Late-Holocene, marginal-deltaic environment is 200 km long and up to 30 km wide, and is composed primarily of mud deposits capped by marsh interspersed with thin sand- and shell-rich ridges (“cheniers”) that have elevations of up to 4 m.In this study, the term “ridge” is used as a morphologic term for a narrow, linear or curvilinear topographic high that consists of sand and shelly material accumulated by waves and other physical coastal processes. Thus, most ridges in the Chenier Plain represent relict open-Gulf shorelines. On the basis of past movement trends of individual shorelines, ridges may be further classified as transgressive, regressive, or laterally accreted. Geomorphic zones that contain two or more regressive, transgressive, or laterally accreted ridges are termed complexes. Consequently, we further refine the Chenier-Plain definition by Otvos and Price [Otvos, E.G. and Price, W.A., 1979. Problems of chenier genesis and terminology—an overview. Marine Geology, 31: 251–263] and define Chenier Plain as containing at least two or more chenier complexes. Based on these definitions, a geomorphic hierarchy of landforms was refined relative to dominant process for the Louisiana Chenier Plain. The Chenier Plain is defined as a first-order feature (5000 km²) composed of three second-order features (30 to 300 km²): chenier complex, beach-ridge complex, and spit complex. Individual ridges of each complex type were further separated into third-order features: chenier, beach ridge, and spit.To understand the long-term evolution of a coastal depositional system, primary process–response mechanisms and patterns found along the modern Chenier-Plain coast were first identified, especially tidal-inlet processes associated with the Sabine, Calcasieu, and Mermentau Rivers. Tidal prism (Ω) and quantity of littoral transport (M_total) are the most important factors controlling inlet stability. Greater discharge and/or tidal prism increase the ability of river and estuarine systems to interrupt longshore sediment transport, maintain and naturally stabilize tidal entrances, and promote updrift deposition. Thus, prior to human modification and stabilization efforts, the Mermentau River entrance would be classified as wave-dominated, Sabine Pass as tide-dominated, and Calcasieu Pass as tide-dominated to occasionally mixed.Hoyt [Hoyt, J.H., 1969. Chenier versus barrier, genetic and stratigraphic distinction. Am. Assoc. Petrol. Geol. Bull., 53: 299–306] presented the first detailed depositional model for chenier genesis and mudflat progradation, which he attributed to changes in Mississippi River flow direction (i.e., delta switching) caused by upstream channel avulsion. However, Hoyt's model oversimplifies Chenier-Plain evolution because it omits ridges created by other means. Thus, the geologic evolution of the Chenier Plain is more complicated than channel avulsions of the Mississippi River, and it involved not only chenier ridges (i.e., transgressive), but also ridges that are genetically tied to regression (beach ridges) and lateral accretion (recurved spits).A six-stage geomorphic process-response model was developed to describe Chenier-Plain evolution primarily as a function of: (i) the balance between sediment supply and energy dissipation associated with Mississippi River channel avulsions, (ii) local sediment reworking and lateral transport, (iii) tidal-entrance dynamics, and (iv) possibly higher-than-present stands of Holocene sea level. Consequently, the geneses of three different ridge types (transgressive, regressive, and laterally accreted) typically occur contemporaneously along the same shoreline at different locations.  相似文献   

Geomorphic and sedimentologic evidence for the separation of Lake Superior from Lake Michigan and Huron     

John W. Johnston  Todd A. Thompson  Douglas A. Wilcox  Steve J. Baedke 《Journal of Paleolimnology》2007,37(3):349-364

A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics. Strandplains were divided into lakeward and landward sets of beach ridges using aerial photographs and topographic surveys to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation-trend changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Superior. Correlation of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred sometime after about 2,400 calendar years ago (after the Algoma phase). Age model results from one site (Grand Traverse Bay) suggest an alternate age closer to about 1,200 calendar years ago but age models need to be investigated further. The landward part of the strandplain was deposited when water levels were common in all three upper Great Lakes basins (Superior, Huron, and Michigan) and drained through the Port Huron/Sarnia outlet. The lakeward part was deposited after the Sault outlet started to help regulate water levels in the Lake Superior basin. The landward beach ridges are commonly better defined and continuous across the embayments, more numerous, larger in relief, wider, have greater vegetation density, and intervening swales contain more standing water and peat than the lakeward set. Changes in drainage patterns, foreshore sediment thickness and grain size help in identifying the break between sets in the strandplain sequences. Investigation of these breaks may help identify possible gaps in the record or missing ridges in strandplain sequences that may not be apparent when viewing age distributions and may justify the need for multiple age and glacial isostatic adjustment models. This is the third in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.  相似文献