桩式离岸堤保滩促淤工程消浪效果试验研究   总被引：9，自引：0，他引：9  

龚崇准  陈美发等 《海洋工程》2001,19(4):72-77

在上海奉贤南北港保滩促淤工程中，采用了一种新型结构型式－桩式离岸堤，并通过物理模式试验进行了桩式离岸堤消浪效果研究。针对离岸堤通常建于近岸水区破波带的特点，重点研究水深，堤高以及堤身结构对波浪衰减的影响，同时对桩式离岸堤堤后水域的波浪底流速 分析探讨。研究结果表明，桩式离岸堤不仅具有良好的消浪效果。而且可在较大范围内改变波态，即由引起水体剧烈紊动的破波转变为浅水推进波，从而有效地改善海滩上的动力条件，促进海滩免受侵蚀，是一种具有广泛应用前景和新型保滩促淤结构。  相似文献   

秦皇岛砂滩海洋线虫的数量研究   总被引：4，自引：2，他引：4  

张志南 《中国海洋大学学报(自然科学版)》1991,(1)

在两年的周期内,对秦皇岛4个砂滩的海洋线虫进行了6次芯样采集。灯塔、新煤码头、汤河口和北戴河赤土山4个砂滩均系分选好的细砂或中细砂,其中值粒径为140-285μm。对连续16个芯样计数的变异性所做的测试证明,1,2和3个芯样计算所得95％C.L.分别是0.539X—1.855X,0.647X—1.547X和0.700X—1.428X。秦皇岛砂滩海洋线虫的年平均密度:中潮带上区为1381±441 inds.10cm~(-2)。中潮带下区为1264±538 inds.10cm~(-2)。灯塔和新煤码头砂滩,8月出现高密度值,与温度的季节变化相符合,而汤河口则出现最低值,可能与污染物的大量排出有关。多数砂滩的大部分芯样显示了明显的重直分布,即种群数量的大部分集中在芯样顶部的两个分层:0～4和5～8cm。没有发现垂直分布的季节变化趋势。与世界其他海区砂滩的资料进行了比较。  相似文献   

Longshore drift estimation using fluorescent tracers: New insights from an experiment at Comporta Beach, Portugal   总被引：1，自引：0，他引：1  

Ana Silva  Rui Taborda  Aurora Rodrigues  Joo Duarte  Joo Cascalho 《Marine Geology》2007,240(1-4):137-150

A fluorescent sand-tracer experiment was performed at Comporta Beach (Portugal) with the aim of acquiring longshore sediment transport data on a reflective beach, the optimization of field and laboratory tracer procedures and the improvement of the conceptual model used to support tracer data interpretation.

The field experiment was performed on a mesotidal reflective beach face in low energetic conditions (significant wave height between 0.4 and 0.5 m). Two different colour tracers (orange and blue) were injected at low tide and sampled in the two subsequent low tides using a high resolution 3D grid extending 450 m alongshore and 30 m cross-shore. Marked sand was detected using an automatic digital image processing system developed in the scope of the present experiment.

Results for the two colour tracers show a remarkable coherence, with high recovery rates attesting data validity. Sand tracer displayed a high advection velocity, but with distinct vertical distribution patterns in the two tides: in the first tide there was a clear decrease in tracer advection velocity with depth while in the second tide, the tracer exhibited an almost uniform vertical velocity distribution. This differing behaviour suggests that, in the first tide, the tracer had not reached equilibrium within the transport system, pointing to a considerable time lag between injection and complete mixing. This issue has important implications for the interpretation of tracer data, indicating that short term tracer experiments tend to overestimate transport rates. In this work, therefore, longshore estimates were based on tracer results obtained during the second tide.

The estimated total longshore transport rate at Comporta Beach was 2 × 10^− 3 m³/s, more than four times larger than predicted using standard empirical longshore formulas. This discrepancy, which results from the unusually large active moving layer observed during the experiment, confirms the idea that most common longshore transport equations under-estimate total sediment transport in plunging/surging waves.  相似文献   

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

E.J. Anthony  F. Levoy 《Marine Geology》2004,208(1):73-100

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.  相似文献   

Investigation on the Deposition in an Excavated Trough at the East Shore of Jiaozhou Bay, China     

Zhang Jinshan Yu Guohua Research Engineer  River  Harbour Department  Nanjing Hydraulic Research Institute  Nanjing Research Senior Engineer  River  Harbour Department  Nanjing Hydraulic Research Institute  Nanjing 《中国海洋工程》1995,(3)

- Based on field investigations, this paper analyzes three types of harbour basinns and navigation channel excavated on seabed in Jiaozhou Bay, get a general rule of deposition for excavated trough, it found that pollution is one of crucial factors resulting in the deposition of the excavated trough in the east shore of Jiaozhou Bay. With these results, it predicted the annual deposition thickness for the excavated trough and disclosed the fact that it can't be deposited deadly during one storm. At the same time, with two-dimensional numerical model, it studied the effects of the excavated trough and the reclamation near shore on tidal cureent and said that the excavated trough can decrease the current velocity passing through the trough about 10- 15%, but only limited inside and near the trough and there are no effect on other regions; reclamation can cut off the pollution sources and no obvious effect on the currents of the Jiaozhou Bay. Connecting the deep trough and Cangkou tidal channel with a new  相似文献   

Reduction of sand demand for shore protection     

Arved J. Raudkivi  Hans-H. Dette   《Coastal Engineering》2002,45(3-4)

Beach nourishment is an environmentally preferred method of shore protection, but the annual sand requirement may lead to substantial maintenance costs. The shoreline processes, involving the surf zone, beach and dune, are reviewed with the aim of reducing the annual sand requirement of eroding shorelines. It is shown that surf zones with equilibrium profiles, on which the wave energy conversion is evenly distributed across the surf zone, from experience for given conditions indicate least loss of sand. On steep, eroding shorelines it may be difficult to establish an equilibrium profile. For such cases, the use of perched surf zones is recommended, which are supported at the seaward limit by an underwater sill. For reduction of littoral transport, the use of pervious pile groynes is recommended. These are arguably more efficient than impervious groynes. The sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment. The loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built-in membrane. These sand losses are usually large and constitute an uneconomic use of this sand resource. The proposed concepts and measures are linked to existing knowledge, augmented by data from the large wave flume (LWF) in Germany and field data from the North and Baltic Sea coasts.  相似文献   

Ecology of beach wrack in northern New England with special reference to Orchestia platensis     

Manaf I. Behbehani  Robert A. Croker   《Estuarine, Coastal and Shelf Science》1982,15(6)

The northern New England beach wrack community with special reference to the cosmopolitan amphipod crustacean, Orchestia platensis, was examined at estuarine and open coastal habitats. Beach wrack was dominated by the plant genera Ascophyllum, Zostera, Spartina and Chondrus, and was most abundant during spring and late summer. Animal community numbers, biomass and frequency in fresh to moderately decomposed wrack were dominated by O. platensis throughout the year at all habitats; oligochaetes and Collembola were also important. The abundance of O. platensis showed high spatial and temporal variability, with low abundance generally associated with decreased amounts of wrack during colder months. An exception was the winter presence of the species at one estuarine habitat, in patchy aggregations within gravel-cobble refuges. The abundance of O. platensis averaged 1280 (0.04 m²)⁻¹, with a maximum of 7040 (0.04 m²)⁻¹. The life cycle of O. platensis is bivoltine, with summer-hatched young reaching maturity within 1 month. Laboratory studies indicate females with up to 4 broods (30 days)⁻¹, averaging 18 eggs brood⁻¹.Orchestia platensis is omnivorous, eating fresh plant tissue, live oligochaetes, Limulus eggs and diatom ‘fuzz’. The rate of laboratory consumption of algae and Zostera was 0.05 mg plant mg⁻¹ wet body weight day⁻¹. Presumptive predators of O. platensis are juvenile green crab, Carcinus maenus, and the earwig. Anisolabis maritima. The mobility, aggregation and aggressiveness of O. platensis assist the species in establishing and maintaining populations in the rigorous wrack habitat. The general competitive superiority of O. platensis over its congener, O. gammarella, and the co-occurrence of these species on both eastern and western Atlantic shores is discussed.  相似文献   

The role of bathymetry and directional wave conditions on observed crescentic bar dynamics     

Rinse L. de Swart  Francesca Ribas  Gonzalo Simarro  Jorge Guillén  Daniel Calvete 《地球表面变化过程与地形》2021,46(15):3252-3270

Nearshore sandbars are important features in the surf zone of many beaches because they strongly influence the mean circulation and evolving morphology. Due to variations in wave conditions, sandbars can experience cross-shore migration and vary in shape from alongshore uniform (shore-parallel) to alongshore rhythmic (crescentic). Sandbar dynamics have been studied extensively, but existing observational studies usually do not quantify the processes leading to crescentic bar formation and straightening. This study analyses the dynamics of crescentic bar events at the fetch-limited beach of Castelldefels (northwestern Mediterranean Sea, Spain) using 7.5 years of hourly time-exposure video images and detailed wave conditions. The results show that, despite the generally calm wave conditions, the sandbars were very dynamic in the cross-shore and longshore directions. They often migrated rapidly offshore during storms (up to 70 m in one day) and more slowly onshore during post-storm conditions. Crescentic bars were often present at the study site (48% of the time), but only when the sandbar was at least 10 m from the shoreline. They displayed a large variability in wavelengths (100–700 m), alongshore migration speeds (0–50 m/day) and cross-shore amplitudes (5–20 m). Wavelengths increased for larger bar–shoreline distances and the alongshore migration speeds were strongly correlated with the alongshore component of the radiation stresses. Crescentic patterns typically developed during low–medium energetic waves with limited obliquity ( $\theta \lesssim 20$° at 10 m depth), while bar straightening occurred during medium–high energetic waves with strong oblique angles of incidence ( $\theta \gtrsim 15$°). Overall, this study provides further proof for the important role of wave direction in crescentic bar dynamics and highlights the strong dependence of crescentic bar development on the initial bathymetric configuration.  相似文献   

A rationale for beach selection by the public on the coast of Wales, UK     

D T Tudor  A T Williams 《Area》2006,38(2):153-164

Questionnaires were completed by 2306 beach users at 19 Welsh beaches with respect to beach selection parameters. The modal group of respondents was female aged 30–39. Beach choice was primarily determined by clean litter-free sand and seawater, followed by safety. Refreshment facilities and beach awards were deemed minor considerations by the public when choosing a beach to visit. Approximately 58 per cent of respondents were aware of beach award and rating schemes. Of coastal visitors interviewed for this paper, 67 per cent rated a beach as 'important' or 'very important' to their holiday, with just 2 per cent replying that they were unimportant.  相似文献   

'Toheroa Wars': Cultural politics and everyday resistance on a northern New Zealand beach     

Brian Murton 《New Zealand geographer》2006,62(1):25-38

Abstract:  This paper examines how the cultural politics of resource management were played out on the North Kaipara beach between about 1900 and 1971 between Māori and the representative of the Crown, the Marine Department. Particular attention is devoted to how, after regulations were introduced to protect toheroa, the giant surf clam, Māori struggled to assert their rights through a range of transgressions. The paper argues that this illustrates how cultural politics works both from the top down (the Marine Department's implementation of policy) and the bottom up (Māori resistance). It concludes that through an examination of this particular 'culture war', the foreshore emerges as a contested domain where politics, culture and epistemology are inseparable.  相似文献