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1.
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   

2.
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   

3.
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   

4.
Landsat enhanced thematic mapper imagery (ETM) of 2002 and aerial photography of 1955, combined with published charts and field observations were used to interpret coastal changes in the zone between Kitchener drain and Damietta spit in the northeastern Nile delta, previously recognized as a vulnerable zone to the effects of any sea level rise resulting from global warming. The interpretation resulted in recognition of several changes in nine identified geomorphological land types: beach and coastal flat, coastal dunes, agricultural deltaic land, sabkhas, fish farms, Manzala lagoon, saltpans, marshes and urban centers. Reclamation of vast areas of the coastal dunes and of Manzala lagoon added about 420 km2 to the agricultural deltaic land. About 48 km2 of backshore flats, marshes, salt pans and Manzala lagoon have been converted to productive fish farms. The main urban centers have expanded; nearly 12.1 km2 have been added to their areas, and new urban centers (Damietta harbor and the New Damietta city) with total area reach of ~35.3 km2 have been constructed at the expense of vast areas of Manzala lagoon, coastal dunes, and backshore flats. As a consequence of human activities, the size of Manzala lagoon has been reduced to more than 65%. Shoreline changes have been determined from beach profile survey (1990–2000), and comparison of 1955 aerial photographs and ETM satellite image of 2002 reveal alongshore patterns of erosion versus accretion. The short-term rate of shoreline retreat (1990–2000) has increased in the downdrift side of Damietta harbor (≃14 m/year), whereas areas of accretion exist within the embayment of Gamasa and in the shadow of Ras El Bar detached breakwaters system, with a maximum shoreline advance of ~15 m/year. A sandy spit, 12 km long, has developed southeast of Damietta promontory. These erosion/accretion patterns denote the natural processes of wave-induced longshore currents and sediment transport, in addition, the impact of man-made coastal protection structures.  相似文献   

5.
The investigations were carried out in order to evaluate change of the beaches profile during the period 1993–2008 and to elucidate main trends of the coastal dynamics. Morphometric indicators (beach width, height and inclination) were measured every year during the period 1993–2008 in 70 measuring stations located along the coastline. It was determined that the dynamic shoreline of the mainland during 1993–2008 receded by 10.2 m and the dynamic shoreline of the Curonian Spit advanced into the sea by 8.3 m. The different morphometric beach indicators changed to varying extents over the period 1993–2008, but comparison of values for 1993 and 2008 showed that those changes were small. The average beach width increased by 1.2 m on the mainland coast and by 0.5 m on the Curonian Spit coast. The average beach height also increased negligibly: by 0.5 m on the mainland coast and by 0.1 m on the Curonian Spit coast. The average beach slope inclination increased by 0.012 (from 0.065 to 0.077) on the mainland coast and by 0.005 (from 0.073 to 0.078) on the Curonian Spit coast. The measurements show that, despite being the most dynamic elements in the coastal system, these beaches managed to retain their morphometric indicators almost unchanged during the period of observation.  相似文献   

6.
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7.
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   

8.
Predicting erosion and accretion of sand beaches in estuaries is important to managing shoreline development and identifying potential relationships between biological productivity and beach change. Wave, sediment and profile data, gathered over twenty-nine days on an estuarine sand beach in Delaware Bay, New Jersey, were used to evaluate the performance of four criteria that predict beach erosion and accretion due to wave-induced cross-shore sediment movement (Dean 1973; Sunamura and Horikawa 1974; Hattori and Kawamata 1980; Kraus et al. 1991). Each criterion defines a relation, between a wave and sediment parameter, and includes a coefficient that discriminates beach erosion and accretion events. Relations, based on small-scale laboratory and field data, were evaluated for predicting erosion or accretion at the study site. Significant wave heights at the study site, monitored near high water, ranged from 0.08 to 0.52 m with periods of 2.4 to 12.8 s. Median grain sizes of sediments on the beach foreshore, gathered at low water, ranged from 0.33 to 0.73 mm. All four criteria showed a clustering of erosion and accretion events. Relations derived from small-scale laboratory data were better predictors of erosion on the profile at the field site than those derived from field data gathered on exposed ocean environments. The planar profile and dominance of incident waves of low height and short period are similar to laboratory conditions characterized by initial planar beach slopes and monochromatic waves. Decreasing the value of the empirical coefficient to account for the differences in the magnitude of wave energy and grain size increases the performance of the criteria tested to predict erosion of the profile.  相似文献   

9.
The nearshore parameters, viz., wave runup, wave setup, and wave energy have been estimated during storm and normal conditions of SW monsoon (June–September) and NE monsoon (November–February) by empirical parameterization along Visakhapatnam coast. These results were compared with the field observations during three storms of SW monsoon season in the year 2007. The higher nearshore wave energies were observed at R.K. Beach, Jodugullapalem beach, and Sagarnagar beach during both the seasons. During storm events, the higher wave energies associated with higher wave runups cause severe erosion along the wave convergence zones. The storm wave runups (SWRUs) were higher at R.K. Beach, Palm beach, Jodugullapalem beach, and Sagarnagar Beach. The yearly low wave energy was observed at Lawson’s Bay with lowest wave runup, considered as safest zone. R.K. Beach, Palm beach, and Jodugullapalem beach are identified as vulnerable zones of wave attack. It is noteworthy that in addition to wave energies, wave runups and wave setups also play a vital role in endangering the coast.  相似文献   

10.
This paper outlines the results of a study recently carried out on the western coast of the Sestri Levante peninsula (Eastern Liguria-Italy), aiming to assess the effects of newly accomplished defensive measures against coastal erosion: the accretion of the beach with natural sand and its protection with artificial structures orthogonal and parallel to the shoreline. Through conventional and more innovative methodologies (respectively single beam echo sounders and global positioning system) the research work has resulted in a new evaluation of the morphological, bathymetric and sedimentological features that make up this shoreline and its volumetrical change over the century. The survey and the research carried out on the studied area have enabled us to give a more detailed picture of the evolution of the littoral, to assess the possible use of “non-traditional” techniques of beach development monitoring, to evaluate the volumetric variations of the emerged and submerged beaches, to establish the sedimentological activity of the beach after the latest nourishment measures, and finally, to verify the effectiveness of the protection measures implemented on this coastline. The acquired data have been stored in the database and a geographic information system has been used to process, analyze, and evaluate the results. The main findings show that the latest intervention has brought about a new phase in the evolution of the coastline, giving rise to a new pseudo-balanced condition. The re-distribution of materials used for the beach nourishment, leads us to believe that the defence underwater barrier has only partially worked. The main conclusion for a correct coastal zone management underline the necessity to plan local and more wide monitoring during at least 8–10 consecutive years.  相似文献   

11.
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   

12.
The Plio-Quaternary conglomeratic sets within the marine environment of the Viranşehir coast (W Mersin, S Turkey) are responsible for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity, wave energy, and organic activity. The conglomeratic sets close to the shoreline (50–150 cm) act as wave breakers, creating hard substratum and high energy, well-oxygenated environment for organisms like Patella sp., Phoronida worms and Brachidontes pharaonis (Fischer P. 1870). The boring activities of these organisms have disintegrated the sandy matrix of these sets. Finer-grained matrix sediments have been transported to the interset and open sea, while cobble–pebbles have been carried landwards and have created imbricated gravely beach deposits without matrix. Sandy beach is evolving where the conglomeratic sets away from the shoreline (5.0–10.0 m). In this example, sets form a bar; causing fivefold division as backshore, berm, surf zone, bar and offshore from land to sea. Poorly sorted, cobbles-pebbles cobbles and pebbles are found associated with the high-energy environments of bars, whilst well-sorted sands are observed in low energetic environments on shore. The sets and recent shell fragments are the main sources of coastal sediments in Viranşehir. However, the amount of shell fragments decrease towards the active river mouth. This is due to sediment and fresh water influx from the river causing deteriorated temperature, salinity and light penetration of the marine environment resulting in less organic diversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

13.
Presque Isle Bay is one of 40 remaining environmental areas of concern (AoCs) on the North American Great Lakes that have one or more water, habitat, or sediment quality impairments as defined by the International Joint Commission. In situ natural capping using sediment from to-be-remediated watersheds and other potential sources is being considered as the most feasible means of remediating an existing contaminated sediment problem at this site. A multi-decade (∼40 year) sediment budget shows that, when localized anthropogenic effects (dredging, reclamation) are discounted, the bay net-accumulated sediment over time. Sediment was supplied from three major sources: bank erosion and bluff retreat (41%), streams (25%), and the Lake Erie littoral system (20%). The non-stream sources supply environmentally clean materials from ancient beach and glacio-lacustrine deposits along the shoreline, and from the modern littoral system. Organic and metallic contaminants supplied primarily by streams and run-off remain a remediation challenge for the AoC. Geologically, natural capping of contaminants over the next several decades is a viable solution for most of the bay. The mechanism may not work effectively in all areas because approximately 25% of the bay floor is moderately net-erosional while several localized areas accumulate sediments very slowly at decadal timescales.  相似文献   

14.
A long-term study (monthly sampling, 1992 to 2007) was conducted in the surf zone of Cassino Beach, Southern Brazil, in order to detect possible natural and/or anthropogenic disturbances. Surface water temperature (6–29°C) was the only parameter with predictable seasonal variation; salinity (14–38) was inversely related to rainfall (3.1–485.2 mm month−1) and low values followed extreme precipitation periods in 1997/1998 and 2002/2003 (El Ni?o years). Asterionellopsis glacialis and chlorophyll a presented high concentrations and peak frequency until 1998, when an intense mud deposition occurred with concomitant extreme rainfall. It affected the surf zone and beach, changing the hydrology and dissolved inorganic nutrient availability. Six phytoplankton species groups were recognized with distinct responses to this mud deposition. We conclude that large-scale climatic changes, like El Ni?o Southern Oscillation, in conjunction with human activities significantly altered the phytoplankton ecology of the highly dynamic Cassino Beach surf zone.  相似文献   

15.
Consideration of human influences is crucial to understanding the coastal sediment supply and associated shoreline responses prior to undertaking coastal hazard management studies. Observation of the widening of some selected Indian beaches, especially over the last 6 decades, is of significance. From this perspective, Miramar Beach, Goa, India, was studied using three ground-penetrating radar shallow subsurface profiles (4 m depth). Based on a series of depositional siliciclastic packages, six progradational packages were recognised, which were interrupted by sharp erosional boundaries. These erosional boundaries represent transgressive phases of the shoreline migration. It was observed that the shoreline migration is coupled with the deposition and erosion of sediments, and this is supported by the historical admiralty charts. The optically simulated luminescence dating of the sediments collected at the first progradation period reveals that the age corresponds to the years 1952–1957, which also corroborates the information provided by the local populace. In the past 6 decades, the shoreline growth has been rapid because of the heavy sediment influx from the Mandovi River caused by increased mining activities (since the 1950s) in upstream areas. Since the 1950s, the shoreline has prograded rapidly, building a beach from ~40 to ~280 m wide (average rate of 4 m/year) in response to enhanced sediment supply from the Mandovi River created by mining activities upstream. Superimposed on this overall regressive trend is a series of deposition and erosion cycles. Perhaps, if a similar trend continues, then there will possibly be a further widening of the beach in the future. A close monitoring network is needed to understand the causes of the cycles in shoreline position and to predict their future behaviour. The present investigation on the nature of the coastal response to anthropogenic activities in a river basin as well as the role of short-time cycles on shoreline behaviour in the last 6 decades could be an ideal reference study and motivate the search for similar areas along other coastal locations.  相似文献   

16.
海滩形态、沉积物组分和粒度参数能反映海滩沉积环境。自2010年7月到2011年12月在辽东湾西岸葫芦岛市龙湾滨海沙滩和兴城第一海水浴场沙滩进行冬夏重复海滩剖面测量和表层沉积物粒度分析,结果表明:①两海滩以85黄海高程-0.6 m和-4.7 m为界划分为海滩、水下岸坡和陆架平原三个地貌单元。②龙湾沙滩海滩形态较稳定,兴城一浴海滩和水下岸坡淤积,均与海滩养护相关。③根据沉积物组分和粒径参数的差异,两海滩可横向划分为I、II、III、IV四个沉积区。各沉积区内中值粒径并没有出现横向递减的趋势,分选系数、偏态和峰态变化复杂。各沉积区间水力条件截然不同。④与兴城一浴相比,龙湾沙滩I沉积区沉积物颗粒较细、分选较好,水下岸坡存在综合动力条件弱的沉积区段,陆架平原缺少潮流作用强烈的区段。  相似文献   

17.
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   

18.
Based on high‐resolution TOPAS acoustic data, bathymetric data sets and sediment cores from the Norwegian Channel, the last retreat of the Norwegian Channel Ice Stream has been investigated. Mapping of ice‐marginal features such as grounding‐zone wedges and terminal moraines off western Norway suggest that the retreat of the grounding line in this part of the channel was interrupted by frequent stillstands, whereas the channel south of the threshold at Jæren does not have crossing ice‐marginal landforms. Three main seismic units have been identified, and, based on their seismic characteristics, in addition to study of sediment cores, these units are interpreted as till (U1), glacial marine sediment (U2) and Holocene hemipelagic sediment (U3). Based on new and published radiocarbon dates of the lower part of U2, combined with dates from the adjacent areas, it is concluded that the grounding line started to retreat from the shelf edge at about 19 ka and that the inner part of Skagerrak was ice free at 17.6 ka. This gives an average retreat rate of 450 m a−1, which is generally higher than mean retreat rates estimated for other palaeo‐ice streams (15–310 m a−1).  相似文献   

19.
《Sedimentology》2018,65(3):721-744
Storm surges generated by tropical cyclones have been considered a primary process for building coarse‐sand beach ridges along the north‐eastern Queensland coast, Australia. This interpretation has led to the development of palaeotempestology based on the beach ridges. To better identify the sedimentary processes responsible for these ridges, a high‐resolution chronostratigraphic analysis of a series of ridges was carried out at Cowley Beach, Queensland, a meso‐tidal beach system with a >3 m tide range. Optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years. The ridge crests sit +3·5 to 5·1 m above Australian Height Datum (ca mean sea‐level). A ground‐penetrating radar profile shows two distinct radar facies, both of which are dissected by truncation surfaces. Hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at +2·5 m Australian Height Datum, equivalent to the fair‐weather swash limit during high tide. The lower facies comprises a sequence of seaward‐dipping reflections. Beach progradation thus occurs via fair‐weather‐wave accretion of sand, with erosion by storm waves resulting in a sporadic sedimentary record. The ridge deposits above the fair‐weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events. Inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide. The ridges may also include an aeolian component as cyclonic winds can transport beach sand inland, especially during low tide, and some layers above +2·5 m Australian Height Datum are finer than aeolian ripples found on the backshore. Coarse‐sand ridges at Cowley Beach are thus products of fair‐weather swash and cyclone inundation modulated by tides. Knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges.  相似文献   

20.
The short and medium-term coastal evolution of Necochea Municipality, Buenos Aires province (Argentina) was studied. The medium-term evolution study was based on aerial photographs from 1967 and 1984, and satellite images from 2004, using the dune or cliff toe as coastline indicator. The short-term evolution was studied from February 2006 to December 2009 by means of seasonal beach profiles and sediment sampling. Results showed that in the medium-term at Necochea, the coastline has remained stable or has advanced. Whereas in the short-term, the analysis has evidenced incipient erosion processes. On the other hand, at Quequén the retreat of the coastline and the negative sedimentary balances (medium and short-term) are clearly indicating an accentuated erosion process. The different degrees of coastal erosion are related in part to beach vulnerability to wave storms but mainly to anthropogenic actions, which have affected the beach sediment supply. These results evidence the necessity to develop a coastal management programme.  相似文献   

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