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1.
Indian River Inlet is located at roughly the mid-point of the Atlantic coast of Delaware and connects the ocean to two Delaware inland bays. Jetties constructed in 1940 have maintained the inlet for navigation purposes but have also acted as a barrier to net northerly alongshore sediment transport causing downdrift erosion. A mobile, land-based bypassing system was initiated in 1990 in an effort to counteract this erosion. Beach profile data from 1985 (pre-bypassing) until 2008 are used to investigate the effect of the sand bypassing system on beaches adjacent to the inlet. The downdrift beach experienced horizontal shoreline erosion between 10 and 60 m during the pre-bypassing period but accreted 10–20 m during the bypassing period. The mean shoreline location on the updrift beach during bypassing is 10–20 m landward (erosion) of its position during the pre-bypassing period. Empirical orthogonal function (EOF) amplitudes from analyses performed on mean-removed elevation surfaces during the periods of highest bypassed volume (average of 83% of design rate) showed that the influence of the bypassing system on the downdrift beach extends to about 1500 m of the inlet. An EOF analysis showed that different morphologic responses were evident following the initiation of bypass operations. Temporal variations of shoreline and beach morphology were correlated to the temporal variations in bypassing rates on the downdrift beach only. The downdrift beach response was greatest near the inlet for larger bypassing volumes. Correlation in these instances occurred with a roughly 1-year time lag suggesting that the beach quickly redistributes the bypassed sand. EOF amplitude and shoreline response are weakly correlated to bypassed volumes when the system bypassed smaller volumes (average of 56% of design rate) of sand suggesting that there is a minimum bypassing rate, regardless of yearly variability, below which the effect on the downdrift beach is obscured. 相似文献
2.
The ability to robustly predict future shoreline position under the influence of changing waves and sea-level rise is a key challenge to scientists and engineers alike. While extrapolating a linear trend out in time is a common baseline approach, the recent development of a number of empirical shoreline models allows the prediction of storm and annual-scale variability as well. The largest constraint in applying these models is the availability of high quality, adequate duration data sets in order to calibrate model free parameters. This contribution outlines several such models and discusses the monitoring programs required to calibrate and hindcast shoreline change from 1 to 10 years at two distinct beach types: a storm-dominated site and the second exhibiting a large seasonal variability. The seasonally-dominated site required longer data sets but was less sensitive to sampling interval, while the storm-dominated site converged on shorter, more frequently sampled data sets. In general, calibration based on a single year of observed shorelines resulted in a large range of model skill and was not considered robust. Monitoring programs of at least two years, with shorelines sampled at dt ≤ 30 days were sufficient to determine initial estimates of calibration coefficients and hindcast short-term (1–5 years) shoreline variability. In the presence of unresolved model processes and noise, hindcasting longer (5 + years) data sets required longer (5 + years) calibration data sets, particularly when sampling intervals exceeded 60 days. 相似文献
3.
This contribution describes the development, calibration and verification of a 1-D behaviour-orientated shoreline prediction model. The model primarily encapsulates shoreline displacement forced by wave-driven cross-shore sediment transport. Hysteresis effects are shown to be important and are included in the model, whereby present shoreline change is influenced by past hydro-/morpho-dynamic conditions. The potential magnitude of shoreline change increases with incident wave power and the degree of disequilibrium. The latter disequilibrium term (Ωeq − Ω) is expressed in terms of the time-evolving equilibrium (Ωeq) and instantaneous (Ω) dimensionless fall velocities and dictates the direction of shoreline movement. Following Wright et al. (1985) the equilibrium fall velocity is defined as a function of the weighted antecedent conditions and is a proxy for the evolving beach state. The decay rate of the weighting function used to compute Ωeq is a model free parameter determined by calibration against measured data, which physically reflects the degree of observed ‘memory’ of the system. The decay in amplitude of this weighting function with time is controlled by a ‘memory decay’ term (ϕ), where the weighting reaches 10%, 1% and 0.1% at ϕ, 2ϕ and 3ϕ days prior to the current calculation time. The model is applied to two multi-year (6 + years) data sets incorporating hourly wave and weekly shoreline measurements, from two contrasting energetic sites in SE Australia. The first is the relatively dissipative, straight Gold Coast (QLD) and the second is a more intermediate embayed beach at Narrabeen (NSW). The model shows significant skill at hindcasting shoreline change at both sites, predicting approximately 60% of the total shoreline variability. The Gold Coast shoreline is dominated by a strong seasonal signal. Conversely, at the Narrabeen embayment, shoreline variability (and morphology) is more dynamic, responding at storm frequency. Evidence suggests that there is a strong coherence between the shoreline position and morphodynamic state and that both have response times characterised by ϕ. It is hypothesised that optimised ϕ values in the shoreline model physically relate to the efficiency of sediment exchanges between the shoreface and offshore bars and the prevalence of one- or two-dimensional horizontal circulation. The general success of this new shoreline model for hindcasting the observed shoreline behaviour at two distinctly different open-coast sites suggests that this approach may be suitable for broader application. 相似文献
4.
Beach erosion and accretion occur across multiple time scales. Over long time scales (decades to millennia) the shoreface ravinement surface, which is recognized as a coarse lag deposit, forms at the shoreface toe as a result of wave- and current-induced erosion during shoreline transgression. Over short time scales (hours to days) the depth of sediment disturbance, which is recognized as coarse lamina and measured at the foreshore by devices and monitoring tracer beds, forms as a result of wave- and current-induced reworking during a tidal cycle. The maximum depth of erosion (MDOE), quantified here over 1 year, is modulated by processes that operate over a time scale that is between the drivers of short-term (e.g. tides and waves) and long-term (e.g. sea-level rise) beach erosion. The MDOE integrates the erosion that occurs over a discrete time interval and records the maximum depth of erosion that is likely principally induced by storms, which is difficult to quantify by other methods that rely on discrete observations (e.g. changes in elevation or movement of the mean high-water line). A novel technique for quantifying the MDOE, based on comparing the bedding and stratigraphy between cores collected at the same locations over a discrete time interval, is presented here and applied at Onslow Beach, NC, USA. This 12 km-long barrier island has irregular shoreline morphology, characterized by two embayments separated by a central headland. This shape is largely the result of variations in the depth of underlying rock strata and produces a steeper beachface at the headland than at the embayments. At each of the six sites examined along the barrier, the MDOE is found to increase from the backshore to the middle intertidal zone and is higher at the sites closer to the headland. These variations in the MDOE are likely due to the increase in average wave energy impacting the beachface from an offshore direction and steeper beaches (intermediate beach state) at the headland. Where the MDOE is within the beach facies, it is not associated with a coarsening, which is due to the heterolithic nature of the Onslow-beach strata. Where the MDOE is the contact between back-barrier and beach facies it is always associated with a coarsening and a gravel-rich lag deposit because in this case, the MDOE is an amalgamation of multiple erosional events, which is similar to the shoreface ravinement surface. Along-beach variation in the MDOE does not correspond with discrete observations of beach change over the same period and is likely a better indicator of erosion potential than long-term discrete observations, such as changes in surface elevation or the position of the mean high-water line. 相似文献
5.
《Coastal Engineering》2006,53(7):573-588
Using shoreline water-level time series collected during 10 dynamically diverse field experiments, an empirical parameterization for extreme runup, defined by the 2% exceedence value, has been developed for use on natural beaches over a wide range of conditions. Runup, the height of discrete water-level maxima, depends on two dynamically different processes; time-averaged wave setup and total swash excursion, each of which is parameterized separately. Setup at the shoreline was best parameterized using a dimensional form of the more common Iribarren-based setup expression that includes foreshore beach slope, offshore wave height, and deep-water wavelength. Significant swash can be decomposed into the incident and infragravity frequency bands. Incident swash is also best parameterized using a dimensional form of the Iribarren-based expression. Infragravity swash is best modeled dimensionally using offshore wave height and wavelength and shows no statistically significant linear dependence on either foreshore or surf-zone slope. On infragravity-dominated dissipative beaches, the magnitudes of both setup and swash, modeling both incident and infragravity frequency components together, are dependent only on offshore wave height and wavelength. Statistics of predicted runup averaged over all sites indicate a − 17 cm bias and an rms error of 38 cm: the mean observed runup elevation for all experiments was 144 cm. On intermediate and reflective beaches with complex foreshore topography, the use of an alongshore-averaged beach slope in practical applications of the runup parameterization may result in a relative runup error equal to 51% of the fractional variability between the measured and the averaged slope. 相似文献
6.
Several levels of increasing complexity of transferring wave information from offshore to nearshore have been studied to quantify their influence on extreme beach erosion estimates. Beach profiles which have been monitored since 1976 were used to estimate extreme beach erosion and compared to predictions. Examination of the wave propagation assumptions revolves around two types of offshore to nearshore transfer: excluding or including wave breaking and bottom friction. A second complication is whether still water level variations (ocean tide plus storm surge) are included.The inclusion of various combinations of wave propagation processes other than shoaling and refraction in the wave transfer function changes on the extreme erosion distribution tail through lowering estimates above one year return period. This brings the predicted tails closer to the observations, but does not capture the upper limit of storm demand implied by the extensive beach profile data set. Including wave breaking has a marked effect on probabilistic estimates of beach erosion. The inclusion of bottom friction is less significant. The inclusion of still water level variability in the wave transfer calculation had minimal impact on results for the case study site, where waves were transferred from offshore to water at 20 m depth. These changes were put into perspective by comparing them to changes resulting from limiting beach erosion by adjusting the statistical distributions of peak wave height and storm duration to have maximum limits. We conclude that the proposed improvements on wave transformation methods are as significant as limiting wave erosion potential and worth including. 相似文献
7.
《Estuarine, Coastal and Shelf Science》2005,62(1-2):41-53
To examine the relationship between near-bottom larval surfclam concentrations and surfclam settlement at an inner continental shelf site off New Jersey (USA), four consecutive sets of settlement experiments were carried out at three stations at the Long-term Ecosystem Observatory (LEO-15) from 14 to 31 July 1997 during upwelling and downwelling. Two inshore stations were on the landward and seaward sides of Beach Haven Ridge at ∼12 m depth, and a third station was 8 km further offshore at ∼20 m depth. In each experiment, four replicate trays of azoic sand from Beach Haven Ridge were placed flush with the seafloor and exposed for 3–7 days. Larval surfclam concentrations were measured every 4 h at 1 m above the bottom (mab) using Moored, Automated, Serial Zooplankton Pumps at the three stations. At all three stations, larval surfclam concentrations (1 mab) were low during upwelling, and higher during and after downwelling. Pulses of highest larval surfclam concentrations coincided with the initial arrival of downwelled warm water. In addition, larval surfclam concentrations were higher at the two inshore stations than at the offshore station. Larval surfclam settlement in the trays was higher during and following downwelling than during upwelling at one inshore station and at the offshore station. At the other inshore station (landward of Beach Haven Ridge), surfclam settlement did not increase during and following downwelling. Overall, surfclam settlement was higher inshore than offshore. The results indicate that spatial and temporal variation in larval surfclam supply was controlled by upwelling and downwelling circulation and that surfclam settlement was influenced by larval supply. Bottom flows across Beach Haven Ridge during a storm may have reduced larval surfclam settlement on the upcurrent side of the ridge, affecting initial densities on a small (∼1 km) scale. 相似文献
8.
Hee Jun Lee Jong-Dae Do Sun Sin Kim Won-Kyung Park Kicheon Jun 《Ocean Science Journal》2016,51(4):681-694
Haeundae Beach represents Korean pocket beaches that are currently erosional and dominated by summertime typhoons. The decadal wave characteristics 9 km offshore of Haeundae Beach were analyzed using the WAM model that was validated through the 2007 wave observations. The wave statistics modelled for 1979–2007 indicates that the seasonal mean significant wave height (H s ) is highest (0.6–0.7 m) in summer due to typhoons, in contrast to the lowest (around 0.5 m) autumn analog. The wave direction is also pronouncedly seasonal with the principal bearings of SSW and NE in the summer and winter seasons, respectively. The WAM results additionally show that the H s has gradually increased over the region of Haeundae Beach since 1993. Beach profiling during June–November 2014 shows the opposite processes of the typhoon and fair-weather on beach sands. During a typhoon, foreshore sands were eroded and then accumulated as sand bars on the surf zone. In the subsequent fair-weather, the sand bars moved back to the beach resulting in the surf-zone erosion and foreshore accretion. A total of 5 cycles of these beach-wide sand movements yielded a net retreat (up to 20 m) of the shoreline associated with large foreshore erosion. However, the surf zone only slightly accumulated as a result of the sand cycles. This was attributed to the sand escape offshore from the westernmost tip of the beach. The present study may provide an important clue to understanding the erosional processes in Haeundae Beach. 相似文献
9.
The possibility of using wave farms for coastal defence warrants investigation because wave energy is poised to become a major renewable in many countries over the next decades. The fundamental question in this regard is whether a wave farm can be used to reduce beach erosion under storm conditions. If the answer to this question is positive, then a wave farm can have coastal defence as a subsidiary function, in addition to its primary role of producing carbon-free energy. The objective of this work is to address this question by comparing the response of a beach in the face of a storm in two scenarios: with and without the wave farm. For this comparison a set of ad hoc impact indicators is developed: the bed level impact (BLI), beach face eroded area (FEA), non-dimensional erosion reduction (NER), and mean cumulative eroded area (CEA); and their values are determined by means of two coupled models: a high-resolution wave propagation model (SWAN) and a coastal processes model (XBeach). The study is conducted through a case study: Perranporth Beach (UK). Backed by a well-developed dune system, Perranporth has a bar between − 5 m and − 10 m. The results show that the wave farm reduces the eroded volume by as much as 50% and thus contributes effectively to coastal protection. This synergy between marine renewable energy and coastal defence may well contribute to improving the viability of wave farms through savings in conventional coastal protection. 相似文献
10.
11.
Numerical models for shoreline evolution have been used for coastal management planning for several decades. The model calibration is a start point to project shoreline scenarios and in this aim the use of data acquired within the scope of monitoring programmes provides the opportunity to assess the models' capabilities under real condition. This work applies calibration data (retrieved from field surveys) to numerical models to predict medium-term shoreline evolution using, as a case study, a beach stretch named AC, about 3.5 km long and located downdrift of a groin on the northwest Portuguese coast. A smaller stretch AB (2.4 km long), included in the total one, which exhibits a pronounced erosive tendency usually better reproduced in shoreline evolution models, was also analysed. Based on topographic surveys, associated wave climate conditions registered between 2003 and 2008 and typical wave conditions registered over a longer wave climate time period, this work compares the calibration of two different shoreline evolution models, Long-term Configuration (LTC) and GENESIS for this period. Then, considering the 2003 topographic conditions for the models' calibration, the results of both models are discussed with respect to simulation scenarios after 10, 15 and 20 years of evolution. The 10-year evolution projections of the models are also compared to the results of a survey performed in February 2012. For the wave data calibration period (2003–2008), the average shoreline retreat of the analysed coastal stretch was reproduced with small differences (around 1% and 10% for LTC and 15% and 14% for GENESIS, considering stretches AB or AC, respectively), though local differences along the AB coastal stretch represent root mean square errors reaching up to 52% and 88% for GENESIS and LTC, respectively, and were above 118% for both models along the AC coastal stretch. 相似文献
12.
Ocean surface gravity waves play a major role in many engineering and environmental problems, both in the open ocean and in coastal zones. Therefore, it is essential to improve our knowledge on spatial and temporal variability of wave climate. This study aims at investigating this variability in the North-East Atlantic Ocean (25°W–0°W and 30°N–60° N), using a 57-year hindcast (1953–2009) obtained with a spectral wave model forced with reanalysis wind fields. The hindcast analysis reveals firstly strong seasonal fluctuations of wave climate, with winters characterized by large and long-period waves of mean direction spreading from south-west to north-west, and summers characterized by smaller and shorter-period waves originating from norther directions. From northern (55°N) to southern (35°N) latitudes, the significant wave height (Hs) decreases by roughly 40%, the mean wave direction (Mwd) rotates clockwise by about 25% while the peak period (Tp) only grows by 5%. These three parameters also exhibit a strong inter-annual variability, particularly when winter-means (from 1st of December to 1st of April) are considered. Linear trend analysis over the studied period shows spatially variable long-term trends, with a significant increase of Hs (up to 0.02 m yr?1) and a counterclockwise shift of Mwd (up to ?0.1° yr?1) at northern latitude, contrasting with a fairly constant trend for Hs and a clockwise shift of Mwd (up to +0.15° yr?1) at southern latitudes. Long-term trends of Tp are less significant, with still a slight increase in the north-eastern part of the study area (up to +0.01 s yr?1). Eventually, a comparison between the inter-annual variability of the winter-means of the three selected wave parameters and the North Atlantic Oscillation (NAO) reveals: (1) a strong positive correlation between Hs and the NAO index at northern latitudes (correlation coefficient up to R = 0.91) and a significant negative correlation at southern latitudes (up to R = ?0.6); (2) no significant correlation for Mwd north of 40°N and a clear positive correlation southward of 40°N (up to R = 0.8) and (3) a northward increasing correlation for Tp (up to R = 0.8). Long-term trends for Hs, Mwd and Tp are finally explained by a significant increase in the NAO index over the studied period. 相似文献
13.
Estimation of erosion volumes for adequate dry beach buffer zones is commonly estimated on the basis of a single extreme event, such as the 1 in 100 year storm. However, the cumulative impact of several smaller, closely spaced storms can lead to equal, if not more, dry beach loss, but this is often not quantified. Here we use a calibrated model for dune erosion, XBeach, to hindcast the cumulative erosion impact of a series of historical storms that impacted the Gold Coast, Queensland region in 1967. Over a 6-month period, four named cyclones (Dinah, Barbara, Elaine, and Glenda) and three East Coast Lows caused a cumulative erosion volume greater than the predicted 1 in 100 year event. Results presented here show that XBeach was capable of reproducing the measured dry beach erosion volume to within 21% and shoreline retreat to within 10%. The storms were then run in 17 different sequences to determine if sequencing influenced final modeled erosion volumes. It is shown that storm sequencing did not significantly affect the total eroded volumes. However, individual storm volumes were influenced by the antecedent state of the beach (i.e. prior cumulative erosion). Power-law relationships between cumulative energy density (∑ E) and eroded volume (∆V) as well as cumulative wave power ((∑ P)) and eroded volume (∆V) both explained more than 94% of the modeled dry beach erosion for the 1967 storm sequences. When the relationship was compared with observed and modeled erosion volumes for similar beaches but different storm forcing, the inclusion of pre-storm beach swash slope (βswash) in the parameterization was found to increase the applicability of the power-law relationship over a broader range of conditions. 相似文献
14.
Torrey Pines State Beach, a site with large seasonal fluctuations in sand level, received a small shoreface beach fill (about 160,000 m3) in April 2001. The 600 m-long, flat-topped nourishment pad extended from a highway riprap revetment seaward about 60 m, terminating in a 2 m-tall vertical scarp. A 2.7 km alongshore span, centered on the nourishment region, was monitored prior to the nourishment and biweekly to monthly for the following 2 years. For the first 7 months after the nourishment, through fall 2001, significant wave heights were small, and the elevated beach fill remained in place, with little change near and above Mean Sea Level (MSL). In contrast, the shoreline accreted on nearby control beaches following a seasonal pattern common in southern California, reducing the elevation difference between the nourished and adjacent beaches. During the first winter storm (3 m significant wave height), the shoreline retreated rapidly over the entire 2.7 km survey reach, forming an alongshore-oriented sandbar in 3 to 4 m water depth [Seymour, R.J., Guza, R.T., O'Reilly, W., Elgar, S., 2004. Rapid erosion of a Southern California beach fill. Coastal Engineering 52 (2), 151–158.]. We show that the winter sandbar, most pronounced offshore of the nourishment, moved back onto the beach face during summer 2002 (following the usual seasonal pattern) and formed a wider beach above MSL at the site of the original nourishment than on the control beaches. Thus, the April 2001 shoreline nourishment was detectable until late fall 2002, persisting locally over a full seasonal cycle. In an extended 7-year time series, total sand volumes (summed between the back beach and 8 m water depth, over the entire 2.7 km reach) exhibit multi-year fluctuations of unknown origin that are twice as large as the nourishment volume. 相似文献
15.
P.S. Pereira L.J. Calliari R. Holman K.T. Holland R.M.C. Guedes C.K. Amorin P.G. Cavalcanti 《Marine Geology》2011,279(1-4):210-221
Besides the different scales within which coastal processes manifest their energy, the majority of the world's coastal regions exhibit forms of sediment heterogeneity that are physically significant. One example of a heterogeneous environment is Cassino beach, located at the southernmost part of Brazil, a fine-grain-sized sandy beach where fluid mud sporadically is transported to the nearshore and eventually onto the beach. At this site in 2005, as part of a field experiment, a video system was installed. Three years after the installation, a large mud transgression event took place in February 2008 and had 5 km of extension. In this context, the goal of the present work is to characterize the mud deposition pattern across the surf zone, describing the consequences of mud on nearshore dynamics using remote sensing techniques, beach profiles and suspended matter concentration. The surveyed beach profiles registered the deposition of fluid mud at the inner surf zone with concentrations up to 12 mg/l. The material was deposited close to the shoreline and had a cross-shore width of 100 m during the first deposition day occupying the entire water column. From surf zone time series of pixel intensity, it was possible to detect the attenuation of the surface wave spectra due to the presence of fluid mud. The combination of video techniques and field data allowed one to follow the formation of a double-layer system, where fluid mud overlays the sandy bottom. The video-based system at Cassino demonstrated that remote detection of fluid mud and quantification of its effect on the nearshore dynamics is feasible. The combination of beach profiles, measurements of suspended matter concentration and intensity timestacks allowed the analysis of the short-term evolution of the mud depositional processes. 相似文献
16.
A diagnostic of coastal erosion and shoreline retreat occurring at a 7-km long sandy beach (Littoral Cell III) located in Todos Santos Bay (Baja California, Mexico) is performed trough the analysis of aerial photographs. Around 82,000 m2 of this sandy beach have been lost in a 20 year period (1985–2005), at a beach loss rate of 2,100 m2 per year. This indicates that coastal erosion is becoming a hazard to human lives and coastal infrastructure. Due to the latter, the implementation of a Shoreline Erosion Management Plan (SEMP) is proposed as the best management approach to deal with the problem. The Littoral Cell III SEMP considers four core policies, eight management strategies and a group of specific measures. 相似文献
17.
《Estuarine, Coastal and Shelf Science》2005,62(1-2):253-270
Evidence suggests that patterns of benthic community structure are functionally linked to estuarine processes and physical characteristics of the benthos. To assess these linkages for coarse-sediment shorelines, we used a spatially nested sampling design to quantify patterns of distribution and abundance of both macroinfauna and macroepibiota. We examined replicate beach segments within a site (∼1 km), sites within areas of relatively uniform salinity and temperature (∼10 km), and areas (∼100 km) in the two major basins of Puget Sound, Washington. Because slight variations in physical characteristics of a beach can lead to significant alterations in biota, we minimized confounding physical influences by working only in the predominant shoreline habitat type in Puget Sound, a mixture of sand, pebbles and cobbles. Species richness decreased steadily from north to south along gradients of declining wave energy, increasing temperature and decreasing salinity. A few taxa were confined to the South Basin, but many more were found in the North. Most of the variability in population abundance was captured at the smaller spatial scales. Physical conditions tend to become increasingly different with distance among sites. Communities became more different from north to south as species intolerant of more estuarine conditions dropped out. There was significant spatial autocorrelation among populations on neighboring beach segments for 73 of the 172 species sampled. Populations of these benthic species may be connected via dispersal on scales of at least km in Puget Sound. Our results strengthen prior conclusions about the strong linkages between the biota and physical patterns and processes in estuaries. It is important for monitoring and impact-detection studies to account for natural variation of physical gradients across the sampling scales used. Nested, replicated sampling designs can facilitate the detection of environmental change at spatial scales ranging from global (e.g., warming or El Niño), to regional (e.g., estuary-wide changes in salinity patterns), to local (e.g., from development at a site). 相似文献
18.
在波浪和水流的作用下,泥沙在不同时间尺度下的运动会引起沙滩的冲淤演变,对海岸资源有重要的影响。因此,了解沙滩季节性演变规律,并采取针对性的防护措施,是近岸沙滩亟须解决的问题。目前,现场观测是研究沙滩剖面冲淤演变的重要方法,通过沉积物组成、岸滩坡度及波浪动力的时空变化,了解沙滩剖面的变化特性,对于沙滩管理和海岸保护具有十分重要的意义。基于2017年9月—2019年11月在荣成楮岛南岸沙滩每个月采集一次的剖面数据,以及波浪动力数据,分别探究了沙滩在不同时间尺度下的变化特征,并对沙滩变化特征与波浪动力因素的相关性进行了探讨。研究发现：楮岛南岸沙滩形态变化具有较强的季节性特征,春季沙滩比较稳定;夏季沙滩受台风影响侵蚀严重,但在风暴过后的短时间内,沙滩泥沙恢复较快;冬季沙滩恢复速度逐渐减缓并趋于稳定。在夏季和冬季期间,波能流密度的向岸分量对楮岛南沙滩的演变产生重要作用,而且波能流密度向岸分量的均值（选取数据采集前15 d的波浪条件参与计算）与沙滩体积的相关性最好,并给出了两者的线性拟合公式。 相似文献
19.
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
20.
Yuning Hong Jinju Geng Song Qiao Lili Ding Xueyuan Gu Xiaorong Wang Dietmar Glindemann Hongqiang Ren 《Marine Chemistry》2010,118(1-2):67-74
Phosphine is a natural gaseous compound in the phosphorus biogeochemical cycle. This paper studies the spatial and temporal distributions of matrix-bound phosphine (MBP) and gaseous phosphine in the offshore area of the Southwest Yellow Sea, East Asia. The results show that MBP concentrations in marine surface sediments range from 0.69 ± 0.06 ng/kg (dry) to 179 ± 29 ng/kg (dry). Higher seasonal MBP concentrations in sediments are found in fall than in spring or winter in most sites. High MBP contents are observed in two fish-breeding areas. MBP concentrations decrease with distance to the coast, except in the southeast of the sampling area. MBP levels in marine sediments are found to be higher than those at several other places: freshwater sediments and soil, except eutrophic lakes. Gaseous phosphine contents in fall range from 0.14 ± 0.00 ng/m3 to 9.83 ± 0.97 ng/m3. No correlation is observed between MBP and gaseous phosphine. 相似文献