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1.
In an earlier paper a particular discrete wavelet transform (DWT) was used to study the complex variation of beach profile changes. However, use of the DWT requires that the sequence of spatial and temporal resolution is fixed as a dyadic sequence, which means that the variability over longer intervals is not characterised well. Here we introduce the discrete wavelet packet transform (DWPT) that uses an adaptive scaling to partition the data variance, according to an entropy cost function. The advantages of this approach are demonstrated by its application to the study of temporal variability of a 22 year record of beach profile data from the Field Research Facility (FRF) at Duck, North Carolina, USA. Time series of beach elevations at three locations across a particular profile are investigated in detail. We conclude that the DWPT provides a superior analysis of non-stationary time series to that of the DWT, with improved resolution of the scale intervals of the variability. The beach elevation around the shoreline is shown to respond at both sub-annual and interannual scales, but variability at an annual scale is weak. Moving seaward into deeper water, the variance is partitioned into fewer and longer scales. It is confirmed that elevation changes around the inner bar at Duck exhibit a strong interannual variation consistent with Plant et al. (Plant, N.G., Holman, R.A. and Freilich, M.H., 1999. A simple model for interannual sandbar behaviour. Journal of Geophysical Research 104(C7), 15755–15776). Around 23% of the variance around the inner bar is explained at the temporal scale of 64–128 months, which is consistent with the bar behaviour of 6 years found by Ruessink et al. (Ruessink, B. G., Wijnberg, K. M., Holman, R. A., Kuriyama, Y. and Van Enckevort, I. M. J., 2003. Intersite comparison of interannual nearshore bar behaviour. Journal of Geophysical Research, 108 (C8): 1–12). A significant new finding is, however, that about 26% of the variance is attributable to temporal scales of 16–21.3 months. Reconstruction of the wavelet packet components for individual temporal scales is shown to provide a means for identifying the impact and scale of non-stationary events, such as storms, on the beach response. This provides further information that can be used to interpret the morphological changes in terms of the forcing processes and also serves to inform morphodynamic modelling. 相似文献
2.
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
3.
对粤西水东弧形海岸长时段重复测量海滩剖面的因子分析说明了各特征岸段剖面的主要地貌状态。频域分析反映了各岸段海滩体积的月周振动峰值和对波能的响应特征。实测海滩剖面波动过程的计算则指示了当前各剖面的蚀积状态。 相似文献
4.
Omar Defeo Anton McLachlan David S. Schoeman Thomas A. Schlacher Jenifer Dugan Alan Jones Mariano Lastra Felicita Scapini 《Estuarine, Coastal and Shelf Science》2009
We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders. 相似文献
5.
The temporal characteristics and spatial structures of high frequency variability of the current in the western channel of the Tsushima/Korea Straits (TKS) are studied using ADCP data from 10?years along the cruise line of a regular ferry, “Camilla”, between Busan and Hakata. The eddy kinetic energy analysis shows that the high frequency variability has strong seasonal and spatial dependencies. From December to April, the variability is prominent in the entire western channel of the TKS. From July to October, it is enhanced only in the Korean coastal zone. The EOF analysis for the component of the high frequency currents normal to the ferry route illuminates three types of dominant modes, a transport mode and a vortex mode in the western channel during December–April, and a baroclinic coastal-trapped mode in the Korean coastal zone during July–October. The transport mode with a uniform current direction throughout the channel shows good correlation with the high frequency variability of the volume transport through the western channel with dominant time scales of 3.5 and 7?days. The vortex mode with alternating current directions across the channel explains well the variability of the eddy vorticity in the western channel with dominant time scales of 5–8?days. The baroclinic coastal-trapped mode in the Korean coastal zone has characteristics of both baroclinic Kelvin wave and topographic Rossby wave in the vertical current structure with dominant time scales of 14 and 32?days. 相似文献
6.
This paper presents a new framework for probabilistic modelling of long-term beach evolution in the vicinity of detached breakwaters. The study focuses on the key physical processes contributing to beach variability over a range of spatial and temporal scales. Based on a one-line model, the framework is enhanced with sophisticated solutions for beach-wave-structure interaction, diffraction together with a treatment of varying tide level. The sediment transport rate is calibrated at regional and local levels using data from bespoke field campaigns and site-specific coefficients are proposed. Monte Carlo simulation is conducted for long-term shoreline simulation under a sequence of time varying sequence of waves, currents and tidal levels. The results of the Monte Carlo simulation give an insight into the statistical characteristics of beach behaviour within the defence system. In particular, regions within the scheme that are relatively stable and those that exhibit greater natural fluctuations are identified. 相似文献
7.
On the basis of the experimental investigations conducted from an oceanographic tower, the variability of the structure of
temperature profiles has been analysed. The paper provides a classification of the basis types of temperature profiles and
determines their frequencies and duration in the annual cycle. Dynamics of the transition from one type of a temperature profile
to another has been found to have synoptic scales. The variability of parameters during an occurrence of some typical profile
have been assessed; it has been deduced that variations in profile shape are linked with fine structure effects of internal
waves.
Translated by Vladimir A. Puchkin. 相似文献
8.
《Coastal Engineering》2001,43(1):41-58
Temporal and spatial variations in shoreline position along the southern Baltic coast were investigated using singular spectrum analysis (SSA) with the overall aim to determine characteristic patterns in the shoreline response and whether these patterns displayed forced or self-organized behavior. The investigated beach is located at Lubiatowo on the Polish Coast and is mildly sloping with multiple bars having a median grain size of 0.22 mm, being typical for the coast in the southern Baltic Sea. Data on coastal morphology have been collected at Lubiatowo including (1) bathymetric surveys since 1987 twice a year to cover changes in the seabed (along 27 lines covering a longshore×cross-shore area of 2600×1000 m), and (2) beach topography surveys since 1983 every 4 weeks on the average, extending from the shoreline to the dune foot (along the same 27 lines). Furthermore, several dedicated field campaigns have been carried out at Lubiatowo, as well as measurements of deep-water wave properties since 1998. SSA was employed to the time series of shoreline position from all 27 survey lines. The analysis method demonstrated a large potential for detecting temporal patterns from fairly short and noisy time series with irregular sampling interval. In summary, three dominant patterns emerged jointly reproducing 70–90% of the overall variation in the data for the different survey lines. These temporal patterns were demonstrated to represent forced and self-organized components describing the variation in shoreline position. The forced components could be related to the mean properties of the wave climate, whereas the self-organized components were mainly influenced by particular events or features of the beach such as storm waves, storm surges, beach type (dune, cliff), and sediment characteristics. 相似文献
9.
湄洲岛西南部海滩因1996年建造对台客运码头，引起了海滩剖面的变化，码头前沿淤积而报废。经过5年后，海滩剖面仍未能完全趋于平衡。为了了解码头建设对重塑后海滩的季节变化影响，在2001年3月、7月、10月和12月对码头所在海滩剖面地形进行季节重复测量，并对剖面变化进行比较分析。结果表明，重塑后海滩剖面的季节变化存在区段差异性，码头工程区海滩剖面仍表现为不断淤积，表明5年来工程建设造成海滩重塑后的变化过程还在继续；过渡区海滩剖面较工程区淤积程度减弱，部分剖面表现为侵蚀趋势，但总体逐渐向正常海滩剖面的季节变化方向发展；正常区海滩剖面的季节变化具有一定的规律性，表现为夏季上部侵蚀（后滨和高潮带）下部淤积（低潮带和浅水区），冬季上部淤积下部侵蚀，春、秋两季为中间过渡剖面形态。 相似文献
10.
以渤海海域为试验区,对经过时间、空间和波段匹配的 MODIS/Aqua 550 nm 气溶胶光学厚度产品与 CALIOP 532 nm 通道反演得到的气溶胶信息在五种不同空间采样窗口(10 km ×10 km,30 km ×30 km,50 km ×50 km,70 km ×70 km 和90 km ×90 km)、三种不同时间尺度(日、月、季度)下进行了相关性拟合分析.研究发现,较小的空间采样窗口可以更准确地反映气溶胶的局部变化特征,而以季度为时间统计单元能更好地体现气溶胶的季节变化特性.实验结果表明,在10 km ×10 km 采样窗口中,春季的日数据之间相关性较高;春季和秋季的月均值之间高度相关(R 均大于0.950).从而证明,在特定时间和空间尺度下,上述两种数据之间确存在良好的相关性,为利用遥感数据反演渤海海域气溶胶光学厚度信息提供了新的途径. 相似文献
11.
Beach profiles characteristics along Giao Thuy and Hai Hau coasts, Vietnam: A field study 总被引：1，自引：0，他引：1
Giao Thuy and Hai Hau coasts are located in Nam Dinh province, Vietnam, with a total coastline of 54.42 km in length. The sea-dike system has been seriously damaged and there have been many dike breaches which caused floods and losses. This situation is considered of a general representative for coastal area in the northern part of Vietnam. A variety of studies have shown that the gradient in the longshore sediment transport rate and the offshore ?ne sediment lost are the main mechanisms causing the beach erosion. This study presents a field investigation of the beach profiles at Giao Thuy and Hai Hau beaches. Three types of empirical functions for the equilibrium beach profile are applied and compared with the observations. Results show that all observed beach pro?les can be described by a single function. However, one specific equilibrium pro?le equation is not sufficient to assess all beach pro?les. In Section 1 of Giao Thuy and Section 3 of Hai Thinh beaches, beach profiles are consistent with the logarithmic function, while the exponential function fits well in Section 2. This difference is explained with respect to coastal morphology, sediment characteristics and hydrodynamic conditions which vary in site. An analysis of the validity of the beach profile functions is recommended for the numerical modeling and engineering designs in this area. 相似文献
12.
《Coastal Engineering》2002,47(2):211-235
Shore and shoreline evolution both due to natural and human-induced causes or factors can be variable over a wide range of different temporal and/or spatial scales. Our capability to understand and especially predict this variability is still limited. This can lead to misinterpretation of coastal change information, which hampers informed decision making and the subsequent design and implementation of (soft) engineering interventions. Collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention. This paper describes causes and factors for the variability and the resulting possible evolutions of wave-dominated shores and shorelines, which are illustrated by a number of case studies. The new element of this work is that the variability is described in terms of a range of different time and space scales, which helps to structure such analysis. However, it is difficult to generalise the results for arbitrary situations, especially on decadal time scales. Scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability. 相似文献
13.
通过物理模型实验研究了海岸沙坝剖面和滩肩剖面的形成和演化过程,给出了稳定的沙坝剖面和滩肩剖面的几何特征。实验中考虑了两种初始坡度(1∶20和1∶10)和不同波高的规则波和不规则波,讨论了不同初始坡度海岸上破碎波空间分布特征。结果表明,沙坝产生后存在向岸和离岸两种运动形态,但最终将停留在稳定位置。稳定的沙坝剖面对应不同初始坡度和波浪存在不同的大沙坝和小沙坝分布。沙坝剖面由长时间小波高波浪序列作用后可转化为稳定滩肩剖面,该剖面不依赖于波浪和初始坡度。实验也给出了平衡剖面与理论曲线的对比以及剖面上泥沙粒径的分布。 相似文献
14.
We analysed the consistence of vertical patterns of distribution (i.e. zonation) for macrofauna at different spatial scales on four intermediate exposed beaches in the North of Portugal. We tested the hypothesis that biological zonation on exposed sandy beaches would vary at the studied spatial scales. For this aim, abundance, diversity and structure of macrobenthic assemblages were examined at the scales of transect and beach. Moreover, the main environmental factors that could potentially drive zonation patterns were investigated. Univariate and multivariate analyses revealed that the number of biological zones ranged from two to three depending on the beach and from indistinct zonation to three zones at the scale of transect. Therefore, results support our working hypothesis because zonation patterns were not consistent at the studied spatial scales. The median particle size, sorting coefficient and water content were significantly correlated with zonation patterns of macrobenthic assemblages. However, a high degree of correlation was not reached when the total structure of the assemblage was considered. 相似文献
15.
The complexity of the relationships between environmental factors and organisms can be revealed by sampling designs which consider the contribution to variability of different temporal and spatial scales, compared to total variability. From a management perspective, a multi-scale approach can lead to time-saving. 相似文献
16.
This paper presents a methodology for modelling medium term (annual to decadal) cross shore beach profile change and erosion. The statistical-process based approach (SPA) presented here combines detailed statistical modelling of offshore storm climate with a process based morphodynamic model (XBeach), to assess, and quantify morphodynamic variability of cross shore beach profiles. Until now, the use of process based models has been limited to simulations at storm event timescales. This methodology therefore represents the first application of a fully process based model in longer term simulations, as such, the approach requires simulation of post-storm beach profile recovery as well as individual event impacts. Narrabeen Beach, NSW, Australia was used as a case study for application of the technique due to the availability of an extensive set of storm and beach profile data. The results presented here demonstrate that the methodology produces encouraging results for determining medium term beach profile variability and erosion. 相似文献
17.
18.
Assessment and integration of conventional,RTK-GPS and image-derived beach survey methods for daily to decadal coastal monitoring 总被引：1，自引：0，他引：1
Coastal monitoring across a broad range of time-scales was recognized in the latest report by the Intergovernmental Panel on Climate Change as key to better understanding the likely impacts of climate change at the coast. A unique and historic coastal monitoring program undertaken at the Collaroy–Narrabeen embayment in south-eastern Australia comprises: 1) 30 years of monthly conventional (Emery method) surveys of five cross-shore profile lines; 2) three years of monthly three-dimensional surveys of the entire embayment using RTK-GPS mounted to an all-terrain vehicle (ATV); and 3) four years of hourly shoreline measurements using coastal imaging technology (ARGUS). This study evaluates the strengths and limitations of conventional, RTK-GPS and image-derived surveys for coastal monitoring at daily to decadal coastal time-scales. High-accuracy RTK-GPS was used to first assess the accuracy of the conventional and image-derived survey methods. The magnitude of daily to decadal coastal variability was then characterized by calculating the temporal semivariogram of the integrated survey dataset. With both measurement errors and the degree of beach variability quantified, the corresponding signal-to-noise ratios (SNR) of each survey method at different time-scales were determined. The value of the simple and cost-effective Emery method was verified by this analysis, with measurement error significantly smaller than the degree of overall beach variability (SNR = 8.4). The accuracy, speed and efficiency of ATV-mounted RTK-GPS meanwhile make it suitable for three-dimensional beach surveys. Image-derived surveys were found to be an effective means of remotely measuring the considerable degree of beach variability identified at time-scales of less than one month. These measurements however become indistinguishable from survey noise (i.e. SNR ≤ 1) when considering typical weekly (or smaller) variations at large distances from the cameras. 相似文献
19.
Zbigniew Pruszak 《Coastal Engineering》1993,19(3-4)
Sea bottom changes in the cross-shore direction have been analysed. The cross-shore profile, as a major factor of beach configuration, has been presented schematically as a superposition of a basic curve reflecting the mean layout and slope of the shore given by Dean's function
and superimposed various bars, troughs, berms, etc. depicting local characteristic features of the profile.The local features of the profile have been analysed by use of one- (1-D) and two-dimensional (2-D) empirical orthogonal functions.On the basis of field observations and measurements the parameter A has been presented as a function of time. Three time scales have been distinguished (short, seasonal and long-term) with respect to which more or less regular changes of the parameter A occur. The modified parameter A was applied to two different field sites, namly Lubiatowo, Baltic Sea (Poland) and Gold Beach, Black Sea (Bulgaria). It has been found that in extreme cases the parameter A can vary in time by a factor of two, or more, for the same grain size distribution. 相似文献
20.
David Balata Stefano Acunto Francesco Cinelli 《Estuarine, Coastal and Shelf Science》2006,67(4):553-561
Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biological factors. This study was conducted in conditions of high turbidity of the water and examined the spatio-temporal variability and the vertical distribution at two different depths of a low rocky subtidal assemblage. Algal and invertebrate organisms were sampled at a range of spatial scales extending from meters to a few kilometers, over a period of 21 months. Results indicated that patterns of distribution and abundance of organisms differed between the two depths and at the smallest spatial scales examined. These differences were due to differences in relative abundance rather than differences in composition of taxa. Results showed that assemblages varied largely among dates of sampling, suggesting that temporal variability of these organisms may be more important than previously stated. The patchy distribution and the peculiar life traits of most taxa of these assemblages allowed the concept of metapopulation and metacommunity to be applied to this system. This might have implications for predictions of the responses of subtidal assemblages to environmental changes due to anthropogenic activities. 相似文献