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1.
T.D. Price  B.G. Ruessink   《Marine Geology》2008,251(1-2):98-109
This paper builds on the work of Masselink [Masselink, G., 1993. Simulating the effects of tides on beach morphodynamics. J. Coast. Res. SI 15, 180–197.] on the use of the residence times of shoaling waves, breaking waves and swash/backwash motions across a cross-shore profile to qualitatively understand temporal beach behaviour. We use a data set of in-situ measurements of wave parameters (height and period) and water depth, and time-exposure video images overlooking our single-barred intertidal measurement array at Egmond aan Zee (Netherlands) to derive boundaries between the shoaling zone, the surf zone and the swash zone. We find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness. This contrasts with the use of constant relative wave heights or water levels in earlier work. We use the obtained boundaries and a standard cross-shore wave transformation model coupled to an inner surf zone bore model to show that large (> 5) relative tide ranges (RTR, defined as the ratio tide range–wave height) indicate shoaling wave processes across almost the entire intertidal profile, with surf processes dominating on the beach face. When the RTR is between 2 and 5, surf processes dominate over the intertidal bar and the lower part of the beach face, while swash has the largest residence times on the upper beach face. Such conditions, associated with surf zone bores propagating across the bar around low tide, were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen. For RTR values less than about 2, surf zone processes dominate across the intertidal bar, while the dominance of swash processes now extends across most of the beach face. The surf zone processes were now observed to lead to offshore bar migration, while the swash eroded the upper beach face.  相似文献   

2.
A video-based technique for mapping intertidal beach bathymetry   总被引：2，自引：0，他引：2  
Measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research, monitoring and design applications. With the advent of digital imaging technology, shore-based video systems provide continuous and automated data collection, encompassing a much greater range of time and spatial scales than were previously possible using field survey methods.A new video-based technique is presented that utilises full-colour image information, which overcomes problems associated with previous grey-scale methods, which work well at steep (reflective) sites, but are less successful at flatter (dissipative) sites. Identification of the shoreline feature is achieved by the automated clustering of sub-aqueous and sub-aerial pixels in ‘Hue–Saturation–Value’ (HSV) colour space, and applying an objective discriminator function to define their boundary (i.e., ‘shoreline’) within a time-series of consecutive geo-referenced images. The elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information, which is incorporated in a model that combines the effects of wave set-up and swash, at both incident and infragravity frequencies.Validation of the technique is achieved by comparison with DGPS survey results, to assess the accuracy of the detection and elevation methods both separately and together. The uncertainties associated with the two sub-components of the model tend to compensate for each other. The mean difference between image-based and surveyed shoreline elevations was less than 15 cm along 85% of the 2-km study region, which corresponded to an horizontal offset of 6 m. The application of the intertidal bathymetry mapping technique in support of CZM objectives is briefly illustrated at two sites in The Netherlands and Australia.  相似文献   

3.
A data–model assimilation method (called “Beach Wizard”) is presented with which the nearshore subtidal bathymetry can be accurately estimated based on video-derived observations of wave roller dissipation and variation of the intertidal shoreline, and/or radar-derived observations of wave celerity. Using many consecutive images, these observed properties are compared with numerical model results, and through a simple, optimal least-squares estimator approach the estimated bathymetry is adjusted gradually for each image in order to improve the fit between model output and observations. The key advantages of the technique are that it is based on multiple sources of information (i.e., different remote sensors and/or data products), depends on only a few free parameters (to which the model results are insensitive), and shows good skill. Herein, the technique is applied to a synthetic case and two sets of field data from sites at Duck, NC (USA) and Egmond (The Netherlands). The method, which may be extended with observations of other properties from other sources than the three described in this paper, can deliver coastal state information (i.e., simultaneous updates of bathymetry, waves, and currents) with high temporal and spatial resolution and can be used in conjunction with or instead of in-situ measured data.  相似文献   

4.
The aim of this paper is to propose an integrated low cost system for monitoring the performance of beach defence works during storms. For this purpose, the site of Igea Marina, Northern Adriatic Sea, Italy, which is protected by low crested detached breakwaters, is selected. The monitoring system is composed by a video installation, for the identification of the shoreline position and of the intertidal bathymetry at high space and time resolution, and a 2DH numerical model, to reconstruct the hydrodynamics induced by coastal defenses. The accuracy of the monitoring system is verified against available measurements of waves and currents performed during a field campaign with acoustic Doppler profilers. Assimilation of data on the shoreline position in 2DH model operatively working is challenging in the improvement of the production of risk maps. These show the current intensities and flooded areas during forecasted storms. First promising results suggest the possibility of setting up an early warning tool.  相似文献   

5.
Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.  相似文献   

6.
Information regarding the composition and extent of benthic habitats on the South East Australian continental shelf is limited. In this habitat mapping study, multibeam echosounder (MBES) data are integrated with precisely geo-referenced video ground-truth data to quantify benthic biotic communities at Cape Nelson, Victoria, Australia. Using an automated decision tree classification approach, 5 representative biotic groups defined from video analysis were related to hydro-acoustically derived variables in the Cape Nelson survey area. Using a combination of multibeam bathymetry, backscatter and derivative products produced highest overall accuracy (87%) and kappa statistic (0.83). This study demonstrates that decision tree classifiers are capable of integrating variable data types for mapping distributions of benthic biological assemblages, which are important in maintaining biodiversity and other system services in the marine environment.  相似文献   

7.
由于近岸视频监测技术具有构建成本低、时空分辨率高的特点,近年来已成为海岸动态监测的互补手段。在近岸视频监测中,水边线可作为岸滩边缘位置变化的替代指标,受复杂海滩地形及不规则的波浪及潮汐变化影响,如何从视频图像中准确检测水边线是近岸视频监测所面临的挑战问题之一。本文针对传统图像处理方法在水边线提取中存在的效率不高和抗噪声能力差等问题,将CIELab颜色模型和蚁群优化算法相结合,对台风风暴潮期间石老人海滩的水边线进行提取和定量分析,并与传统算法进行对比。对青岛石老人海滩2011年台风期间的实时影像资料分析结果表明,与传统的提取算法相比,本文提出的方法在数字视频影像的水边线监测应用中可靠性高,并具有良好的细节呈现能力和抗边缘噪声能力,适用于弱边缘水边线的提取。分析结果验证了本方法在极端天气条件下对视频影像中水边线动态变化的自动提取可行性,对构建长时序海滩岸线动态变化影像自动分析系统具有较好的应用价值。  相似文献   

8.
The performance of two well-known equations to predict the depth-averaged alongshore suspended sediment flux [Van Rijn, L.C., 1984. Sediment transport, part II: suspended load transport. Journal of Hydraulic Engineering 110, 1613–1641; and Bailard, J.A., 1981. An energetics total load sediment transport model for a plane sloping beach. Journal of Geophysical Research 86, 10938–10954] was assessed by comparing predictions with 2306 field estimates based on a vertical stack of three optical backscatter sensors and a single electromagnetic flow meter. The observations were collected at four cross-shore positions on the intertidal beach of Egmond aan Zee, the Netherlands, during calm to storm conditions, with the offshore significant wave height peaking at 3.7 m. Measured hydrodynamics were employed in the computations of both models. Also, default parameter values were used without calibration to the data. We found that both models underpredicted the observations. Overall, the Van Rijn model outperformed the Bailard model, with about 70% of the model prediction lying between 1/5 to 5 of the observations under energetic conditions. For the Bailard model this was only about 20%. The performance of the Van Rijn model is, however, sensitive to the wave-related roughness, one of its highly uncertain free parameters. This may allow for an easy calibration when estimates of the depth-averaged alongshore sediment flux are available but may lead to serious errors in situations without data to constrain the predictions. We suspect that the discrepancy between the observations and model predictions is due to an overestimation of the observed fluxes (high turbidity, air bubbles) and an underestimation of the modeled fluxes because of missing physics related primarily to breaking waves.  相似文献   

9.
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   

10.
Digital filters designed using wavelet theory are applied to high resolution deep-towed side-scan sonar data from the median valley walls, crestal mountains, and flanks of the Mid-Atlantic Ridge at 29°10 N. With proper tuning, the digital filters are able to identify the location, orientation, length, and width of highly reflective linear features in sonar images. These features are presumed to represent the acoustic backscatter from axis-facing normal faults. The fault locations obtained from the digital filters are well correlated with visual geologic interpretation of the images. The side-scan sonar images are also compared with swath bathymetry from the same area. The digitally filtered bathymetry images contain nine of the eleven faults identified by eye in the detailed geologic interpretation of the side-scan data. Faults with widths (measured perpendicular to their strike) of less than about 150 m are missed in the bathymetry analysis due to the coarser resolution of these data. This digital image processing technique demonstrates the potential of wavelet-based analysis to reduce subjectivity and labor involved in mapping and analyzing topographic features in side-scan sonar and bathymetric image data.  相似文献   

11.
《Coastal Engineering》2007,54(6-7):493-505
This contribution evaluates the application of coastal video systems to monitoring and management of coastal stability problems on sandy coastlines. Specifically, video-derived parameters (coastal state indicators or CSIs) are developed which facilitate the measurement of the shoreline evolution (erosion/accretion) and response to storms, seasonal cycles and anthropogenic interventions like beach/shoreface nourishment and dredging. The primary variable which forms the basis for all the CSIs discussed in this contribution is the shoreline position derived from time-averaged video images. These waterlines are used to generate secondary products including shoreline contours at a constant pre-defined level, (intertidal) beach volumes, and momentary shoreline positions which reflect the sand volume in a meter wide section of the intertidal coast. Video-derived coastal state indicators were verified via comparisons with traditional topographical/bathymetric surveying techniques and a good agreement was found in all cases. CSIs were computed for three contrasting sandy coastal environments including an unprotected natural beach, a protected beach and a spit. Firstly, results are presented which demonstrate the advantages of coastal video systems over and above infrequent traditional topographic/bathymetric surveying methods. Namely, the ability of video-derived CSIs to quantify the magnitude, accurate location, precise timing and rates of change associated with individual extreme events and seasonal variability in the wave climate. Secondly, video-derived coastal state indicators were used to monitor two different types of human intervention, including beach nourishments and a dredged pit in a navigation channel. The video-derived datasets of coastal state indicators offered significant improvement to current CZM practices, facilitating better timing of management interventions as well as more effective monitoring of the spatial impact and longevity of these actions.  相似文献   

12.
The formation of beach megacusps along the shoreline of southern Monterey Bay, CA, is investigated using time-averaged video and simulated with XBeach, a recently developed coastal sediment transport model. Investigations focus on the hydrodynamic role played by the bay's ever-present rip channels. A review of four years of video and wave data from Sand City, CA, indicates that megacusps most often form shoreward of rip channels under larger waves (significant wave height (Hs) = 1.5–2.0 m). However, they also occasionally appear shoreward of shoals when waves are smaller (Hs ~ 1 m) and the mean water level is higher on the beach. After calibration to the Sand City site, XBeach is shown to hindcast measured shoreline change moderately well (skill = 0.41) but to overpredict the erosion of the swash region and beach face. Simulations with small to moderate waves (Hs = 0.5–1.2 m) suggest, similar to field data, that megacusps will form shoreward of either rip channels or shoals, depending on mean daily water level and pre-existing beach shape. A frequency-based analysis of sediment transport forcing is performed, decomposing transport processes to the mean, infragravity, and very-low-frequency (VLF) contributions for two highlighted cases. Results indicate that the mean flow plays the dominant role in both types of megacusp formation, but that VLF oscillations in sediment concentration and advective flow are also significant.  相似文献   

13.
海滩对风暴的响应是一个复杂的过程,尤其在连续风暴发生时。本研究利用Argus视频监测系统拍摄的连续图像,从海滩地貌、剖面、海滩滨线、海滩宽度等方面,定量分析了舟山东沙海滩对连续风暴"马勒卡"和"暹芭"的响应特征,并初步探讨了影响海滩地形地貌变化对连续风暴响应的因素。结果表明:(1)风暴"马勒卡"发生后海滩单宽体积变化量平均值为?73.75m3/m,风暴"暹芭"发生后海滩单宽体积变化量的平均值为?54.56m3/m,风暴"马勒卡"使整个海滩滨线平均后退14.75m,风暴"暹芭"使得海滩滨线相对于两次风暴前后退10.91m;(2)在海滩自身因素、外部动力因素以及人类活动等共同作用下海滩对连续风暴产生了复杂的响应。  相似文献   

14.
The Cuu Long Basin (Mekong Basin) is a rift basin off southern Vietnam, and the most important petroleum producing basin in the country. However, information on petroleum type and characteristics has hitherto been largely unavailable to the public. This paper presents petroleum geochemical data on nine oil samples from four different producing fields in the Cuu Long Basin: the Dragon (Rong), Black Lion (Sutu-Den), Sunrise (Rang ?ong) and White Tiger (Bach Ho) Fields. The oils are highly paraffinic with bimodal normal alkane distributions and show moderate pristane to phytane ratios and a conspicuous hyperbolic decrease in abundance with increasing carbon number of hopane homologues from C30 to C35. The TPP-index of Holba et al. (Holba, A.G., Dzou, L.I., Wood, G.D., Ellis, L., Adam, P., Schaeffer, P., Albrecht, P., Greene, T., Hughes, W.B., 2003. Application of tetracyclic polyprenoids as indicators of input from fresh–brackish water environments. Organic Geochemistry 34, 441–469) is equal to 1 in all samples which in combination with tricyclic triperpane T26/T25 ratios >1 and the n-alkane and hopane distributions mentioned above provide a strong indication of an origin from lacustrine source rocks. This is supported by the absence of marine C30 desmethyl steranes (i.e. 24-n-propylcholestanes) and marine diatom-derived norcholestanes. Based on the overall biological marker distributions, the lakes probably belonged to the overfilled or balanced-fill types defined by Bohacs et al. (Bohacs, K.M., Carroll, A.R., Neal, J.E., Mankiewicz, P.J., 2000. Lake-basin type, source potential, and hydrocarbon character. An integrated sequence-stratigraphic–geochemical framework. AAPG Studies in Geology 46, 3–34). The oils were generated from source rocks at early- to mid-oil-window maturity, presumably Oligocene lacustrine shales that are present in the syn-rift succession. Oils from individual fields may, however, be distinguished by a combination of biological marker parameters, such as the oleanane index, the gammacerane index, the relative abundance of tricyclic terpanes, the proportions of diasteranes and 28-norspergulane, complemented by other parameters. The oils of the Cuu Long Basin show an overall similarity to the B-10 oil from the Song Hong Basin off northern Vietnam, but are markedly different from the seepage oils known from Dam Thi Nai on the coast of central Vietnam.  相似文献   

15.
《Coastal Engineering》2007,54(6-7):539-553
Owing to intensified use of the coastal region and the frequent application of small-scale, tailored interventions such as beach nourishments, there is a growing need for coastal state information and knowledge on spatiotemporal scales of meters to kilometers and days to months. The design and implementation of engineering and management measures at these scales is hampered by limited predictability of their impact. Advanced, automated video stations open the door towards the collection of long-term, high-resolution data sets, which offer enhanced opportunities for the prediction of coastal processes at smaller scales. In this paper, the added value of high-resolution data sets for prediction purposes is explored. In particular the application of data-driven approaches as well as process models supported by video data are explored. In the data-driven approach, the inclusion of monthly video-derived data was found to not only improve confidence intervals on the predicted shoreline evolution, but also to facilitate the use of more sophisticated data extrapolation methods. Short-term, operational forecasts of the nearshore flow and sediment transport field were found to benefit from the inclusion of intertidal bathymetric data derived from video imagery. Though in its pioneering stage for video-based research, it is foreseen that significant advancement in prediction skill will be achieved through development of data-assimilation schemes which combine the best of existing process and empirical knowledge on coastal morphodynamics.  相似文献   

16.
At high bed shear stress sheet flows often occur in coastal waters in which high-concentration bedload sediments are transported in a thin layer near the bed. This paper firstly constructs a theoretical model (partial differential equations, PDEs) for the intense transport of non-cohesive bedload sediments by unidirectional currents and then seeks a special solution to the PDEs to determine the thickness of the bedload particle–water mixture, which could serve as the “reference height” that is often invoked in numerical computation and simulation of suspended sediment transport in turbulent flows. Moreover, a modified formula is presented to determine the “reference concentration”. Using a “uch” approach the present study derives a 1D formula for predicting bedload transport rate in sheet flows driven by asymmetric waves, with the help of a novel formula for evaluating wave friction factor. The new bedload formula can generically take into account slope angle (positive and negative), wash load concentration in the driving water flow and other factors that affect bedload transport rate. It compares well with measured data in a large-scale wave flume [Dohmen-Janssen, C.M., Hanes, D.M., 2002. Sheet flow dynamics under monochromatic non-breaking waves. Journal of Geophysical Research, 107(C10), 1301–1321], a large-scale oscillatory water tunnel [ Hassan, W.N., Ribberink, J.S., 2005. Transport processes of uniform and mixed sands in oscillatory sheet flow. Coastal Engineering, 52, 745–770] and in a swash zone of natural beach [Masselink, G., Hughes, M.G., 1998. Field investigation of sediment transport in the swash zone. Continental Shelf Research, 18, 1179–1199].  相似文献   

17.
The rate of wave overtopping of a barrier beach is measured and modeled. Unique rate of wave overtopping field data are obtained from the measure of the Carmel River, California, lagoon filling during a time when the lagoon is closed-off with no river inflow. Volume changes are based on measured lagoon height changes applied to a measured hypsometric curve. Wave heights and periods are obtained from directional wave spectra data in 15 m fronting the beach. Beach morphology was measured by GPS walking surveys. Three empirical overtopping models by Van der Meer and Janssen (1995), Hedges and Reis (1998) and Pullen et al. (2007) with differing parameterizations on wave height, period and beach slope and calibrated using extensive laboratory data obtained over plane, impermeable beaches are applied in a quasi-2D manner and compared with the field observations. Three overtopping events are considered when morphology data were available less than 2 weeks prior to the event. The models are tuned to fit the data using a reduction factor to account for beach permeability, berm characteristics, non-normal wave incidence and surface roughness influence. In addition, the run-up model by Stockdon et al. (2006) based on field data is examined and found to underestimate run-up as the calculated values were too small to predict any of the observed overtopping. The three overtopping models performed similarly well with values of 0.72–0.87 for the two narrow-banded wave cases, with an average reduction factor of 0.78. The European model (Pullen et. al., 2007) performed best overall and in particular for the case of the broad-banded, double peaked wave spectrum.  相似文献   

18.
Data-based forecasting of beach volumes on monthly to yearly timescales   总被引：2，自引：0，他引：2  
Data-based methods for forecasting beach volumes are tested using ground-measured bathymetry from Duck, North Carolina, comprising 26 profiles, 20 year duration and one-month resolution. Derived beach volume time series show weak seasonal and strong event signals. The forecasting methods used are: Holt–Winters (standard and modified), three types of linear regression, and a default forecast in which the latest measurement persists unchanged into the future. Improved forecast accuracies are obtained by two modifications to Holt–Winters, involving an autocorrelation correction and long-term trend-damping, and by smoothing the fitting data using running medians or wavelet approximations. Beach volume forecasts are tested mainly at monthly intervals up to 12 months ahead, with further tests at up to 36 months ahead. Overall, modified Holt–Winters performs best and the default forecast second-best. With an added artificial seasonal signal, modified Holt–Winters outperforms the other methods more substantially.  相似文献   

19.
Field experiments were conducted on a low-gradient, high-energy sandy beach (Truc Vert, France) and a steep, low-energy gravel beach (Slapton, UK) to examine alongshore-directed currents within the swash zone. At Truc Vert, data were collected over 33 tidal cycles with offshore significant wave heights of 1–4 m and periods of 5–12 s. At Slapton data were collected during 12 tides with wave heights of 0.3–1 m and periods of 4–9 s. The swash motion was predominantly at infragravity frequencies at Truc Vert and incident frequencies at Slapton.  相似文献   

20.
Steve Sramek 《Marine Geodesy》2013,36(2-3):151-163
Local changes in the marine geoid (<100 nm in size) correspond well with bathymetric features such as seamounts. Thus the marine geoid height may be used to verify existing features, predict the bathymetry of unsurveyed areas, and fill gaps in existing data. The application of matching high‐pass filters to both the geoid and bathymetry data of an area allows the regional trends to be removed so that only the features remain. Filter values that begin to pass data with wavelengths less than 125 miles and all data with wave lengths less than 70 miles were selected. The high‐frequency variations of the geoid can then be correlated to the bathymetry and a scaling factor between the two calculated. The highest correlations (.81) were achieved using a cut‐off value for the filtered geoid data. A gridded synthetic bathymetry file was created by scaling the filtered geoid to the filtered bathymetry and adding the low pass background bathymetry. The gridded historical bathymetry could then be subtracted from the synthetic bathymetry in an automated method to display probable new features. A final selection of 458 previously unreported major features was then made.  相似文献   

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