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1.
Velegrakis  A. F.  Trygonis  V.  Chatzipavlis  A. E.  Karambas  Th.  Vousdoukas  M. I.  Ghionis  G.  Monioudi  I. N.  Hasiotis  Th.  Andreadis  O.  Psarros  F. 《Natural Hazards》2016,83(1):201-222
This contribution presents the results of a study on the shoreline variability of a natural perched urban beach (Ammoudara, N. Crete, Greece). Shoreline variability was monitored in high spatio-temporal resolution using time series of coastal video images and a novel, fully automated 2-D shoreline detection algorithm. Ten-month video monitoring showed that cross-shore shoreline change was, in some areas, up to 8 m with adjacent sections of the shoreline showing contrasting patterns of beach loss or gain. Variability increased in spring/early summer and stabilized until the end of the summer when partial beach recovery commenced. Correlation of the patterns of beach change with wave forcing (as recorded at an offshore wave buoy) is not straightforward; the only discernible association was that particularly energetic waves from the northern sector can trigger changes in the patterns of shoreline variability and that increased variability might be sustained by increases in offshore wave steepness. It was also found that the fronting beachrock reef exerts significant geological control on beach hydrodynamics. Hydrodynamic modelling and observations during an energetic event showed that the reef can filter wave energy in a highly differential manner, depending on its local architecture. In some areas, the reef allows only low-energy waves to impinge on the shoreline, whereas elsewhere penetration of higher waves is facilitated by the low elevation and limited width of the reef or by the presence of an inlet. Wave/reef interaction can also generate complex circulation patterns, including rip currents that appeared to be also constrained by the reef architecture.  相似文献   

2.
津冀海岸线现状、变化特征及保护建议   总被引：1，自引：0，他引：1  
根据覆盖全区的3期遥感影像和实地调查,以及对滨海新区和滦河口2个典型区更深入的案例研究(包括回溯至1870年、1950年的基准岸线及逐年遥感信息),对津冀沿海海岸线现状进行解译和分类,并分析岸线变化特征及成因。津冀沿海现状岸线总长度894km,可以划分为自然岸线、半开发岸线和人工岸线3类,长度分别为90km、329km和475km。1950年以前为自然因素主导的岸线变化,1950年以后变为人类活动主导的岸线向海推进,逐渐加强的人类活动至2010年达到顶峰。在全球海面上升和区域地面下沉的大背景下,海岸线的自然演化趋势应该是向陆蚀退,但是人类活动主导的岸线变化却表现为违反自然趋势的向海推进。今后,向海推进最前沿的围海造陆区将受到来自海洋越来越强烈的影响,亟需加强监测和防护。兼顾环境保护与开发两方面的长远需求,建议赋予海岸线新的定义与内涵,划定岸线保护红线,恢复部分岸线的自然属性。  相似文献   

3.
本文介绍了自主研发的DFG型断层形变垂直分量测量仪的测量原理及自动化标定系统。结合在北京市丰台区大灰厂地震台该仪器的安装,介绍了标定的实现过程,标定结果满足地壳形变观测仪器相关技术标准的要求。  相似文献   

4.
One of the most effective means of monitoring the cumulative effects of natural processes and human activities on the shoreline is to study the patterns of shoreline change over time. An attempt has been made to study the shoreline changes along Al Batinah, Sultanate of Oman, at the outlet of Wadi Al Hawasnah. The previous studies showed that Al Batinah coastline is generally stable except where coastal engineering structures like harbors, corniches, ports, and recharge dams are present. Remote sensing and GIS techniques are widely used in the coastal geomorphology because they provide the best sources to study the long-term shoreline changes. Rapid shoreline changes at the mouth of Wadi Al Hawasnah have been measured using proxy data derived mainly from satellite images from 2000 to 2005. The mouth of Wadi Al Hawasnah is now completely blocked after the construction of recharge dam at the upper stream of Wadi Al Hawasnah and Wadi Bani Umar in 1995. There has been no discharge to the sea after the construction of the dam. Furthermore, beach profiles of this area show erosion close to the south of the tidal inlet and accretion further south. The shorelines in the northwest of the tidal inlet remained stable.  相似文献   

5.
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   

6.
The coastal zone of the Nile Delta is a promising area for energy resources and industrial activities. It also contains important wetland ecosystems. This coastal area witnessed several changes during the last century. A set of four satellite images from the multi-spectral scanner (MSS), thematic mapper (TM) and Systeme Pour l’Observation de la Terre (SPOT) sensors were utilized in order to estimate the spatio-temporal changes that occurred in the coastal zone between Damietta Nile branch and Port-Said between 1973 and 2007. Image processing applied in this study included geometric rectification; atmospheric correction; on-screen shoreline digitizing of the 1973 (MSS) and 2007 (SPOT) images for tracking the shoreline position between Damietta promontory and Port-Said; and water index approach for quantifying Manzala lagoon surface area change using 1973 (MSS), 1984 (TM) and 2003 (TM) images. Results showed that coastal erosion was severe near Damietta promontory and decreased eastward, however, accretion was observed near Port-Said. About 50% of the coastal strip was under erosion and 13% was under accretion. In addition, a remarkable decline (34.5%) of the Manzala lagoon surface area was estimated. These changes were attributed mainly to the control of the River Nile flooding and the land use change by anthropogenic activities.  相似文献   

7.
渤海湾海岸带近现代地质环境变化   总被引：23，自引：3，他引：23       下载免费PDF全文
钟新宝  康慧 《第四纪研究》2002,22(2):131-135
淤泥质海岸带地区10～102a级别的相对快速的“缓变型地质环境变化”,主要包括水体、湿地和盐沼-湖退化或消失、贝壳堤和牡蛎礁被破坏、村镇和城市面积剧增、海岸线(平均大潮高潮线)被侵蚀后退、潮间带和近海河道被淤积、潮间带变宽变缓等。这些变化,已对我国东部沿海地区的经济和社会发展造成不利影响,并将对该类地区的可持续发展构成潜在威胁。在该类地区正在进行的1∶50000区域地质调查,充分发挥其高精度和规范化的优势,并辅以对近百年来不同时期的地形图、航空照片和遥感影像的数字化处理和对比研究,试图对这些变化做出形象、直观和定量的二维(2D)表达。本文介绍的是正在渤海湾海岸带进行的工作,充分显示出地质调查服务社会的公益性、基础性和战略性特点。对这一研究方向所显示的巨大潜力的进一步开发,将可能形成供政府决策部门和各方面用户广泛利用的、可二次开发的平台,从而使该类地区的可持续发展建立在对近现代地质环境变化详细了解的扎实基础之上。  相似文献   

8.
A set of six Landsat satellite images with 5–9 years apart was used in a post-classification analysis to map changes occurred at Rosetta promontory between 1973 and 2008 due to coastal erosion. Spectral information were extracted from two multi-spectral scanner (MSS) images (1973 and 1978), three thematic mapper (TM) images (1984, 1990, and 1999), and one enhanced thematic mapper plus (ETM+) image (2008). To estimate the quantity of land loss in terms of coastal erosion, a supervised classification scheme was applied to each image to highlight only two classes: seawater and land. The area of each class was then estimated from the number of pixels pertaining to this class in every image. In addition, the shoreline position was digitized to address retreat/advance pattern throughout the study period. Results showed that Rosetta promontory had lost 12.29 km2 of land between 1973 and 2008 and the shoreline withdrew southward about 3.5 km due to coastal erosion. Most land loss and shoreline retreat occurred between 1973 and 1978 (0.55 km2/year and 132 m/year, respectively). Coastal protection structures were constructed successively at the promontory. These structures have considerably contributed to reduce coastal erosion; however, they promoted downdrift erosion.  相似文献   

9.

Debris flows are hazardous phenomena occurring at volcanoes, and monitoring them has proved as challenging as imperative in several cases. The use of seismic instruments to measure and study the physical properties of debris flows has witnessed significant progress in the last years, with the use of improved sensors, innovative methodologies and high-resolution analysis. However, the application of such studies to the practical task of providing early warnings remains limited by the significant amount of infrastructural and technological resources commonly required for their deployment. In Ecuador, debris flows at volcanoes are detected by means of seismic instruments which are usually part of broader monitoring networks, thus requiring calibration to provide quantitative information about the flows and feed early-warning systems. In the present work, a theoretical approach based on the Buckingham Π-theorem is used to determine an expression that linearly correlates the seismic signal produced by a transiting debris flow with its discharge rate, for instruments installed in different substrata and at variable distances from the drainage. The expression is experimentally tested with Acoustic Flow Monitors and Broad-band seismometers installed in the vicinity of drainages at Tungurahua and Cotopaxi volcanoes, where actual debris flows occurred in relation to eruptive activity. The experiments consist in comparing the measured peak amplitude values of the seismic signal envelopes with the estimated peak discharge rates of several events. The results confirm the validity of the theoretical expression with linear correlations observed between the seismic amplitudes and the discharge rates, thus defining calibration expressions that can be generally applied to varied environments and instruments. The seismic instruments calibrated through this methodology can provide instantaneous and reliable predictions of debris flow discharge rates within less than an order of magnitude and only requiring limited data processing and storage. Such level of prediction could help to improve early warning systems based on seismic instruments installed in locations where more developed instrumental arrays are unavailable or unpractical.

  相似文献   

10.
Shoreline is one of the rapidly changing landform in coastal area. So, accurate detection and frequent monitoring of shorelines are very essential to understand the coastal processes and dynamics of various coastal features. The present study is to investigate the shoreline changes along the coast between Kanyakumari and Tuticorin of south India, where hydrodynamic and morphologic changes occur continuously after the December 2004 tsunami. Multi-date satellite data of Indian Remote Sensing (IRS) satellites (1999, 2000, 2003, 2005, and 2006) are used to extract the shorelines. The satellite data is processed by using the ERDAS IMAGINE 9.1 software and analyzed by ArcGIS 9.2 workstation. The different shoreline change maps are developed and the changes are analyzed with the shoreline obtained from the Survey of India Toposheets (1969). The present study indicates that accretion was predominant along the study area during the period 1969–1999. But recently (from 1999 onwards), most of the coastal areas have experienced erosion. The study also indicates the reversal of shoreline modifications in some coastal zones. The coastal areas along the headlands have experienced both erosion and accretion. Though the coastal erosion is due to both natural and anthropogenic activities, the coastal zones where sand is mined have more impacts and relatively more rate of erosion than that of other zones. Improper and in-sustainable sand mining leads to severe erosion problem along this area. So the concept of sustainable management should be interpreted in the management of the near-shore coastal sand mining industry.  相似文献   

11.
针对煤矿掘进工作面视频光照较低、亮度不均、纹理模糊、噪声较多等问题,提出一种煤矿掘进工作面低照度视频增强算法。首先,利用卷积的可分离性将视频图像进行一维水平卷积与垂直卷积,再利用完美反射法实现视频图像自动白平衡,并使用图像混合增强技术提高视频图像整体亮度。然后,基于大气散射模型与暗通道先验方法,通过递归分割将图像分割为高光区、中间调和暗调区,并求取对应区间通道像素最大值,将其3者均值作为大气光照估计值,引入调节因子对透射率进行调整优化,并使用拉普拉斯锐化操作,增加图像高频成分、抑制图像低频成分,提高图像对比度。最后,基于改进的大气散射模型对掘进工作面低照度视频进行去雾处理。实验结果表明,视频增强算法能够对煤矿掘进工作面低照度视频进行实时增强、去雾处理,避免了视频图像暗淡、失真、模糊和突变等问题。相较于Retinex算法、ALTM算法和暗通道先验算法,视频增强算法大幅度提高了视频图像的信息熵、标准差和平均梯度,且具有较好的实时处理速度,能够为掘进工作面视频的目标识别、目标跟踪、目标监测和图像分割等后续处理提供优质、可靠的支撑。   相似文献   

12.
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   

13.
One of the most important aspects of coastal zone management is the analysis of shoreline dynamics. Over the last years, beaches of the Ravenna coast (NE Italy) experienced large modifications, in some places narrowing or even being completely lost, thus threatening tourism, coastal assets and nature. Coastal erosion has direct consequences for Ravenna tourist-based economy, which largely depends on the attraction provided by sandy beaches. In this study, long-term (>?50 years) coastal analysis was used to identify the sectors along the coast where the shoreline position has changed, either advancing or retreating. Shoreline changes were measured on GIS environment by means of Digital Shoreline Analysis System (DSAS) extension. Net Shoreline Movement (NSM) and Linear Regression Rate (LRR) strategies were employed to examine shoreline variability and reveal erosional/accretional trends. The results show that significant shoreline changes affected the entire coastal region, with most of the study area under retreat, mainly in the most valuable tourist assets of the littoral. The effects were found to be worsened by impacts of land subsidence, presence of harbor infrastructure and deficit in sediment budget. A simple shoreline classification was performed over the DSAS results and cross-checked with local knowledge of the area. The measurement of erosion or accretion rates in each studied segment is found to be useful for land use planning and coastal management plans, especially regarding the prediction of future shoreline positions. Especially important is the potential of the classification to identify areas of significant position change, with current and future implications for the design of sustainable shoreline management and mitigation measures.  相似文献   

14.
激光雷达测量技术在地学中的若干应用   总被引：3，自引：0，他引：3  
马洪超 《地球科学》2011,36(2):347-354
对激光雷达测量技术在全球冰川监测、局部断裂带提取、滑坡监测和稳定性评价以及海岸线提取和海岸侵蚀等方面的应用做了较为全面的综述.作为一种新型的对地观测手段,激光雷达(含星载、机载、车载和地面)的应用已经从传统的测绘扩大到包括文物保护在内的诸多其他应用领域.所综述的激光雷达技术在地学研究中的4个应用方面,是传统地学研究中与全球变化和人居环境最为密切的方向.分析表明,激光雷达技术在这些研究方向中的应用大有作为.   相似文献   

15.
Sea level rise is causing shoreline erosion, increased coastal flooding, and marsh vulnerability to the impact of storms. Coastal marshes provide flood abatement, carbon and nutrient sequestration, water quality maintenance, and habitat for fish, shellfish, and wildlife, including species of concern, such as the saltmarsh sparrow (Ammodramus caudacutus). We present a climate change adaptation strategy (CCAS) adopted by scientific, management, and policy stakeholders for managing coastal marshes and enhancing system resiliency. A common adaptive management approach previously used for restoration projects was modified to identify climate-related vulnerabilities and plan climate change adaptive actions. As an example of implementation of the CCAS, we describe the stakeholder plans and management actions the US Fish and Wildlife Service and partners developed to build coastal resiliency in the Narrow River Estuary, RI, in the aftermath of Superstorm Sandy. When possible, an experimental BACI (before-after, control-impact) design, described as pre- and post-sampling at the impact site and one or more control sites, was incorporated into the climate change adaptation and implementation plans. Specific climate change adaptive actions and monitoring plans are described and include shoreline stabilization, restoring marsh drainage, increasing marsh elevation, and enabling upland marsh migration. The CCAS provides a framework and methodology for successfully managing coastal systems faced with deteriorating habitat, accelerated sea level rise, and changes in precipitation and storm patterns.  相似文献   

16.
C. Pereira  C. Coelho 《Natural Hazards》2013,69(1):1033-1050
Several coastal zones are facing shoreline retreat problems, losing territory due to energetic sea actions, negative sediment transport balances and climate change phenomena. To deal with this problem, efficient tools are necessary to help decision-makers choose the right procedures to follow. These tools should assess, estimate and project scenarios of coastal evolution in a medium-to-long-term perspective. To perform reliable projections, as many variables as possible should be analysed, and the impact of each of these variables on the shoreline evolution should be understood. This study aimed to analyse three climate change phenomena that are considered the most important in a Portuguese west coast stretch (at Aveiro region). The considered phenomena are the wave height increasing due to storms, the wave direction changes and the sea level rise. A shoreline evolution numerical model, long-term configuration, developed to support coastal zone planning and management in relation to erosion problems was applied. This work defined a methodology for classification of risk areas, considering the uncertainty associated with different wave climate sequences on simulations. As a result, different risk maps according to considered climate change effects were obtained, defining areas of high, medium and low risk of territory loss due to erosion. A generalized erosion tendency and shoreline retreat were observed, particularly in the downdrift side of groins. The sea water level rise showed lower impacts in the shoreline evolution than wave direction changes, or wave height increasing, which presents the highest impact.  相似文献   

17.
This paper illustrates the main characteristics of the newly developed landslide model r.massmov, which is based on the shallow water equations, and is capable of simulating the landslide propagation over complex topographies. The model is the result of the reimplementation of the MassMov2D into the free and open-source GRASS GIS with a series of enhancements aiming at allowing its possible integration into innovative early warning monitoring systems and specifically into Web processing services. These improvements, finalized at significantly reducing computational times, include the introduction of a new automatic stopping criterion, fluidization process algorithm, and the parallel computing. Moreover, the results of multi-spatial resolution analysis conducted on a real case study located in the southern Switzerland are presented. In particular, this analysis, composed by a sensitivity analysis and calibration process, allowed to evaluate the model capabilities in simulating the phenomenon at different input data resolution. The results illustrate that the introduced modifications lead to important reductions in the computational time (more than 90 % faster) and that, using the lower dataset resolution capable of guaranteeing reliable results, the model can be run in about 1 s instead of the 3.5 h required by previous model with not optimized dataset resolution. Aside, the results of the research are a series of new GRASS GIS modules for conducting sensitivity analysis and for calibration. The latter integrates the automated calibration program “UCODE” with any GRASS raster module. Finally, the research workflow presented in this paper illustrates a best practice in applying r.massmov in real case applications.  相似文献   

18.
Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments.  相似文献   

19.
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   

20.
This paper aims at illustrating different case examples of monitoring active coastal evolutions using remote sensing synthetic aperture radar images (ERS 1–2 and Envisat) in humid tropical areas. Effectively, the radar satellite images may be acquired under most climate conditions, especially in cloudy tropical areas. As case examples, we studied herein French Guiana shoreline and its fast evolution under the combined influences of sea currents, sediments and swells. We focused on two aspects of French Guiana littoral evolution: (1) sedimentation and erosion processes linked to mud banks displacements around Kourou City, and (2) around Iracoubo village. Lastly, we compared this short-term sedimentation balance with long-term data showing the discrepancies of short- and long-term littoral evolutions on whole French Guiana. To conclude, this work demonstrates the importance of SAR imagery to provide high-quality and high-frequency update geographic information for coastal management and littoral hazards especially in such tropical humid and cloudy areas. To cite this article: H. Trebossen et al., C. R. Geoscience 337 (2005).  相似文献   

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