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1.
Studies of the Nile Delta coast have indicated wide values of local subsidence, ranging from 0.4 to 5 mm/yr. Trend analysis of sea-level rise and shoreline retreat at two Nile Delta promontories have been studied. Records from tide gauges at Alexandria (1944–1989) and Port Said (1926–1987), north of the Nile delta coast, indicate a submergence of the land and/or a rise of the sea-level of 2 and 2.4 mm/yr, respectively. Dramatic erosion has occurred on some beaches of the Nile Delta. This is greatest at the tips of the Rosetta and Damietta promontories, with shoreline retreat up to 58 m/yr. Relationship between the shoreline retreat and sea level trends in terms of correlation analysis and application of the Bruun Rule indicates that the sea level rise has, by itself, a relatively minor effect on coastal erosion. The sea-level trend at the Nile delta coast is found to be only one of several effects on shoreline retreat. Major recent effects include a combination of cut-off of sediment supply to the coast by damming the River Nile and local hydrodynamic forces of waves and currents. Estimates of local future sea-level rise by the year 2100 at Alexandria and Port Said, respectively, is expected to be 37.9 and 44.2 cm. These expectations, combined with other factors, could accelerate coastal erosion, inundate wetlands and lowlands, and increase the salinity of lakes and aquifers.  相似文献   

2.
Previous studies have indicated that the Nile River deltaic plain is vulnerable to a number of aspects, including beach erosion, inundation, and relatively high rates of land subsidence. This issue motivates an update and analysis of new tide-gauge records, from which relative sea-level changes can be obtained. Estimated rates from five tide gauges are variable in terms of magnitude and temporal trend of rising sea level. Analysis of historical records obtained from tide gauges at Alexandria, Rosetta, Burullus, Damietta, and Port Said show a continuous rise in mean sea level fluctuating between 1.8 and 4.9 mm/year; the smaller rate occurs at the Alexandria harbor, while the higher one at the Rosetta promontory. These uneven spatial and temporal trends of the estimated relative sea-level rise (RSLR) are interpreted with reference to local geological factors. In particular, Holocene sediment thickness, subsidence rate and tectonism are correlated with the estimated rates of relative sea-level change. From the relatively weak correlation between them, we presume that tectonic setting and earthquakes, both recent and historical ones, contribute more to accelerated RSLR than that of dewatering and compression/dewatering of Holocene mud underlying the Nile Delta plain. As a result, large areas of the coastal plain have been subsided, but some sectors have been uplifted in response to tectonic activities of thick underlying older strata. Projection of averaged sea-level rise trend reveals that not all the coastal plain of the Nile Delta and Alexandria is vulnerable to accelerated sea-level rise at the same level due to wide variability of the land topography, that includes low-lying areas, high-elevated coastal ridges and sand dunes, accretionary beaches, and artificially protective structures. Interaction of all aspects (tectonic regime, topography, geomorphology, erosion rate, and RSLR rate) permitted to define risk areas much vulnerable to impacts of sea incursion due to accelerated sea-level rise.  相似文献   

3.
Frihy Omran E. 《GeoJournal》1992,26(3):389-394
Carbon dating data of changes in seal level during the Holocene at the Nile delta coast provide eustatic depth-time curve of the region. The curve reveals that sea level was approximately 41 meters below the present level around 8,500 years ago. Trend analysis indicates that with melting of glaciers there was a rapid rise in sea level of about 3 mm/yr. The constructed data points are found to be comparable with other curves in the Mediterranean and wold-wide regions. The general changes of the data points are fairly correlated with the ancient shoreline indicators of morphological features (shelf terraces and slopes, old dunes, sand accretion ridges) and sediments at continental shelf and its contiguous coastal zone that belong to Holocene transgression.  相似文献   

4.
Three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the Holocene transgression in southern Long Island, New York: (1) the Holocene transgressive stratigraphic sequence behind the present barriers, (2) the stratigraphic patterns of the inner shelf, and (3) the morphology of the now-buried late Pleistocene coastal features. The extensive preservation of backbarrier sediments, radiocarbon dated between 7000 and 8000 yr BP, on the inner shelf of southern Long Island suggests that the barriers have not retreated by continuous shoreface erosion alone, but have also undergone discontinuous retreat by in-place ‘drowning’ of barriers and stepwise retreat of the surf zone. Such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked. Based on the presence of submerged barrier sand bodies in seismic records, it is inferred that about 9000 years ago, when the sea stood about 24 m below the present sea level, a chain of barriers developed on the present shelf about 7 km offshore of the present barriers. With continued sea-level rise, the – 24 m barrier built upward until the sea reached about – 15 m MSL, just prior to 7000 yr BP. The barriers were then submerged by the rapidly rising sea, and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline. The surf zone overstepped to the landward margin of the old lagoon, which had become fixed at the steep seaward face of mid-Wisconsinan (?) or Sangamonian coastal barriers. During the past 5000 or 6000 years, the shoreface has retreated continuously by about 2 km. Evidence from southern Long Island and elsewhere in regions of coastal submergence indicates that rapid sea-level rise and low sand supply seem to favour the stepwise retreat of barriers, whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat. Stationary upbuilding, or seaward progradation of barriers may occur when supply of sand is great, and/or submergence is slowed or reversed. Morphologic highs on the pretransgression surface (such as old barrier ridges) tend to fix the migrating barrier shoreline during either continuous retreat, or stepwise retreat of barriers.  相似文献   

5.
Shoreline changes are largely dependent on coastal morphology. South-west coast of India is a high energy coast characterised by monsoon high waves, steep beach face and medium-sized beach sand. Waves are generally from west and west south-west during rough monsoon season and from south-west during fair weather season. Shoreline change along this coast is studied with reference to coastal morphological features. Various morphological features, modifications and chronological positions of shoreline are analysed with the information derived from multidated satellite imageries, toposheets and GPS shoreline mapping along with extended field survey. Image processing and GIS techniques have been used for the analysis of data and presentation of results. Sediment accumulation on the leeward side of artificial structures such as harbour breakwaters and groynes is used as a sediment transport indicator. Artificial structures such as seawalls, groynes and harbour breakwaters modify morphology. Shoreline south of headlands/promontories and breakwaters are stable or accreting due to net northerly longshore sediment transport while erosion tendency is observed on the north side. Lateritic cliffs fronting the sea or with seasonal beach undergo slumping and cliff edge retreat as episodic events. Spits adjoining tidal inlets are prone to shoreline variations due to oscillations of inlet mouth. Interventions in the form of inlet stabilization and construction of coastal protection structures trigger erosion along adjoining coasts. Seawalls constructed along highly eroding coasts get damaged, whereas those constructed along monsoon berm crest with frontal beaches for protection against monsoon wave attack are retained. Fishing gaps within seawalls are areas of severe temporary erosion during rough monsoon season. Accretion or erosion accompanies construction of harbour breakwaters in a stable coastal plain. Close dependence of shoreline changes on morphology necessitates detailed understanding of impacts on morphology prior to introducing any intervention in the coastal zone.  相似文献   

6.
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   

7.
Densely populated coastal zones of India are highly exposed to natural environment. These are impacted by episodic natural events, continuous coastal process, gradually rising sea levels and coexisting human interventions. The present study is an attempt to assess the implication of the sea level rise and coastal slope in the coastal erosion for entire mainland of India. In this regard, two methods were employed to estimate the shoreline change rate (SCR): (1) satellite-derived SCR using the Landsat TM and ETM+ acquired during 1989–2001 and (2) SCR derived by Bruun Rule using the parameters coastal slope and sea level trend derived from satellite altimetry. Satellite-derived SCR has been compared with the shoreline change estimated based on Bruun Rule, revealing a better agreement with each other in terms of trend. Peaks of shoreline retreat calculated using Bruun model and satellite-observed SCR offset by 25–50 km. Offset in these peaks was observed due to net drift towards north in the east coast and south in the west coast of India, revealing the applicability of the Bruun Rule along the Indian coast. The present study demonstrates that coastal slope is an additional parameter responsible for the movement of shoreline along with sea level change. The results of satellite-derived SCR reveal the highest percentage of erosion along West Bengal coast with 70% followed by Kerala (65%), Gujarat (60%) and Odisha (50%). The coastlines of remaining states recorded less than 50% of coasts under erosion. Results of this study are proving critical inputs for the coastal management.  相似文献   

8.
The active accretional features that have developed along the modern Nile Delta promontories during shoreline retreat are analysed using topographic maps, remote imagery, ground and hydrographic surveys, together providing 15 time-slice maps (1922–2000) at Rosetta and 14 time-slice maps (1909–2000) at Damietta. Small double sandy spits developed and persisted at Rosetta between 1986 and 1991. At Damietta, a much larger single spit, 9 km long, formed approximately east of the mouth of the Damietta Nile branch between 1955 and 1972, although its source has now been depleted. Both the Rosetta and Damietta inlets are associated with submerged mouth bars that accumulated prior to the damming of the Nile, but that continue to contribute to local sedimentation problems, particularly at Rosetta. The development of the active accretional features along the Nile promontories reflects a combination of factors including sediment availability, transport pathways from source areas, a decrease in the magnitude of Nile flood discharges, as well as the impact of protective structures at the river mouths.  相似文献   

9.
Shennan  Ian  Tooley  Michael  Green  Frances  Innes  Jim  Kennington  Kevin  Lloyd  Jeremy  Rutherford  Mairead 《Geologie en Mijnbouw》1998,77(3-4):247-262
Analyses of geomorphologically contrasting sites in Morar, NW Scotland, describe the forcing mechanisms of coastal change. Isolation basins (i.e. basins behind rock sills and now isolated from the sea following isostatic uplift) accumulated continuous marine and freshwater sediments from c.12 to 2 ka BP. Raised dune, marsh and wetland sites register breaching, migration and stability of dunes from c. 9 to 2 ka BP. High-resolution methods designed to address issues of macroscale and microscale sea-level changes and patterns of storminess include 1-mm sampling for pollen, dinocyst and diatom analyses, infra-red photography, X-ray photography and thin-section analysis. The data enhance the record of relative sea-level change for the area. Major phases of landward migration of the coast occurred during the period of low sea-level rise in the mid-Holocene as the rate of rise decreased from c. 3 to < 1 mm/year. Relative sea-level change controls the broad pattern of coastal evolution at each site; local site-specific factors contribute to short-term process change. There is no record of extreme events such as tsunami. Within a system of dynamic metastable equilibrium, the Holocene records show that site-specific factors determine the exact timing of system breakdown, e.g. dune breaching, superimposed on regional sea-level rise. The global average sea-level rise of 3 to 6 mm/yr by AD 2050 predicted by IPCC would only partly be offset in the Morar area by isostatic uplift of about 1 mm/yr. A change from relative sea-level fall to sea-level rise, in areas where the regional rate of uplift no longer offsets global processes, is a critical factor in the management of coastal resources.  相似文献   

10.
Along the southern coast of the North Sea, a large proportion of the Flemish coastal plain consists of densely populated reclaimed land, much of which lying below mean high tide level. This is particularly the case along the northern coast of France, from Dunkirk to the Belgium border, where the shoreline consists of coastal dunes that protect low-lying reclaimed lands from marine flooding. This area is vulnerable and subject to several risks. Extreme weather conditions could induce strong surges that could cause (1) a shoreline retreat, (2) marine submersion and (3) land and/or urban flooding due to drainage problems of the polders. Highly energetic events such as the November 2007 storm could have had much more severe consequences especially if they occurred at high tide and/or during a spring tide. In the current context of global change and projected sea-level rise, it is then important for the local authorities to take into account the potential impacts and return periods of such events, in order to implement coastal risk policies prevention and management, to reinforce sea defense, increase pumping station efficiency and plan warning systems against marine submersion and polder flooding, which is not the case yet in Northern France.  相似文献   

11.
战庆  王张华 《古地理学报》2014,16(4):548-556
根据对长江三角洲北部海安地区4个钻孔标志性沉积物(潮上带盐沼泥炭、高潮滩沉积)的年龄测定和高程测量,以及沉积物压实沉降量的分析研究,重建了本研究区全新世中期8.1～7.3 cal kyr BP和5.6～5.4 cal kyr BP的相对海平面位置。结果显示,8.1～7.3 cal kyr BP海平面缓慢上升1.46m,上升速率仅为0.2cm/yr, 与三角洲南部全新世早期海平面的快速上升(2cm/yr)形成鲜明对比,验证了冰盖控制下的全球海平面阶段性波动上升模式。对比长江三角洲地区海平面曲线发现,三角洲北部海平面曲线较南部低5～6m,长江三角洲海平面曲线与世界各地海平面曲线也存在明显差异,分析认为主要是由长江口地区的差异性沉降和中国东部边缘海的水均衡作用两个因素引起的。  相似文献   

12.
《China Geology》2018,1(4):512-521
Shandong has more than 70% of natural coasts are under erosion. Coastal erosion started from the 1970’s and became a very serious problem at 1990’s. The dramatic decrease of sediment supplies from rivers caused rapid erosion at the delta and estuary areas, especially in the abandoned Yellow River Delta. Most sandy coasts along the Peninsula were eroded due to lack of sand supply and interruption of alongshore sediment drift, sand dredging from the beach or the offshore area caused serious erosion during short time. Sea-level rise causes slow but constant shoreline retreats and became a more serious threat. Different types of hard solutions for coastal protection against erosion were used in Shandong. Seawalls are most widely used, especially at the Yellow River Delta and city center waterfront. Groynes, jetties and breakwater are used on the north and east sandy coast of the Peninsula. Hard approaches are effective to protect the coast erosion but not change the erosion causes and led secondary impact on the coast. Soft engineering solution or the combined solutions are taken into acts. Beach nourishment is mostly considered as the better soft solution, especially to those tourists attracting sandy beaches along the Shandong coast. Long term monitoring and continuous lessons learning from the coastal erosion management will be adaptive for better coast solution in the future.  相似文献   

13.
Climate change and its impacts on the coastal zone of the Nile Delta,Egypt   总被引：3，自引：3，他引：0  
The main objectives of the current work are (1) to determine historic pattern of shoreline changes (erosion and accretion) along the north coast of the Nile Delta, (2) to present a future view on what to be expected regarding climate change impacts, sea-level rise (SLR) scenarios, expected land losses and alteration of some soil characteristics (3) to recognize negative impacts of SLR on the Nile Delta coast and (4) to assess and suggest protection measures. The current investigation was conducted using the advanced techniques of remote sensing and geographic information system. The investigated area with 394 measured locations is located along the northern coast of the Nile Delta between Alexandria and ElTina plain in Sinai peninsula exactly between 29°20′ and 32°40′ E and 29°54′ and 31°35′ N with the minimum erosion values of 1.11 m2, maximum of 6,044,951.64 m2 and total of 16.02 km2. On the other hand, 177 sites showed minimum accretion values of 0.05 m2, maximum of 2,876,855.86 m2 and total of 13.19 km2. SLR was determined by applying the quadrant equation for 10-year intervals using 1990 as the base year. Mediterranean SLR along the Nile Delta coast could be estimated considering three different scenarios (low 0.20 m, medium 0.50 m, and high 0.90 m). Impacts of SLR are divided into (1) primary and (2) secondary impacts. Over the coming decades, the Nile Delta will face greater threat due to SLR and land subsidence as well. Regarding climate change and its impacts on soil characteristics, rapid increase in salinity values during the former three decades were found. This increase may be due to the intrusion of salty water of the Mediterranean. On the other hand, organic matter content decreased due to higher temperature, especially during the summer season. Some protection measures were assessed and suggested to combat or tackle SLR.  相似文献   

14.
Vizianagaram–Srikakulam coastal shoreline consisting of beaches, mangrove swamps, tidal channel and mudflats is one of the vulnerable coasts in Andhra Pradesh, India. Five site-specific parameters, namely rate of geomorphology, coastal elevation, coastal slope, shoreline change and mean significant wave height, were chosen for constructing coastal vulnerability index and assessing coastal landscape vulnerability. The findings revealed a shift of 2.5 km in shoreline towards the land surface because of constant erosion and that of 1.82 km towards the sea due to accretion during 1997–2017. The rate of high erosion was found in zones IV and V, and high accretion was found in zones II and III. Coastal vulnerability index analysis revealed constant erosion along shoreline and sea level rise in the study area. Most of the coast in zone V has recorded very high vulnerability due to erosion, high slope, significant wave height and sea level rise. Erosion and accretion, significant wave height, sea level rise and slope are attributed to high vulnerability in zones III and IV. Zone II recorded moderate vulnerability. Relatively lower slope, mean sea wave height and sea level rise have made this zone moderately vulnerable. Very low vulnerability was found in zone I, and low vulnerability was recorded in zone II. Accretion, low slope and low sea level rise were found to be causative factors of lower vulnerability. Thus, zones III, IV and V should be accorded higher priorities for coastal management. The findings can be helpful in coastal land planning and management and preparing emergency plans of the coastal ecosystems.  相似文献   

15.
 Impacts on nearshore sedimentation arising from potential sea level change of the magnitude predicted in Intergovernmental Panel on Climatic Change scenarios associated with global warming are reviewed. For sandy duned coasts, the obvious sedimentation impacts include potential erosion of coastal dunes with implied deposition of the eroded material in the nearshore, possible deepening of embayments, and flooding of wetlands. For the sandy coasts a number of two-dimensional models are available for predicting shoreline change, but there are significant difficulties in applying Bruun-type models for dune erosion and assessment of sediment redistribution over the inner shelf, and for predicting the amount of shoreline retreat for a given rate of sea level rise. If the beach profile contains excessive sand relative to its equilibrium profile, sensu Dean (1991), then shoreline retreat may not occur upon sea level rise. From the evidence of Kiel Bay, at least in these semi-enclosed basin types, it is during major transgressions that maximum deposition in adjacent basins occurs, due to the sea eroding weakly consolidated and weathered surface regolith. But at the same time climatic patterns were re-adjusting and probably contributed to maximum deposition in adjacent shelf and basins below wave base. Received: 16 June 1995 / Accepted: 29 January 1996  相似文献   

16.
《China Geology》2019,2(1):26-39
Bulletins of China’s National Sea Level show that the average rising rate of sea-levels in China is 3.3 mm/a over the past 40 years, with an obviously accelerated rising trend in the last decade. The rate of relative sea-level rise of the Yangtze River Delta reached >10 mm/a after considering the land subsidence, and Bohai Bay is even greater than 25 mm/a. The impact of the sea level rise to the coastal area will be greater in the coming years, so carrying out an assessment of this rising trend is urgent. This paper, taking the coastal area of Tianjin and Hebei as examples, comprehensively evaluates the impact of sea-level rise through multitemporal remote sensing shoreline interpretation, ground survey verification, elevation measurements for both seawall and coastal lowlands. The results show that the average elevation of the measured coastal areas of Tianjin and Hebei is about +4 m, and the total area of >100 km2 is already below the present mean sea level. More than 270 km, ca. 31% of the total length of the seawall, cannot withstand a 1-in-100-year storm surge. Numerical simulations of the storm flooding on the west coast of Bohai Bay, for 1-in-50-years, 1-in-100-years, 1-in-200-years and 1-in-500-years, show that if there were no coastal dykes, the maximum flooding area would exceed 3000 km2, 4000 km2, 5300 km2 and 7200 km2, respectively. The rising sea has a direct and potential impact on the coastal lowlands of Tianjin and Hebei. Based on the latest development in international sea-level rise prediction research, this paper proposes 0.5 m, 1.0 m and 1.5 m as low, middle and high sea level rise scenarios by 2100 for the study area, and combines the land subsidence and other factors to the elevation of the existing seawall. Comprehensive evaluation results indicate that even in the case of a low scenario, the existing seawall will not be able to withstand a 1-in-100-years storm surge in 2030, and the potential flooding areas predicted by the model will become a reality in the near future. Therefore, the seawall design in the coastal areas of Tianjin and Hebei must consider the combined effects of land subsidence, sea level rise and the extreme storm surges caused by it.©2019 China Geology Editorial Office.  相似文献   

17.
Land subsidence due to decline in head in confined aquifers, related to municipal and industrial water pumpage, is widespread in the Atlantic Coastal Plain. Although not a major engineering problem, subsidence greatly complicates adjustment of precise leveling and distorts prediction of future sea-level rise. When preconsolidation stress equivalent to about 20 m of head decline is exceeded compaction of fine-grained sediments of the aquifer system begins, and continues until a new head equilibrium is attained between fine and coarse units. The ratio subsidence/head decline is quite consistent, ranging from 0.0064 in southeastern Virginia to 0.0018 at Dover, Delaware and Atlantic City, New Jersey. Higher values are related to the occurrence of montmorillonite as the predominant clay mineral present. Review of tide gauge records indicates that gauges not affected by land subsidence or other local secular effects have been sinking relative to sea level since 1940 at rates averaging about 2.5 mm/yr, of which 0.6 mm/yr is ascribed to glacio-isostatic adjustment to unloading of North America resulting from melting of late Pleistocene glaciers, and about 0.9 mm/yr is ascribed to steric sea-level rise related to ocean warming. The residual 1 mm/yr of relative sea-level rise is not well understood, but may be related to regional tectonic subsidence of the Atlantic coast.  相似文献   

18.
Application of dendrochronology and geomorphology to a recently emerged coastal area near Juneau, Alaska, has documented a Little Ice Age (LIA) sea-level transgression to 6.2 m above current sea level. The rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century, based on a sea-cliff eroded into late-Pleistocene glaciomarine sediments. Land began emerging between A.D. 1770 and 1790, coincident with retreat of regional glaciers from their LIA maximums. This emergence has continued since then, paralleling regional glacier retreat. Total Juneau uplift since the late 18th century is estimated to be 3.2 m. The rate of downward colonization of newly emergent coastline by Sitka spruce during the 20th century closely parallels the rate of sea-level fall documented by analysis of local tide-gauge records (1.3 cm/yr). Regional and Glacier Bay LIA loading and unloading are inferred to be the primary mechanisms driving subsidence and uplift in the Juneau area. Climate change rather then regional tectonics has forced relative sea-level change over the last several hundred years.  相似文献   

19.
The Tiber Delta lies on the passive continental margin of central western Italy. The Tiber Delta is a Late Pleistocene—Holocene sedimentary succession and constitutes an ‘incomplete’high-frequency depositional sequence (4th or 5th order), which developed from the last post-glacial rise in sea level to the present stillstand. It is bound by a type 1 basal unconformity which cuts Pleistocene deposits. Five depositional systems have been identified: (1) coastal barrier—lagoon; (2) shelf-transition; (3) fluvial braided; (4) Tiber lagoonal deltas (T1, T2, T3); and (5) Tiber wave-dominated delta. The first four systems constitute the transgressive system tract (TST) which is characterized by a retrogradational parasequences set, while the fifth system represents the highstand system tract (HST) characterized by only one parasequence (progradational). The evolution of these depositional systems has been mostly controlled by sea-level rise, which was not continuous, but punctuated by eight minor stillstands and rapid rises. This mechanism of sea-level change led to the formation of parasequences that developed within the depositional systems. From a palaeogeographical point of view the present Tiber Delta area was mainly characterized by a coastal barrier, lagoon and Tiber lagoonal deltas (T1, T2, T3), which migrated landwards during the sea-level rise. Throughout the time of the present stillstand, the T3 lagoonal delta prograded rapidly into the lagoon, reaching the coastal barrier, and the lagoon was replaced first by marshes and then by the alluvial plain. Finally, the Tiber River overcame the littoral barrier supplying the coast, giving rise to the present wave-dominated delta.  相似文献   

20.
Arctic coastal infrastructure and cultural and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this paper are to provide such a tool by assessing potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site. This study focused on Simpson Point and the adjacent coastal sections because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost path analysis based on a high-resolution light detection and ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from ?5.5 to 2.7 m·a?1 (mean ?0.6 m·a?1). Mean coastal retreat decreased from ?0.6 m·a?1 to ?0.5 m·a?1, for 1952–1970 and 1970–2000, respectively, and increased to ?1.3 m·a?1 in the period 2000–2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion. This study demonstrates that transgressive forcing may provide ample sediment for the expansion of depositional landforms, while growing more susceptible to overwash and flooding.  相似文献   

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