Coastal erosion on islands is increasing due to sea level rise,frequent extreme events,and anthropogenic activities.However,studies on the multifactorial coastal erosion risk and the vulnerability of islands are limit...Coastal erosion on islands is increasing due to sea level rise,frequent extreme events,and anthropogenic activities.However,studies on the multifactorial coastal erosion risk and the vulnerability of islands are limited.In this study,the Coastal Erosion Risk Assessment(CERA)method was applied for the first time to the study area in China to assess the erosion risk on the coast of Hainan Island;to explore the effects of coastal ocean dynamics,sediment movement characteristics,and anthropogenic construction;and to discuss the suitability of the method and countermeasures for coastal protection.The results show that the coast of Hainan Island shows high sensitivity,high value,low exposure,and moderate erosion.The whole island showed high vulnerability but low erosion risk,with the eastern region being more affected by erosion,particularly the eastern side of Wulong Port and Yalin Bay in Wenchang,and the shore section of Yalong Bay in Sanya,having a very high risk of coastal erosion.In addition,Monte Carlo simulation was used to check the applicability of the CERA method,and it was found that the rate of shoreline change,population density,and number of storms significantly contributed to coastal erosion,but only the short-term effects of sea level rise were considered.The effects of sea level rise and sediment grain size were primarily analyzed as influencing factors.The effects of sea level rise continue to strengthen,with coastal retreat expected to be greater than 2 m by the mid-21st century.Moreover,Hainan Island is primarily composed of the fine and medium sand types,which have little resistance to coastal erosion.Currently,the impact of sediment grain size is rarely considered in coastal erosion risk assessment studies.However,it can be incorporated into the indicator system in the future,and the spatial variation of indicators can be fully considered to strengthen the refinement study.展开更多
The coastal zone of Benin is inherited from the last marine oscillations of the Quaternary. A rich and very fragile environment, it presented until the 1960s, a shoreline in dynamic equilibrium over the entire 125 km ...The coastal zone of Benin is inherited from the last marine oscillations of the Quaternary. A rich and very fragile environment, it presented until the 1960s, a shoreline in dynamic equilibrium over the entire 125 km of coastal line. Since the 1960s, with the construction of important development infrastructures (ports, dams, groins), the Beninese coast is now subject to risks of coastal erosion and seasonal flooding due to the overflow of lagoon water bodies. The present study, based on socio-economic surveys in the communes of Ouidah, Comè and Grand Popo, exposes the extent of coastal risks and socio-economic and environmental damage in the southwestern coastal zone of Benin. The results show that in terms of land, 2.9 ha and 5.7 ha of land have been permanently lost to coastal erosion in the communes of Ouidah and Grand Popo respectively. Similarly, 212 ha of crops of all types were affected by the flooding, including 35 ha destroyed, i.e. 6.67 ha, 11.3 ha in Comè, 4.67 ha Ouidah and 14 ha Grand Popo. Also, 6435 buildings were affected, and 4235 huts were damaged. In addition, working tools, food stocks and other items are counted among the losses recorded by coastal hazards with their corollaries of diseases. The cost of losses and damages in the 08 districts amount to 418,000,000f cfa of which 266,000,000f cfa of damage and 152,000,000f cfa of loss.展开更多
Coastal erosion may have many different causes. Wherever we came across erosion problems on the Yasawa Islands in Fiji, they had causes other than sea level rise. We present two case studies. At one site, the beach er...Coastal erosion may have many different causes. Wherever we came across erosion problems on the Yasawa Islands in Fiji, they had causes other than sea level rise. We present two case studies. At one site, the beach erosion was caused by the construction of a stonewall diverting the currents in a gyre that hit the shore causing local beach erosion. At another site, extensive erosion caused removal and lateral re-deposition of huge quantities of sand. From the Google Earth images we can infer a date between 2005 and 2009 for this change in shore conditions. We suggest that the shallow-water sand was destabilized by the commercial harvesting of thousands of sea cucumbers (Holothuria scabra). These animals, by their sheer numbers and ecological behavior, were exerting a stabilizing influence on the shallow-water sandy deposits off the beach at Yageta Village. In both cases, the erosion was caused by human action. The coasts all along the Yasawa Islands are characterized by coastal stability. The presence of extensive rock-cut platforms and notches, as well as the occurrence of corals grown into “mini-atolls” are indicative of a stable sea level throughout the islands.展开更多
Coastline changes were analyzed considering the land cover types and the analysis of the causes that have determined these changes during the past decades.Through the overlapping of aerial photographs and GIS an...Coastline changes were analyzed considering the land cover types and the analysis of the causes that have determined these changes during the past decades.Through the overlapping of aerial photographs and GIS analysis,the results showed that the land surface increased with respect to the previous stage,gaining terrain to the sea,but this increment was caused by anthropogenic processes.In fact,without human pressure,the land surface beside the coastal line would have decreased,especially on the sandy beaches and coastal dunes.Therefore,the beaches are one of the most vulnerable ecosystems and geomorphological systems due to erosion and lack of sediment supply associated with the modified river courses(i.e.by the construction of reservoirs,concrete channeling,etc.),the inner land use changes,and the effects of global warming on the sea level.Climate change studies predict specific increases in the sea level along the coast.The aim of this work is to know if anthropic activity can reverse the effects of sea level rise and coastal erosion.In fact,it has been done for decades with measures aimed to correct impacts and favour economic activity(i.e.maintaining tourism resources)and not from the environmental issues.展开更多
An ideal nature system for the study of post-depositional submarine mass changing under wave loading was selected in the intertidal platform of the subaqueous Huanghe River Delta, a delta formed during period from 196...An ideal nature system for the study of post-depositional submarine mass changing under wave loading was selected in the intertidal platform of the subaqueous Huanghe River Delta, a delta formed during period from 1964 to 1976 as the Huanghe River discharged into the Bohai Gulf by Diaokou distributary. A road embankment constructed for petroleum recovery on the inter-tidal platform in 1995 induced the essential varieties of hydrodynamic conditions on the both sides of the road. With both sides sharing similarities in (1) initial sedimentary environment, (2) energetic wave loading, (3) differential hydrodynamic conditions in later stages, (4) enough long-range action, and (5) extreme shallow water inter-tidal platforms; the study is representative and feasible as well. Two study sites were selected on each side of the road, and a series of measurements, samplings, laboratory experiments have been carried out, including morphometry, hydrodynamic conditions, sediment properties, granularity composition, and fractal dimension calculation of the topography in the two adjacent areas. It was observed that in the outer zone, where wave loading with high magnitude prevailed, the tidal flat was bumpy and exhibited a high erosion rate and high fractal dimension. Further, the fractal dimension diminished quickly, keeping with the enlarging of calculative square size. However in the inner zone, where the hydrodynamic condition was weak, the tidal fiat was fiat and exhibited a low erosion rate and low fractal dimensions; the fractal dimension diminished with the enlarging of calcu- lative square size. The fractal dimensions in the different hydrodynamic areas equalized increasingly as the calculative square size accreted to threshold, indicating that the hydrodynamic condition plays a significant role in topography construction and submarine delta erosion process. Additionally, the later differentiation of sediment properties, granularity composition, microstructure characteristics, and mineral composition induced by the different hydrodynamic conditions can also contribute to the variation of topography and sea-bed erosion in the two adjacent areas.展开更多
The Boao coastal system along the eastern coast of Hainan Island is a dynamic delta-tidal inlet-barrier formed during the late Holocene. The delta developed inside a shallow lagoon barred by a sandy barrier with a nar...The Boao coastal system along the eastern coast of Hainan Island is a dynamic delta-tidal inlet-barrier formed during the late Holocene. The delta developed inside a shallow lagoon barred by a sandy barrier with a narrow, shallow tidal inlet opening. Two major distributary channels separated by small islands characterize the delta. The lagoon is silting up receiving and trapping sediments from both the river and, in minor measure during storms, through the tidal inlet opening and barrier washovers. The barrier at the tidal inlet is highly dynamic and changes its form, accreting (migrating spit) against the inlet during fair-weather conditions and being eroded during storms and river floods. The delta has almost completely filled the lagoon and major concerns exist on the effect that ongoing large development plans may have on the environment. These concerns include the effect on floods and rate of siltation once banks of the islands have been stabilized and floodwater and sediment load are impeded from spreading over the lowlands, and the effect of increasing pollutant loads from the new facilities on the ecosystems of the increasingly restricting lagoon water and on the seashores.展开更多
This paper reviews the history of coast evolution and coastal protection in the area of the abandoned Yellow River mouth in Jiangsu Province, analyzes the erosion characteristics and dynamic environment, evaluates the...This paper reviews the history of coast evolution and coastal protection in the area of the abandoned Yellow River mouth in Jiangsu Province, analyzes the erosion characteristics and dynamic environment, evaluates the efficiency of coastal protection engineering works and designs the dimensions of the main seadike and offshore submerged dam. A gerneral scheme of shore protection for this area is proposed.展开更多
Coastal change has merited attention because of heated arguments in the literature on this subject at national,regional,southern African,and international levels.The city of Maputo,the capital of Mozambique,which had ...Coastal change has merited attention because of heated arguments in the literature on this subject at national,regional,southern African,and international levels.The city of Maputo,the capital of Mozambique,which had been undergoing intense coastal erosion actions,was the target of large-scale intervention aimed at halting the advance of the sea and the consequent destruction of infrastructure.Coastal protection consisted of soft forms,artificial feeding,and heavy,longitudinal and transversal structures.This study was carried out along the protected line,about 3 km long,and aims to understand the morphological transformations in the Maputo city shoreline that occurred after the coastal protection.For that,the following technical methods were used:observation,a topographic survey of the beach cross-sections,and the shoreline evolution before and after coastal protection using 2008 and 2010 Google Earth satellite imagery prior to protection 2015,project completion year and 2018 monitoring year.The findings of the study revealed that the causes of coastal erosion persist,like constant removal by deflation of the borrowed sediment.Besides,vertical structures(groynes)intensify erosion in the downdrift while adherent structures interrupt the return of sediment deposited on the sidewalk and the road.The beach that experienced a positive sedimentary balance with artificial feeding has been losing more sediment than it gets.The transversal profiles show the beach shore has depressions that are submerged in the presence of high tides,bringing the sea closer to the adherent structure.Despite the sped up erosion observed,embryonic dunes were detected in some parts of the beach,signs of the establishment of dynamic equilibrium,becoming sites of sand accumulation and sediment source to the beach,through the exchange between the dune and the beach.With these results,a pilot station for artificial dune construction is being designed for beach stability.展开更多
With offshore resource exploration moving to the deep water, marine geohazards have been attracting attention from the academic and industry. Research achievements of marine geohazards were reviewed in this paper. We ...With offshore resource exploration moving to the deep water, marine geohazards have been attracting attention from the academic and industry. Research achievements of marine geohazards were reviewed in this paper. We analyzed and discussed typical issues among marine geohazards, including coastal erosion, submarine slope failure, turbidity current and special hazards induced by gas hydrate dissociation, in terms of their definition, distribution, characteristics and case studies. Major international projects on marine geohazards headed by the United States, Europe, Japan and other international organizations are introduced as well. Three marine geohazard survey methods, including geophysical survey, geotechnical exploration and in-situ observation, were summarized with a brief description of each approach, respectively. Especially, the history of marine geohazard researches in China is briefly reviewed, showing the disparity between China and developed countries in the study of marine geohazards narrows gradually. The potential research tendency in future was suggested.展开更多
In studying sand beach erosion and protection tactics in Liaoning Province, the authors calculated the wavedata of 27 a Period (1963-1991) at Bayuquan Observation Station in Liaodong Gulf. Together with the beach leve...In studying sand beach erosion and protection tactics in Liaoning Province, the authors calculated the wavedata of 27 a Period (1963-1991) at Bayuquan Observation Station in Liaodong Gulf. Together with the beach levellingsand some simple marking stakes monitoring and by having the aid of local annals, the paper analysed the present situationsof the coastline and the causes of sand coastal recession and serious consequences, and then discussed the dynamic processof alongshore sand transport. Simultaneously, based on alongshore sand transport model, oneline cut-and-fill theory anddynamical water model(sea level rise), the authors preliminary estimated beach process for the future in the area.Recently, the coastline is being eroded and 2/3 of the sand coast is subjected to erosion, which the recession rate ofthe individual sector exceed 7. 0 m/a. Coastal erosion has threatened villages, roads, factories and tourist resources. Sealevel rises and the decreasing amount of materials by rivers discharged into the sea and the activities of man, made coast line recession rate accelerate, and cause a great loss of land in the area.展开更多
Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline lea...Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline leads to coastal erosion with significant damage on socio-economic infrastructures and hu</span><span style="font-family:Verdana;">man habitats. This research, basing on geospatial techniques, focuses on coastal </span><span style="font-family:Verdana;">erosion monitoring from 1988 to 2018 in Togo. It is interested in the extrac</span><span style="font-family:Verdana;">tion of shoreline and in the analysis of change. Various satellite images index</span></span><span style="font-family:Verdana;">es</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">have been developed for shoreline extraction but the major scientific problem concerns the precision of the different classification algorithms methods used for the extraction of the shoreline from these water index. This study used NDWI index from multisource satellite images. It assesses the performance of </span><span style="font-family:Verdana;">Otsu threshold segmentation, Iso Cluster Unsupervised Classification and Supp</span><span style="font-family:Verdana;">ort Vector Machine (SVM) Supervised Classification methods for the</span><span style="font-family:Verdana;"> extraction of the shoreline on NDWI index. The topographic morphology such </span><span style="font-family:Verdana;">as linear and non-linear coastal surfaces have been considered. The estimation</span><span style="font-family:Verdana;"> of the rates of change of the shoreline was performed using the statistical linear regression method (LRR). The results revealed that the SVM Supervised </span><span style="font-family:Verdana;">Classification method showed good performance on linear and non-linear coastal </span><span style="font-family:Verdana;">surface than the other methods. For the kinematics of the shoreline, the southwest of the Togolese coast has an average erosion rate ranging from 2.49 to 5.07 m per year. The results obtained will serve as decision-making support tools for the design and implementation of appropriate adaptations plans to avoid the immersion of the asphalt road by sea, displacement of population</span><b> </b><span style="font-family:Verdana;">and disturbance of human habitats.展开更多
The headland-bay beach is one of the most common coastal types in the world.Its morphology reflects the changes that occurred during long-term evolution of the sandy coast.Several headland-bay beach models have been p...The headland-bay beach is one of the most common coastal types in the world.Its morphology reflects the changes that occurred during long-term evolution of the sandy coast.Several headland-bay beach models have been proposed to simulate the coastline’s configuration in equilibrium.In this paper,a new elliptical model is proposed,described,and applied.On the east coast of Laizhou Bay in Shandong Province from Longkou Port to Diaolongzui,four typical headland-bay beaches have developed,and four headland-bay beach models are used in this paper to simulate the morphology of these beaches to assess the applicability of each model.The simulation results of the elliptical model verify that it is applicable to the study area.In addition,the elliptical model is easy to use.Through simulation and field investigations,we concluded that most of the coastal segments in this area will remain in an erosion state,and the human activity has a significant impact on the shoreline’s evolution.展开更多
The Sagar Island,located north of the Bay of Bengal,intercepts the flow in the Hoogly estuary that comprises a network of several estuarine distributaries and creeks,which is considered to be one of the largest estuar...The Sagar Island,located north of the Bay of Bengal,intercepts the flow in the Hoogly estuary that comprises a network of several estuarine distributaries and creeks,which is considered to be one of the largest estuarine systems in the world.The Hooghly River experiences a tidal range in the order of about 4 m,due to which the tide-generated currents drive the sediments which are continuously set in motion.The temple,Kapil Muni(21°38'15.35"N,88°4'30.56"E)is located on the south-western side of Sagar Island,where an annual religious festival and rituals with about a million pilgrims is conducted.The pertinent erosion problem at a rate of about 5 m/year is prevalent at the site has considerably reduced the beach width,thereby,resulting in reduced space for religious as well as recreational activities along the coast.A novel cross-section for the proposed submerged reef using geosynthetic materials is designed considering the different sitespecific,environmental,and socio-economic conditions.The submerged reef can effectively be devised to redistribute the current circulation pattern and trap the sediment for beach restoration.The performance of such a structure depends on its geometrical and structural characteristics,the location of the reef(i.e.)the water depth at the toe,distance from the coastline,wave-structure interaction,sediment transport and local morpho dynamics.The aforesaid criteria were optimized using a numerical model which predicted the average residual velocity in the site to be in the order of about 1 m/s.Owing to logistical constraints geosynthetic materials had to be employed.The detailed design of such a system arrived through numerical modelling and field measurements are presented and discussed in this paper.展开更多
Wireless Sensor Networks (WSNs) are a pioneering technology in many environmental monitoring applications owing to their ability to be deployed for long periods of time in locations that cannot be reached manually. On...Wireless Sensor Networks (WSNs) are a pioneering technology in many environmental monitoring applications owing to their ability to be deployed for long periods of time in locations that cannot be reached manually. One such use-case is the monitoring of underwater sediment transport, a process that plays a significant role in coastal erosion. Previous examples of WSNs deployed for this purpose have been in the form of underwater sensor networks (UWSNs), which have a number of shortcomings from both a practical and technical viewpoint. As such, this paper provides a comparative assessment of UWSNs and an alternative deployment approach of floating echo- sounding sensor networks for the purpose of monitoring underwater sediment transport.展开更多
基金The National Natural Science Foundation of China under contract No.42176167the Innovation Fund of Guangdong Ocean University under contract No.Q18307the Postgraduate Education Innovation Project of Guangdong Ocean University under contract No.202252.
文摘Coastal erosion on islands is increasing due to sea level rise,frequent extreme events,and anthropogenic activities.However,studies on the multifactorial coastal erosion risk and the vulnerability of islands are limited.In this study,the Coastal Erosion Risk Assessment(CERA)method was applied for the first time to the study area in China to assess the erosion risk on the coast of Hainan Island;to explore the effects of coastal ocean dynamics,sediment movement characteristics,and anthropogenic construction;and to discuss the suitability of the method and countermeasures for coastal protection.The results show that the coast of Hainan Island shows high sensitivity,high value,low exposure,and moderate erosion.The whole island showed high vulnerability but low erosion risk,with the eastern region being more affected by erosion,particularly the eastern side of Wulong Port and Yalin Bay in Wenchang,and the shore section of Yalong Bay in Sanya,having a very high risk of coastal erosion.In addition,Monte Carlo simulation was used to check the applicability of the CERA method,and it was found that the rate of shoreline change,population density,and number of storms significantly contributed to coastal erosion,but only the short-term effects of sea level rise were considered.The effects of sea level rise and sediment grain size were primarily analyzed as influencing factors.The effects of sea level rise continue to strengthen,with coastal retreat expected to be greater than 2 m by the mid-21st century.Moreover,Hainan Island is primarily composed of the fine and medium sand types,which have little resistance to coastal erosion.Currently,the impact of sediment grain size is rarely considered in coastal erosion risk assessment studies.However,it can be incorporated into the indicator system in the future,and the spatial variation of indicators can be fully considered to strengthen the refinement study.
文摘The coastal zone of Benin is inherited from the last marine oscillations of the Quaternary. A rich and very fragile environment, it presented until the 1960s, a shoreline in dynamic equilibrium over the entire 125 km of coastal line. Since the 1960s, with the construction of important development infrastructures (ports, dams, groins), the Beninese coast is now subject to risks of coastal erosion and seasonal flooding due to the overflow of lagoon water bodies. The present study, based on socio-economic surveys in the communes of Ouidah, Comè and Grand Popo, exposes the extent of coastal risks and socio-economic and environmental damage in the southwestern coastal zone of Benin. The results show that in terms of land, 2.9 ha and 5.7 ha of land have been permanently lost to coastal erosion in the communes of Ouidah and Grand Popo respectively. Similarly, 212 ha of crops of all types were affected by the flooding, including 35 ha destroyed, i.e. 6.67 ha, 11.3 ha in Comè, 4.67 ha Ouidah and 14 ha Grand Popo. Also, 6435 buildings were affected, and 4235 huts were damaged. In addition, working tools, food stocks and other items are counted among the losses recorded by coastal hazards with their corollaries of diseases. The cost of losses and damages in the 08 districts amount to 418,000,000f cfa of which 266,000,000f cfa of damage and 152,000,000f cfa of loss.
基金supported by a kind grant from the CO_(2) Coalition.
文摘Coastal erosion may have many different causes. Wherever we came across erosion problems on the Yasawa Islands in Fiji, they had causes other than sea level rise. We present two case studies. At one site, the beach erosion was caused by the construction of a stonewall diverting the currents in a gyre that hit the shore causing local beach erosion. At another site, extensive erosion caused removal and lateral re-deposition of huge quantities of sand. From the Google Earth images we can infer a date between 2005 and 2009 for this change in shore conditions. We suggest that the shallow-water sand was destabilized by the commercial harvesting of thousands of sea cucumbers (Holothuria scabra). These animals, by their sheer numbers and ecological behavior, were exerting a stabilizing influence on the shallow-water sandy deposits off the beach at Yageta Village. In both cases, the erosion was caused by human action. The coasts all along the Yasawa Islands are characterized by coastal stability. The presence of extensive rock-cut platforms and notches, as well as the occurrence of corals grown into “mini-atolls” are indicative of a stable sea level throughout the islands.
基金Acknowledge to the National Geographic Institute for supporting the free access and availability of geographical data for researchers.
文摘Coastline changes were analyzed considering the land cover types and the analysis of the causes that have determined these changes during the past decades.Through the overlapping of aerial photographs and GIS analysis,the results showed that the land surface increased with respect to the previous stage,gaining terrain to the sea,but this increment was caused by anthropogenic processes.In fact,without human pressure,the land surface beside the coastal line would have decreased,especially on the sandy beaches and coastal dunes.Therefore,the beaches are one of the most vulnerable ecosystems and geomorphological systems due to erosion and lack of sediment supply associated with the modified river courses(i.e.by the construction of reservoirs,concrete channeling,etc.),the inner land use changes,and the effects of global warming on the sea level.Climate change studies predict specific increases in the sea level along the coast.The aim of this work is to know if anthropic activity can reverse the effects of sea level rise and coastal erosion.In fact,it has been done for decades with measures aimed to correct impacts and favour economic activity(i.e.maintaining tourism resources)and not from the environmental issues.
基金The National Natural Science Foundations of China under contract Nos 41372287 and 41272316the Comprehensive Investigation Plan of Marine Geology Security Engineering under contract No.GZH201100203
文摘An ideal nature system for the study of post-depositional submarine mass changing under wave loading was selected in the intertidal platform of the subaqueous Huanghe River Delta, a delta formed during period from 1964 to 1976 as the Huanghe River discharged into the Bohai Gulf by Diaokou distributary. A road embankment constructed for petroleum recovery on the inter-tidal platform in 1995 induced the essential varieties of hydrodynamic conditions on the both sides of the road. With both sides sharing similarities in (1) initial sedimentary environment, (2) energetic wave loading, (3) differential hydrodynamic conditions in later stages, (4) enough long-range action, and (5) extreme shallow water inter-tidal platforms; the study is representative and feasible as well. Two study sites were selected on each side of the road, and a series of measurements, samplings, laboratory experiments have been carried out, including morphometry, hydrodynamic conditions, sediment properties, granularity composition, and fractal dimension calculation of the topography in the two adjacent areas. It was observed that in the outer zone, where wave loading with high magnitude prevailed, the tidal flat was bumpy and exhibited a high erosion rate and high fractal dimension. Further, the fractal dimension diminished quickly, keeping with the enlarging of calculative square size. However in the inner zone, where the hydrodynamic condition was weak, the tidal fiat was fiat and exhibited a low erosion rate and low fractal dimensions; the fractal dimension diminished with the enlarging of calcu- lative square size. The fractal dimensions in the different hydrodynamic areas equalized increasingly as the calculative square size accreted to threshold, indicating that the hydrodynamic condition plays a significant role in topography construction and submarine delta erosion process. Additionally, the later differentiation of sediment properties, granularity composition, microstructure characteristics, and mineral composition induced by the different hydrodynamic conditions can also contribute to the variation of topography and sea-bed erosion in the two adjacent areas.
文摘The Boao coastal system along the eastern coast of Hainan Island is a dynamic delta-tidal inlet-barrier formed during the late Holocene. The delta developed inside a shallow lagoon barred by a sandy barrier with a narrow, shallow tidal inlet opening. Two major distributary channels separated by small islands characterize the delta. The lagoon is silting up receiving and trapping sediments from both the river and, in minor measure during storms, through the tidal inlet opening and barrier washovers. The barrier at the tidal inlet is highly dynamic and changes its form, accreting (migrating spit) against the inlet during fair-weather conditions and being eroded during storms and river floods. The delta has almost completely filled the lagoon and major concerns exist on the effect that ongoing large development plans may have on the environment. These concerns include the effect on floods and rate of siltation once banks of the islands have been stabilized and floodwater and sediment load are impeded from spreading over the lowlands, and the effect of increasing pollutant loads from the new facilities on the ecosystems of the increasingly restricting lagoon water and on the seashores.
文摘This paper reviews the history of coast evolution and coastal protection in the area of the abandoned Yellow River mouth in Jiangsu Province, analyzes the erosion characteristics and dynamic environment, evaluates the efficiency of coastal protection engineering works and designs the dimensions of the main seadike and offshore submerged dam. A gerneral scheme of shore protection for this area is proposed.
文摘Coastal change has merited attention because of heated arguments in the literature on this subject at national,regional,southern African,and international levels.The city of Maputo,the capital of Mozambique,which had been undergoing intense coastal erosion actions,was the target of large-scale intervention aimed at halting the advance of the sea and the consequent destruction of infrastructure.Coastal protection consisted of soft forms,artificial feeding,and heavy,longitudinal and transversal structures.This study was carried out along the protected line,about 3 km long,and aims to understand the morphological transformations in the Maputo city shoreline that occurred after the coastal protection.For that,the following technical methods were used:observation,a topographic survey of the beach cross-sections,and the shoreline evolution before and after coastal protection using 2008 and 2010 Google Earth satellite imagery prior to protection 2015,project completion year and 2018 monitoring year.The findings of the study revealed that the causes of coastal erosion persist,like constant removal by deflation of the borrowed sediment.Besides,vertical structures(groynes)intensify erosion in the downdrift while adherent structures interrupt the return of sediment deposited on the sidewalk and the road.The beach that experienced a positive sedimentary balance with artificial feeding has been losing more sediment than it gets.The transversal profiles show the beach shore has depressions that are submerged in the presence of high tides,bringing the sea closer to the adherent structure.Despite the sped up erosion observed,embryonic dunes were detected in some parts of the beach,signs of the establishment of dynamic equilibrium,becoming sites of sand accumulation and sediment source to the beach,through the exchange between the dune and the beach.With these results,a pilot station for artificial dune construction is being designed for beach stability.
基金granted by the National Natural Science Foundation of China(Grant No.41427803)
文摘With offshore resource exploration moving to the deep water, marine geohazards have been attracting attention from the academic and industry. Research achievements of marine geohazards were reviewed in this paper. We analyzed and discussed typical issues among marine geohazards, including coastal erosion, submarine slope failure, turbidity current and special hazards induced by gas hydrate dissociation, in terms of their definition, distribution, characteristics and case studies. Major international projects on marine geohazards headed by the United States, Europe, Japan and other international organizations are introduced as well. Three marine geohazard survey methods, including geophysical survey, geotechnical exploration and in-situ observation, were summarized with a brief description of each approach, respectively. Especially, the history of marine geohazard researches in China is briefly reviewed, showing the disparity between China and developed countries in the study of marine geohazards narrows gradually. The potential research tendency in future was suggested.
文摘In studying sand beach erosion and protection tactics in Liaoning Province, the authors calculated the wavedata of 27 a Period (1963-1991) at Bayuquan Observation Station in Liaodong Gulf. Together with the beach levellingsand some simple marking stakes monitoring and by having the aid of local annals, the paper analysed the present situationsof the coastline and the causes of sand coastal recession and serious consequences, and then discussed the dynamic processof alongshore sand transport. Simultaneously, based on alongshore sand transport model, oneline cut-and-fill theory anddynamical water model(sea level rise), the authors preliminary estimated beach process for the future in the area.Recently, the coastline is being eroded and 2/3 of the sand coast is subjected to erosion, which the recession rate ofthe individual sector exceed 7. 0 m/a. Coastal erosion has threatened villages, roads, factories and tourist resources. Sealevel rises and the decreasing amount of materials by rivers discharged into the sea and the activities of man, made coast line recession rate accelerate, and cause a great loss of land in the area.
文摘Climate change is a major concern of humanity. One of the consequences of climate change is global warming causing melting glaciers, rising sea levels and shoreline regression. In Togo, the regression of shoreline leads to coastal erosion with significant damage on socio-economic infrastructures and hu</span><span style="font-family:Verdana;">man habitats. This research, basing on geospatial techniques, focuses on coastal </span><span style="font-family:Verdana;">erosion monitoring from 1988 to 2018 in Togo. It is interested in the extrac</span><span style="font-family:Verdana;">tion of shoreline and in the analysis of change. Various satellite images index</span></span><span style="font-family:Verdana;">es</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">have been developed for shoreline extraction but the major scientific problem concerns the precision of the different classification algorithms methods used for the extraction of the shoreline from these water index. This study used NDWI index from multisource satellite images. It assesses the performance of </span><span style="font-family:Verdana;">Otsu threshold segmentation, Iso Cluster Unsupervised Classification and Supp</span><span style="font-family:Verdana;">ort Vector Machine (SVM) Supervised Classification methods for the</span><span style="font-family:Verdana;"> extraction of the shoreline on NDWI index. The topographic morphology such </span><span style="font-family:Verdana;">as linear and non-linear coastal surfaces have been considered. The estimation</span><span style="font-family:Verdana;"> of the rates of change of the shoreline was performed using the statistical linear regression method (LRR). The results revealed that the SVM Supervised </span><span style="font-family:Verdana;">Classification method showed good performance on linear and non-linear coastal </span><span style="font-family:Verdana;">surface than the other methods. For the kinematics of the shoreline, the southwest of the Togolese coast has an average erosion rate ranging from 2.49 to 5.07 m per year. The results obtained will serve as decision-making support tools for the design and implementation of appropriate adaptations plans to avoid the immersion of the asphalt road by sea, displacement of population</span><b> </b><span style="font-family:Verdana;">and disturbance of human habitats.
基金supported by the Marine Public Benefit Scientific Research Special Fund Project of the State Oceanic Administration (Nos. 200905008 and 201405037)
文摘The headland-bay beach is one of the most common coastal types in the world.Its morphology reflects the changes that occurred during long-term evolution of the sandy coast.Several headland-bay beach models have been proposed to simulate the coastline’s configuration in equilibrium.In this paper,a new elliptical model is proposed,described,and applied.On the east coast of Laizhou Bay in Shandong Province from Longkou Port to Diaolongzui,four typical headland-bay beaches have developed,and four headland-bay beach models are used in this paper to simulate the morphology of these beaches to assess the applicability of each model.The simulation results of the elliptical model verify that it is applicable to the study area.In addition,the elliptical model is easy to use.Through simulation and field investigations,we concluded that most of the coastal segments in this area will remain in an erosion state,and the human activity has a significant impact on the shoreline’s evolution.
文摘The Sagar Island,located north of the Bay of Bengal,intercepts the flow in the Hoogly estuary that comprises a network of several estuarine distributaries and creeks,which is considered to be one of the largest estuarine systems in the world.The Hooghly River experiences a tidal range in the order of about 4 m,due to which the tide-generated currents drive the sediments which are continuously set in motion.The temple,Kapil Muni(21°38'15.35"N,88°4'30.56"E)is located on the south-western side of Sagar Island,where an annual religious festival and rituals with about a million pilgrims is conducted.The pertinent erosion problem at a rate of about 5 m/year is prevalent at the site has considerably reduced the beach width,thereby,resulting in reduced space for religious as well as recreational activities along the coast.A novel cross-section for the proposed submerged reef using geosynthetic materials is designed considering the different sitespecific,environmental,and socio-economic conditions.The submerged reef can effectively be devised to redistribute the current circulation pattern and trap the sediment for beach restoration.The performance of such a structure depends on its geometrical and structural characteristics,the location of the reef(i.e.)the water depth at the toe,distance from the coastline,wave-structure interaction,sediment transport and local morpho dynamics.The aforesaid criteria were optimized using a numerical model which predicted the average residual velocity in the site to be in the order of about 1 m/s.Owing to logistical constraints geosynthetic materials had to be employed.The detailed design of such a system arrived through numerical modelling and field measurements are presented and discussed in this paper.
文摘Wireless Sensor Networks (WSNs) are a pioneering technology in many environmental monitoring applications owing to their ability to be deployed for long periods of time in locations that cannot be reached manually. One such use-case is the monitoring of underwater sediment transport, a process that plays a significant role in coastal erosion. Previous examples of WSNs deployed for this purpose have been in the form of underwater sensor networks (UWSNs), which have a number of shortcomings from both a practical and technical viewpoint. As such, this paper provides a comparative assessment of UWSNs and an alternative deployment approach of floating echo- sounding sensor networks for the purpose of monitoring underwater sediment transport.