Coastal erosion risk assessment of Hainan Island, China

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.

Assessment of the Vulnerability of the Southwestern Coast of Benin to the Risk of Coastal Erosion and Flooding

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.

Coastal Erosion Feature and Mechanism at Feiyantan in the Yellow River Delta

Feiyantan was the discharge area of Diaokou River distributary of the Yellow River during the period of 1964 to 1976. The coastal erosion feature and morphological evolution at the Feiyantan coast are studied in the light of the topography and section depth, and the corresponding dynamics of wave and current. Results indicate that the protruding topography left after the Diaokou River distributary was abandoned is the main cause of strong coastal erosion. Further research suggests that waves start up the sediment and the tidal current transports it, and the waves and tidal current are combined to be the dominant dynamic mechanism of coastal erosion, in which the tidal residual current takes and transports the sediment outward, thus causing the sediment to wane in the coast.

Coastal Erosion in Yasawa Islands,Fiji

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.

Changes in Mediterranean Coastline According to the Coastal Type and Land Cover under Climate Change:The Case of South-east Spain

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.

Tidal flat erosion of the Huanghe River Delta due to local changes in hydrodynamic conditions

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.

Geomorphology of the Boao coastal system and potential effects of human activities-Hainan Island,South China

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.

Study on Coastal Protection Engineering in the Area of Abandoned Yellow River Mouth

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.

Investigating the Effect of Winds and Storms on Shoreline Erosion along the Coast of Tanzania

Wind data spanning 28 years （1977-2004） from four meteorological stations （Tanga, Zanzibar, Dar es Salaam and Mtwara） were analyzed to elucidate the effect of winds on coastal erosion along the coast of Tanzania. The investigation entailed wavelet analysis of the time series of winds which were related with past erosion events at each site. The study also analyzed qualitatively the incidences of tropical storms in relation to coastal erosion events along the coast. The results revealed that most of the critical erosion incidents in the past few decades were associated with periods of occurrence of extreme wind speeds and tropical storms. Furthermore, the results indicated that the wind speeds and the frequency and intensity of tropical storms had generally been increasing during the past three decades. The findings were consistent to those recently reported for the coast of Dar es Salaam. The increasing trends of winds and storms are considered to have direct impact on the wave climate with increased risk of shoreline wave-induced erosion that is already affecting relatively many parts of Tanzania.

Morphological Changes Induced by Coastal Protection on the Coast of Maputo City, Mozambique

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.

莱州湾南岸海岸侵蚀过程与原因研究

采用历史资料对比分析的方法，对莱州湾南岸1958-2004年的海岸侵蚀进行了研究。结果表明，1958-1984年，莱州湾南岸岸线平均侵蚀后退速率为27m／a，0m等深线后退速率为27～65m／a，岸滩平均蚀低速率为2．1cm／a。1984-2004年，莱州湾南岸岸线位置基本无变化，岸滩平均蚀低速率为1.04cm／a，水深5m以浅的区域表层沉积物变粗。海面相对上升、入海泥沙量减少和风暴潮是研究区海岸侵蚀主要原因，三者对海岸侵蚀影响权重比为3：5：2。

Marine Geohazards： Review and Future Perspective

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.

Impact of and adaptation strategies for sea-level rise on Yangtze River Delta

The Yangtze River Delta characterized by a dense population and a rapidly developing economy is highly vulnerable to sea-level rise. The data from the China Oceanic Information Network and the Zhejiang Provincial Hydrology Bureau are used to analyze sea-level rise. The rate of sea-level rise in the delta was 2.4 mm per year in 1981-2015. The annual sea-level at Daishan, Dinghai, and Dongtou stations in the south wing of the delta were 4.3, 3.1, and 5 mm per year respectively over the same period. The 10-year averaged results at each station also indicate a perceptible trend of sea-level rise. Sea-level rise is contributed to a larger proportion of intensified erosion, ranging from 3% to 14% in the delta. Meanwhile, the 100-year return period of tidal level has decreased to the 50-year rank at Dongtou and Dinghai stations. Moreover, the arrival time of tidal bores at Yanguan is 4 min earlier under sea-level rise of 0.145 m than that of 0 m. The height of tidal bores and the velocities at the surface and bottom layers have an increase under sea-level rise. The maximum increases of high and low tide levels are 0.122 m and 0.016 m while the maximum increases of the velocities at the surface and bottom layers are 0.07 m s^- 1 and 0.05 m s ^-1, respectively. Sea-level rise will bring about the damage of seawall, thus the design standard of constructing seawalls should adopt a higher level to minimize the associated risks in the Yangtze River Delta and its south wing.

废弃的黄河三角洲的地貌特征及演化

本文通过对废弃的黄河三角洲北部沿岸的潮滩和附近海域的地形、地貌对比研究，认为废弃的黄河河口沙嘴，废弃５０年后仍处于侵蚀状态，河口附近海域３０─４０年后己无明显侵蚀。钓口附近海域经５０年冲蚀，目前已不具备水下三角洲的地貌特征，但─１５ｍ以上仍处于侵蚀状态，侵蚀强度随水深增加而减小。－１５ｍ以下已无侵蚀作用。

黄河三角洲海岸剖面类型与演变规律

根据1976—2002年黄河三角洲滨海区36个断面的地形实测资料以及利津水文站的水沙资料,运用动力地貌学的方法,对黄河三角洲海岸剖面形态及冲淤演变进行了研究。结果表明,黄河三角洲海岸剖面可分为建设型、破坏型和稳定型三种基本类型。建设型海岸分布于行水河口,等深线向海推进的距离取决于入海泥沙的堆积过程与海洋动力对泥沙的侵蚀过程两者之间的对比;破坏型海岸主要分布于停止行河不久的废弃河口附近,剖面侵蚀深度与海洋动力条件尤其是潮流流速大小密切相关;而稳定型海岸主要分布于长时间不行河的湾湾沟口附近和广利河以南岸段,前者受河海动力因素影响较小,而后者主要与莱州湾潮流流场有关。

The modern change and evolution tendency of sand coast in the eastern area of Liaodong Gulf

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.

Environmental Impact of Artificial Harbors in Tropic Pacific Oceanic Islands

For loading and unloading of boats or ships round the clock, the access channel and its expanded part-a port are excavated on the lagoon and ocean reef flats in the tropic Pacific oceanic islands. Without moles, the access channel port traps sediment and further transports it to the ocean or lagoon, resulting in coastal erosion. The wide uneven reef flat with a large catchment area tends to cause the formation of tide currents in the channel port, while strong waves on the narrow even reef flat can give rise to rip currents. An access channel port with a mole on one side or two moles on both sides results in less erosion. A model is recommended as an artificial harbor on the ocean coast, which is an excavated port surrounded by a mole, connected with the ocean by an access channel and with the shore by a bridge shaped pier.

Natural and Artificial Connections between Atoll Islets in the Pacific,Their Process and Environmental Impact

Three types of natural connection between atoll islets are described. Causeway, as an artificial way of connecting islets, makes a connection to be completed in a few months. In this case shore adjustment becomes more vigorous than that in natural conditions, resulting in lagoon shore erosion. A causeway without short bridges or culverts should be built close to the lagoon shore to reduce lagoon shore erosion. A causeway-crossing channel assemblage is the worst type among all of the connection engineering constructions because the crossing channel traps sediment and further transports it out of the channel, resulting in long period coastal erosion. Reforming Nippon Causeway in Tarawa Atoll, Kiribati by simple means will stop sand loss, reduce shore erosion and greatly upgrade its stability.

侵蚀型与淤长型海岸湿地景观时空演变特征及差异研究

在盐城国家级自然保护区,选取侵蚀型和淤长型海岸湿地代表区。根据1987年、1997年、2007年3个时相的景观资料,运用RS、G IS技术和景观生态学方法,分析不同海岸类型湿地景观格局演变差异。结果表明:(1)侵蚀型海岸湿地:碱蓬湿地退化消失,人工湿地减少,向光滩集中。景观破碎化指数上升,景观异质性指数降低。景观格局演替呈现多样性特征,1987—1997年,从陆地向海洋方向演替;1997—2007年,从海洋向陆地方向演替。(2)淤长型海岸湿地,景观破碎化指数下降,景观异质性指数上升,景观格局从陆地向海洋方向单向演替。(3)地貌过程和植物群落演替过程等呈连续性变化,导致景观演变呈带状连续性发展;人为干扰往往使生态过程的连续性发生突变,从而使景观演变呈现逆向特征。

Coastline Change Modelling Induced by Climate Change Using Geospatial Techniques in Togo (West Africa)

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 human habitats. This research, basing on geospatial techniques, focuses on coastal erosion monitoring from 1988 to 2018 in Togo. It is interested in the extraction of shoreline and in the analysis of change. Various satellite images indexes 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 Otsu threshold segmentation, Iso Cluster Unsupervised Classification and Support Vector Machine (SVM) Supervised Classification methods for the extraction of the shoreline on NDWI index. The topographic morphology such as linear and non-linear coastal surfaces have been considered. The estimation of the rates of change of the shoreline was performed using the statistical linear regression method (LRR). The results revealed that the SVM Supervised Classification method showed good performance on linear and non-linear coastal 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 and disturbance of human habitats.