Shoreline Retreat Research Articles

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Nile Delta exhibited a spatial reversal in the rates of shoreline retreat on the Rosetta promontory comparing pre- and post-beach protection

The coastline of the Nile Delta experienced accelerated erosion since the construction of the Aswan High Dam in 1964 and, consequently, the entrapment of a large amount of river sediments behind it. The coastline of the Rosetta promontory showed the highest erosion in the Delta with an average retreat rate of 137.4m year−1. In 1991, in an effort to mitigate sediment loss, a 4.85km long seawall was built on the outer margin of the promontory. For additional beach protection, 15 groins were constructed along the eastern and western sides of the seawall in 2003 and 2005. To quantify erosion and accretion patterns along the Rosetta promontory, 11 Landsat images acquired at unequal intervals during a 40year time span (1972 and 2012) were analyzed. The positions of shorelines were automatically extracted from satellite imagery and compared with three very high resolution QuickBird and WorldView2 images for data validation. Analysis of the rates of shoreline change revealed that the construction of the seawall was largely successful in halting the recession along the tip of the promontory, which lost 10.8km2 prior to coastal protection. Conversely, the construction of the 15 groins has negatively affected the coastal morphology of the promontory and caused a reversal from accretion to fast erosion along the promontory leeside, where some segments of the shoreline have undergone as much as 30.8m year−1 of erosion. Without hard structures, the tip of the Rosetta promontory would have retreated 2.3km by 2013 and lost 7.2km2 of land. About 10% of this land is deltaic fertile cultivated farms. Moreover, without additional protection the sides of the promontory will lose about 1.3km2 of land and the coastline would recede at an average rate of 200m by 2020. Unless action is taken, coastal erosion, enhanced by rising sea level, will steadily eat away the Nile Delta at an alarming rate. The successful demonstration of the advocated procedures in this study could be adopted, with appropriate modifications, for other deltas worldwide.

Rapid flooding of the southern Vietnam shelf during the early to mid‐Holocene

ABSTRACTA new sea‐level record derived from coastal deposits of the South Vietnam shelf covers the deglacial sea‐level history between 13.0 and 9.0 ka BP. This record reveals a relatively constant rate of sea‐level rise and matches well with model results based on the RSES‐ANU global ice‐sheet model. However, the sea‐level observations reveal a significant discrepancy with model results based on the ICE‐5G global ice‐sheet model, which further questions the existence of Meltwater Pulse 1B The incised‐valley deposits of the South Vietnam shelf also complete the deglacial coastal evolution of southern Vietnam. The regional sea‐level records of the South Vietnam shelf, the Mekong Delta and the Cambodian lowlands reveal an offset of about 18 m between 9.0 and 8.2 ka BP. The shoreline retreat of more than 200 km related to this offset was mainly caused by the differential hydro‐isostatic adjustment between the South Vietnam shelf and the Cambodian lowlands. However, the GIA‐model results cannot fully explain this fast relative sea‐level rise due to the topographic changes and, possibly, alternative melt‐water sources not accounted for in the current models.

Vulnerability of Mediterranean ecosystems to long-term changes along the coast of Israel.

Although human activity is considered to be a major driving force affecting the distribution and dynamics of Mediterranean ecosystems, the full consequences of projected climate variability and relative sea-level changes on fragile coastal ecosystems for the next century are still unknown. It is unclear how these waterfront ecosystems can be sustained, as well as the services they provide, when relative sea-level rise and global warming are expected to exert even greater pressures in the near future (drought, habitat degradation and accelerated shoreline retreat). Haifa Bay, northern Israel, has recorded a landward sea invasion, with a maximum sea penetration 4,000 years ago, during an important period of urban development and climate instability. Here, we examine the cumulative pressure of climate shifts and relative sea-level changes in order to investigate the patterns and mechanisms behind forest replacement by an open-steppe. We provide a first comprehensive and integrative study for the southern Levant that shows that (i) human impact, through urbanization, has been the main driver behind ecological erosion in the past 4,000 years; (ii) climate pressures have reinforced this impact; and (iii) local coastal changes have played a decisive role in eroding ecosystem resilience. These three parameters, which have closely interacted during the last 4,000 years in Haifa Bay, clearly indicate that for an efficient management of the coastal habitats, anthropogenic pressures linked to urban development must be reduced in order to mitigate the predicted effects of Global Change.

Beach Profile Model with Size-Selective Sediment Transport. II: Numerical Modeling

AbstractBeach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations.

Amplification of Shoreline Response To Sea-Level Change By Back-Tilted Subsidence

Abstract Shorelines move in response to the balance of geodynamic processes acting on sedimentary basins; thus the stratigraphic record of shoreline migration is an important tool for reconstructing climate, tectonic, and eustatic histories from ancient deposits. Here we test whether subsidence geometry influences shoreline migration in response to sea-level change by comparing two physical experiments conducted in the Experimental EarthScape (XES) basin. The experiments had similar sediment supply, subsidence rate, and sinusoidal sea-level cycles, but one experiment had a fore-tilted subsidence profile, where subsidence rates increased with distance from the sediment source (similar to a passive-margin setting) and the other had a back-tilted subsidence profile, where maximum subsidence was close to the sediment source with subsidence rates decreasing downstream. In the recent back-tilted experiment, decreasing subsidence rates downstream resulted in a tendency for shoreline regressions to self-amplify during base-level fall, whereas increasing subsidence rates upstream caused a rapid shoreline retreat during base-level rise, causing amplified shoreline fluctuations during sea-level cycles compared to the previous fore-tilted experiment. These results indicate that the spatial pattern of subsidence in a basin has a significant effect on shoreline migration in response to eustatic cycles. Shorelines in back-tilted basins are substantially more sensitive to changes in relative sea level than comparable coastlines in passive-margin settings, all else being equal.

Erosion and reorientation of the Sapodilla Cays, Mesoamerican Reef Belize from 1960 to 2012

The Sapodilla Cays Marine Reserve in southern Belize includes nine low-relief sand cays that were first surveyed in 1960. The purpose of this study is to reconstruct a 52-year history of the Sapodilla Cays (1960–2012) using a combination of historical topographic surveys, satellite imagery, and additional field data collection. Results suggest that the majority of islands are eroding with some islands having lost over 70% of their area, and many have become swash aligned, which suggests limited sediment availability. The proportion of area lost on each island is related to the width of the reef platform (to the 5 m isobaths) in the direction of the reef edge, while island area is dependent on the width of the reef platform in the direction of the resultant wind. This suggests that the width of the reef platform is a primary determinant of sediment supply between storms that tend to erode the eastern shoreline of the island through refraction along the reef edge. While storm erosion tends to be concentrated along the eastern shoreline through the loss of sediment offshore, alongshore transport to the lagoon shoreline, and the transfer of sediment to the interior of the island, net shoreline retreat is greatest along the lagoon, suggesting that the relatively small winter “northers” and a lack of sediment supply from the reef lagoon are responsible for the observed erosion. Extrapolations based on contemporary loss-rates suggest that the smallest cays will disappear by 2020, while the largest cays will begin to disappear by the end of century.

Influence of climate change on the Ria de Aveiro littoral: adaptation strategies for flooding events and shoreline retreat

Dias, J.M., Lopes, C.L., Coelho, C., Pereira, C., Alves, F.L., Sousa, L.P., Antunes, I.C., Fernandes, M. da L., Phillips, M.R., 2014. Influence of mean sea level rise on Ria de Aveiro littoral: adaptation strategies for flooding events and shoreline retreat. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 320–325, ISSN 0749-0208.Floods and shoreline retreat in coastal areas threaten many millions of people across Europe. Moreover, it is agreed that climate change can amplify the magnitude and frequency of flooding events and accelerate the shoreline retreat. The main goal of this work is to assess flood and shoreline retreat risk, and define adaptation strategies under present conditions and future climate change scenarios on the Ria de Aveiro and its littoral. The hydrodynamic model ELCIRC was implemented for the Ria de Aveiro lagoon and GENESIS (U.S. Army Corps of Engineers) and LTC (Long-Term Configuration) shoreline evolution models for the littoral stretch between Esmoriz and Mira. Numerical results in present and future scenarios were used to map the flooded lagoon extension and the shoreline evolution of this coastal stretch. Analysis showed an increase of the lagoon's flooded area, relative to the present, with regions more exposed to sea level rise being lowland areas located at the margins of the lagoon's deeper channels. Examination of the littoral stretch showed a slight increasing trend of shoreline retreat under predicted future climate change scenarios, thereby increasing the probability of sand spit rupture. Data from numerical predictions were integrated into Geographical Information Systems covering the coastal and lagoon study areas, and produced hazard and risk maps including the identification of regional use and activities. Structural and non-structural measures were subsequently developed in order to mitigate flood and shoreline retreat effects.

Trend Change(s) in Coastal Management Plans: the integration of short and medium term perspectives in the spatial planning process

Alves, F.L., Sousa, L.P., Esteves, T.C., Oliveira, E.R., Antunes, I.C., Fernandes, M.L., Carvalho, L., Barroso, S., Pereira, M., 2014. Trend Change(s) in Coastal Management Plans: the integration of short and medium term perspectives in the spatial planning process. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 437–442, ISSN 0749-0208.Spatial planning can be seen as an interdisciplinary science that ensures sustainable development and land use, since it integrates policy, social, cultural, economic and environmental management issues. Marine and coastal spatial planning is particularly challenging due to their vulnerable, dynamic and complex nature and to the problems associated with sea level rise, erosion processes and land-use pressures in the coastal zone. Coastal erosion, flooding and shoreline retreat are serious problems along the coast of mainland Portugal. By using an innovative approach of coastal zone spatial planning, this study developed an Integrated Coastal Zone Management Plan for the Portuguese central region (stretch Ovar - Marinha Grande), where alternative planning policies to the previous ones were suggested. The study revealed that socio-economic analysis and the identification and valuation of ecosystems services and land use need to be incorporated in spatial planning to support decision-making favouring sustainable development. According to these approaches the Coastal Plan was developed considering three environmental scenarios to respond to the coastal erosion trends, based on a development model for the coastal region. In addition, the scenarios consider the public investments constraints (national budget) expected in the next decade and the short and medium term of the Plan. This Plan is differentiated from the previous by attempting to lessen further coastal erosion through the integration of different jurisdictions, legislations and directive measures and applying them to the terrain. This strategy shows itself as relevant to promote further forward-thinking Plans for other Portuguese coastal areas.

Managing shoreline retreat: a US perspective

As sea level rises, coastal communities will face increased risks of flooding, storm surge, and inundation. In some areas, structural protective measures will be built, and for some properties, accommodation to sea level rise may be possible. For other areas, however, some form of retreat will be either preferred on economic or sociopolitical grounds or required given fiscal constraints. This paper considers how society can proactively manage shoreline retreat in those locations where it is deemed the preferable policy. A three-part strategy is proposed: (1) reduce new development in the highest-risk areas; (2) adopt policies that allow for expected and orderly removal or modification of development as inundation occurs; and (3) take advantage of disasters to implement managed retreat approaches. Specific policies are recommended and the challenges of institutional change discussed.

Evaluation Of Policy And Legal Environment For The Management Of Coastal Zones In Ghana With Special Emphasis On Bukom, A Coastal Suburb Of Accra District

The world's population is increasing at an exponential level and coupled with rural-urban migration and other detrimental activities of human beings, the Earth's natural resources is constantly being subjected to intense negative pressures. These pressures have contributed immensely to the degradation of the environment especially the coastal zones. Ghana as a coastal zone country is not spared this global degradation. Ghana is home to one of the largest artificial lakes in the world, the lake Bosomtwe. The country is widely known for famous rivers, lagoons, estuaries and the country generates most of its income from tourism activities. It is therefore expedient that the country should promulgate and implement policies that will help protect its coastal resources to ensure sustainable use of the coastal and marine zones. This paper reviews the availability of an Integrated Coastal Management Policy in Ghana and how it is been implemented to ensure sustainability. At the end of the research, it was concluded that Ghana has no coastal zone policy and this has resulted in the over- exploration of coastal resources. Bokum, a typical coastal town in Accra was used as a case study. Most residents interviewed showed no knowledge of coastal zone distraction at all. Ghana has to promulgate and implement coastal zones policy as soon as possible to ensure that resources are not over-exploited but they are managed in a sustainable manner to ensure that future generation are not deprive of their fair share of coastal zone resources. 2012 to have exceeded 7 billion people. This current population growth is alarming with Ghana being a developing nation is faced with such situation of increase in the population of the country. The current population of Ghana as released by the Ghana Statistic Service (2010) stands at 24 million. The total land cover of Ghana is 238 533 km 2 and out of this, 550 km is coastlines. Available statistics as referenced from Churcher (2006) indicate that this 7 per cent of Ghana's coastline is home to 25 per cent of the nation's population and it is also where 75 per cent of Ghana's industry is located. What is alarming is the fact that 51.5 per cent of these coastal regions is urbanised as compared with the national 35.4 per cent urbanised areas. The rate of unemployment in Ghana is also very high due to the fact that the number of graduates from the various universities in a year far exceeds the annual rate of job creation. Ghana is bordered by the Atlantic Ocean in the southern part of the country. This has created employment in these coastal regions as fishing activities has boomed. There are also two harbours in the country, namely the Tema Harbour and the Takoradi Harbour. These two harbours as well as activities along the coastal regions have created so many opportunities for the country. Due to the rate of increase in Ghana's population, the pressure on the country's coastal zones is very alarming as most Ghanaians from the other regions of the country troop to these coastal regions to seek employment and also to engage in other activities in order to generate income. Flooding, shoreline retreat and coastal erosions are part of the major negative impacts along Ghana's coastline (Ly, 1980). In Hardin's book, the ''The tragedy of the commons'', Hardin explained vividly how a common good which is mutually shared can be over-exploited to destruction (Hardin, 1968). This situation is paramount in Ghana's situation and it is unbearable as to the kind of human activities taking place in the country's coastal region or zones. Ghana being a signatory to Agenda 17 has the duty to promulgate and enforce laws to protect its coastal waters in a sustainable manner to be able to serve the current as well as the future generation. This paper will therefore take a look at integrated coastal management policies in Ghana, how it is being implemented, challenges facing enforcing agencies and the way forward. Special focus will be given to a local coastal community in Ghana called Bukom.

Coastal Erosion Studies—A Review

The land ward displacement of the shoreline caused by the forces of waves and currents is termed as Coastal Erosion. The Coastal areas have become more prone and vulnerable to natural and human made hazards which lead to Coastal Erosion. The Shoreline retreat is recognized as a burgeoning threat because of global climate change and other anthropogenic activities that alter the natural processes of sustaining beaches and coasts. Coastal Erosion mainly occurs when wind, waves and long shore currents move sand from shore and deposit it somewhere else. The sand can be moved to another beach, to the deeper ocean bottom, into an ocean trench or onto the landside of a dune. The removal of the sand from the sand sharing system results in permanent changes in beach shape and structure. The impact of the event is not seen immediately as in the case of Tsunami or Storm Surge but it is equally important when we consider loss of property. It generally takes months or years to note the impact of Erosion; therefore, this is generally classified as a “Long Term Coastal Hazard”. The present paper attempts to describe a Review on Coastal Erosion Process, Parameters’ affecting, and methodologies are adopted to identify the erosion and recommend a solution.

Late Holocene sedimentation in a high Arctic coastal setting: Simpson Lagoon and Colville Delta, Alaska

Arctic coastal environments near major river outfalls, like Simpson Lagoon, Alaska and the adjacent Colville River Delta, potentially contain high-resolution sediment records useful in elucidating late Holocene Arctic sediment transport pathways and coupled terrestrial-ocean evidence of paleoclimate variability. This study utilizes a multi-tracer geochronology approach (137Cs, 239,240Pu, and 14C) tailored for high-latitude environments to determine the age models for cores collected from Simpson Lagoon, and to date seismic boundaries in shallow acoustic reflection data (CHIRP) to examine late Holocene infill patterns. Modern (~100y) sediment accumulation rates range from <0.02 to 0.46±0.04cmy−1, with a primary depocenter in western Simpson Lagoon adjacent to the Colville Delta and a secondary depocenter in eastern Simpson Lagoon. CHIRP reflectors, age-constrained by 14C analysis, reveal rapid late Holocene (0–3500y BP) transgression consistent with high modern shoreline retreat rates. The western depocenter contains >5m of late Holocene interbedded sediments, likely derived primarily from the Colville River, with onset of accumulation occurring prior to ~3500y BP. A paleo-high in central Simpson Lagoon, separating the two depocenters, was subaerially exposed prior to ~600y BP. The millimeters-per-year sedimentation rates across the lagoon, coupled with the undisturbed, interbedded sediment record, indicate that these settings hold great potential to develop new Arctic paleoenvironmental records.

Variable response of coastal environments of the northwestern Gulf of Mexico to sea-level rise and climate change: Implications for future change

The results from nearly three decades of marine geological research in the northwestern Gulf of Mexico are compiled in an effort to understand those factors (e.g., sea-level rise, sediment supply, subsidence, antecedent topography) that influenced coastal evolution during the last eustatic cycle (~ 120 ka to Present). Armed with this information, we evaluate coastal response to variable sea-level rise of the Holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes. The early Holocene evolution of northwestern Gulf of Mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea-level rise. Two of these events, one between ~ 8.4 and 8.0 ka and the other between ~ 7.4 and 6.8 ka, were associated with known episodes of ice sheet retreat in North America and Antarctica, respectively. During the middle and late Holocene, the east Texas and western Louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat, while the central Texas coast remained relatively stable. This variability in coastal response to sea-level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed. Sand that nourished the evolving east and south Texas, as well as westernmost Louisiana, coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level (MIS5e–MIS2). The loci of these deltas controlled the spatial variability of this offshore sand supply. Sand supply to the central Texas coast has been dominated by converging longshore currents and throughout the middle to late Holocene was large enough to keep pace with sea-level rise. Moreover, sand supply from rivers has varied considerably in response to climate change. During the early Holocene, when the average rate of linear sea-level rise was 4.2 mm/yr, the Brazos, Colorado and Rio Grande Rivers all formed deltas on the inner continental shelf. Today, only the Brazos contributes enough sediment to the Gulf of Mexico to form a delta, but its sand delivery is minimal. A reversal from late Holocene growth of western Louisiana–east Texas and south Texas barrier islands and peninsulas to erosion occurred during the last ~ 2.0 ka, after the rate of sea-level rise began to decelerate. The actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward-advancing shoreface (transgressive ravinement). Differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness, which results from the underlying relief on the Pleistocene surface. The late Holocene was also the time of chenier plain development in western Louisiana and east Texas that was marked by localized differences in growth and retreat. The current rate of eustatic sea-level rise in the northern Gulf of Mexico is in the range of 2.0 and 3.0 mm/yr and is approaching rates of the early Holocene. This is on average about five times the long-term rate of the past 4.0 ka. This larger rate is associated with an increase in coastal erosion in historical time relative to long-term rates. Current rates of Gulf shoreline erosion are approaching rates of the early to mid-Holocene and the rate of retreat of some barriers is not sustainable. Core transects off central Texas reflect a late Holocene history of shoreface progradation, but the modern shoreline is currently eroding, albeit at slower rates than elsewhere along the coast. Overall, the sand supply needed to sustain the Gulf shoreline is lacking. Likewise, baylines are experiencing erosion rates that are faster than the late Holocene average and bayhead deltas are at the tipping point of catastrophic retreat. Spatial variability in erosion rates highlights the importance of factors such as sediment supply, subsidence, and anthropogenic influences on coastal evolution. Tropical storms and hurricanes, while exerting the most noticeable coastal change, merely exacerbate overall shoreline retreat and migration. Along the entire northwestern Gulf Coast, the impact of human intervention to natural processes is particularly evident, primarily due to alterations in river discharge and sediment supply to the coast, interruptions in along-shore and cross-shore sand transport, and increases in rates of subsidence through fluid withdrawal. Compared to natural changes that took place during the Holocene, the impacts of human activity have been virtually instantaneous. The geological record indicates that the ongoing increase in the rate of sea-level rise, coupled with diminished sediment supply and human intervention, will continue to severely impact the low-gradient coastal environments of the northwestern Gulf of Mexico.

Beach morphology and shoreline evolution: Monitoring and modelling medium-term responses (Portuguese NW coast study site)

Numerical models for shoreline evolution have been used for coastal management planning for several decades. The model calibration is a start point to project shoreline scenarios and in this aim the use of data acquired within the scope of monitoring programmes provides the opportunity to assess the models' capabilities under real condition. This work applies calibration data (retrieved from field surveys) to numerical models to predict medium-term shoreline evolution using, as a case study, a beach stretch named AC, about 3.5km long and located downdrift of a groin on the northwest Portuguese coast. A smaller stretch AB (2.4km long), included in the total one, which exhibits a pronounced erosive tendency usually better reproduced in shoreline evolution models, was also analysed. Based on topographic surveys, associated wave climate conditions registered between 2003 and 2008 and typical wave conditions registered over a longer wave climate time period, this work compares the calibration of two different shoreline evolution models, Long-term Configuration (LTC) and GENESIS for this period. Then, considering the 2003 topographic conditions for the models' calibration, the results of both models are discussed with respect to simulation scenarios after 10, 15 and 20years of evolution. The 10-year evolution projections of the models are also compared to the results of a survey performed in February 2012. For the wave data calibration period (2003–2008), the average shoreline retreat of the analysed coastal stretch was reproduced with small differences (around 1% and 10% for LTC and 15% and 14% for GENESIS, considering stretches AB or AC, respectively), though local differences along the AB coastal stretch represent root mean square errors reaching up to 52% and 88% for GENESIS and LTC, respectively, and were above 118% for both models along the AC coastal stretch.

Hurricane, Habitat Degradation, and Land Loss Effects on Brown Pelican Nesting Colonies

Walter, S.T.; Carloss, M.R.; Hess, T.J., and Leberg, P.L., 2013. Hurricane, habitat degradation, and land loss effects on Brown Pelican nesting colonies.Nesting colonies of coastal avifauna are perennially threatened by hurricanes, land loss, and environmental contamination. To understand how nest substrate and habitat availability influence reproductive success of Brown Pelicans (Pelecanus occidentalis), we monitored 802 nests and quantified vegetation cover on two barrier islands in Louisiana from 2008 to 2010. In 2008, Hurricanes Gustav and Ike caused habitat degradation and land loss at our study sites and thus allowed comparison of pelican productivity in pre- and post-hurricane conditions. As habitat availability changed across years and islands, pelicans shifted from nesting in woody vegetation, to grasses, forbs, and bare ground. More chicks that survived until the age of 3 to 4.5 weeks old were from higher nests, and the loss of woody vegetation might have elicited colony abandonment. Habitat reduction was attributed to hurricane-induced erosion, and shoreline retreat was an average 5.5 times (range 3.3 to 11) greater than regional rates from 1887 to 2002. Furthermore, land loss (16% to 99% of vegetated regions) was restricted to areas without protective breakwaters. In addition to the effects of habitat decline on pelican reproduction, contamination by the Deepwater Horizon oil spill might have further decreased nest success. Large and productive seabird colonies can be rapidly degraded by both human and natural disturbance, making amelioration of such threats a management priority.

Assessing sea level rise costs and adaptation benefits under uncertainty in Greece

Although sea-level rise (SLR) is not the only driver of coastal change, it is expected to radically alter the living conditions and prosperity of coastal communities in the decades to come. The economic assessment of sea level rise impacts and of coastal adaptation measures proves to be rather demanding due to the fact that these are complex phenomena, affected by both global conditions and local parameters. All these factors add to the uncertainty involved in climate change assessments, in general, and in SLR impacts in particular, creating significant ambiguity during the policy-making process. This paper wishes to contribute to existing literature by exploring modern management tools for assessing the economic impacts of SLR and the effectiveness of proactive coastal adaptation under uncertain conditions. To this end, first, the economic damages from long-term shoreline retreat and land inundation for scenarios of 0.5-m and 1-m SLR up to 2100 are estimated for the Greek coastal zone, both deterministically and probabilistically. The results indicate that probabilistic damages are lower than the deterministic ones by 6%, on average. However, the uncertainty results in a range of probable values, which are 45% lower and up to 40% higher than the deterministic estimates. Second, and most important, the application of real options valuation (ROV) in the economic assessment of adaptation measures is illustrated using four specific case sites. The findings show that ROV provides decision-makers with the flexibility to ‘adjust’ the so-called hard engineering structures to future SLR conditions by keeping all options (i.e. scale, deferral, acceleration or abandonment) open till further knowledge is gained. In this way, ROV creates an additional value that cannot be captured by ‘conventional’ valuation methods and, thus, it offers the potential to maximize long-term benefits for the society by making efficient use of fiscal resources for adaptation strategies.

실용적 해안선 후퇴 반영 알고리즘

일반적 형태의 해안영역에서의 퇴적물이동, 퇴적 및 지형변화를 예측하는 수치모형에서 전빈의 침식으로 인한 해안선 후퇴가 가능한 알고리즘을 제시한다. 평균해수면 기준의 해안선 인근 영역에서는 저면 경사가 저면 퇴적물의 종류, 조석과 조류, 파랑, 연안류 등 외력의 영향을 받는다. 그러나, 해안선에서의 저면경사는 어느 정도 안정된 범위내의 값을 가지는 것으로 보고된 바 있으며, 연중 변화 또한 거의 일정 범위 내에 있는 것으로 알려져 있다. 이러한 경사의 변동 한계값을 이용하여, 해중 침식이 지속되어 해안선에서의 저면 경사가 계속 증가하는 경우, 이러한 한계 경사를 넘게 되면, 이를 조정하기 위한 방법으로서 저면경사가 한계값 내로 돌아오도록 해안선 인근에서의 저면 형상을 조정하도록 하였다. 이렇게 함으로써 침식이 지속되는 경우 해안선이 지속적으로 후방으로 후퇴하는 현상을 수치모형에서 재현할 수 있게 된다. 개발한 알고리즘을 우물함수형의 침식 상황, 즉 한 점에서 일정 플럭스로 준설을 지속할때 주변 지형이 우물함수 분포 형상으로 침식되어 가는 과정을 잘 재현하였다. 발달하는 해안선의 형태가 거의 원형의 동심원으로 나타나므로 알고리즘의 유용함을 확인하였다. 또 개발한 알고리즘을 침식지역이 일정속도로 하강하는 가상상황에 적용하여 보았으며, 동심원적 지형 변화를 잘 재현하였다. 본 알고리즘을 기존의 수치모형 CST3D 시스템에 채택하여, 등경사 평판형 해안에 이안제가 놓여 있을 경우에 대한 지형변화 수리모형실험의 조건과 동일한 조건을 대상으로 모형실험을 수행한 결과, 해안선의 변화를 정성적으로 만족스럽게 재현하였다. An algorithm to allow shoreline movement during numerical experiment on sediment transport, deposition or resuspension for general coastal morphology is proposed here. The bed slope near shoreline, i.e. mean sea level, is influenced by bed material, tidal current, waves, and wave-induced current, but has been reported to remain within a stable range. Its annual variation is not large, either. The algorithm is adjusting the bathymetry, if the largest bed slope within shoreline band exceeds a given bed slope due to continuous erosion at zones below the shoreline. This algorithm automatically describes retreat of shoreline caused by erosion, when used within a numerical system. The algorithm was tested to a situation which includes a continuous dredging at a point, and showed satisfactory development of concentric circle contours. Next, the algorithm was tested to another situation which includes sinking of eroded part of bed plate, and produced satisfactory results, too. Finally, the algorithm was tested to a movable-bed laboratory experimental conditions. The shoreline movement behind detached breakwater was reasonably reproduced with this algorithm.

Effects of shoreline erosion on salt-marsh floral zonation

The loss of salt-marsh habitat is proceeding at an alarming rate worldwide, resulting in the loss of ecosystem function and reduced exchange with adjacent habitats. The immediate result of shoreline erosion is the loss of fringing vegetation, but it is unclear how, and at what temporal scale, intertidal floral zones respond to shoreline loss. Using a transect-based approach over a 3 yr period, we compared community composition among 3 intertidal salt marshes in coastal Alabama that differ in the intensity of wave-generated disturbance. Each study marsh exhibited net annual rates of shoreline retreat, but differed in its exposure to wave-induced disturbance and erosional state. We also examined whether wave attenuation by oyster break waters reduced annual rates of shoreline erosion, providing a means to test whether the intensity of shoreline erosion affects inter-annual patterns of marsh zonation. Community composition differed across sites, but not between breakwater treatments and site-specific rates of shoreline loss, suggesting that differences in community composition are not due to differences in erosion intensity, but to other contrasts across sites. The cohesive nature of the floral communities at each site suggests that marshes maintain their zonation structure by migrating inland as the shoreline recedes. The inland migration of marsh zones will, however, ultimately be limited by the lack of area available for marsh colonization. The preservation of coastal salt marshes is, therefore, vitally contingent on effective shoreline management strategies.

Coastal landforms and environments in the central sector of Gallocanta saline lake (Iberian Range, Spain)

Gallocanta Lake (NE Spain), with a high ecological value, is the largest and best preserved saline lake in Western Europe. The aim of this study is to map the landforms developed in the margins of the central sector of Gallocanta Lake, at adequate scale for the study of soils and habitats, which is needed for the delineation, management and protection of the wetland. Photointerpretation was combined with topographical, geological, and satellite data in a geographical information system. This study, applied in two selected areas of the central body of the lake, allowed the identification of contrasting landforms and processes in the lake margins. The southern margin, which receives most of the fluvial materials in the zone exhibits coastal progradation by means of barrier-island generation and sedimentation in the resulting coastal lagoon, a process that can be inferred from the map presented in this work and was confirmed by comparison of aerial photographs taken in different decades. With virtually no sediment supply on the margin, coastal erosion and shoreline retreat prevail. In summary, coastal landforms are a result of a complex combination of fluvial and lacustrine processes operating during high and low water-level periods.