Shoreline Retreat Research Articles

Combination of Aerial, Satellite, and UAV Photogrammetry for Mapping the Diachronic Coastline Evolution: The Case of Lefkada Island

Coastline evolution is a proxy of coastal erosion, defined as the wasting of land along the shoreline due to a combination of natural and/or human causes. For countries with a sea border, where a significant proportion of the population lives in coastal areas, shoreline retreat has become a very serious global problem. Remote sensing data and photogrammetry have been used in coastal erosion mapping for many decades. In the current study, multi-date analogue aerial photos, digital aerial photos, and declassified satellite imagery provided by the U.S. Geological Survey (USGS), Pleiades satellite data, and unmanned aerial vehicle images were combined for accurate mapping of the southwestern Lefkada (Ionian Sea, Greece) coastline over the last 73 years. Different photogrammetric techniques were used for the orthorectifation of the remote sensing data, and geographical information systems were used in order to calculate the rates of shoreline change. The results indicated that the southwest shoreline of Lefkada Island is under dynamic equilibrium. This equilibrium is strongly controlled by geological parameters, such as subsidence of the studied shoreline during co-seismic deformation and mass wasting. The maximum accretion rate was calculated at 0.55 m per year, while the respective erosion rate reached −1.53 m per year.

Climate Change and Man-made Interventions, as Destabilizing Factors of the Coastal Zone: Some Examples of Coasts and Coastal Wetlands in Urban, Peri-Urban Areas and Natural Parks in Greece

The consequences of man-made interventions, Climate Change and future Sea-level rise upon some coastal plains of Greece are examined. Many urban, peri-urban areas and Natural Parks, in low elevation coastal zones in Greece are experiencing or are at risk of Sea-level rise, storm surges, water and soil pollution, saline water intrusion (salinity), coastal erosion and shoreline retreat, floods, and droughts. Sea-level rise could erode and inundate coastal ecosystems and disrupt wetlands, Urban and peri-Urban areas. Characteristic examples of these are the protected wetlands that exist in Greece such as those in the Delta and the river mouth areas of the Sperchios, Alfeios, Arachthos, Louros, and Inois rivers, and the small town of Tolo. Man-made interventions affect the coastal wetland ecosystems, Urban and peri-Urban areas under study. At the same time, an important factor of the destabilization of the ecological balance is the Climate Change and the expected sea-level rise. The main anthropogenic degradation and stresses on the under investigation areas, in recent decades, includes wetland draining, exsiccation of lagoons and lakes, river engineering works, dam construction, intensification and development of agriculture projects, sand mining from riverbeds and beaches, construction of motorways, construction of harbor structures, such as harbors, jetties, seawalls, groins, and breakwaters, rapid urbanization processes, holiday home building and tourist facilities, massive tourism and intense coastal development, water pollution, human-induced land subsidence (uncontrolled water abstraction from surface and underground water tables), and removal of coastal vegetation. Satellite images, maps and systematic in situ observations, integrated with the direct digitizing on the basis of different aged aerial photographs was adopted to estimate the coastal erosion and accretion rates in recent decades (1945-2019) in the areas, under study.

Major shoreline retreat and sediment starvation following Snowball Earth

AbstractWhile cap dolostones are integral to the Snowball Earth hypothesis, the current depositional model does not account for multiple geological observations. Here we propose a model that rationalises palaeomagnetic, sequence‐stratigraphic and sedimentological data and supports rapid deglaciation with protracted cap dolostone precipitation. The Snowball Earth hypothesis posits that a runaway ice‐albedo can explain the climate paradox of Neoproterozoic glacial deposits occurring at low palaeolatitudes. This scenario invokes volcanic degassing to increase atmospheric greenhouse gases to a critical threshold that overcomes the albedo effect and brings the planet back from the ice‐covered state. Once this occurs, Earth should shift rapidly from a snowball to an extreme greenhouse. However, cap dolostone units overlying glacial sediments, typically interpreted as transgressive deposits, exhibit multiple magnetic reversals indicating they accumulated in >105 years. By reviewing modern post‐glacial systems, sequence stratigraphic concepts and principles of sedimentology, we suggest that cap dolostones are not restricted to the transgression but rather represent sediment starvation following a major landward shoreline migration associated with the demise of Snowball Earth. Thus, the duration in which cap dolostone accumulated is not directly coupled to the timescale of the Snowball Earth deglaciation.

Modeling the dynamics of a sand beach governed by the wave and underwater bar interaction

Effect of bar position on underwater profile of sandy beach was studied at the timescale of one storm using the xBeach numerical model. Beach profiles were extracted from the bathymetry of the Shkorpilovtsy beach (the Bulgarian coast of the Black Sea). Computed results were verified by field measurements. The largest shoreline retreat occurred in the first hour of a storm. For the chosen wave regime (largest wave height 1.5 m, wave period 10.5 s), an equilibrium profile was formed after 6 hours. The resulting profile contained an underwater terrace with the slope close to that of the theoretical equilibrium profile. It was shown that the position of the underwater bar affects the shoreline retreat rate. The smallest and the largest shore retreat occur if bar crest is located at a distance about 0.7–0.8 and 0.5 of the deep water wavelength, correspondingly. It was found that the shoreline retreat depends on the height of infragravity waves and mean wave period: the smaller mean wave period and the higher infragravity waves near the coast, the smaller is the retreat of the coastal line. Distance of seaward sediment transfer is directly relates to the height of large waves near the shore.

Photogrammetric assessment of shoreline retreat in North Africa: Anthropogenic and natural drivers

Shoreline retreat along extended semi-arid areas of North African coasts are indicative of the imbalance of coastal sedimentary processes due to modern abrupt changes in precipitation patterns and urban growth. Monitoring of the diachronic shoreline position and land-use from 1952 to 2018 in the coast of the Hammamet Bay in central-east Tunisia, using both aerial and orbital photogrammetric scenes and the Digital Shoreline Analysis System from 1887 to 2018, suggests shoreline retreat rates ranging from −1.3 to −5.6 m/yr. Such rates are abnormal when compared to the average of −0.07 m/yr suggested by global-scale assessment modeling for sandy beach evolution. These abnormal erosions extend over 65 km of sandy beaches, resulting from a severe deficit of sediment transport caused primarily by rapid coastal urban growth that obstructs sediment flow to the shoreline. We suggest that the high retreat rates observed in the low-population period of 1884–1931 originated mainly from storm surges and tsunamis, or potentially subsidence in the coastal substratum. Moreover, our analysis of the salinity of shallow coastal aquifers and land coverage suggests that shoreline retreat coupled with rapid urban growth accelerated seawater intrusion ~5 km inland, causing soil desiccation, the development of salt lakes, and reduction of vegetation coverage by ~18%. These abrupt environmental changes have a severe, adverse impact on crop production and food security in these densely populated and economically important areas across significant parts of the North African coasts, sharing similar key environmental parameters with our study site. We conclude that anthropogenic drivers are the major source of shoreline retreat rather than natural ones.

The spatiotemporal shoreline dynamics of a delta under natural and anthropogenic conditions from 1950 to 2018: A dramatic case from the Eastern Mediterranean

The construction of dams on rivers feeding deltas has caused rapid shoreline retreat of many deltas around the world. To show that the retreat has been due to anthropogenic effects, it is very important to observe the natural shoreline changes before the dams effects on a delta. This study investigated shoreline changes in the Seyhan Delta in the Eastern Mediterranean from 1950 to 2018 employing long-term Landsat satellite images and aerial photographs. The results indicated that the shoreline accreted nearly +131 m with a maximum rate of +22.9 m yr−1 from 1950 to 1956. In this period an area of +322 071 m2 was added to the delta. Contrary to this, following the construction of the Seyhan Dam in 1956, the Seyhan Delta lost a total area of -4 039 251 m2 from 1956 to 2018. The shoreline retreated −2293 m at the river mouth, with a maximum rate of retreat of −37 m yr−1. The major cause of this retreat is the trapping behind the Seyhan Dam of sediments transported by the Seyhan River. In the future, it is expected that the shoreline will retreat even more rapidly from causes such as the construction of further planned dams, deltaic subsidence and rising of global sea level. This situation will have a great impact upon wetland areas and upon agricultural and tourism areas and structures in the delta.

Shoreline evolution in an embayed beach adjacent to tidal inlet: The impact of anthropogenic activities

Embayed beaches are widely distributed around the world. Their shoreline evolution is controlled primarily by the upstream headland and prevailing wave conditions. Tidal inlets are also ubiquitous in sandy coasts. They are quite dynamic and act as a sediment source or sink, depending on the sediment transport pattern and budget. An embayed beach may develop downstream of a tidal inlet if a protruding headland is formed at the inlet, owing to either natural processes or human construction. In this study, Gaolong Bay, located downstream of a tidal inlet (Qinglan Inlet) in Wenchang City, Hainan Island, China, is used as an example to examine the effects of an upstream tidal inlet on the evolution of an embayed beach. Emphasis is placed on the impact of anthropogenic activities, such as landfilling and jetty construction. Historical remote sensing data were collected, and the evolution of the shoreline from 1998 to 2018 was analyzed. The shoreline change pattern in Gaolong Bay was identified with the empirical orthogonal function (EOF) method, and the mechanisms behind these changes were explored with a coupled current–wave–sediment transport modeling system. Our results indicate that the construction of an artificial peninsula and a jetty beside the inlet channel dramatically changed the evolution of the Gaolong Bay shoreline. Defying the classical expectation of shoreline retreat downdrift of a tidal inlet, a clockwise shoreline rotation was prevalent in Gaolong Bay, with the shadow zone accreting and the distal zone retreating, along with an overall shoreline propagation (translation). The static equilibrium shoreline planform model (model of equilibrium of bay beaches [MEPBAY]) was further used to predict the future evolution of the shoreline. This study demonstrates that an embayed beach downdrift of a tidal inlet can exhibit a complex response to human interventions at the inlet and highlights the necessity of considering adjacent shoreline changes when assessing the impact of inlet stabilization.

Impact assessment of sea level rise over coastal landforms: a case study of Cuddalore coast, south-east coast of India

Densely populated south-east coast of India is susceptible to disasters such as tsunami, coastal flooding storm-surge and shoreline erosion. Apart from episodic events, the gradual sea-level rise (SLR) has got more attention to coastal researchers recently relating to the potentially impacted coastal zone, its anthropogenic/environment associations, and the possible future scenarios. Global average SLR rate has increased in recent decades from 1.7 mm year−1 1901 to 2010, 3.1 mm year−1 from 1993 to 2003 and 3.12 mm year−1 from 1993 to 2012. The present study is an aim to assess the impact of future sea-level rise along Pondicherry—Chidambaram coast using Bruun Rule and Modified Bruun Rule. Eight satellite-derived data sets were used to study the shoreline change trends during 1990–2015. 25 years of shoreline change trend reveals that ~ 49% of the coastline is under erosion. Shoreline retreat to an increase in local sea level was also mapped by Bruun Rule. Bruun Rule has some limitations, and hence Modified Bruun Rule was used to analyze the inundation factor. The horizontal inundation of the study area was estimated as ~ 1.1 km (Bruun Rule) and ~ 1.6 km (Modified Bruun Rule). The impacts of SLR in the study area were determined by integrating inundation data with geomorphological and land use/land cover data. The study reveals that about 16.08 sq.km area of geomorphological features is likely to be highly affected, while 17.5 sq.km of the area likely to be affected on land use/land cover features. This study provides an interactive means to identify the vulnerable zone. The output maps can be used to visualize the affected areas spatially.

Current and future mudflat losses in the southern Huanghe Delta due to coastal hard structures and shoreline retreat

Coastal wetlands, especially broad mudflats, are facing an unprecedented crisis due to combined influence of intensified coastal development activities, drastic river sediment reduction and rapid relative sea level rise. However, it is still a huge challenge to accurately assess the evolution of mudflats for the lack of reliable shoreline indicators on satellite images, especially the indicators for shoreline at low tide. This study, based on instantaneous shoreline positions derived from 430 Landsat satellite images during 1983–2019, uses sea level correction and statistical analysis methods to study the evolution of Laizhou Mudflat, and the intertidal mudflat loss in Laizhou Mudflat was accurately assessed and the effects of multiple factors, especially the effects of various coastal hard structures, on the evolution of Laizhou Mudflat were quantitatively estimated for the first time. The results show that the intertidal mudflat loss caused by the construction of cofferdams was 98 km2, 93% of the total intertidal mudflat loss. Although the previous intertidal mudflat loss caused by shore-parallel structures was less, the shore-parallel structures will cause great mudflat loss in the future, and the broad Laizhou Mudflat will disappear in 110 years owing to the barrier effect of the widespread shore-parallel structures if the current rapid shoreline retreat is not improved. The construction of shore-normal structures can slow the shoreline retreat of adjacent mudflat but accelerate downstream shoreline retreat. As far as coastal protection is concerned, the construction of shore-normal structures in Laizhou Mudflat is inadvisable. Diverting 13 M ton/year of Huanghe sediment can totally offset the mudflat loss on the upstream of Dongying Pier, however, the mudflat located on the downstream of Dongying Pier is hard to restore owing to the block effect of the shore-normal structures to the alongshore transported sediment. Another option is demolishing the shore-parallel structures to recover the landward movement of shoreline, avoiding the mudflat loss at the expense of land loss.

Systems tracts and their bounding surfaces in the low- accommodation Upper Mannville group, Saskatchewan, Canada

Abstract Sequence stratigraphic interpretations of paralic successions can be challenging, because such settings are commonly controlled by a combination of allogenic controls and autogenic processes, leading to complex depositional architectures. In low-accommodation systems where parasequences are less than 15 m thick, the challenges in recognizing discrete stratigraphic surfaces are exacerbated by limited vertical separation between surfaces or their outright erosional amalgamation, requiring high-resolution facies analysis to resolve their geometries. Herein, we present criteria derived from core data and well logs to differentiate between allogenic and autogenic surfaces in a low-accommodation paralic setting, using the Lower Cretaceous Mannville Group of west-central Saskatchewan, Canada as a case study. The upper part of the Mannville Group (Sparky, Waseca and McLaren formations) displays complex stratigraphic relationships related to base-level changes. Marine flooding surfaces (MFS) and transgressive surfaces of erosion (TSE) of 3rd and 4th order record allogenic changes ( e.g., basin subsidence and/or eustatic changes in sea level), and are used to define parasequence boundaries of strandplain-shoreface successions. Deltaic deposits not only possess these allogenic transgressive surfaces, but autogenic 5th-order flooding surfaces, which are broadly similar in appearance, as well. These autogenic surfaces record responses to channel avulsion or lobe abandonment, separate discrete delta lobes, and display limited lateral extents. Shoreface-related flooding surfaces, by contrast, bound true allogenic parasequences and, therefore, have regional correlatability. The Waseca Formation also possesses surfaces related to base-level fall. To the north, a subtle regressive surface of marine erosion (RSME) marks the base of the falling stage systems tract. Elsewhere, a widespread subaerial unconformity (SU) separates the Waseca into lower and upper members. In most areas, the SU is amalgamated with surfaces generated by later base-level rise. Upper Mannville strata in the study area, therefore, can be separated into parts of two depositional sequences. The main deposits of the lower sequence comprise a highstand systems tracts (HST) in the Sparky Formation. The base of the Lower Waseca Member marks the onset of a transgressive systems tract (TST), associated with widespread shoreline retreat. A 3rd-order maximum flooding surface (MxFS) marks the end of transgression and resumption of normal progradational regression in a highstand systems tract associated with the Lower Waseca Member. Following highstand normal regression, a major base-level fall initiated a subaerial unconformity that marks the base of the upper sequence. Fluvial valley incision led to sediment bypass and deposition of forced regressive and lowstand shoreface and delta complexes of the falling stage systems tract (FSST) and lowstand systems tract (LST), respectively, in the northern part of the study area. Pedogenic modification of subaerially exposed sediment occurred in interfluve areas. Ensuing TST accumulation was initially confined to the tidal-fluvial estuarine infill of the incised valleys and transgressive bay deposits of the Upper Waseca Member. The Upper Waseca is capped by a 3rd-order maximum flooding surface (MxFS), which separates it from the overlying McLaren Formation. This marks the return to regional shoreline progradational regression and corresponds to the highstand systems tract (HST) of the upper sequence.

Bimodal climate control of shoreline change influenced by Interdecadal Pacific Oscillation variability along the Cooloola Sand Mass, Queensland, Australia

Wave climate in southeast Queensland, Australia has been correlated to changes in the Southern Oscillation Index (SOI), but observations of shoreline change associated with the variable wave climate have been limited due to a paucity of aerial photography, LiDAR, and other beach profiling datasets in this region. A multi-decadal, sub-annual temporal resolution shoreline dataset spanning 1996 to 2017 was produced using satellite imagery collected by Landsat 5, 7, and 8. A total of 147 shoreline positions were delineated using the Modified Normalized Difference Water Index on cloud-free imagery and corrected for horizontal offsets forced by variable tide stages at the satellite flyover time. The relative influence of SOI, the Southern Annular Mode (SAM), Pacific Decadal Oscillation (PDO), and Subtropical Ridge Latitude (STR-L) and Pressure (STR-P) on shoreline dynamics along the Cooloola Sand Mass in Queensland are assessed by performing cross correlations between their respective index values and shoreline change distances calculated by the Digital Shoreline Analysis System. A bimodal climate control of shoreline change is observed dependent upon the phase of the Interdecadal Pacific Oscillation (IPO). IPO modulates the impacts of ENSO on eastern Australia through its control over the position of the South Pacific Convergence Zone and elevating/lowering of tropical Pacific sea surface temperatures. During negative IPO, SOI is negatively correlated to the Cooloola Sand Mass shoreline indicating that the shoreline retreats during negative SOI phases. During positive IPO, the impacts of SOI are weakened and the STR becomes the primary driver of shoreline change with shoreline response being contingent upon its orientation. The SW-NE aligned Noosa North shoreline erodes in response to poleward movement of the STR, likely due to the enhanced cross-shore wave attack as a result of anti-clockwise wave rotation. The opposite response is shown at the SE-NW aligned Rainbow Beach shoreline, which is oriented almost parallel to the incident wave direction and is sheltered by the Double Island Point headland. These results suggest that climate control on shoreline change at Cooloola Sand Mass, and likely other sand islands in the region, is two-tiered, whereby interdecadal variability of the IPO governs the relative influence of SOI and STR under the different IPO phases. The linked climate and shoreline variability correlation shown in this study provides significant insight into how the Cooloola Sand Mass shoreline will respond to future climate changes under a global warming scenario.

The formation and closure of the Big Breach of Sacalin spit associated with extreme shoreline retreat and shoreface erosion

AbstractWe document a case of exceptionally large natural breaching of a sandy spit (Sacalin spit, Danube Delta) using multiannual to seasonal surveys of topography and bathymetry on successive cross‐barrier and shoreface profiles, LiDAR data, satellite imagery, and wind and wave data.The large breach, which quickly reached 3.4 km in May 2014, is attributed to morphological preconditioning of the narrow (50–150 m) barrier, which was susceptible to breaching even during moderate storm conditions. The event switched the barrier's decadal evolution from low cross‐shore transport to high cross‐shore transport over the barrier, which is an order of magnitude larger than during the non‐breach period. Upper shoreface erosion, as indicated by the extensive erosion down to −4 m, indicates that this zone is a significant source for the rebuilding of the barrier. Barrier recovery and widening trigger a negative feedback which limits the back‐barrier sediment transfer. As a result, back‐barrier deposition decreases whilst the barrier aggradation through overwash becomes more frequent.The Big Breach (TBB) closed naturally in three years. The very high deposition rate of sediment in the breach is a testimony of the high sediment volumes supplied by the longshore transport and the high sediment released through shoreface retreat, and resulted in widening the barrier to a maximum of 1 km. Since the newly‐formed barrier shoreline retreated 500 m, this reveals that barrier breaching is an important mechanism which significantly accelerates the landward migration of the barrier system and is a proof of the highly non‐linear morphodynamics involved in the barrier island translation. © 2019 John Wiley & Sons, Ltd.

Analysis of the Mamaia Bay shoreline Retreat with Hard and Soft Protection Works

Integrated Coastal Zone Management is a complex concept that involves various economic, social and environmental factors. There are often conflicting approaches to these factors. Furthermore, when it is decided to implement structural works in the coastal area, it must be taken into account the particularity of the area, the way in which it is developed and the type of work to be done. The Gulf of Mamaia in the Romanian Black Sea coast is the target of structural changes through the implementation of an extensive coastal rehabilitation program. The works made are of “hard” type and aim to change the shore line configuration. From this perspective, the target of the present paper is to make an analysis between the type of work that is being carried out and another kind of "soft" work aiming especially to favor the ecological reconstruction of the area and the approach of an environmentally friendly concept. Thus, we propose to analyze the two types of works with a view to apply the Bruun rule in order to mitigate the effect of the increase of the sea level and to prevent the shoreline retreat.

Analysis of the Mamaia Bay shoreline Retreat with Hard and Soft Protection Works

Integrated Coastal Zone Management is a complex concept that involves various economic, social and environmental factors. There are often conflicting approaches to these factors. Furthermore, when it is decided to implement structural works in the coastal area, it must be taken into account the particularity of the area, the way in which it is developed and the type of work to be done. The Gulf of Mamaia in the Romanian Black Sea coast is the target of structural changes through the implementation of an extensive coastal rehabilitation program. The works made are of “hard” type and aim to change the shore line configuration. From this perspective, the target of the present paper is to make an analysis between the type of work that is being carried out and another kind of "soft" work aiming especially to favor the ecological reconstruction of the area and the approach of an environmentally friendly concept. Thus, we propose to analyze the two types of works with a view to apply the Bruun rule in order to mitigate the effect of the increase of the sea level and to prevent the shoreline retreat.

Implications for Provenance since the Last Glaciations in Southeastern Andaman Sea Sediments by Clay Mineralogy

This study presents high-resolution clay mineralogy of Core MASS-III-10, located in the southeastern Andaman Sea. The study aimed to investigate terrigenous sedimentary input from various potential provenances throughout different periods of geological time. The clay mineral assemblages of MASS-III-10 reveal a high amount of smectite at 73% (65-79%), a moderate kaolinite at 12% (10-17%), and a low illite and chlorite content(<15%) over the last 45 ka. Provenance analysis suggests the most fine-grained terrigenous sediments originated from the Irrawaddy Delta Shelf (IDS), with minor sediments deriving from the Andaman Islands, the East Continental Shelf (ECS), and Sumatra provenance. The results show that IDS were predominantly smectite (~44%) while the ECS largely produced kaolinite (47%). The provenance interpretation based on the smectite content revealed that over time there has been no change in the main source of sediment in the Andaman Sea, despite changes in the volume of sedimentary input. Since the last glaciation, the Myanmar provenance (including IDS) has always contributed clay minerals, while other sources made up only minor contributions to the Andaman Sea. The clay minerals from the Myanmar provenance increased when the sea level was at a low stand (MIS 2), potentially due to shoreline retreat which enabled easier transportation of sediment from other sources. During the interglacial period (MIS 1 and 3), the study found a decrease in Myanmar-sourced clay minerals, which may be because the higher sea level made clay mineral deposition more difficult.

Geomorphic response of inlet barrier islands to storms

Inlet Barrier Islands (IBIs) are infrequently studied, and are often poorly represented in coastal lidar records. The fetch limited barrier island (FLBI) model was introduced to describe geomorphic changes of IBIs over time. The FLBI model predicts that the morphology of IBIs should remain largely static during predominate weather conditions due to sheltering from oceanic wave energy but undergo significant erosion when local and non-local waves magnify during storms, subsequently failing to recover volume and elevation losses. Using three years of high-frequency small unoccupied aircraft systems (sUAS, aka drone) surveys and existing lidar records, we document geomorphic changes on Bird Shoal (a protective IBI near the town of Beaufort, NC) resulting from storms and predominate conditions, testing the FLBI model and documenting island evolution. Our results indicate that Bird Shoal exhibits different spatial trends in erosion, accretion, and shoreline migration across its 4 km length, likely driven by varying shoreline orientation to the Beaufort Inlet and back barrier bathymetry in Back Sound. Our data indicate that the geomorphic behavior of Bird Shoal currently does not adhere to the classic FLBI model. Foreshore storm recovery and growth on Western Bird Shoal and shoreline retreat on Central Bird Shoal occurred during predominate conditions, and beach morphology was not an artifact of past storm events. The Western Bird Shoal shoreline consistently retreated landward in decades of historic imagery, but transitioned to seaward expansion sometime between 2011 and 2014. This shift is likely driven by erosion of the western end of Shackleford Banks and concurrent widening of the Beaufort Inlet, allowing increased wave energy to enter the back-barrier sound and push flood deltas onto Bird Shoal during predominate conditions. Our results suggest that open ocean inlet width and location interact with back-barrier deltas to control sediment supply and wave energy for IBIs, and that IBIs may fall into and out of conformance with the FLBI archetype over time. This study demonstrates sUAS deploying frequently over a municipal scale to fill spatial and temporal gaps in traditional coastal remote sensing datasets.

Sub-annual to multi-decadal shoreline variability from publicly available satellite imagery

The ability to repeatedly observe and quantify the changing position of the shoreline is key to present-day coastal management and future coastal planning. This study evaluates the capability of satellite remote sensing to resolve at differing temporal scales the variability and trends in shoreline position along sandy coastlines. Shorelines are extracted from 30 + years of publicly available satellite imagery and compared to long-term in-situ measurements at 5 diverse test sites in Europe, Australia, the USA and New Zealand. These sites span a range of different beach characteristics including wave energy and tide range as well as timescales of observed shoreline variability, from strongly seasonal (e.g., Truc Vert, France), to storm-dominated (e.g., Narrabeen-Collaroy, Australia), to only minor annual to multi-annual signals (e.g., Duck, USA). For the 5 sites, the observed typical horizontal errors varied between a root-mean-squared error (RMSE) of 7.3 m and 12.7 m. An analysis of the typical magnitudes of shoreline variability at temporal scales ranging from a single month up to 10 years indicates that, by the implementation of targeted image pre-processing then the application of a robust sub-pixel shoreline extraction technique, the resulting satellite-derived shorelines are generally able to resolve (signal-to-noise ratio > 1) the observed shoreline variance at timescales of 6 months and longer. The only exception to this is along coastlines where minimal annual to multi-annual shoreline variability occurs (e.g. Duck, USA); at these sites decadal-scale variations are successfully captured. The results of this analysis demonstrate that satellite-derived shorelines spanning the past 30 years as well as into the future can be used to explore and quantify intra- and inter-annual shoreline behaviour at a wide range of beaches around the world. Moreover, it is demonstrated that present-day satellite observations are also capable of capturing event-scale shoreline changes (e.g. individual storms) that occur at timescales shorter than 6 months, where this rapid response exceeds the typical magnitude of shoreline variability. Finally, several practical coastal engineering applications are presented, demonstrating the use of freely-available satellite imagery to monitor inter-annual embayed beach rotation, rapid storm-induced shoreline retreat and a major sand nourishment.

Legacy effects of Hurricane Katrina influenced marsh shoreline erosion following the Deepwater Horizon oil spill

Disturbance interactions occur when one perturbation influences the severity and perhaps the baseline state of succeeding disturbances. Natural and anthropogenic disturbances are frequent in dynamic coastal ecosystems and can often be linked. We evaluated potential for disturbance interactions associated with the 2010 Deepwater Horizon (DWH) oil spill, which was preceded by disturbance from Hurricane Katrina in 2005, by quantifying marsh shoreline retreat across both events. Our goal was to determine the degree to which Hurricane Katrina altered baseline rates of erosion prior to the DWH spill. We quantified erosion rate and fetch from aerial images of northern Barataria Bay, Louisiana marsh shorelines classified as reference, moderately-oiled, and heavily-oiled over three pre-spill time periods (1998–2004, prior to Hurricane Katrina; 2004–2005, during Katrina; 2005–2010, post-Katrina but pre-oil spill) and a post-spill period from 2010 to 2013. Prior to Hurricane Katrina, marsh shoreline erosion rates were low (from 0.38 to 1.10 m yr−1). In contrast during Hurricane Katrina (2004–2005), erosion increased by 661% and 756%, respectively, for shorelines that would subsequently become moderately and heavily-oiled; reference shoreline erosion increased by 59%. These high erosion rates were associated with increased fetch and higher wave action due to loss of protective geomorphic features such as small islands and spits and persisted during the post-Katrina/pre-spill period of 2005–2010 (0.62, 1.38, and 2.07 m yr−1 for reference, moderately, and heavily-oiled shorelines, respectively). Erosion rates increased modestly after the DWH event (reference = 1.13 m yr−1, moderate oiling = 1.45 m yr−1; heavy oiling = 2.77 m yr−1), but not significantly, compared to the post-Katrina period. Consequently, we could not detect a post-spill increase in marsh shoreline erosion. Rather, we concluded that Hurricane Katrina reset the erosion baseline, thereby connecting the two disturbances, and was the major driver of marsh shoreline erosion at our research sites during the study period.

Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles

Based on an approach coupling geomatics (i.e. satellite imagery analysis) and fieldwork, this paper provides an in-depth analysis of the impacts of September 2017 hurricanes on the beaches of Saint-Barthélemy Island. First, it highlights the key role of low-frequency high-intensity events in driving high rates of changes on coastal systems. Importantly, all the studied beaches underwent shoreline retreat, detected along 47.73–100.00% of transects (mean shoreline movement ranging from −2.76 to −18.39 m). The stability line retreat was lower on highly-modified beaches because of the presence of longitudinal structures compared to natural beaches that mostly suffered severe vegetation destruction. Second, the methodology proposed here allowed attributing changes to specific anthropogenic drivers. Both natural (i.e. the hurricane's path and hurricane waves' direction) and anthropogenic (especially shoreline hardening and vegetation modification) drivers explain the high variability observed in the nature, intensity and spatial distribution of hurricanes' impacts on beaches. Based on the quantitative assessment of impacts, this paper advocates for the restoration of a 50 m-wide buffering area in front of human constructions, the exposure of which has considerably increased due to wave impact, which implies to establish new setback guidelines. So as to better assist decision-makers in disaster risk reduction on small islands, we therefore recommend the systematic inclusion, i.e. documentation and integration into GIS datasets, of human disturbances, as the latter highly influence shoreline and beach response. We propose a replicable methodology to address this challenge.

Progradation and retrogradation of the Medjerda delta during the 20th century (Tunisia, western Mediterranean)

The aim of this study is the reconstitution of the recent morpho-sedimentary evolution of the Medjerda River delta. We examine the spatio-temporal evolution of the Medjerda shoreline between 1936 and 2016 using satellite images, complemented by sedimentological and geochemical analyses and 210Pbex and 137Cs radiometric data. The general tendency of the shoreline evolution shows an increasing progradation (300 ± 12 m) between 1936 and 2016. Yet the mesoscale Net Shoreline Movement position (NSM) and the End Point Rate (EPR) reveal an erosion pattern estimated to be −20 m ± 0.15 m/yr during the period 1988–1999.The sedimentological analyses reveal four main lithostratigraphic units. The fine sand substratum layer (Md = 0.08 mm) decreases toward clay and silt facies (Md < 0.063 mm), rich in continental plant debris. The geochemical results reveal gradual incoming of the terrigenous component instead of marine deposits. The 137Cs/210Pbex radiometric dating confirms the functioning of the new river flow by the 1950s with the highest sedimentation rate being 3.3 cm/yr. Our results show that the Sidi-Salem dam impoundment (1981) led to a dramatic reduction of sediment discharge, a decrease of the grain size with nearly no more sand reaching the coast, and the shoreline retreat.