Monitoring the medium-term retreat of a gravel spit barrier and management strategies, Sillon de Talbert (North Brittany, France)

Stéphan, Pierre; Suanez, Serge; Fichaut, Bernard; Autret, Ronan; Blaise, Emmanuel; Houron, Julien; Ammann, Jérôme; Grandjean, Philippe

doi:10.1016/j.ocecoaman.2018.03.030

Cited by 18 publications

(16 citation statements)

References 28 publications

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“…Among these factors are hydrodynamic context and conditions such as waves (Allard et al ., 2008; Ashton et al ., 2016), tidal range and prism (Powell et al ., 2006; Robin et al ., 2007), inlet discharge and migration (Chaumillon et al ., 2014; Adams et al ., 2015), and storm‐induced breaching (Sanchez‐Arcilla and Jimenez, 1994; Zainescu et al ., 2019), as well as sediment availability (Héquette and Ruz, 1991; Firth et al ., 1995), sea‐level rise (van de Plassche and van Heteren, 1997; Billy et al ., 2018a), and geological processes and framework (Riggs et al ., 1995; Billy et al ., 2018b; Cooper et al ., 2018). In the last few decades, anthropogenic impacts have assumed increasing importance (Garel et al ., 2014; Miselis and Lorenzo‐Trueba, 2017; Sadio et al ., 2017; Kombiadou et al ., 2019a), especially in terms of sediment budget applications and engineering interventions (Psuty et al ., 2014; Stéphan et al ., 2018).…”

Section: Introductionmentioning

confidence: 99%

Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes

Robin

Levoy

Anthony

et al. 2020

Earth Surf Processes Landf

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Sand spits with distal hooks have been well documented from coasts with low to moderate tidal ranges, unlike high tidal‐range environments. Datasets from 15 LiDAR and 3 UAV surveys between 2009 and 2019 on the Agon spit in Normandy (France), a setting with one of the largest tidal ranges in the world (mean spring tidal range: 11 m), combined with in‐situ hydrodynamic records between 2013 and 2017, highlight a three‐stage pattern of spit hook evolution. Stage 1 (2009–2013) commenced with the onshore migration and attachment of a swash bar, followed by persistent spit accretion updrift of the bar and erosion downdrift because of the slow speed of bar migration in this large tidal‐range environment. In stage 2 (2013–2016), three overwash events and a 220 m‐wide breach culminating in the total destruction of the spit during winter 2015–2016 involved the landward mobilization of thousands of cubic metres of sand. These events occurred during short durations (a few hours) when spring high tides coincided with relatively energetic waves, underscoring the importance of storms in rapid spit morphological change. Strong spring tidal currents maintained the breach. Stage 3 (2016–2019) has involved new hook construction through welding of a swash bar and spit longshore extension, highlighting the resilience of the spit over the 10‐year period, and involving a positive sediment balance of 244 000 m3. The three stages bring out, by virtue of the temporal density of LiDAR and UAV data used, a high detail of spit evolution relative to earlier studies in this macrotidal setting. The large tidal range strongly modulates the role of waves and wave‐generated longshore currents, the main process drivers of spit evolution, by favouring long periods of inertia in the course of the spring–neap tidal cycle, but also brief episodes of significant morphological change when storm waves coincide with spring high tides. © 2020 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 99%

Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes

Robin

Levoy

Anthony

et al. 2020

Earth Surf Processes Landf

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“…Firstly, some topographic profiles can be surveyed with a tachometer or a DGNSS (Table 1). These topographic profiles allow observation of the surface elevation evolution of the entities along some punctual cross-or long-shore transects [6]. Handborne topographic monitoring can also be done in 2D through a digital elevation model (DEM) using a DGNSS figure field, which enables the volume evolution of the sediment deposit to be estimated, in addition to the topographic profiles [6].…”

Section: Handborne Monitoring Methodsmentioning

confidence: 99%

Morpho–Sedimentary Monitoring in a Coastal Area, from 1D to 2.5D, Using Airborne Drone Imagery

Mury

Collin

James

2019

Drones

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Coastal areas are among the most endangered places in the world, due to their exposure to both marine and terrestrial hazards. Coastal areas host more than two-thirds of the world’s population, and will become increasingly affected by global changes, in particular, rising sea levels. Monitoring and protecting the coastlines have impelled scientists to develop adequate tools and methods to spatially monitor morpho-sedimentary coastal areas. This paper presents the capabilities of the aerial drone, as an “all-in-one” technology, to drive accurate morpho-sedimentary investigations in 1D, 2D and 2.5D at very high resolution. Our results show that drone-related fine-resolution, high accuracies and point density outperform the state-of-the-science manned airborne passive and active methods for shoreline position tracking, digital elevation model as well as point cloud creation. We further discuss the reduced costs per acquisition campaign, the increased spatial and temporal resolution, and demonstrate the potentialities to carry out diachronic and volumetric analyses, bringing new perspectives for coastal scientists and managers.

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“…Such thresholds have been identified for gravel barriers elsewhere. For example, observations following extreme event impacts at Sillion de Talbert, Brittany, France suggest that crest lowering below the MHWL is critical because it leaves certain parts of the barrier vulnerable to high tides in addition to infrequent storm events [45].…”

Section: Pre-storm Morphology Influences Morphological Change During Storm Eventsmentioning

confidence: 99%

“…The proposed benefits include an inherent ability to self-repair and recover from external disturbances such as storm damage [39], an ability to provide a multiplicity of benefits [40], and sustainability under uncertain future environmental conditions [41,42]. Accordingly, many gravel beaches and barriers have been allowed to relax towards a more natural state (e.g., Medmerry, south coast, U.K. [43]; Porlock, south-west coast, U.K. [44]; Sillon de Talbert, north-west coast, France [45]). In these cases, barriers have undergone relatively dramatic changes (landward rollover, crest lowering, and inlet widening) in the period following cessation of active management.…”

Section: Introductionmentioning

confidence: 99%

Impact of Management Regime and Regime Change on Gravel Barrier Response to a Major Storm Surge

Pollard

Christie

Brooks

et al. 2021

JMSE

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Gravel barriers represent physiographic, hydrographic, sedimentary, and ecological boundaries between inshore and open marine offshore environments, where they provide numerous important functions. The morphosedimentary features of gravel barriers (e.g., steep, energy reflective form) have led to their characterization as effective coastal defense features during extreme hydrodynamic conditions. Consequently, gravel barriers have often been intensively managed to enhance coastal defense functions. The Blakeney Point Barrier System (BPBS), U.K., is one such example, which offers the opportunity to investigate the impact of alternative management regimes under extreme hydrodynamic conditions. The BPBS was actively re-profiled along its eastern section from the 1950s to the winter of 2005, whilst undergoing no active intervention along its western section. Combining an analysis of remotely sensed elevation datasets with numerical storm surge modeling, this paper finds that interventionist management introduces systemic differences in barrier morphological characteristics. Overly steepened barrier sections experience greater wave run-up extents during storm surge conditions, leading to more extreme morphological changes and landward barrier retreat. Furthermore, while high, steep barriers can be highly effective at preventing landward flooding, in cases where overwashing does occur, the resultant landward overtopping volume is typically higher than would be the case for a relatively lower crested barrier with a lower angled seaward slope. There is a growing preference within coastal risk management for less interventionist management regimes, incorporating natural processes. However, restoring natural processes does not immediately or inevitably result in a reduction in coastal risk. This paper contributes practical insights regarding the time taken for a previously managed barrier to relax to a more natural state, intermediary morphological states, and associated landward water flows during extreme events, all of which should be considered if gravel barriers are to be usefully integrated into broader risk management strategies.

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Monitoring the medium-term retreat of a gravel spit barrier and management strategies, Sillon de Talbert (North Brittany, France)

Cited by 18 publications

References 28 publications

Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes

Sand spit dynamics in a large tidal‐range environment: Insight from multiple LiDAR, UAV and hydrodynamic measurements on multiple spit hook development, breaching, reconstruction, and shoreline changes

Morpho–Sedimentary Monitoring in a Coastal Area, from 1D to 2.5D, Using Airborne Drone Imagery

Impact of Management Regime and Regime Change on Gravel Barrier Response to a Major Storm Surge

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