Nicolas Le Dantec

Université de Bretagne Occidentale | UBO

In extreme tidal environment, occurrences of saltating pebbles have been observed. The ambition to instal hydrokinetic turbines in such environment requires knowledge on the presence of pebbles in saltation in the water column because they can damage the structures. An experimental study is realized in a free‐surface flume with no slope and differe...

Monitoring coastal seabed in very shallow waters (0–5 m) is a challenging methodological issue, even though such data is of major importance to many scientific and technical communities. Over the years, Structure-from-Motion (SfM) photogrammetry has emerged as a flexible and inexpensive method able to provide both a 3D model and high-resolution ima...

Les aléas côtiers (érosion, submersion, migration dunaire) et les dynamiques côtières sont souvent méconnus par le grand public. Or, dans un contexte de changement climatique et d’évolution de la législation (loi « Climat et résilience » en 2021) sur la gestion des aléas et des risques côtiers (risque(s) combinant aléa(s) et enjeu(x)), le suivi de...

The Causeway Coast World Heritage Site (Northern Ireland) is subject to rockfalls occurring on the coastal cliffs, thus raising major safety concerns given the number of tourists visiting the site. However, such high tourist frequentation makes this site favorable to implement citizen science monitoring programs. Besides allowing for the collection...

The attractiveness of the coasts tends to increase their exposure to erosion and marine flooding risks. This exposure is exacerbated by the effects of climate change, in particular sea level rise. To contribute to strategic thinking on the vulnerability of coastal areas, it is essential to develop, share and collectively maintain relevant knowledge...

Sediment structures including submarine banks and dune fields are ubiquitous on tide-dominated continental inner shelves such as in the Iroise Sea. These are of current interest to human activities in several respects: they constitute an obstacle to navigation, they are dredged for beach nourishment or exploited for marine aggregates. In addition,...

Between November 2018 and January 2020, a continuous multi-parameter survey, using nine types of sensors, was carried out on a coastal chalk cliff in Sainte-Marguerite-sur-Mer (Normandy, France) with the objective of gaining a deeper understanding of the forcing agents and processes that lead to cliff fatigue and failure. This paper will present th...

Long-term datasets documenting the evolution of coastal forms and processes, through the provision of recurring beach as well as shoreface morphological observations and accompanying time-series of environmental controls, remain difficult to collect and are rarely made available. However, they are increasingly needed to further our understanding of...

Hyper-DRELIO (Hyperspectral DRone for Environmental and LIttoral Observations) is a custom, mini-UAV (unmanned aerial vehicle) platform (<20 kg), equipped with a light push broom hyperspectral sensor combined with a navigation module measuring position and orientation. Because of the particularities of UAV surveys (low flight altitude, small spatia...

Understanding the interactions between dune systems and beaches is critical to determining the short‐term shoreline response and the long‐term resilience. In this study, almost 15 years of monthly beach/dune measurements were analyzed for three different profiles at Vougot Beach, France to understand and predict shoreline changes from intra‐annual to...

The sensitivity of a one-line longshore shoreline change model to the incident wave direction is evaluated at Narrabeen Beach (Australia). As previously observed, the application of the one-line model using wave conditions generated along the 10-m depth contour produces a long-term reorientation of the coastline, with an initial transition period a...

A novel laboratory device was developed to generate homogeneous suspended sediment concentration and to provide sufficient volume, ≈ 1 m3, for several sensors functioning simultaneously. The hydrodynamic characteristics and the functionalities of the new device were evaluated. Experiments using four types of sediments were also conducted to investi...

Acoustic scattering can be used to estimate Suspended Sediment Concentration (SSC) through acoustic inversion methods. Current SSC quantification methods are mostly unable to observe both spatial and temporal variations. Here, we assess the possibility to measure both using a Multibeam Echosounder (MBES). MBES combine a large spatial covering in th...

A novel laboratory device was developed to generate homogeneous suspended sediment concentration and to provide sufficient volume, ≈ 1 m3, for several sensors functioning simultaneously. The hydrodynamic characteristics and the functionalities of the new device were evaluated. Experiments using four types of sediments were also conducted to investi...

The impacts of climate change, including sea level and wave climate changes, may increase future erosion risks. Thus, it is important to improve knowledge of the dominant physical processes controlling medium- to long-term shoreline evolution, as well as the performance of beach evolution models reproducing past observations and predicting future c...

The objective of this chapter is to understand the processes involved in the coastal dynamics. Nevertheless, the development of new miniaturized image sensors (digital cameras, thermal sensors, hyperspectral, Lidar, etc.) and positioning systems associated with the development of new platforms such as unmanned aerial vehicles (UAVs) have led to the...

The Platform for Atlantic Geohazard Risk Management (AGEO) is a new project co-nanced under the Interreg Programme for the Atlantic Area which aims to launch ve Citizens' Observatory pilots on geohazards according to regional priorities: Citizens' observatory on rockfalls and rockfall-triggers in the Canary Islands, Spain Peat-slides and peat massm...

We present the hydroacoustic inversion tool HYDRAC. This versatile open-source software, developed in Python 3, offers the capability to read hydroacoustic data from widelyused instruments (eg. ABS, ADCP,…) and perform acoustic inversions following several advanced methods found in the literature to estimate the Suspended Particulate Matter mass co...

Coastal development, combined with the intrinsic mobility of coasts and the context of climate change, tends to increase the vulnerability of coastal territories. This article proposes, on one hand, a renewed interdisciplinary approach to the concept of vulnerability allowing to overcome the nature/society dichotomy. On the other hand, the paper pr...

Littoralisation, or the concentration of people and activities in coastal areas, associated with the intrinsic mobility of coasts and with the context of climate change, tends to increase the vulnerability of coastal areas. This article presents a new interdisciplinary approach towards the concept of vulnerability that makes it possible to move bey...

This paper aims to analyze the shoreline changes of coastal accumulations (sandy and gravel beaches/barriers) of Brittany (Western France). Three long, medium, and short term spatio-temporal scale observations are taken into consideration for the assessment of shoreline dynamics at this regional scale. Firstly, the long-term shoreline position evol...

This paper presents results from an experiment designed to improve the understanding of the relationship between extreme breaking waves and their mechanical loading on heritage offshore lighthouses. The experiment, conducted at La Jument, an iconic French offshore lighthouse, featured several records of wave, current and structure accelerations acq...

Impacts from natural and anthropogenic coastal hazards are substantial and increasing significantly with climate change. Coasts and coastal communities are increasingly at risk. In addition to short-term events, long-term changes, including rising sea levels, increasing storm intensity, and consequent severe compound flooding events are degrading c...

In the dual context of coastal hazard intensification and the growing number of stakes exposed to these hazards, coastal observatories are in demand to provide a structured framework dedicated to long-term monitoring. This article describes the drone-based photogrammetry monitoring performed since 2006 on Porsmilin Beach (Brittany, France) in the f...

UAVs are relevant for monitoring cliff faces. In this study, several flights are performed with various imaging angles (nadir, 20° 30° and 40° off-nadir) to assess the impact of the imaging angle on the 3D cliff face reconstruction. Occlusions issues arising with sub-vertical cliffs make nadir surveys nearly irrelevant. The results obtained with 20...

En France, la cartographie réglementaire des risques littoraux d’érosion s’appuie sur la connaissance du taux de recul moyen du trait de côte et de l'événement maximal de recul. Par opposition à cette méthode préconisée par les instances ministérielles et communément employée aujourd’hui, le regard du géomorphologue conduit à proposer un nouveau pa...

Owing to the combination of technological progress in Unmanned Aerial Vehicles (UAVs) and recent advances in photogrammetry processing with the development of the Structure-from-Motion (SfM) approach, UAV photogrammetry enables the rapid acquisition of high resolution topographic data at low cost. This method is particularly widely used for geomorp...

Coral reef degradation due to environmental change, including anthropogenic disturbances, is a major concern worldwide. Detecting and assessing both temporal and spatial changes in benthic cover is a crucial requirement to inform policy makers and guide conservation measures. Here, we introduce a spatial approach based on high resolution multispect...

Dispositif conçu pour pouvoir tester la réponse et la sensibilité des capteurs à une large gamme de Matière En Suspension et mettre en place des protocoles de mesure in-situ. Il s’intègre dans un processus permettant de passer de la théorie aux tests en laboratoire et enfin à l'application sur le terrain. La cuve est ouverte à la communauté scienti...

Eleven-year long time series of monthly beach profile surveys and hourly incident wave conditions are analyzed for a macrotidal Low Tide Terrace beach. The lower intertidal zone of the beach has a pluriannual cycle, whereas the upper beach profile has a predominantly seasonal cycle. An equilibrium model is applied to study the variation of the cont...

Hyperspectral imagery has proven its potential in many research applications, especially in the field of environmental sciences. Currently, hyperspectral imaging is generally performed by satellite or aircraft platforms, but mini-UAV (Unmanned Aerial Vehicle) platforms (<20 kg) are now emerging. On such platforms, payload restrictions are critical,...

This reports on a project that combined evidence gleaned from aerial photographs, place-names, interviews, topography, LIDAR data, and sonar bathymetry to locate stone tidal fish weirs in the Molène Archipelago. The results were verified by diver and pedestrian visual surveys. Models of Holocene sea-level change allowed a group of possibly Late Mes...

This paper aims to compare models from terrestrial laser scanning (TLS), terrestrial photogrammetry (TP) and unmanned aerial vehicle photogrammetry (UAVP) surveys to evaluate their potential in cliff erosion monitoring. TLS has commonly been used to monitor cliff face erosion (monitoring since 2010 in Normandy) because it guarantees results of high...

Investigating waves in the nearshore zone is of key importance for coastal management, marine spatial planning, coastal risk mitigation and also for the understanding of coastal geomorphology. Among the existing systems to measure wave parameters in the nearhsore, the deployment of pressure sensors in the intertidal zone is an easy, low cost and en...

Under natural and anthropogenic pressure, the coastal regions are evolving rapidly (population growth, erosion, modification of services, etc.), and some of these changes increase their vulnerability. Monitoring the evolution of the coastal regions has thus become essential to understand how they respond to the various pressures and to define how t...

Despite wave-setup and runup being widely studied over the past decades, current empirical formulations largely under-estimate water levels in specific zones. The calculation of intertidal topography from video images is then not trivial. Discrepancies on the setup / runup values can lead to large mistakes in the topography determination. In this s...

The study of the suspended particulate matter (SPM) transport is essential to understanding oceans and rivers, for their presence can impact the environment, from marine habitats or water quality degradations to important changes of the seabed morphology. Among a large number of surrogate techniques in traditional water sampling, acoustical methods...

The georeferencing process is crucial to the accuracy of terrestrial laser scanner (TLS) data, in particular in the context of diachronic studies relying on multi-temporal surveys. The use of Ground Control Points in the georeferencing process can however be complex when confronted with the practical constraints of coastal surveying. A simple and q...

In order to gain new insights into the agents and processes controlling hard rock coast erosion and retreat, a high frequency and multi-parameter monitoring field experiment was carried out from February until May 2017 in Porsmilin cliffs (Plougonvelin, Finistère, Brittany). This survey aimed to discriminate the relative contributions of subaerial...

Subaquatic canyons are an important pathway for sediment transport into oceanic and lacustrine basins. Understanding the mechanisms governing their geomorphological evolution is a key to predict the sediment distribution patterns through these sediment conduits as well as to implement geo-hazard assessments. Submerged channels developed in large la...

For monitoring purposes and in the context of geomorphological research, Unmanned Aerial Vehicles (UAV) appear to be a promising solution to provide multi-temporal Digital Surface Models (DSMs) and orthophotographs. There are a variety of photogrammetric software tools available for UAV-based data. The objective of this study is to investigate the...

Intertidal mudflats play a critical role in estuarine exchange, connecting marine and continental supplies of nutrients and sediments. However, their complex morphodynamics, associated with a wide range of physical and biological processes, are still poorly understood and require further field investigation. In addition, mudflats are challenging ar...

We present preliminary results on the morphology of the upper reaches of the Kukuy Canyon and Selenga shelf in front of Proval Bay (Lake Baikal), derived from newly acquired, high-resolution bathymetry. Numerous and varied erosional and transport features provide an interpretation framework for source to sink transfer and gravity flow processes in...

Morphodynamics of sandy, macrotidal, embayed beaches is complex because of the numerous physical processes interacting at the same location over a wide range of temporal scales. As most of these processes are controlled by beach morphology, dynamic feedbacks are generally observed between hydro- and morphodynamics. Investigating short-term processe...

The recent completion of a coupled seismic and swath bathymetric survey, conducted across the sand ridge system of the Banc du Four located on the Atlantic continental shelf of Brittany (Mer d’Iroise, France), provided new data for the study of the long term evolution of deep tidal sand ridges. Five seismic units are distinguished within the ridge,...

HYPXIM, is a preliminary study (i.e. phase 0) which begun in 2009, lead and funded by CNES. The synthesis of the needs collegially addressed by a national group of hyperspectral experts, helped us to set up the mission requirements in terms of spectral domain [0,4-2.5 microns), spectral resolution (10nm), signal-to-noise ratio (depends on the rang...

Tréguier A.M., Floc’H-Laizet C., 22 others, Paulet Y.M. and V. Pichereau, 2015.- LabexMER, A changing Ocean; 2012-2014 report. 90 p. available at http://www.labexmer.eu/fr/en/labexmer-2012-2014-report.pdf. Abstract: The cluster of excellence LabexMER was created in November 2011 in the framework of the French “investments for the future” program....

With its smaller size, well-known boundary conditions, and the availability of detailed bathymetric data, Lake Geneva's subaquatic canyon in the Rhone Delta is an excellent analogue to understand sedimentary processes in deep-water submarine channels. A multidisciplinary research effort was undertaken to unravel the sediment dynamics in the active...

Book of abstract international conference ICAWA 2014 : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters Kite aerial photography system : a low cost and high resolution solution for beach monitoring (2D map and 3D topography) [résumé]

Dynamic penetrometers reveal information about seafloor strength, stratification, stability, and sediment remobilization. However, positioning is often limited to a range of meters making it difficult to target small-scale geomorphologic features. Deployments from submersed vessels (manned or remotely operated) can extend the possibilities of in si...

Field measurements and numerical simulations were used to determine the effects of dominant meteorological conditions on the hydrodynamics of a wide (aspect ratio ~2), relatively deep (seasonally stratified) and open lake embayment (Vidy Bay, Lake Geneva). A three-dimensional hydrodynamic model (Delft3D-FLOW) was employed to simulate flow in the la...

Subaquatic canyons in deltas are major pathways for the transport of particles from land to the deep basins. They represent active environments with frequent deltaic failures and mass-movement deposits potentially leading to hazardous (tsunami waves) and economic (infrastructure damages) implications. Understanding sedimentary processes and mass-mo...