This study analyses the contribution of a multi-scale, multi-source monitoring system to improve knowledge of groundwater flooding hazards in Norman coastal agricultural areas. These low-lying territories are particularly exposed, with significant impacts on farms. In the context of climate change, this hazard is expected to intensify due to the combined effect of increasing winter precipitation and rising sea levels. At the regional scale, the DREAL Normandie "groundwater depth at very high water levels" database constitutes the main reference, but its comprehensiveness remains limited by the spatial resolution adopted. To overcome these limitations, a monitoring framework integrating high-resolution elevation data, Sentinel-2 satellite imagery, drone surveys, camera traps, and piezometric measurements was deployed across two sites on the western coast of the Manche department: the Havre de Lessay and the C & ocirc;te des Isles. The results show a concentration of groundwater rise in low-lying back-coastal areas, close to the shoreline. They highlight the structural role of microtopography, lithology and agricultural infrastructure in the distribution of flooded areas. Drone observations reveal strong spatial heterogeneity, with discontinuous water patches absent from existing regional maps. Piezometric data confirm a marked seasonal dynamic, primarily between November and April. Finally, satellite imagery enables the spatial mapping of the recurrence of saturation episodes at the regional scale. This monitoring system thus provides a better understanding of flood dynamics and their agricultural impacts.
Like many other little streams draining a granitic watershed, the Scorff river (southwest Armorican Massif, Brittany, France) is suspected to suffer an increase in sand sedimentation due to human activities in the recent decades, a matter of concern for environment local managers. The presence of potentially increased sand intersects with numerous issues related to the preservation of the Scorff particularly given the presence of several threatened diadromous species, such as the Atlantic salmon or the Sea lamprey, and the habitats that support them. The present study aims to analyse the spatial relationships between various supposed factors of sand sedimentation-potential sand production from agricultural land in the differents sub-watersheds, morphometric factors, instream barriers-and the sand cover of stream geomorphic units (facies) on the 32 km downstream main river course. The evolution of some of these parameters during the last two to five decades is also studied. Our study found that sand sedimentation in the streams is mainly controlled by the water slope and the presence of weirs. It is also influenced by the presence of wood. No significant input of sands were observed downstream from confluences with tributaries which are the most sensitive to sand transfers from agricultural land. The biggest tributary (the Kerustang) was an exception. On this stream, the Pont-Calleck dam (XVIIth century) was accidentally opened in 2011, providing a huge sand load to the main stream. The sand sedimentation spread downstream, however affecting fewer lotic stream facies-runs, and riffles and rapids.
The western coast of Iceland, between the towns of Akranes and & Iacute;safj & ouml;r & eth;ur, exhibits a wide variety of deposit forms that, until now, had never been described or analyzed from a morphosedimentary perspective. Thus, the objective of this study is to propose a morphological classification of these barriers by relating them to existing typologies in the literature. A total of 84 barriers were identified through the analysis of satellite imagery, aerial photographs, and field investigations. This analytical work also drew upon the study of topographic and geological maps. In a second step, these barriers were classified based on their environmental characteristics using qualitative and quantitative parameters describing the topographic, morphological, and hydrodynamic context. A hierarchical ascending classification (HAC) followed by an AFDM-type factor analysis was used for this purpose. The results led to the identification of 7 distinct classes corresponding to different morphological types, ranging from beaches to mobile forms such as spits and barriers. For each type of accumulation forms, the statistical analysis highlights the key environmental parameters, such as the bathymetry of the foreshore, the underlying continental topography, and local hydrodynamic conditions.
La côte occidentale de l’Islande, entre les villes d’Akranes et d’Ísafjörður, présente une très grande diversité de formes d’accumulation qui n’avaient jusqu’à ce jour jamais été décrites ni analysées d’un point de vue morpho-sédimentaire. Ainsi, l’objectif de cette étude est de proposer une classification morphologique de ces cordons en les replaçant au sein des typologies déjà existantes dans la littérature. 84 cordons ont ainsi été identifiés à partir de l’analyse d’images satellitaires, de photographies aériennes et d’investigations de terrain. Ce travail analytique s’est aussi appuyé sur l’étude de cartes topographiques et géologiques. Dans un deuxième temps, ces cordons ont été classés en tenant compte de leurs caractéristiques environnementales à partir de paramètres qualitatifs et quantitatifs décrivant le contexte topographique, morphologique et hydrodynamique. Une classification ascendante hiérarchisée (CAH) suivie d’une analyse factorielle de type AFDM ont été pour cela utilisées. Les résultats ont permis d’aboutir à 7 classes distinctes qui correspondent à différent types morphologiques allant des formes adossées (plages) aux formes fuyantes et mobiles (flèches et barrières non adossées). Pour chaque type de cordon, l’analyse statistique met en évidence les paramètres environnementaux déterminants, tel que la bathymétrie de l’avant côte, le relief continental hérité ou encore les conditions hydrodynamiques locales.
Rivers transport macroplastics (> 1 cm), which can remain trapped in several parts of the floodplain: banks, islands, lateral channels, infrastructures, and vegetation. Residence times vary and can be up to years. This work focuses on the Sa & ocirc;ne River, a lowland river, where 19 organic flood deposits were sampled on islands and riverbanks. They are located in four sectors characterized by variations in slope, specific stream power and land-use. Macroplastics were collected, weighed, and characterized visually during the field trip by boat, and then identified using ATR-FTIR. Seventy percent of the 1324 macroplastics were unknown fragments, which suggests that they have undergone river transport and fragmentation processes. Point deposits in calm water areas along the riverbanks accumulate mostly foam-type macroplastics, while diffuse deposits on densely vegetated islands particularly trap film-type macroplastics. Sectors characterized by low specific stream power may concentrate more macroplastics, but with a lower mass. Macroplastics with a higher median mass were observed in the upstream sector, where slopes are steeper. Our results confirm the existence of preferential trapping zones for macroplastics in areas with gentle slopes and dense vegetation. They also highlight the existence of several trapping modes, which could imply variable residence times and microplastic fragmentation rates depending on the storage areas and types of debris considered.
