The recognition and quantification of fluvial transport and depositional processes has widely been studied. However, few works have focused on the interpretation and quantification of sedimentary processes in low-energy fluvial environments. This paper features and compares the results of five methods of grain size data processing (statistic moments, textural analysis, multivariate statistics combining Principal Component Analysis and hierarchical cluster analysis, and CM image and end-member modeling analysis) and discusses their efficiencies in characterizing low-energy alluvial plain deposits. These environments are characterized by fine grain size, high-homogeneity deposits at the macroscopic scale, and low grain size variability, hence presenting a difficulty in identifying and splitting an apparently homogeneous sedimentary record into sedimentary sequences. These statistical methods are applied on a ~9 m long core extracted from the fluvial island of la Baine located in the downstream section of the Charente River (Chaniers, Charente-Maritime, France). In the light of these results, elementary statistical parameters (statistical moments, modes, and sorting index) have limited interest in the sedimentary description and interpretation of fine fluvial deposits. Textural analyses are more informative but highly dependent on the classification scheme. Only the multivariate statistics approach and end-member modeling analysis present interesting results and allow the robust identification of sub-units. However, multivariate statistics results are dependent on the choice of input variables and do not support non-zero values, while the second method, the most recent and complex one, needs further developments to clearly connect end-member classes to sedimentary processes.
<p><span>Although many studies have analyzed the impact of human interventions on European rivers over decades or centuries, researchers have rarely evaluated the geomorphological effects of these anthropogenic pressures on fluvial systems. However, quantifying anthropogenic impacts is fundamental to understanding how rivers are affected by human interventions and to improving the river management and restoration. The aim of this study is to propose a new and original qualitative method to estimate the importance of human impacts on rivers over the last three centuries using the middle Charente River as a test case. The study area is an anastomosing, low-energy and little mobile river of the lowlands of Western France. It extends from the city of Angoul&#234;me (Charente) to the city of Saintes (Charente-Maritime), with a length of approximately 100 km. The study segment has been subjected to high anthropogenic pressure since the High Middle Ages, and it was enhanced during the 19th century to facilitate navigation and terrestrial transportation, to ensure the exploitation of the water's driving force (water mills and paper mills), to maintain the local people (fishing dams and agro-pastoral uses) and to allow for flood protection. To understand and estimate the anthropogenic heritage of the Charente River, this study employed a two-stage method: 1) an inventory of the human interventions on the fluvial system through the consultation of geo-historical data (textual archives, historical maps and iconography) dating from the end of the 17th century to the 2010s and 2) an evaluation of the human impact of each human intervention, sub-category and category of intervention based on the calculation of the Cumulative Human Impact Index. The Cumulative Human Impact Index is composed of several qualitative attributes graded by an evaluator. The results allow one 1) to generate a database and typology of the human interventions affecting the middle Charente River over the long term; 2) to map the cumulative impacts of human interventions on the study area; and 3) to analyze the unitary and overall impact of each human intervention, sub-category and category of intervention on the river landscape's heritage. Finally, this study concludes with 1) a discussion of the advantages of using a qualitative methodology for the estimation of anthropogenic impacts and 2) a reflection on the use of the maps of cumulative human impacts for Charente River management and restoration.</span></p>
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