Mieux comprendre la perception des paysages de bras morts en vue d’une restauration écologique : quels sont les liens entre les qualités esthétique et écologique perçues par les acteurs ?

Le contexte actuel des restaurations écologiques demande de porter une attention particulière à la perception du public. Il est en effet désormais bien admis que la sensibilisation du public à la restauration des écosystèmes et, en définitive, la pérennité des actions engagées, dépendent en partie de l’apparence du milieu après travaux. La qualité du paysage constitue donc un indicateur de succès des projets de restauration. Plus largement, le paysage constitue un vecteur de diffusion des enjeux environnementaux auprès du public. La mise en œuvre de restaurations de bras morts sur le fleuve Rhône et sur la rivière d’Ain a motivé la réalisation d’une enquête de perception. Elle porte précisément sur un objet bien spécifique : les plans d’eau de ces bras morts. Deux objectifs prévalent dans le cadre de cette étude : (1) Mettre en évidence les facteurs explicatifs de la perception des plans d’eau de bras morts ; (2) Comprendre si les connaissances environnementales conditionnent, ou non, les préférences. Ces interrogations sont nécessaires dans la perspective d’une définition concertée des futurs projets de restauration. Une enquête par photo-questionnaires a donc été menée. Les résultats confirment que certaines variables relatives à l’aspect de l’eau expliquent en grande partie les préférences. En effet, certaines induisent des jugements positifs (transparence de l’eau, végétation aquatique dont la forme est bien définie, contrastes de couleurs, etc.) tandis que d’autres engendrent davantage des jugements négatifs (opacité, sédiments, végétation aquatique dont la forme est mal définie, etc.). Des analyses multivariées ont permis de définir une typologie de plans d’eau en fonction de leur perception (4 types visuels). Ces résultats concrets permettent d’envisager une modélisation de la perception des plans d’eau de bras morts. Elle consisterait à anticiper les réactions esthétiques à partir d’un jeu de variables concernant l’apparence de l’eau. Cette perspective semble prometteuse dans le cadre d’une gestion participative des zones humides.The current context of ecological restorations requires specific attention to public perception. The public’s adhesion to any given restoration project is instrumental in the success and the durability of its operations. This adhesion depends partly on the appearance of the environments after the engineering works have been performed. Landscape quality is thus an indicator of success for restoration projects. Widely, landscape may be considered as an efficient tool to communicate the environmental stakes to the public. Within the context of the floodplain lakes restorations in the Upper Rhône and Lower Ain Rivers, a perception survey has been conducted which focussed on water appearance. Two main objectives were defined: (1) defining the structural criteria which explain the floodplain lakes perceptions; (2) defining if environmental knowledge influences – or not – landscape preferences. These are necessary considerations in order to establish a dialogue between stakeholders when elaborating the restoration goals. The survey used photo-questionnaires. The results confirm that some criteria concerning the water appearance explain a large part of preferences. Some criteria (transparency of water, well shape-defined aquatic vegetation, colour-contrasted lakes, etc.) induce positive judgments whereas some other criteria (opacity of water, bad shape-defined aquatic vegetation, presence of sediments, etc.) imply negative assessments. Thanks to multivariate analysis, a typology of floodplain lakes was defined as a function of their perception (4 visual types). These concrete results open new perspectives. A model of the floodplain lakes perception could be built in order to anticipate the aesthetic reactions as a function of a set of water appearance criteria. It would be an efficient tool in order to initiate a participative management of wetland

Structural properties of floodplain width in the Rhone catchment: methodology and results

status: publishe

Can we characterize river corridor evolution at a continental scale from historical topographic maps? A first assessment from the comparison of four countries

International audienc

Geomorphological discontinuities and ecological organisation (a case study of the River Drôme)

La morphologie rocheuse et alluviale d un tronçon de la rivière Drome a fait l objet de ce travail. La première partie de thèse analyse les changements fluviaux et le développement de la zonation géomorphologique actuelle du tronçon, au cours d une période de 58 années. La deuxième partie examine l organisation longitudinale actuelle des communautés benthiques. Il est prévu que le tronçon soit soumis à une recharge sédimentaire afin de restaurer l enfoncement du chenal. La troisième partie de thèse évalue les impacts morphologiques de cette intervention et la réponse du benthos. Le développement de la zonation morphologique met en évidence que l incision n est pas une tendance linéaire mais un processus complexe et discontinu, dans le temps et dans l espace. A la suite d une crue morphogène en 1978, le tronçon est en perpétuelle phase d ajustement et semble se caractériser ainsi par une dynamique autorégulatrice. La mise en évidence d une zonation morphologique assez dynamique nous a conduit à interpréter l organisation de benthos en fonction des processus longitudinaux, transversaux et verticaux, en particulier les perturbations du lit associées au régime sédimentaire, tous opérant selon des dynamiques spécifiques à l échelle de chacune des zones. La morphologie hétérogène du tronçon accueille un benthos relativement plus intéressant que celui des chenaux antérieurs. On considère qu une recharge sédimentaire qui n est pas excédentaire ou qui est inférieure aux capacités de transport des zones, ainsi que la conservation de la connexion entre le chenal et ses marges actives, maintiendra la zonation morphologique et dès lors l organisation des communautés benthiques actuelles. On en conclut ainsi que la restauration de la charge de fond au tronçon serait une stratégie morphologiquement et écologiquement judicieuse.A mixed bedrock-alluvial reach of the River Drôme, France forms the central focus of this thesis. The first part examines long-term changes in channel morphology, and the development of present-day geomorphic zonation. The second part examines the present-day organisation of in-stream macroinvertebrate communities and associations with channel morphology. The study reach is located 200 m downstream from the Béoux sub-catchment, a site chosen for the experimental remobilisation of sediment to rehabilitate degradation along the reach and in downstream parts of the Drôme. The third part evaluates the likely morphological and ecological impacts of this management strategy. Analyses reveal that degradation is a discontinuous process both in time and in space. A large flood in 1978 is seen as the catalyst of zonation. By locking the reach into a particular geometry it imposed substantial spatial discontinuity in the capacity and the propensity of the channel to adjust. Spatial differences in macroinvertebrate community structure reflect spatial differences in channel behaviour. Zone-scale variation in longitudinal, lateral and vertical connectivity, and in particular bed disturbances associated with zone-scale regimes of sediment transfer and storage, control the organization of in-stream fauna. It is considered that the present-day mixed bedrock-alluvial morphology supports a more diverse fauna than historical, alluvial channels. If fluxes of bedload reintroduced to the Drôme are not inferior or excessive to the present-day regimes responsible for maintaining zonation, then this self-regulating dynamic could be maintained. This would also maintain the present-day patterns of macroinvertebrate community structure and so it is concluded that if the reach is secured with a moderate and frequent supply of bedload then the remobilization of sediment is a desirable management strategy.LYON3-Bibliothèques (693872102) / SudocSudocFranceF

Assessing river geomorphic alteration at regional scale: the case of piedmont region, Convegno Nazionale di Idraulica e Costruzioni Idrauliche Bologna. Atti del XXXV Convegno Nazionale di Idraulica e Costruzioni Idrauliche

Remote Sensing (RS) technologies over the last decade have made substantial progresses in terms of data accuracy, spatial coverage and temporal frequency of acquisitions. A valuable amount of information to investigate river systems have begun to emerge, which was not available in the past (Marcus and Fonstad 2010). This novel context opens new opportunities for river science and management whose uptake is just starting to occur amongst scientists and managers (Carbonneau and Piegay 2012). Orthophotos and high-resolution multi-spectral images have been utilised by fluvial geomorphologists and hydrologists for a long time to manually draw the recent (i.e. last 50-70 years) historical evolution of key channel geomorphic features (e.g. active channel width) and to map riparian corridors and ecological habitats over large scale using multi-spectral information (Surian and Rinaldi 2003; Clerici et al 2013). More recently LiDAR information has begun to provide accurate information on river topography opening exciting opportunity to map river morphology (Passalacqua et al 2012). However, large-scale analysis of river systems exploiting the availability of already acquired datasets of multi-spectral high-resolution images and LiDAR is surprising limited. Bizzi et al (2016) in a recent review points out the large availability of these datasets at European scale and discussed the fact that these datasets are rarely acquired for river characterizations purposes although they are valuable information to this aim. They also note that these days the bottleneck for river science and management is not data generation but data processing. RS data poses a number of data analysis challenges (Alber and Piégay 2011; Schmitt et al 2014), which cannot be handled solely by river geomorphologists and engineers, and call for multi-disciplinary working groups where river experts work side by side with remote sensing experts and data analysts. In this work, we show how a regional available dataset in the Piedmont region (north east of Italy) acquired in 2008 for landscape monitoring and urban planning purposes, including high-resolution multi-spectral images and LiDAR data, can be used to extract valuable information about geomorphic character of river systems. We provide one of the first applications at regional level where extent and topographic river geomorphic features have been classified through semi-automated procedures and tools creating a regional DataBase (DB) suitable for river geomorphic investigation. The developed tools can be easily applied in the future in other contexts with similar data availability. A regional classification of the main river typologies in the region has been developed using the DB. Moreover, statistical analyses have been used to exploit the information embedded in the spatial heterogeneity of the regional DB in order to enhance our understanding of how river systems shape their channels under various contexts of geology, hydrology and human pressures. We have been able to detect meaningful relationships between geomorphic drivers (e.g. channel gradient, basin area, geology, geographic area), human pressures and channel features providing robust basis to generate a firsts assessments of river system alterations induced by human activities at regional level, and generating valuable evidences to discuss the design of more effective river management plans and rehabilitation measures

Combining hillslope erosion and river connectivity models to assess large scale fine sediment transfers: Application over the Rhône River (France)

International audienceAbstract Sediment connectivity at the catchment scale includes the processes linking sediment sources, sinks and the river outlet. Soil erosion models usually estimate yields without considering riverine processes or human infrastructure that may affect sediment connectivity. Quantifying these processes at a large scale is a determinant of understanding sediment transfers from continental lands to marine ecosystems. This study tries to fill this gap by coupling the soil erosion model WaTEM/SEDEM (WS) with the riverine connectivity tool CASCADE to quantify sediment fluxes in the Rhône watershed. The coupling returned a good fit, with deviations of −51.7%. WS alone predicts the exported fluxes better with a deviation of −34.9%. Nevertheless, this paper shows the importance of considering connectivity and transport capacity to develop a more realistic representation of fine sediment dynamics at a large scale. However, connectivity tools depend on the quality of the models (soil erosion and hydrology) and the geomorphological data on which they depend, which is a limiting factor in large‐scale studies

Perception and evaluation of dead wood in streams and rivers by German students

Journal ArticleInternational audienceDead wood is a significant element of natural streams and rivers in temperate climate zones. Established stream management removes wood, whereas some scientists recently promoted the reintroduction of wood in stream rehabilitation and restoration. It is desirable to know if wood in streams and rivers would be accepted. A survey was therefore conducted in order to assess the spontaneous visual perception of 10 stream and 10 river scenes with and without wood in terms of naturalness, risk, aesthetics and need for improvement using visual analog scales. Three hundred and sixty-five German students from five subjects related to water management and from one subject without any professional association to running waters were surveyed before their first contact to teaching of aquatic ecology. They clearly perceived wood in streams and rivers as natural. Scenes with wood were most frequently associated with danger for sport activities while scenes without wood were most frequently associated with danger by flooding. When comparing scenes with and without wood, scenes with wood were clearly considered more positive as significantly more aesthetic, less dangerous and needing less improvement. The disciplinary groups showed variations in the absolute evaluation scores but the relative evaluation of scenes with wood versus scenes without wood was similar among all groups. The results indicate an acceptance for the reintroduction of wood in stream rehabilitation and restoration by young students who are potential future players in water management

Channel changes over the last 200 years: A meta data analysis on European rivers

International audienceAbstract The combined analysis of past evolutionary trajectories of channel morphology and temporal patterns of driving factors is fundamental to understanding present river conditions, supporting river management and evaluating future changes. Rivers in Europe underwent important channel changes during the Anthropocene in response to changing natural drivers and anthropogenic pressures. A considerable number of papers have been published on this topic, in the last decades. In this study, a comprehensive meta‐analysis on channel changes during the last 200 years in Europe was performed, aiming to provide quantitative information on the intensity of changes, to highlight regional scale similarities and dissimilarities in evolutionary morphological trajectories and to discuss the main causes of such changes. Based on a review, 102 papers were selected, addressing 145 channel reaches flowing through five main mountain ranges (Iberians, Alps, Apennines, Balkans and Carpathians) in the southern and eastern parts of Europe. The results show that active channel narrowing (between 26% and 36% on average) and incision (between 1 and 2 m) prevailed in most rivers between the 1800s and the 1950s, although widening was documented in some rivers of the Alps and the Apennines. Most multi‐thread reaches maintained their pattern until the mid‐20th century. Active channel changes accelerated during the 1950s–1990s (or 2000s) period, with channel narrowing up to 60% and channel incision up to 14 m. Multi‐thread patterns strongly decreased in frequency, with anabranching channels disappearing and single‐thread patterns becoming predominant. The cumulative effect of multiple and concomitant human pressures (gravel mining, channelisation and damming) was identified as the main driving factor for these accelerated changes. These findings must feed the public debate about preventing alterations of river ecosystems—exerted by anthropic disturbances—in a context of rapid economic development, especially in river systems still poorly altered and thus preserving wide, active and heterogeneous fluvial corridors

LiDAR-based fluvial remote sensing to assess 50–100-year human-driven channel changes at a regional level: The case of the Piedmont Region, Italy

Remote Sensing (RS) technology has recently offered new and promising opportunities to analyze river systems. In this paper, we present a calibration of characteristic Hydraulic Scaling Law (HSL) using a regional database of river geomorphic features. We consistently linked discharge with channel geometry features for estimated Bankfull Channel Depth (eBCD), Active Channel Width (ACW), and Low Flow water Channel Width (LFCW), which are continuously available from RS data along the river course. We then used historical information and external sources of information on channel reaches that were relatively unaffected by hu- man pressure over periods ranging from a few decades to a century (measured in comparable geographical areas) to infer relatively Unaltered HSLs (rUHSLs). Adopting rUHSL validated with available local historical evidence on channel geometry, we were able to assess historical changes in channel geometry consistently over the entire region and within the studied temporal window. The case study was conducted for the Po basin in the Piedmont Region, north-west Italy. From our analysis, it emerges that region- ally 74% of the river network has riverbed incisions exceeding 1 m, while 66% of channels have halved their historical widths with a total of 617 ha of land subtracted from the active channel. LFCW is, on average, wider in Alpine rivers compared with those located in the North Apennines. Although it is currently not possible to measure the accuracy of these estimates, the evidence generated is coherent with available historical information, characteristic hydraulic scaling laws, evidence from relatively unaltered reaches and the available literature on local fluvial systems. This methodology provides robust, novel and quantitative information regarding decadal to secular channel changes that have occurred on a regional scale. This new layer of information enriches our ability to rationally address assessments of large-scale past and future channel trajectories.JRC.D.2-Water and Marine Resource

Deep learning ancient map segmentation to assess historical landscape changes

ABSTRACTAncient geographical maps are our window into the past for understanding the spatial dynamics of last centuries. This paper proposes a novel approach to address this problem using deep learning. Convolutional neural networks (CNNs) are today the state-of-the-art methods in handling a variety of problems in the fields of image processing. The Cassini map, created in the eighteenth century, is used to illustrate our methodology. This approach enables us to extract the surfaces of classes of lands in the Cassini map: forests, heaths, arboricultural, and hydrological. The evolution of land use between the end of the eighteenth century andtoday was quantified by comparison with Corine Land Cover (CLC) database. For the Rhone watershed, the results show that forests, arboriculture, and heaths are more extensive on the CLC map, in contrast to the hydrological network. These unprecedented results are new findings that reveal the major anthropo-climatic changes