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Floods are among natural disasters that increasingly threaten society, especially with current and future climate change trends. Several tools have been developed to help planners manage the risks ...

Riparian areas are important ecosystems that need to be restored and protected in the Anthropocene era. In Quebec, Canada, conservation laws and management strategies focus on ecological services provided by riparian communities, such as erosion and flood control, carbon sequestration, and pollutants filtration. However, there is a need to incorporate fluvial biogeomophological approaches to improve our understanding of those systems. Biogeomorphology explores both the impacts of flood regime and disturbances on plant structure and composition and the role of plant communities in altering hydrosedimentary processes. Approaches anchored in biogeomorphology have proven to be efficient to understand interactions and feedbacks between fluvial dynamics and plant ecology in many contrasted environments, from temperate to arid regions and from small streams to large rivers. However, those approaches have never been applied to rivers disturbed by ice dynamics. Ice jams and mechanical breakups are known to disturb fluvial systems, both geomorphologically and ecologically. Moving ice during breakups has the potential to severely erode banks and transport sediment, thus destroying riparian habitat and disturbing plant succession dynamics. Feedback dynamics between plants and rivers are thus obviously affected by ice disturbances regime. There is a need to understand how fluvial biogeomorphic systems respond to such disturbances to assess better management strategies and improve prevision models in a context of climatic change. In this poster, we expose a research project aiming at conceptualizing how ice disturbances regime controls the biogeomorphic interactions in two rivers located in eastern Quebec, Canada. To do so, analyses will be held in three distinct spatiotemporal scales: 1) decennial biogeomorphological trajectories, 2) plant community structure and composition on distinct fluvial landforms and 3) functional traits of ice-disturbed indicator species.

The consensus around the need for a shift in river management approaches to include more natural processes is steadily growing amongst scientists, practitioners, and governmental agencies. The freedom space for rivers concept promotes the delineation of a single space that integrates multiple fluvial dynamics such as floods, lateral migration, channel avulsions, and riparian wetlands connectivity. The objective of this research is to assess the validity of the hydrogeomorphological approach to delineate the freedom space for an extensive sampling of river reaches, covering 167 km, in contrasting watersheds in Quebec (Canada). Comparative analysis was conducted on the relative importance of erosion and flood processes on the freedom space delineation for various fluvial types. Semiautomated tools based on light detection and ranging (LiDAR) digital elevation models were also tested on an additional 274 km of watercourses to facilitate freedom space mapping over extensive zones and for highly dynamics environments such as alluvial fans. In the studied reaches, flood and erosion processes occur respectively, on average, in a space equivalent to 2.6 and 20.6 channel widths. In unconfined landscapes, flood processes represent an area up to almost four times the area of erosion processes expected in a 50‐year period. In partly confined and confined environments, erosion processes are more likely to exceed flooding zone, and therefore need to be integrated in the mapping. This study helps better determine the conditions for which the full methodology of freedom space mapping is required or where semiautomated methods can be used. It provides useful guidelines for the implementation of the freedom space approach.

I - Introduction Au Quebec, dans le cadre des responsabilites devolues localement au milieu municipal en matiere d'amenagement du territoire, les municipalites doivent assumer la protection des milieux riverains et des plaines inondables en fonction des orientations et normes minimales definies par la Politique de Protection des Rives, du Littoral et des Plaines Inondables (PPRLPI) (MDDEFP, 2012). Cette politique propose un cadre normatif compose de deux types de zones inondables : un premier...

La gestion intégrée des risques d’inondation (GIRI) fait appel à la coordination de tous les niveaux et secteurs du gouvernement et de la société civile. Afin de favoriser la responsabilisation et l’appropriation des plans de GIRI par les communautés, l’implication des acteurs non gouvernementaux et des citoyens est de plus en plus valorisée. D’abord, l’émergence des approches participatives est exacerbée par l’optimisme face à la possibilité d’améliorer substantiellement la qualité et la portée des décisions, de gérer les conflits, de faciliter l'implantation des mesures non structurelles et de renforcer les capacités sociales au sein des communautés. Toutefois, certains avancent que l'intégration des non-experts dans le processus décisionnel brime l'impartialité de la procédure technocratique et que leur manque d’intérêt et de compétences limite la portée des démarches participatives. Des lacunes dans la représentativité des parties prenantes affectées et concernées au sein des instances peuvent aussi biaiser les aboutissants de la participation. De plus, la réticence des autorités à partager le pouvoir décisionnel limite l’institutionnalisation des approches participatives, tandis que la rigidité de l’appareil gouvernemental freine les élans participatifs des collectivités. Considérant l’intérêt grandissant des chercheurs, des décideurs et de la société civile envers les approches participatives dans le contexte de la gestion des inondations, cet article propose une synthèse de la littérature pour démêler les principales retombées et les limites de la participation., In order to promote community accountability for flood risks, the involvement of non-governmental actors and citizens is increasingly valued. The emergence of participatory approaches is consolidated by optimism about the possibility of improving the quality and scope of decisions, managing conflicts, facilitating the implementation of non-structural measures and strengthening social capacity within communities. However, some argue that the integration of non-experts undermines the impartiality of the decision-making process and that their lack of interest and expertise limits the scope of participatory approaches. Moreover, the authorities’ reluctance to share decision-making power limits the institutionalization of participatory approaches, whereas the rigidity of the governmental framework hampers participatory impulses within communities. Lack of stakeholder representativeness within the decision-making framework may also bias the outcome of participation. In addition, the reluctance of the authorities to share decision-making power limits the institutionalization of participatory approaches, while the rigidity of the government apparatus hinders the participatory momentum of communities. Considering the growing interest of researchers, policymakers and civil society in participatory approaches in the context of flood management, this article provides a synthesis of the literature to unravel the major benefits and limitations of participation.

Hydrosedimentary connectivity refers to the potential fluxes of water and sediment moving throughout a catchment. In forested catchments, these fluxes are altered by anthropogenic and natural disturbances. In this study, we modelled the interannual spatiotemporal evolution of hydrosedimentary connectivity influenced by forest cover change over the last four decades in the Mont-Louis catchment, a snow-dominated mountainous catchment in eastern Canada, which had 62% of its total surface affected by forest disturbances (mainly logging, but also wildfires and diseases) between 1979 and 2017. Using a geomorphometric index of connectivity (IC) and a historical forest cover database, we produced one IC map per year that considered anthropogenic and natural disturbances affecting the forest cover of the studied catchment. To account for vegetation recovery, forest disturbances were weighted with local hydrological recovery rates. Over the four decades, the mean IC of the Mont-Louis catchment dramatically increased by 35% in response to different types of disturbances. The spatial evolution of IC over the whole catchment and at the sub-catchment scale revealed that disturbance location has a strong influence on hydrosedimentary connectivity to the main channel. Our results also highlight the sharp contrast between IC computed from topography-based impedance to those computed from vegetation-based impedance. Forest disturbances appear to connect hillslopes with the hydrological network by producing pathways for sediment and water. The proposed reproducible framework might be used as a tool to assess and predict the potential impact of harvesting on rivers morphological dynamics and eventually preventing damage to fish habitat and sensitive river reaches.

There is growing support amongst scientists worldwide about the need for a shift in river management approaches to include hydrogeomorphic processes. However, the degree to which these concepts are transferred to governmental agencies and practitioners varies widely. In Quebec, for example, many stream restoration projects are based on the (incorrect) assumption that river mobility and its inevitable consequences (bank erosion of meanders, presence of woody debris in the channel) are problematic for salmonids. This paper presents examples drawn from current guidelines on stream restoration for fish habitat in Quebec to demonstrate the need to improve the knowledge exchange among scientists and decision makers about the positive impact of river mobility and large wood dynamics on biodiversity. Our observations reveal that existing guidelines for stream restoration in Quebec need to be revised to better integrate hydrogeomorphic concepts and to no longer assume that maintaining rivers in a static state is beneficial for fish. Adopting the “freedom space for rivers” approach would likely result in improved habitat as it combines natural processes related to mobility, flooding, and riparian wetland connectivity to determine the minimal space around rivers where development should not be allowed, thus allowing river processes to be restored.

This study presents the first regional groundwater hydrogeochemical portrait of the Bas-Saint-Laurent region (BSL), a region shaped by the Appalachians, a strong Quaternary glacial heritage, and co...

Large wood (LW) is a ubiquitous feature in rivers of forested watersheds worldwide, and its importance for river diversity has been recognized for several decades. Although the role of LW in fluvial dynamics has been extensively documented, there is a need to better quantify the most significant components of LW budgets at the river scale. The purpose of our study was to quantify each component (input, accumulation, and output) of a LW budget at the reach and watershed scales for different time periods (i.e., a 50-year period, decadal cycle, and interannual cycle). The LW budget was quantified by measuring the volumes of LW inputs, accumulations, and outputs within river sections that were finally evacuated from the watershed. The study site included three unusually large but natural wood rafts in the delta of the Saint-Jean River (SJR; Quebec, Canada) that have accumulated all LW exported from the watershed for the last fifty years. We observed an increase in fluvial dynamics since 2004, which led to larger LW recruitment and a greater LW volume trapped in the river corridor, suggesting that the system is not in equilibrium in terms of the wood budget but is rather recovering from previous human pressures as well as adjusting to hydroclimatic changes. The results reveal the large variability in the LW budget dynamics during the 50-year period and allow us to examine the eco-hydromorphological trajectory that highlights key variables (discharge, erosion rates, bar surface area, sinuosity, wood mobility, and wood retention). Knowledge on the dynamics of these variables improves our understanding of the historical and future trajectories of LW dynamics and fluvial dynamics in gravel-bed rivers. Extreme events (flood and ice-melt) significantly contribute to LW dynamics in the SJR river system.

For more than 20 years, hydrogeomorphological mapping in France has been considered as an efficient method of flood mapping that contributes to sustainable land development by taking into account occurrences of extreme events. The European Floods Directive (2007/60/CE) requires the production of maps showing water depths during extreme flood events. This article provides an overview of the numerical floodplain models (NFM) methodology, which uses hydrogeomorphological observations and LiDAR DEM data to produce water depth mapping. This article focuses on the NFM realised for the Meurthe River, close to the city of Nancy, France. The NFM methodology initially charts the floodplain from hydrogeomorphological mapping, then uses simple hydraulics for validation, and finally produces water depth maps with GIS processing. The resulting NFM shows good agreement with the historic 1947 flood. This methodology is a simple and complementary solution to hydraulics modelling. It provides a better way to communicate information on the extent extreme floods and shows the importance of hydrogeomorphology in flood hazard study and management.

Semi-alluvial rivers of the Gaspe Peninsula, Quebec, are prone to produce and transport vast quantities of large wood (LW). The high rate of lateral erosion owing to high energy flows and noncohesive banks is the main process leading to the recruitment of large wood, which in turn initiates complex patterns of wood accumulation and reentrainment within the active channel. The delta of the Saint-Jean River (SJR) has accumulated large annual wood fluxes since 1960 that culminated in a wood raft of > 3-km in length in 2014. To document the kinetics of large wood on the main channel of SJR, four annual surveys were carried out from 2010 to 2013 to locate and describe > 1000 large wood jams (LWJ) and 2000 large wood individuals (LWI) along a 60-km river section. Airborne and ground photo/video images were used to estimate the wood volume introduced by lateral erosion and to identify local geomorphic conditions that control wood mobility and deposits. Video camera analysis allowed the examination of transport rates from three hydrometeorological events for specific river sections. Results indicate that the volume of LW recruited between 2010 and 2013 represents 57% of the total LW production over the 2004–2013 period. Volumes of wood deposited along the 60-km section were four times higher in 2013 than in 2010. Increases in wood amount occurred mainly in upper alluvial sections of the river, whereas decreases were observed in the semi-alluvial middle sections. Observations suggest that the 50-year flood event of 2010 produced large amounts of LW that were only partly exported out of the basin so that a significant amount was still available for subsequent floods. Large wood storage continued after this flood until a similar flood or an ice-breakup event could remobilise these LW accumulations into the river corridor. Ice-jam floods transport large amounts of wood during events with fairly low flow but do not contribute significantly to recruitment rates (ca. 10 to 30% early). It is fairly probable that the wood export peak observed in 2012 at the river mouth, where no flood occurred and which is similar to the 1-in 10-year flood of 2010, is mainly linked to such ice-break events that occurred in March 2012.

International audience

There is great interest worldwide to reconnect floodplain wetlands to their rivers. Whilst the surface water connection between rivers and wetlands is fairly well understood, the linkages via groundwater are not well known. In this study, it is hypothesized that the significance of the groundwater pathways between rivers and wetlands is largely determined by the geomorphic setting of the riverine corridor. This was tested by measuring the response of water levels and temperatures in floodplain groundwater and in wetlands to river pulses in two geomorphologically distinct riverine corridors in Southern Quebec. In the De la Roche River (DLR; 145 km2), the floodplain is narrow and the alluvial sediments consist of sandy silt (wetland A; abandoned meander) or clayey silt (wetland B; stable floodplain), depending on the location. During within-channel floods, exchanges of water between the river and the floodplain are limited to some bank recharge where the alluvial sediments are permeable, and over-bank stora...

Une coulée de slush (bouillie de neige fondante) est un écoulement rapide constitué d’un mélange de neige fondante, d’eau, de boue et de débris de toutes sortes. Les sept sites analysés démontrent que les coulées de slush peuvent survenir dans des contextes topographiques fort différents qui présentent toutefois des similitudes au niveau du mode d’enneigement et des conditions hydro-météorologiques. Les coulées de slush étudiées démarrent dans des ruisseaux d’ordre 1 ou 2, étroits et peu profonds, de pente très variable (de 1° à plus de 30°), qui sont comblés par des bouchons de neige dense soufflée par le vent ou transportée par les avalanches. Parce qu’ils s’opposent à la libre circulation des eaux de fusion lors des périodes de fonte accélérée, ces bouchons de neige favorisent la saturation du manteau neigeux jusqu’à la rupture sous l’effet combiné de la pression hydrostatique et de la gravité. Les onze coulées analysées, qui se sont produites entre 1936 et 2013, permettent de définir deux scénarios hydro-météorologiques propices à leur déclenchement : 1) des redoux de longue durée caractérisés par des températures qui restent positives pendant plusieurs jours consécutifs sans apport de précipitations liquides; 2) des redoux relativement courts (moins de 48 heures) couplés à des précipitations liquides abondantes. Largement méconnues au Québec, les coulées de slush pourraient être plus fréquentes à l’avenir en réponse au réchauffement climatique en cours.

Menee sur un troncon de riviere de taille moyenne, cette recherche analyse quotidiennement les processus de formation et de croissance de la glace dans une riviere graveleuse caracterisee par une succession seuil-mouille. Elle documente egalement l’effet de la morphologie du chenal et des conditions hydrometeorologiques sur la croissance et l’evolution du couvert de glace. Des photographies numeriques perpendiculaires au chenal et une documentation des caracteristiques morphologiques du chenal et de la glace ont ete realisees quotidiennement. Les resultats montrent que la glace apparait simultanement dans les seuils et la mouille, mais que la formation complete du couvert de glace survient un mois plus tot dans la mouille. Cette difference s’explique par des mecanismes de croissance variables selon les unites morphologiques. Dans les seuils, la glace croit des berges vers le centre du chenal par accumulation de particules de frasil et par la croissance de la glace thermique. La croissance du couvert se produit egalement autour des blocs protuberants dans le centre du chenal grâce a l’emergence de la glace de fond. Dans la mouille, le couvert de glace progresse a partir des berges vers le centre du chenal principalement par la glace thermique, mais aussi par accumulation de minces particules de frasil. Dans les seuils et la mouille, les taux de croissance quotidiens cumules revelent des profils similaires avec une transition marquee dans la vitesse de croissance du couvert (rapide/lente). Le suivi quotidien de la couverture glacielle a permis de documenter la dynamique de formation et l’evolution spatio-temporelle de la couverture glacielle. Une coulee de neige liquefiee est survenue au mois de janvier dans un tributaire mineur et a provoque la desorganisation de la morphologie glacielle ainsi que la formation d’un imposant cone glaciel a la confluence.

In gravelly floodplains, streamflood events induce groundwater floodwaves that propagate through the alluvial aquifer. Understanding groundwater floodwave dynamics can contribute to groundwater flood risk management. This study documents groundwater floodwaves on a flood event basis to fully assess environmental factors that control their propagation velocity, their amplitude and their extension in the floodplain, and examines the expression of groundwater flooding in the Matane River floodplain (Quebec, Canada). An array of 15 piezometers equipped with automated level sensors and a river stage gauge monitoring at 15-minute intervals from September 2011 to September 2014 were installed within a 0.04-km2 area of the floodplain. Cross-correlation analyses were performed between piezometric and river-level time series for 54 flood events. The results reveal that groundwater floodwave propagation occurs at all flood magnitudes. The smaller floods produced a clear groundwater floodwave through the floodplain, while the largest floods affected local groundwater flow orientation by generating an inversion of the hydraulic gradient. Propagation velocities ranging from 8 to 13 m/h, which are two to three orders of magnitude higher than groundwater velocity, were documented while the induced pulse propagated across the floodplain to more than 230 m from the channel. Propagation velocity and amplitude attenuation of the groundwater floodwaves depend both on flood event characteristics and the aquifer characteristics. Groundwater flooding events are documented at discharge below bankfull (< 0.5 Qbf). This study highlights the role of flood event hydrographs and environmental variables on groundwater floodwave properties and the complex relationship between flood event discharge and groundwater flooding. The role that groundwater floodwaves play in flood mapping and the ability of analytical solutions to reproduce them are also discussed.

The freedom space concept applies hydrogeomorphic principles to delineate zones that are either frequently flooded or actively eroding, or that include riparian wetlands. Freedom space limits mapped for three rivers in southern Quebec (Canada) were assessed to determine whether they would still be valid under a future climate using a sensitivity analysis approach with numerical models predicting mobility of meanders (RVRMeander) and flood stage (HEC-RAS). The freedom space limits were also used in a cost–benefit analysis over a 50-year period where costs consist of loss or limitations to the right of farming and construction in this zone, whereas benefits are avoided costs for existing or future bank stabilization structures and avoided costs of flooding in agricultural areas. The economic value of ecosystem services provided by riparian wetlands and increased buffer zones within the freedom space were also included in the analysis. Results show that freedom space limits would be robust in future climate, and show net present values ranging from CDN$0.7 to $3.7 million for the three rivers, with ratios of benefits over costs ranging between 1.5:1 and 4.8:1. River management based on freedom space is thus beneficial for society over a 50-year period.

The study is based on a complex and unique data set of 222Rn activity, water stable isotopes, and physicochemical parameters (i.e., temperature, electrical conductivity, pH) produced to better understand the hydrogeochemical connectivity between groundwater and river water in a meander floodplain of the Matane River, QC, Canada. Using an array of 21 piezometers implanted into an 18 ha meander floodplain, the geochemical properties of shallow groundwater were investigated over nine sampling campaigns between 2011 and 2017. The river is in gaining conditions most of the year, although losing conditions are temporally observed along high river discharge. The objective was to explore the seasonal geochemical variations in response to river discharge with a specific focus on the spatial extent of the hyporheic zone. A thorough examination of temperature, δ18O, electrical conductivity, and 222Rn in groundwater indicated that the geochemical properties of shallow groundwater varied in space and time. Multivariate statistical analyses (i.e., clustering and canonical redundancy analysis) showed that river discharge is a key factor controlling shallow groundwater geochemistry, whatever the season. The hyporheic zone, where groundwater mixes with river water, extended far from the riverbank. These results support the concept of the hyporheic corridor and integrated river management by providing a geochemical viewpoint on river-aquifer connectivity.

Confluences are key nodes of river systems that have the potential of disrupting downstream longitudinal trends in the main river through inputs of water, sediment, wood or ice delivered from tributaries. From a geomorphological perspective, confluence zones are particularly active and thus susceptible to increased flooding and bed instability, which, in turn, pose serious threats to infrastructure. However, not all confluences are active. Despite major advances in our knowledge of confluence dynamics, there has been limited progress in the development of low complexity, practical tools that use remotely sensed data to predict the spatial distribution of the main river's sensitivity to tributary inputs. We have thus developed a novel semi-automated GIS model that uses a fuzzy approach to integrate key factors (unit stream power, valley confinement and sediment connectivity potential) in order to map the distribution of the confluence morphological sensitivity (CMS) index at the watershed scale. The GIS model was tested using digital elevation models of high (LiDAR, 1 m) and coarser (10 m) resolution in the Coaticook and Gaspesie watersheds (Quebec, Canada). Results indicate that the model is useful for detecting geomorphologically active confluences and the resulting sensitivity of the main channel and thus has potential to be used in diverse river management applications (e.g., hazard reduction and freedom space mapping).

This study aims to investigate ice-jam regimes on the Mistassini River by analyzing the impacts of ice-jams on riverbank morphologies and ecosystems. The Mistassini River experienced severe ice-jams in May 2011, which caused the destruction of 20 riverside houses. Geomorphological and ecological descriptions of riverbanks helped identify and spatialize ice impacts along four sections of the river with contrasted morphologies: meanders, linear with islands, linear, and sinuous. Channel characteristics were investigated to document the typical spatial context in which ice-impact features dominate on the Mistassini River. In each section, ice-jam frequencies and magnitude were determined through the dendrochronological analysis of ice scars found on riparian trees. Our results show that ice-impacted banks are characterized by a two-level structure separated by a steep (average slope = 25 %) and irregular talus overlaid by freshly deposited alluvia. Those banks are colonized by abundant shrubs and few trees, both presenting numerous ice scars. This bank type forms during severe eroding events where the ice flood reaches levels that are much higher than bankfull. Most ice-impacted banks tend to occur in two preferential hydro-geomorphological contexts: (1) a downstream increase in the flow area and width–depth ratio within a mild slope channel; (2) a sudden narrowing in an entrenched channel. We finally show that the proportion of two-level banks increases in the downstream direction as ice-jam frequencies decrease and magnitudes increase. These results suggest that ice-impact features are more likely to be formed in the downstream sections, due to ice-jam higher level of magnitude.

Les Atlas de Zones Inondables (AZI) par approche hydrogéomorphologique (HGM) sont-ils efficaces pour communiquer sur l’aléa inondation ? Quelles évolutions sont envisageables pour une plus large diffusion de l’approche ? Une enquête menée auprès de personnes non expertes et une analyse du contenu de la légende d’AZI du Sud de la France nous permettent de mettre en avant les principales limites de ces cartes. Ces limites concernent non seulement le type d’informations géographiques produites, ou encore la sémiologie graphique, mais aussi le décalage possible entre l’interprétation du terrain par le géomorphologue et la compréhension de la carte finale par un lecteur. La mise en évidence de ces limites nous conduit à proposer une légende simplifiée qui assurerait une meilleure compréhension des informations géographiques produites et une réalisation plus rapide pour le géomorphologue. Are Flood Zones Atlas (AZI; Atlas de Zones Inondables) by hydrogeomorphological (HGM) approach effective in communicating flood hazard? What changes are possible to promote the dissemination of this approach? A survey carried out among semi-experts and non-experts and an analysis of legend contents of flood zone atlas allow us to highlight the main limitations of the actual maps. Such limitations include the type of geographic information created, graphic semiology, but also the possible gap between the interpretation of the field by geomorphologists and the understanding of the final mapping by non-experts. Highlighting these limits leads to the proposal of a simplified AZI legend which should allow a better understanding of geographic information and a faster achievement for geomorphologists. 洪水区地图集（AZI; Atlas de Zones Inondables）是否能通过水文地貌（HGM）方法有效地显示洪水发生的风险？大规模地推广该方法将带来哪些方面的变革？针对 半专家和非专家进行的一项调查以及对洪水区地图集图例内容的分析使我们能够指出地图的主要局限性。 这些限制包括所创建的地理信息的类型，图形符号，以及地貌学家对所绘制区域的解释与非专家的理解之间可能存在的差距。 鉴于这些限制，我们提出简化AZI图例，如此应该能够使普通读者更好地理解地理信息，而地貌学家也能提高绘图的效率。

The management tools for understanding and preventing flood risk are generally developed from knowledge pertaining to the fields of hydrology and hydraulics. Hazard mapping is mainly based on hydraulic modeling, while the analysis of the flood risk trajectory considers the effect of climate change, spatial planning and socioeconomic policies on the hydrological regime. In the vast majority of cases, the analysis of the flood hazard is based on the link between hydrology and hydraulics, leading to an incomplete representation of the phenomenon. The flood hazard depends on the evolution of the hydrological regime, but also on changes in the geometry and hydraulic capacity of the channels that are related to the hydrological and sedimentary regimes of the drainage basin. Integrating concepts and knowledge from hydrogeomorphology can contribute to the emergence of a more holistic vision of flooding phenomena. At a time when flood risk management must increasingly be considered in a cross-disciplinary way, hydrogeomorphology tools and concepts can enhance the work of any manager or professional in the field of flood risk.

Ground imagery, which produces large amounts of valuable data at high frequencies, is increasingly used by fluvial geomorphologists to survey and understand processes. While such technology provides immense quantities of information, it can be challenging to analyze and requires automatization and associated development of new methodologies. This paper presents a new approach to automate the processing of image analysis to monitor wood delivery from the upstream Rhone River (France). The Genissiat dam is used as an observation window; all pieces of wood coming from the catchment are trapped here, hence a wood raft accumulates over time. In 2011, we installed an Axis 211W camera to acquire oblique images of the reservoir every 10 min with the goal of automatically detecting a wood raft area, in order to transform it to wood weight (t) and flux (t/d). The methodology we developed is based on random forest classification to detect the wood raft surface over time, which provided a good classification rate of 97.2%. Based on 14 mechanical wood extractions that included weight of wood removed each time, conducted during the survey period, we established a relationship between wood weight and wood raft surface area observed just before the extraction (R2 = 0.93). We found that using such techniques to continuously monitor wood flux is difficult because the raft undergoes very significant changes through time in terms of density, with a very high interday and intraday variability. Misclassifications caused by changes in weather conditions can be mitigated as well as errors from variation in pixel resolution (owing to camera position or window size), but a set of effects on raft density and mobility must still be explored (e.g., dam operation effects, wind on the reservoir surface). At this stage, only peak flow contribution to wood delivery can be well calculated, but determining an accurate, continuous series of wood flux is not possible. Several recommendations are made in terms of maximizing the potential benefit of such monitoring.

summary Interactions between surface water and groundwater can occur over a wide range of spatial and temporal scales within a high hydraulic conductivity gravelly floodplain. In this research, dynamics of river– groundwater interactions in the floodplain of the Matane River (eastern Canada) are described on a flood event basis. Eleven piezometers equipped with pressure sensors were installed to monitor river stage and groundwater levels at a 15-min interval during the summer and fall of 2011. Results suggest that the alluvial aquifer of the Matane Valley is hydraulically connected and primarily controlled by river stage fluctuations, flood duration and magnitude. The largest flood event recorded affected local groundwater flow orientation by generating an inversion of the hydraulic gradient for 16 h. Piezometric data show the propagation of a well-defined groundwater floodwave for every flood recorded as well as for discharges below bankfull (

Terraces in the lower Matane River Valley (eastern Quebec, Canada) were studied to describe the stratigraphic architecture of a glacially eroded valley fill. The Matane River Valley hosted a glacial tongue connected with a regional ice cap during the early opening of a calving bay in the modern St. Lawrence Estuary and was subsequently flooded by the Goldthwait Sea as the Laurentide Ice Sheet margin retreated. Stratigraphic, sedimentological, light detection and ranging (LIDAR), and geochemical analyses as well as radiocarbon measurements allowed the identification of four stratigraphic units deposited during and following deglaciation: glacial outwash (unit I), delta bottomsets (unit II), delta foresets (unit III), and fluvial deposits (unit IV). Stable isotope (13C) and C/N ratio values reveal the relative influence of the two end-members (algae and terrestrial plants) on organic matter sources between the stratigraphic units. Climate, major relative sea level fluctuations, and sediment yield are recognized as the main controls on depositional environments in glacially eroded valleys of the northern shore of the Gaspé Peninsula during the Holocene. This paper presents a model of the evolution of the Matane River Valley, which in many points is similar to existing conceptual fjord-valley fill models.

Trois processus distincts agissant en interrelation contribuent a l’erosion des berges en bordure des cours d’eau : les mouvements de masse, l’erosion fluviale et les mouvements subaeriens. Ces derniers resultent de l’effet conjugue des cycles gel-degel, des cycles d’humidification-dessiccation et de la desagregation des sediments par les gouttes de pluie et le ruissellement. Les deux premiers processus erosifs sont les plus connus. Les mouvements subaeriens sont moins documentes car ils sont generalement consideres comme un mecanisme preparatoire affaiblissant la berge et facilitant l’erosion par les deux autres processus. Cette etude examine les mouvements subaeriens en tant que processus erosifs a l’aide d’observation in situ permettant de decrire et de quantifier leur contribution a l’erosion des berges. Une berge en erosion sur la riviere Ouelle, Quebec, a ete etudiee a l’aide de leves topographiques mensuels issus d’un LIDAR terrestre (Scan-station II de Leica). Les leves d’une resolution d’1 cm (10 000 points/m2) couvrent une periode de dix mois et permettent de suivre l’evolution saisonniere des processus erosifs. Les resultats revelent que les mouvements subaeriens entrainent des epaisseurs d’erosion entre 5 et 50 mm/mois sur l’ensemble de la berge ; l’epaisseur d’erosion variant fortement selon le mois et la position sur la berge. Une analyse qualitative des processus contribuant a l’evolution de la berge a ete faite a l’aide d’une serie horaire de photographies issues d’une camera automatisee installee en permanence sur le site. Les variations saisonnieres des taux d’erosion lies aux mouvements subaeriens ont ete mises en relation avec les donnees meteorologiques d’Environnement Canada (2010). Les mouvements subaeriens sont plus frequents lorsque la temperature oscille autour de zero. Les mouvements subaeriens sont plus que de simples processus preparatoires et que leur contribution a titre d’agent erosif est probablement sous-estimee. Les variations temporelles soulignent l’importance de considerer les saisons dans l’etude de l’erosion des berges pour une meilleure evaluation de l’amplitude et de la frequence des differents processus d’erosion des berges des cours d’eau.

Hydro-geomorphological assessments are an essential component for riverine management plans. They usually require costly and time-consuming field surveys to characterize the spatial variability of key variables such as flow depth, width, discharge, water surface slope, grain size and unit stream power throughout the river corridor. The objective of this research is to develop automated tools for hydro-geomorphological assessments using high-resolution LiDAR digital elevation models (DEMs). More specifically, this paper aims at developing geographic information system (GIS) tools to extract channel slope, width and discharge from 1 m-resolution LiDAR DEMs to estimate the spatial distribution of unit stream power in two contrasted watersheds in Quebec: a small agricultural stream (Des Feves River) and a large gravel-bed river (Matane River). For slope, the centreline extracted from the raw LiDAR DEM was resampled at a coarser resolution using the minimum elevation value. The channel width extraction algorithm progressively increased the centerline from the raw DEM until thresholds of elevation differences and slopes were reached. Based on the comparison with over 4000 differential global positioning system (GPS) measurements of the water surface collected in a 50 km reach of the Matane River, the longitudinal profile and slope estimates extracted from the raw and resampled LiDAR DEMs were in very good agreement with the field measurements (correlation coefficients ranging from 0 · 83 to 0 · 87) and can thus be used to compute stream power. The extracted width also corresponded very well to the channel as seen from ortho-photos, although the presence of bars in the Matane River increased the level of error in width estimates. The estimated maximum unit stream power spatial patterns corresponded well with field evidence of bank erosion, indicating that LiDAR DEMs can be used with confidence for initial hydro-geomorphological assessments. Copyright © 2013 John Wiley & Sons, Ltd.

The Saint-Jean River (SRJ) in Eastern Canada is prone to the formation of very large rafts of wood. Managers of the SJR suspected these jams to influence salmon migration and carried out a dismantling operation to remove large wood accumulated in a 1.2 km long wood raft. This operation became a great opportunity to address key issues relating to large wood dynamics in a fluvial system: residence time and flood contribution to wood recruitment and transport. During the dismantling, we systematically sampled 319 trees from which year of death could be estimated from dendrochronology and year of accumulation in the raft could be obtained from satellite and aerial photos. These two dates allowed us to quantify the residence time for 262 datable large wood (LW) within the fluvial system, to examine the peak years of LW recruitment and to correlate the raft growth rate with hydrometeorological conditions since 1993. The results also emphasized four types of LW flood related to wood dynamics: 1) an erosive flood that produces a large amount of wood in river, 2) a mobilizing flood that carries large quantities of wood, 3) a flood mix that both recruits and transports large quantities of wood, and 4) an ice-breakup flood.

The aim of this work is to compare macroturbulent coherent structures (MCS) geometry and organization between ice covered and open channel flow conditions. Velocity profiles were obtained using a Pulse-Coherent Acoustic Doppler Profiler in both open channel and ice-covered conditions. The friction imposed by the ice cover results in parabolic shaped velocity profiles. Reynolds stresses in the streamwise (u) and vertical (v) components of the flow show positive values near the channel bed and negative values near the ice cover, with two distinctive boundary layers with specific turbulent signatures. Vertically aligned stripes of coherent flow motions were revealed from statistics applied to space-time matrices of flow velocities. In open channel conditions, the macroturbulent structures extended over the entire depth of the flow whereas they were discontinued and nested close to the boundary walls in ice-covered conditions. The size of MCS is consequently reduced in scale under an ice cover. The average streamwise length scale is reduced from 2.5 to 0.4Y (u) and from 1.5 to 0.4Y (v) where Y is the flow depth. In open channel conditions, the vertical extent of MCS covers the entire flow depth, whereas the vertical extent was in the range 0.58Y–1Y (u) and 0.81Y–1Y (v) in ice-covered conditions. Under an ice cover, each boundary wall generates its own set of MCS that compete with each other in the outer region of the flow, enhancing mixing and promoting the dissipation of coherent structures. Copyright © 2012 John Wiley & Sons, Ltd.

Closed access. This book chapter was published in the book, Fluvial Remote Sensing for Science and Management [© John Wiley & Sons, Ltd.] and the definitive version of the chapter is available at: http://dx.doi.org/10.1002/9781119940791.ch15

En 2002, le gouvernement du Québec a instauré la Politique nationale de l’eau, qui consacre la gestion intégrée de l’eau par bassin versant (GIEBV) comme le mode de gestion le plus approprié. L’étude se concentre sur la représentation des connaissances scientifiques dans la GIEBV. Dix-huit administrateurs ont été interrogés sur leur perception de cette gestion et du rôle qu’y jouent les connaissances scientifiques. Il ressort de cette étude toute l’importance des connaissances scientifiques dans les prises de décision, en comparaison des connaissances traditionnelles, ainsi que le rôle de certains administrateurs dans l’explication des connaissances scientifiques aux autres. Les gestionnaires ont soulevé plusieurs problèmes comme le manque de financement, le manque de connaissances scientifiques disponibles et le manque de pouvoir pour agir., In 2002, a national water policy was announced by the Québec government, The objective of this policy was to promote integrated water resources management (IWRM) as the most appropriate to the province. Our study focuses on the perception of scientific knowledge by the people directly involved in the implementation of the IWRM in Québec. Eighteen administrators were asked questions regarding their opinion of management procedures and the role of scientific knowledge within the IWRN. Scientific knowledge was considered to be paramount compared to traditional knowledge; the contribution of some managers toward imparting scientific knowledge to others was also included. Management highlighted a number of issues, such as inadequate funding, a shortfall in the availability of scientific knowledge and restricted authority to act., En el año 2002, el gobierno de Quebec instaura la Política Nacional de Agua, que afecta la gestión integral del agua por cuenca (GIEBV) como el mejor medio de gestión. Este artículo se concentra en la representación de conocimientos científicos en el GIEBV. Dieciocho administradores fueron interrogados sobre su percepción de esta gestión y sobre el rol de los conocimientos científicos. Este estudio hace resaltar toda la importancia de los conocimientos científicos en las tomas de decisión, en comparación con los conocimientos tradicionales; así como el rol de algunos administradores en la explicación de conocimientos científicos hacia otros. Los administradores han planteado varios problemas: la falta de financiamiento, la ausencia de conocimientos científicos disponibles y el poco poder para actuar.

L’hydrogeomorphologie fluviale est peu reconnue dans les politiques de gestion et d’amenagement du territoire quebecois. Une meilleure reconnaissance permettrait pourtant une gestion plus eclairee des cours d’eau par une integration de leur dimension dynamique. Cette etude teste l’applicabilite d’une methode de sectorisation de cours d’eau en unites morphodynamiques homogenes. Cette compartimentation resulte d’une division longitudinale sur la base des changements des valeurs de puissance specifique, de composition sedimentaire des berges, du confinement dans la vallee et de geometrie planimetrique. La caracterisation est appliquee a un corridor de la riviere Neigette comportant une diversite de formes et de processus frequemment retrouves dans les rivieres du Quebec. Les resultats suggerent la presence de trois unites morphodynamiques: divagant a chenaux multiples, meandres dynamiques et meandres stables. La methode presente une forte capacitea discriminer ces environnements morphodynamiques ainsi que leurs limites respectives. La puissance specifique presente a elle seule une forte capacite de discrimination. L’efficacite de la demarche, l’aisance de son application et sa flexibilite font de cette approche un solide outil a integrer dans le processus de gestion des environnements fluviaux. An illustrated methodology for the morphodynamic sectoring of the Neigette River (Quebec) Fluvial hydrogeomorphology is little recognized in policy management and planning in Quebec. A better understanding would result in more enlightened planning for waterways. The deficiency could result from the fact that too few methodologies have been developed that take account of the particular nature of Quebec rivers. This study tests the applicability of a methodology of dividing rivers into homogeneous morphodynamic units. This compartmentalization results from the analysis of longitudinal changes in stream power, sedimentary composition of the banks, channel entrenchment, and planform geometry. The method is tested on a section of the Neigette River, which encompasses a wide variety of forms and processes frequently found in Quebec rivers. Results suggest the presence of three morphodynamic sections: wandering with multiple channels, dynamic meandering and stable meandering. The method provides an effective basis for discriminating between these morphodynamic environments and their respective limits. Stream power is the variable with the greatest discriminating capacity. The efficacy of the approach, the ease of its application, and its flexibility make this a valuable tool for the management of fluvial environments.

Frazil ice forms in open water areas of high turbulent intensity and accumulates downstream along flatter river segments. The activation of production zones, in relation to hydro-climatic parameters, directly affects the infilling of frazil sinks. Past field investigations have described strong relationships between riverbed scour and undercover frazil accumulation but few have documented the dynamics of bed deformation in relation to the accumulation of frazil ice over an entire winter season. Here, we present the chronology of the development of a hanging dam at a pool section over the 2007–2008 ice period. The characteristics of upstream frazil ice production and ice cover growth is documented using a river corridor approach. At a pool section, undercover frazil ice accumulation behaviour, water level variations, hydro-climatic conditions and riverbed deformations are also documented. Innovative dynamic bed-rods integrating three-axis accelerometer pendant loggers were deployed at the bed to obtain a dynamic measurement of erosional and depositional activity over the frazil pool. Data shows a relation between bedform deformation and ice cover formation. Analysis reveals the spatio-temporal variation of physical attributes of ice cover, undercover frazil accumulation and bedforms. Collected data is used to analyse the relationship between riverbed deformation and overlying ice forms. Copyright © 2011 John Wiley & Sons, Ltd.

This paper proposes a conceptual model relating the large-scale distribution of river ice types and dynamics to the longitudinal sequence of river forms and flows typically encountered along the sedimentary links of gravel-bed rivers. Sedimentary links are discrete river segments each characterized by a node of coarse sediment recruitment followed by a gradual downstream fining of substrate and an associated reduction of channel slope. Because these downstream changes in substrate and slope are associated with changes in channel morphology and hydraulics, they create a longitudinal sequence of river environments moving from steep, fast flowing and highly turbulent boulder bed channels at the head of links to meandering low-gradient sand channels with calm flows at the downstream end. We describe and show examples of how these spatial variations in the geomorphology and flow characteristics of gravel-bed rivers should interact with river ice processes to produce a predictable ‘most probable’ large-scale pattern of river ice types and dynamics. Copyright © 2011 John Wiley & Sons, Ltd.

Cet article examine l’effet des barrages sur le synchronisme des crues du fleuve Moulouya (Maroc) ainsi que les incidences sur l’ajustement morphologique de ses tributaires intermittents. Une analyse comparative des débits mensuels moyens enregistrés de part et d’autre des infrastructures de retenue montre une diminution du débit moyen de 52 % et une diminution des débits annuels maximaux de 33 %. Les fréquences des débits mensuels qui dépassent des seuils de 50, 75 et 100 m³•s-1 sont respectivement diminuées de 55, 47 et 22 %. L’interception des eaux nivèle les variations intermensuelles et conduit à une homogénéisation du régime des débits (le coefficient d’immodération des valeurs médianes passe de 8,99 à 1,23). L’analyse de la coïncidence temporelle des crues indique que l’activation du tronçon principal à l’aval des infrastructures est indépendante des apports perçus à l’amont. La description de profils longitudinaux de tributaires situés à l’aval des infrastructures révèle plusieurs singularités morphologiques, tels des profils convexes, ruptures de pentes et formes d’accumulation perchées sur la plaine alluviale. Trois modèles d’ajustements morphologiques (convexe, mixte et par inondation) sont proposés pour expliquer ces singularités et reposent sur la nature du synchronisme hydrologique entre le tronçon principal et ses affluents. Le modèle d’ajustement convexe est lié à un type d’activation hydrologique synchrone (tronçon principal et tributaire actif) et permet d’expliquer la présence de profils convexes. Le modèle d’ajustement mixte est associé à une activation hydrologique asynchrone (tributaire actif et tronçon principal inactif) et explique l’incision et le prolongement de tributaires ainsi que des formes d’accumulation perchées sur la plaine alluviale. Enfin, le modèle d’ajustement par inondation (tronçon principal actif et tributaire inactif) rend compte des indices de mauvaise intégration tels que les ruptures de pente. Il est suggéré que l’effet d’asynchronisme des crues induit par les barrages est le principal facteur qui détermine le type d’ajustement morphologique des tributaires dans les environnements semi-arides., This paper looks at the effect of dam impoundments on the flood synchronicity of the Moulouya River (Morocco) and its consequences on the morphological adjustments of its ephemeral tributaries. The comparative analysis of monthly discharges measured upstream and downstream of the dams shows a diminution of 52% of mean discharges and a diminution of 33% of annual maximum discharges. The frequencies of discharges reaching 50, 75 and 100 m³•s-1 values are respectively reduced by 55, 47 and 22%. Monthly variations are levelled and this leads to a homogeneous discharge regime (coefficient of immoderation for median values decreases from 8.99 to 1.23). Flood coincidence in time is assessed and shows that downstream discharges are independent of upstream discharges. The description of longitudinal profiles of tributaries downstream of the dams reveals morphological singularities such as convex profiles, perched accumulation forms on the alluvial plain and knickpoints. Three models of morphological adjustments (convex, mixed and by flooding) based on the synchronicity of floods between the main channel and its tributaries are proposed to explain these morphological observations. The convex adjustment model occurs when floods are synchronous and explains the observation of convex profiles. The mixed adjustment model occurs when tributaries are flooded and the main channel remains to its base level and explains morphological forms such as scouring of tributaries or perched accumulation forms on the alluvial plain. Finally, the model of adjustment by flooding occurs when the main channel is activated and the tributaries remain inactive and explains knickpoints and the lack of integration observed at the mouths of the tributaries. Asynchronous flooding induced by dam impoundments is proposed as the main factor affecting tributary adjustments in semi-arid environments.