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Vegetation is a key driver for carbon uptake from the atmosphere to the land. Yet episodes of plant stress and mortality associated with drought and heat waves due to persistent lack of precipitation have been reported over the last decades and are expected to increase under ongoing climate change. It is presumed that climate-related vegetation stress results in progressively worsening plant health and rising mortality. However, the mechanisms driving such mortality are still up for debate because of the complex interconnections between the processes and the factors. Monitoring plant stress and mortality at the ecosystem level remains challenging to quantify since long-term, tree-individual, reliable observations are uncertain. For this reason, here we adapted a satellite-model approach to work on regional forests, before up scaling the results to the global forest.In Belgium, the Wallonia region is covered by 30% forests which are the highest among all the three regions. While with the consecutive recent extreme events especially the droughts and heat waves of 2018, 2019, 2020, and 2022 caused water stress and bark beetle attack. According to the 35 years (1985-2022), land use land cover change extracted by LANDSAT 5,7, and 8 satellites, there is no significant change in forest land in Wallonia, Belgium. Meanwhile, in the current years 2021-2022, there is a decrease in the tree canopy with intensive forest management due to tree plant stress. On the other hand, in Wallonia, the forest is distributed in a significant patch of broadleaves, coniferous leaves, and mixed forest. However, we found that consecutive drought events cause water stress on specific plant species like Norway spruce which are in vulnerable states. For example: in a mixed forest when bark beetle or Scolytinae attacked the spruce tree it is more attracted to the other trees and in this consequence tree species –like birch and oak –are now also in premature death or deteriorating tree health. In this study, we are using a high spatial resolution (25cm) remote sensing images using Artificial Intelligence and machine learning techniques to find out pixel-based individual plant stress or mortality. In addition, the high-resolution tree mortality extracted data will be used to calibrate CARAIB dynamic vegetation model and analyze the impact of extreme events on trees during the recent past and the future (until 2070). In conclusion, from this study, we plan to improve our model regarding the implementation of plant traits and species mortality aspects towards a better prediction of forest tree species' vulnerability to future extreme weather events.

Landfill managers are subject to obligations which include the regular monitoring of the topographical and land cover (LC) evolution of the site. This research aims at developing a cost-effective non-intrusive methodology for mapping landfill LC features. To this end, a state-of-the-art OBIA open-source workflow based on an integration of GRASS GIS and Python programming environment was adapted and applied to 3-cm optical UAV image acquired over the landfill site of Hallembaye (Belgium). The results of this 8-class supervised classification are promising with an overall accuracy of 80.5%. This study shows that existing open-source processing chain can be adapted to UAV imagery. In addition, the added value of feature selection and of textural information provided by very high-resolution optical data is also highlighted. Finally, this study illustrates the potential of machine learning for the monitoring of landfill sites.

Land Use/Cover changes are crucial for the use of sustainable resources and the delivery of ecosystem services. They play an important contribution in the climate change mitigation due to their ability to emit and remove greenhouse gas from the atmosphere. These emissions/removals are subject to an inventory which must be reported annually under the United Nations Framework Convention on Climate Change. This study investigates the use of Sentinel-2 data for analysing lands conversion associated to Land Use, Land Use Change and Forestry sector in the Wallonia region (southern Belgium). This region is characterized by one of the lowest conversion rates across European countries, which constitutes a particular challenge in identifying land changes. The proposed research tests the most commonly used change detection techniques on a bi-temporal and multi-temporal set of mosaics of Sentinel-2 data from the years 2016 and 2018. Our results reveal that land conversion is a very rare phenomenon in Wallonia. All the change detection techniques tested have been found to substantially overestimate the changes. In spite of this moderate results our study has demonstrated the potential of Sentinel-2 regarding land conversion. However, in this specific context of very low magnitude of land conversion in Wallonia, change detection techniques appear to be not sufficient to exceed the signal to noise ratio.

Through the practice of irrigation, surface water reservoirs (SWRs) contribute to the socio-economic development and food production activities of populations in Sub-Saharan Africa (SSA). However, they tend to dry up prematurely. One solution to circumvent these irrigation water shortages is to ensure their conjunctive use with groundwater. The objective of this study is to better understand the contribution of SWRs to groundwater recharge and to determine if groundwater may be considered as a complementary local resource for irrigation. The study was carried out on two watersheds in Burkina Faso, Kierma and Mogtedo. The spatiotemporal analysis of piezometric and SWRs level records coupled with physico-chemical analyses of water was used to characterize exchanges between SWRs and groundwater. The regional groundwater recharge at the scale of the watersheds was assessed. At the SWRs scale, a water balance methodology was developed and used to estimate focused recharge. The results show that SWRs interact almost continuously with groundwater and contribute focused recharge. The magnitude of this recharge is a function of the geological context and the sediment texture of the SWRs. It is estimated at 5 mm/day in Kierma and 4 mm/day in Mogt&eacute, do. These values are higher than the natural recharge estimated at 0.2 mm/day in Kierma and 0.1 mm/day in Mogt&eacute, do. Additionally, the values of hydraulic conductivity are between 0.01 and 2 m/day in Kierma and between 1 &times, 10&minus, 4 and 0.2 m/day in Mogt&eacute, do. These conductivities could allow pumping in large-diameter hand-dug wells with a significant yield between 0.5 and 120 m3/day in Kierma and between 0 and 10 m3/day in Mogt&eacute, do to palliate the early drying up of the SWRs.

Changes in land use/land cover (LU/LC) practices are critical to determine and this is one of the crucial driving forces of terrestrial ecosystem productivity and carbon sink variability. However, relatively few studies have quantified the impact of LU/LC change on the terrestrial carbon cycle. In the present study, we developed a workflow for quantifying and assessing changes in terrestrial carbon stocks due to land use change using a dynamic vegetation model. The main objectives are to assess status and variation in carbon stocks across land covers, towards the quantification of spatial distribution and dynamic variation of terrestrial carbon sinks in response to LU/LC change. Here, with the CARAIB dynamic vegetation model, we perform simulations using several sets of LU/LC data to analyse the sensitivity of the carbon sink. We propose a new method of using satellite – and machine learning-based observation to reconstruct historical LU/LC change and compare it with static data from the cadastral map and dynamic data from an agent-based model coupled with CARAIB. It will quantify the spatial and temporal variability of land use during the 2000-2019 period over Belgium at high resolution. This study will give the space to analyse past information and hence calibrate the dynamic vegetation model to minimize uncertainty in the future projection (until 2035). Overall, this study allows us to understand the effect of changing land use pattern and identify the input dataset which minimizes the uncertainty in model estimation.

Restoring in-stream spawning habitats in degraded rivers has received increasing attention as a tool for mitigating local wild fish population declines, notably in response to the European Water Framework Directive (WFD). However, spawning gravel placements are far too often designed without accurate knowledge of the morphodynamic river processes, resulting in a limited efficacy and longevity of the artificial spawning ground. To address the combined effects of bedload transport and fine sediment clogging processes on the sustainability of artificial spawning gravel habitats, we examined the effects of such rehabilitation actions on six degraded river reaches in Wallonia, Belgium. The monitoring scheme was based on the evolution of the thickness and clogging of the spawning gravel (using wooden stakes driven into the gravel layer to measure the depth of the anoxia) and on the PIT-tagged tracking of gravel dispersion over a period of 3.6–8.5 yrs. On the one hand, the results highlighted that several artificial spawning grounds were quickly clogged because of improper sizing of the spawning material. Gravel that was too coarse to be mobilized by the river and that had a narrow grain size range favoured fine sediment accumulation within the interstices of the gravel layer. On the other hand, one spawning gravel placement was rapidly scoured (after 2.2 yrs) because of an undersizing of the gravel with respect to flow competence. In the end, one gravel placement presented adequate gravel sizing, allowing periodic gravel transport over short distances (the mean annual travel distance was ~3 m). The longevity of a gravel placement and the ability of the displaced gravel to form new spawning grounds downstream were strongly dependent on the distance that the placed gravel was likely to travel, which in turn depended on several hydromorphological parameters, such as unit stream power, channel morphology and bed texture. The key parameters highlighted in this study need to be acknowledged when designing spawning gravel placement projects.

Restoring active bedload transfer in human-impacted rivers has received increasing attention in recent years, notably in response to the European Water Framework Directive (WFD), which requires that the continuity of rivers not be disturbed by anthropogenic features such as dams or weirs. The Bocq River (233 km2), a moderate-gradient stream in Wallonia, Belgium, has a hydraulic resource that was formerly largely exploited with 74 weirs (up to 2.3 m high) along 43 km. We examined the effects of seven old abandoned weirs on bedload transport for three different types of weirs (defined by the presence and position of the sluice gate system). First, the volume estimates of bedload stored in reservoirs indicated that, despite their old age, the reservoirs were not completely filled (between 25 and 50% filled compared to the reservoir volume capacity) and did not evolve very much since 1990. Second, the grain size analysis of bed material upstream, downstream and within the reservoirs, and the direct measurements of sediment transport (slag particles and PIT-tagged pebbles) demonstrated that bedload continues to be transported out of the reservoir, even though the selective trapping of coarser elements was observed within the reservoir. Particles in the range of the median can pass over the crest of weirs, but the coarser elements tend to remain in the reservoirs. This trapping effect is mitigated when the weir has open or collapsed flushing gates that facilitate bedload transfer. This indicates that weirs act as leaky barriers that allow bedload to pass through, although the individual geomorphic setting plays a primary role in determining the local sediment continuity. These findings suggest that river connectivity is less impacted than initially thought and is likely to increase over time as old weirs gradually fall into disrepair. This needs to be acknowledged when planning barrier removal projects.

Un ensemble de dix-neuf ouvrages de protection de berges en génie végétal a fait l’objet d’un suivi à court et long termes sur plusieurs rivières de Wallonie. Les aménagements, dont la mise en place remonte pour certains à 20 ans, ont dans l’ensemble bien rempli leur rôle de stabilisation de berge, même si plusieurs d’entre eux sont aujourd’hui partiellement détruits. Dans certains cas, l’endommagement des aménagements a conduit à une reprise de l’érosion de la berge à protéger. Le facteur principal de dégradation des ouvrages est l’énergie de la crue destructrice. Elle est quantifiée par la valeur de puissance spécifique limite, qui représente la valeur maximale de puissance à laquelle l’ouvrage peut résister. Déterminée sur la base des observations de terrain, elle est de l’ordre de 130 W/m² pour des fascines, 65 W/m² pour des peignes, 200 W/m² pour des caissons et 150 W/m² pour des épis végétaux. Toutefois d’autres facteurs d’échec font en sorte que l’aménagement est dégradé avant d’être détruit par les crues, ce qui le rend vulnérable pour des puissances spécifiques moins importantes. Les facteurs de dégradation mis en évidence sont (i) une mauvaise reprise de la végétation liée à un problème d’exposition, à des coupes non gérées et aux dégâts provoqués par les animaux s’attaquant aux plantations (bétail et rongeurs), (ii) des défauts de conception des aménagements (remplissage inadapté, mauvais dimensionnement) et (iii) une mauvaise prise en compte des caractéristiques géomorphologiques de la rivière. Ainsi, outre la puissance spécifique, un deuxième facteur important à prendre en compte est la quantité de Matières En Suspension (MES) disponible, étant donné que la plupart de ces ouvrages nécessitent un remplissage par des sédiments fins. Nineteen streambank stabilisation projects using bioengineering techniques were monitored in the short and the long term on several rivers in Wallonia. Most of the bank protections, installed between 3 and 20 years ago, were effective, although many of them are now partially destroyed. In some cases, damage to the protective structure has led to a renewed erosion of the bank. The main factor of degradation is the magnitude of stream discharge, which is quantified by the critical stream power (the maximum power value at which the bank protection can resist). Permissible stream power thresholds were determined empirically, and are in order of 130 W/m² for fascine, 65 W/m² for tree revetment, 200 W/m² for cribwall and 150 W/m² for groynes system. Nevertheless, several factors might undermine the bank protection before its flood destruction, which lead to a lower threshold of critical power. The deterioration factors highlighted are (i) a poor vegetation recovery due to lack of sunlight, unmanaged cutting, and damage caused by animals (livestock and rodents), (ii) an inadequate design or filling, and (iii) a lack of consideration of fluvial processes, such as unit stream power and Total Suspended Solids (TSS) as most of these structures require filling with fine sediments. As a result, this study underlined the importance of characterising the geomorphological context in addition to the regular hydrological technical factors prior to the bank stabilisation project.

This paper first compiles critical shear stress values from 26 studies of gravel-bed rivers (GBRs) worldwide. The most frequently proposed value of the Shields criterion (θc) is 0.045, but three major groups with θc values ranging from 0.100 were identified. Second, dimensionless critical shear stresses (the Shields criterion) were evaluated for 14 GBRs (18 sites) with watershed areas ranging from 12 to 3000 km2. Different approaches were used to identify the initial movement of the bed material: painted and PIT-tag pebbles, sediment traps, and bedload samplers. The Shields criterion (θc) was estimated using the total shear stress (τ) and the grain shear stress (τ′). Several shear stresses were also estimated using shear velocities. For bedload transport, we obtained an average Shields criterion (θc) of 0.040. The values were higher in small rivers (> 0.050) than larger rivers (

In many gravel-bed rivers, bed material transfer has been interrupted or perturbed by anthropogenic activities. Currently, restoration projects are being conducted in many countries in order to re-establish bedload continuity. However, until now, few studies have provided indications of the velocity of bed material over the long-term (at least decade to century time-scale). In the context of river restoration projects (e.g. weir removal, addition of spawning gravel), these data are nevertheless crucial to predict the downstream propagation of the geomorphological and biological benefits (e.g. supply-transport equilibrium, morphological and substratum diversity). In our study, PIT-tag tracers were used in eight medium-sized gravel-bed rivers (Ardenne Region, Belgium) to propose a flow competence relationship based on specific stream power, on the one hand, and to determine the long-term virtual velocity of the bed material corresponding to the median diameter (D 50 ) of the surface layer of riffles, on the other hand. After each flow event that exceeded the threshold for sediment entrainment, tagged particles were sought and located, even when they were buried in the subsurface layer. Afterwards, all of the data were used to estimate the virtual velocity of the bed material over the long-term using three approaches. Finally, the results were compared with long-term transport estimations based on iron slag dispersed by the rivers since the end of the middle ages.

The cuesta landscape of Belgian Lorraine and Luxembourg’s Gutland belongs to the north-eastern rim of the Paris Basin, characterized by the wide syncline of the Gulf of Luxembourg. Highlighting the underlying geological structure and lithology, the cuestas were progressively sculpted in close relation with the contrasted evolutions of the Meuse and Rhine river systems. The landscape was established during the Cenozoic in Triassic and Jurassic rocks. These are formed of alternating hard pervious and soft, generally impervious units, the latter with a limited resistance to superficial weathering under the climatic conditions of the Neogene and Quaternary. The hard units frequently appear as thick homogenous layers, not only making the core of the cuestas but featuring also many escarpments. Height and lateral extent of the cuestas are controlled by the thickness of the hard layers and lateral changes in facies, as exemplified in the Middle Liassic sandstone and Triassic rocks. Remnants of an extended Neogene erosional surface cut the cuesta summits at ~400–420 m asl. Later fluvial erosion incised this surface, allowing for the development of lower planation surfaces down to 300 m, including a prominent level at ~350 m. Lower structural surfaces also exist on top of hard layers. Finally, landsliding is shown to participate actively in sculpting the cuesta landscape.

Much research has been devoted to the development of numerical models of river incision. In settings where bedrock channel erosion prevails, numerous studies have used field data to calibrate the widely acknowledged stream power model of incision and to discuss the impact of variables that do not appear explicitly in the model's simplest form. However, most studies have been conducted in areas of active tectonics, displaying a clear geomorphic response to the tectonic signal. Here, we analyze the traces left in the drainage network 0.7 My after the Ardennes region (western Europe) underwent a moderate 100–150 m uplift. We identify a set of knickpoints that have traveled far upstream in the Ourthe catchment, following this tectonic perturbation. Using a misfit function based on time residuals, our best fit of the stream power model parameters yields m = 0.75 and K = 4.63 × 10-8 m-0.5y-1. Linear regression of the model time residuals against quantitative expressions of bedrock resistance to erosion shows that this variable does not correlate significantly with the residuals. By contrast, proxies for position in the drainage system prove to be able to explain 76% of the residual variance. High time residuals correlate with knickpoint position in small tributaries located in the downstream part of the Ourthe catchment, where some threshold was reached very early in the catchment's incision history. Removing the knickpoints stopped at such thresholds from the data set, we calculate an improved m = 0.68 and derive a scaling exponent of channel width against drainage area of 0.32, consistent with the average value compiled by Lague for steady state incising bedrock rivers. Copyright © 2014 John Wiley & Sons, Ltd.

Several methods were employed in the Ardennian rivers (Belgium) to determine the depth of the active layer mobilized during floods and to evaluate the bedload discharge associated with these events. The use of scour chains has shown that the depth of the active layer is systematically less than the b-axis of the average particle size (D50) of the elements which compose the surface layer of the riffles. This indicates that only a partial transport exists during low magnitude floods. The bedload discharge has been evaluated by combining data obtained using the scour chains technique and the distance covered by tracers. Quantities of sediment transported during frequent floods are relatively low (0·02 t km–2) due to the armour layer which protects the subsurface material. These low values are also related to the fact that the distance calculated for mobilized bedload only applies to tracers fitted with PIT (passive integrated transponder)-tags (diameter > 20 mm), whereas part of the bedload discharge is composed of sand and fine gravel transported over greater distances than the pebbles. The break-up of the armour layer was observed only once, for a decennial discharge. During this event, the bedload discharge increased considerably (2 t km–2). The use of sediment traps, data from dredging and a Helley–Smith sampler confirm the low bedload transport in Ardennian rivers in comparison to the bedload transport in other geomorphological contexts. This difference is explained by the presence of an armoured layer but also by the imbricated structures of flat bed elements which increase the resistance to the flow. Finally, the use of the old iron industry wastes allowed to quantify the thickness of the bed reworked over the past centuries. In the Lembree River, the river-bed contains slag elements up to a depth of about 50 cm, indicating that exceptional floods may rework the bed to a considerable depth. Copyright © 2012 John Wiley & Sons, Ltd.

Gisele VERNIERS : Gisele Verniers est chercheur a l'Unite de Recherche en Biologie des Organismes des Facultes Universitaires de Namur et chargee de mission pour le GIREA (Groupe Interuniversitaire de Recherches en Ecologie Appliquee). Ses recherches portent sur la gestion integree et l'amenagement ecologique des cours d'eau. Elle s'est investie egalement dans les methodes d'evaluation de l'environnement dans le cadre des etudes d'incidences, domaine dans lequel elle a assure de nombreuses formations en Afrique.

The variables commonly used to describe the physical habitat of Atlantic salmon Salmo salar parr are average velocity, water depth, and substrate. A variety of micro- and mesohabitat models have been developed using these variables to assess habitat quality. However, Atlantic salmon parr live in highly turbulent streams and rivers in which intense fluctuations of water velocity occur. Laboratory experiments have shown that turbulence affects the behavior and energetics of fish. Nevertheless, habitat use in relation to the strong temporal variability of velocity in natural environments has rarely been studied. In this study, Atlantic salmon parr habitat was examined in relation to turbulence in the Patapedia River, Quebec. Rather than taking the usual approach of surveying a large population at one point in time, we used an intensive radiotelemetry tracking survey that focused on the habitat use of a few individual fish over an extended period. We analyzed habitat use in relation to several dynami...

It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations, we calculate the amount of river incision and interfluve denudation in the Meuse basin upstream of Maastricht since 0·7 Ma and we show that the main response to tectonic forcing was incision. This allows us to provide first-order estimates of the tectonic and climatic contributions to the denudation of the Ardennes. From a dataset of 71 remnants of a terrace level dated ∼0·7 Ma, we first derive a basin-scale functional relationship linking incision with distances to the regional base level (Lc) and to the source (Ls) in the Ourthe basin (pertaining to the Ardennian part of the Meuse basin). Expressed as I = I0*(1 – a*Lcb/Lsc), I0 being the incision measured at the basin outlet, this relationship calculates that river incision has removed 84 km3 of rock in the Meuse basin upstream of Maastricht since 0·7 Ma. In the same time, 292 km3 were eroded from the interfluves. A comparison of these volumes shows that the tectonically forced river incision accounts for ∼22% of the total post-0·7 Ma denudation. Furthermore, the mean denudation rate corresponding to our geomorphological estimate of the overall denudation in the Meuse basin since 0·7 Ma amounts to 27 mm/ky, a figure significantly lower than the ∼40 mm/ky mean rate derived from 10Be studies of terrace deposits of the Meuse (Schaller et al., 2004). This suggests that, taken as a basin average, the 10Be-derived rate is overestimated, probably due to an overrepresentation of the erosion products of the rapidly incising valleys in the alluvial deposits. Copyright © 2009 John Wiley & Sons, Ltd.

article i nfo A good evaluation of the Quaternary uplift of the Rhenish shield is a key element for the understanding of the Cenozoic geodynamics of the western European platform in front of the alpine arc. Previous maps of the massif uplift relied on fluvial incision data since the time of the rivers' Younger Main Terrace to infer a maximum post-0.73 Ma uplift of ~290 m in the SE Eifel. Here, we propose a new interpretation of the incision data of the intra-massif streams, where anomalies in the terrace profiles would result from knickpoint retreat in the tributaries of the main rivers rather than from tectonic deformation. We also use additional geomorphological data referring to (1) deformed Tertiary planation surfaces, (2) the history of stream piracy that severely affected the Meuse basin in the last 1 Ma, and (3) incision data outside the Rhenish shield. A new map of the post-0.73 Ma uplift of the Rhenish shield is drawn on the basis of this enlarged dataset. It reduces the maximum amount of tectonic uplift in the SE Eifel to ~140 m and modifies the general shape of the uplift, namely straightening its E-W profile. It is also suggested that an uplift wave migrated across the massif, starting from its southern margin in the early Pleistocene and currently showing the highest intensity of uplift in the northern Ardennes and Eifel. These features seem to favour an uplift mechanism chiefly related to lithospheric folding and minimize the impact on the topography of a more local Eifel plume.

L’analyse du transport de la charge de fond de plusieurs rivières du massif ardennais (Belgique) par différentes techniques de marquage de galets (peinture, charge métallique, émetteurs radio) a permis d’identifier le débit critique où débute le charriage. Pour les rivières les plus importantes (plus de 500 km2), la mise en mouvement se produit à des débits légèrement inférieurs au débit à plein bord (0,7 à 1 Qb), débits qui se présentent en moyenne 5 à 11 jours par an. Pour les rivières de taille intermédiaire (entre 100 et 500 km2), le charriage débute à un débit avoisinant 0,5 fois le débit à plein bord, avec une récurrence de 0,3 an et une durée variant entre 8 et 12 jours par an. Pour les rivières de dimension modeste (moins de 100 km2), la mise en mouvement se produit à des débits compris entre 0,5 et 0,8 Qb, mais leur récurrence est relativement faible et le charriage peut se produire jusqu’à 20 jours par an. Par ailleurs, le transport solide a été évalué à l’aide de pièges à sédiments dans les rivières de petite dimension (moins de 10 km2) ; il est relativement peu important dans les bassins forestiers (0,5 t/km2/an), en raison de la multiplication des embâcles végétaux qui accroissent la rugosité du lit. Pour les rivières plus importantes, le transport solide a été estimé entre 0,4 et 2,5 t/km2/an grâce à l’analyse des quantités curées systématiquement aux mêmes sites et à la réalisation de levés topographiques de contrôle. Nous avons ensuite analysé l’évolution des quantités charriées en fonction de la puissance spécifique à plein bord développée par ces rivières. La relation établie sur la base de ces données a permis de mettre en évidence le déficit en sédiments de certaines rivières ainsi que plusieurs facteurs influençant le charriage., The analysis of bedload transport of several rivers of the Ardenne (Belgium) using various marking techniques (painted pebbles, metallic-tagged pebbles, radio-transmitters) has allowed to identify the critical discharge when bedload transport begins. In large rivers (more than 500 km2), bedload mobilisation occurs when the discharge is slightly lower than the bankfull (0.7 to 1Qb), which takes place on average 5 to 11 days per year. In medium size rivers (between 100 and 500 km2), bedload transport occurs when the discharge is around 0.5Qb, which corresponds to a recurrence of approximately 0.3 years and to a mobilisation period of 8 to 12 days per year. In smaller rivers (less than 100 km2), the critical discharge occurs between 0.5 and 0.8Qb, but its reccurence is relatively low and bedload can be mobilized up to 20 days per year. Moreover, the bedload solid discharge was estimated using sediment traps in headwater streams (less than 10 km2). In small forested catchments, bedload transport is not significant (around 0.5 t/km2/yr), partially due to numerous vegetation log-jams increasing bed roughness. In larger rivers, the specific bedload discharge was estimated between 0.4 and 2.5 t/km2/yr using quantities of dredged material extracted systematically in the same place, in relation to topographical surveys. Finally, the evolution of the bedload discharge in relation to the specific stream power at the bankfull discharge was analysed. The relation obtained with this data shows the deficit of sediment in some rivers and explains some of the factors that influence bedload transport.

Flash floods and muddy floods may cause severe human and material damage despite their small spatial extent and low occurrence. In late May 2008, a major event has affected the area of Liège. This paper describes the methodology used to reconstruct the hydrosedimentological parameters of the flood from the geomorphological evidences observed in the field. Bed load and suspended load transport rates estimated during this extreme event were compared to the average values observed in other Walloon rivers and more specifically in the Ardennes Massif. The spatial distribution and the temporal evolution of the flash flood and muddy flood events are then analysed across Wallonia based on several works compiling press archives since the early twentieth century. The biases associated with this type of historical sources and the consequences of flash floods and muddy floods on the vulnerability and the risk of flooding in Wallonia are finally addressed. Les crues éclairs et les coulées boueuses, malgré leur extension spatiale réduite et leur occurrence peu fréquente, peuvent être à l’origine de dégâts importants tant sur le plan matériel que sur le plan humain. Fin mai 2008, un événement majeur a affecté la région liégeoise. Ce papier décrit la méthodologie employée pour reconstituer, en milieu forestier, ses paramètres hydrosédimentologiques à partir des éléments géomorphologiques observés sur le terrain. Les taux de transport de la charge de fond et de la charge en suspension au cours de cet événement extrême sont comparés aux valeurs moyennes observées dans d’autres rivières wallonnes et plus spécifiquement dans le massif ardennais. La répartition spatiale et l’évolution temporelle des crues éclairs sont ensuite analysées à l’échelle de la Wallonie sur base de plusieurs travaux académiques compilant l’ensemble des événements recensés dans la presse depuis le début du XXème siècle. Les biais liés à ce type de sources historiques sont abordés ainsi que les conséquences des crues éclairs sur la vulnérabilité et le risque d’inondation soudaine en Wallonie.

This study performed in the Patapedia River (Quebec, Gaspesie) was designed to examine the space utiliza- tion and mobility patterns of individual Atlantic salmon parr over short time scales with frequent detections of position. In August 2004, n = 7 radio-tagged Atlantic salmon parr were located every 20 min during 10 tracking periods cho- sen to take into account the dawn, day, dusk and night periods. Parr showed important inter individual variability in space utilization and mobility patterns, occupying large home ranges (123 to 5602 m 2 ) and sometimes migrating 2 km upstream in the river. No differences were observed in the mean distance travelled among the four daily periods by individual fish, but the estimated home ranges utilized during the four daily periods overlapped only partially, demon- strating that parr partly occupy different areas of the river during different parts of the daily cycle. The results suggest that an intense survey on a small number of fish may contribute to a complementary comprehension of space utilization and mobility patterns of Atlantic salmon parr when viewed in association with results from studies surveying larger number of fish at lower frequency.