References of "Van Campenhout, Jean"
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See detailAnalysis of the temporal dynamics of suspended sediment fluxes using discrete sampling and continuous turbidity measurements in the Meuse and Scheldt watersheds (Wallonia, Belgium)
Van Campenhout, Jean ULg

Conference (2016, June 27)

Soil erosion may be apprehended at different scales and different time intervals in order to quantify the transport of suspended sediment at the outlet of large watersheds. In the Walloon region, several ... [more ▼]

Soil erosion may be apprehended at different scales and different time intervals in order to quantify the transport of suspended sediment at the outlet of large watersheds. In the Walloon region, several projects were conducted to estimate the erosion rates in watersheds ranging from 16 to 2900 km². Both discrete sampling methods (allowing the coverage of a large area through field campaigns during major floods or moderate hydrological events) and continuous turbidity measurements devices (studying a small number of locations with a small sampling interval and a wide range of sampled flow rates) were tested in these projects. At the region scale (Figure 1), the mean annual sediment erosion rate reaches several hundreds of tons per square kilometre and per year in the loess belt (Senne, Dyle and Gette watersheds) with a huge sensibility to extreme hydrological events while the mean annual sediment transport value reaches 20 t.km-2.yr-1 in Lorraine, 34 t.km-2.yr-1 in Ardenne and 69 t.km-2.yr-1 in Entre-Vesdre-et-Meuse. The aims of our researches are 1) the determination of the effect of the sampling frequency on the annual sediment transport rate estimation ; 2) the definition of the prerequisites to perform efficient turbidity measurements in rivers with high suspended load concentrations ; 3) the identification of the sources of errors due to the interpolation methods through a comparison of several methods proposed in the literature allowing the quantification of long-term erosion rates using a small number of discrete samples ; 4) the observation and explanation of clockwise and anti-clockwise hysteresis loops in relationship with the sequence of floods occurring in large watersheds and 5) the highlighting of the regional differentiation in the erosion rates, particle size and proportion of organic matter in the suspended load samples due to spatial variations of the soil substrate and the land cover characteristics. [less ▲]

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See detailDecrease in climatic conditions favouring floods in the south-east of Belgium over 1959-2010 using the regional climate model MAR
Wyard, Coraline ULg; Scholzen, Chloé ULg; Fettweis, Xavier ULg et al

in International Journal of Climatology (2016)

The Ourthe River, in the south-east of Belgium, has a catchment area of 3,500 km2 and is one of the main tributaries of the Meuse River. In the Ourthe, most of the flood events occur during winter and ... [more ▼]

The Ourthe River, in the south-east of Belgium, has a catchment area of 3,500 km2 and is one of the main tributaries of the Meuse River. In the Ourthe, most of the flood events occur during winter and about 50% of them are due to heavy rainfall events combined to an abrupt melting of the snowpack covering the Ardennes massif during winter. This study aims to determine whether trends in extreme hydroclimatic events generating floods can be detected over the last century in Belgium, where a global warming signal can be observed. Hydroclimatic conditions favourable to floods were reconstructed over 1959- 2010 using the regional climate model MAR (“Modèle Atmosphérique Régional”) forced by the ERA-Interim/ERA-40, the ERA-20C and the NCEP/NCAR-v1 reanalyses. Extreme run-off events, which could potentially generate floods, were detected using run-off caused by precipitation events and snowpack melting from the MAR model. In the validation process, the MAR-driven temperature, precipitation and snow depth were successfully compared to daily weather data over the period 2008-2014 for 20 stations in Belgium. MAR also showed its ability to detect up to 90% of the hydroclimatic conditions which effectively generated observed floods in the Ourthe River over the period 1974- 2010. Conditions favourable to floods in the Ourthe River catchment present a negative trend over the period 1959-2010 as a result of a decrease in snow accumulation and a shortening of the snow season. This trend is expected to accelerate in a warmer climate. However, regarding the impact of the extreme precipitation events evolution on conditions favouring floods, the signal is less clear since the trends depend on the reanalysis used to force the MAR model. [less ▲]

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See detailFlash floods and muddy floods in Wallonia: recent temporal trends, spatial distribution and reconstruction of the hydrosedimentological fluxes using flood marks and sediment deposits
Van Campenhout, Jean ULg; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

in Belgeo (2015), 1

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 ... [more ▼]

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. [less ▲]

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See detailEvaluation of long-term bedload virtual velocity in gravel-bed rivers (Ardenne, Belgium)
Houbrechts, Geoffrey ULg; Levecq, Yannick; Peeters, Alexandre ULg et al

in Geomorphology (2015), 251

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 ... [more ▼]

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 (D50) 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. [less ▲]

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See detailQuantitative and qualitative evaluation of sediment and contaminant transport in the Samme river catchment (Brabant region - Belgium)
Denis, Anne-Cécile ULg; Van Campenhout, Jean ULg; Bouffioux, Anne et al

in Proceedings of 4th International Symposium on Sediment Management (2014, September)

In Wallonia (Belgium), the maintenance of waterways is currently exclusively managed in a curative way. When local sediment accumulations are detected in waterways, bathymetric surveys are conducted in ... [more ▼]

In Wallonia (Belgium), the maintenance of waterways is currently exclusively managed in a curative way. When local sediment accumulations are detected in waterways, bathymetric surveys are conducted in order to quantify the volume of sediment to be removed and chemical analyses of samples allow the characterization of sediment quality. Collected data only allow a short-term management of the matter generated by dredging operations. Medium- or long-term planning of dredging operations is currently not possible, due to a lack of knowledge on sediment fluxes and associated pollutant transport. In particular, issues related to the interactions and mixing of recent and older sediments, or to the input of sediment from unnavigable waterways into larger navigable waterways, are poorly understood. Operational tools allowing the assessment of the effectiveness of preventive measures to be implemented in order to improve the management of sediment in Walloon waterways also have to be developed. This research project aims at contributing to the development of such tools and focuses on the Samme river watershed (Senne catchment – loamy Brabant Region), deemed to be representative of Walloon issues. The Samme river is categorized as an unnavigable waterway. It runs along the old Charleroi-Brussels canal and flows into the new Charleroi-Brussels canal at the foot of the Ronquières inclined plane. The sediments of the bed of the Samme river are characterized by a high concentration of micropollutants (mainly PCB) and contribute to the contamination of a greater volume of sediments in the new Charleroi-Brussels canal, significantly increasing the cost of periodic dredging operations in the canal. The methodology developed is based on (I) an extended monitoring of sediment and pollutant fluxes at the outlet of the catchment and (II) an assessment of within-catchment sediment and pollutant transport. The origin of the Samme riverbed sediments contamination by PCB is poorly understood. Chemical analyses of the sediments of the bed were carried out along the linear course of the Samme river and its main tributary in order to identify the source of pollution. However, numerous connections between the old canal and the Samme river contribute to the transfer of stream sediments and pollutants between both systems and complicate the identification of the source of PCB. At the outlet of the catchment, different methods of river sediment sampling (automatic samplers, turbidity sensors, Time Integrated Samplers) are currently being implemented in order to (I) monitor the amount of suspended matter carried by the Samme river into the Charleroi-Brussels canal, (II) evaluate the associated fluxes of pollutants and (III) evaluate the possibility of setting up a system of retention of the sediments in the Samme catchment. [less ▲]

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See detailCaractérisation de la couche active et du débit solide dans les rivières à charge caillouteuse du massif ardennais
Levecq, Yannick ULg; Houbrechts, Geoffrey ULg; Van Campenhout, Jean ULg et al

Poster (2013, October 15)

Plusieurs techniques existent pour calculer l’épaisseur de la couche active de charriage et le débit solide des rivières. Il peut s’agir de chaînes d’érosion, de pièges à sédiments, d’échantillonneurs de ... [more ▼]

Plusieurs techniques existent pour calculer l’épaisseur de la couche active de charriage et le débit solide des rivières. Il peut s’agir de chaînes d’érosion, de pièges à sédiments, d’échantillonneurs de charge de fond de type Helley-smith, de galets marqués, ou encore du dépouillement d’archives de curages (Houbrechts et al., 2012). Ces techniques permettent également de déterminer l’impact de travaux d’aménagements ou de restauration de cours d’eau. Dans le cadre de conventions de recherches financées par la DCENN, deux techniques complémentaires ont été utilisées afin d’analyser le transport de charge de fond de rivières de Wallonie. Tout d’abord des chaînes d’érosion ont été implantées en travers du fond du lit, elles permettent de calculer l’épaisseur et la section de la couche de sédiments mobilisés lors des crues. Les puissances spécifiques des crues analysées varient entre 15 et 195 W/m² et ont généré une épaisseur de couche active comprise entre 9 et 80 mm. Ensuite, la distance parcourue par la charge de fond durant des crues mobilisatrices a été estimée à l’aide de galets marqués par des transpondeurs passifs (PIT-tags). Selon l’importance des crues, les distances moyennes de transport observées sont comprises entre 4 et 297 m. En croisant les données obtenues à l’aide de ces deux techniques, le débit solide de charge de fond a également pu être estimé. A titre d’exemple, le débit solide des rivières varie entre 0,02 t.km-2/crue et 2 t.km-2/crue, lorsque la rupture de la couche d’armurage se produit. [less ▲]

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See detailFlux des sédiments en suspension dans les rivières du bassin de la Meuse : proposition d'une typologie régionale basée sur la dénudation spécifique des bassins versants
Van Campenhout, Jean ULg; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

Poster (2013, October 15)

L'érosion des sols peut être appréhendée à l'échelle du bassin versant en quantifiant le transport sédimentaire en suspension à son exutoire. Environ 2.000 mesures de concentration des matières en ... [more ▼]

L'érosion des sols peut être appréhendée à l'échelle du bassin versant en quantifiant le transport sédimentaire en suspension à son exutoire. Environ 2.000 mesures de concentration des matières en suspension ont permis d'estimer les débits solides annuels en fonction des débits liquides observés dans ces cours d'eau. Une méthodologie simple a été mise en place et appliquée à un réseau de 80 stations, à l’exutoire de bassins versants d’une superficie comprise entre 16 et 2.900 km² situées en région wallonne. Des différenciations régionales ont pu être mises en évidence en fonction du substrat et de l'occupation du sol des bassins versants. La granulométrie des particules transportées et la proportion de matière organique complètent l'analyse et confirment les différenciations observées selon les régions agro-géographiques. L’impact de la fréquence d’échantillonnage (et de sa synchronisation avec les débits de crue) sur l’estimation de la dénudation annuelle a été mis en évidence, ainsi que la grande variabilité interannuelle, qui est fonction de l’intensité et de la hauteur des précipitations. L’érosion des sols est ainsi très sensible aux événements extrêmes. Par ailleurs, l’intérêt de longues campagnes de mesures est souligné. Des données issues de travaux antérieurs ont également été intégrées à la base de données. Son interprétation a permis de définir les meilleurs sites susceptibles d’accueillir à long terme un réseau de mesure en continu de la concentration des matières en suspension en Wallonie. [less ▲]

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See detailCaractérisation d’un état de référence de l’Eau Blanche pour guider les travaux de restauration écologique
Peeters, Alexandre ULg; Hallot, Eric ULg; Van Campenhout, Jean ULg et al

Poster (2013, October)

Sur l’ensemble de son parcours de 14,5 km à travers la Fagne, l’Eau Blanche a subi d’importants travaux de rectification et de recalibrage, principalement dans les années soixante lors de travaux ... [more ▼]

Sur l’ensemble de son parcours de 14,5 km à travers la Fagne, l’Eau Blanche a subi d’importants travaux de rectification et de recalibrage, principalement dans les années soixante lors de travaux d’assainissement agricole. Ces travaux ont eu pour conséquence de banaliser les habitats aquatiques et rivulaires, entrainant des répercussions sur la faune et la flore aquatique. Dans le cadre du projet Walphy, des travaux de restauration de la continuité transversale ont été réalisés entre 2010 et 2011 sur plus de 6 km de linéaire (comprenant l’Eau Blanche et son affluent, le Grand Morby). Avant ces travaux de restauration et de manière à définir l’état de référence à atteindre, une étude des caractéristiques de l’Eau Blanche avant sa rectification a été entreprise. Ainsi, plusieurs données cartographiques ont pu être rassemblées et analysées, telles que des cartes anciennes et des plans terriers accompagnés de profils transversaux et longitudinaux, ainsi qu’un modèle numérique de terrain à haute résolution MNT-LIDAR. Nous avons dés lors pu comparer le tracé de l’Eau Blanche avant et après sa rectification. Par ailleurs, afin de caractériser l’état de référence visé par les travaux de restauration, les données cartographiques et topographiques anciennes ont été utilisées pour calculer les caractéristiques morphométriques du cours d’eau avant la rectification : pente, indice de sinuosité, longueur d’onde, amplitude et rayon de courbure des méandres, largeur à plein bord, rapport largeur/profondeur... [less ▲]

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See detailL’effet des barrages de castors sur le système hydrographique
Denis, Anne-Cécile ULg; Petit, François ULg; Levecq, Yannick ULg et al

Poster (2013, October)

L’augmentation croissante des populations de castors sur nos rivières ces dernières années n’est pas sans conséquence notamment sur la géomorphologie et l’hydrologie des fonds de vallée. En effet, les ... [more ▼]

L’augmentation croissante des populations de castors sur nos rivières ces dernières années n’est pas sans conséquence notamment sur la géomorphologie et l’hydrologie des fonds de vallée. En effet, les barrages construits par les castors constituent des pièges à sédiments susceptibles d’entrainer une incision en aval par déficit en sédiments. La présence de barrages a également pour principal effet de réduire localement la vitesse du courant et de réguler les débits. De plus, les barrages créés par les castors constituent de véritables obstacles à l’écoulement qui peuvent engendrer une modification du tracé du cours d’eau voir du style fluvial. Enfin, en cas de destruction des barrages, le lâcher soudain d’un volume d’eau conséquent peut engendrer un effet « domino » sur les barrages situés en aval entrainant une évacuation importante des sédiments et une incision du cours d’eau. En région Wallonne, il existe plus de 150 barrages de castor. Une analyse récente de leur localisation montre que le castor s’installe principalement sur des rivières ardennaises de dimension modeste mais également sur des rivières de Lorraine et de Famenne. Les barrages sont généralement observés sur des cours d’eau plutôt incisé, en tête de bassin et dans des plaines alluviales plutôt étroites. Différents stades et modes de construction des barrages ont été mis en relation avec la morphologie des rivières. Il en ressort que ces différences impliquent des processus spécifiques de rupture éventuelle de ces barrages. Ces différents aspects ont été plus particulièrement étudiés dans deux rivières ardennaises (la Chavanne et la Lienne). [less ▲]

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See detailFlux des sédiments en suspension dans les rivières du bassin de la Meuse : proposition d’une typologie régionale basée sur la dénudation spécifique des bassins versants
Van Campenhout, Jean ULg; Denis, Anne-Cécile ULg; Hallot, Eric ULg et al

in Bulletin de la Société Géographique de Liège (2013), 61

Soil erosion may be apprehended at the watershed scale by quantifying the transport of suspended sediment at its outlet. Approximately 2000 measurements of suspended sediment concentration were used to ... [more ▼]

Soil erosion may be apprehended at the watershed scale by quantifying the transport of suspended sediment at its outlet. Approximately 2000 measurements of suspended sediment concentration were used to estimate the annual sediment discharge at 80 stations located in the Walloon region (Belgium), at the outlet of watershed from 16 to 2900 km². Some regional differences have been highlighted depending on the substrate and the land use in the watershed. At the region scale, the mean annual sediment yield reaches 20 t.km-2.yr-1 in Lorraine, 34 t.km-2.yr-1 in Ardenne and 69 t.km-2.yr-1 in Entre-Vesdre-et-Meuse. The size of suspended particles and the proportion of organic matter also show differences between each agro-geographical area. Data from other academic or administrative works were incorporated into the database to identify the best sites for continuous measuring of the suspended load concentration in Wallonia. [less ▲]

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See detailImages CM de Passega des rivières ardennaises
Houbrechts, Geoffrey ULg; Hallot, Eric ULg; Levecq, Yannick ULg et al

in Bulletin de la Société Géographique de Liège (2013), 61

A method of grain-size distribution data interpretation was proposed by Passega (1957; 1964) to differentiate the deposits of various modes of fluvial and marine transport (uniform suspension, graded ... [more ▼]

A method of grain-size distribution data interpretation was proposed by Passega (1957; 1964) to differentiate the deposits of various modes of fluvial and marine transport (uniform suspension, graded suspension, rolling). This method consists of using two characteristic percentiles (D99 and D50) of a grain-size distribution sediment curve, that are applied to a chart with a double logarithmic scale. The position of the point is compared with a model (CM diagram) determined on the basis of samples collected from deposits for which the conditions of establishment are known. Several studies have also shown that this method allows sedimentary bedforms to be differentiated based on the grain-size characteristics of the sediments that have been deposited, thus permitting the conditions of sedimentation and the transport of old alluvium to be retrospectively determined. However, a number of parameters specific to each water course influence the characteristics of the CM diagram and there is not one universal diagram that may be transposed to all fluvial environments (Bravard and Peiry, 1999). This article presents tens of CM diagrams of Ardennian rivers, obtained on the basis of samples taken from deposits that were laid down in known hydrodynamic conditions and for which the mode of implementation can be reconstituted. The purpose of this article is therefore to provide a reliable tool to provide solid interpretations of the conditions of sedimentation of ancient fluvial deposits of the Ardennian rivers and, more generally, of gravel bed rivers (Eifel, Vosges, Morvan, etc.) in low mountain areas (ω = 15 to 150 W/m²). [less ▲]

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See detailReconstitution de la dynamique d'une rivière ardennaise (La Lienne) depuis le Tardiglaciaire grâce à l'analyse géomorphologique et chronostratigraphique d'une tourbière de fond de vallée
Denis, Anne-Cécile ULg; Wastiaux, Cécile ULg; Petit, François ULg et al

in Géomorphologie : Relief, Processus, Environnement (2013), 2

The geomorphological dynamics (incision, lateral mobility, sedimentation rate) of a river typical of the Ardenne region (the Lienne River) were studied at the level of a valley floor peat deposit. This ... [more ▼]

The geomorphological dynamics (incision, lateral mobility, sedimentation rate) of a river typical of the Ardenne region (the Lienne River) were studied at the level of a valley floor peat deposit. This type of site is of major interest as the morphology of ancient fluvial deposits is preserved underneath peat deposits and pollen conserved in the peat allows different phases of the evolution of the river to be dated. The presence of pollen from the Younger Dryas above a pebble sheet perched 1.4 m above the present-day bed, as well as peat deposits from the Preboreal at the level of the present-day bed indicate that a phase of incision occurred during the Younger Dryas-Preboreal transition. Reworked Laacher See tephra was found in the upper part of the perched pebble sheet, which confirms that it had been laid down during the Younger Dryas, in a periglacial context. The Lienne River had probably multiple channels during the Preboreal. After the abandonment of one of the channels, it moved laterally, allowing the peat to spread until it occupied more than two-thirds of valley from the Atlantic phase. The use of slag from steel working as a stratigraphic marker shows low lateral mobility in the Lienne River as well as a low rate of aggradation of the alluvial plain over the last centuries. [less ▲]

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See detailL'effet des barrages de castors sur le système hydrographique
Petit, François ULg; Denis, Anne-Cécile ULg; Levecq, Yannick ULg et al

Conference given outside the academic context (2012)

Estimation de la sédimentation dans les retenues provoquées par les barrages de castor. Impact en aval des barrages sur l'incision des rivières. Localisarion des barrages de castor en relation avec la ... [more ▼]

Estimation de la sédimentation dans les retenues provoquées par les barrages de castor. Impact en aval des barrages sur l'incision des rivières. Localisarion des barrages de castor en relation avec la tailled es rivières (ordination des cours d'eau). Discussion sur les conséquences éventuelles des retenues sur les débits d'étiage. [less ▲]

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See detailAnalyse des débits en période de tarissement : Essai d'une typologie régionale appliquée à des rivières du bassin de la Meuse (Belgique)
Gischer, Loïc; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

in Bulletin de la Société Géographique de Liège (2012), 59

Low flow discharge was analysed in twenty-five rivers of the midlands and highlands of Belgium, particularly during periods when base flow was supplied by aquifers. Recession curves were elaborated: these ... [more ▼]

Low flow discharge was analysed in twenty-five rivers of the midlands and highlands of Belgium, particularly during periods when base flow was supplied by aquifers. Recession curves were elaborated: these were “sequence curves” and not “tangent curves”. In general, two recession coefficients may be identified. In addition, we determined the percentage of “rapid runoff flood” within a regional perspective. It is apparent that this flow varies with the level of the water table. We also tried to estimate the groundwater recharge used in Thornthwaite’s simplified model. This was undertaken by estimating the amount of rain needed before observing a significant increase in discharge, following pronounced drought episodes such as those of 1976 and 2003. Finally, working on discharges during periods of low flow, we looked at the role of beaver dams as a factor contributing to low flow, as has been suggested recently in the literature. From our observations, it appears beaver dams do not influence the characteristic low flow discharge. Furthermore, an analysis of the evolution of the characteristic low flow dicsharge in rivers where there are no beaver dams shows some variability. This leads us, first of all, to qualify the influence of beaver dams, at least on the hydrological regime of these water courses (which are always located at the top of the watershed) but also to question the relevance of characteristic low flow discharge as a descriptor of low flow. [less ▲]

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See detailComparison of methods for quantifying active layer dynamics and bedload discharge in armoured gravel-bed rivers
Houbrechts, Geoffrey ULg; Van Campenhout, Jean ULg; Levecq, Yannick ULg et al

in Earth Surface Processes & Landforms (2012), 37

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 ... [more ▼]

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 Lembrée 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. [less ▲]

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See detailImpact de la glace de ségrégation sur l'érosion des berges d'un ruisseau ardennais (la Chavanne, Belgique)
Wallemacq, Véronique; Petit, François ULg; Van Campenhout, Jean ULg et al

in Géomorphologie : Relief, Processus, Environnement (2011), 1

L’impact érosif de la glace de ségrégation a été analysé dans les berges d’un ruisseau ardennais (la Chavanne, Belgique), dans une région soumise à un climat tempéré. Sur une période de 19 mois (février ... [more ▼]

L’impact érosif de la glace de ségrégation a été analysé dans les berges d’un ruisseau ardennais (la Chavanne, Belgique), dans une région soumise à un climat tempéré. Sur une période de 19 mois (février 2008-septembre 2009), des mesures de recul de berges à l’aide de barres d’érosion ont montré un recul moyen d’une dizaine de centimètres. Cette érosion s’est essentiellement produite durant le mois de janvier 2009 à la suite d’une vague de froid. Par la suite, l’érosion par entraînement hydraulique des matériaux désagrégés par la glace de ségrégation a été plus lente. D’autre part, la glace de ségrégation joue un rôle majeur dans l’accélération de l’incision des chenaux de recoupement de méandres. Enfin, l’érosion latérale moyenne mesurée durant la période d’étude (10,3 cm en 19 mois) a été comparée au recul moyen des berges déterminé sur la base de comparaison diachronique du tracé de la rivière sur photographies aériennes à grande échelle (1952-1982, 1982-2007). Le recul annuel moyen des berges de la rivière s’élève à 0,24 m/a pour la première période et à 0,18 m/a pour la seconde, ce qui est supérieur à la valeur observée entre 2008 et 2009, bien que cette période ait été caractérisée par un hiver rigoureux. Ce ralentissement de l’érosion pourrait s’expliquer par une érosion fluviatile plus faible suite au développement des méandres qui semblent avoir atteint un stade de stabilité et qui tendent maintenant au recoupement. [less ▲]

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