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See detailHolocene floodplain deposition and scale effects in a typical European upland catchment : A case study from the Amblève catchment, Ardennes (Belgium)
Notebaert, Bastiaan; Verstraeten, Gert; Houbrechts, Geoffrey ULg et al

in Holocene (2013), 23(8), 1184-1197

This study quantifies Holocene alluvial sediment deposition in the Belgian Amblève catchment (1080 km2), situated in the Ardennes uplands. An extended coring data set is used for a quantitative ... [more ▼]

This study quantifies Holocene alluvial sediment deposition in the Belgian Amblève catchment (1080 km2), situated in the Ardennes uplands. An extended coring data set is used for a quantitative description and a quantification of the alluvial depositions. The floodplains fall into three main types: the upper and lower floodplains and the steep reaches. Total Holocene alluvial sediment deposition amounts to 32 Tg, or 0.029 Tg/km2. Dating of sediments using iron slag as tracer shows that on average 42% of contemporary storage was accumulated during the last 600 years. Radiocarbon dating of fluvial deposits at eight sites in the catchment confirms that the majority of the sediment is relatively recent. The increased sedimentation rates for this period are related to anthropogenic land use, possibly enhanced by climatic variations. A fluvial sediment budget was constructed for this 600 yr time period and shows that export from the catchment has about the same importance as storage in the floodplains, while lateral reworking of existing floodplain deposits only affects half the quantity of sediments. Overall, floodplain sediment storage in the Amblève catchment, comparable with other upland catchments, is of lesser importance compared with catchments dominated by loess. This can mainly be explained by lower sediment supply resulting from less intense anthropogenic land use, despite the higher sediment transport efficiency through the fluvial system. Floodplain sediment storage is scale-dependent, with initially a sharp increase in catchment area-specific sediment deposition, followed by a steady decrease with increasing catchment area. [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 detailCharacterisation of sand transport in gravel-bed rivers using iron slag dated by historical studies
Houbrechts, Geoffrey ULg; Levecq, Yannick; Petit, François ULg

Poster (2012, April 25)

Considerable quantities of iron-smelting slag are present in the bed of the Ardennian rivers. These waste products come from hundreds of ironworks (mainly blast furnaces and finery forges) built close to ... [more ▼]

Considerable quantities of iron-smelting slag are present in the bed of the Ardennian rivers. These waste products come from hundreds of ironworks (mainly blast furnaces and finery forges) built close to different-sized rivers between the 14th and the 19th centuries. In general, slag was crushed by hammers, sorted and piled up in heaps around the furnaces, generally onto the floodplains. Furthermore, some archives mention that they were sometimes thrown out directly into the rivers. This means that for centuries, slag elements have been swept away by floods, mixed with the sediment and spread out along river courses. Due to their distinctive appearance, slag particles are easily recognizable among the natural elements. Thanks to many historical studies conducted on the early iron industry, we are able to date quite precisely the inception and the periods of activity of the different sites established in the catchments. These data are indispensable in order to use slag as a tracer to quantify the particles’ velocity in rivers. Downstream of ironworks, samples of sand have been collected in the surface layer of many gravel-bed rivers. Then, the slag concentration of each sample has been measured in the coarse sand fraction. The representation of the longitudinal evolution of slag concentration in these rivers permits the dispersion of slag to be analysed, the relative bed-material discharges at confluences to be quantified and the velocity of coarse sand to be determined. A survey of the bedload discharge in the Ardennian rivers established that more than 90 % of the bedload transport consists of coarse sand grains that are transported on the bottom of the bed. However, in the literature, this grain-size fraction is generally not considered in bedload discharge estimations because the sandy particles are very difficult to tag and to recover. Consequently, the huge amounts of slag injected in rivers several centuries ago can be considered as a very useful opportunity to characterise the sand transport in gravel-bed rivers. [less ▲]

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See detailPilot project « Walphy » : Walloon experimentation of river restoration
Peeters, Alexandre ULg; Verniers, Gisèle; de le Court, Bernard et al

Conference (2012, April 20)

According to the Water Framework Directive (WFD 2000/60), our rivers and water bodies are required to achieve the “good ecological status” by 2015. This requirement is related to the physico-chemical ... [more ▼]

According to the Water Framework Directive (WFD 2000/60), our rivers and water bodies are required to achieve the “good ecological status” by 2015. This requirement is related to the physico-chemical, biological water quality as well as the hydromorphological quality. In this context, a LIFE Environment project, co-founded by the European Union and the Service Publique de Wallonie, was launched in 2009 for a period of five years. It aims to realize the experimental and demonstrative river restoration works on three “at risk” water bodies, based on two axes: longitudinal continuity and transversal continuity. The first two selected water bodies (Bocq, eastern tributary of the Meuse) are suitable for the restoration works which concern the longitudinal continuity due to the presence of dams and other obstacles between 1 and 3 m high. These works consist in dam management (weir removal or fish ladders) taking into account hydromorphological (bedload transport) and biological (invertebrate or fish species free movement) impacts. The third water body (Eau Blanche, western tributary of the Meuse) presents straightened rivers with artificial banks which consequently lead to poor connections between the stream and its floodplain. This water body is therefore appropriated for the works based on the transversal continuity recovery. These works consist in enhancing straightened river channel and restoring meanders or banks. Until now, these works have been realized on more than 5 km. These works are being monitored on the basis of geomorphological and ecological analysis. The geomorphological monitoring is based on surveys conducted before and after the works. It concerns the bedload transport, the clogging of the gravel layer and the morphological changes of the river following the works. The ecological monitoring is based on two indicators: macroinvertebrates and fishes. Standardized and repeatable methods were developed to compare the situation before and after the works, especially through the analysis of microhabitats. In addition, we use another two complementary indexes of physical quality for this monitoring. Developed by the consulting office Teleos, these indexes have a fish orientation and have been implemented in many of our stations. [less ▲]

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See detailL'origine des mégalithes du Fond de Quarreux (Ardenne, Belgique)
Collard, Sébastien; Juvigné, Etienne ULg; Marion, Jean-Marc ULg et al

in Bulletin de la Société Géographique de Liège (2012), 58

Origin of megaliths of the Fond de Quarreux (Ardenne, Belgium). Distribution of megaliths was studied in the Ambleve valley throughout its gorge developed within the quartzites of the Cambrian-aged La ... [more ▼]

Origin of megaliths of the Fond de Quarreux (Ardenne, Belgium). Distribution of megaliths was studied in the Ambleve valley throughout its gorge developed within the quartzites of the Cambrian-aged La Venne Formation (Fond de Quarreux) in the south-eastern part of high Belgium. The high concentration of megaliths at this place can be essentially explained by mass movements which have occurred on the adjacent slopes in periglacial periods of cold Ocean Isotopic Stages in Quaternary times, and especially the coldest ones i.e. even O.I.S.#22 through #2. Stratigraphical studies of deposits in the Chefna and Ambleve valleys allowed us to place final periglacial deposits during the Younger Dryas. The critical shear stress and the critical unit stream power are used in order to evaluate the Ambleve River competence. It results that, under the present climatic conditions, this river cannot move boulders of more than 50 cm in diameter. Hence, it is concluded that ice rafting has been the main process responsible for carrying away the megaliths which have got the Ambleve river bed throughout the Quaternary Period. [less ▲]

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See detailL'envasement du lac de Butgenbach (Ardenne, Belgique)
Hallot, Eric ULg; Benoit, Morgan; Stasse, Guillaume et al

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

In 2004, the Butgenbach lake reservoir (Warche river) has been emptied for the first time since 1932. The sediments deposited have been studied with a double objective : on the one hand to determine the ... [more ▼]

In 2004, the Butgenbach lake reservoir (Warche river) has been emptied for the first time since 1932. The sediments deposited have been studied with a double objective : on the one hand to determine the volume of sediment deposits, and on the other hand to estimate mean soil erosion rate in the catchment. Some five hundreds manual augerings were made using a thin auger (15 mm) throughout the wet and soft sediments (mud) in order to identify the lake deposits that have overlain the previous soft material (flood silts in the flood plain of the river Warche, silty soils on the slopes). Since the expected boundary between both types of materials could not be identified by the naked eye, a qualitative analysis of diatoms, magnetic susceptibility, grain-size distribution and calcination has been made for fifteen thicker cores (3.6 mm across) taken at representative sites. Mean annual area-specific sediment yield amounts to 28 – 33 t.km-².y-1 [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 detailMicrohabitats survey used in river restoration
Peeters, Alexandre ULg; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

Conference (2011, October 14)

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See detailRestauration hydromorphologique : Les échelles de travail optimales ?
Hallot, Eric ULg; Peeters, Alexandre ULg; Verniers, Gisèle et al

Conference (2011, October 03)

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See detailFluvial architecture of Belgian river systems in contrasting environments:implications for reconstructing the sedimentation history
Notebaert, Bastiaan; Houbrechts, Geoffrey ULg; Verstraeten, G. et al

in Netherlands Journal of Geosciences - Geologie en Mijnbouw (2011), 90(1), 31-50

Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the ... [more ▼]

Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the floodplain. In this study we discuss the fluvial architecture of three contrasting Belgian catchments (Dijle, Geul and Amblève catchment) and how this influences the dating possibilities of net floodplain sediment storage. Although vertical aggradation occurred in all three floodplains during the last part of the Holocene, they differ in the importance of lateral accretion and vertical aggradation during the entire Holocene. Holocene floodplain aggradation is the dominant process in the Dijle catchment. Lateral reworking of the floodplain sediments by river meandering was limited to a part of the floodplain, resulting in stacked point bar deposits. The fluvial architecture allows identifying vertical aggradation without erosional hiatuses. Results show that trends in vertical floodplain aggradation in the Dijle catchment are mainly related to land use changes. In the other two catchments, lateral reworking was the dominant process, and channel lag and point bar deposits occur over the entire floodplain width. Here, tracers were used to date the sediment dynamics: lead from metal mining in the Geul and iron slag from ironworks in the Amblève catchment. These methods allow the identification of two or three discrete periods, but their spatial extent and variations is identified in a continuous way. The fluvial architecture and the limitation in dating with tracers hampered the identification of dominant environmental changes for sediment dynamics in both catchments. Dating methods which provide only discrete point information, like radiocarbon or OSL dating, are best suited for fluvial systems which contain continuous aggradation profiles. Spatially more continuous dating methods, e.g. through the use of tracers, allow to reconstruct past surfaces and allow to reconstruct reworked parts of the floodplain. As such they allow a better reconstruction of past sedimentation rates in systems with important lateral reworking. [less ▲]

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See detailFacteurs de variabilité spatiale des caractéristiques des débits minimums annuels des rivières wallonnes (Belgique)
Vadnais, Marie-Ève; Assani, Ali A.; Hallot, Eric ULg et al

in Revue des Sciences de l'Eau = Journal of Water Science (2011), 24(3), 311-327

The goal of this study was to determine which environmental factors affect the spatial variability of annual minimum streamflow characteristics for 34 rivers in Wallonia (Belgium) using two complementary ... [more ▼]

The goal of this study was to determine which environmental factors affect the spatial variability of annual minimum streamflow characteristics for 34 rivers in Wallonia (Belgium) using two complementary methods: theascending hierarchical classification method and the linear correlation method. Both methods were applied after principal component analysis transformation was applied to the data. The ascending hierarchical classification method (Ward’s method) identified the effect of lithology and anthropogenic activity (groundwater pumping) on the fundamental characteristics of annual minimum flows. Rivers that drain a relatively permeable substrate are characterized by very high flow volumes with low interannual variability, high interannual variability of the period of occurrence, and small asymmetry coefficients. Rivers that drain low permeability or impermeable substrates show the opposite patterns. Rivers in which flow is subjected to artificial influences are characterized by greater variability of the magnitude and of the period of occurrence of annual minimum flows than natural rivers. Analysis of linear correlations between streamflow characteristics and environmental factors highlighted a correlation between the form of the distribution curves of annual minimum flows and several environmental factors (climate, land use, location and physiographic characteristics of the watersheds). [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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See detailLong-term bedload mobility in gravel-bed rivers using iron slag as a tracer
Houbrechts, Geoffrey ULg; Levecq, Yannick ULg; Vanderheyden, Vincent ULg et al

in Geomorphology (2011), 126

Bedload dispersion is evaluated in gravel-bed rivers using slag elements from ironworks established along rivers in the Ardenne region, between the fourteenth and the nineteenth centuries. Large ... [more ▼]

Bedload dispersion is evaluated in gravel-bed rivers using slag elements from ironworks established along rivers in the Ardenne region, between the fourteenth and the nineteenth centuries. Large quantities of slag were dumped close to these rivers or even directly into the channels. For centuries, slag elements were dispersed in the bedload and transported by floods of varying importance. Consequently, slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries. The size of slag elements was studied along 16 Ardenne rivers. The longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined (between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 W/m²). A direct relationship doesn’t exist between these two parameters as the size of slag elements must be considered with regard to the D50 of the bed. Selective transport was analyzed directly downstream of the input sites. The sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry. Downstream of two metallurgic sites, the slag propagation fronts were located. As the periods of activity at these sites are known from historical studies, the virtual velocity of bedload movement in these rivers was estimated to be 2-4 km/century. [less ▲]

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See detailUtilisation des scories sidérurgiques comme marqueur stratigraphique pour l'étude de l'évolution géomorphologique des plaines alluviales
Houbrechts, Geoffrey ULg; Petit, François ULg

Conference (2010, November 22)

Afin d’analyser la dynamique récente des plaines alluviales des rivières du massif ardennais, nous avons utilisé les scories, résidus de la transformation du minerai de fer en métal, comme marqueur ... [more ▼]

Afin d’analyser la dynamique récente des plaines alluviales des rivières du massif ardennais, nous avons utilisé les scories, résidus de la transformation du minerai de fer en métal, comme marqueur stratigraphique. Les scories constituent un traceur particulièrement exceptionnel ; elles sont présentes en grande quantité dans les alluvions des rivières ardennaises et les périodes d’activités des sites sidérurgiques et donc de rejets de scories sont connues précisément grâce aux études historiques. C’est à partir du XIVe siècle que les sidérurgistes wallons commencèrent à utiliser la roue hydraulique pour actionner les soufflets et les martinets des forges. Ils installèrent donc leurs fourneaux et leurs forges d’affinage à proximité des cours d’eau et produisirent de grandes quantités de scories. Ainsi, un haut fourneau du 16e siècle, qui fonctionnait en moyenne 130 jours par an, produisait de l’ordre de 80 m³ de scories par an. Ces scories étaient généralement rejetées sur les plaines alluviales, voire directement dans le lit des cours d’eau. Par la suite, ces scories ont été emportées lors des crues débordantes ou par érosion latérale de la rivière. Entre le XIVe et le XIXe siècle, plus de 300 sites sidérurgiques ont été actifs le long de plusieurs dizaines de rivières du massif ardennais. L’utilisation des scories comme marqueur stratigraphique a été proposée par le Professeur A. Pissart en 1972 et appliquée par Henrottay (1973), afin de déterminer des taux de sédimentation et de mobilité latérale postérieurs à l’apparition de l’activité sidérurgique dans les vallées. A la suite de cette étude, nous avons développé une méthode de mesure de concentration en scories qui permet de mieux localiser le contact entre les sédiments pré-et post-sidérurgiques, et de tenir compte de l’influence de la bioturbation et des contaminations lors des prélèvements. De plus, cette méthode montre que les teneurs en scories dans les sédiments ont varié dans le temps en relation avec les périodes de fonctionnement, d’expansion et d’arrêt des sites sidérurgiques situés en amont. Grâce aux scories, nous avons montré que la sédimentation en plaine alluviale a été particulièrement importante depuis la fin du Moyen Âge, de l’ordre de 10 à 20 cm/siècle en fonction des cours d’eau. La mobilité latérale des rivières est par ailleurs relativement faible et moins importante que les valeurs basées sur la comparaison de tracés sur cartes anciennes. [less ▲]

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See detailÉtude cartographique et projet de restauration sur une rivière rectifiée, l’Eau Blanche
Peeters, Alexandre ULg; Verniers, Gisèle; Hallot, Eric ULg et al

Conference (2010, October 04)

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See detailDesign of a decision tool for hydromorphological restoration of water bodies in Walloon Region
Peeters, Alexandre ULg; Hallot, Eric ULg; Verniers, Gisèle et al

Poster (2010, May 05)

The pilot project WALPHY (LIFE + Environment LIFE07 ENV/B/000038, UE-funded) develops a structured approach aiming at improving hydromorphological quality of the upstream Meuse basin in order to achieve ... [more ▼]

The pilot project WALPHY (LIFE + Environment LIFE07 ENV/B/000038, UE-funded) develops a structured approach aiming at improving hydromorphological quality of the upstream Meuse basin in order to achieve the “good ecological status” required by the Water Framework Directive (WFD 2000/60). It began in January 2009 for a period of 5 years. River’s biological recovery needs the recovery of river’s structure and physical dynamics. Returning to "good ecological status" inevitably involves physical restoration of affected rivers. Physical component of aquatic environment acts as a limiting factor for their functioning. Three types of modification are key obstacles for river good ecological status: (i) fluxes alteration (discharge, sedimentation. . . ), (ii) forms alteration (uniform facies. . . ) and (iii) biotopes access alteration (lateral connections breaks, modification of the continuity upstream/ downstream. . . ). Therefore hydromorphology is needed to implement the WFD. To respond to this legal necessity, we develop a unique, useful and suitable methodology in Walloon Region to determine and schedule river physical quality restoration works. This methodology has been applied on 3 “risk water bodies”. The works are based on two axes : longitudinal continuity and transversal continuity. The two first selected water bodies (Bocq river, eastern tributary of the Meuse) seem to be convenient for the restoration works which concern the longitudinal continuity due to the presence of dams and other obstacles usually between 1 and 3 m high. These works consist in dam management (weir removal or fish passage) taking into account hydromorphological (bedload transport) and biological (invertebrate or fish species free movement) impacts. The third water bodies (Eau Blanche river, western tributary of the Meuse) presents straightened rivers with artificial banks, witch consequently own bad connections between the stream and its floodplain. This water bodies should therefore be appropriated for the works based on the transversal continuity recovery. They consist in enhancing straightened river channels, restoring meanders or bank restoration. The first river restoration works will take place from summer 2010. A monitoring has already been undertaken to draw up the situation before the restoration works, witch will be able to compare to the situations during and after works. In addition, a natural site has been chosen to enable any comparison with the intervention sites. The geomorphological monitoring is based on physical and sedimentological parameters (substrate cartography, velocity measures, stream channel DEM, topography and sedimentological index). The ecological monitoring consists in analysing the physical and chemical parameters (turbidity, suspended sediment load). It also analyses the biological quality through 3 indicators: macrophytes, macroinvertebrates and fishes. Among other, a microhabitats method has been improved and applied on 3 intervention sites and 1 natural site. The microhabitats cartography results from both the flow velocity cartography and the substrate cartography. With this method, the physical quality of each intervention site could be compared with the natural site and above all with the future situation. Our method is also useful to inventory precisely invertebrates and to characterise fish habitats. [less ▲]

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