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See detailStudy of the bedload transport in gravel bed rivers
Houbrechts, Geoffrey ULg; Hallot, Eric ULg; Peeters, Alexandre ULg et al

Conference (2009, July)

Bedload transport has been studied in Ardenne rivers using different methods. Experiments with marked pebbles were carried out on gravel bed rivers in order to determine critical parameters of ... [more ▼]

Bedload transport has been studied in Ardenne rivers using different methods. Experiments with marked pebbles were carried out on gravel bed rivers in order to determine critical parameters of mobilisation. The tracking of more than 1000 elements marked with PIT-tags (Passive Integrated Transponder) has been performed on different sized rivers during three hydrological seasons. These surveys allowed us to determine the initial motion of bed material, to measure the distance of particle travel from flood to flood, to reconstruct the trajectories of pebbles, to analyze the burying of particles into the subsurface layer and to identify the trapping sites and their effects on the bedload progression. On the same rivers, the thickness of the active bed layer has been measured using scour chains. It appears that the mobilised layer thickness increases with specific stream power. Bedload discharge of several floods has also been estimated crossing the active layer thickness and the mean progression distance of marked pebbles. Pits have been dug across the bed of a gravel bed stream (catchment area of 12 km²) in order to trap all particles moving on the bed. Volume of sediments trapped has been measured after each flood event and the largest elements mobilised have been measured. These observations show that bedload trapped is clearly more important that bedload discharge estimated by the method of scour chains and marked pebbles. This difference is for the most part explained by the trapping of sandy matrix from the subsurface layer, which is also moving on the bed. In this headwater stream (forested floodplain), the specific bedload discharge is only 0.4 t.km-1.year-1. Such a value is relatively low in comparison with other Ardenne rivers (up to 2,5 t.km-1.year-1), but may be partly explained by numerous vegetation logjams, which slow down bedload progression and increase bed roughness. [less ▲]

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See detailEvolution of floodplain sedimentation during the last millennia in the Ardenne Massif (Belgium)
Houbrechts, Geoffrey ULg; Notebaert, Bastiaan; Verstraeten, Gert et al

Poster (2009, July)

In the Ardenne massif, several periods of increased sediment deposition have been identified during the last millennia. They can be correlated to increasing anthropogenic land use pressure. The majority ... [more ▼]

In the Ardenne massif, several periods of increased sediment deposition have been identified during the last millennia. They can be correlated to increasing anthropogenic land use pressure. The majority of the sediments found in floodplains were deposited in the last 4000 years, and in many cases even in the last 1000 years. In the Amblève catchment, the first increase in sediment deposition of the Holocene occurred during the Bronze Age (3200 BP), related to first deforestations and crop cultures in the area. Several organic depositions have occurred between 2700 BP and 1000 BP and probably indicate low anthropogenic pressures or more humid periods. From the 11th century onwards, there was an increase in sedimentation, and alluvial deposits contain more charcoal. A second important increase in sedimentation is observed in headwater catchments at the end of the 14th century, which can be related to the development of many iron factories. In the Ardenne massif, more than 300 iron factories existed between the 14th and the 19th century and about 20 ha of forest were cleared each year for the consumption of a refining forge or a blast furnace. Analysis of slag concentration produced in former factories and redistributed in the floodplain allows us to reconstruct the evolution of floodplains since the inception of the iron industries. The results show that not all floodplains in the Amblève catchment are equally sensitive to catchment disturbances. In the headwater stream (Chavanne river, 10-20 km²), about 80 cm of sediment has been deposited since the inception of the iron industries (towards 1540 AD). In the lower Lienne valley (100-150 km²), almost no sediment accumulation occurred in the floodplains after the beginning of iron melting (towards 1400 AD). This difference could be explained by the larger stream power of the Lienne river (100-120 W/m2 for Qb). [less ▲]

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See detailBedload progression in gravel bed rivers using iron slag as a tracer
Houbrechts, Geoffrey ULg; Levecq, Yannick; Mols, Julien et al

Poster (2009, July)

In fluvial dynamics studies, different methods are used to evaluate bedload transport and particle travel lengths. However, results are mostly based on a few transported elements and on a relatively short ... [more ▼]

In fluvial dynamics studies, different methods are used to evaluate bedload transport and particle travel lengths. However, results are mostly based on a few transported elements and on a relatively short time scale. Consequently, it is difficult to extrapolate these results to whole bedload, because of the burying of particles into the subsurface layer or the trapping of elements in fluvial forms (point bars, riffles, …), which can immobilise elements during long periods. Bedload progression has been evaluated in Ardenne rivers using slag elements produced by the past factories established along rivers between the 14th and the 19th centuries. Important quantities of slag were dumped close to rivers or even directly into channels. For several centuries, slag elements were dispersed in the bedload and transported by floods of varying importance. Consequently, slag can be considered as a tracer to analyze bedload progression over several centuries. The size of slag elements has been studied in many Ardenne rivers. The longitudinal size trend of the largest slag particles allows us to determine the effective competence of rivers and to analyze the hydraulic sorting. Moreover, downstream of some metallurgic sites, we have constrained the presence of slag elements to the most downstream riffles. Because we know from historical studies the periods of activities of these sites, we may estimate the speed of bedload progression in several gravel bed rivers from the Ardenne Massif (2-3 km/century). [less ▲]

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See detailAnalysis of lateral mobility of channels at different spatial and time scales (Ardenne massif, Belgium)
Houbrechts, Geoffrey ULg; Van Campenhout, Jean ULg; Hallot, Eric ULg et al

Poster (2009)

Lateral mobility of Ardenne rivers has been studied at different scales using three complementary methods. We firstly compared the layout of channels on topographic maps (since the 18th century) and ... [more ▼]

Lateral mobility of Ardenne rivers has been studied at different scales using three complementary methods. We firstly compared the layout of channels on topographic maps (since the 18th century) and aerial pictures. Given that these documents have different scales and projection systems, they were transformed into a common referencing system. This method allowed us to study the lateral shifting of channels, however, as the mobility of Ardenne rivers is relatively low, the errors of geometric rectifications are often more important than lateral displacements. Therefore, to visualize these deformations, georeferenced documents were overlaid with a regular grid of points. We represented the imprecision vector based on x and y residual components for each point. These vectors show the direction of the deformation and its amplitude. Large quantities of iron slag are present in the sediments of Ardenne rivers. These waste products come from hundreds of ironworks built close to rivers since the 14th century. Analyses of slag concentrations in alluvial deposits allowed us to delimitate the sectors of floodplains eroded by rivers during the last centuries. In these sectors, slag elements are present at the contact with the gravel sheet. Finally, we analysed the topography of floodplains from a DEM-LIDAR. This digital elevation model has been established by the Walloon Region for the cartography of flood risk in floodplains. It presents a Z mean error of only 15 cm and a X-Y resolution of 1 m. In order to reveal paleochannels and topographic alluvial units, we subtracted a surface, corresponding to the longitudinal water surface slope, extracted from the DEM. By using this method, we are able to obtain the relative height of any point of the floodplain with regard to the water surface, projected perpendicularly to the layout, on this point. This procedure reveals paleochannels even if they are almost infilled and allows us to delimitate, for several kilometres, alluvial units, which have been formed at different periods. [less ▲]

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See detailResponse of floodplain sedimentation to catchment disturbances in different environments
Notebaert, Bastiaan; Houbrechts, Geoffrey ULg; Verstraeten, Gert et al

Poster (2009)

Holocene floodplain sediments are an important environmental archive, that can be accesed for reconstructing the past landscape dynamics either qualitatively (e.g. palynology) and quantitatively (e.g ... [more ▼]

Holocene floodplain sediments are an important environmental archive, that can be accesed for reconstructing the past landscape dynamics either qualitatively (e.g. palynology) and quantitatively (e.g. sediment budgeting). In this study Holocene alluvial sediment deposition in two contrasting Belgian catchments was quantified and dated: the Lienne (148 km²) in the Ardennes massif and the Dijle (750 km2) in the loess region. These catchments experienced a comparable Holocene climatic variation, but differ in topography and geology with highest relief energy in the Lienne catchment. Land use history also differs with high land use intensities in the Dijle catchment since Roman times, but at least since the Middle Ages there were also large deforestations in the Lienne catchment. Detailed cumulative Holocene sediment deposition was assessed for each catchment using more then 1000 hand augerings. Detailed radiocarbon dating of fluvial deposits was performed in the Dijle catchment, while iron slag was used as a tracer for sediments deposited after 1350 AD in the Lienne catchment. Results show that sediment deposition is much larger in the Dijle catchment (~4.5 Mg ha-1 catchment area) then in the Lienne catchment (~0.2 Mg ha-1 catchment area). Dating results from the Dijle catchment show an increase of sediment deposition in the late Holocene, first starting in the colluvial valleys and later on prograding towards the main valleys. Variations in sedimentation rates can clearly be related to anthropogenous land use pressure, and the majority of the sediments found in colluvial and alluvial valleys were deposited in the last 4000 years, and in many cases even in the last 1000 years. Variations in sediment deposition within the catchment can partially be explained by differences in river valley physical settings (mainly valley slope), while in other cases hill slope sediment delivery (upstream erosion, connectivity between hill slopes and the river system) is the explaining factor. In the Lienne catchment, between 80 and 100% of the sediments present in the main valley were deposited before 1350AD, thus before the main period of forest clearance. On the other hand, about 50% of the Holocene sediment present in a main tributary was deposited after 1537 (local start of iron industry). This difference with the main valley can be explained by a difference in physical settings of the river (valley slope, stream power). These results show that the physical settings of river valleys determine how sensible the river systems are to catchment disturbances. Floodplain deposition is determined by an interplay of hill slope sediment delivery (hill slope erosion and connectivity) and physical settings of the valley itself (valley slope, discharge). As a result, quantification of floodplain deposition alone, cannot be used as a measure for historic soil erosion within a catchment or to determine intensity of human impact on the catchment. [less ▲]

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See detailFluctuation of sediment production during the last millennia in the Ardenne Massif (Belgium)
Houbrechts, Geoffrey ULg; Notebaert, Bastiaan; Petit, François ULg et al

Poster (2009)

In the Ardenne massif, floodplains have recorded fluctuations in the production of sediment and several periods of increased sediment deposition have been identified. Before the first deforestations ... [more ▼]

In the Ardenne massif, floodplains have recorded fluctuations in the production of sediment and several periods of increased sediment deposition have been identified. Before the first deforestations rivers developed multiple channels in alluvial forests. Floodplains were not well-developed and probably very humid, which explains the presence of peat layers within the alluvial sequences. In the Amblève catchment, the first increased sedimentary deposition of the Holocene occurred during the Bronze Age (3200 BP), in relation to deforestation and the first crop cultures in the area. An organic deposition has occurred around 2700 BP and could correspond with a period of climatic degradation. Several peat layers have also been dated to around 1000 BP and probably indicate very low anthropogenic pressure. From the 11th Century onwards, there was an increase in sedimentation and a greater concentration of charcoal is present in the alluvial deposits. In many catchments there is an important increase in the sedimentation at the end of the 14th century, which can be related to the development of many iron factories. Analyses of slag concentration produced in these former factories allow us to reconstruct the evolution of the floodplain topography since the inception of the iron industries, in relation to the periods of activity. Total sedimentation in the smaller valleys since the initiation of iron industries amounts 0.5 to 1.0 m, which is in most cases about 50% of the total sediment present in the floodplains and corresponds to a mean sedimentation rate ranging between 10 and 20 cm/century. Such values are explained by various former agricultural practices and forest clearings associated with the huge demand for charcoal by the iron industry. About 20 ha of forest were cleared for the yearly consumption of a refining forge or a blast furnace and more than three hundred iron factories existed in the Ardenne Massif between the 14th and the 19th century. [less ▲]

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See detailMulti-disciplinary approach for sediment dynamics study of active floodplains
Gautier, E.; Corbonnois, J.; Petit, François ULg et al

in Geomorphologie (2009)

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See detailHabitat Choice by Atlantic Salmon Parr in Relation to Turbulence at a Reach Scale
Enders, Eva C; Roy, Mathieu L; Ovidio, Michaël ULg et al

in North American Journal of Fisheries Management (2009), 29(6), 1819-1830

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 ... [more ▼]

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 dynamic hydraulic variables. Our results revealed that under naturally turbulent conditions, the parr displayed high individual variability in their habitat use. Such heterogeneous use of habitat suggests that individuals are not constrained to a single habitat type. Furthermore, no differences were observed in habitat use among the four daily periods (dawn, day, dusk, and night) for individual parr. [less ▲]

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See detailGeomorphology of streams and rivers
Bravard, J. P.; Petit, François ULg

in Encyclopedia of Inland Waters (2009)

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See detailCan turbulence statistics reflect the meso-habitat choice of juvenile salmonids
Enders, Eva; Ovidio, Michaël ULg; Hallot, Eric ULg et al

in Proceedings of the combined conference on Hydro-Informatics and Ecohydraulics, Concepcion, Chile, January 2009. (2009)

Variables commonly used to describe the physical habitat of Atlantic salmon Salmo salar L. parr are average velocity, water depth, and substrate. A variety of micro- and meso-habitat models have been ... [more ▼]

Variables commonly used to describe the physical habitat of Atlantic salmon Salmo salar L. parr are average velocity, water depth, and substrate. A variety of micro- and meso-habitat 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 Patapédia River, Québec, Canada. We analyzed meso-habitat use in relation to several dynamic hydraulic variables. Our results revealed that in a natural turbulent condition, parr displayed high individual variability in habitat use in relation to turbulence. Such heterogeneous use of habitat suggests that individuals are not constrained to a single habitat type but that they have a tendency to use areas with lower turbulence. [less ▲]

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See detailAnalysis of lateral mobility of Ardenne rivers during the last centuries using iron slag
Houbrechts, Geoffrey ULg; Snijders, Jean-Philippe; Petit, François ULg

Poster (2008)

In the Ardenne region, old maps of different periods indicate that the layout of major rivers has been relatively stable since the end of the 18th century. However, given the scale of the different ... [more ▼]

In the Ardenne region, old maps of different periods indicate that the layout of major rivers has been relatively stable since the end of the 18th century. However, given the scale of the different documents and the relative inaccuracy of their georeferencing, it is not possible to precisely measure the rivers’ lateral erosion or to study the dynamic of small rivers. Moreover, maps older than the 18th century are not precise enough to permit this type of approach. Quantities of slag elements are present in the Ardenne rivers. These waste products come from hundreds of ironworks (blast furnaces and bloomeries) built close to different-sized rivers between the 14th and the 19th centuries. Slag was piled onto the floodplains and frequently thrown out directly into the rivers. For centuries, these slag elements were carried away during floods and were spread out along rivers. Given their properties, slag elements can be easily identified in sediments. When the slag elements are present in fine sediments at the point of contact with the gravel sheet, it means that the river has moved laterally since the inception of the iron industry, swept away older sediments and deposited more recent sediments contaminated by the slag. From historical studies, we precisely dated the periods of ironwork activity in several valleys. We also analysed the vertical concentrations of slag elements in several borings carried out along perpendicular cross sections. These data allowed us to estimate the lateral erosion velocity of some channels over several centuries. Moreover, we reconstructed the topography of several alluvial plains at the time ironworks were established and we evaluated sedimentation rates. [less ▲]

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See detailHolocene sediment deposition in contrasting Belgian catchments
Notebaert, Batsiaan; Houbrechts, Geoffrey ULg; Verstraeten, Gert et al

in LUCIFS Workshop December 2008: Programme and Abstracts (2008)

Holocene alluvial sediment deposition was studied in several contrasting Belgian catchments: the Geul (380 km2) and its tributary the Gulp (47 km2), the Amblève (1070 km2) and its tributary the Lienne ... [more ▼]

Holocene alluvial sediment deposition was studied in several contrasting Belgian catchments: the Geul (380 km2) and its tributary the Gulp (47 km2), the Amblève (1070 km2) and its tributary the Lienne (148 km²), and the Dijle (750 km2). These catchments have a comparable Holocene climatic evolution, but they differ largely in land use history. Detailed total Holocene sediments deposition was assessed for each catchment using more then 1000 hand augerings. Detailed radiocarbon dating of fluvial deposits was performed in the Dijle catchment, while iron slag was used as a tracer for sediments deposited after 1350 AD in the Lienne catchment. For the Geul River the presence of lead contamination, originating from 19th century mining activities, were used as a tracer. Results show that sediment deposition is much largest in the Dijle catchment (4.6 Mg/ha catchment area) then in the Gulp catchment (1.3 Mg/ha catchment area), while the lowest deposition is found in the Amblève catchment (0.2 Mg/ha catchment area). It is clear that these differences are mainly due to historical land use differences, although it can not be excluded that part of these differences are due to physical factors, especially for the Amblève catchment. For the latter catchment, the distribution of iron slags in the floodplain sediments showed that large parts of the alluvial plane were eroded after 1350 AD, and thus that there is no net aggradation as for the Dijle and Gulp floodplain. Remobilization of floodplain sediment in the Amblève makes it also difficult to estimate Holocene erosion rates. Nevertheless it is clear that an important part of the sedimentation took place after the Middle Ages, and that during Medieval times the river changed from a system with two or more channels to a system with one single channel. This is probably related to increasing deforestation after 1350 AD. Dating results of the Dijle floodplain show that the sedimentation rates are largely influenced by land use with main deposition after the Middle Ages. There is a gradual increase in sedimentation rate since Neolithic times and each new cultural period is recognized by an increase in sedimentation rate related to the intensification of land use. Several sites show that sedimentation rates have recently decreased, probably due to a reduction in cropland area. 12 Dating of the Geul River floodplain suggests a high sedimentation rate during the 19th century and lower rates for more recent times, which can be related to the more intense 19th century land combined with mobilization of sediments by the mining activities, which ended at the end of that century. From the data collected in these catchments it is clear that land use changes are the main driving factors for accelerated alluvial sediment deposition rates, although climate fluctuations can have influenced the impact of land use changes. [less ▲]

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See detailEtude géomorphologique des barrages de travertin du Hoyoux
Franco, Bruno ULg; Houbrechts, Geoffrey ULg; Van Campenhout, Jean ULg et al

in Bulletin de la Société Géographique de Liège (2008)

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See detailLa typologie et les caractéristiques hydromorphologiques des cours d'eau wallons
Petit, François ULg; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

in Bilan d'une décennie d'ingénierie écologique (2008)

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See detailEvaluation de la résistance des aménagements par techniques végétales face aux événements hydrologiques
Peeters, Alexandre ULg; Hallot, Eric ULg; Houbrechts, Geoffrey ULg et al

Poster (2007, October)

Lors du suivi géomorphologique d’aménagement ou de restauration de cours d’eau par techniques végétales réalisé en Région Wallonne, nous nous sommes entre autres intéressés à la résistance que ces ... [more ▼]

Lors du suivi géomorphologique d’aménagement ou de restauration de cours d’eau par techniques végétales réalisé en Région Wallonne, nous nous sommes entre autres intéressés à la résistance que ces techniques offraient face aux différents évènements hydrologiques. Nous avons étudié plusieurs types de techniques (telles que plantations, caissons, épis, peignes et fascines, végétalisation de gabions, techniques combinées...) réalisés sur des rivières de différentes tailles, situées dans des contextes géomorphologiques régionaux variés (impliquant une dynamique différente). La résistance de ces techniques a été évaluée en utilisant la puissance spécifique calculée lors des différentes crues subies par l’aménagement. Cette dernière représente la capacité de travail qu'une rivière peut effectuer et elle permet, ente autres, d'appréhender l'activité des rivières en ce qui concerne les formes et la dynamique des méandres (Ferguson, 1981 ; Bravard, 1991) mais également la possibilité de réaction et d'adaptation des rivières en réponse à des travaux d'aménagement (Brookes, 1998). Les puissances spécifiques ont été calculées non seulement pour le débit à plein bord mais aussi pour la première crue importante survenue après la mise en place du chantier. Par ailleurs, les récurrences des crues ont également été déterminées. Ces premiers résultats nous permettent de proposer une synthèse s’intégrant dans un guide technique (Technique végétales : conception, application et recommandations, GIREA - LHGF) destinés aux différents gestionnaires. BRAVARD J.P., 1991. La dynamique fluviale à l’épreuve des changements environnementaux : Quels enseignements applicables à l’aménagement des rivières ? La Houille Blanche, 7-8, 515-521. BROOKES A., 1988. Channelized rivers, perspectives for environmental management. Wiley, New York, 326 p. FERGUSON R.I., 1981. Channel form and channel changes ; In British Rivers, Lewin J. (Ed), Allen, London,, 91- 125. [less ▲]

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