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See detailCritical specific stream power in gravel-bed rivers
Petit, François ULg; Gob, Frédéric ULg; Houbrechts, Geoffrey ULg et al

in Geomorphology (2005), 69(1-4), 92-101

Experiments with marked pebbles were carried out on different sized rivers of the Belgian Ardenne (catchment areas varying from less than I km(2) to 2700 km(2)). Specific stream power required to cause ... [more ▼]

Experiments with marked pebbles were carried out on different sized rivers of the Belgian Ardenne (catchment areas varying from less than I km(2) to 2700 km(2)). Specific stream power required to cause bedload movement was evaluated and critical values were obtained. Three types of relationship between critical specific stream power (omega(0)) and grain size (D) were established. The values for coo in the largest river (the Ourthe) were the lowest and were close to the values obtained for mountainous rivers carrying large boulders. In medium sized rivers (catchment area between 40 and 500 km(2)), the critical unit stream power was higher. It is likely that it is due to the bedform's greater resistance. This resistance would use up some of the energy that can cause movement and transport of bedload. The amount of resistance of the bedform can be expressed as bedform shear stress (tau ''), determined by the relationship between grain shear stress (tau'-that determines movement and transport of the bedload) and the total shear stress (tau). This ratio varies between 0.4 and 0.5 in the medium sized rivers, compared to 0.7 in the Ourthe. In headwater streams (less than 20 km(2)), there is greater loss of energy due to bedform resistance (tau'/tau < 0.3). Critical specific stream power is higher in this third type of river than in the other two. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailHabitat use of juvenile Atlantic salmon (Salmo salar): the relation between physical variables and individual mobility.
Roy, Mathieu; Ovidio, Michaël ULg; Enders, Eva et al

Conference (2005, May)

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See detailEvaluation des puissances spécifiques de rivières de moyenne et de haute Belgique
Petit, François ULg; Hallot, Eric ULg; Mols, J. et al

in Bulletin de la Société Géographique de Liège (2005)

Specific stream powers were calculated at more than 70 discharge stations along rivers with catchments between 10 and 2500 km². In order to calculate the stream power, bankfull discharge, average slope ... [more ▼]

Specific stream powers were calculated at more than 70 discharge stations along rivers with catchments between 10 and 2500 km². In order to calculate the stream power, bankfull discharge, average slope and width were calculated at each station. The relationship between, on one hand, the size of the catchments and the bankfull discharge and, on the other, the size of the catchments and the width of the channels were highlighted. These allow several regional differentiations to be highlighted. With regard to the specific stream power, there is a clear contrast between the rivers from the South and the North Ardenn which show an East-West gradient of decreasing stream power. Rivers from Condroz and Entre-Vesdre-et-Meuse have intermediary values. Rivers from Hesbaye have very low stream powers. Stream power values partly account for the evolution of the river bed dynamics : in Hesbaye, where the rivers have low stream power (less than 15 W/m²), the river’s course is rather stable for a few centuries. In the South Ardenn (stream power lower than 30 W/m²), meanders are quite active and the meandering cycle is longer than a century. In the Entre-Verdre-et-Meuse (stream power between 30 and 40 W/m²), meanders are active and the river is able to readjust following anthropogenic constructions (deflectors). However, our observations deviate from threshold values proposed in the literature. Thus, the Geer (Hesbaye) is able to readjust and to create a secondary meandering following log-jams edifications, despite a stream power lower than 15 W/m². In the rivers such as the Ourthe in Famenne, despite rather high stream power values (higher than 50 to 70 W/m²), the meandering cycle is longer than a century. But, still in Famenne, braided channels are observed whereas the stream powers are clearly lower than the threshold proposed in the literature (stream power higher then 100 W/m²). Finally, in Ardenn, when we reach a threshold of 100 W/m², rivers develop an active low sinuosity system in place of an active free meander system. This active low sinuosity system is comparable to a step-pool system. [less ▲]

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See detailMetallurgic slag as a tracer in floodplain evolution studies
Houbrechts, Geoffrey ULg; Petit, François ULg; Juvigné, Etienne ULg et al

Conference (2005)

The aim of this study was to estimate sedimentation rates in floodplains and to investigate lateral channel migrations over the last centuries. Considering the difficulties in determining these parameters ... [more ▼]

The aim of this study was to estimate sedimentation rates in floodplains and to investigate lateral channel migrations over the last centuries. Considering the difficulties in determining these parameters using traditional dating methods, we have used different kinds of slag rejected from former metal works. In the Ardenne region (southern part of Belgium), at the end of 14th century, iron factories moved near to rivers in order to take advantage of the hydraulic energy. At the same time, large quantities of slag produced in primitive blast furnaces were piled onto the floodplains, often very close to rivers. Consequently, microslag could be carried away either during floods or by lateral erosion to be deposited on the floodplains downstream. In order to use slag as a stratigraphical tracer, we located slag waste sites along rivers and we dated the periods of furnace activity from historical studies. Afterwards, we measured slag concentrations in the alluvium and we studied their evolutions in different borings. These results allowed us to reconstruct the appearance of the floodplain at the inception of the metal works and to estimate lateral channel mobility over several centuries. Moreover, different kind of tephra and 14C dating have been used in order to date the deposits that have been established before the settlement of metallurgy. [less ▲]

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See detailRiver dredging, channel dynamics and bedload transport in an incised meandering river (the River Semois, Belgium).
Gob, F.; Houbrechts, Geoffrey ULg; Hiver, J. M. et al

in River Research & Applications (2005), 21(7), 791-804

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See detailSedimentary dynamics and bedload transport in the Semois River (Ardenne, Belgium)
Gob, Frédéric ULg; Houbrechts, Geoffrey ULg; Petit, François ULg

in River Research & Applications (2005), 21(7), 791-804

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See detailAnalyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et au Bénin).
Ago, Expédit Evariste ULg; Petit, François ULg; Ozer, Pierre ULg

in Geo-Eco-Trop (2005), 29

The analysis of risk of flood downstream from the hydroelectric dam of Nangbeto in the Mono River was about the survey of interannual variability of rainfall and rivers flows from 1955 to 1999, the ... [more ▼]

The analysis of risk of flood downstream from the hydroelectric dam of Nangbeto in the Mono River was about the survey of interannual variability of rainfall and rivers flows from 1955 to 1999, the population vulnerability, the hydrological modification and the impacts downstream in Togo and Benin from the dam constructed in 1987. The analysis of the mean annuel discharge has revealed no tendency, showing thus that the change of land use, the increase of waterproof areas and even the functioning of the hydroelectric dam have not modified in a significant manner the river's rate of flow. Apart from the return to the improvement in rainfull as far back as the end of years 80, the anthropic pressure and the demographic explosion have best explained the magnitude and frequency of flooding downstream from the hydroelectric dam of Nangbeto. The soil degradation, the deforestation of the floodplain, the increase in the number of human settlements in the river boundary increases the vulnerability of population faced with flooding. [less ▲]

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See detailDetermining the competence of mountainous Mediterranean streams using lichenometric techniques
Gob, F.; Jacob, N.; Bravard, J. P. et al

in International Association of Hydrological Sciences : “River Catchment Dynamics : Natural Processes and Human Impacts (2005)

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See detailParamètres hydrologiques et physico-chimiques de sources du Crétacé du Pays de Herve et de la Hesbaye sèche
Mols, J.; Petit, François ULg

in Bulletin de la Société Géographique de Liège (2005)

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See detailImpact of hydroelectric power releases on the morphology and the sedimentology of the bed of the Warche River (Belgium).
Assani, A. A.; Petit, François ULg

in Earth Surface Processes & Landforms (2004)

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See detailTurbulence et patron d’utilisation de l’habitat du saumon atlantique juvénile
Roy, M. L.; Ovidio, Michaël ULg; Hallot, Eric ULg et al

Scientific conference (2004)

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See detailElaboration d’une typologie hydro-géomorphologique de cours d’eau dans l’Euregio Meuse-Rhin
Hallot, Eric ULg; Schmitt, L.; Mols, J. et al

in Mosella - XXIX, 3-4 (2004)

This paper shows the first results of a method of river hydro-geomorphological typology applied on the Euregio Maas-Rhine. This is based on non factorial multivariate analysis (clusters) of only ... [more ▼]

This paper shows the first results of a method of river hydro-geomorphological typology applied on the Euregio Maas-Rhine. This is based on non factorial multivariate analysis (clusters) of only quantitative data automatically extracted from DEM or obtained by field measurements with a simplified protocol. The regional differentiation of variables allows the automatic characterization of rivers especially with the specific stream power. [less ▲]

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See detailMorphodynamics of the Meuse River and its tributaries in the Ardenne Massif
Petit, François ULg

in Symposium pour la Protection de la Meuse (2004)

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See detailCaractérisation et utilisation du micro-habitat du saumon atlantique (Salmo salar) selon la stucture turbulente del'écoulement.
Brown, Julie; Boyer, Claudine; Enders, Eva et al

Conference (2003, May)

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See detailEtude des impacts hydrauliques, sédimentologiques et écologiques liés aux travaux hydrauliques sur la Semois
Gob, Frédéric ULg; Houbrechts, Geoffrey ULg; Mols, Julien et al

in Schmitz, Serge (Ed.) Les Journées des Géographes Belges: Evaluer la capacité du milieu (2003)

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