Publications of Eric Hallot
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See detailCan coarse bedload pass through weirs?
Peeters, Alexandre ULiege; Houbrechts, Geoffrey ULiege; Hallot, Eric ULiege et al

in Geomorphology (2020), 359

Restoring active bedload transfer in human-impacted rivers has received increasing attention in recent years, notably in response to the European Water Framework Directive (WFD), which requires that the ... [more ▼]

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

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See detailUsing multi-temporal landsat images and support vector machine to assess the changes in agricultural irrigated areas in the mogtedo region, burkina faso
Traoré, Farid; Bonkoungou, Joachim; Compaoré, Jérôme et al

in Remote Sensing (2019), 11(12),

Over the last few decades, small-scale irrigation has been implemented in Burkina Faso as a strategy to mitigate the impacts of adverse climate conditions. However, the development of irrigated perimeters ... [more ▼]

Over the last few decades, small-scale irrigation has been implemented in Burkina Faso as a strategy to mitigate the impacts of adverse climate conditions. However, the development of irrigated perimeters around small and medium water reservoirs has put the water resources under significant pressure, given the uncontrolled exploitation and lack of efficacious management plan. Insights into changes in irrigated areas around these reservoirs are therefore crucial for their sustainable management while meeting the different agricultural water needs. They will help to center policy priorities in terms of major impacts on the reservoirs; and thereby elaborate relevant mitigation and/or adaptation strategies. The main objectives of this study were to (1) quantify the changes in irrigated land areas surrounding the Mogtedo water reservoir between 1987 and 2015; and (2) determine whether the irrigable potential of this reservoir could sustainably meet the agricultural water needs under a more variable and changing climate. A low-cost remote sensing method based on Landsat imagery (Thematic Mapper, Enhanced Thematic Mapper Plus, and Operational Land Imager) and using Support Vector Machine (SVM) classification was developed to detect the changes in proportion of land use/land cover (LULC) in the Mogtedo region. A forward and backward change detection analysis requiring agronomic expertise was also applied to correct the pixels temporal trajectories. In addition, an intensity analysis was performed to assess land changes at time intervals, category, and transition levels. Five main LULC classes were identified: bare and hydromorphic soils, irrigated and rainfed agricultural areas, and water bodies. Overall, the classification of LULC was satisfactory with the overall accuracy and kappa coefficients ranging from 94.22 to 95.60% and 0.92 to 0.94, respectively. Results showed that LULC transformations were faster between 2000 and 2015, compared to the 1987-2000 period. The majority of categories (LULC classes) were active in terms of intensity of change (gain or loss) during the 1987-2000 and 2000-2015 periods, except hydromorphic soils. During these periods, the transition from rainfed agricultural areas to irrigated agricultural areas were targeted and stationary. Our findings revealed a 54% increase in irrigated areas between 1987 and 2015. The reservoir water volume decreased markedly from 9,077,000 m3 to 7,100,000 m3 during the same period. Such a decrease threatens the satisfaction of agricultural water requirements, since the reservoir is the unique source of irrigation water in the region. It could potentially lead to conflicts between users if adequate strategies for the sustainable management of the Mogtedo reservoir are not implemented. The methodology used in this study also addressed the challenge of building up historical spatial information database in data-scarce environments, and could be replicated readily in regions or countries like Burkina Faso. © 2019 by the authors. [less ▲]

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See detailEfficacité et résistance de techniques de protection de berges en génie végétal
Peeters, Alexandre ULiege; Houbrechts, Geoffrey ULiege; Hallot, Eric ULiege et al

in Géomorphologie: Relief, Processus, Environnement (2018), 24(2 (2018)), 121-138

Nineteen streambank stabilisation projects using bioengineering techniques were monitored in the short and the long term on several rivers in Wallonia. Most of the bank protections, installed between 3 ... [more ▼]

Nineteen streambank stabilisation projects using bioengineering techniques were monitored in the short and the long term on several rivers in Wallonia. Most of the bank protections, installed between 3 and 20 years ago, were effective, although many of them are now partially destroyed. In some cases, damage to the protective structure has led to a renewed erosion of the bank. The main factor of degradation is the magnitude of stream discharge, which is quantified by the critical stream power (the maximum power value at which the bank protection can resist). Permissible stream power thresholds were determined empirically, and are in order of 130 W/m² for fascine, 65 W/m² for tree revetment, 200 W/m² for cribwall and 150 W/m² for groynes system. Nevertheless, several factors might undermine the bank protection before its flood destruction, which lead to a lower threshold of critical power. The deterioration factors highlighted are (i) a poor vegetation recovery due to lack of sunlight, unmanaged cutting, and damage caused by animals (livestock and rodents), (ii) an inadequate design or filling, and (iii) a lack of consideration of fluvial processes, such as unit stream power and Total Suspended Solids (TSS) as most of these structures require filling with fine sediments. As a result, this study underlined the importance of characterising the geomorphological context in addition to the regular hydrological technical factors prior to the bank stabilisation project. [less ▲]

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See detailThe Semois valley in southern Ardenne: short-wavelength, large-Amplitude meanders incised into a slaty basement
Petit, François ULiege; Hallot, Eric ULiege; Houbrechts, Geoffrey ULiege

in Landscapes and landforms of Belgium and Luxembourg (2018)

The incised meanders of the Semois Valley, in Southern Ardenne, are remarkably elongated, forming a nearly 100-km-long meander belt. Their elongation is conditioned by the relative orientation of the ... [more ▼]

The incised meanders of the Semois Valley, in Southern Ardenne, are remarkably elongated, forming a nearly 100-km-long meander belt. Their elongation is conditioned by the relative orientation of the meander loops and the regional slaty cleavage, as theorized by Strahler. These meanders already existed in the Early Quaternary, some cut-off meanders lying more than 100 m above the present floodplain. Although the Quaternary incision rates of the Semois were low ( 0.05 mm/year), several meanders look more entrenched than ingrown, probably because lateral erosion was fairly slow (*0.3–0.5 mm/year), owing to the large quantity of material to evacuate by a rather small river. The combined aesthetic and scientific interests of this particularly well-developed meander belt speak in favour of the preservation of the nicest meanders as geomorphosites. [less ▲]

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See detailFlux sédimentaires des rivières de Wallonie : du Pléistocène à Demain
Houbrechts, Geoffrey ULiege; Gob, Frédéric; Hallot, Eric ULiege et al

Scientific conference (2016, July 11)

Livret-guide des journées 2016 de la Commission des hydrosystèmes continentaux du CNFG. Depuis plus de 40 ans, de nombreuses études ont été menées par François Petit et ses collaborateurs sur le transport ... [more ▼]

Livret-guide des journées 2016 de la Commission des hydrosystèmes continentaux du CNFG. Depuis plus de 40 ans, de nombreuses études ont été menées par François Petit et ses collaborateurs sur le transport des sédiments par les rivières du massif ardennais et des régions périphériques. La diversité des processus et des problématiques abordées, des méthodes d'analyse et des périodes considérées nous ont amené à proposer un thème relativement général permettant de regrouper les études portant sur les sédiments de taille variée, depuis les fractions fines jusqu'aux éléments les plus grossiers de la charge de fond ainsi que d'aborder des échelles de temps différentes, depuis les héritages géomorphologiques des périodes froides du Quaternaire jusqu'aux futures évolutions dans le cadre de projets de restauration de cours d'eau. [less ▲]

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See detailEvaluation of suspended sediments dynamics in a catchment contaminated with PCBs (Samme River – Belgium)
Denis, Anne-Cécile ULiege; Frippiat, Christophe; Houbrechts, Geoffrey ULiege et al

Conference (2015, October 13)

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See detailControls on knickpoint migration in a drainage network of the moderately uplifted Ardennes Plateau, Western Europe
Beckers, Arnaud ULiege; Bovy, Benoît ULiege; Hallot, Eric ULiege et al

in Earth Surface Processes and Landforms (2015), 40

Much research has been devoted to the development of numerical models of river incision. In settings where bedrock channel erosion prevails, numerous studies have used field data to calibrate the widely ... [more ▼]

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

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See detailDimensionless critical shear stress in gravel-bed rivers
Petit, François ULiege; Houbrechts, Geoffrey ULiege; Peeters, Alexandre ULiege et al

in Geomorphology (2015), 250

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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 ULiege; Hallot, Eric ULiege; Houbrechts, Geoffrey ULiege 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 ULiege; Levecq, Yannick; Peeters, Alexandre ULiege 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 ULiege; Van Campenhout, Jean ULiege; 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 detailEstimation de la sédimentation des retenues hydro -agricoles de Kierma et de Wedbila : Méthodologie et résultats obtenus.
Guyon, Francis; Hallot, Eric ULiege; Kima, Etienne et al

Conference (2014, March 17)

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See detailEvaluation et planification des ressources en eau des petites retenues hydro -agricoles : Application du modèle WEAP aux retenues de Kierma et de Wedbila (Burkina Faso).
Razanamahandry Lovasoa, Christine; Hallot, Eric ULiege; Guyon, Francis et al

Conference (2014, March 17)

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See detailSuivi géomorphologique de la restauration de la continuité longitudinale du Bocq
Peeters, Alexandre ULiege; Hallot, Eric ULiege; Houbrechts, Geoffrey ULiege et al

Conference (2013, October 16)

Le Bocq est un cours d’eau condruzien dont le bassin versant s’étend sur 233 km² et dont le cours est caractérisé par la présence de nombreux obstacles à la continuité écologique (déversoirs, lits ... [more ▼]

Le Bocq est un cours d’eau condruzien dont le bassin versant s’étend sur 233 km² et dont le cours est caractérisé par la présence de nombreux obstacles à la continuité écologique (déversoirs, lits bétonnés et pertuis). Dans le cadre du projet Walphy, des travaux de restauration de la continuité longitudinale ont été réalisés sur 23 obstacles. Plusieurs d’entre-eux ont fait l’objet d’un diagnostic avant travaux de restauration de manière à évaluer leur impact sur le transport des sédiments. Ce diagnostic comprend un descriptif de l’obstacle (type d’aménagement, franchissabilité et remplissage de la retenue par les sédiments), complété par des mesures granulométriques. De plus, des marquages de la charge de fond ont été réalisés à l’amont de plusieurs obstacles pour évaluer leur franchissabilité. Le suivi géomorphologique des travaux de restauration de la continuité longitudinale s’est focalisé sur les travaux de types suppression d’obstacle et rampe rugueuse, les autres types (passe à bassins, pré-barrages et rivière de contournement) ne permettant pas un rétablissement complet du transport sédimentaire. Ce suivi est basé sur la comparaison de relevés topographiques réalisés avant et après les travaux de restauration, ainsi que avant et après les éventuelles crues mobilisatrices. Nous avons ainsi mis en évidence un rétablissement du transport solide de la charge de fond suite à la suppression du déversoir de Spontin, ce qui a été confirmé par le relevé du marquage effectué à l’amont de l’ancien déversoir. Enfin, le suivi s’est étendu au cas particulier que représente l’aménagement de la rampe rugueuse sur le site de protection de captages à Spontin. Avant les travaux de restauration, ce site était caractérisé par un lit bétonné présentant une faible lame d’eau avec d’importantes vitesses de courant. Nous avons effectué plusieurs estimations de la taille des matériaux à injecter pour créer la rampe rugueuse. Des marquages de la charge de fond ont été réalisés pour compléter ces estimations. Les galets utilisés pour créer les frayères ont également été marqués pour évaluer la survie de ces frayères en fonction des différentes crues. [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 ULiege; Houbrechts, Geoffrey ULiege; Van Campenhout, Jean ULiege 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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