A reference site for very high river terraces in the confluence area of the Ourthe and Meuse Rivers at Bois de Breux (Liège)

Des cailloutis fluviatiles ont été largement excavés à Bois de Breux / Liège au niveau des très hautes terrasses, à la faveur de l’enfouissement des impétrants du lotissement du Verger de Fayenbois. Les alluvions ainsi mises au jour sont décrites et des données nouvelles sont apportées concernant ces lambeaux qui n’étaient connus que par des observations de surface. Trois lambeaux en gradin bien documentés sont présents dans une tranche d’altitude de moins de 20 m, si bien que ce site a maintenant valeur de référence unique pour les terrasses concernées. Une tentative de raccord transversal entre les cailloutis des deux flancs de la vallée de Bois de Breux jusqu’à Rocourt met en exergue l’impossibilité de proposer des corrélations suivant la méthode traditionnelle qui veut que des lambeaux de même altitude sur des flancs opposés d’une vallée appartiennent à une même terrasse.Fluvial gravel has been widely excavated in Bois de Breux / Liège at the level of very high terraces, thanks to the burial of tubes in the Verger de Fayenbois subdivision. The alluvial deposits are described and new data are brought in concerning these shreds which were only known by surface observations. Three well-documented sheets are present in an elevation range of less than 20 m, so this site now has a unique reference value for the terraces concerned. An attempt at a transverse connection between the gravel on both sides of the valley from Bois de Breux to Rocourt highlights the impossibility of proposing correlations according to the traditional method which requires that schreds of the same altitude on opposite sides of a valley belong to the same terrace

Si photonic device uniformity improvement using wafer-scale location specific processing

We report two-fold improvement in Si photonic device uniformity over a 200mm SOI wafer through location specific processing. A within wafer thickness non-uniformity of 0.8nm yielding a grating fiber-coupler peak-wavelength non-uniformity of 1.8nm is achieved

From the primitive Ourthe to the primitive Meuse in the Lower Meuse of Liège - Part 2: Model and discussion

editorial reviewedThe gravel that covers the sub-flat surfaces above 180 m a.s.l. around Liège are the subject of a sedimentological study, in relation to the state of knowledge in terms of Oligocene stratigraphy taking into account the uplift/tilting of the NW flank of the Ardenne. General as well as field and laboratory data are set out in the preceding article published in the same volume of the Journal. This leads to a new model of morpho-sedimentary evolution of the hydrographic network linked to an indeterminate Oligocene marine regression in a sub-coastal environment. Two successive routes of the Ourthe through the Hesbaye (north of Liège) join the regression oligocene coast northwards. The first terrace of the Meuse upstream of Liège attests a flow also directed towards that shore. The entry into the scene of the Meuse downstream from Liège and therefore in the Netherlands requires captures in order to successively divert the Vesdre, the Ourthe and then only the Meuse. The validity of the earlier models which connect the Traînée mosane s.l. to terraces in Dutch Limburg is therefore disputed

From the primitive Ourthe to the primitive Meuse in the Lower Meuse of Liège - Part 1: Generalities and data

editorial reviewedThe gravel that covers the sub-flat surfaces above 180 m a.s.l. around Liège are the subject of a sedimentological study, in relation to the state of knowledge in terms of Oligocene stratigraphy taking into account the uplift/tilting of the NW flank of the Ardenne. This article reports the generalities and the field and laboratory data that have led to the construction of a new model of the morpho-sedimentary evolution of the hydrographic network of the Ourthe and the Meuse in the area of their current confluence. The interpretation of these data and the resulting model are published in the article that follows in this issue of the journa

La typologie et les caractéristiques hydromorphologiques des cours d'eau wallons

peer reviewe

Flash floods and muddy floods in Wallonia: recent temporal trends, spatial distribution and reconstruction of the hydrosedimentological fluxes using flood marks and sediment deposits

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.Les crues éclairs et les coulées boueuses, malgré leur extension spatiale réduite et leur occurrence peu fréquente, peuvent être à l’origine de dégâts importants tant sur le plan matériel que sur le plan humain. Fin mai 2008, un événement majeur a affecté la région liégeoise. Ce papier décrit la méthodologie employée pour reconstituer, en milieu forestier, ses paramètres hydrosédimentologiques à partir des éléments géomorphologiques observés sur le terrain. Les taux de transport de la charge de fond et de la charge en suspension au cours de cet événement extrême sont comparés aux valeurs moyennes observées dans d’autres rivières wallonnes et plus spécifiquement dans le massif ardennais. La répartition spatiale et l’évolution temporelle des crues éclairs sont ensuite analysées à l’échelle de la Wallonie sur base de plusieurs travaux académiques compilant l’ensemble des événements recensés dans la presse depuis le début du XXème siècle. Les biais liés à ce type de sources historiques sont abordés ainsi que les conséquences des crues éclairs sur la vulnérabilité et le risque d’inondation soudaine en Wallonie

Impacts des lâchers dus à une centrale hydroélectrique sur l'avancée de la charge de fond et sur l'altération du lit sur la Warche (Belgique)

This study is based on the Warche River in the northern Ardennes (Belgium), on a 5 km stretch downstream of the Bütgenbach hydroelectric powerplant built in 1932. The hydroelectric powerplant releases a flow of 10 m³/s almost daily, which corresponds to the morphogenic flow (0.6 bank flow). But then, the dams play an important role in flood control and significantly reduce the number of large floods above the bankfull discharge. A study in the 1990s showed that after the dam’s construction, a general incision of the whole 5 km stretch occured in about 30 years, followed by a doubling of the channel width in 45 years. Other changes such as a reduction in the number of riffles and pools, an increase in rocky outcrops in the channel have also taken place. The increase in the number of gravel bars and islands is the result of frequent releases which are very efficient in terms of bank erosion. The objective is to quantify the impact of hydropeaks on bedload velocity to understand the grain-size sorting of the bed and the downstream propagation of the bed morphology’s degradation caused by the sediment deficit. For this purpose, about 200 RFID tags were implanted in pebbles. As the morphogenic flow was reached almost daily, the surveys were accomplished directly in the days following the deployment of the PIT tags. Then, more spaced surveys were also accomplished. One of the main results is the decrease in tagged particles velocity with the duration of the hydraulic releases

Mid-IR heterogeneous silicon photonics

In this paper we discuss silicon-based photonic integrated circuit technology for applications beyond the telecommunication wavelength range. Silicon-on-insulator and germanium-on-silicon passive waveguide circuits are described, as well as the integration of III-V semiconductors, IV-VI colloidal nanoparticle films and GeSn alloys on these circuits for increasing the functionality. The strong nonlinearity of silicon combined with the low nonlinear absorption in the mid-infrared is exploited to generate picosecond pulse based supercontinuum sources and optical parametric oscillators that can be used as spectroscopic sensor sources