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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 detailEvidence of a changing size-frequency distribution of landslides in the Kyrgyz Tien Shan, Central Asia
Schlögel, Romy; Torgoev; De Marneffe, Cédric et al

in Earth Surface Processes & Landforms (2011), 36/12

There is a strong possibility that environmental change (whether climate or land use) will be manifest as changes in the size–frequency distribution of landslides. Here, evidence is presented for this ... [more ▼]

There is a strong possibility that environmental change (whether climate or land use) will be manifest as changes in the size–frequency distribution of landslides. Here, evidence is presented for this from western Kyrgyzstan, Central Asia. Remote sensing and spatial analysis have been applied to map mass movements in the central part of the Maily‐Say Valley and to detect recent landslide activations. The evolution of landslide activity over the past 50 years has been analysed on the basis of pre‐existing landslide maps and new analyses of aerial photographs as well as Quickbird images. Five inventories were produced for the years 1962 (based on the existing map of 1962 and aerial photographs of 1962), 1984 (based on the existing map of 1977 and aerial photographs of 1984), 1996 (based on aerial photographs of 1996), 2002 (based on the existing map of 2003 and Quickbird imagery of 2002) and 2007 (based on Quickbird imagery of 2007). The geomorphologic features contained in the catalogues represent the landslide bodies observed from remote imagery of the corresponding year. Mapped landslides are generally considered as the result of a series of slope failure events. Size–frequency analyses applied to the five landslide inventories show that both the number and size of unstable slopes increased from 1962 (162 objects) to 2007 (208 objects) and the power‐law exponent decreased over time. This changing power‐law exponent may indicate that landslide‐related hazards are increasing. This tendency is documented in more detail for two active landslide zones, one in the main valley and one located to the west of it. Landslide detection methods were used to assist the evolution of slope instabilities. Choosing appropriate thresholds, the image subtraction method based on normalized difference vegetation index (NDVI) allowed accurate detection of new sliding activation in these two zones. This confirmed the results of the more extensive survey that there is a systematic shift in power law exponents and size–frequency distributions for Central Asian landslides. [less ▲]

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See detailThe influence of sediment size, relative grain size and channel slope on initiation of sediment motion in boulder bed rivers. A lichenometric study
Gob, F.; Bravard, J. P.; Petit, François ULg

in Earth Surface Processes & Landforms (2010), 35

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See detailAmount and controls of the Quaternary denudation in the Ardennes massif (western Europe)
Demoulin, Alain ULg; Hallot, Eric ULg; Rixhon, Gilles ULg

in Earth Surface Processes & Landforms (2009), 34

It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations ... [more ▼]

It is still debated whether the primary control on the middle Pleistocene denudation of the uplifted Ardennes massif (western Europe) is tectonic or climatic. Here, based on geomorphological observations, we calculate the amount of river incision and interfluve denudation in the Meuse basin upstream of Maastricht since 0·7 Ma and we show that the main response to tectonic forcing was incision. This allows us to provide first-order estimates of the tectonic and climatic contributions to the denudation of the Ardennes. From a dataset of 71 remnants of a terrace level dated ~0·7 Ma, we first derive a basin-scale functional relationship linking incision with distances to the regional base level (Lc) and to the source (Ls) in the Ourthe basin (pertaining to the Ardennian part of the Meuse basin). Expressed as I = I0*(1 – a*Lcb/Lsc), I0 being the incision measured at the basin outlet, this relationship calculates that river incision has removed 84 km3 of rock in the Meuse basin upstream of Maastricht since 0·7 Ma. In the same time, 292 km3 were eroded from the interfluves. A comparison of these volumes shows that the tectonically forced river incision accounts for ~22% of the total post-0·7 Ma denudation. Furthermore, the mean denudation rate corresponding to our geomorphological estimate of the overall denudation in the Meuse basin since 0·7 Ma amounts to 27 mm/ky, a figure significantly lower than the ~40 mm/ky mean rate derived from 10Be studies of terrace deposits of the Meuse (Schaller et al., 2004). This suggests that, taken as a basin average, the 10Be-derived rate is overestimated, probably due to an overrepresentation of the erosion products of the rapidly incising valleys in the alluvial deposits. [less ▲]

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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 detailBankfull discharge recurrence interval in gravel bed rivers
Petit, François ULg; Pauquet, A.

in Earth Surface Processes & Landforms (1997)

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See detailDimensionless critical shear stress evaluation from flume experiments using different gravel beds
Petit, François ULg

in Earth Surface Processes & Landforms (1994)

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See detailEvaluation of grain shear stresses required to initiate movement of particles in natural rivers
Petit, François ULg

in Earth Surface Processes & Landforms (1990)

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See detailThe evaluation of grain shear stress from experiments in a pebble-bedded flume
Petit, François ULg

in Earth Surface Processes & Landforms (1989)

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See detailContribution to the development of an erosivity index adapted to the prediction of erosion in Belgium
Sinzot, Anne; Bolline, Arthur; Laurant, Adrien et al

in Earth Surface Processes & Landforms (1989), 14

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See detailCarbon dioxide in cave atmospheres. New results in Belgium and comparison with some other countries.
Ek, Camille ULg; Gewelt, Michel

in Earth Surface Processes & Landforms (1985), 10

More than 600 measurements of the carbon dioxide content of cave air in Belgium lead up to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and ... [more ▼]

More than 600 measurements of the carbon dioxide content of cave air in Belgium lead up to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and diffusing in the soil and the voids of bedrock; (2) a trend, discernible in very still air only, to go down by density; (3) in some caves, draughts caused, for instance, by a swift underground stream. Results in Belgium are compared with published and unpublished data from other countries, showing that CO2 is often less abundant in cold climate caves and in caves of semi-arid regions (influence of the biomass). Special attention is paid to human contamination during analyses: the influence of people passing through the cave nearby the operator, but also the influence of the operator himself, are discussed, and the use of special precautions (including a CO2-absorbing mask) in defined critical situations is stressed. [less ▲]

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See detailCarbon dioxide in cave atmospheres: new results in Belgium and comparison with some other countries
Ek, Camille ULg; Gewelt, Michel

in Earth Surface Processes & Landforms (1985), 10

More than 600 measurements of carbon dioxide in cave air in Belgium lead to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and diffusing in the soil ... [more ▼]

More than 600 measurements of carbon dioxide in cave air in Belgium lead to the conclusion that the main factors of its distribution are: (1) a flow originating from the biomass and diffusing in the soil and the voids of bedrock; (2) a trend to go down by density; (3) in some caves, draughts caused, for instance, by a swift underground stream. Results in Belgium are compared to other countries. l'usage d'un masque absorbant le CO2Special attention is paid to human contamination and the use of a CO2-absorbing mask in defined situations is stressed. [less ▲]

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