Article (Scientific journals)
Comparison of methods for quantifying active layer dynamics and bedload discharge in armoured gravel-bed rivers
Houbrechts, Geoffrey; Van Campenhout, Jean; Levecq, Yannick et al.
2012In Earth Surface Processes and Landforms, 37, p. 1501-1517
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Keywords :
active layer; armour; scour chains; PIT-tag; iron slag
Abstract :
[en] 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.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Houbrechts, Geoffrey  ;  Université de Liège - ULiège > Département de géographie > Département de géographie
Van Campenhout, Jean  ;  Université de Liège - ULiège > Département de géographie > Hydrographie et géomorphologie fluviatile
Levecq, Yannick ;  Université de Liège - ULiège > Département de géographie > Hydrographie et géomorphologie fluviatile
Hallot, Eric ;  Université de Liège - ULiège > Département de géographie > Hydrographie et géomorphologie fluviatile
Peeters, Alexandre  ;  Université de Liège - ULiège > Département de géographie > Hydrographie et géomorphologie fluviatile
Petit, François  ;  Université de Liège - ULiège > Département de géographie > Hydrographie et géomorphologie fluviatile
Language :
English
Title :
Comparison of methods for quantifying active layer dynamics and bedload discharge in armoured gravel-bed rivers
Publication date :
2012
Journal title :
Earth Surface Processes and Landforms
ISSN :
0197-9337
eISSN :
1096-9837
Publisher :
John Wiley & Sons, Inc, Chichester, United Kingdom
Volume :
37
Pages :
1501-1517
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 25 October 2012

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