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The raft of the Saint-Jean River, Gaspé (Québec, Canada): A dynamic feature trapping most of the wood transported from the catchment

Boivin Maxime, Buffin-Bélanger Thomas et Piégay Hervé. (2015). The raft of the Saint-Jean River, Gaspé (Québec, Canada): A dynamic feature trapping most of the wood transported from the catchment. Geomorphology, 231, p. 270-280.

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The rivers of the Gaspé Peninsula, Québec (Canada), a coastal drainage system of the St. Lawrence River, receive and transport vast quantities of large wood. The rapid rate of channel shifting caused by high-energy flows and noncohesive banks allows wood recruitment that in turn greatly influences river dynamics. The delta of the Saint-Jean River has accumulated wood since 1960, leading to frequent avulsions over that time period. The wood raft there is now more than 3-km in length, which is unusual but natural. This jam configuration allows a unique opportunity to estimate a wood budget at the scale of a long river corridor and to better understand the dynamics of large wood (LW) in rivers. A wood budget includes the evaluation of wood volumes (i) produced by bank erosion (input), (ii) still in transit in the river corridor (deposited on sand bars or channel edges), and (iii) accumulated in the delta (output). The budget is based on an analysis of aerial photos dating back to 1963 as well as surveys carried out in 2010, all of which were used to locate and describe large wood accumulations along a 60-km river section. The main results of this paper show that the raft formation in the delta is dynamic and can be massive, but it is a natural process. Considering the estimated wood volume trapped in the delta from 1963 to 2013 (≈ 25,000 m3), two important points are revealed by the quantification of the wood recruitment volume from 1963 to 2004 (≈ 27,000 m3 ± 400 m3) and of the wood volume stored on the bars in 2010 (≈ 5950 m3). First, the recruitment of large wood from lateral migration for the 40-year period can account for the volume of large wood in the delta and in transit. Second, the excess wood volume produced by lateral migration and avulsion represents a minimum estimation of the large wood trapped on the floodplain owing to wood volume that has decomposed and large wood that exited the river system. Rafts are major trapping structures that provide good potential sites to monitor wood delivery from the catchment through time and allow estimations of LW residence time while in transit. These results contribute to understanding the interannual large wood dynamics in the Saint-Jean River and can assist river managers in determining sustainable solutions for coping with the issue of wood rafts in rivers.

Type de document:Article publié dans une revue avec comité d'évaluation
Pages:p. 270-280
Version évaluée par les pairs:Non
Sujets:Sciences naturelles et génie > Sciences appliquées > Eau et environnement
Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences humaines > Module des sciences humaines
Unités de recherche > Laboratoire d’expertise et de recherche en géographie appliquée
Unités de recherche > Chaire de recherche sur les espèces aquatiques exploitées (CREAE)
Mots-clés:Large wood, large raft, wood budget, watershed scale, wood transport, delta dynamics
Déposé le:25 janv. 2023 20:11
Dernière modification:17 oct. 2023 20:23
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