Implementation and validation of large wood analysis for wood budgeting in a semi-alluvial river

International audienceThe semi-alluvial rivers of the Gaspé Peninsula, Québec (Canada), recruit and transport vast quantities of large wood. The rapid rate of channel shifting due to high-energy flows and non-cohesive banks allows the recruitment of large quantities of wood that in turn greatly influence river dynamics. The delta of the Saint-Jean River has accumulated a flux of wood since 1960, creating frequent avulsions, and now has a wood raft of more than 3 km in length. The Raft of the Saint-Jean River on the Gaspé Peninsula, Québec, Canada is an exceptional amount of wood that is unusual but natural. The river has complex large-wood dynamics that promote the formation of large wood jams in the river delta. The jam configuration allows a unique opportunity to apply a wood budget at the scale of a long river corridor and to better understand dynamics of large wood in river. 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 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 between 2010 and 2014, all of which were used to locate and describe large wood accumulations along a 60 km river section. Understanding the interannual large wood dynamics in the Saint-Jean River can assist river managers determine sustainable solutions for the issue of wood rafts