Modes of response of a gravel bed river to meander straightening: The case of the Sainte-Marguerite River, Saguenay Region, Quebec, Canada

[1] In the 1960s, extensive meander straightening (rectification) was conducted along 8 km of the Sainte-Marguerite River to facilitate highway construction along the valley bottom. Comparison of long profiles and data on bed pavement caliber from the current river channel and the man-made oxbows sheds light on the multifaceted responses to this anthropogenic perturbation of the river over the last 4 decades: (1) reprofiling consisting of 1 m of bed incision in the upper 4 km coupled with 2 m of bed aggradation in the lower 2 km of the straightened reach; (2) a doubling of the caliber of bed pavement in the zone of maximum degradation; (3) regrowth of three meanders within the reach, increasing its length by 7% (400 m); and (4) net input of 4 x 10(4) m(3) of valley-side sediment from channel erosion into three terraces. Hydraulic and sediment transport reconstructions indicate that reprofiling and pavement coarsening over nearly 4 decades equally contributed to transport reequilibration along the reach, while meander regrowth and lateral sediment inputs from terraces played minor roles.