Controls on channel form and floodplain character along the Bulstrode River, southern Quebec, Canada

The hydraulic dimensions and planform character of a river channel are very much affected by the channel gradient and the calibre of the bed materials. One of the two major objectives of this study is to analyze these effects on selected reaches along the Bulstrode River, near Victoriaville.The second objective is to relate the variations in gradient, sediment calibre and channel geometry to the changes in floodplain character along the river valley.The river is about 85 km long and flows across the Appalachian highlands and foothills in southern Quebec. This study focuses on six alluvial reaches along the river, ranging from 0.7 to 1.5 km in length. The channel gradient ranges from 0.0036 to 0.0001. The decline in gradient is associated with rapid downstream fining from small cobble and gravel-bed in the 'upvalley reaches' to a sand-bedded channel in the 'downvalley' reaches.The discharge remains fairly constant over the river length, averaging about 140 m$ sp3$/sec. Channel depth, particularly the thalweg depth, increases appreciably in the downstream direction. The channel width decreases appreciably in the downstream direction. The channel capacity varies significantly without a clear pattern in the steeper cobble-gravel bed reaches and generally declines in the more hydraulically efficient, gentler and more hydraulically efficient fine gravel-sand bed downstream reaches.This study finds that floodplain characteristics vary with specific stream power and within-channel processes, but not in the same manner as suggested in the Nanson and Croke (1992) model. (Abstract shortened by UMI.