The relationships between local and catchment-wide land use patterns and the spatial distribution of stream habitat variables within the Grande Cascapedia drainage basin were investigated using a geographic information system (GIS). Stream habitat variables including substrate composition and channel morphology were sampled at 48 study sites, ranging from highly disturbed to relatively pristine forest conditions in 2nd to 5th order tributaries. Land use and geology-structure variables were extracted for each catchment at four spatial scales using a GIS. The transition between pool-riffle and boulder-rapid morphologies occurred between channel gradients of 1.5% and 1.7%. The surface grainsize distribution is affected by the hydraulic power of the reach, while the subsurface grainsize distribution is associated with the degree of valley incision. The amount of logging within a 1 km radius of a sample site increases the occurrence of fine sediment within the substrate. There was, however, a surprising lack of relationship between the majority of road density metrics and the level of fines within the substrate.

The segmenting of gravel-bed rivers into 'sedimentary links', characterized by single-sediment sources and downstream fining of alluvial sediments, is a relatively new technique which has had limited application. The sedimentary link concept has been primarily applied to alpine river environments where link formations are supplied by coarse sediment from active point sources. The purpose of this study is to apply the sedimentary link concept on the Ste Marguerite River in the Saguenay region of the Canadian Shield, where valley-segment deposits of coarse sediment from ancient glacial processes are dominant in forming links. / Specifically, this study examines link-scale trends in surface grain size and channel slope. This study also uses the sedimentary link concept within an ecological context to explain the spatial organization and quality of Atlantic salmon spawning and rearing habitat. (Abstract shortened by UMI.)

Changes in channel morphology in response to two flood events were measured within three reaches on the Sainte Marguerite River, Quebec. The first event was the spring freshet---peaking in mid-May, 1996---while the second event---peaking on July 20, 1996---was the largest flood on record for the region. The resultant channel adjustments can be classified as either bedform evolution---in which a clear, systematic pattern of adjustment is evident---or as bedform change, in which local hydraulic and sedimen tologic conditions produce a seemingly random pattern of channel mobilization. Where bedform evolution has occurred, it is consistent with the existing paradigm for meander development. Sediment transport calculations based on the 'inverse' or 'morphologic' method were strongly correlated to reach average mobility ratios. The average rate of transport in response to the larger flood approached those reported by others for a braided system (Goff and Ashmore, 1994). Potential spawning zones within the three reaches were all subjected to significant net scour and/or fill following the second event; several potential spawning zones were significantly affected by the first event The presence of bank protection upstream of a potential spawning zone seems to be a determinant 10 the severity of the impact by promoting erosion of these zones.

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