CGRG Bibliography of Canadian Geomorphology
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Author : Buttle, J.M.
Date : 1995
Title : Channel changes following headwater afforestation: The Ganaraska River, Ontario, Canada.
Publication : Geografiska Annaler
Issue : 77A (3)
Page(s) : 107-118
Abstract
Reforestation of headwater slopes of the Ganaraska River basin in southern Ontario following Word War II has resulted in decreased peak flows and has likely reduced sediment yields. Changes in channel morphology produced by these modfiications to the hydrologic regime were examined for a 6.7 km section of the river in the context of Schumm's (1977) qualitative model of channel response to reforestation. Flood channel width (measured from air photographs) has decreased since 1928, while cross-sectional measurements during stream gauging in the study section revealed a decrease in the channel's width/depth ratio between 1960 and 1975. Both of these trends agree with Schumm's model. Changes in channel planform were dominated by downstream translation of meander bends and by meander cutoffs. The model predicted an increase in channel sinuosity in response to decreased peak flows and bed-material yield from the basin. However, sinuosity for the entire river section decreased significantly between 1928 and 1988, and only one reach experienced an increase in sinuosity following reforestation. A possible explanation for the model's failure to describe temporal changes in the Ganaraka's sinuosity involves a negative feedback whereby the increased sinuosity produced by decreased flow and sediment yield enhances potential for ice jams and meander cuttoffs, which in turn reduce sinuosity. This limited test of Schumm's model suggests that caution be used when applying the model and its variants to reconstruction of basin paleohydrology, and predictions of channel response to anthropogenic and natural changes to the hydrologic regime.
Bibliography of Canadian Geomorphology