Abstract

The preferred position model postulates that the shape of the transverse profile of a valley is a product of the relative duration of occupation by the stream of each position across the valley. Data on distribution of streams in their valleys indicate that streams preferentially occupy the outer half of their valleys at a bend but have no preferred position within straight reaches. The symmetry variations in the transverse profiles of bedrock valleys reflect these position variations by being asymmetrical at bends and symmetrical in straight reaches. Borehole data suggest that, on the average, maximum flood scour occurs to a depth twice the bank height. These data indicate that many streams that are flowing on alluvium may scour the bedrock floor of their valleys. These conclusions indicate that some streams that flow on alluvium and appear underfit may, in fact, be fit and that some aspects of the underfit stream model are in need of re-evaluation.

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