ABSTRACT: Pattern of instability in a wandering gravel bed channel.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Bella Coola River drains 5,450 square km (7% glacierized) of the Coast Mountains and Fraser Plateau of British Columbia, whence early summer nival floods and autumn rainstorms may yield flows greater than 1, 000 cubic m/sec. The river flows over early post-glacial alluvial cobble gravels. Sediment entrained from the river banks and delivered from tributaries is stored in the channel principally in 'sedimentation zones' where the river is laterally unstable. These are connected by stable, cobble-paved 'transport reaches'. Overall morphology is that of a 'wandering gravel river'. A sequence of maps beginning in the late nineteenth century shows that the river has become more stable and that the locus of lateral instability in the lower course has progressed downstream from near 25 km ca 1900 to near the mouth today. One of two mechanisms might be invoked to explain the effect: (i) introduction of unusual volumes of sediment into the main channel by the erosion of Neoglacial (eighteenth- and nineteenth-century) moraines of alpine glaciers, now becoming exhausted; (ii) recent progradation of the alluvial fan at Nusatsum River constricting the main channel and blocking sediment transfer downstream. The pattern is disturbed by sediment yield to the main channel from occasional extreme floods in tributaries

Bibliography of Canadian Geomorphology