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Geomorphic process domains in a mountain basin White, Russell

Abstract

This study seeks to identify geomorphic process domains in a mountain basin by examining the manner in which channel widths and channel gradients change with increasing drainage basin scale. A conceptual model was proposed which identified hillslope, colluvial and alluvial process domains. These domains were thought to be governed by processes of mass wasting, deposition of hillslope materials and fluvial processes and purely fluvial processes, respectively. Channel widths and gradients were measured in 62 reaches. Drainage areas were determined cartographically, except for basins smaller than approximately 0.01 km2 , which were mapped in the field. Results show that process domains can be delineated on the basis of spatial scale as power law exponents were significantly different between the hillslope and colluvial process domains. The alluvial process domain was not detected. Three distinct groups were identified at the hillslope scale. At the smallest scale channels are unincised and have not experienced mass wasting. At larger scale channels are incised and reflect the magnitude/frequency regime of mass wasting events. No significant difference was detected between the slope co-efficients of the three hillslope classes. However, offsets were significantly different, reflecting changes in sediment transport regime. Two geomorphic thresholds were identified by this study; the constants of channel maintenance for unincised and incised channels, with values of 0.01 and 0.06 km respectively. The value of the constant of channel maintenance is therefore a function of the process by which the channel is maintained.

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