EVOLUTION OF RIVER LONG-PROFILES, ORGANIZATION OF PROCESS DOMAINS AND DOWNSTREAM HYDRAULIC GEOMETRY IN GLACIATED DRAINAGE BASINS OF COASTAL BRITISH COLUMBIA

In glaciated regions of British Columbia, Canada, Quaternary climate changes are responsible for profound spatial reorganization of earth surface processes. These changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs. Currently, fluvial and hillslope processes dominate the landscape, and are slowly reshaping the glacial inherited anisotropy. The aim of our study is to examine the evolution of glaciated mountainous landscapes by analysing the structure of geomorphic process domains, channel long-profiles, downstream trends of hydraulic geometry and channel morphology. The methodological approach entailed extensive channel surveys and GIS analysis to plot area-slope transects along the main stem of drainage basins. This analysis reveals generalized process-form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains. In debris-flow dominated channels the glacial/paraglacial signature commonly overrides that produced by contemporary debris flows. Along the axis of former ice flows, relict glacial cirques introduce a “hanging” fluvial domain at contributing areas as small as 6*10-2 km2 and produce channel long-profiles similar to those observed for rivers responding to tectonic forcing. The well-established area-slope relations with simple downstream power law relations for unglaciated environments do not apply here, although the concept of process domains appears to hold. In other words, the spatial distribution of process domains on an area-slope plot may be similar but where the topography plots on these process domains varies between landscape types. At the reach scale, these same glaciated basins display significant deviations from simple downstream variation of channel slope, width, stream power and consequently the sequencing of channel morphology. Such variations are due to local, glacially-induced influences that typically reset downstream trends. The combination of glacial and post-glacial fingerprints and the effects of ongoing earth surface processes generate a more complex landscape pattern of process domains and morphologies than typical for “equilibrium” unglaciated watersheds.