Variability of Valley Floor Widths in a Mountain Landscape, Canadian Rockies

Valley floors influence a range of environmental processes in mountain regions. For example, valley floors serve as a deposition zone for geomorphological processes occurring on hillslopes. Valley floors represent relative low points in the landscape, thereby affecting basin hydrology and influencing soil moisture in these locations. Valley floors also serve as important locations of organic carbon storage in soils and vegetation. While it has been recognized that valley floor widths in mountain regions often show high variability due to complex geology and geomorphology, few studies have quantified and analyzed values and controls of valley floor widths in these settings. Objectives of this study are to measure valley floor widths for three small tributary drainage basins in Kananaskis, Canadian Rockies and to analyze possible controls, including geology and geomorphology, on valley floor widths. First, delineation of valley floor extent for alluvial parts of the channel network in the three study basins is undertaken using GIS-based methods. Valley floor polygons consist of DEM grid cells that fall within a threshold height relative to the channel height. Next, valley floor widths are obtained by measuring width in a direction perpendicular to the channel for valley floor polygons along the entire channel network. The complex geological and geomorphological characteristics in our study region suggest that generalizations about valley floor widths relevant to larger, lowland drainage basins are not likely to be applicable for our study area. Upper Kananaskis Creek and Ribbon Creek basins show overall higher values of valley floor width relative to Porcupine Creek basin, likely due to their topographical positioning, which is expected to result in higher precipitation and discharge values and greater possible impacts of past glaciation. Results show a very high variability in valley floor widths along the channel network for all three study basins. Valley floor widths show distinct fluctuations between groups of below-average and above-average values in an upstream direction, with any particular group often persisting for a relatively short distance before a notable change in valley floor width is observed. Channel junction locations along the channel network are often associated with local increases in valley floor width for all study basins, although such increases sometimes only last for short distances. Bedrock lithology is found to influence valley floor widths in the study basins, with either below-average or above-average values being associated respectively with more resistant Palaeozoic formations or somewhat more erodible Mesozoic formations. Geological structures situated near channel networks are also shown to be a possible control of valley floor width in some situations. Parts of the channel network in Upper Kananaskis Creek basin and Ribbon Creek basin show evidence of glacial activity, with greater valley floor widths often found in these locations.