Hillslope-Valley Floor Coupling Along Steep Mountain Channel Networks, Kananaskis, Canada

Sediment transfer from hillslopes to valley floors represents a major component of the sediment routing regime in mountainous environments. Valley floors are connected to a range of physical, chemical and biological processes, including hydrological flow routing, soil moisture, vegetation growth and organic carbon storage. The degree of connection between hillslopes and valley floors depends on variables that affect geomorphic process operation on hillslopes, including slope morphology, land cover, rock and/or soil characteristics, and precipitation regimes. This study measures and analyzes the degree and variability of hillslope-valley floor coupling along channel networks in small drainage basins in Kananaskis, Canadian Rockies. First, key morphometric and land cover variables derived from DEM and satellite-based data are analyzed for study basins. These variables influence hillslope sediment transfers to local valley floors. A large proportion of landscapes in tributary study basins is defined as 1^st order or 2^nd order sub-basins with slope gradients often in the range of 30 degrees to 60 degrees. These landscapes have significant potential for mass movements. Geology and geomorphology are shown to influence the complex arrangement of landscape morphology and land cover within study basins. Ribbon Creek and Upper Kananaskis Creek basins show a greater extent of steep, rock areas compared to Porcupine Creek basin. Next, parts of surrounding hillslopes that have potential for sediment transfer to valley floors are identified. Significant breaks in slope gradient on hillslopes above local valley floors are shown to limit the hillslope length with potential to connect with the valley floor. Lower-order stream links show a higher percentage of surrounding hillslopes that are coupled with valley floors relative to higher-order stream links. Next, coupled parts of landscapes in study basins are classified into categories of mass movement potential based on primary controlling variables (e.g., slope gradient, land cover). Mass movement potential within coupled parts of the landscape determines the degree of hillslope-valley floor coupling. Maps show significant variability in mass movement potential along channel networks in study basins. Variability in hillslope-valley floor coupling results from the complex geological and geomorphological controls on landscape characteristics in this region. Glacial oversteepening of hillslopes is more notable in Ribbon Creek and Upper Kananaskis Creek basins and results in more landscape areas with a high degree of hillslope-valley floor coupling compared to Porcupine Creek basin. Parts of channel networks with resistant lithology typically show relatively uniform, steep hillslopes, with limited buffers between hillslopes and valley floors. In contrast, areas with less resistant lithology often display lower slope gradients and more buffers that limit hillslope coupling with valley floors. Finally, parts of the landscape with overall greater heterogeneity in bedrock lithology show smaller and more complex-shaped units of hillslope connection with valley floors compared to areas with more uniform lithology.