Adam Mawer

River networks have been proposed to be scale invariant patterns characterized by approximately constant bifurcation, length, and area ratios across all stream orders. Moreover, the ratios appear to vary over a relatively small range across a wide range of geology, climate, and relief. However, Arctic river networks remain a poorly examined facet of fluvial geomorphology. First order, qualitative observations suggest processes are significantly different than temperate networks. For example, dominant discharges may be thaw lake floods, not freshets, and many hillslopes appear to be drained by highly channelized flow through 1 10 m wide linear regions of porous peat, referred to as water tracks. To investigate scaling behaviour, and underlying physical processes, in Arctic networks, I compare Hortonian classification and laws of drainage networks in the Yukon coastal plain with lower latitude networks including the Peace River hills of Northern Alberta, the Okanagan Valley of south central British Columbia, and the coastal plains of eastern Nova Scotia. Comparisons use channel networks extracted from DEM, tested against aerial photographs. Water tracks have a critical basin area of 0.10 ± 0.09 km², whereas open water channels form where basin areas exceed 11.0 ± 9.67 km2 in the Running River basin. Ratios in Arctic networks are atypically not uniform across different channel orders with jumps in bifurcation (4.6 to 3.0), length (1.7 to 1.1), area (4.5 to 3.5) and gradient (1.2 to 1.3) ratios from the third to fourth order respectively. High bifurcation ratios of low order streams, depressed length ratios, and similar area ratios of high latitude (Arctic) networks are a hydrological response to frozen, impermeable permafrost, and coherent fibric peat which resists channelization. At lower latitudes, channels also originate as focused flows (rills) that incise and cross grade owing to erodible substrate, not cemented by permafrost, eventually evolving into numerous incised channels. Fibric peat in permafrost regions further resists channelization owing to hydraulic conductivity 10 times higher than typical soils, which prevents erosive overland flow. Under current and anticipated degradation of permafrost by anthropogenic warming, incision of water tracks into low order streams may force Arctic drainage networks to mirror their lower latitude counterparts and obey fractal classifications.

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Pages: 98
Supervisor: Lawrence Plug