Investigating spatial variability in channel slope and flow energy within and among watersheds

Over four decades ago, Hack demonstrated power-law scaling among study sites with differing lithologies when channel slope is regressed against the ratio of median substrate diameter to drainage area. The widespread availability of geospatial data has subsequently facilitated research on the substantial spatial variability in channel slope in and between watersheds with different climatic and geologic regimes. We are examining the spatial variability in channel slope and energy dissipation characteristics within and between watersheds from which channel networks are derived from digital elevation models (DEMs). Key goals of this investigation are to study: (1) the effect of DEM resolution on the observed spatial variability in slope and stream power within a watershed, (2) energy-based methodologies to represent channel initiation in DEMs, and (3) the physical basis for choosing representative lengths of channel over which to compute slope and surrogates for stream power using derived networks. The third goal will ensure representation of the variability in relief of the network structure and minimization of the redundancy in geomorphic attributes. This approach will then be applied to test the hypothesis that measures of spatial variability in slope and/or stream power upstream of a site can, in part, explain inherent variation about the mean condition of Hack's relationship between slope, drainage area, and sediment size. Implications regarding aquatic ecosystem habitat structure and fluvial classification will also be discussed.