Sediment supply and channel morphology in mountain river systems: 1. Relative importance of lithology, topography, and climate

Quantifying landscape-scale variations in sediment supply to streams and rivers is fundamental to our understanding of both denudational processes and stream channel morpho-dynamics. Previous studies have linked a variety of sediment-supply proxies to climatic, topographic, or geologic factors, but few have connected these directly to the characteristics of fluvial systems draining these landscapes. Here we correlate landscape controls on sediment supply to observed sedimentology and channel patterns through direct measurements of water and sediment fluxes in over 80 drainage basins ranging in area from 1.4 to 35,000km(2) in the northern Rocky Mountains, USA. These data show that the relative sediment supply, defined by the bankfull sediment concentration, is dominated by basin lithology, while exhibiting little correlation to factors such as relief, mean basin slope, and drainage density. Bankfull sediment concentrations (bed load and suspended load) increase as much as 100-fold as basin lithology becomes dominated by softer sedimentary and volcanic rocks, relative to basins with more resistant lithologies. As bed load concentrations increase, stream beds become less armored, and bed load grain size coarsens. At very high sediment concentrations, bed surface, subsurface, and bed load grain sizes converge and a transition from single-thread to to braided channel patterns is commonly observed.