VARIABLE VALLEY WIDTH AND HETEROGENEOUS LITHOLOGY IN THE BUFFALO NATIONAL SCENIC RIVER, ARKANSAS

Valley bottom width, sinuosity, and meander wavelength were measured in different lithologies of the Buffalo National River from 1:24-k digital raster graphics (DRG) overlain on a 5-m digital elevation model (DEM) of the watershed using ArcGIS 10.1. Valley width was measured at 100-m intervals. Sinuosity and meander wavelength were measured in representative reaches within each lithology type. The upstream reach of the main stem of the river is incised into the Boone Formation, a chert-bearing Mississippian limestone and has a mean valley width of 498 m. The valley narrows to 178-m mean valley width as the channel transitions to sandstone of the Everton Formation. Downstream, faulting has brought the Boone Formation back to the surface and the pattern is repeated; the valley widens to 442-m mean valley width and then narrows to 174-m valley mean width where down cutting has exposed the Everton at the surface. Sinuosity increases downstream as expected, but the river has a highly irregular meandering habit; i.e., meander wavelength and radius of curvature vary greatly from upstream to downstream. For rivers worldwide, expected meander wavelength ratios range from 10 to 20 times the valley width. Meander wavelengths in the Boone reaches of the Buffalo River are < 5.6 times the valley width, and in the Everton reach the meander wavelength is < 8.3 times the valley width. Meander wavelengths are within the expected range only in the lower sandstone reaches of the watershed. The atypical downstream pattern of valley width and wavelength/valley width ratios suggests that lithology is a strong control on valley formation and likely results in spatial variation in the rates and modes of vertical and lateral fluvial processes that contribute to the creation and preservation of unpaired stream terraces in the watershed.