VALLEY WIDTH AND HETEROGENEOUS LITHOLOGY IN THE BUFFALO RIVER WATERSHED, NORTHERN ARKANSAS

The Buffalo National River valley exhibits different morphologies due to lithology changes along the longitudinal profile. Using ArcGIS 10.1 the 1:24,000 Digital Raster Graphics and Geologic Quadrangle Maps were superimposed upon the 5-m Digital Elevation Model Hillshade layer for the Buffalo River watershed. Valley width was measured every 250 meters along the longitudinal profile and every 100 meters within 7 sample sites. Valley cross-sections were analyzed within the sample sites. Slope and sinuosity were also measured. There are four main lithologic reaches made up of two dominant lithologies, the Boone and Everton Formations. The Boone Formation is a Mississippian chert-bearing limestone with up to 70% chert in some locations. The Everton Formation is an Ordovician interbedded dolostone, sandstone, and limestone. Mean valley width is greater and more variable in the Boone reaches than in the Everton reaches regardless of location along the longitudinal profile. Where the channel occupies the Boone, valley cross-sections are broad with a relatively flat floor and the channel meanders across a wide continuous floodplain. Where the channel occupies the Everton, valley cross-sections are steep and v-shaped with characteristic features of an ingrown meandering bedrock channel. Bedrock bluffs exist on the outsides of meanders with high amplitude; local floodplains occupy the insides of such meanders. Other characteristics do not exhibit significant differences between lithologic reaches. Valley slope generally decreases downstream and river sinuosity generally increases downstream. Valley sinuosity is less than river sinuosity within the study sites, although this difference is not significant. These findings have implications for understanding the role of heterogeneous lithology on importance of lateral erosion and vertical down-cutting in valley formation in a setting with mixed physical and chemical erosion.