Stream classification and gravel-bar inventory for Buffalo National River and Ozark National Scenic Riverways

The data summarized in this report provide a baseline characterization of the physical attributes of the riverine ecosystems in two landscapes managed by the National Park Service—Ozark National Scenic Riverways, Missouri, and Buffalo National River, Arkansas—to inform understanding and management of aquatic habitat. The study utilized a basin-scale approach and consisted of two components: a basin-scale channel classification and a longitudinal inventory of gravel bars. We evaluated the Jacks Fork and Current River in Ozark National Scenic Riverways and the main stem Buffalo River in Buffalo National River. The primary objective of the study was to characterize geomorphic patterns that affect channel stability and rates of geomorphic change in both national park units. Findings may be used to inform understanding of the distribution and availability of aquatic habitat.

For the basin-scale channel classification, we performed exploratory statistical analyses using nine geomorphic variables (channel width, standard deviation in channel width, valley width, distance to valley wall, confinement, bar area, bluff area, braid index, and sinuosity). Each metric was quantified along the length of the river system at 200-meter intervals. We then performed a cluster analysis for each river using a subset of variables, resulting in 2 to 5 distinct geomorphic classes depending on criteria used for determining number of clusters. Longitudinal patterns in clusters vary for each river system but reflect a combination of landscape factors including valley width, influence of tributaries, and lithology, which affect channel stability and aquatic habitat.

We developed a longitudinal inventory of gravel bars by quantifying the area of gravel bars from a series of imagery in each park. In Ozark National Scenic Riverways we analyzed five time periods, with the earliest being 1992 and most recent being 2014. In Buffalo National River, we also analyzed five series of aerial imagery, ranging from 1982 to 2013. The analysis indicated a general decrease in gravel storage in upstream reaches of each river evaluated, accompanied by a general increase in storage farther downstream. Local patterns in gravel-bar area are associated with longitudinal patterns in geomorphic setting, such as valley geometry and channel width, that affect depositional patterns and sediment storage at the reach scale.