128-12 Comparative Morphometric Analysis of Riverscour and Non-Riverscour Watersheds: A Case Study of Little River Canyon and the Buffalo River

Abstract:

Riverscour grasslands are unique, dynamic riparian habitats occurring along high energy bedrock streams in the Southeastern United States. Maintained by high velocity floodwaters and occasional ice scours rather than fire or grazing, these systems support a disproportionately high number of endemic and threatened plant species. While riverscours have received increasing ecological attention, their geomorphological characteristics remain poorly defined, and no standardized geomorphic framework exists for their identification. This study seeks to create a conceptual geomorphic model for riverscour grasslands using watershed and reach-scale morphometric analysis. High resolution (1m) lidar DEMs were analyzed in ArcGIS Pro to calculate 14 morphometric parameters for watersheds containing well documented riverscour grasslands, with the Little River Canyon, Alabama, serving as the primary case study. Morphometric characteristics of riverscour watersheds were compared to those of the Buffalo River, Arkansas, a geomorphically similar watershed lacking documented riverscour grasslands. Hydrologic analyses were also conducted to evaluate differences in flood regime characteristics between the two systems, and field investigations were used to document local geomorphic conditions at riverscour sites along the East Fork, West Fork, and main stem of the Little River.

Preliminary results indicate that riverscour grasslands occupy a distinct geomorphic setting characterized by differences in valley width, sinuosity, drainage texture, mean bifurcation ratio, overall watershed size and localized channel gradient. Field observations revealed that each documented riverscour in the Little River watershed occurred immediately downstream of a knickpoint, suggesting that localized increases in flow may play an important role in riverscour formation and maintenance. Hydrologic analyses indicated that the Little River flow regime is characterized by frequent and sustained moderate flood events, whereas the Buffalo River experiences less frequent but larger and shorter duration flood events. Together, these findings suggest that geomorphic configuration and flow regime influence the development and persistence of riverscour grasslands across the southeastern United States.

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