EXPLORING CRITICAL ZONE CONTROLS ON RUNOFF GENERATION IN 92 WATERSHEDS ACROSS THE SOUTHERN APPALACHIAN MOUNTAIN REGION

Streamflow regimes vary due to climate and physical metrics such as topography, land cover, soils, and bedrock properties. For example, previous studies suggest watersheds in the Blue Ridge physiographic province in the eastern United States have lower baseflow variability and higher proportion of baseflow than the Piedmont due to regional differences in soil depth and flow-restricting horizons. In this study, we examined several descriptive metrics of streamflow variation, called hydrologic signatures, and critical zone structure across the Appalachian mountains. We calculated baseflow index, baseflow variability, flashiness, and mean flow of 92 reference watersheds over 30 years using data from the USGS GAGESII dataset. We also gathered metrics describing critical zone structure in these watersheds, such as slope, depth to bedrock, elevation, and soil permeability. We then used random forest and multiple linear regression models to predict hydrologic signatures using the critical zone metrics. Initial results suggest streamflow indices are driven by relationships between soil thickness and bedrock depth. Critical zone structure therefore may have greater influence over surface topography in flow generation relationships. These findings can help further our understanding of hydrologic partitioning within physiographic regions and help to better understand critical zone influence on regional runoff generation.