Gully erosion and freeze-thaw processes in clay-rich soils, northeast Tennessee, USA

This study examines gully erosion in northeast Tennessee hillslopes in the Southern Appalachian Valley and Ridge physiographic province, where a thick sequence of red clay Ultisols (Acrisol, according to the World Reference Base for Soil) overlies dolomite and limestone bedrock. The role of freeze-thaw processes in gully erosion was examined weekly from 6/3/2012 to 9/17/2014 using a network of n = 78 erosion pins in three geomorphic areas: channels, interfluves, and sidewalls. Freeze-thaw days were identified using meteorological data collected on site. When freeze-thaw days occurred, erosion and deposition increased and gully conditions were more dynamic. When daily temperature did not plunge below freezing, more stable gully conditions persisted. Ordinary Least Square regression models of erosion pin length using freeze-thaw events explained significant portions of variability in channels (R² = 0.113, p < 0.01), interfluves (R² = 0.141, p < 0.01), and sidewalls (R² = 0.263, p < 0.01). Repeat analysis on only the winter-spring months minimally improved the sidewall model (R² = 0.272, p < 0.01). Erosion in interfluves exhibited a lagged effect, and was best correlated to freeze-thaw events during the prior period while erosion in channels and sidewalls was related to freeze-thaw events in the current week. Of the three geomorphic areas studied, sidewall erosion was best modeled by freeze-thaw events which contribute to widening of gullies through mobilization of sediment and mass wasting. This research demonstrates that freeze-thaw processes are a significant contributor to erosion in gully channels, interfluves, and especially sidewalls, and therefore temperature variability should be considered in erosion studies in similar climates.