The South Carolina piedmont region underwent accelerated gully erosion during a century of cotton farming (1800s to 1930s). Even though the region is currently covered by pine forests, large gully erosion still happens occasionally during the hurricane season. Majority of the investigations on gully erosion in this region have focused on soil mass loss, soil carbon exchange and storm water response. How gully erosion impacts the soil moisture and groundwater storage distribution, and what could be its consequences on vegetation adaptation remain unexplored. In this study, we developed a physically-based 2D hydrologic model that accounts for interception (Rutter model), evapotranspiration (Penman-Monteith equation), and subsurface flow (variably saturated Richards’ equation) processes, to investigate the effects of gully erosion on hydrologic states. The model equations were solved using a finite-volume scheme on a representative 2D hillslope from the Calhoun critical zone observatory (CZO). Numerical experiments with different gully incision depths (from 0.25 m to 3.75 m below the toe of hillslope), and soil types (including sand, silt and clay) were conducted to explore the effects on soil moisture, groundwater, baseflow, runoff, evapotranspiration, and streamflow statistics. Preliminary results indicate that more intense gully erosion will lead to lower steady-state groundwater storage, lower soil moisture in the root zone and less evapotranspiration. This means that gully erosion is likely to force ecohydrologic adaptations to mitigate enhanced vegetation moisture stress. Also, localized erosive effects in the streams can have profound ecohydrologic impacts that propagate far into the hillslope. The result also has implications on the impact of stream restoration strategies on watershed hydrology.
Chen, Xing, and Mukesh Kumar (2016): Impact of gullying on hillslope hydrology at the Calhoun Critical Zone Observatory. American Geophysical Union 2016 Fall Meeting, San Francisco, CA.
This Paper/Book acknowledges NSF CZO grant support.