Dr. Stephen DeLong, Mendenhall Postdoctoral Fellow with the USGS Earthquake Science Center

Please join us for an informal seminar by Dr. Stephen DeLong, who will speak
on: Linking hydrology and gully erosion in an intensely monitored field laboratory in southeastern Arizona

Wednesday, November 18 from 4:00pm – 5:00pm – 5th floor of Marshall Building (Room, 531)

Rates and patterns of landscape change in low-relief semiarid rangelands are controlled by complex and poorly understood feedbacks among hydrology, topography, substrate properties and vegetation.  Erosion and deposition occur at timescales of individual hydrological events, and a process-based understanding of hydrological forcing and land surface response over flood durations is a necessary component for predicting the sensitivity of particular landscapes to possible climate scenarios over anthropogenic timescales.  In order to quantify the coupling between hydrology and surface processes in a semiarid landscape, we have instrumented a zone of process transition from sheetflow to channelized flow within a discontinuous arroyo network in southeast Arizona.  Since June 2008, we have measured precipitation, soil moisture, unchannelized surface runoff and channel discharge at 1-2 minute intervals.  We have measured channel head and channel bed erosion with repeated surveys employing ground-based LiDAR, RTK GPS and time-lapse stereo photography.  Between June 2008 and October 2009, gully headwalls in clay-rich, cohesive alluvial soil retreated up to 1.1 m.

Three key processes combined to cause headwall erosion while maintaining vertical to overhanging headwall profiles: inter-event mass wasting from wetting and drying of clay-rich soils; grain and aggregate-scale erosion on headwall faces during runoff events; and plunge-pool erosion.  Downstream of the monitored headwalls, channels also evolve during moderate to large runoff events.  These channel reaches deepen as knickpoints migrate upstream, and then rapidly widen.  Our data can be used to quantify the relationships among the hydrology, ecology and erosion of semiarid landscapes, and may improve predictions of landscape responses to differing hydrological and climatic regimes and constrain parameters in models of landscape development.