Ph.D. Geosciences, Penn State, 1996
Professor, Department of Geological Sciences
Landscape evolution, tectonic geomorphology, impacts of climate change on hillslope and fluvial systems, numerical simulation of landform development.
Current Research: Storms, sediment, and saltcedar
Large floods can strongly impact river valleys. A powerful flood can alter channel geometry and conveyance capacity; erode or bury riparian vegetation; enhance or degrade the fertility of floodplain soils; and in extreme cases even change the entire channel pattern. A fundamental goal in fluvial geomorphology is to understand these impacts at a quantitative and ultimately predictive level. Currently, our ability to forecast potential flood impacts is limited by a lack of good test cases and a lack of fully coupled morphodynamic models. We are addressing this knowledge and technology gap by analyzing and modeling a remarkable case study from the Rio Puerco, a high-desert river in northern New Mexico. In 1926, the exotic shrub saltcedar (Tamarix) was introduced to the Rio Puerco watershed to limit erosion and prevent the infilling of Elephant Butte Reservoir, which is located downstream on the Rio Grande. Since then, recognition of the adverse impacts of saltcedar in river valleys throughout the western United States has inspired widespread efforts to control it. In September 2003, herbicide spraying along a 12-kilometer section of the Rio Puerco killed all woody vegetation. A major flood three years later caused extensive erosion and channel widening along the defoliated reach; the eroded material was deposited downstream where living vegetation prevented erosion. Because the vegetation was the only factor that varied significantly, the 2006 Rio Puerco flood makes an excellent natural experiment for studying feedbacks among vegetation, erosion, and river morphology. We obtained airborne lidar topography data from before and after the 2006 flood. These data reveal, in unprecedented detail, the patterns of erosion and sedimentation along the river valley. Among other things, the data show that most of the sediment that eroded from the defoliated reach ended up being deposited along a stretch of floodplain several kilometers downstream. This finding suggests that the erosional impact of limited saltcedar control may be confined to within several kilometers of the control area. On the other hand, the impact of more widespread saltcedar death remains to be discovered. The recent introduction of the tamarisk leaf beetle as a biocontrol agent adds urgency to this question.