Current and past research projects

Solute transport modeling and dynamics at landscape scales

A large component of our research is concerned with understanding the dynamics of solutes in the landscape, and the controls of climate and landscape properties on their fate and transport. We have developed the concept of a rank StorAge Selection (rSAS) function as a tool for characterizing and modeling the emergent transport dynamics, and applied it in several field sites and experimental systems. The results are helping to clarify the way climate variability affects flow pathways through the landscape, and have led to the development of new tools for modeling the effects at the watershed scale.

Experimental analysis of new hillslope-scale flow and transport theories at Biosphere2's Landscape Evolution Observatory

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This research project is focused on hillslope-scale flow and transport theories at Biosphere2’s Landscape Evolution Observatory (LEO). The LEO consists of three hillslopes (12m x 30m x 1m) constructed inside a controlled facility operated by University of Arizona. Flow in these hillslopes is measured by a dense sensor network. This gives us a unique opportunity to perform experiments in a controlled environment at a scale not normally possible in an experimental lab, and to get experimental observations with a density that cannot normally be obtained at a natural experimental site.

For the first 2-3 years of the LEO operation, the hillslope will be used in the absence of vegetation. During this period, we will test hypotheses about hillslope-scale hydrologic transport using tracer experiments, and develop new theories of hillslope-scale transport tested against measurements made in the LEO.

We will also develop experimental methods such as the PERTH (PERiodic Tracer Hierarchy) method. The PERTH method has been developed by our lab for estimating time-variable travel time distributions under periodic environmental forcing conditions using a limited number of tracers. It is suitable for application in facilities like the LEO. We are currently conducting numerical experiments using hydrological models to aid our experimental design for implementing PERTH. Ultimately, the hydrological transport model will be improved by measuring their predictions against experimental observations made in the hillslopes.

Field study of water balance and transport pathways in the crystalline Piedmont

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This research project is focused on developing a perceptual model of how water moves from uplands to streams in the Piedmont Province of the Eastern United States. Hydrologic models are often built on theorized runoff generation mechanisms to describe the response of a stream during a storm event. Topographically-sensitive models (such as TOPMODEL and HsB) often assume that the soil profile is thin and underlain by an impervious bedrock. In the heavily populated Piedmont Province, the soil is underlain by highly permeable saprolite which can be up to 20 meters thick. The importance of this saprolite on influencing runoff generation mechanisms and controlling flow pathways will be examined, as well as the impacts of land use on these mechanisms. This investigation into runoff mechanisms and flow pathways will be used to inform a conceptual model which will be tested in areas of the Piedmont where minimal data is collected. To approach this problem, traditional surficial mapping techniques will be combined with geophysical surveys and digital elevation data to help characterized preferential flow pathways within the saprolite. Water samples from natural reservoirs and hydrologic features will be analyzed for natural tracers over a range of moisture conditions and used in conjunction with gauged hydrologic features to determine runoff generation mechanisms, flow pathways and water residence time distributions.