The vadose zone - where air, water, soil, and rock interact to support life - is a highly dynamic environment with complex flow and transport processes that remain poorly understood. Vadose zone hydrological studies struggle to resolve scale related dichotomies emerging between point measurements and 'broad-brush' geophysical methods. Field methods are needed to accurately describe flow and transport in the vadose zone to bridge the observational gap in scales from centimeters to meters and provide a three dimensional picture of flow processes.
Objectives: (1) To characterize and quantify vadose zone flow and transport in the Miami carbonate environment at scales from centimeter to meters; and (2) to develop and disseminate 4D Ground Penetrating Radar (GPR) methodology and workflow for application in other vadose zone environments.
Methods: A hydrological framework will be assembled by combining repeated high resolution 3D GPR surveys with borehole logging and direct sampling. A three-stage approach will be implemented in each study site: The first stage focuses on identifying key factors, particularly the role of water, influencing GPR reflections, using both laboratory measurements and synthetic GPR modeling. The second stage entails repeated 3D GPR surveys of field sites to quantify hydraulic parameters based on dynamic changes of water content caused by natural rainfall and controlled injection. The third stage involves inverse flow modeling with field data to estimate 3D hydraulic conductivity volumes.
Intellectual Merit and Broader Impact: The proposed research advances knowledge of vadose zone flow pathways and dynamics in carbonates at the field scale. Availability of a uniquely efficient 3D GPR system, combined with the proximity of field sites allows for rapid and efficient data collection and facilitates involvement of both undergraduate and graduate students in this research. The resulting 3D hydrological data will be available in unprecedented detail and at unique bridging scales. Data sharing and technology transfer efforts will help the near-surface community examine other vadose zones for improved understanding of groundwater recharge, contaminant migration, carbonate diagenesis and chemical / microbiological processes. Society will benefit from the accurate description of flow and transport in the vadose zone helping to protect drinking water resources.
