Date of Award

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Ronald Falta, Committee Chair

Committee Member

Stephen Moysey

Committee Member

Christophe Darnault

Abstract

Unsaturated flow in the vadose zone often manifests as preferential flow resulting in transport of water and solutes through the soil much faster than would occur for uniform matrix flow. Time-lapse ground penetrating radar (TLGPR) shows promise as a non-invasive means to monitor unsaturated flow and here is used to monitor lab-scale forced infiltration events for capturing evidence of non-uniform and preferential flow phenomena directly from arrivals in the GPR images while simultaneously characterizing parameters of the flow system, such as bulk water content and rates of wetting front movement. This was accomplished by 1) directly interpreting transient arrivals in GPR profiles for evidence of ono-uniform flow and 2) with the aid of migration processing techniques to improve the quality of GPR images for identification and tracking of transient arrivals related to wetting in the soil. A novel method is described and evaluated to characterize the 2D velocity structure of a soil and used to migrate the GPR images. This method incorporates multi-offset measurements to characterize the depth to a potentially unknown static reflector and root mean square (RMS) velocity above the reflector with incremental changes in travel time to the static reflector and a transient reflector (i.e. the wetting front) determined from single-offset constant offset profiles to determine incremental changes in velocity above and below the transient arrival. The method is applied to TLGPR data during infiltration experiments in a 60 cm deep sand-filled tank and monitored with water content probes. To verify the approach the methodology is applied to GPR data simulated using transient water contents generated by the unsaturated flow simulator HYDRUS 2D given lab-measured hydraulic properties of the soil. For both the empirical and simulated data, we found that the 2D velocity analysis was effective in monitoring changes in the wetting front and that migration of the reflection profiles was able to improve the interpretation of non-uniform flow.

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