Managed Aquifer Recharge (MAR) systems have become an increasingly important approach to the management of groundwater in Southern California in recent years. This thesis describes an experimental investigation of the vadose zone dynamics beneath a recharge basin used by the Orange County Water District. Soil moisture probes, pressure transducers, and fiber optic distributed temperature sensing (FODTS) at multiple depths beneath the basin were used to monitor infiltration. The purpose was to measure the diurnal temperature flux using heat as a tracer of infiltrating water to gain insight on the influence of basin stage (i.e., water level) on infiltration rate. To increase the temperature resolution from the standard 1 m, we installed a wrapped fiber optic cable at two locations using direct push technology. The wrapped FODTS cable was spliced to a trenched cable that ran laterally across the basin at depths of 30 cm and 1 m, installed during a previous experiment. The wrapped cable was then installed vertically at two locations to observe both the spatial distribution and vertical dynamics of fluid flow at 10 cm intervals. Propagation of the diurnal heat flux at the surface was related to water velocity. The infiltration behavior was affected by subtle changes in stratigraphy below the basin. The heat tracer suggests strong components of horizontal flow due to the presence of thin fine-grained hydrostratigraphic units. Water movement during initial saturation was particularly complex and suggested that simple one-dimensional vertical flow models will not accurately predict infiltration rates. The FODTS system provided high-resolution dynamic imaging of percolation that is not possible using a multi-level transducer system.
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|Advisor:||Becker, Matthew W.|
|Commitee:||Hutchinson, Adam, Kelty, Tom|
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 58/05M(E), Masters Abstracts International|
|Subjects:||Geology, Hydrologic sciences|
|Keywords:||Distributed temperature sensing, Fiber optic distributed temperature sensing, Heat as a tracer, Managed aquifer recharge, Recharge basin, Vadose zone|
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