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Ephemeral streamflow infiltration through alluvial channels has been identified as an important source of aquifer replenishment in arid and semi-arid environments. In this dissertation, two field methods were developed for monitoring streamflow timing in ephemeral stream channels. The first streamflow timing method exploits differences in the advective and conductive thermal transport mechanisms during the presence and absence of streamflow. The second method of streamflow timing utilized the relationship between soil water content and electrical conductance. Electrical resistance sensors were designed to detect saturated soil conditions and thus to infer streamflow timing during periods of saturation. Both methods were field-tested in Rillito Creek, Tucson, Arizona. The electrical resistance method proved more suitable than the temperature method because it was not depth dependent and was able to more accurately infer streamflow timing with less data post processing. Transient and steady state infiltration fluxes were simulated in a coarse-grained alluvial channel to determine the relative contribution the onset of streamflow provides to potential recharge. Water content, temperature, and pore pressure measurements were incorporated into a variably saturated heat and fluid transport model to simulate infiltration. Infiltration fluxes at the onset of streamflow were about 2-3 orders of magnitude higher than steady state fluxes and were inversely proportional to antecedent water content. The time duration from the onset of streamflow to steady-state infiltration ranged from 1.8 to 20 hours. Two transient and steady state periods were observed indicating a lower permeable layer at depth. During steady state periods, infiltration fluxes averaged 0.33 meters per day and ranged from 0.14 to 0.45 meters per day. A long-term decline was observed in all three events. Higher frequency diurnal and episodic changes were prompted by fluctuations in atmospheric temperature and discharge. The simulated steady state values were consistent with the effective vertical conductivity values (0.22 meters per day) of an underlying less permeable layer. The average contribution from the cumulative transient infiltration for the events was approximately 18 percent. Therefore, it is apparent that potential recharge calculations for alluvial channels that do not consider infiltration during the onset transient period may underestimate the true potential for recharge.

A series of experiments has been conducted for comparison with the results of a computer code called CHYMES. It is intended to calculate the coarse mixing of molten metal with water by solving the equations of the Separated Flow Model. These are derived by volume averaging and the terms that relate them to the particular case of participate flow are discussed. An experimental apparatus that is compatible with CHYMES and coarse mixing has been constructed which projects a jet of ball bearings into a thin tank of water. Experiments over a wide range of conditions were conducted at room temperature. Owing to practical difficulties only one, poorly controlled experiment with hot ball bearings was performed. Under nearly all sets of conditions an arrow-shaped plume was obtained. The speed of penetration of the plume varied little with changes in experimental conditions. The width of the plume was most strongly influenced by the widths of the tank and the jet. The individual paths of some particles were followed; it appeared that their motion was mostly dependent on their position in the plume. A model of the plume is proposed, based upon its front being impermeable to water in the vertical direction. Much of the detail of the experimental plumes was not present in the computational results and they responded differently to changes in conditions. It is proposed that this is a result of the different forms of the two sets of plumes. To rectify this an experimental plume was volume averaged. A method to determine a suitable averaging volume size is described. The process results in a plume similar to the computational ones. The length scales required for volume averaging to be successful are discussed and the possibility that this method is inappropriate for describing coarse mixing is admitted.

Turbulent flow measurements were performed in the wake of a slender axisymmetric body in the presence of a flat plate strut and an image plane representing the "rigid lid" approximation to a free surface. The tests were performed in a wind tunnel at a nominal Reynolds number of 6.0 x 10⁵. All turbulent flow parameters were measured at three streamwise stations. A Yawhead probe was used for the mean flow measurements, and a Constant Temperature Anemometer System with a 'x'-wire probe was used to obtain the turbulent flow characteristics. The presence of the image plane was found to increase the velocity defect and the static pressure as the image plane was approached. A redistribution among the various components of velocity fluctuations was noted near the "rigid lid" plane. The transverse component was enhanced at the expense of the normal component. The image plane also was found to influence the magnitudes and radial spread of turbulence intensities and Reynolds stresses. Some interactions between the wake of the axisymmetric body and that of the plate strut were observed. Overall, the mean velocities and the turbulence quantities indicated symmetry about the image plane throughout the wake. / M.S.