Thesis Defense Announcement
Herff College of Engineering announces the Final Thesis Defense of
for the Degree of Master of Science
June 28, 2019 at 2:00 PM in Engineering Administration,Room 101
Advisor:Claudio Ivan Meier
Validation of a method for measuring hydraulic conductivity in gravel-bed rivers using minipiezometers.
ABSTRACT:Describing surface-groundwater flow interactions along rivers requires a good understanding of Ksat, the saturated hydraulic conductivity of the streambed. However, its spatial variability is huge, so that measurements are needed at multiple locations and depths. Because of this, most methods for in-situ estimation of Ksat are either too expensive or time-consuming to capture the detailed behavior of Ksat over a reach in an affordable manner. Current research on the hyporheic zone and surface water - groundwater interactions makes extensive use of PVC minipiezometers, as an inexpensive method to sample piezometric levels, water quality, organisms, etc. As a result, it has become popular to also use them for conducting injection or slug tests to determine Ksat, due to their ease of application and affordability. However, the field data obtained in this way are most often analyzed using equations based on the Bouwer and Rice method, originally developed for completely or partially penetrating wells. These are much bigger than typical minipiezometers, and have larger screens, suited for testing aquifers with low Ksat values (< 10-3 cm/s). This method and its posterior modifications have not been fully validated for low-diameter PVC minipiezometers; this is clearly reflected in the fact that different equations give widely different Ksat values when applied to the same field-collected data. We developed a laboratory apparatus to independently measure Ksat with two different approaches, for a range of sediment samples of increasing permeability (10-2 cm/s to 10 cm/s). We first used it as a large-scale permeameter, to obtain what we consider to be our true Ksat values, and then conducted injection tests using minipiezometers, without disturbing the samples. We conclude that the different equations available in the literature for estimating Ksat from minipiezometer data do a poor job in our range of Ksat. Also, the available equation for calculating shape factors for partially and completely penetrating wells does not work for this case, as the screens are very different. Thus, new equations need to be developed for determining Ksat from minipiezometer data.